Angewandte Chemie International Edition

Current research reports and chronological list of recent articles.


The scientific chemistry journal Angewandte Chemie International Edition (german = applied chemistry) with its impact factor of 11.261 (2014) strengthens its leading position among the general chemistry journals. It is one of the prime chemistry journals in the world, with an Impact Factor higher than those of comparable journals.

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Additional research articles in the field of general chemistry, see Current Chemistry Research Articles. Magazines with similar content:

 - Chemical Communications, ChemComm,

 - Chemical Monthly,

 - The Chemical Record,

 - Chemistry Central Journal,

 - Chemistry Letters,

 - Journal of the American Chemical Society,

 - Nature Chemistry.



Angewandte Chemie International Edition - Abstracts



C3-Symmetric Tricyclo[2.2.1.02,6]heptane-3,5,7-triol

A straightforward access to a hitherto unknown C3-symmetric tricyclic triol both in racemic and enantiopure forms has been elaborated. Treatment of 7-tert-butoxynorbornadiene with peroxycarboxylic acids provided mixtures of C1- and C3-symmetric 3,5,7-triacyloxy-nortricyclenes via transannular π-cyclization and substitution of the tert-butoxy group. Refluxing in formic acid, the C1-symmetric esters were converted to the C3-symmetric formate. Hydrolysis gave diastereoisomeric triols, which were separated by recrystallization. Enantiomer resolution via diastereoisomeric tri(O-methylmandelates) delivered the target triols in gram scale. The pure enantiomers are useful as core units of dopants for liquid crystals.
Datum: 18.10.2017


Magnetless Device for Conducting Three-Dimensional Spin-Specific Electrochemistry

Electron spin states play an important role in many chemical processes. Most spin-state studies require the application of a magnetic field. Recently it was found that the transport of electrons through chiral molecules also depends on their spin states and may also play a role in enantiorecognition. Electrochemistry is an important tool for studying spin-specific processes and enantioseparation of chiral molecules. A new device is presented, which serves as the working electrode in electrochemical cells and is capable of providing information on the correlation of spin selectivity and the electrochemical process. The device is based on the Hall effect and it eliminates the need to apply an external magnetic field. Spin-selective electron transfer through chiral molecules can be monitored and the relationship between the enantiorecognition process and the spin of electrons elucidated. Spinmeister: A 3D spin-electrochemistry method enables monitoring of spin-selective electron transfer through chiral molecules. A Hall device incorporated within an electrochemical set-up allows direct measurement of spin polarization in the electrochemical process without the need for a magnetic field.
Datum: 18.10.2017


Programmable Supra-Assembly of a DNA Surface Adapter for Tunable Chiral Directional Self-Assembly of Gold Nanorods

An important challenge in molecular assembly and hierarchical molecular engineering is to control and program the directional self-assembly into chiral structures. Here, we present a versatile DNA surface adapter that can programmably self-assemble into various chiral supramolecular architectures, thereby regulating the chiral directional “bonding” of gold nanorods decorated by the surface adapter. Distinct optical chirality relevant to the ensemble conformation is demonstrated from the assembled novel stair-like and coil-like gold nanorod chiral metastructures, which is strongly affected by the spatial arrangement of neighboring nanorod pair. Our strategy provides new avenues for fabrication of tunable optical metamaterials by manipulating the directional self-assembly of nanoparticles using programmable surface adapters. Coding with DNA: DNA adapters can be programmably assembled into chiral supramolecular architectures following the distinct binding modality enabled by the selective interactions between specific binding domains. Gold nanorods site-specifically decorated on the DNA adapters self-assemble into new plasmonic chiral metastructures with facilely tunable configurations and handedness following the DNA chiral supramolecular matrix.
Datum: 18.10.2017


Biosynthesis of the Enterotoxic Pyrrolobenzodiazepine Natural Product Tilivalline

The nonribosomal enterotoxin tilivalline was the first naturally occurring pyrrolobenzodiazepine to be linked to disease in the human intestine. Since the producing organism Klebsiella oxytoca is part of the intestinal microbiota and the pyrrolobenzodiazepine causes the pathogenesis of colitis it is important to understand the biosynthesis and regulation of tilivalline activity. Here we report the biosynthesis of tilivalline and show that this nonribosomal peptide assembly pathway initially generates tilimycin, a simple pyrrolobenzodiazepine with cytotoxic properties. Tilivalline results from the non-enzymatic spontaneous reaction of tilimycin with biogenetically generated indole. Through a chemical total synthesis of tilimycin we could corroborate the predictions made about the biosynthesis. Production of two cytotoxic pyrrolobenzodiazepines with distinct functionalities by human gut resident Klebsiella oxytoca has important implications for intestinal disease. The Klebsiella oxytoca enterotoxin tilivalline was the first naturally occurring pyrrolobenzodiazepine to be linked to disease in the human intestine. In the biosynthesis of tilivalline the nonribosomal peptide assembly pathway initially generates the cytotoxic pyrrolobenzodiazepine tilimycin. Tilivalline results from the non-enzymatic reaction of tilimycin with biogenetically generated indole.
Datum: 18.10.2017


P−B Desulfurization: An Enabling Method for Protein Chemical Synthesis and Site-Specific Deuteration

Cysteine-mediated native chemical ligation is a powerful method for protein chemical synthesis. Herein, we report an unprecedentedly mild system (TCEP/NaBH4 or TCEP/LiBEt3H; TCEP=tris(2-carboxyethyl)phosphine) for chemoselective peptide desulfurization to achieve effective protein synthesis via the native chemical ligation–desulfurization approach. This method, termed P−B desulfurization, features usage of common reagents, simplicity of operation, robustness, high yields, clean conversion, and versatile functionality compatibility with complex peptides/proteins. In addition, this method can be used for incorporating deuterium into the peptides after cysteine desulfurization by running the reaction in D2O buffer. Moreover, this method enables the clean desulfurization of peptides carrying post-translational modifications, such as phosphorylation and crotonylation. The effectiveness of this method has been demonstrated by the synthesis of the cyclic peptides dichotomin C and E and synthetic proteins, including ubiquitin, γ-synuclein, and histone H2A. An unprecedentedly mild system (TCEP/NaBH4 or TCEP/LiBEt3H; TCEP=tris(2-carboxyethyl)phosphine) for chemoselective peptide desulfurization for effective protein synthesis via the native chemical ligation–desulfurization approach has been developed. This method can be used for incorporating deuterium into the peptides after cysteine desulfurization by running the reaction in D2O buffer.
Datum: 18.10.2017


Polyion Covalency: Exotic Species from the Unexplored World of Electrostatically Shielded Molecular Ion Chemistry

Standard quantum chemical methods have been employed to describe a variety of kinetically stable polyionic molecular species that are trapped in appreciable potential wells by chemical bonding forces, despite powerful electrostatic opposition that challenges conventional chemical detection and characterization. The studied species are covalent or dative analogs of “anti-electrostatic” hydrogen-bonded (AEHB) species, all illustrating how short-range quantum covalency can overcome the powerful “shielding” opposition of long-range electrostatic forces to form highly charged molecular species, analogous to known neutral or singly ionic counterparts. Computational predictions of representative structural, spectroscopic, and NBO-based electronic signatures of multiply charged analogs of common neutral species (CH3CH3, CO2, FeCO) are provided to suggest the unique material properties characteristic of this shielded domain of polyionic chemical phenomena. Anti-electrostatic hydrogen bonds: Kinetically stable polyionic species have been studied by quantum chemical methods. The polyionic species are trapped in potential wells by chemical bonding forces, despite powerful electrostatic opposition that challenges conventional chemical detection and characterization.
Datum: 18.10.2017


Fast, Efficient and Low E-Factor One-Pot Palladium-Catalyzed Cross-Coupling of (Hetero)Arenes

The homocoupling of aryl halides and the heterocoupling of aryl halides with either aryl bromides or arenes bearing an ortho-lithiation directing group are presented. The use of a Pd catalyst, in combination with t-BuLi, allows for the rapid and efficient formation of a wide range of polyaromatic compounds in a one pot procedure bypassing the need for the separate preformation of an organometallic coupling partner. These polyaromatic structures are obtained in high yields, in 10 min at room temperature, with minimal waste generation (E-factors as low as 1.5) and without the need for strict inert conditions, making this process highly efficient and practical in comparison to classical methods. As illustration, several key intermediates of widely used BINOL-derived structures are readily prepared including the highly desired precursor to the chiral TRIP phosphoric acid. Quick-and-clean: The cross-coupling of distinct (hetero)arenes is achieved in a rapid and efficient manner under ambient conditions with very little waste. By using a Pd catalyst and t-BuLi, many polyaromatic compounds are obtained including highly sterically hindered ones. Of these, several are advanced intermediates for widely used chiral Brønsted acid catalysts normally obtained via a rather cumbersome process.
Datum: 18.10.2017


Induction of Single-Handed Helicity of Polyacetylenes Using Mechanically Chiral Rotaxanes as Chiral Sources

Effective induction of preferred-handed helicity of polyacetylenes by pendant mechanically chiral rotaxanes is discussed. Polyacetylenes possessing optically active mechanically chiral rotaxanes in the side chains were synthesized by the polymerization of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepared by the chiral-phase HPLC separations. The CD Cotton effects revealed that the polyacetylenes took preferred-handed helical conformations depending on the rotaxane chirality. The preferred-handed helix was not disturbed by an additional chiral substituent on the rotaxane side chain. These results demonstrate the significance and utility of mechanically chiral rotaxanes for the effective construction of asymmetric fields. Mechanically chiral compounds are utilized as a chiral source. Polyacetylenes with optically active mechanically chiral rotaxanes in the side chains show strong circular dichroism on the main-chain absorption regions, indicating that the rotaxanes efficiently induce helicity with preferred handedness. These results demonstrate the significance and utility of mechanically chiral rotaxanes for the construction of asymmetric fields.
Datum: 18.10.2017


Frontispiece: Because the Light is Better Here: Correlation-Time Analysis by NMR Spectroscopy

NMR Spectroscopy In their Communication on page 13590, M. Ernst, B. H. Meier, and A. A. Smith examine potential pitfalls for the NMR analysis of protein dynamics and propose the use of dynamics detectors to characterize different ranges of correlation times.
Datum: 18.10.2017


Graphical Abstract: Angew. Chem. Int. Ed. 44/2017


Datum: 18.10.2017


Low-Temperature Molten-Salt Production of Silicon Nanowires by the Electrochemical Reduction of CaSiO3

Silicon is an extremely important technological material, but its current industrial production by the carbothermic reduction of SiO2 is energy intensive and generates CO2 emissions. Herein, we developed a more sustainable method to produce silicon nanowires (Si NWs) in bulk quantities through the direct electrochemical reduction of CaSiO3, an abundant and inexpensive Si source soluble in molten salts, at a low temperature of 650 °C by using low-melting-point ternary molten salts CaCl2–MgCl2–NaCl, which still retains high CaSiO3 solubility, and a supporting electrolyte of CaO, which facilitates the transport of O2− anions, drastically improves the reaction kinetics, and enables the electrolysis at low temperatures. The Si nanowire product can be used as high-capacity Li-ion battery anode materials with excellent cycling performance. This environmentally friendly strategy for the practical production of Si at lower temperatures can be applied to other molten salt systems and is also promising for waste glass and coal ash recycling. From old glass to batteries: A new and more sustainable method to produce Si nanowires in bulk quantities through the direct electrochemical reduction of CaSiO3 at a low temperature of 650 °C was developed. The method uses the low-melting-point ternary molten salts of CaCl2–MgCl2–NaCl, which retain high CaSiO3-solubility, and a supporting electrolyte of CaO, which drastically improves the reaction kinetics and enables the electrolysis at low temperatures.
Datum: 18.10.2017


Side Group-Mediated Mechanical Conductance Switching in Molecular Junctions

A key target in molecular electronics has been molecules having switchable electrical properties. Switching between two electrical states has been demonstrated using such stimuli as light, electrochemical voltage, complexation and mechanical modulation. A classic example of the latter is the switching of 4,4'-bipyridine, leading to conductance modulation of ~1 order of magnitude. Here, we describe the use of side-group chemistry to control the properties of a single-molecule electromechanical switch, which can be cycled between two conductance states by repeated compression and elongation. While bulky alkyl substituents inhibit the switching behaviour, -conjugated side-groups reinstate it. DFT calculations show that weak interactions between aryl moieties and the metallic electrodes are responsible for the observed phenomenon. This represents a significant expansion of the single-molecule electronics "tool-box" for the design of junctions with electromechanical properties.
Datum: 17.10.2017


Semiconductive Copper(I)–Organic Frameworks for Efficient Light-Driven Hydrogen Generation Without Additional Photosensitizers and Cocatalysts

As the first example of a photocatalytic system for splitting water without additional cocatalysts and photosensitizers, the comparatively cost-effective Cu2I2-based MOF, Cu-I-bpy (bpy=4,4′-bipyridine) exhibited highly efficient photocatalytic hydrogen production (7.09 mmol g−1 h−1). Density functional theory (DFT) calculations established the electronic structures of Cu-I-bpy with a narrow band gap of 2.05 eV, indicating its semiconductive behavior, which is consistent with the experimental value of 2.00 eV. The proposed mechanism demonstrates that Cu2I2 clusters of Cu-I-bpy serve as photoelectron generators to accelerate the copper(I) hydride interaction, providing redox reaction sites for hydrogen evolution. The highly stable cocatalyst-free and self-sensitized Cu-I-bpy provides new insights into the future design of cost-effective d10-based MOFs for highly efficient and long-term solar fuels production. No additives required: A low-cost Cu2I2-based MOF exhibits efficient photocatalytic H2 production without additional photosensitizers and cocatalysts. DFT calculations reveal a good band alignment with the water redox energy levels. The proposed mechanism demonstrates that Cu2I2 clusters in Cu-I-bpy (bpy=4,4′-bipyridine) serve as photoelectron generators to accelerate copper(I) hydride interaction for hydrogen evolution.
Datum: 17.10.2017


Flexible Zirconium MOFs as Bromine-Nanocontainers for Bromination Reactions under Ambient Conditions

A series of flexible MOFs (PCN-605, PCN-606, and PCN-700) are synthesized and applied to reversible bromine encapsulation and release. The chemical stability of these Zr-MOFs ensures the framework's integrity during the bromine adsorption, while the framework's flexibility allows for structural adaptation upon bromine uptake to afford stronger host–guest interactions and therefore higher bromine adsorption capacities. The flexible MOFs act as bromine-nanocontainers which elongate the storage time of volatile halides under ambient conditions. Furthermore, the bromine pre-adsorbed flexible MOFs can be used as generic bromine sources for bromination reactions giving improved yields and selectivities under ambient conditions when compared with liquid bromine. Bromine that's better than bromine: A series of flexible Zr-based metal–organic frameworks (MOFs) are prepared using a topology guided strategy. During desolvation and bromine adsorption these MOFs undergo significant structural transformations. The bromine pre-adsorbed flexible MOFs are used as generic bromine sources for bromination reactions giving improved yields and selectivities compared to liquid bromine.
Datum: 17.10.2017


Stereoselective Direct Chlorination of Alkenyl MIDA Boronates: Divergent Synthesis of E and Z α-Chloroalkenyl Boronates

The individual molecules of α-chloroalkenyl boronates include both an electrophilic C−Cl bond and a nucleophilic C−B bond, which makes them intriguing organic synthons. Reported herein is a stereodivergent synthesis of both E and Z α-chloroalkenyl N-methyliminodiacetyl (MIDA) boronates through the direct chlorination of alkenyl MIDA boronates using tBuOCl and PhSeCl reagents, respectively. Both reaction processes are stereospecific and the use of sp3-B MIDA boronate is the key contributor to the reactivity. The synthetic value of the boronate products was also demonstrated. One Way or Another: Stereodivergent syntheses of both E and Z α-chloroalkenyl N-methyliminodiacetyl (MIDA) boronates were achieved through the direct chlorination of E-alkenyl MIDA boronates using tBuOCl and PhSeCl reagents, respectively. Both reaction processes are stereospecific and the sp3-B MIDA boronate plays the key role to the reactivity. Broad substrate scope was observed and the synthetic value of the boronate products was demonstrated.
Datum: 17.10.2017


Influence of Polyethylene Glycol Unit on Palladium- and Nickel-Catalyzed Ethylene Polymerization and Copolymerization

The transition-metal-catalyzed copolymerization of olefins with polar functionalized co-monomers represents a major challenge in the field of olefin polymerization. It is extremely difficult to simultaneously achieve improvements in catalytic activity, polar monomer incorporation, and copolymer molecular weight through ligand modifications. Herein we introduce a polyethylene glycol unit to some phosphine-sulfonate palladium and nickel catalysts, and its influence on ethylene polymerization and copolymerization is investigated. In ethylene polymerization, this strategy leads to enhanced activity, catalyst stability, and increased polyethylene molecular weight. In ethylene copolymerization with polar monomers, improvements in all copolymerization parameters are realized. This effect is most significant for polar monomers with hydrogen-bond-donating abilities. PEGged forward: Polyethylene glycol (PEG) substituents are installed in phosphine-sulfonate palladium and nickel catalysts. The polyethylene glycol unit shows beneficial effects in ethylene polymerization and copolymerization reactions.
Datum: 17.10.2017


Surface-assisted self-assembly strategies leading to supramolecular hydrogels

Localized molecular self-assembly processes leading to the growth of nanostructures exclusively from the surface of a material is one of the great challenges in surface chemistry. In the last decade, several works have been reported about the ability of modified or unmodified surfaces to manage the self-assembly of low molecular weight hydrogelators (LMWH) resulting in localized supramolecular hydrogel coatings mainly based on nanofiber architectures. This minireview highlights all strategies that emerged recently to initiate and localize LMWH supramolecular hydrogel formation, their related fundamental issues and applications.
Datum: 17.10.2017


A Highly Reactive Oxoiron(IV) Complex Supported by a Bioinspired N3O Macrocyclic Ligand

The sluggish oxidants [FeIV(O)(TMC)(CH3CN)]2+ (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and [FeIV(O)(TMCN-d12)(OTf)]+ (TMCN-d12=1,4,7,11-tetra(methyl-d3)-1,4,7,11-tetraazacyclotetradecane) are transformed into the highly reactive oxidant [FeIV(O)(TMCO)(OTf)]+ (1; TMCO=4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane) upon replacement of an NMe donor in the TMC and TMCN ligands by an O atom. A rate enhancement of five to six orders of magnitude in both H atom and O atom transfer reactions was observed upon oxygen incorporation into the macrocyclic ligand. This finding was explained in terms of the higher electrophilicity of the iron center and the higher availability of the more reactive S=2 state in 1. This rationalizes nature's preference for using O-rich ligand environments for the hydroxylation of strong C−H bonds in enzymatic reactions. The oxoiron(IV) center in [FeIV(O)(TMCO)(OTf)]+ (TMCO=4,8,12-trimethyl-1-oxa-4,8,12-triazacyclotetradecane; see picture) in an N3O environment exhibits drastically enhanced reactivity relative to the [FeIV(O)(TMC)(CH3CN)]2+ (TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) complex in an N4 environment. This explains nature's preference for using oxygen-rich ligand environments for the hydroxylation of strong C−H bonds.
Datum: 17.10.2017


Construction of π-Surface-Metalated Pillar[5]arenes which Bind Anions via Anion–π Interactions

By simple ligand exchange of the cationic transition-metal complexes [(Cp*)M(acetone)3](OTf)2 (Cp*=pentamethylcyclopentadienyl and M=Ir or Rh) with pillar[5]arene, mono- and polynuclear pillar[5]arenes, a new class of metalated host molecules, is prepared. Single-crystal X-ray analysis shows that the charged transition-metal cations are directly bound to the outer π-surface of aromatic rings of pillar[5]arene. One of the triflate anions is deeply embedded within the cavity of the trinuclear pillar[5]arenes, which is different to the host–guest behavior of most pillar[5]arenes. DFT calculation of the electrostatic potential revealed that the metalated pillar[5]arenes featured an electron-deficient cavity due to the presence of the electron-withdrawing transition metals, thus allowing encapsulation of electron-rich guests mainly driven by anion–π interactions. Cavity filling: A simple yet highly efficient approach gives pillar[5]arene hosts with metalated π-surfaces. The metalated pillar[5]arenes have an electron-deficient cavity owing to the presence of the electron-withdrawing transition-metal moieties, thus allowing the encapsulation of anion guests via anion–π interactions.
Datum: 17.10.2017


Versatile Tri(pyrazolyl)phosphanes as Phosphorus Precursors for the Synthesis of Highly Emitting InP/ZnS Quantum Dots

Tri(pyrazolyl)phosphanes (5R1,R2) are utilized as an alternative, cheap and low-toxic phosphorus source for the convenient synthesis of InP/ZnS quantum dots (QDs). From these precursors, remarkably long-term stable stock solutions (>6 months) of P(OLA)3 (OLAH=oleylamine) are generated from which the respective pyrazoles are conveniently recovered. P(OLA)3 acts simultaneously as phosphorus source and reducing agent in the synthesis of highly emitting InP/ZnS core/shell QDs. These QDs are characterized by a spectral range between 530–620 nm and photoluminescence quantum yields (PL QYs) between 51–62 %. A proof-of-concept white light-emitting diode (LED) applying the InP/ZnS QDs as a color-conversion layer was built to demonstrate their applicability and processibility. Taking stock: Tri(pyrazolyl)phosphanes are utilized as a less-toxic P1 source for the synthesis of long-term stable stock solutions of P(OLA)3 (OLAH=oleylamine). The stock solutions are used for the preparation of InP/ZnS quantum dots emitting in the spectral range between 530–620 nm with photoluminescence quantum yields between 51–62 %. The liberated pyrazoles can easily be recovered and reused.
Datum: 17.10.2017


Aqueous Gold Overgrowth of Silver Nanoparticles: Merging the Plasmonic Properties of Silver with the Functionality of Gold

To date, it has not been possible to combine the high optical quality of silver particles with good chemical stability and synthetic convenience in a fully aqueous system, while simultaneously allowing chemical surface functionalization. We present a synthetic pathway for future developments in information, energy and medical technology where strong optical/electronic properties are crucial. Therefore, the advantages inherent to gold are fused with the plasmonic properties of silver in a fully aqueous Au/Ag/Au core-shell-shell system. These nanoparticles inherit low dispersity from their masked gold cores, yet simultaneously exhibit the strong plasmonic properties of silver. Protecting the silver surface with a sub-skin depth gold layer enables oxidant stability and functionality without altering the Ag-controlled optical properties. This combines both worlds - optical quality and chemical stability - and furthermore it is not limited to a specific particle shape.
Datum: 17.10.2017


Direct Synthesis of Polymer Nanotubes via Aqueous Dispersion Polymerization of Cyclodextrin/Styrene Complex

We report a one-step synthesis of nanotubes by RAFT dispersion polymerization of cyclodextrin/styrene (CD/St) complexes directly in water. The resulted amphiphilic PEG-b-PS diblock copolymers self-assemble in situ into nanoparticles with various morphologies. Spheres, worms, lamellae, and nanotubes were controllably obtained. Because of the complexation, the swelling degree of polystyrene (PS) blocks by free St is limited, resulting limited mobility of PS chains. Consequently, kinetically trapped lamellae and nanotubes were obtained instead of spherical vesicles. During the formation of nanotubes, small vesicles firstly formed at the ends of the tape-like lamellae, then grew and fused into nanotubes with limited chain rearrangement. The introduction of host-guest interaction based on CDs enables the aqueous dispersion polymerization of water-immiscible monomers, and produces kinetically trapped nanostructures, which could be a powerful technique for nanomaterials synthesis.
Datum: 17.10.2017


Supramolecular recognition allows remote, site-selective C-H oxidation of methylenic sites in linear amines

Site-selective C-H functionalization of aliphatic alkyl chains stands as a longstanding challenge in oxidation catalysis, given the comparable relative reactivity of the different methylenes. Herein, we describe a supramolecular, bioinspired approach to address this challenge. We decorated a manganese complex, able to catalyze C(sp3)-H hydroxylation with H2O2, with a supramolecular receptor (an 18-benzocrown-6 ether) that binds ammonium substrates via hydrogen bonding. Reversible pre-association of protonated primary aliphatic amines with the crown ether thus selectively exposes only remote positions (C8 and C9) to the oxidizing unit, yielding the site-selective oxidation and overriding the intrinsic reactivity of C-H bonds. Remarkably, the supramolecular control of the selectivity holds true for a whole series of linear amines, no matter the chain length and the presence of more (sterically) activated sites.
Datum: 17.10.2017


Pnictogen (As, Sb, Bi) Nanosheets for Electrochemical Applications Are Produced by Shear Exfoliation Using Kitchen Blenders

Group 5 elements (pnictogens) are attracting attention as mono-elemental 2D materials with semiconducting properties. In their Communication (DOI: 10.1002/anie.201706389), M. Pumera et al. present a green, scalable method for the aqueous shear-force exfoliation of pnictogens using household kitchen blenders. The exfoliated nanosheets were evaluated in water-splitting reactions, in which Sb showed the best performance. These results are significant for future electrochemical applications of pnictogens.
Datum: 17.10.2017


Unlocking the Electrocatalytic Activity of Antimony for CO2 Reduction by Two-Dimensional Engineering of the Bulk Material

Two-dimensional (2D) materials are known to be useful in catalysis. Engineering 3D bulk materials into the 2D form can enhance the exposure of the active edge sites, which are believed to be the origin of the high catalytic activity. Reported herein is the production of 2D “few-layer” antimony (Sb) nanosheets by cathodic exfoliation. Application of this 2D engineering method turns Sb, an inactive material for CO2 reduction in its bulk form, into an active 2D electrocatalyst for reduction of CO2 to formate with high efficiency. The high activity is attributed to the exposure of a large number of catalytically active edge sites. Moreover, this cathodic exfoliation process can be coupled with the anodic exfoliation of graphite in a single-compartment cell for in situ production of a few-layer Sb nanosheets and graphene composite. The observed increased activity of this composite is attributed to the strong electronic interaction between graphene and Sb. Less is more: By engineering bulk antimony using an electrochemical exfoliation method, two-dimensional antimony nanosheets and their composite with graphene were formed. The electrocatalytic activity of these two materials towards reducing CO2 to formate were evaluated, thus showing that the materials were more active than bulk antimony.
Datum: 17.10.2017


Edith Flanigen Award for Jovana Zečević / Hamburger Wissenschaftspreis for Xinliang Feng and Klaus Müllen / And also in the News


Datum: 17.10.2017


Authors Profile


Datum: 17.10.2017


Meso-aryl [20]π Homoporphyrin: The simplest expanded porphyrin with smallest Möbius Topology

The unstable conjugated homoporphyrin is successfully stabilized by introducing the meso-aryl substitutents. It was evident from the moderate diatropic ring current in NMR analysis that the newly formed 20π conjugated freebase and its protonated form exhibit the Möbius aromatic character. Further, the complexation of ligand with Rh(I) salt afforded a unique binding mode and retaining Möbius aromaticity. Overall, these are the smallest Möbius aromatic molecules, which are unambiguously confirmed by spectral, crystal analyses and supported by theoretical studies.
Datum: 17.10.2017


Tuneable Transient Thermogels Mediated by a pH- and Redox-Regulated Supramolecular Polymerization

We present a multi-stimuli responsive transient supramolecular polymerization of ß-sheet encoded dendritic peptide monomers in water. The glutamic acid and methionine containing amphiphiles undergo a glucose oxidase-catalyzed, glucose-fueled transient hydrogelation in response to an interplay of pH- and oxidation-stimuli, promoted by the production of reactive oxygen species (ROS). By adjusting the enzyme and glucose concentration we tune the assembly and the disassembly rates of the supramolecular polymers, which dictate the stiffness and transient stability of the hydrogels. The incorporation of triethylene glycol chains introduces thermoresponsive properties to the materials. We further show that repair enzymes are able to reverse the oxidative damage in the methionine-based thioether side chains. Since ROS play an important role in signal transduction cascades, our strategy offers great potential for applications of these dynamic biomaterials in redox microenvironments.
Datum: 17.10.2017


Identification of Ubiquitin Chain Interacting Proteins

Ubiquitylation, the modification of proteins by ubiquitin (Ub), is one of the most prevalent and versatile post-translational modifications in eukaryotic cells. As Ub also serves as its own substrate, proteins can be modified by numerous different Ub chains, in which the individual moieties are linked via one or several of the seven lysines of Ub. Homogeneous Ub chains, in which the moieties are sequentially linked via the same residue, have been most extensively studied. Yet, due to their restricted availability, the functions of Ub chains linked via K27, K29 or K33 are poorly understood. We have developed an approach that, for the first time, allows the generation of all seven homogeneous Ub chains in large quantities. We show that the chains enable the identification of Ub chain binding proteins by affinity-based proteomics. The potential of our approach is demonstrated by the identification of previously unknown interaction partners of K27-, K29-, and K33-linked Ub chains.
Datum: 17.10.2017


Single-Molecule Observation of The Photoregulated Conformational Dynamics of DNA Origami Nanoscissors

We demonstrate direct observation of the dynamic opening and closing behavior of photo-controllable DNA origami nanoscissors (NS) using high-speed AFM. First the conformational change between the open and closed state controlled by adjustment of salt concentration could be directly observed during AFM scanning. Then light-responsive moieties were incorporated into the NS to control the structural changes by irradiation. Using photo-switchable DNA strands, we created a photoresponsive NS variant and were able to distinguish between the open and closed conformations after respective irradiation with UV and visible (Vis) light via gel electrophoresis and AFM imaging. Additionally, these reversible changes in shape during photoirradiation were directly visualized using HS-AFM. Moreover, four photo-switchable NS were assembled into a scissor-actuator-like higher-order object whose configuration could be controlled by the open and close switching as induced by UV and Vis light irradiation.
Datum: 17.10.2017


Analytical Description of NMR Relaxation Highlights Correlated Dynamics in Intrinsically Disordered Proteins

The potential energy landscapes of intrinsically disordered proteins are remarkably flat compared their folded counterparts, making their functional modes difficult to study. In their Communication (DOI: 10.1002/anie.201706740), M. Blackledge and co-workers use a combination of high-resolution NMR spectroscopy and advanced molecular dynamics simulation to investigate the extent of functionally important correlated motions in this essential class of proteins.
Datum: 17.10.2017


Noncovalent Functionalization and Charge Transfer in Antimonene

Antimonene, a novel group 15 two-dimensional material, is functionalized with a tailormade perylene bisimide through strong van der Waals interactions. The functionalization process leads to a significant quenching of the perylene fluorescence, and surpasses that observed for either graphene or black phosphorus, thus allowing straightforward characterization of the flakes by scanning Raman microscopy. Furthermore, scanning photoelectron microscopy studies and theoretical calculations reveal a remarkable charge-transfer behavior, being twice that of black phosphorus. Moreover, the excellent stability under environmental conditions of pristine antimonene has been tackled, thus pointing towards the spontaneous formation of a sub-nanometric oxide passivation layer. DFT calculations revealed that the noncovalent functionalization of antimonene results in a charge-transfer band gap of 1.1 eV. Flake off: Reported for the first time is the noncovalent functionalization of antimonene using perylene bisimides (PDI). The significant quenching of the fluorescence of the PDI allows straightforward characterization of the antimonene flakes deposited on Si/SiO2 substrates. This work paves the way for the development of novel applications based on antimonene by tailoring its electronic properties.
Datum: 17.10.2017


Asymmetric Squaramide Catalyzed Domino aza-Friedel-Crafts/N,O Acetalization Reactions Between 2-Naphthols and Pyrazolinone Ketimines

Pyrazolin-5-one derived N-Boc ketimines have been explored to develop an unprecedented domino aza-Friedel-Crafts/N,O-acetalization reaction with 2-naphthols. The novel protocol requires only a catalyst loading of 0.5 mol% of a bifunctional squaramide catalyst, is scalable to gram amounts, and provides a new series of furanonaphthopyrazolidinone derivatives bearing two vicinal tetra-substituted stereogenic centers in excellent yields (95-98%) and stereoselectivities (>99:1 dr and 97-98% ee). A different reactivity was observed in the case of 1-naphthols and other electron-rich phenols, which led to the aza-Friedel-Crafts adducts in 70-98% yield and 47-98% ee.
Datum: 17.10.2017


Mechanism-based Inhibitors of the Human Sirtuin 5 Deacylase: Structure-Activity Relationship, Biostructural, and Kinetic Insight

The sirtuin enzymes are important regulatory deacylases in a variety of biochemical contexts and may therefore be potential therapeutic targets through either activation or inhibition by small molecules. Here, we describe the discovery of the most potent inhibitor of sirtuin 5 (SIRT5) reported to date. We provide rationalization of the mode of binding by solving co-crystal structures of selected inhibitors in complex with both human and zebrafish SIRT5, which provide insight for future optimization of inhibitors with more "drug-like" properties. Importantly, enzyme kinetic evaluation revealed a slow, tight-binding mechanism of inhibition, which is unprecedented for sirtuins. This is important information when applying inhibitors to probe mechanisms in biology.
Datum: 17.10.2017


An easy-to-machine electrochemical flow microreactor: Efficient isoindolinone synthesis and flow functionalization

Flow electrochemistry is an efficient methodology to generate radical intermediates. An electrochemical flow microreactor has been designed and manufactured to improve the efficiency of electrochemical flow reactions. With this device only little or no supporting electrolytes are needed, making processes less costly and enabling easier purification. This is demonstrated by the facile synthesis of amidyl radicals used in intramolecular hydroaminations to isoindolinones. The combination with inline mass spectrometry facilitates a much easier telescoping of chemical steps in a single flow process.
Datum: 17.10.2017


Discovery of New Click and Release Reactions by Screening of Mesoionics and Cycloalkynes Combinations

We report the discovery of a new bioorthogonal click and release reaction involving imino-sydnones and strained alkynes. This transformation leads to two products resulting from both ligation and fragmentation of imino-sydnones under physiological conditions. Optimized imino-sydnones were successfully used to design innovative cleavable linkers for protein modifications opening new areas in the fields of drug release and target fishing applications. This click and release technology offers for the first time the possibility to exchange tags on proteins with functionalized cyclooctynes under mild and bioorthogonal conditions.
Datum: 17.10.2017


Docking of Antibodies into the Cavities of DNA Origami Structures

Immobilized antibodies are extensively employed for medical diagnostics, such as in enzyme-linked immunosorbent assays. Despite their widespread use, the ability to control the orientation of immobilized antibodies on surfaces is very limited. Herein, we report a method for the covalent and orientation-selective immobilization of antibodies in designed cavities in 2D and 3D DNA origami structures. Two tris(NTA)-modified strands are inserted into the cavity to form NTA–metal complexes with histidine clusters on the Fc domain. Subsequent covalent linkage to the antibody was achieved by coupling to lysine residues. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) confirmed the efficient immobilization of the antibodies in the origami structures. This increased control over the orientation of antibodies in nanostructures and on surfaces has the potential to direct the interactions between antibodies and targets and to provide more regular surface assemblies of antibodies. Fits like a glove: Antibodies are immobilized in the cavities of a DNA origami structure by chelation to metal complexes at each side of the cavity and by covalent coupling to activated esters inside the cavity.
Datum: 17.10.2017


Cove-Edge Nanoribbon Materials for Efficient Inverted Halide Perovskite Solar Cells

Two cove-edge graphene nanoribbons hPDI2-Pyr-hPDI2 (1) and hPDI3-Pyr-hPDI3 (2) are used as efficient electron-transporting materials (ETMs) in inverted planar perovskite solar cells (PSCs). Devices based on the new graphene nanoribbons exhibit maximum power-conversion efficiencies (PCEs) of 15.6 % and 16.5 % for 1 and 2, respectively, while a maximum PCE of 14.9 % is achieved with devices based on [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). The interfacial effects induced by these new materials are studied using photoluminescence (PL), and we find that 1 and 2 act as efficient electron-extraction materials. Additionally, compared with PC61BM, these new materials are more hydrophobic and have slightly higher LUMO energy levels, thus providing better device performance and higher device stability. Blue (nano)ribbon solar cells: Two electron-deficient graphene nanoribbons are used as the electron-transporting materials (ETMs) in inverted perovskite solar cells (PSCs). The nanoribbons provide improved performance over the commonly used PC61BM. The most important benefits are the improved PCE (>10 % over PC61BM) and improved device lifetime owing to the hydrophobic nature of the solubilizing chains on the ribbons.
Datum: 17.10.2017


Morphology-Dependent Cell Imaging by Using a Self-Assembled Diacetylene Peptide Amphiphile

Herein, a novel cationic peptide gemini amphiphile containing diacetylene motifs (DA2P) is presented, which self-assembles into novel tadpole- and bola-shaped nanostructures at low concentrations and nanofibers at higher concentrations. Interestingly, the DA2P assemblies can be polymerized into a fluorescent red phase but only during incubation with HeLa cells, most likely owing to the reorganization of the diacetylene chains of DA2P upon interaction with the cell membrane. The red-fluorescent polymerized DA2P assemblies can serve as a novel cell imaging probe. However, only vesicles, tadpole- and bola-shaped DA2P assemblies can be translocated into HeLa cells, whereas the nanofiber-like DA2P assemblies are trapped by the cell membranes and do not enter the cells. Hence, morphology-dependent cell imaging is observed. Novel nanostructure: A peptide gemini amphiphile containing diacetylene motifs self-assembles into novel tadpole- and bola-shaped nanostructures at low concentrations, as well as nanofibers at higher concentrations. Interestingly, morphology-dependent cell imaging is achieved owing to the polymerization of the diacetylenes upon interaction with the cell membrane.
Datum: 17.10.2017


Intrinsic Broadband White-Light Emission from Ultrastable, Cationic Lead Halide Layered Materials

We report a family of cationic lead halide layered materials, formulated as [Pb2X2]2+[−O2C(CH)2CO2−] (X=F, Cl, Br), exhibiting pronounced broadband white-light emission in bulk form. These well-defined PbX-based structures achieve an external quantum efficiency as high as 11.8 %, which is comparable to the highest reported value (ca.9 %) for broadband phosphors based on layered organolead halide perovskites. More importantly, our cationic materials are ultrastable lead halide materials, which overcome the air/moisture-sensitivity problems of lead perovskites. In contrast to the perovskites and other bulk emitters, the white-light emission intensity of our materials remains undiminished after continuous UV irradiation for 30 days under atmospheric conditions (ca.60 % relative humidity). Our mechanistic studies confirm that the broadband emission is ascribed to short-range electron-phonon coupling in the strongly deformable lattice and generated self-trapped carriers. White out: Cationic lead halide layered materials formulated as [Pb2X2]2+[−O2C(CH)2CO2−] (X=F, Cl, Br) are ultrastable, broadband white-light emitters with an external quantum efficiency as high as 11.8 % and long-term photostability under atmospheric conditions, which overcome the air/moisture-sensitivity problems of lead perovskites.
Datum: 17.10.2017


Oxyfunctionalization of the remote C-H bonds of aliphatic amines via decatungstate photocatalysis

Remotely oxygenated aliphatic amines represent an important class of synthetic building blocks to which there are currently no direct means of access. Reported here is an efficient and scalable solution that relies upon decatungstate photocatalysis under acidic conditions using either H2O2 or O2 as the terminal oxidant. Using these conditions a series of simple and unbiased aliphatic amine starting materials can be oxidized to value added ketone products. Lastly, in situ LED-irradiated NMR spectroscopy was utilized to monitor the kinetics of the reaction, enabling direct translation of the reaction in flow.
Datum: 16.10.2017


Enantioselective Copper-Catalyzed Alkylation of Quinoline N-Oxides with Vinylarenes

We report an asymmetric copper-catalyzed alkylation of quinoline N-oxides with chiral Cu-alkyl species generated by migratory insertion of vinylarene into a chiral Cu-H complex. A variety of quinoline N-oxides and vinylarenes underwent this Cu-catalyzed enantioselective alkylation reaction, yielding the corresponding chiral alkylated N-heteroarenes in high isolated yields with high to excellent enantioselectivities. This enantioselective protocol represents the first general and practical approach to access a wide range of chiral alkylated quinolines.
Datum: 16.10.2017


Experimental proof of the bifunctional mechanism for the hydrogen oxidation in alkaline media

Realization of the hydrogen economy relies on effective hydrogen production, storage, and utilization. The slow kinetics of hydrogen evolution and oxidation reaction (HER/HOR) in alkaline media limits many practical applications involving hydrogen generation and utilization, and how to overcome this fundamental limitation remains debatable. Here we present a kinetic study of the HOR on representative catalytic systems in alkaline media. Electrochemical measurements show that the HOR rate of Pt-Ru/C and Ru/C systems is decoupled to their hydrogen binding energy (HBE), challenging the current prevailing HBE mechanism. The alternative bifunctional mechanism is verified by combined electrochemical and in situ spectroscopic data, which provide convincing evidence for the presence of hydroxyl on surface Ru sites in the HOR potential region and its key role in promoting the rate-determining Volmer step. The conclusion presents important references for design and selection of HOR catalysts.
Datum: 16.10.2017


High-Temperature Formation of a Functional Film at the Cathode/Electrolyte Interface in Lithium–Sulfur Batteries: An In Situ AFM Study

Lithium–sulfur (Li–S) batteries have been attracting wide attention for their promising high specific capacity. A deep understanding of Li–S interfacial mechanism including the temperature (T) effect is required to meet the demands for battery modification and systematic study. Herein, the interfacial behavior during discharge/charge is investigated at high temperature (HT) of 60 °C in an electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI). By in situ atomic force microscopy (AFM), dynamic evolution of insoluble Li2S2 and Li2S is studied at the nanoscale. An in situ formed functional film can be directly monitored at 60 °C after Li2S nucleation. It retards side reactions and facilitates interfacial redox. The insight into the interfacial processes at HT provides direct evidence of the existence of the film and reveals its dynamic behavior, providing a new avenue for electrolyte design and performance enhancement. Caught on film: By electrochemical AFM investigation at 60 °C, in situ formation of a functional film can be directly monitored at a highly oriented pyrolytic graphite (HOPG) cathode/polysulfide electrolyte interface in Li–S batteries. The film forms by a LiF net capturing polysulfide (PS) intermediates by both physical confinement and chemical anchoring effects.
Datum: 16.10.2017


Asymmetric Cycloisomerization of o-Alkenyl-N-Methylanilines to Indolines by Iridium-Catalyzed C(sp3)−H Addition to Carbon–Carbon Double Bonds

Highly enantioselective cycloisomerization of N-methylanilines, bearing o-alkenyl groups, into indolines is established. An iridium catalyst bearing a bidentate chiral diphosphine effectively promotes the intramolecular addition of the C(sp3)−H bond across a carbon–carbon double bond in a highly enantioselective fashion. The reaction gives indolines bearing a quaternary stereogenic carbon center at the 3-position. The reaction mechanism involves rate-determining oxidative addition of the N-methyl C−H bond, followed by intramolecular carboiridation and subsequent reductive elimination. Build a bridge: Highly enantioselective cycloisomerization of N-methylanilines, bearing o-alkenyl groups, into indolines was established. An iridium catalyst bearing a bidentate chiral diphosphine effectively promotes the intramolecular addition of the C(sp3)−H bond across a C=C bond in an enantioselective fashion. The reaction gives indolines bearing a quaternary stereogenic carbon center at the 3-position.
Datum: 16.10.2017


Medium-Sized-Ring Analogues of Dibenzodiazepines by a Conformationally Induced Smiles Ring Expansion

Analogues of dibenzodiazepines, in which the seven-membered nitrogen heterocycle is replaced by a 9–12-membered ring, were made by an unactivated Smiles rearrangement of five- to eight-membered heterocyclic anthranilamides. The conformational preference of the tertiary amide in the starting material leads to intramolecular migration of a range of aryl rings, even those lacking electron-withdrawing activating groups, and provides a method for nn+4 ring expansion. The medium-ring products adopt a chiral ground state with an intramolecular, transannular hydrogen bond. The rate of interconversion of their enantiomeric conformers depends on solvent polarity. Ring size and adjacent steric hindrance modulate this hidden hydrophilicity, thus making this scaffold a good candidate for drug development. Smiles rearrangement of readily prepared amide derivatives of benzo-fused nitrogen heterocycles requires no electronic activation to give medium-sized-ring analogues of the dibenzodiazepine tricyclic antidepressants.⋅The reaction tolerates electron-rich and electron-poor rings, delivers 9-12-membered rings, and leads to conformationally restricted products
Datum: 16.10.2017


Chemistry / Physiology or Medicine, and Physics


Datum: 16.10.2017


An Eighteen-Membered Macrocyclic Ligand for Actinium-225 Targeted Alpha Therapy

The 18-membered macrocycle H2macropa was investigated for 225Ac chelation in targeted alpha therapy (TAT). Radiolabeling studies showed that macropa, at submicromolar concentration, complexed all 225Ac (26 kBq) in 5 min at RT. [225Ac(macropa)]+ remained intact over 7 to 8 days when challenged with either excess La3+ ions or human serum, and did not accumulate in any organ after 5 h in healthy mice. A bifunctional analogue, macropa-NCS, was conjugated to trastuzumab as well as to the prostate-specific membrane antigen-targeting compound RPS-070. Both constructs rapidly radiolabeled 225Ac in just minutes at RT, and macropa-Tmab retained >99 % of its 225Ac in human serum after 7 days. In LNCaP xenograft mice, 225Ac-macropa-RPS-070 was selectively targeted to tumors and did not release free 225Ac over 96 h. These findings establish macropa to be a highly promising ligand for 225Ac chelation that will facilitate the clinical development of 225Ac TAT for the treatment of soft-tissue metastases. Actinium in action! A macrocyclic ligand exhibits unprecedented radiolabeling efficiency for the large α-emitting radionuclide 225Ac3+. This ligand is extremely promising for the implementation of 225Ac in targeted alpha therapy for cancer. RCY=radiochemical yield.
Datum: 16.10.2017


Synthesis of Biphenylenes and Their Higher Homologues by Cyclization of Aryne Derivatives

This investigation demonstrates that a series of biphenylenes can be easily prepared from their corresponding halobiphenyls by the cyclization of in situ generated 2′,3′-didehydro-2-lithiobiphenyls at low temperature. Two remarkable advantages of this synthetic method include 1) the lack of any need for transition-metal catalysts or reagents in the cyclization, and 2) the ability to obtain C1-functionalized products by treating the reaction intermediate 1-lithiobiphenylene with an electrophilic reagent. π-Extended derivatives, such as benzobiphenylenes, dibenzobiphenylene, linear/angular [3]phenylenes, and biphenyleno[2,3-b]biphenylenes, were synthesized similarly using suitable biaryls or teraryls. Biphenylenes can be easily and efficiently obtained at low temperature by the organolithium-mediated cyclization of halobiphenyls via an aryne intermediate. This synthetic protocol provides an advantage for the direct and controlled functionalization at the C1 position.
Datum: 16.10.2017


Living Supramolecular Polymerization of a Perylene Bisimide Dye into Fluorescent J-Aggregates

Self-assembly of a new, in bay-position 1,7- dimethoxy-substituted perylene bisimide (PBI) organogelator affords non-fluorescent H-aggregates at fast cooling rates and fluorescent J-aggregates at slow cooling rates. Under properly adjusted conditions the kinetically trapped "off-pathway" H-aggregates transform into the thermodynamically favored J-aggregates, a process that can be accelerated by the addition of J-aggregate seeds. Spectroscopic studies revealed a subtle interplay of pi-pi interactions and intra- and intermolecular hydrogen bonding for monomeric, H- and J-aggregated PBIs. Multiple polymerization cycles initiated from the seed termini demonstrate the living character of this chain-growth supramolecular polymerization process.
Datum: 16.10.2017


(4+3) Cycloaddition Reactions of N-Alkyl Oxidopyridinium Ions

N-Methylation of methyl 5-hydroxynicotinate followed by reaction with a diene in the presence of triethylamine afforded (4+3) cycloadducts in good to excellent yields. High regioselectivity was observed with 1-substituted and 1,2-disubstituted butadienes. Density functional theory calculations indicate that the cycloaddition involves concerted addition of the diene onto the oxidopyridinium ion. The process provides rapid access to bicyclic nitrogenous structures resembling natural alkaloids. Greater than the sum of its parts: N-Methylated methyl 5-hydroxynicotinate reacted with dienes in the presence of triethylamine to afford bicyclic nitrogenous structures resembling natural alkaloids through (4+3) cycloaddition (see scheme). High regioselectivity was observed with 1-substituted and 1,2-disubstituted butadienes. DFT calculations indicate that the reaction involves concerted addition of the diene to the oxidopyridinium ion.
Datum: 16.10.2017


Main Group Metal Coordination Polymers. Structures and Nanostructures By Ali Morsali and Lida Hashemi.

John Wiley and Sons, Hoboken 2017. 272 pp., hardcover, € 195.00.—ISBN 978-1119370239
Datum: 16.10.2017


Two-Dimensional Calix[4]arene-based Metal–Organic Coordination Networks of Tunable Crystallinity

A flexible and versatile method to fabricate two-dimensional metal–organic coordination networks (MOCNs) by bottom-up self-assembly is described. 2D crystalline layers were formed at the air–water interface, coordinated by ions from the liquid phase, and transferred onto a solid substrate with their crystallinity preserved. By using an inherently three-dimensional amphiphile, namely 25,26,27,28-tetrapropoxycalix[4]arene-5,11,17,23-tetracarboxylic acid, and a copper metal node, large and monocrystalline dendritic MOCN domains were formed. The method described allows for the fabrication of monolayers of tunable crystallinity on liquid and solid substrates. It can be applied to a large range of differently functionalized organic building blocks, also beyond macrocycles, which can be interconnected by diverse metal nodes. Transferable monolayer: A metal–organic coordination network consisting of a calix[4]arene derivative as the first example of 3D building blocks and copper nodes forms as a monolayer at the air–water interface. The monolayer can be transferred successfully onto a solid surface.
Datum: 16.10.2017


New Insights into the Activation and Deactivation of Au/CeZrO4 in the Low-Temperature Water-Gas Shift Reaction

Gold on ceria-zirconia is an active catalyst for the low-temperature water-gas shift reaction (LTS), a key stage of upgrading H2 reformate streams for fuel cells. However, this catalyst rapidly deactivates and the mechanism remains unclear. Using stop-start scanning transmission electron microscopy (STEM) to follow the exact same area of the sample at different stages of the LTS reaction, as well as complementary X-ray photoelectron spectroscopy, we observed the activation and deactivation of the catalyst at various stages. During the heating of the catalyst to reaction temperature, we observed the formation of small Au nanoparticles (1-2 nm) from sub-nm Au species. These nanoparticles then agglomerated further over 48 h on-stream, most rapidly in the first 5 h when the highest rate of deactivation was observed. These findings suggest that the primary deactivation process consists of the loss of active sites through the agglomeration and possible dewetting of Au nanoparticles.
Datum: 16.10.2017


Silicon Wafers Revealing Facet-Dependent Electrical Conductivity Properties

By breaking intrinsic Si (100) and (111) wafers to expose sharp {111} and {112} facets, electrical conductivity measurements on single and different silicon crystal faces have been performed through contacts with two tungsten probes. While Si {100} and {110} faces are barely conductive at low applied voltages as expected, Si {112} surface is highly conductive and Si {111} surface also shows good conductivity. Asymmetrical I-V curves have been recorded for the {111}/{112}, {111}/{110}, and {112}/{110} facet combinations because of different degrees of conduction band bending at these crystal surfaces presenting different barrier heights to current flow. In particular, the {111}/{110}, and {112}/{110} facet combinations give I-V curves resembling those of p-n junctions, suggesting a novel field effect transistor design is possible capitalizing on the pronounced facet-dependent electrical conductivity properties of silicon.
Datum: 16.10.2017


Near-Infrared-Light-Driven Hydrogen Evolution from Water using a Polypyridyl Triruthenium Photosensitizer

In order to realize the artificial photosynthetic devices splitting water to H2 and O2 (2H2O + hν 2H2 + O2), it is desirable to utilize a wider wavelength range of light that extends to a lower energy region of solar spectrum. Here we report a triruthenium photosensitizer [Ru3(dmbpy)6(μ-HAT)]6+ (dmbpy = 4,4'-dimethyl-2,2'-bipyridine, HAT = 1,4,5,8,9,12-hexaazatriphenylene), which absorbs near-infrared light up to 800 nm based on its 1MLCT transition. Importantly, [Ru3(dmbpy)6(μ-HAT)]6+ is found to be the first example of a photosensitizer which can drive H2 evolution under the illumination of near-infrared light above 700 nm. The electrochemical and photochemical studies reveal that the reductive quenching within the ion-pair adducts of [Ru3(dmbpy)6(μ-HAT)]6+ and ascorbate anions affords a singly reduced form of [Ru3(dmbpy)6(μ-HAT)]6+, which is used as a reducing equivalent in the subsequent water reduction process.
Datum: 16.10.2017


Reduction of a CeIII Siloxide Complex Affords a Tetradecker Arene-bridged CeII Sandwich

Organometallic multiple-decker sandwich complexes containing f-elements remain rare in spite of their attractive magnetic and electronic properties. The reduction of the CeIII siloxide complex, [KCeL4] (1; L = OSi(OtBu)3) with excess potassium in a THF/toluene mixture affords a rare tetradecker arene-bridged complex [K(2.2.2-crypt)]2[{(KL3Ce)(µ-η6:η6-C7H8)}2Ce] (3). The structure of 3 features a [Ce(C7H8)2] sandwich capped by [KL3Ce] moieties with a linear arrangement of the Ce ions. Structural parameters, UV-Vis data and DFT studies indicate the presence of CeII ions involved in δ bonding between the Ce cations and toluene dianions. Complex 3 is a rare lanthanide multidecker complex and the first containing non-classical divalent lanthanide ions. Moreover, oxidation of 1 by AgOTf (OTf = O3SCF3) yielded the CeIV complex, [CeL4] (2), showing that siloxide ligands can stabilize Ce in three oxidation states.
Datum: 16.10.2017


Enantioselective Synthesis of Tetrahydropyrano[3,4-b]indoles: Palladium(II)-Catalyzed Aminopalladation/1,4-Addition Sequence

A novel palladium(II)-catalyzed cyclization of aniline-tethered alkynyl cyclohexadienones is reported. This reaction offers an atom-economical and redox-neutral access to various cyclohexenone-fused tetrahydropyrano[3,4-b]indoles with high yield and excellent enantioselectivity. Remarkably, this work represents the first example on a transition-metal-catalyzed asymmetric intramolecular aminopalladation/1,4 addition sequence. At the end of a tether: Palladium(II)-catalyzed asymmetric cyclization of aniline-tethered alkynyl cyclohexadienones leads to functionalized tetrahydropyrano-[3,4-b]indoles in good yields and excellent enantioselectivities. The process involves a novel intramolecular aminopalladation/1,4 addition sequence.
Datum: 16.10.2017


An Epitope-Imprinted Biointerface with Dynamic Bioactivity for Modulating Cell–Biomaterial Interactions

In this study, an epitope-imprinting strategy was employed for the dynamic display of bioactive ligands on a material interface. An imprinted surface was initially designed to exhibit specific affinity towards a short peptide (i.e., the epitope). This surface was subsequently used to anchor an epitope-tagged cell-adhesive peptide ligand (RGD: Arg-Gly-Asp). Owing to reversible epitope-binding affinity, ligand presentation and thereby cell adhesion could be controlled. As compared to current strategies for the fabrication of dynamic biointerfaces, for example, through reversible covalent or host–guest interactions, such a molecularly tunable dynamic system based on a surface-imprinting process may unlock new applications in in situ cell biology, diagnostics, and regenerative medicine. Ad-here we go again: An epitope-peptide-imprinted polymeric film was used to reversibly anchor the cell-adhesive peptide RGD. Functionality was demonstrated by a controllable cell-adhesion behavior (see picture).
Datum: 16.10.2017


Asymmetric Intermolecular Heck Reaction of Propargylic Acetates and Cycloalkenes to Access Fused Cyclobutenes

An asymmetric Heck annulation of propargylic acetates with several types of cyclic olefins affords highly strained cyclobutenes in high enantioselectivity. An intermolecular Heck reaction between propargylic acetates and cyclic olefins results in the enantioselective synthesis of highly strained cyclobutenes.
Datum: 16.10.2017


Controlling Lanthanide Exchange in Triple-Stranded Helicates: A Way to Optimize Molecular Light-Upconversion

The kinetic lability of hexadentate gallium-based tripods is sufficient to ensure thermodynamic self-assembly of luminescent heterodimetallic [GaLn(L3)3]6+ helicates on the hour time scale, where Ln is a trivalent 4f-block cation. The inertness is, however, large enough for preserving the triple-helical structure when [GaLn(L3)3]6+ is exposed to lanthanide exchange. The connection of a second gallium-based tripod further slows down the exchange processes to such an extent that spectroscopically active [CrErCr(L4)3]9+ can be diluted into closed-shell [GaYGa(L4)3]9+ matrices without metal scrambling. This feature is exploited for pushing molecular-based energy-transfer upconversion (ETU) at room temperature. Inert noncovalent [GaL3]3+ ions promote an unprecedented keystone mechanism for the capture/release of labile trivalent lanthanides on hour time scales. The cooperative operation of two [GaL3]3+ tripods pushes the limit of inertness to over months, which makes these new materials compatible with the preparation of solid-state solutions displaying molecular-based energy-transfer upconversion at room temperature.
Datum: 16.10.2017


Synthesis of Anisotropic Hydrogels and Their Applications

Owing to their water-rich structures similar to biological tissues, hydrogels have long been regarded as promising scaffolds for artificial tissues and organs. However, in terms of structural anisotropy, most synthetic hydrogels are substantially different from biological systems. Synthetic hydrogels are usually composed of randomly oriented three-dimensional polymer networks, whereas biological systems adopt anisotropic structures with hierarchically integrated building units. Such anisotropic structures often play an essential role in biological systems to exhibit their particular functions, as represented by muscular textures comprising unidirectionally oriented actin-myosin units. In this context, anisotropic hydrogels provide an entry point for exploring the biomimetic applications of hydrogels. Reflecting these aspects, an increasing number of studies on anisotropic hydrogels have been reported recently. This Minireview highlights the outline and perspective of these anisotropic hydrogels, particularly focusing on their preparation, structures, and applications.
Datum: 16.10.2017


Ynamide Preactivation Allows a Regio- and Stereoselective Synthesis of α,β-disubstituted Enamides

A novel ynamide preactivation strategy enables the use of otherwise incompatible reagents and allows preparation of α,β-disubstituted enamides with high regio- and stereoselectivity. Mechanistic analysis reveals the intermediacy of a triflate-bound intermediate as a solution-stable, effective keteniminium reservoir, whilst still allowing subsequent addition of organometallic reagents.
Datum: 16.10.2017


Radical Heterocyclization and Heterocyclization Cascades Triggered by Electron Transfer to Amide-Type Carbonyl Compounds

Radical heterocyclizations triggered by electron transfer to amide-type carbonyls, using SmI2-H2O, provide straightforward access to bicyclic heterocyclic scaffolds containing bridgehead nitrogen centers. Furthermore, the first radical heterocyclization cascade triggered by reduction of amide-type carbonyls delivers novel, complex tetracyclic architectures containing five contiguous stereocenters with excellent diastereocontrol. Building bridges: Radical heterocyclization and heterocyclization cascades triggered by electron transfer to amide-type carbonyl groups provide straightforward access to heterocyclic scaffolds containing bridgehead nitrogen atoms. The radical cascade cyclizations deliver novel tetracyclic architectures, containing five contiguous stereocenters, with excellent diastereocontrol.
Datum: 13.10.2017


Low-Temperature Reductive Aminolysis of Carbohydrates to Diamines and Aminoalcohols by Heterogeneous Catalysis

Short amines, such as ethanolamines and ethylenediamines, are important compounds in today's bulk and fine chemicals industry. Unfortunately, current industrial manufacture of these chemicals relies on fossil resources and requires rigorous safety measures when handling explosive or toxic intermediates. Inspired by the elegant working mechanism of aldolase enzymes, a novel heterogeneously catalyzed process—reductive aminolysis—was developed for the efficient production of short amines from carbohydrates at low temperature. High-value bio-based amines containing a bio-derived C2 carbon backbone were synthesized in one step with yields up to 87 C%, in the absence of a solvent and at a temperature below 405 K. A wide variety of available primary and secondary alkyl- and alkanolamines can be reacted with the carbohydrate to form the corresponding C2-diamine. The presented reductive aminolysis is therefore a promising strategy for sustainable synthesis of short, acyclic, bio-based amines. Carbon–carbon bond scission is facilitated by amine reagent in the reductive aminolysis of carbohydrates. Short diamines and aminoalcohols are formed, at low temperature, in the presence of heterogeneous metal catalysts.
Datum: 13.10.2017


Total Syntheses of the Isomeric Aglain Natural Products Foveoglin A and Perviridisin B: Selective Excited-State Intramolecular Proton-Transfer Photocycloaddition

Selective excited-state intramolecular proton-transfer (ESIPT) photocycloaddition of 3-hydroxyflavones with trans, trans-1,4-diphenyl-1,3-butadiene is described. Using this methodology, total syntheses of the natural products (±)-foveoglin A and (±)-perviridisin B were accomplished. Enantioselective ESIPT photocycloaddition using TADDOLs as chiral hydrogen-bonding additives provided access to (+)-foveoglin A. Mechanistic studies have revealed the possibility for a photoinduced electron-transfer (PET) pathway. Light the way: Selective excited-state intramolecular proton-transfer (ESIPT) photocycloaddition of 3-hydroxyflavones with trans,trans-1,4-diphenyl-1,3-butadiene has enabled the total syntheses of isomeric aglain natural products foveoglin A and perviridisin B. Mechanistic studies have revealed the possibility of a photoinduced electron-transfer (PET) pathway.
Datum: 13.10.2017


Copper-Catalyzed Synthesis and Applications of Yndiamides

The first synthetic route to yndiamides, a novel class of double aza-substituted alkyne, has been established by the copper(I)-catalyzed cross-coupling of 1,1-dibromoenamides with nitrogen nucleophiles. The utility of these compounds is demonstrated in a range of transition-metal-catalyzed and acid-catalyzed transformations to afford a wide variety of 1,2-diamide functionalized products. Die, amide! The first synthetic route to yndiamides, a novel class of double aza-substituted alkyne, has been established by the copper(I)-catalyzed cross-coupling of 1,1-dibromoenamides with nitrogen nucleophiles. The utility of these compounds is demonstrated in a range of transition-metal-catalyzed and acid-catalyzed transformations to afford a wide variety of 1,2-diamide functionalized products.
Datum: 13.10.2017


Nickel-Catalyzed N-Alkylation of Acylhydrazines and Arylamines Using Alcohols and Enantioselective Examples

A borrowing-hydrogen reaction between amines and alcohols is an atom-economic way to prepare alkylamines, ideally with water as the sole byproduct. Herein, nickel catalysts are used for direct N-alkylation of hydrazides and arylamines using racemic alcohols. Moreover, a nickel catalyst of (S)-binapine was used for an asymmetric N-alkylation of benzohydrazide with racemic benzylic alcohols. Hydrogen autotransfer: Herein, nickel catalysts are used for direct N-alkylation of hydrazides and arylamines using racemic alcohols. The reaction proceeds by a hydrogen-borrowing pathway. Also described is an asymmetric version of the reaction of N-acylhydrazines.
Datum: 13.10.2017


Photoluminescence Lifetime Imaging of Synthesized Proteins in Living Cells Using an Iridium–Alkyne Probe

Designing probes for real-time imaging of dynamic processes in living cells is a continuous challenge. Herein, a novel near-infrared (NIR) photoluminescence probe having a long lifetime was exploited for photoluminescence lifetime imaging (PLIM) using an iridium-alkyne complex. This probe offers the benefits of deep-red to NIR emission, a long Stokes shift, excellent cell penetration, low cytotoxicity, and good resistance to photobleaching. This example is the first PLIM probe applicable to the click reaction of copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC) with remarkable lifetime shifts of 414 ns, before and after click reaction. The approach fully eliminates the background interference and distinguishes the reacted probes from the unreacted probes, thus enabling the wash-free imaging of the newly synthesized proteins within single living cells. Based on the unique properties of the iridium complexes, it is anticipated to have applications for imaging other processes within living cells. It takes a lifetime: A novel bioorthogonal probe, an Ir-alkyne complex, was designed and synthesized. It showed deep-red to near-IR emission and unexpected large lifetime shifts of 414 ns before and after click reaction. This probe enabled the wash-free imaging of the newly synthesized proteins within living cells. NP=nanoparticle.
Datum: 13.10.2017


Decatwistacene with a 170 Torsion

Two different lengths of twistacenes, namely hexatwistacene and decatwistacene induced by the steric-hindrance effect between imide groups and neighbouring annulated benzene rings, were synthesized via bottom-up synthesis of palladium-catalyzed Suzuki cross-coupling and C-H activation reaction. Single-crystal X-ray analyses revealed that decatwistacene, which is the longest twistacene reported until now, exhibits an astonishing overall end-to-end torsion angle of about 170, the largest torsion angle reported so far. Both twistacenes have an enhanced solubility and stability with respect to light and oxygen due to their large twisting deformations together with much lower LUMO levels caused by the introduction of imide groups, opening a window to the narrowest chiral graphene nanoribbons with good stability and processability.
Datum: 13.10.2017


Theoretical Treatment of CH3NH3PbI3 Perovskite Solar Cells

Hybrid halide perovskite solar cells (PSCs) giving over 22 % power conversion efficiencies (PCEs) have attracted considerable attention. Although perovskite plays a significant role in the operation of PSCs, the fundamental theories associated with perovskites have not been resolved in spite of the increase in research. In this Minireview, we assess the current understanding, based on the first-principles calculations, of structural and electronic properties, defects, ionic diffusion, and shift current for CH3NH3PbI3 perovskite, and the effect of ionic transport on the hysteresis of current–voltage curves in PSCs. The shift current connected to the possible presence of ferroelectricity is also discussed. The current state-of-the-art and some open questions regarding PSCs are also highlighted, and the benefits, challenges, and potentials of perovskite for use in PSCs are stressed. Better by calculation: First principles calculations of CH3NH3PbI3, including structural and electronic properties, defects, ionic diffusion, and shift current, can provide valuable support for further developing perovskite solar cells (PSCs).
Datum: 13.10.2017


An NMR Method To Pinpoint Supramolecular Ligand Binding to Basic Residues on Proteins

Targeting protein surfaces involved in protein–protein interactions by using supramolecular chemistry is a rapidly growing field. NMR spectroscopy is the method of choice to map ligand-binding sites with single-residue resolution by amide chemical shift perturbation and line broadening. However, large aromatic ligands affect NMR signals over a greater distance, and the binding site cannot be determined unambiguously by relying on backbone signals only. We herein employed Lys- and Arg-specific H2(C)N NMR experiments to directly observe the side-chain atoms in close contact with the ligand, for which the largest changes in the NMR signals are expected. The binding of Lys- and Arg-specific supramolecular tweezers and a calixarene to two model proteins was studied. The H2(C)N spectra track the terminal CH2 groups of all Lys and Arg residues, revealing significant differences in their binding kinetics and chemical shift perturbation, and can be used to clearly pinpoint the order of ligand binding. Lysine- and arginine-specific NMR experiments were conducted to selectively observe the side-chain atoms involved in the binding of supramolecular tweezers and to reveal the distinct binding order to multiple sites on a protein surface.
Datum: 13.10.2017


Chemical and Biological Aspects of Nutritional Immunity—Perspectives for New Anti-Infectives that Target Iron Uptake Systems

Upon bacterial infection, one of the defense mechanisms of the host is the withdrawal of essential metal ions, in particular iron, which leads to “nutritional immunity”. However, bacteria have evolved strategies to overcome iron starvation, for example, by stealing iron from the host or other bacteria through specific iron chelators with high binding affinity. Fortunately, these complex interactions between the host and pathogen that lead to metal homeostasis provide several opportunities for interception and, thus, allow the development of novel antibacterial compounds. This Review focuses on iron, discusses recent highlights, and gives some future perspectives which are relevant in the fight against antibiotic resistance. Fighting fit: The fight for essential metal ions is like a tug of war between pathogens and host cells. Interference in this struggle can lead to new ways to fight antibiotic resistance.
Datum: 13.10.2017


The Rolling-Up of Oligophenylenes to Nanographenes by a HF-Zipping Approach

Intramolecular aryl–aryl coupling is the key transformation in the rational synthesis of nanographenes and nanoribbons. In this respect the C−F bond activation was shown to be a versatile alternative enabling the synthesis of several unique carbon-based nanostructures. Herein we describe an unprecedentedly challenging transformation showing that the C−F bond activation by aluminum oxide allows highly effective domino-like C−C bond formation. Despite the flexible nature of oligophenylene-based precursors efficient regioselective zipping to the target nanostructures was achieved. We show that fluorine positions in the precursor structure unambiguously dictate the “running of the zipping-program” which results in rolling-up of linear oligophenylene chains around phenyl moieties yielding target nanographenes. The high efficiency of zipping makes this approach attractive for the synthesis of unsubstituted nanographenes which are difficult to obtain in pure form by other methods. Roll up, roll up: Virtually linear fluorinated oligophenylenes are converted into the “preprogrammed” challenging nanographenes via effective domino-like aryl–aryl coupling. The fluorine positions in the precursor structure unambiguously dictate the running of the “HF-zipping-program” leading to the formation of the target nanographene structure.
Datum: 13.10.2017


Flexible Viologen-Based Porous Framework Showing X-ray Induced Photochromism with Single-Crystal-to-Single-Crystal Transformation

A viologen-based Borromean entangled porous framework was found to be sensitive to both CuKα and MoKα X-ray sources, showing rapid photochromic response and recovery within one minute. The X-ray-induced photochromic process is accompanied by a reversible single-crystal-to-single-crystal (SC-SC) structural transformation, an unprecedented phenomenon for X-ray sensitive materials. The complex can be further processed into portable thin films for detecting the dose of the X-ray exposure. Moreover, the photochromism can occur over a broad temperature range of 100–333 K, both in the form of single crystals and thin films, making it a potential candidate for practical indoor and outdoor applications. X-ray specs: A viologen-based Borromean-entangled porous framework was found sensitive to X-rays and undergo a rapid photochromic response and recovery. This process is accompanied by a reversible single-crystal-to-single-crystal transformation. The material can be further processed into a thin film for detecting the dose of X-ray exposure.
Datum: 13.10.2017


Improved Biocompatibility of Black Phosphorus Nanosheets by Chemical Modification

Ultrasmall black phosphorus nanosheets (BPs) can trigger systemic inflammations. In their Communication (DOI: 10.1002/anie.201706228) X.-F. Yu, G. Jiang et al. report a method to reduce this side effect by surface modification of bare BPs with titanium sulfate (TiL4@BPs). The girl represents a potential candidate exposed to bare BPs through various routes during a wide application of this material. The effect of the bare BPs is shown by red shading. The BPs are less harmful after conversion to TiL4@BPs.
Datum: 13.10.2017


Characterization of Doubly Ionic Hydrogen Bonds in Protic Ionic Liquids by NMR Deuteron Quadrupole Coupling Constants: Differences to H-bonds in Amides, Peptides, and Proteins

Hydrogen bonds between ions are identified by the first deuteron quadrupole coupling constants (DQCCs) for protic ionic liquids (PILs), measured by solid-state NMR spectroscopy. In their Communication (DOI: 10.1002/anie.201708340) D. I. Kolokolov, R. Ludwig, et al. show that this NMR parameter is a sensitive probe of the doubly ionic hydrogen bonds present in PILs. The picture shows the NMR spectra as bridges symbolizing the doubly ionic hydrogen bonds between oppositely charged ions in PILs and mimicking the rocky mountains in the background.
Datum: 13.10.2017


A Strategy for Specific Fluorescence Imaging of Monoamine Oxidase A in Living Cells

Monoamine oxidase (MAO) has two isoforms, MAO-A and MAO-B, which show different functions and thus selective fluorescence imaging of which is important for biological studies. Currently, however, specific detection of MAO-A remains a great challenge. Herein, we report a new strategy for specific imaging of MAO-A via designing fluorescent probes by combining the characteristic structure of the enzymatic inhibitor with propylamine as a recognition moiety. The high specificity of our representative probe is demonstrated by imaging MAO-A in different live cells such as SH-SY5Y (high level of MAO-A) and HepG2 (high level of MAO-B), as further validated by both control probe and western blot analyses. The superior specificity of the probe may benefit the accurate detection of MAO-A in complex biosystems. Importantly, in this work the use of the characteristic structure of an inhibitor may serve as a general strategy to design a specific recognition moiety of fluorescent probes for an enzyme.
Datum: 13.10.2017


Feedback kinetics in mechanochemistry; the importance of cohesive states

Abstract: Although mechanochemical synthesis is becoming more widely applied and even commercialised, greater basic understanding is needed if the field is to progress on less of a trial-and-error basis. We report that a mechanochemical reaction in a ball mill exhibits unusual sigmoidal feedback kinetics that differ dramatically from the simple first-order kinetics for the same reaction in solution. An induction period followed by a rapid increase in reaction rate before the rate decreases again as the reaction goes to completion. The origin of these unusual kinetics is found to be a feedback cycle involving both chemical and mechanical factors. During the reaction the physical form of the reaction mixture changes from a powder to a cohesive rubber-like state, and this results in the observed reaction rate increase. The study reveals that non-obvious and dynamic rheological changes in the reaction mixture must be appreciated to understand how mechanochemical reactions progress.
Datum: 12.10.2017


Diastereoselective C-H bond amination for disubstituted pyrrolidines

We report herein on the improved diastereoselective synthesis of 2,5-disubstituted pyrrolidines from aliphatic azides. Experimental and theoretical studies of the C-H amination reaction mediated by the iron dipyrrinato complex (AdL)FeCl(OEt2) provided a model for diastereoinduction and allowed for systematic variation of the catalyst to enhance selectivity. Among the iron alkoxide and aryloxide catalysts evaluated, the iron-phenoxide complex exhibited superior performance towards the generation of syn 2,5-disubstituted pyrrolidines with high diastereoselectivity.
Datum: 12.10.2017


Biocatalytic Routes to Enantiomerically Enriched Dibenz[c,e]azepines

Biocatalytic retrosynthetic analysis of dibenz[c,e]azepines has highlighted the use of imine reductase (IRED) and w-transaminase (w-TA) biocatalysts to establish the key stereocentres of these molecules. Several enantiocomplementary IREDs were identified for the synthesis of (R)- and (S)-5-methyl-6,7-dihydro-5H-dibenz[c,e]azepine with excellent enantioselectivity by reduction of the parent imines. Crystallographic evidence suggests that IREDs may be able to bind one conformer of the imine substrate such that, upon reduction, the major product conformer is generated directly. ω-TA biocatalysts were also successfully employed for the production of enantiopure 1-(2-bromophenyl)ethan-1-amine enabling an orthogonal route for the installation of chirality into dibenz[c,e]azepine frameworks.
Datum: 12.10.2017


Enzyme Encapsulation by a Ferritin Cage

Ferritins, conserved across all kingdoms of life, are protein nanocages that evolved to mineralize iron. The last several decades have shown that these cages have considerable technological and medical potential owing to their stability and tolerance to modification, as well as their ability to template nanoparticle synthesis and incorporate small molecules. Here we show that it is possible to encapsulate proteins in a ferritin cage by exploiting electrostatic interactions with its negatively charged interior. Positively supercharged green fluorescent protein is efficiently taken up by Archaeoglobus fulgidus ferritin in a tunable fashion. Moreover, several enzymes were readily incorporated when genetically tethered to this fluorescent protein. These fusion proteins retained high catalytic activity and showed increased tolerance to proteolysis and heat. Equipping ferritins with enzymatic activity paves the way for many new nanotechnological and pharmacological applications. The caged bird sings: The natural ferritin nanocage from Archaeoglobus fulgidus can encapsulate positively charged proteins (green) within its lumenal cavity through electrostatic interactions. Enzymes (gray) attached to such charged guests retain their activity [substrate (S)product (P)], thus equipping the ferritin cages with new catalytic functions and opening new avenues for their use in nanotechnology and pharmacology.
Datum: 12.10.2017


C-H Functionalization for Hydrogen Isotope Exchange

The varied applications of hydrogen isotopes (deuterium, D, and tritium, T) in the physical and life sciences demands a range of methods for their installation in an array of molecular architectures. In this review, we describe recent advances in synthetic C-H functionalization for hydrogen isotope exchange.
Datum: 12.10.2017


Far-UV-Excited Luminescence of Nitrogen-Vacancy Centers: Evidence for Diamonds in Space

The nitrogen-vacancy (NV) centers in diamond are among the most thoroughly investigated defects in solid-state matter; however, our understanding of their properties upon far-UV excitation of the host matrix is limited. This knowledge is crucial for the identification of NV as the carrier of extended red emission (ERE) bands detected in a wide range of astrophysical environments. Herein, we report a study on the photoluminescence spectra of NV-containing nanodiamonds excited with synchrotron radiation over the wavelength range of 125–350 nm. We observed, for the first time, an emission at 520–850 nm with a quantum yield greater than 20 %. Our results share multiple similarities with the ERE phenomena, suggesting that nanodiamonds are a common component of dust in space. Luces in the sky, with diamonds: The fluorescence emission of nitrogen-vacancy centers at 520–850 nm upon far-UV excitation and with a quantum yield greater than 20 % is demonstrated. Sharing multiple similarities with the extended red emission observed in the interstellar medium, these results provide strong evidence for nanodiamonds as an important component of cosmic dust.
Datum: 12.10.2017


Direct Observation of Hemithioindigo-Motor Unidirectionality

Hemithioindigo molecular motors undergo very fast unidirectional rotation upon irradiation with visible light, which has prevented a complete analysis of their working mechanism. In this work, we have considerably slowed down their motion by using a new synthesis for sterically hindered motor derivatives. This method allowed the first observation of all four intermediate states populated during rotation. The exact order in which each isomeric state is formed under irradiation conditions was elucidated using low temperature 1H NMR spectroscopy in conjunction with other analytical methods. At the same time, complete unidirectionality could also be directly shown. Access to slowly rotating hemithioindigo motors opens up a plethora of new applications for visible-light-induced unidirectional motions, especially in areas such as catalysis, smart materials, and supramolecular chemistry. Rotation is a one-way street: Using a new methodology for the synthesis of sterically hindered hemithioindigo-based molecular motors, the full rotation cycle and its complete unidirectionality could be experimentally demonstrated for the first time. The new synthetic access allows the reliable synthesis of substituted hemithioindigo motors for advanced molecular machinery.
Datum: 12.10.2017


Gold Catalysis for Heterocyclic Chemistry: A Representative Case Study on Pyrone Natural Products

2-Pyrones and 4-pyrones are common structural motifs in bioactive natural products. However, traditional methods for their synthesis, which try to emulate the biosynthetic pathway of cyclization of a 1,3,5-tricarbonyl precursor, are often harsh and, therefore, not particularly suitable for applications to polyfunctionalized and/or sensitive target compounds. π-Acid catalysis, in contrast, has proved to be better for a systematic exploration of the pyrone estate. To this end, alkynes are used as stable ketone surrogates, which can be activated under exceedingly mild conditions due to the pronounced carbophilicity of [LAu]+ fragments (L=two electron donor ligand); attack of a tethered ester carbonyl group onto the transient alkyne–gold complex then forges the pyrone ring in a fully regiocontrolled manner. Pars pro toto: Various total syntheses of pyrone natural products showcase the practicality, efficiency, functional-group tolerance, and flexibility of heterocyclic chemistry based on π-acid catalysis. In conceptual terms, these case studies are representative of a modern approach to heterocycles that is largely complementary to established carbonyl condensation reactions.
Datum: 12.10.2017


Lanthanide-Coordinated Semiconducting Polymer Dots Used for Flow Cytometry and Mass Cytometry

Simultaneous monitoring of biomarkers as well as single-cell analyses based on flow cytometry and mass cytometry are important for investigations of disease mechanisms, drug discovery, and signaling-network studies. Flow cytometry and mass cytometry are complementary to each other; however, probes that can satisfy all the requirements for these two advanced technologies are limited. In this study, we report a probe of lanthanide-coordinated semiconducting polymer dots (Pdots), which possess fluorescence and mass signals. We demonstrated the usage of this dual-functionality probe for both flow cytometry and mass cytometry in a mimetic cell mixture and human peripheral blood mononuclear cells as model systems. The probes not only offer high fluorescence signal for use in flow cytometry, but also show better performance in mass cytometry than the commercially available counterparts. Lanthanide-coordinated semiconducting polymer nanoparticles with bright fluorescence show outstanding performances in both flow cytometry and mass cytometry for cell analyses.
Datum: 12.10.2017


Visible light-driven and Iron-promoted Thiocarboxylation of Styrenes and Acrylates with CO2

The first thiocarboxylation of styrenes and acrylates with CO2 is realized by using visible light as a driving force and catalytic iron salts as promoters. A variety of important β-thioacids are obtained in high yields. This multicomponent reaction proceeds in an atom- and redox-economical way with broad substrate scope under mild reaction conditions. Notably, high regio-, chemo- and diastero-selectivity are observed. Mechanistic studies indicate that a radical pathway can account for the unusual regioselectivity.
Datum: 12.10.2017


A Zwitterionic, 10 π Aromatic Hemisphere

A new concept in anionic 10 π aromaticity is described by the embedding of a compensating charge within an aromatic cyclononatetraenide ring by the symmetric superposition of an alkyl ammonium bridge. This is accomplished by the methylation of azatriquinacene to give a quaternary ammonium salt, followed by oxidation to the tetraene and final deprotonation. The resulting zwitterion is a stable [9]annulene with strong aromaticity as shown by its degree of C−C bond equalization and a nucleus-independent chemical shift value lower than that of benzene. The solid-state structure shows an eclipsed stacking motif with the electron-poor ammonium methyl groups occupying the electron-rich cavity of the aromatic bowl. Opposites do more than just attract: An ammonium center is suspended above an anionic, 10 π carbon toroid, leading to a novel, symmetric, bowl-shaped, strongly aromatic system that, despite being zwitterionic, is hydrocarbon soluble. Internal charge compensation results in unusual stability for an anionic annulene.
Datum: 12.10.2017


A Chemical Disruptor of the ClpX Chaperone Complex Attenuates the Virulence of Multidrug-Resistant Staphylococcus aureus

The Staphylococcus aureus ClpXP protease is an important regulator of cell homeostasis and virulence. We utilized a high-throughput screen against the ClpXP complex and identified a specific inhibitor of the ClpX chaperone that disrupts its oligomeric state. Synthesis of 34 derivatives revealed that the molecular scaffold is restrictive for diversification, with only minor changes tolerated. Subsequent analysis of the most active compound revealed strong attenuation of S. aureus toxin production, which was quantified with a customized MS-based assay platform. Transcriptome and whole-proteome studies further confirmed the global reduction of virulence and revealed characteristic signatures of protein expression in the compound-treated cells. Although these partially matched the pattern of ClpX knockout cells, further depletion of toxins was observed, leading to the intriguing perspective that additional virulence pathways may be directly or indirectly addressed by the small molecule. Clp its wings: A high-throughput screen against the ClpXP protease revealed the first non-covalent inhibitors of the chaperone ClpX. Binding of the inhibitors induces disruption of the ClpX hexamer and even of the whole ClpXP proteolytic complex. Treatment of Staphylococcus aureus with the compounds leads to the global down-regulation of a plethora of secreted virulence factors.
Datum: 12.10.2017


A Space-Charge Treatment of the Increased Concentration of Reactive Species at the Surface of a Ceria Solid Solution

A space-charge theory applicable to concentrated solid solutions (Poisson–Cahn theory) was applied to describe quantitatively as a function of temperature and oxygen partial pressure published data obtained by in situ X-ray photoelectron spectroscopy (XPS) for the concentration of Ce3+ (the reactive species) at the surface of the oxide catalyst Ce0.8Sm0.2O1.9. In contrast to previous theoretical treatments, these calculations clearly indicate that the surface is positively charged and compensated by an attendant negative space-charge zone. The high space-charge potential that develops at the surface (>0.8 V) is demonstrated to be hardly detectable by XPS measurements because of the short extent of the space-charge layer. This approach emphasizes the need to take into account defect interactions and to allow deviations from local charge neutrality when considering the surfaces of oxide catalysts. A Poisson–Cahn treatment explains the experimentally observed complex behaviour of [Ce3+] at the surface of the ceria-based catalyst, Ce0.8Sm0.2O1.9. Even at the surface of such a highly concentrated solid solution, local charge neutrality is found to be violated, with the formation of a positively charged surface and an extended negative space-charge zone.
Datum: 12.10.2017


Ligand and Solvent Controlled Regio- and Chemo-divergent Carbonylative Reactions

The development of high selective procedures is one of the core goals in organic chemistry, and the target which generations of chemists are pursuing. Among the known organic transformations, carbonylation reactions present an ideal choice for carbonyl-containing compounds preparation. In this review, the recent achievements on selectivity controlled carbonylation reactions have been summarized. The effects of ligands, solvents and bases on the selectivity have been discussed.
Datum: 12.10.2017


Unprecedented Sensitivity in a Probe for Detection and Imaging of Cathepsin B: Chemiluminescence Microscopy Cell Images of Natively-Expressed Enzyme

Until recently, chemiluminescence cell images could be obtained only using luciferase-activated probes. Moreover, chemiluminescence microscopy cell-imaging was never demonstrated for natively expressed enzymes like cathepsin B. Here we describe the design synthesis and evaluation of the first chemiluminescence probe for detection and imaging of cathepsin B. The probe activation mechanism relies on the release of a dioxetane intermediate, which undergoes chemiexcitation to emit green light with high efficiency under physiological conditions. Using the probe, we obtained clear images of cancerous leukemia and colon cells. This is the first demonstration of chemiluminescence cell images obtained by a probe for a natively-expressed endogenous enzyme. We anticipate that the concept presented in this study will be broadly used to develop analogous probes for other important proteases relevant to biomolecular processes.
Datum: 12.10.2017


Lanthanide-based T2ex and CEST complexes provide new insights into the design of pH sensitive MRI agents

A series of Eu3+ and Dy3+ DOTA-tetraamide complexes with four appended primary amine groups were prepared and their CEST and T1/T2 relaxation properties measured as a function of pH. The CEST signals in the Eu3+ complexes show a surprisingly strong CEST signal after the pH was reduced from 8 to 5. The opposite trend was observed for the Dy3+ complexes where the r2ex of bulk water protons increased dramatically from ~1.5 mM-1s-1 to ~13 mM-1s-1, while r1 remained unchanged. A fit of the CEST data (Eu3+ complexes) to Bloch theory and the T2 data (Dy3+ complexes) to Swift-Connick theory provided the proton exchange rates as a function of pH. These data showed that the four amine groups contribute significantly to proton catalyzed exchange of the Ln3+-bound water protons even though their pka's are much higher than the observed CEST or T2ex effects. This demonstrated the utility of using appended acidic/basic groups to catalyze prototropic exchange for imaging tissue pH by MRI.
Datum: 11.10.2017


Sequence Mandated, Distinct Assembly of Giant Molecules

Although controlling primary structures is by itself an enormous challenge for synthetic polymers, the potential of sequence control for tailoring hierarchical structures remains to be exploited, especially in the creation of new and unconventional phases. Herein, we design a series of model amphiphilic chain-like giant molecules by connecting both hydrophobic and hydrophilic molecular nanoparticles in precisely defined sequence and composition to investigate their intriguing sequence-dependent phase structures. Not only has composition changed the self-assembled phases, but also specific sequences are found to induce unconventional phase formation, including Frank-Kasper phases. The formation mechanism has been attributed to the conformational change driven by the collective hydrogen bonding and the sequence-mandated topology of the molecules. These results support that sequence-control in synthetic polymers can have dramatic impacts on the polymer properties and self-assembly.
Datum: 11.10.2017


Double Catalytic Kinetic Resolution (DoCKR) of Acyclic anti-1,3-Diols using Additive Horeau Amplification

The concept of synergistic double catalytic kinetic resolution (DoCKR) described in this article, was successfully applied to racemic acyclic anti-1,3-diols, a common motif in natural products. This process takes advantage of an additive Horeau amplification involving two successive enantioselective organocatalytic acylations reactions, and leading to diesters and recovered diols with high enantiopurities. It was first developed with C2-symmetrical diols and then further extended to non-C2-symmetrical anti diols to prepare useful chiral building blocks. The protocol is highly practical as it only requires 1 mol% of a commercially available organocatalyst and leads to easily separable products. This procedure was applied to the shortest reported total synthesis of (+)-cryptocaryalactone, a natural product with anti-germinative activity.
Datum: 11.10.2017


Detailed Evidence for an Unparalleled Interaction Mode between Calmodulin and Orai Proteins

Calmodulin (CaM) binds most of its targets by wrapping around an amphipathic α-helix. The N-terminus of Orai proteins contains a conserved CaM-binding segment but the binding mechanism is only partially characterized. Here, microscale thermophoresis (MST), surface plasmon resonance (SPR), and atomic force microscopy (AFM) were employed to study the binding equilibria, the kinetics, and the single-molecular interaction forces involved in the binding of CaM to the conserved helical segments of Orai1 and Orai3. The results consistently indicated step-wise binding of two separate target peptides to the two lobes of CaM. An unparalleled high affinity was found when two Orai peptides were dimerized or immobilized at high lateral density, thereby mimicking the close proximity of the N-termini in native Orai oligomers. The analogous experiments with smooth muscle myosin light chain kinase (smMLCK) showed only the expected 1:1 binding, confirming the validity of our methods.
Datum: 11.10.2017


Total Synthesis of Lycoricidine and Narciclasine via Chemical Dearomatization of Bromobenzene

The total synthesis of lycoricidine and narciclasine is enabled by the use of arenophile-mediated dearomative dihydroxylation of bromobenzene. Subsequent transpositive Suzuki coupling and cycloreversion deliver a key biaryl dihydrodiol intermediate, which is rapidly converted to lycoricidine through site-selective syn-1,4-hydroxyamination and deprotection. The total synthesis of narciclasine is accomplished via a late stage, amide-directed C-H hydroxylation of a lycoricidine intermediate. Moreover, the general applicability of this strategy to access dihydroxylated biphenyls has been demonstrated with several examples.
Datum: 11.10.2017


CODH-IV: A novel high efficiency CO-scavenging CO dehydrogenase with increased resistance to O2

CO dehydrogenases (CODHs) catalyse the reversible conversion between CO and CO2. Genomic analysis indicated that the metabolic functions of CODHs vary. The genome of Carboxydothermus hydrogenoformans encodes five CODHs (CODH-I - V), of which CODH-IV is found in a gene cluster near a peroxide reducing enzyme. Our kinetic and crystallographic experiments reveal that CODH-IV differs from other CODHs by characteristic properties: it has a very high affinity for CO, oxidizes CO at diffusion-limited rate over a wide range of temperatures, and is more tolerant to oxygen than CODH-II. Thus, our observations support the idea that CODH-IV is a CO scavenger in defence against oxidative stress and highlight that CODHs are more diverse in terms of reactivity than expected.
Datum: 11.10.2017


Mass-production of Mesoporous MnCo2O4 Spinel with MnIV- and CoII-rich Surface for Superior Bifunctional Oxygen Electrocatalysis

A mesoporous MnCo2O4 electrode materials is successfully fabricated for bifunctional oxygen electrocatalysis. The MnCo2O4 exhibits both Co3O4-like activity for oxygen evolution reaction (OER) and Mn2O3-approaching performance for oxygen reduction reaction (ORR). The potential difference between ORR metric and OER metric of MnCo2O4 is as low as 0.84 V. By XANES and XPS investigation, the notable activity is resulted from the preferred MnIV- and CoII-rich surface. Valuably, the products can be obtained in large-scale with the precise chemical components at relatively low temperature. The surface state engineering maybe open a new avenue to optimize electrocatalysis performance of electrode materials. The prominent bifunctional activity shows that MnCo2O4 has the possibility of being used in metal-air batteries and/or other energy devices.
Datum: 11.10.2017


A Lewis Base Catalysis Approach for the Photoredox Activation of Boronic Acids and Esters

We report herein the use of a dual catalytic system comprising of a Lewis base catalyst such as quinuclidin-3-ol or 4-dimethylaminopyridine combined with a photoredox catalyst to generate carbon radicals from either boronic acids or esters. This system enabled a wide range of alkyl boronic esters and aryl or alkyl boronic acids to react via radical addition with electron-deficient olefins to efficiently form C-C coupled products in a redox neutral fashion. The Lewis base catalyst was shown to form a redox-active complex with either boronic esters or the trimeric form of the boronic acids (boroxines) in solution.
Datum: 11.10.2017


Selective Radical Fluorination of Tertiary Alkyl Halides at Room Temperature

Direct fluorination of tertiary alkyl bromides and iodides with Selectfluor reagent is described. The halogen-exchange fluorination proceeds efficiently in acetonitrile at room temperature under metal-free conditions and exhibits a wide range of functional group compatibility. Furthermore, the reactions are highly selective in that alkyl chlorides and primary and secondary alkyl bromides remain intact. A radical mechanism is proposed for this selective fluorination.
Datum: 11.10.2017


Non-Uniform Optical Inscription of Actuation Domains in a Liquid Crystal Polymer of Uniaxial Orientation: An Approach to Complex and Programmable Shape Changes

Achieving complex shape change of liquid-crystal polymer networks (LCNs) under stimulation generally requires spatial configuration of the orientation direction, that is, patterned directors, of liquid crystal monomers prior to polymerization by means of treated surfaces. A strategy is demonstrated that needs only the simple uniaxial orientation of mesogens (monodomain) induced by mechanical stretching of LCNs. Using a rationally designed liquid crystal polymer, photocrosslinking is utilized to pattern or spatially organize the actuating monodomains in order to generate a differential contractile and/or extensional force field required for targeted shape change. Moreover, the approach enables versatile actuation modes and allows multiple shape changes to be programmed on a single piece of the polymer. This important feature is demonstrated with a specimen cut to have eight strips that, upon thermal stimulation, simultaneously display eight types of shape morphing. Roll with the changes: An easily processable liquid crystal polymer with only uniaxial orientation of mesogens can be programmed to display multiple, complex shape morphing on a single piece of the material (eight changes are shown in the picture). The approach consists in using photocrosslinking to spatially configure and organize the actuation domains in mechanically stretched specimen.
Datum: 11.10.2017


Singlet Oxygen during Cycling of the Aprotic Na-O2 Battery

Aprotic sodium-O2 batteries require the reversible formation/dissolution of sodium superoxide (NaO2) on cycling. Poor cycle life has been associated with parasitic chemistry caused by the reactivity of electrolyte and electrode with NaO2, a strong nucleophile and base. Its reactivity can, however, not consistently explain the side reactions and irreversibility. Here we show that singlet oxygen (1O2) forms at all stages of cycling and that it is a main driver for parasitic chemistry. It was detected in- and ex-situ via a 1O2 trap that selectively and rapidly forms a stable adduct with 1O2. The 1O2 formation mechanism involves proton mediated superoxide disproportionation on discharge, rest, and charge below ~3.3 V, and direct electrochemical 1O2 evolution above ~3.3 V. Trace water, which is needed for high capacities drives at the same time parasitic chemistry. Controlling the highly reactive singlet oxygen is thus crucial for achieving highly reversible cell operation.
Datum: 11.10.2017


Hydrogen-bonded Hexagonal Buckybowl Framework

We report a hydrogen-bonded two-dimensionally networked buckybowl architecture for the first time. Two types of hexagonal network (HexNet) structures (CPSM-1 and -2) have been achieved based on a sumanene derivative (CPSM) possessing 4,4'-dicarboxy-o-terphenyl groups in the periphery. CPSM-1 has a waved HexNet structure with an alternate alignment of upward and downward bowls. CPSM-2 has a bilayered HexNet structure composed of hamburger-shaped dimers of the bowls. This demonstrates that non-planar π-systems can be networked two-dimensionally by an appropriate supramolecular synthon to achieve structurally well-defined unique bumpy π-sheets. Furthermore, we revealed that CPSM-2 undergoes anisotropic shrinking along the c axis by 11% under high pressure conditions (970 MPa). The shrinkage is brought about by offset sliding between bumpy π-surfaces of the bilayered HexNet sheets.
Datum: 11.10.2017


Precise Assembly of Particles for Zigzag or Linear Patterns

Precise control of particles assembly has tremendous potential for fabricating intricate structures and functional materials. However, it is still a challenge to achieve one-dimensional assembly with precisely controlled morphology. In this work, we report an effective strategy to precisely assemble particles into well-defined patterns by liquid confinement through controlling the viscosity of the assembly system. It is found that high viscosity of the system impedes particles rearrangement, and facilitates the generation of zigzag or twined zigzag assembly structures; while low viscosity of the system allows particles to rearrange into linear or zipper structures driven by lowering the surface deformation of the liquid. As a result, precise control of different assembly patterns can be achieved through tuning the viscosity of solvent and size confinement ratios. This facile approach shows generality for particles assembly of different sizes and materials.
Datum: 11.10.2017


Non-enzymatic Oxidation of a Pentagalloylglucose Analog to Ellagitannins

The occurrence of more than 1,000 structural diversity in ellagitannins has been hypothesized to begin with oxidation of penta-O-galloyl--D-glucose (-PGG) to couple the galloyl groups. However, the non-enzymatic behavior of -PGG in the oxidation is unknown. Here, we disclose which galloyl groups on glucose tended to couple and which axial chirality was predominant in the derived hexahydroxydiphenoyl groups, when an analog of -PGG was subjected to oxidation. The study revealed that the galloyl groups coupled, in the following order of production ratio: at the 4,6-, 1,6-, 1,2-, 2,3-, and 3,6-positions with respective S, S, R, S, and R-axial chirality. Among them, the most preferred 4,6-coupling reflected the tendency observed in natural ellagitannins. An astonishing fact was that the second best was the 1,6-coupling. With the detection of a 3,6-coupled product, this work demonstrated that even ellagitannin skeletons with an axial-rich glucose core may generate non-enzymatically.
Datum: 11.10.2017


O2 Activation on Ceria Catalysts - The Importance of Substrate Crystallographic Orientation

An atomic-level understanding of dioxygen activation on metal oxides remains one of the major challenges in heterogeneous catalysis. By performing a thorough surface-science study of all three low-index single-crystal surfaces of ceria, probably the most important redox catalysts, we provide a direct spectroscopic characterization of reactive dioxygen species at defect sites on the reduced ceria (110) and (100) surfaces. Surprisingly, neither of these superoxo and peroxo species was found on ceria (111), the thermodynamically most stable surface of this oxide. Applying density functional theory, we could relate these apparently inconsistent findings to a sub-surface diffusion of O-vacancies on (111) substrates, but not on the less closely packed surfaces. These observations resolve a long standing debate concerning the location of O-vacancies on ceria surfaces and the activation of O2 on ceria powders.
Datum: 11.10.2017


Phosphorylation-Responsive Membrane Transport of Peptides

Phosphorylation and dephosphorylation of peptides by kinases and phosphatases is essential for signal transduction in biological systems and many diseases involve abnormal activities of these enzymes. Herein, we introduce amphiphilic calixarenes as key components for supramolecular, phosphorylation-responsive membrane transport systems. Dye efflux experiments with liposomes demonstrated that calixarenes are highly active counterion activators for established cell-penetrating peptides with EC50 values in the low nanomolar range. We have now found that they can even activate membrane transport of short peptide substrates for kinases involved in signal transduction, whereas the respective phosphorylated products are much less efficiently transported. This allows regulation of membrane transport activity by protein kinase A (PKA) and protein kinase C (PKC) as well as monitoring their activity in a label-free kinase assay.
Datum: 11.10.2017


Blockable Zn10L15 ion channels via subcomponent self-assembly

Metal-organic ion channels based on Zn10L15 pentagonal prisms have been prepared by subcomponent self-assembly. The insertion of these prisms into lipid membranes was investigated by ion-current and fluorescence measurements. The channels were found to mediate the transport of Cl- anions through planar lipid bilayers and into vesicles. Toluenesulfonate anions were observed to bind and plug the central channels of the prisms in the solid state and in solution. In membranes, adding dodecylsulfate impeded ion transport by channel blocking. Our Zn10L15 prism thus inserts into lipid bilayers to turn on ion transport, which can then be turned off through addition of the blocker dodecylsulfate.
Datum: 11.10.2017


Facile Supramolecular Processing of Carbon Nanotubes and Polymers Enabling Electromechanical Sensors

We herein report a facile, cost-competitive, and scalable method for producing viscoelastic conductors via one-pot melt-blending using polymers and supramolecular gels composed of carbon nanotubes (CNTs), diphenylamine (DP), and benzophenone (BP). When mixed, a non-volatile eutectic liquid (EL) produced by simply blending DP with BP (1:1 molar ratio) enabled not only the gelation of CNTs (EL-CNTs) but also the dissolution of a number of commodity polymers. In order to take these advantages, viscoelastic conductors were produced via one-pot melt-blending the EL and CNTs with a model thermoplastic elastomer, poly(styrene-b-butadiene-b-styrene) (SBS, styrene 30 wt%). The resulting composites displayed an excellent electromechanical sensory along with re-mendable properties. This simple method using cost-competitive EL components is expected to provide an alternative to the use of expensive ionic liquids as well as to facilitate the fabrication of novel composites for various purposes.
Datum: 11.10.2017


Evolving accelerated amidation by SpyTag/SpyCatcher to analyze membrane dynamics

SpyTag is a peptide that forms a spontaneous amide bond with its protein partner SpyCatcher. This protein superglue is a broadly useful tool for molecular assembly, locking together biological building blocks efficiently and irreversibly in diverse architectures. We initially developed SpyTag and SpyCatcher by rational design, through splitting a domain from a Gram-positive bacterial adhesin. Here we establish a phage display platform able to select for specific amidation, achieving an order of magnitude acceleration for interaction of the SpyTag002 variant with the SpyCatcher002 variant. We show that the 002 pair bonds rapidly under a wide range of conditions and at either protein terminus. SpyCatcher002 was fused to an intimin derived from enterohemorrhagic Escherichia coli. SpyTag002 reaction enabled specific and covalent decoration of intimin, for live cell fluorescent imaging of the dynamics of the bacterial outer membrane as cells divide.
Datum: 11.10.2017


Size and Interface Modulated Metal-Insulator Transition in Solution-Synthesized Nanoscale VO2-TiO2-VO2 Heterostructures

The M1 form of vanadium dioxide, which exhibits a reversible insulator-metal transition above room temperature, has been incorporated into nanoscale heterostructures through solution-phase epitaxial growth on the tips of rutile TiO2 nanorods. Four distinct classes of VO2-TiO2-VO2 nanorod heterostructures are accessible by modulating the growth conditions. Each type of VO2-TiO2-VO2 nanostructure has a different insulator-metal transition temperature that depends on the VO2 domains sizes and the TiO2-VO2 interfacial strain characteristics.
Datum: 11.10.2017


Copper-Catalyzed Synthesis of gamma-Amino Acids Featuring Quaternary Stereocenters

The first general asymmetric synthesis of gamma,gamma-disubstituted gamma-amino acids via Cu-catalyzed ring opening of non-strained lactones with amines is reported. This approach features ample scope, operational simplicity and wide functional group diversity. The catalytic process allows to access a series of highly functionalized enantioenriched gamma-amino acids featuring quaternary stereocenters with excellent enantiomeric ratios up to 98:2 and excellent yields up to 98%.
Datum: 10.10.2017


Post Graphene 2D Chemistry: The Emerging Field of Molybdenum Disulfide and Black Phosphorus Functionalization

The current state of the chemical functionalization of three types of single sheet 2D materials, namely, graphene, molybdenum disulfide (MoS2), and black phosphorus (BP) is summarized. Such 2D sheet polymers represent currently an emerging field at the interface of synthetic chemistry, physics, and materials science. Both covalent and non-covalent functionalization of sheet architectures allows for a systematic modification of their properties, i.e. an improvement of solubility and processability, the prevention of re-aggregation or a band gap tuning. Next to successful functionalization concepts also fundamental challenges are addressed. These include the insolubility and polydispersity of most 2D sheet polymers, the development of suitable characterization tools, the identification of effective binding strategies, the chemical activation of the usually rather unreactive basal planes for covalent addend binding, and the regioselectivity of plane addition reactions. Although a number of these questions remain elusive in this review, the first promising concepts to overcome such hurdles have been listed.
Datum: 10.10.2017


Characterization of conjugation pattern in large polysaccharide-protein conjugates by NMR

Carbohydrate-based vaccines are among the safest and most effective vaccines and represent potent tools for prevention of life-threatening bacterial infectious diseases, like meningitis and pneumonia. The chemical conjugation of a weak antigen to protein as a source of T-cell epitopes generates a glycoconjugate vaccine, that results more immunogenic. Several methods have been used so far to characterize the resulting polysaccharide-protein conjugates. However, a reduced number of methodologies has been proposed for measuring the degree of saccharide conjugation at the possible protein sites. Here we show that detailed information on large proteins conjugated with large polysaccharides can be achieved by a combination of solution and solid state NMR. As a test case, a large protein assembly, L-asparaginase II, has been conjugated with Neisseria meningitidis serogroup C capsular polysaccharide and the pattern and degree of conjugation were determined.
Datum: 10.10.2017


Catalytic Enantioselective Synthesis of Mariline A and Related Isoindolinones via a Biomimetic Approach

The catalytic enantioselective synthesis of isoindolinones was achieved via the condensation of ortho-formyl-arylketones and anilines. In the presence of 1 mol% of a chiral phosphoric acid catalyst, reactions reach completion within 10 minutes and provide products with up to 98% ee. Anilines with an ortho t-butyl group form atropisomeric products, enabling the simultaneous generation of axial and point chirality from two achiral substrates. This method was applied to the first synthesis of mariline A.
Datum: 10.10.2017


Three-dimensionally π-Conjugated Diradical Molecular Cage

π-Conjugated molecular cages are very challenging targets in structural organic chemistry, supramolecular chemistry and materials science. Herein, we report the synthesis and physical characterizations of the first three-dimensionally π-conjugated diradical molecular cage PTM-C, in which two polychlorotriphenylmethyl (PTM) radicals are linked by three bis(3,6-carbazolyl) bridges. This cage compound was synthesized mainly by intermolecular Yamamoto coupling followed by deprotonation and oxidation. It is stable and its structure was confirmed by X-ray crystallographic analysis. The two carbon-centered PTM radicals are weakly coupled through electronic interactions with the carbazole spacers, as revealed by optical, electronic and magnetic measurements as well as theoretical calculations.
Datum: 10.10.2017


Decoupled Thermo- and pH-responsive Hydrogel Microspheres Cross-linked by Rotaxane Networks

Rotaxane cross-linked (RC) microgels that exhibit a decoupled thermo- and pH-responsive volume transition were developed. The pH-induced changes of the aggregation/disaggregation states of cyclodextrin in the RC networks were used to control the swelling capacity of the entire microgels. Different from conventional thermo- and pH-responsive microgels, which are usually obtained from copolymerizations involving charged monomers, the RC microgels respond to temperature as intended, even in the presence of charged functional molecules such as dyes in the microgel dispersion. The results of this study should lead to new applications, including drug delivery systems, that require a retention of their "smart" functions even in environments that may contain foreign ions, e.g. in in vivo experiments.
Datum: 10.10.2017


Selective activation of C-H bonds by cascading photochemistry with biocatalysis

Selective oxyfunctionalisation of inert C-H bonds under mild conditions can be achieved using peroxygenases. This approach, however, is impaired by the poor robustness of these enzymes in the presence of hydrogen peroxide as the stoichiometric oxidant. Here, we demonstrate that inorganic photocatalysts such as gold-titanium dioxide efficiently provide H2O2 from methanol-driven reductive activation of ambient oxygen in suitable amounts to ensure high reactivity and robustness of the enzyme. Using this approach stereoselective hydroxylation of ethyl benzene to (R)-1-phenyl ethanol in high enantioselectivity (>98% ee) and excellent turnover numbers of the biocatalyst (>71.000) was achieved.
Datum: 10.10.2017


Targeting the Protein Kinases Cysteinome

Drugs that function by covalent bond formation represent a considerable fraction of our repository of effective medicines but safety concerns and the complexity of developing covalent inhibitors has rendered covalent targeting a less attractive strategy for rational drug design. The recent approval of four covalent kinase inhibitors and the development of highly potent covalent kinase probes with exceptional selectivity has raised significant interest in industry and academic research and validated the concept of covalent kinase targeting for clinical applications. The abundance of cysteines at diverse positions in and around the kinase active site suggests that a large fraction of kinases can be targeted by covalent inhibitors. Here we review recent developments of this rapidly growing area in kinase drug development and highlight the unique opportunities and challenges of this strategy.
Datum: 10.10.2017


Società Chimica Italiana Medals 2017


Datum: 05.10.2017


Back Cover: Potential-Cycling Synthesis of Single Platinum Atoms for Efficient Hydrogen Evolution in Neutral Media (Angew. Chem. Int. Ed. 44/2017)

Single Pt atoms can be synthesized on CoP-based nanotube arrays supported by Ni foams through potential cycling. In their Communication on page 13694 ff., X. J. Liu, J. Luo, and co-workers use this strategy to transfer single Pt atoms from a Pt source to a nanotube substrate in a neutral phosphate buffer solution (PBS). As an electrocatalyst for the hydrogen evolution reaction (HER) in PBS, these single atoms exhibit a higher Pt-mass activity and a better stability than commercial Pt/CIn.
Datum: 05.10.2017


Inside Back Cover: Olefins from Natural Gas by Oxychlorination (Angew. Chem. Int. Ed. 44/2017)

Turning myth into reality. Pérez-Ramírez et al. show in their Communication on page 13670 ff. the outstanding performance of EuOCl for the production of light olefins from ethane and propane by oxychlorination chemistry. The high activity, selectivity, and stability of the system are illustrated by the mythological princess Europa, who was carried from Asia to the Hellenic world by Zeus, who was disguised as a white bull. Both the continent of Europe and the element europium later took her name.
Datum: 05.10.2017


Inside Cover: Precisely Assembled Cyclic Gold Nanoparticle Frames by 2D Polymer Single-Crystal Templating (Angew. Chem. Int. Ed. 44/2017)

Free-standing frames can be prepared by a directed assembly method in which nanoparticles are precisely linked together by using polymer single crystals (PSCs) as a template. In their Communication on page 13645 ff., C. Y. Li and co-workers use preformed PSCs to direct the crystallization of block copolymers, which in turn direct gold NPs (AuNPs) to form precisely controlled AuNP frames. These AuNP frames topologically resemble nanoparticle rings and cyclic polymer chains, and show unique surface plasmon resonance behaviors.
Datum: 05.10.2017


Cover Picture: A Pyrene-Linked Cavity within a β-Barrel Protein Promotes an Asymmetric Diels–Alder Reaction (Angew. Chem. Int. Ed. 44/2017)

A pyrene-linked protein cavity attracts two substrate molecules like the scent of a flower attracts butterflies. In their Communication on page 13618 ff., A. Onoda, T. Hayashi, and co-workers demonstrate that a polycyclic pyrene moiety linked within the rigid protein scaffold of the β-barrel of nitrobindin acts as a platform to provide an aromatic interaction with a substrate. An asymmetric Diels–Alder reaction between azachalcone and cyclopentadiene proceeds smoothly with high stereoselectivity within the reaction scaffold.
Datum: 05.10.2017


Regioselective Intermolecular Allylic C−H Amination of Disubstituted Olefins via Rhodium/π-Allyl Intermediates

A method for catalytic intermolecular allylic C−H amination of trans-disubstituted olefins is reported. The reaction is efficient for a range of common nitrogen nucleophiles bearing one electron-withdrawing group, and proceeds under mild reaction conditions. Good levels of regioselectivity are observed for a wide range of electronically diverse trans-β-alkyl styrene substrates. A method for catalytic intermolecular allylic C−H amination of trans-disubstituted olefins has been developed that is efficient for a range of common nitrogen nucleophiles bearing one electron-withdrawing group (EWG), and proceeds under mild reaction conditions. Good levels of regioselectivity are observed for a wide range of electronically diverse trans-β-alkyl styrene substrates.
Datum: 04.10.2017


Reductive Coupling of Acrylates with Ketones and Ketimines by a Nickel-Catalyzed Transfer-Hydrogenative Strategy

Nickel-catalyzed coupling of benzyl acrylates with activated ketones and imines provides γ-butyrolactones and lactams, respectively. The benzyl alcohol byproduct released during the lactonization/lactamization event is relayed to the next cycle where it serves as the reductant for C−C bond formation. This strategy represents a conceptually unique approach to transfer-hydrogenative C−C bond formation, thus providing examples of reductive heterocyclizations where hydrogen embedded within an alcohol leaving group facilitates turnover. Catch and release: Nickel-catalyzed coupling of benzyl acrylates with activated ketones and imines provides a direct entry to γ-butyrolactones and lactams, respectively. The benzyl alcohol by-product released during the lactonization/lactamization event is relayed to the next cycle, where it then serves as the reductant for C−C bond formation.
Datum: 04.10.2017


Organocatalytic Enantioselective Protonation for Photoreduction of Activated Ketones and Ketimines Induced by Visible Light

The first catalytic asymmetric photoreduction of 1,2-diketones and α-keto ketimines under visible light irradiation is reported. A transition-metal-free synergistic catalysis platform harnessing dicyanopyrazine-derived chromophore (DPZ) as the photoredox catalyst and a non-covalent chiral organocatalyst is effective for these transformations. With the flexible use of a chiral Brønsted acid or base in H+ transfer interchange to control the elusive enantioselective protonation, a variety of chiral α-hydroxy ketones and α-amino ketones were obtained with high yields and enantioselectivities. Enantioselective protonation: The first catalytic asymmetric photoreduction of 1,2-diketones and α-keto ketimines under visible light irradiation relies on a transition-metal-free cooperative catalysis platform that harnesses dicyanopyrazine-derived chromophore (DPZ) as the photoredox catalyst and a noncovalent chiral organocatalyst. A variety of chiral α-hydroxy ketones and α-amino ketones was obtained with high yields and enantioselectivities.
Datum: 04.10.2017


Mass Production and Pore Size Control of Holey Carbon Microcages

Architectural control of porous solids, such as porous carbon cages, has received considerable attention for versatile applications because of their ability to interact with liquids and gases not only at the surface, but throughout the bulk. Herein we report a scalable, facile spray-pyrolysis route to synthesize holey carbon microcages with mosquito-net-like shells. Using the surfaces of water droplets as the growth templates, styrene–butadiene rubber macromolecules are controllably cross-linked, and size-controllable holes on the carbon shells are generated. The as-formed carbon microcages encapsulating Si nanoparticles exhibit enhanced lithium-storage performances for lithium-ion batteries. The scalable, inexpensive synthesis of porous carbon microcages with controlled porosity and the demonstration of outstanding electrochemical properties are expected to extend their uses in energy storage, molecular sieves, catalysis, adsorbents, water/air filters, and biomedical engineering. Holey controllable: Holey carbon microcages with controllable pore sizes are easily synthesized by a scalable spray-pyrolysis technique. Beyond energy storage, these porous, hollow carbon microcages can be further constructed into micro-containers for holding other functional materials with promising applications. Their lithium-ion storage ability for use in lithium-ion batteries is demonstrated.
Datum: 04.10.2017


Catalytic Asymmetric Mannich Reaction with N-Carbamoyl Imine Surrogates of Formaldehyde and Glyoxylate

N,O-acetals (NOAcs) were developed as bench stable surrogates for N-carbamoyl, (Boc, Cbz and Fmoc) formaldehyde and glyoxylate imines in asymmetric Mannich reactions. The NOAcs can be directly utilized in the chiral primary amine catalyzed Mannich reactions of both acyclic and cyclic β-ketocarbonyls with high yields and excellent stereoselectivity. The current reaction offers a straightforward approach in the asymmetric synthesis of α- or β-amino carbonyls bearing chiral quaternary centers in a practical and highly stereocontrolled manner. On the bench: N,O-acetals (NOAcs) were developed as bench-stable surrogates for N-carbamoyl (Boc, Cbz, Fmoc) formaldehyde and glyoxylate imines in asymmetric Mannich reactions. This reaction offers a straightforward approach for the asymmetric synthesis of α- or β-amino carbonyls bearing chiral quaternary centers in a practical and highly stereocontrolled manner. EWG=electron-withdrawing group, PG=protecting group.
Datum: 02.10.2017


Benzodisilacyclobutadienes: 8π-Electron Systems with an Antiaromatic Silicon Ring

Benzodisilacyclobutadienes 2 a–c were isolated as blue to green crystalline solids from the reaction of stable disilyne 1 and 1,2-dibromobenzenes in the presence of potassium graphite. In the solid state, substantial bond alternation was observed within the benzene rings of 2 a–c. In hexane, 2 a–c showed remarkable bathochromic shifts of the ππ* (HOMOLUMO) absorption bands at 625–670 nm. NMR spectra and theoretical calculations indicated that the diamagnetic ring currents of the benzene rings of 2 a–c are considerably reduced by contributions from the antiaromatic 1,2-disilacyclobutadienes. In their entirety, the obtained results indicate that 2 a–c represent 8π-electron systems that contain an antiaromatic 1,2-disilacyclobutadiene. Slowing the flow: Benzodisilacyclobutadienes (see structure) were synthesized and isolated as blue and green crystalline solids. According to their solid-state structures, UV/Vis absorption and NMR spectra, and theoretical calculations, these benzodisilacyclobutadienes exist as 8π-electron systems that contain an antiaromatic 1,2-disilacyclobutadiene.
Datum: 02.10.2017


Extended Ladder-Type Benzo[k]tetraphene-Derived Oligomers

Well-defined, fused-ring aromatic oligomers represent promising candidates for the fundamental understanding and application of advanced carbon-rich materials, though bottom-up synthesis and structure–property correlation of these compounds remain challenging. In this work, an efficient synthetic route was employed to construct extended benzo[k]tetraphene-derived oligomers with up to 13 fused rings. The molecular and electronic structures of these compounds were clearly elucidated. Precise correlation of molecular sizes and crystallization dynamics was established, thus demonstrating the pivotal balance between intermolecular interaction and molecular mobility for optimized processing of highly ordered solids of these extended conjugated molecules. Aromatic “rungs” of the ladder: A highly efficient thermodynamic annulation enables the bottom-up syntheses of well-defined, fused-ring oligomers that imitate graphene nanostripes. Electronic structures and crystallization dynamics of these oligomers are highly dependent on the molecular size.
Datum: 02.10.2017


Enzymatic Cascade Catalysis for the Synthesis of Multiblock and Ultrahigh-Molecular-Weight Polymers with Oxygen Tolerance

Synthesis of well-defined multiblock and ultrahigh-molecular-weight (UHMW) polymers has been a perceived challenge for reversible-deactivation radical polymerization (RDRP). An even more formidable task is to synthesize these extreme polymers in the presence of oxygen. A novel methodology involving enzymatic cascade catalysis is developed for the unprecedented synthesis of multiblock polymers in open vessels with direct exposure to air and UHMW polymers in closed vessels without prior degassing. The success of this methodology relies on the extraordinary deoxygenation capability of pyranose oxidase (P2Ox) and the mild yet efficient radical generation by horseradish peroxidase (HRP). The facile and green synthesis of multiblock and UHMW polymers using biorenewable enzymes under environmentally benign and scalable conditions provides a new pathway for developing advanced polymer materials. Ultrahigh: Enzymatic cascade catalysis enables the synthesis of multiblock (up to 10 blocks) copolymers and ultrahigh-molecular-weight polymers (UHMW; up to 2.3×106 g mol−1). The reaction employs a P2Ox-HRP system and can be run in vessels open to air, thus highlighting the oxygen tolerance of the process. P2Ox=pyranose oxidase, HRP=horseradish peroxidase, ACAC=acetylacetone, RAFT=reversible addition-fragmentation chain transfer.
Datum: 02.10.2017


Integration of Bromine and Cyanogen Bromide Generators for the Continuous-Flow Synthesis of Cyclic Guanidines

A continuous-flow process for the in situ on-demand generation of cyanogen bromide (BrCN) from bromine and potassium cyanide that makes use of membrane-separation technology is described. In order to circumvent the handling, storage, and transportation of elemental bromine, a continuous bromine generator using bromate–bromide synproportionation can optionally be attached upstream. Monitoring and quantification of BrCN generation was enabled through the implementation of in-line FTIR technology. With the Br2 and BrCN generators connected in series, 0.2 mmol BrCN per minute was produced, which corresponds to a 0.8 m solution of BrCN in dichloromethane. The modular Br2/BrCN generator was employed for the synthesis of a diverse set of biologically relevant five- and six-membered cyclic amidines and guanidines. The set-up can either be operated in a fully integrated continuous format or, where reactive crystallization is beneficial, in semi-batch mode. Cyanogen bromide on tap: The highly toxic but synthetically powerful reagent cyanogen bromide (BrCN) was generated in a fully continuous fashion from benign precursors and directly used for the synthesis of medicinally relevant N-heterocycles.
Datum: 02.10.2017


Visualization of Stereoselective Supramolecular Polymers by Chirality-Controlled Energy Transfer

Chirality-driven self-sorting is envisaged to efficiently control functional properties in supramolecular materials. However, the challenge arises because of a lack of analytical methods to directly monitor the enantioselectivity of the resulting supramolecular assemblies. Presented herein are two fluorescent core-substituted naphthalene-diimide-based donor and acceptor molecules with minimal structural mismatch and they comprise strong self-recognizing chiral motifs to determine the self-sorting process. As a consequence, stereoselective supramolecular polymerization with an unprecedented chirality control over energy transfer has been achieved. This chirality-controlled energy transfer has been further exploited as an efficient probe to visualize microscopically the chirality driven self-sorting. To the core: Presented herein are two fluorescent core-substituted naphthalene-diimide-based donor and acceptor molecules with minimal structural mismatch, and they comprise self-recognizing chiral motifs to facilitate the self-sorting process. Visual discrimination of the stereoselective self-sorted and co-assembled supramolecular polymers is presented by using chirality-controlled energy transfer.
Datum: 02.10.2017


Gold(III) Alkyne Complexes: Bonding and Reaction Pathways

The synthesis and characterization of hitherto hypothetical AuIII π-alkyne complexes is reported. Bonding and stability depend strongly on the trans effect and steric factors. Bonding characteristics shed light on the reasons for the very different stabilities between the classical alkyne complexes of PtII and their drastically more reactive AuIII congeners. Lack of back-bonding facilitates alkyne slippage, which is energetically less costly for gold than for platinum and explains the propensity of gold to facilitate C−C bond formation. Cycloaddition followed by aryl migration and reductive deprotonation is presented as a new reaction sequence in gold chemistry. Good as gold: The synthesis of hitherto hypothetical gold(III) π-alkyne complexes highlights the differences between classical platinum alkyne complexes and their drastically more reactive AuIII congeners. Alkyne bonding in these complexes is subject to a strong trans influence, with ligands trans to a pyridine N atom being bound significantly more strongly than those trans to an anionic C donor.
Datum: 02.10.2017


Selective C−O Bond Cleavage of Sugars with Hydrosilanes Catalyzed by Piers’ Borane Generated In Situ

Described herein is the selective reduction of sugars with hydrosilanes catalyzed by using Piers’ borane [(C6F5)2BH] generated in situ. The hydrosilylative C−O bond cleavage of silyl-protected mono- and disaccharides in the presence of a (C6F5)2BH catalyst, generated in situ from (C6F5)2BOH, takes place with excellent chemo- and regioselectivities to provide a range of polyols. A study of the substituent effects of sugars on the catalytic activity and selectivity revealed that the steric environment around the anomeric carbon (C1) is crucial. Piers’ borane [(C6F5)2BH], generated in situ, is demonstrated to promote the hydrosilylative reduction of sugars, thereby providing a series of linear or cyclic polyols with high chemo- and regioselectivities under mild conditions. Studies of catalytic reactivity and regioselectivity with regard to the C−O bond cleavage with hydrosilanes suggest an importance of the steric environment around the anomeric carbon center of the sugar.
Datum: 02.10.2017


A Biomimetic Escape Strategy for Cytoplasm Invasion by Synthetic Particles

The translocation of nanomaterials or complex delivery systems into the cytosol is a major challenge in nanobiotechnology. After receptor-mediated endocytosis, most nanomaterials are sequestered and undergo degradation, therapy inactivation, or exocytosis. Herein we explore a novel surface particle coating made of adsorbed carbon nanotubes that provides coated materials with new properties that reproduce the viral cell-invasive mechanisms, namely, receptor-mediated endocytosis, endolysosomal escape, and cytosolic particle release preserving cell viability. This novel biomimetic coating design will enable the intracytoplasmic delivery of many different functional materials endowed with therapeutic, magnetic, optical, or catalytic functionalities, thus opening the door to a wide array of chemical and physical processes within the cytosolic or nuclear domains, and supporting new developments in the biotechnological, pharmaceutical, and biomedical industries. A clean getaway: An engineered nanocoating composed of carbon nanotubes enabled particles with nano/micrometer dimensions to break through lysosomal membranes and invade the intracellular realm (see picture). The coated materials resemble viruses in terms of their structure and reproduce the viral cell-invasive mechanisms of receptor-mediated endocytosis, endolysosomal escape, and cytosolic particle release with the preservation of cell viability.
Datum: 02.10.2017


Electron-Transfer and Hydride-Transfer Pathways in the Stoltz–Grubbs Reducing System (KOtBu/Et3SiH)

Recent studies by Stoltz, Grubbs et al. have shown that triethylsilane and potassium tert-butoxide react to form a highly attractive and versatile system that shows (reversible) silylation of arenes and heteroarenes as well as reductive cleavage of C−O bonds in aryl ethers and C−S bonds in aryl thioethers. Their extensive mechanistic studies indicate a complex network of reactions with a number of possible intermediates and mechanisms, but their reactions likely feature silyl radicals undergoing addition reactions and SH2 reactions. This paper focuses on the same system, but through computational and experimental studies, reports complementary facets of its chemistry based on a) single-electron transfer (SET), and b) hydride delivery reactions to arenes. Transfers: Triethylsilane and potassium tert-butoxide react to form a highly attractive and versatile system. The work herein highlights the reductive transformations which lead to 1) C−N bond cleavage in N-benzyl- and N-allylindoles and 2) reduction of polycyclic arenes to their dihydro derivatives.
Datum: 02.10.2017


An Ultraflexible Silicon–Oxygen Battery Fiber with High Energy Density

To satisfy the rapid development of portable and wearable electronics, it is highly desired to make batteries with both high energy densities and flexibility. Although some progress has been made in recent decades, the available batteries share critical problems of poor energy storage capacity and low flexibility. Herein, we have developed a silicon–oxygen battery fiber with high energy density and ultra-high flexibility by designing a coaxial architecture with a lithiated silicon/carbon nanotube hybrid fiber as inner anode, a polymer gel as middle electrolyte and a bare carbon nanotube sheet as outer cathode. The fiber showed a high energy density of 512 Wh kg−1 and could effectively work after bending for 20 000 cycles. These battery fibers have been further woven into flexible textiles for a large-scale application. A silicon–oxygen battery fiber with high energy density and ultra-high flexibility has been created. The coaxial architecture of the fiber was obtained by using a lithiated silicon/carbon nanotube hybrid fiber as inner anode, a polymer gel as middle electrolyte and a carbon nanotube sheet as outer cathode.
Datum: 02.10.2017


Regioselective para-Carboxylation of Catechols with a Prenylated Flavin Dependent Decarboxylase

The utilization of CO2 as a carbon source for organic synthesis meets the urgent demand for more sustainability in the production of chemicals. Herein, we report on the enzyme-catalyzed para-carboxylation of catechols, employing 3,4-dihydroxybenzoic acid decarboxylases (AroY) that belong to the UbiD enzyme family. Crystal structures and accompanying solution data confirmed that AroY utilizes the recently discovered prenylated FMN (prFMN) cofactor, and requires oxidative maturation to form the catalytically competent prFMNiminium species. This study reports on the in vitro reconstitution and activation of a prFMN-dependent enzyme that is capable of directly carboxylating aromatic catechol substrates under ambient conditions. A reaction mechanism for the reversible decarboxylation involving an intermediate with a single covalent bond between a quinoid adduct and cofactor is proposed, which is distinct from the mechanism of prFMN-associated 1,3-dipolar cycloadditions in related enzymes. Biocatalytic CO2 fixation: 3,4-Dihydroxybenzoic acid decarboxylases are shown to catalyze the regioselective para-carboxylation of the aromatic core of catechols under ambient conditions. The enzymes depend on the recently discovered prenylated FMN cofactor for catalysis, which is proposed to proceed via a monocovalently bound quinoid–cofactor intermediate.
Datum: 02.10.2017


Rotational Spectroscopy Probes Water Flipping by Full Fluorination of Benzene

The topology of the interaction of water with benzene changes drastically upon full HF substitution on the aromatic ring: the weak O−H⋅⋅⋅π hydrogen bond is replaced by a O⋅⋅⋅π linkage, of about the same strength. Hexafluorobenzene–water appears to be the prototype system to investigate this kind of weak bond. The pulsed Fourier transform microwave technique has been used for the detection of the rotational spectra of the normal species and five isotopologues which unambiguously led to the identification of the geometry. Quantum mechanical calculations have been performed to interpret the experimental evidence. Flipping water: The prototype system for the lone-pair⋅⋅⋅π-hole interaction, hexafluorobenzene–water, has been investigated by rotational spectroscopy. Interesting chemical and dynamic features have been found: a) fluorine substitution flips the water bond with benzene, from O−H⋅⋅⋅π to O⋅⋅⋅π hole; b) water is almost freely rotating above the ring and the spectrum of the complex appears to be that of a symmetric top.
Datum: 02.10.2017


Catanionic Coacervate Droplets as a Surfactant-Based Membrane-Free Protocell Model

We report on the formation of surfactant-based complex catanionic coacervate droplets in mixtures of decanoic acid and cetylpyridinium chloride or cetyltrimethylammonium bromide. We show that coacervation occurs over a broad range of composition, pH, and ionic strength. The catanionic coacervates consist of elongated micelles, sequester a wide range of solutes including water-soluble organic dyes, polysaccharides, proteins, enzymes, and DNA, and can be structurally stabilized by sodium alginate or gelatin-based hydrogelation. These results suggest that catanionic coacervates could be exploited as a novel surfactant-based membrane-free protocell model. Catanionic coacervates as protocells: Proteins, enzymes, and DNA are spontaneously sequestered within catanionic surfactant coacervates, thereby affording a novel protocell model.
Datum: 02.10.2017


Manganese Dioxide Nanozymes as Responsive Cytoprotective Shells for Individual Living Cell Encapsulation

A powerful individual living cell encapsulation strategy for long-term cytoprotection and manipulation is reported. It uses manganese dioxide (MnO2) nanozymes as intelligent shells. As expected, yeast cells can be directly coated with continuous MnO2 shells via bio-friendly Mn-based mineralization. Significantly, the durable nanozyme shells not only can enhance the cellular tolerance against severe physical stressors including dehydration and lytic enzyme, but also enable the survival of cells upon contact with high levels of toxic chemicals for prolonged periods. More importantly, these encased cells after shell removal via a facile biomolecule stimulus can fully resume growth and functions. This strategy is applicable to a broad range of living cells Hard cell: Individual living cells were encapsulated within biodegradable MnO2 nanozyme shells. These shells not only enhanced the cellular tolerance against severe physical stressors, but also enabled the survival of cells upon encountering high levels of toxic chemicals for prolonged times.
Datum: 02.10.2017


Manipulation of Biomolecule-Modified Liquid-Metal Blobs

Soft and deformable liquid metals (LMs) are building components in various systems related to uncertain and dynamic task environments. Herein we describe the development of a biomolecule-triggered external-manipulation method involving LM conjugates for the construction of future innovative soft robotics operating in physiological environments. Functional soft hybrids composed of a liquid-metal droplet, a thiolated ligand, and proteins were synthesized for the expression of diverse macroscopic commands, such as attachment to cells, binary fusion, and self-propelled movement through molecular recognition and enzymatic reactions. Our technology could be used to create new state-of-the-art soft robots for chemical and biomedical engineering applications. No interest in blobbing out: Biomolecule-functionalized liquid-metal (LM) blobs (see picture) were developed with macroscopic behavior promoted by molecular recognition, for example, through formation of the biotin–avidin complex. Bubble formation on the surface of enzyme-modified LM conjugates also enabled self-propelled dynamic motion. These behaviors could lead to efficient LM soft robots for operation in physiological environments.
Datum: 02.10.2017


Regioselective Transformation of Long π-Conjugated Backbones: From Oligofurans to Oligoarenes

We demonstrate the transformation of oligofurans through sequential Diels–Alder cycloaddition reactions to provide oligoarenes in two chemical steps, regardless of the oligomer length. By this method, oligonaphthalenes containing up to six units were obtained in high yield through the formation of up to 12 new C−C bonds. The versatility of this method was demonstrated for various polyaromatic hydrocarbons. The regioselectivity of this process enabled the synthesis of a library of substituted triarylenes from a single terfuran precursor by modification of the dienophile strength and the order of addition. Overall, this study demonstrates that long oligofurans are interesting not only as organic electronic materials, but also as starting materials for the formation of various conjugated systems. To cut a long story short: Oligofurans underwent sequential Diels–Alder reactions to provide oligoarenes in two chemical steps, regardless of the oligomer length (see picture). Different maleimide and benzyne dienophiles were also used to construct a range of substituted oligoarenes from a single oligofuran precursor in a highly regioselective manner.
Datum: 02.10.2017


Transition-Metal-Free Ring-Opening Silylation of Indoles and Benzofurans with (Diphenyl-tert-butylsilyl)lithium

A practical method is presented for ring opening various indoles and benzofurans with concomitant stereoselective silylation using readily generated (diphenyl-tert-butylsilyl)lithium to afford ortho-β-silylvinylanilines or -phenols. Dearomatization of the heteroarene core proceeds in the absence of any transition-metal catalyst through addition of a silyl anion and a subsequent stereoselective β-elimination. DFT calculations provide insight into the mechanism. Functionalizing C−X bond cleavage of heteroarenes is rare and generally requires transition-metal catalysts. Open for business: Ring-opening silylation of various indoles and benzofurans using diphenyl-tert-butylsilyllithium affords ortho-β-silylvinyl anilines or phenols. Dearomatization of the heteroarene core proceeds in the absence of any transition-metal catalyst through addition of a silyl anion and a subsequent stereoselective β-elimination.
Datum: 29.09.2017


Synthesis of Acylborons by Ozonolysis of Alkenylboronates: Preparation of an Enantioenriched Amino Acid Acylboronate

A concise synthesis of acylborons was achieved by ozonolysis of alkenyl MIDA (N-methyliminodiacetic acid) boronates. This reaction exhibits excellent functional-group tolerance and is applicable to various acyl MIDA boronates and potassium acyltrifluroborates (KATs) which could not be synthesized by previous methods. In addition, α-amino acylborons, which would be essential for peptide ligations, were prepared for the first time. The acylboron of l-alanine was obtained in high enantiopurity and found to be configurationally stable. Oligopeptide synthesis between the α-amino KATs and amino acid in dilute aqueous media was studied. In the (o)zone: Highly functionalized acylborons are prepared by ozonolysis of alkenyl MIDA boronates. The first synthesis of α-amino acylborons, including the enantiopure alanine-type acylboron was achieved by using this method. The products are essential for protein–protein conjugation by potassium acyltrifluoroborate ligation. Oligopeptide synthesis using α-amino acylborons proceeded in dilute aqueous medium and the alanine-type acylboron is configurationally stable under ligation conditions.
Datum: 29.09.2017


Diradicaloid or Zwitterionic Character: The Non-Tetrahedral Unsaturated Compound [Si4{N(SiMe3)Dipp}4] with a Butterfly-type Si4 Substructure

The reduction of the tribromoamidosilane {N(SiMe3)Dipp}SiBr3 (Dipp=2,6-iPr2C6H3) with potassium graphite or magnesium resulted in the formation of [Si4{N(SiMe3)Dipp}4] (1), a bicyclo[1.1.0]tetrasilatetraamide. The Si4 motif in 1 does not adopt a tetrahedral substructure and exhibits two three-coordinate and two four-coordinate silicon atoms. The electronic situation on the three-coordinate silicon atoms is rationalized with positive and negative polarization based on EPR analysis, magnetization measurements, and DFT calculations as well as 29Si CP MAS NMR and multinuclear NMR spectroscopy in solution. Reactivity studies with 1 and radical scavengers confirmed the partial charge separation. Compound 1 reacts with sulfur to give a novel type of silicon sulfur cage compound substituted with an amido ligand, [Si4S3{N(SiMe3)Dipp}4] (2). A change in structure: The unsaturated butterfly-shaped Si4 ring compound 1 ([Si4{N(SiMe3)Dipp}4]; Dipp=2,6-iPr2C6H3) was obtained by reduction of {N(SiMe3)Dipp}SiBr3. Compound 1 exhibits positively and negatively polarized three-coordinate Si atoms with flexible geometry, as determined by experimental and computational studies. Reactions of 1 with 5 or 8 equiv of sulfur afforded compound 2, a new amido-substituted Si4S3 cage compound.
Datum: 27.09.2017


Synergistic Effects between Atomically Dispersed Fe−N−C and C−S−C for the Oxygen Reduction Reaction in Acidic Media

Various advanced catalysts based on sulfur-doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur-doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template-sacrificing method. The incorporated sulfur gives a thiophene-like structure (C−S−C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e− ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur-free variant (Fe/NC) in 0.5 m H2SO4. A sulfur-doped Fe/N/C catalyst with much better activity in the oxygen reduction reaction (ORR) in 0.5 m H2SO4 solution than the sulfur-free variant was developed. The incorporated sulfur atoms reduce the electron localization around the iron centers, improve the interaction with oxygenated species, and therefore facilitate the complete 4 e− ORR in acidic solution.
Datum: 27.09.2017


AFM Imaging of Hybridization Chain Reaction Mediated Signal Transmission between Two DNA Origami Structures

Signal transfer is central to the controlled exchange of information in biology and advanced technologies. Therefore, the development of reliable, long-range signal transfer systems for artificial nanoscale assemblies is of great scientific interest. We have designed such a system for the signal transfer between two connected DNA nanostructures, using the hybridization chain reaction (HCR). Two sets of metastable DNA hairpins, one of which is immobilized at specific points along tracks on DNA origami structures, are polymerized to form a continuous DNA duplex, which is visible using atomic force microscopy (AFM). Upon addition of a designed initiator, the initiation signal is efficiently transferred more than 200 nm from a specific location on one origami structure to an end point on another origami structure. The system shows no significant loss of signal when crossing from one nanostructure to another and, therefore, has the potential to be applied to larger multi-component DNA assemblies. Molecular domino chain reaction: The hybridization chain reaction (HCR) between metastable DNA hairpins is immobilized on a DNA origami structure and implemented for signal transfer across two DNA origami structures.
Datum: 27.09.2017


Specific and Direct Amplified Detection of MicroRNA with MicroRNA:Argonaute-2 Cleavage (miRACle) Beacons

MicroRNA detection is a valuable method for determining cell identity. Molecular beacons are elegant sensors that can transform intracellular microRNA concentration into a fluorescence intensity. While target binding enhances beacon fluorescence, the degree of enhancement is insufficient for demanding applications. The addition of specialty nucleases can enable target recycling and signal amplification, but this process complicates the assay. We have developed and characterized a class of beacons that are susceptible to the endogenous nuclease Argonaute-2 (Ago2). After purification of the complex by co-immunoprecipitation, microRNA:Ago2 cleavage (miRACle) beacons undergo site- and sequence-specific cleavage, and show a 13-fold fluorescence enhancement over traditional beacons. The system can be adapted to any microRNA sequence, and can cleave nuclease-resistant, non-RNA bases, potentially allowing miRACle beacons to be designed for cells without interference from non-specific nucleases. Simple sensors simulate substrate: MicroRNA detection with molecular beacons can be used for in situ genetic profiling. Beacons that are susceptible to the endogenous nuclease Argonaute-2 (Ago2) have now been developed. After purification of the complex by co-immunoprecipitation, microRNA:Ago2 cleavage (miRACle) beacons undergo site- and sequence-specific cleavage, and show a 13-fold fluorescence enhancement over traditional beacons.
Datum: 27.09.2017


Bioinspired Total Synthesis of (−)-Vescalin: A Nonahydroxytriphenoylated C-Glucosidic Ellagitannin

The first total synthesis of the 2,3,5-O-(S,R)-nonahydroxytriphenoylated (NHTP) C-glucosidic ellagitannin (−)-vescalin was accomplished through a series of transformations mimicking the sequence of events leading to its biogenesis. The key steps of this synthesis encompass a Wittig-mediated ring opening of a glucopyranosic hemiacetal, a C-glucosidation event through a phenolic aldol-type reaction, and a Wynberg–Feringa–Yamada-type oxidative phenolic coupling, which forged the NHTP unit of (−)-vescalin. Catch a tan(nin): The total synthesis of a first member of the nonahydroxytriphenoylated (NHTP) C-glucosidic ellagitannins, (−)-vescalin, is described. The route is closely tailored to the commonly proposed sequence of events leading to its biogenesis. Its characteristic 2,3,5-(S,R)-NHTP unit was elaborated by a copper(II)-mediated Wynberg–Feringa–Yamada-type phenolic coupling using the achiral bicyclic diamine N,N′-dimethylbispidine.
Datum: 27.09.2017


Organocatalytic Intramolecular [4+2] Cycloaddition between In Situ Generated Vinylidene ortho-Quinone Methides and Benzofurans

Described herein is the enantioselective construction of oxygen-containing [5-6-5] tricyclic heterocycles by an organocatalyzed asymmetric [4+2] cycloaddition of vinylidene ortho-quinone methides and benzofurans. According to this methodology, a series of oxygen-containing [5-6-5] tricyclic heterocycles with various functional groups were synthesized in excellent enantio- and diastereoselectivities (>99 % ee, >20:1 d.r.). Furthermore, the deuterium-labeling experiments and high-resolution mass spectroscopy demonstrated that a vinylidene ortho-quinone methide intermediate was involved and possibly resulted from a prototropic rearrangement of 2-ethynylphenol. Remarkably, a catalyst loading as low as 0.1 mol %, and a gram-scale synthesis were achieved for this transformation. Triple play: The enantioselective construction of oxygen-containing [5-6-5] tricyclic heterocycles by a thiourea-catalyzed asymmetric [4+2] cycloaddition of vinylidene ortho-quinone methides (VQMs) and benzofurans is reported. A series of oxygen-containing [5-6-5] tricyclic heterocycles having various functional groups were synthesized with excellent enantio- and diastereoselectivities.
Datum: 27.09.2017


Enantioselective Total Synthesis of (−)-Deoxoapodine

The first enantioselective total synthesis of (−)-deoxoapodine is described. Our synthesis of this hexacyclic aspidosperma alkaloid includes an efficient molybdenum-catalyzed enantioselective ring-closing metathesis reaction for the desymmetrization of an advanced intermediate that introduces the C5-quaternary stereocenter. After C21-oxygenation, the pentacyclic core was accessed by electrophilic C19-amide activation and transannular spirocyclization. A biogenetically inspired dehydrative C6-etherification reaction proved highly effective to secure the F-ring and the fourth contiguous stereocenter of (−)-deoxoapodine with complete stereochemical control. A molybdenum-catalyzed enantioselective ring-closing metathesis reaction for the desymmetrization of an advanced intermediate is one of the key steps of the total synthesis of (−)-deoxoapodine. After C21-oxygenation, the pentacyclic core was accessed through amide activation and transannular spirocyclization. A dehydrative C6-etherification introduced the F-ring and the fourth contiguous stereocenter.
Datum: 27.09.2017


Phosphate Transfer in Activated Protein Complexes Reveals Interaction Sites

For many proteins, phosphorylation regulates their interaction with other biomolecules. Herein, we describe an unexpected phenomenon whereby phosphate groups are transferred non-enzymatically from one interaction partner to the other within a binding interface upon activation in the gas phase. Providing that a high affinity exists between the donor and acceptor sites, this phosphate transfer is very efficient and the phosphate groups only ligate to sites in proximity to the binding region. Consequently, such phosphate-transfer reactions may define with high precision the binding site between a phosphoprotein and its binding partner, as well as reveal that the binding site in this system is retained in the phase transfer from solution to the gas phase. Pass the P: Phosphate groups can be transferred non-enzymatically from one interaction partner to the other during gas-phase activation. In high-affinity complexes, this phosphate transfer occurs within the binding site, thereby revealing the interaction interface within the protein/phosphopeptide complex.
Datum: 27.09.2017


Combining Orthogonal Chain-End Deprotections and Thiol–Maleimide Michael Coupling: Engineering Discrete Oligomers by an Iterative Growth Strategy

Orthogonal maleimide and thiol deprotections were combined with thiol–maleimide coupling to synthesize discrete oligomers/macromolecules on a gram scale with molecular weights up to 27.4 kDa (128mer, 7.9 g) using an iterative exponential growth strategy with a degree of polymerization (DP) of 2n−1. Using the same chemistry, a “readable” sequence-defined oligomer and a discrete cyclic topology were also created. Furthermore, uniform dendrons were fabricated using sequential growth (DP=2n−1) or double exponential dendrimer growth approaches (DP=22n −1) with significantly accelerated growth rates. A versatile, efficient, and metal-free method for construction of discrete oligomers with tailored structures and a high growth rate would greatly facilitate research into the structure–property relationships of sophisticated polymeric materials. Discrete oligomers were fabricated by a versatile, efficient, and metal-free chemical process, which combines orthogonal deprotections of maleimide and thiol groups together with thiol–maleimide Michael coupling. Key: iterative exponential growth (IEG); double exponential dendrimer growth (DEDG); degree of polymerization (DP).
Datum: 27.09.2017


Conversion of Methane into Methanol and Ethanol over Nickel Oxide on Ceria–Zirconia Catalysts in a Single Reactor

The conversion of methane into alcohols under moderate reaction conditions is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value-added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria–zirconia (NiO/CZ) can convert methane to methanol and ethanol in a single, steady-state process at 723 K using O2 as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO2 as the product of catalytic combustion. The unusual activity of this catalyst is attributed to the synergy between the small Lewis acidic NiO clusters and the redox-active CZ support, which also stabilizes the small NiO clusters. Controlled oxidation: Methanol and ethanol are produced continuously from methane and oxygen in a single reaction over a catalyst consisting of NiO clusters on ceria–zirconia. Oxygen is the abundantly available oxidant for this reaction and the presence of steam ensures the production of alcohols as opposed to products of the complete combustion of methane.
Datum: 26.09.2017


Repairing Nanoparticle Surface Defects

Solar devices based on semiconductor nanoparticles require the use of conductive ligands; however, replacing the native, insulating ligands with conductive metal chalcogenide complexes introduces structural defects within the crystalline nanostructure that act as traps for charge carriers. We utilized atomically thin semiconductor nanoplatelets as a convenient platform for studying, both microscopically and spectroscopically, the development of defects during ligand exchange with the conductive ligands Na4SnS4 and (NH4)4Sn2S6. These defects can be repaired via mild chemical or thermal routes, through the addition of L-type ligands or wet annealing, respectively. This results in a higher-quality, conductive, colloidally stable nanomaterial that may be used as the active film in optoelectronic devices. Solar devices based on semiconductor nanoparticles require the use of conductive ligands; however, the exchange of insulating ligands with conductive metal chalcogenide complexes introduces structural defects that act as traps for charge carriers. CdSe nanoplatelets were used as a model system to show that it is possible to minimize the formation of defects, as well as trigger surface healing, by a judicious choice of mild treatments.
Datum: 26.09.2017


Efficient Aryl Migration from an Aryl Ether to a Carboxylic Acid Group To Form an Ester by Visible-Light Photoredox Catalysis

We have developed a highly efficient aryl migration from an aryl ether to a carboxylic acid group through retro-Smiles rearrangement by visible-light photoredox catalysis at ambient temperature. Transition metals and a stoichiometric oxidant and base are avoided in the transformation. Inspired by the high efficiency of this transformation and the fundamental importance of C−O bond cleavage, we developed a novel approach to the C−O cleavage of a biaryl ether to form two phenolic compounds, as demonstrated by a one-pot, two-step gram-scale reaction under mild conditions. The aryl migration exhibits broad scope and can be applied to the synthesis of pharmaceutical compounds, such as guacetisal. Primary mechanistic studies indicate that the catalytic cycle occurs by a reductive quenching pathway. A great migration: In a retro-Smiles rearrangement under visible-light photoredox catalysis at ambient temperature, one aryl group of a diaryl ether migrated to the carboxy group to form an ester (see scheme). The transformation requires no transition metals and no stoichiometric oxidant or base and could be followed by saponification in a one-pot, two-step process enabling overall C−O cleavage of the aryl ether.
Datum: 26.09.2017


Engineered Fluorine Metabolism and Fluoropolymer Production in Living Cells

Fluorine has become an important element for the design of synthetic molecules for use in medicine, agriculture, and materials. Despite the many advantages provided by fluorine for tuning key molecular properties, it is rarely found in natural metabolism. We seek to expand the molecular space available for discovery through the development of new biosynthetic strategies that cross synthetic with natural compounds. Towards this goal, we engineered a microbial host for organofluorine metabolism and show that we can achieve the production of the fluorinated diketide 2-fluoro-3-hydroxybutyrate at approximately 50 % yield. This fluorinated diketide can be used as a monomer in vivo to produce fluorinated poly(hydroxyalkanoate) (PHA) bioplastics with fluorine substitutions ranging from around 5–15 %. This system provides a platform to produce mm flux through the key fluoromalonyl coenzyme A (CoA) building block, thereby offering the potential to generate a broad range of fluorinated small-molecule targets in living cells. Live action: An engineered microbial host for organofluorine metabolism can produce a fluorinated diketide at around 50 % yield. The diketide can be used as a monomer to produce fluorinated poly(hydroxyalkanoate) bioplastics in vivo with fluorine substitution of up to 15 %. This system provides a platform to generate a broad range of fluorinated small-molecule targets in living cells.
Datum: 26.09.2017


From Precursor Powders to CsPbX3 Perovskite Nanowires: One-Pot Synthesis, Growth Mechanism, and Oriented Self-Assembly

The colloidal synthesis and assembly of semiconductor nanowires continues to attract a great deal of interest. Herein, we describe the single-step ligand-mediated synthesis of single-crystalline CsPbBr3 perovskite nanowires (NWs) directly from the precursor powders. Studies of the reaction process and the morphological evolution revealed that the initially formed CsPbBr3 nanocubes are transformed into NWs through an oriented-attachment mechanism. The optical properties of the NWs can be tuned across the entire visible range by varying the halide (Cl, Br, and I) composition through subsequent halide ion exchange. Single-particle studies showed that these NWs exhibit strongly polarized emission with a polarization anisotropy of 0.36. More importantly, the NWs can self-assemble in a quasi-oriented fashion at an air/liquid interface. This process should also be easily applicable to perovskite nanocrystals of different morphologies for their integration into nanoscale optoelectronic devices. Cubes, wires, and assemblies: Single-crystalline perovskite nanowires were prepared directly from precursor powders in a single-step ligand-assisted process by ultrasonication. The nanowires likely resulted from the oriented attachment of nanocubes. Quasi-oriented self-assemblies of the perovskite nanowires were fabricated at air/liquid interfaces.
Datum: 26.09.2017


One-Step Multigram-Scale Biomimetic Synthesis of Psiguadial B

A gram-scale synthesis of psiguadial B, a purported inhibitor of human hepatoma cell growth, has been achieved in one step by a biomimetic three-component coupling of caryophyllene, benzaldehyde, and diformylphloroglucinol. This cascade reaction is catalyzed by N,N′-dimethylethylenediamine, and proceeds at ambient temperature to generate four stereocenters, two rings, one C−O bond, and three C−C bonds. Combined computational and experimental investigations suggest the biosynthesis of the natural product is non-enzyme mediated, and is the result of a Michael addition between caryophyllene and a reactive ortho-quinone methide, followed by two sequential intramolecular cationic cyclization events. A one-step multigram-scale synthesis of psiguadial B has been achieved using a biomimetic three-component coupling, thus generating three C−C bonds, one C−O bond, two rings, and four stereocenters. Combined synthetic and computational experiments suggest the reaction proceeds by a Michael addition of caryophyllene to an in situ generated ortho-quinone methide, followed by two sequential cationic cyclization events.
Datum: 26.09.2017


Bioactive Macrocyclic Inhibitors of the PD-1/PD-L1 Immune Checkpoint

Blockade of the immunoinhibitory PD-1/PD-L1 pathway using monoclonal antibodies has shown impressive results with durable clinical antitumor responses. Anti-PD-1 and anti-PD-L1 antibodies have now been approved for the treatment of a number of tumor types, whereas the development of small molecules targeting immune checkpoints lags far behind. We characterized two classes of macrocyclic-peptide inhibitors directed at the PD-1/PD-L1 pathway. We show that these macrocyclic compounds act by directly binding to PD-L1 and that they are capable of antagonizing PD-L1 signaling and, similarly to antibodies, can restore the function of T-cells. We also provide the crystal structures of two of these small-molecule inhibitors bound to PD-L1. The structures provide a rationale for the checkpoint inhibition by these small molecules, and a description of their small molecule/PD-L1 interfaces provides a blueprint for the design of small-molecule inhibitors of the PD-1/PD-L1 pathway. Circle of life: Macrocyclic peptide inhibitors can block the PD-1/PD-L1 pathway by directly binding to PD-L1 and, similarly to anti-PD-L1 antibodies, they can restore the function of T-cells. Structures of the macrocycle/PD-L1 interfaces provide a foundation for the design of small-molecule inhibitors with antitumor properties.
Datum: 26.09.2017


Expanding the Structural Space of Ribosomal Peptides: Autocatalytic N-Methylation in Omphalotin Biosynthesis

Tail-Me: The N-methylation of backbone amide bonds in peptide natural products was thought to be exclusive to non-ribosomal peptides. A newly discovered methylation mechanism now brings this structural feature into the world of ribosomal peptides, thereby significantly expanding the structural diversity of ribosomally synthesized and post-translationally modified peptides (RiPPs).
Datum: 26.09.2017


High-Performance CsPb1−xSnxBr3 Perovskite Quantum Dots for Light-Emitting Diodes

All inorganic CsPbBr3 perovskite quantum dots (QDs) are potential emitters for electroluminescent displays. We have developed a facile hot-injection method to partially replace the toxic Pb2+ with highly stable Sn4+. Meanwhile, the absolute photoluminescence quantum yield of CsPb1−xSnxBr3 increased from 45 % to 83 % with SnIV substitution. The transient absorption (TA) exciton dynamics in undoped CsPbBr3 and CsPb0.67Sn0.33Br3 QDs at various excitation fluences were determined by femtosecond transient absorption, time-resolved photoluminescence, and single-dot spectroscopy, providing clear evidence for the suppression of trion generation by Sn doping. These highly luminescent CsPb0.67Sn0.33Br3 QDs emit at 517 nm. A device based on these QDs exhibited a luminance of 12 500 cd m−2, a current efficiency of 11.63 cd A−1, an external quantum efficiency of 4.13 %, a power efficiency of 6.76 lm w−1, and a low turn-on voltage of 3.6 V, which are the best values among reported tin-based perovskite quantum-dot LEDs. Suppressed trion formation: CsPb1−xSnxBr3 quantum dots (QDs) were synthesized by a hot-injection approach. As trion formation is suppressed by the SnIV substitution, light-emitting diodes (LEDs) based on these highly luminescent QDs performed very well, with the highest current efficiencies and external quantum efficiencies ever reported for such Sn-based systems.
Datum: 26.09.2017


Three-Dimensional Hierarchical Architectures Derived from Surface-Mounted Metal–Organic Framework Membranes for Enhanced Electrocatalysis

Inspired by the rapid development of metal–organic-framework-derived materials in various applications, a facile synthetic strategy was developed for fabrication of 3D hierarchical nanoarchitectures. A surface-mounted metal–organic framework membrane was pyrolyzed at a range of temperatures to produce catalysts with excellent trifunctional electrocatalytic efficiencies for the oxygen reduction, hydrogen evolution, and oxygen evolution reactions. Burnt to a crisp: Surface-mounted metal–organic framework (MOF) membranes were pyrolyzed to produce electrocatalytic nanomaterials with 3D nanoarchitectures and abundant catalytic sites. Cobalt contained in the MOF thin-film has a dual function; it facilitates growth of nitrogen-doped carbon nanotubes and promotes oxygen reduction, hydrogen evolution, and oxygen evolution reactions.
Datum: 25.09.2017


Single Turnover at Molecular Polymerization Catalysts Reveals Spatiotemporally Resolved Reactions

Multiple active individual molecular ruthenium catalysts have been pinpointed within growing polynorbornene, thereby revealing information on the reaction dynamics and location that is unavailable through traditional ensemble experiments. This is the first single-turnover imaging of a molecular catalyst by fluorescence microscopy and allows detection of individual monomer reactions at an industrially important molecular ruthenium ring-opening metathesis polymerization (ROMP) catalyst under synthetically relevant conditions (e.g. unmodified industrial catalyst, ambient pressure, condensed phase, ca. 0.03 m monomer). These results further establish the key fundamentals of this imaging technique for characterizing the reactivity and location of active molecular catalysts even when they are the minor components. Singled out: Single-turnover detection has enabled the spatiotemporal resolution of individual reactions within growing polymers. The addition of a spectator fluorophore to the polymerization of norbornene enabled individual monomer reactions at an industrially important molecular ruthenium ring-opening metathesis polymerization catalyst to be observed as a bright-green point flash by fluorescence microscopy.
Datum: 25.09.2017


Valence Interconversion of Octahedral Nickel(II/III/IV) Centers

Three oxidation states (+2, +3, +4) of an octahedral nickel center were stabilized in a newly prepared RhNiRh trinuclear complex, [Ni{Rh(apt)3}2]n+ (apt=3- aminopropanethiolate), in which the nickel center was bound by six thiolato donors sourced from two redox-inert fac-[RhIII(apt)3] octahedral units. The three oxidation states of the octahedral nickel center were fully characterized by single-crystal X-ray crystallography, as well as spectroscopic, electrochemical, and magnetic measurements; all three were interconvertible, and the conversion was accompanied by changes in color, magnetism, and Jahn–Teller distortion. Bridge over troubled water: A series of S-bridged RhNiRh trinuclear complexes capable of supporting an octahedral nickel center in three different oxidation states (+2, +3, +4) have been isolated. Oxidation state interconversion is accompanied by changes in color, magnetism, and geometric Jahn–Teller distortions, with retention of the trinuclear structure.
Datum: 22.09.2017


H2S-Activable MOF Nanoparticle Photosensitizer for Effective Photodynamic Therapy against Cancer with Controllable Singlet-Oxygen Release

Photodynamic therapy (PDT) has emerged as an important minimally invasive tumor treatment technology. The search for an effective photosensitizer to realize selective cancer treatment has become one of the major foci in recent developments of PDT technology. Controllable singlet-oxygen release based on specific cancer-associated events, as another major layer of selectivity mode, has attracted great attention in recent years. Here, for the first time, we demonstrated that a novel mixed-metal metal–organic framework nanoparticle (MOF NP) photosensitizer can be activated by a hydrogen sulfide (H2S) signaling molecule in a specific tumor microenvironment for PDT against cancer with controllable singlet-oxygen release in living cells. The effective removal of tumors in vivo further confirmed the satisfactory treatment effect of the MOF NP photosensitizer. Selective cancer treatment: A mixed-metal metal–organic framework nanoparticle photosensitizer has been activated by a H2S-signaling molecule in a specific tumor microenvironment for photodynamic therapy of cancer using controllable singlet-oxygen release. The effective removal of tumors in vivo confirms the satisfactory treatment effect of the photosensitizer.
Datum: 22.09.2017


Gas-Phase Synthesis of the Elusive Cyclooctatetraenyl Radical (C8H7) via Triplet Aromatic Cyclooctatetraene (C8H8) and Non-Aromatic Cyclooctatriene (C8H8) Intermediates

The 1,2,4,7-cyclooctatetraenyl radical (C8H7) has been synthesized for the very first time via the bimolecular gas-phase reaction of ground-state carbon atoms with 1,3,5-cycloheptatriene (C7H8) on the triplet surface under single-collision conditions. The barrier-less route to the cyclic 1,2,4,7-cyclooctatetraenyl radical accesses exotic reaction intermediates on the triplet surface, which cannot be synthesized via classical organic chemistry methods: the triplet non-aromatic 2,4,6-cyclooctatriene (C8H8) and the triplet aromatic 1,3,5,7-cyclooctatetraene (C8H8). Our approach provides a clean gas-phase synthesis of this hitherto elusive cyclic radical species 1,2,4,7-cyclooctatetraenyl via a single-collision event and opens up a versatile, unconventional path to access this previously largely obscure class of cyclooctatetraenyl radicals, which have been impossible to access through classical synthetic methods. Carbon eight-ed: Gas-phase reaction of ground-state carbon atoms and cycloheptatriene (C7H8) under single-collision conditions leads to the production of the 1,2,4,7-cyclooctatetraenyl radical (C8H7). Ab initio electronic structure calculation shows the reaction proceeds via exotic triplet C8H8 reaction intermediates: the non-aromatic 2,4,6-cyclooctatriene and the aromatic 1,3,5,7-cyclooctatetraene. The picture shows the flux contour map of the reaction.
Datum: 22.09.2017


Formation of Stable Tin Perovskites Co-crystallized with Three Halides for Carbon-Based Mesoscopic Lead-Free Perovskite Solar Cells

We synthesized and characterized methylammonium (MA) mixed tri-halide tin perovskites (MASnIBr2−xClx) for carbon-based mesoscopic solar cells free of lead and hole-transporting layers. Varied SnCl2/SnBr2 ratios yielded tin perovskites with three halides (I, Br, and Cl) co-crystallized inside the tin-perovskite. When the SnCl2 proportion was ≥50 % (x≥1), phase separation occurred to give MASnI3−yBry and MASnCl3−zBrz in the stoichiometric proportions of their precursors, confirmed by XRD. A device with MASnIBr1.8Cl0.2 (SnCl2=10 %) showed the best photovoltaic performance: JSC=14.0 mA cm−2, VOC=380 mV, FF=0.573, and PCE=3.1 %, and long-term stability. Electrochemical impedance spectra (EIS) show superior charge recombination and dielectric relaxation properties for the MASnIBr1.8Cl0.2 cell. Transient PL decays showed the intrinsic problem of tin-based perovskites with average lifetimes less than 100 ps. Tin in: Stable tin perovskites co-crystalized with three different halide elements (I, Br, and Cl) were produced by the reaction of methylammonium (MA) iodide with SnCl2/SnBr2 mixtures at ratios equal to or less than 25/75. The best device made of a carbon-based mesoscopic electrode and MASnIBr1.8Cl0.2 exhibited a PCE of 3.1 %.
Datum: 22.09.2017


Black Pigment Gallstone Inspired Platinum-Chelated Bilirubin Nanoparticles for Combined Photoacoustic Imaging and Photothermal Therapy of Cancers

Bilirubin (BR), a bile pigment that exerts potent antioxidant and anti-inflammatory effects, is also a major constituent of black pigment gallstones found in bile ducts under certain pathological conditions. Inspired by the intrinsic metal-chelating power of BR found in gallstones, herein we report a cisplatin-chelated BR-based nanoparticle (cisPt@BRNP) for use as a new photonic nanomedicine for combined photoacoustic imaging and photothermal therapy of cancers. The cisPt@BRNPs were prepared by simply mixing cisplatin with BRNPs, yielding ca. 150-nm-size NPs. Upon near-IR laser irradiation at 808 nm, cisPt@BRNPs generated considerable heat and induced clear death of cancer cells in vitro. Following intravenous injection into human colon cancer-bearing mice, cisPt@BRNPs allowed effective tumor visualization by photoacoustic imaging and remarkable antitumor efficacy by photothermal therapy, suggesting their potential for use as a new photonic nanomedicine for cancer therapy. The gall of it: A new class of near infrared light-responsive photonic nanomaterial which is biodegradable and biocompatible is developed based on the inherent metal-chelating ability of bilirubin, a bile pigment found in gall stones. The resulting cisplatin-chelated bilirubin nanoparticles (cisPt@BRNPs) are promising for combined photoacoustic imaging (PAI) and photothermal therapy (PTT) of cancers.
Datum: 22.09.2017


Spin Changes Accompany Ultrafast Structural Interconversion in the Ground State of a Cobalt Nitrosyl Complex

Ultrafast, reversible intersystem crossing (ISC) is reported under ambient conditions for the electronic ground state of the pentacoordinate cobalt nitrosyl complexes, [CoX2(NO)(PMePh2)2] (X=Cl, Br), in solution. ISCs on such short timescales are more typically observed in electronically excited states reached by absorption of ultraviolet or visible light. Singlet and triplet electron spin states of the complex, corresponding to two different isomers, are populated at room temperature, and the two isomers exchange on a timescale of a few picoseconds. Ultrafast two-dimensional infrared spectroscopy observes the change in wavenumber of the NO ligand band accompanying the isomerization and associated ISC on the (spin) adiabatic ground potential energy surface. Comparison of the dynamics of the chloro- and bromo-complexes shows that inertial effects of the ligand motion have a greater effect than spin–orbit coupling on determining the forward and reverse isomerization and ISC rates. The ground state intersystem crossing of a cobalt nitrosyl complex is shown to occur on an ultrafast time scale. The electron spin changing dynamics can be observed with 2DIR spectroscopy by probing the nuclear vibrational frequencies associated with each electronic state. Comparison of the spin-state exchange rates in two halido-substituted complexes shows that inertial effects outweigh ligand spin–orbit coupling effects.
Datum: 22.09.2017


Black Phosphorus Quantum Dots Used for Boosting Light Harvesting in Organic Photovoltaics

Although organic photovoltaic devices (OPVs) have been investigated for more than two decades, the power conversion efficiencies of OPVs are much lower than those of inorganic or perovskite solar cells. One effective approach to improve the efficiency of OPVs is to introduce additives to enhance light harvesting as well as charge transportation in the devices. Here, black phosphorus quantum dots (BPQDs) are introduced in OPVs as an additive. By adding 0.055 wt % BPQDs relative to the polymer donors in the OPVs, the device efficiencies can be dramatically improved for more than 10 %. The weight percentage is much lower than that of any other additive used in OPVs before, which is mainly due to the two-dimentional structure as well as the strong broadband light absorption and scattering of the BPQDs. This work paves a way for using two-dimentional quantum dots in OPVs as a cost-effective approach to enhance device efficiencies. Strong light absorption: The power conversion efficiencies of organic photovoltaics have been improved by introducing black phosphorus quantum dots (BPQDs; 0.055 wt % relative to the donor polymers) due to the boosted light harvesting of the devices. The effect is attributed to the strong light absorption as well as the two-dimensional structure of the BPQDs. A pronounced size effect of BPQDs on the performance enhancement is observed.
Datum: 22.09.2017


Peristome-Mimetic Curved Surface for Spontaneous and Directional Separation of Micro Water-in-Oil Drops

Separation of micro-scaled water-in-oil droplets is important in environmental protection, bioassays, and saving functional inks. So far, bulk oil–water separation has been achieved by membrane separation and sponge absorption, but micro-drop separation still remains a challenge. Herein we report that instead of the “plug-and-go” separation model, tiny water-in-oil droplets can be separated into pure water and oil droplets through “go-in-opposite ways” on curved peristome-mimetic surfaces, in milliseconds, without energy input. More importantly, this overflow controlled method can be applied to handle oil-in-oil droplets with surface tension differences as low as 14.7 mN m−1 and viscous liquids with viscosities as high as hundreds centipoises, which markedly increases the range of applicable liquids for micro-scaled separation. Furthermore, the curved peristome-mimetic surface guides the separated drops in different directions with high efficiency. Keep 'em separated: A curved surface resembling the peristome, that is, the fringe of small projections around the opening of a capsule of a tropical pitcher plant is prepared. It enables the spontaneous separation of water and oil from micro-scale water-in-oil drops without energy input. The separation occurs within milliseconds and the separated liquids are spontaneously and uni-directionally transported in different directions.
Datum: 22.09.2017


An Extensive Family of Heterometallic Titanium(IV)–Metal(III) Rings with Structure Control through Templates

A family of heterometallic [Cat][TixMO(x+1)(O2CtBu)2x+2] rings is reported where Cat=a secondary or tertiary alkyl ammonium ion, x=7, 8 or 9, and M=FeIII, GaIII, CrIII, InIII and AlIII. The structures are regular polygons with eight, nine or ten vertices with each edge bridged by an oxide and two pivalates. The size of the ring formed is controlled by the alkylammonium cation present. In each case a homometallic by-product is found [Cat][TixO(x+1)(O2CtBu)2x−1]. Size control: A family of heterometallic [Cat][TixMO(x+1)(O2C tBu)2x+2] rings is reported where Cat=a secondary or tertiary alkyl ammonium ion, x=7, 8 or 9, and M=Fe, Ga, Cr, In and Al. The structures are regular polygons with eight, nine or ten vertices with each edge bridged by an oxide and two pivalates. The size of the ring formed is controlled by the alkylammonium cation present.
Datum: 22.09.2017


One-Step Reforming of CO2 and CH4 into High-Value Liquid Chemicals and Fuels at Room Temperature by Plasma-Driven Catalysis

The conversion of CO2 with CH4 into liquid fuels and chemicals in a single-step catalytic process that bypasses the production of syngas remains a challenge. In this study, liquid fuels and chemicals (e.g., acetic acid, methanol, ethanol, and formaldehyde) were synthesized in a one-step process from CO2 and CH4 at room temperature (30 °C) and atmospheric pressure for the first time by using a novel plasma reactor with a water electrode. The total selectivity to oxygenates was approximately 50–60 %, with acetic acid being the major component at 40.2 % selectivity, the highest value reported for acetic acid thus far. Interestingly, the direct plasma synthesis of acetic acid from CH4 and CO2 is an ideal reaction with 100 % atom economy, but it is almost impossible by thermal catalysis owing to the significant thermodynamic barrier. The combination of plasma and catalyst in this process shows great potential for manipulating the distribution of liquid chemical products in a given process. Liquid fuels and chemicals (e.g. acetic acid, methanol, ethanol, and formaldehyde) were synthesized in a one-step process from CO2 and CH4 at room temperature (30 °C) and atmospheric pressure for the first time by using a novel plasma reactor with a water electrode. The total selectivity to oxygenates was approximately 50–60 %, with acetic acid as the major component.
Datum: 19.09.2017


Polyamine-Mediated Stoichiometric Assembly of Ribonucleoproteins for Enhanced mRNA Delivery

Messenger RNA (mRNA) represents a promising class of nucleic acid drugs. Although numerous carriers have been developed for mRNA delivery, the inefficient mRNA expression inside cells remains a major challenge. Inspired by the dependence of mRNA on 3′-terminal polyadenosine nucleotides (poly A) and poly A binding proteins (PABPs) for optimal expression, we complexed synthetic mRNA containing a poly A tail with PABPs in a stoichiometric manner and stabilized the ribonucleoproteins (RNPs) with a family of polypeptides bearing different arrangements of cationic side groups. We found that the molecular structure of these polypeptides modulates the degree of PABP-mediated enhancement of mRNA expression. This strategy elicits an up to 20-fold increase in mRNA expression in vitro and an approximately fourfold increase in mice. These findings suggest a set of new design principles for gene delivery by the synergistic co-assembly of mRNA with helper proteins. Although numerous carriers have been developed for mRNA delivery, the inefficient mRNA expression inside cells remains a major challenge. Inspired by the dependence of mRNA on 3′-terminal polyadenosine nucleotides (poly A) and poly A binding proteins (PABPs) for optimal expression, synthetic mRNA containing a poly A tail was complexed with PABPs in a stoichiometric manner.
Datum: 19.09.2017


Enantioselective [2,3]-Sigmatropic Rearrangements: Metal-Bound or Free Ylides as Reaction Intermediates?

Out of bounds: Enantioselective rearrangement reactions are a long-standing challenge in organic synthesis. Recent advances are highlighted that led to the development of the first enantioselective Doyle–Kirmse reaction and enantioselective rearrangement reactions of iodonium ylides.
Datum: 18.09.2017


Because the Light is Better Here: Correlation-Time Analysis by NMR Spectroscopy

Relaxation data in NMR spectra are often used for dynamics analysis, by modeling motion in the sample with a correlation function consisting of one or more decaying exponential terms, each described by an order parameter, and a correlation time. This method has its origins in the Lipari–Szabo model-free approach, which originally considered overall tumbling plus one internal motion and was later expanded to several internal motions. Considering several of these cases in the solid state it is found that if the real motion is more complex than the assumed model, model fitting is biased towards correlation times where the relaxation data are most sensitive. This leads to unexpected distortions in the resulting dynamics description. Therefore dynamics detectors should be used, which characterize different ranges of correlation times and can help in the analysis of protein motion without assuming a specific model of the correlation function. Fighting bias: NMR Dynamics data are more sensitive to some correlation times than to others. Models of the correlation function tend to be biased towards where the light is better, that is, where the experiment is more sensitive, thereby yielding an unreliable characterization of the motion. Replacing modeling by detectors that are sensitive to different ranges of correlation times could help to overcome this bias.
Datum: 14.09.2017


Cascades in Compartments: En Route to Machine-Assisted Biotechnology

Biological compartmentalization is a fundamental principle of life that allows cells to metabolize, propagate, or communicate with their environment. Much research is devoted to understanding this basic principle and to harness biomimetic compartments and catalytic cascades as tools for technological processes. This Review summarizes the current state-of-the-art of these developments, with a special emphasis on length scales, mass transport phenomena, and molecular scaffolding approaches, ranging from small cross-linkers over proteins and nucleic acids to colloids and patterned surfaces. We conclude that the future exploration and exploitation of these complex systems will largely benefit from technical solutions for the integrated, machine-assisted development and maintenance of a next generation of biotechnological processes. These goals should be achievable by implementing microfluidics, robotics, and added manufacturing techniques supplemented by theoretical simulations as well as computer-aided process modeling based on big data obtained from multiscale experimental analyses. Machine-generated multienzyme cascades: The machine-assisted development of biomimetic compartments and catalytic cascades will pave the way towards a novel generation of biotechnological processes. Molecular scaffolds with small cross-linkers, proteins, nucleic acids, colloids, and patterned surfaces can be used to arrange the catalytic units. S: substrate, P: product.
Datum: 14.09.2017


Correct Modeling of Cisplatin: a Paradigmatic Case

Quantum chemistry is a useful tool in modern approaches to drug and material design, but only when the adopted model reflects a correct physical picture. Paradigmatic is the case of cis-diaminodichloroplatinum(II), cis-[Pt(NH3)2Cl2], for which the correct simulation of the structural and vibrational properties measured experimentally still remains an open question. By using this molecule as a proof of concept, it is shown that state-of-the-art quantum chemical calculations and a simple model, capturing the basic physical flavors, a cis-[Pt(NH3)2Cl2] dimer, can provide the accuracy required for interpretative purposes. The present outcomes have fundamental implications for benchmark studies aiming at assessing the accuracy of a given computational protocol. Two are needed for a valid prediction: A dimer of cis-[Pt(NH3)2Cl2] as a quantum chemical model for cisplatin provides the first quantitative agreement with experiment for structural and vibrational properties. This result indicates that a reliable in silico drug design requires a model capturing the essential physical picture of the system and a proper theoretical protocol.
Datum: 14.09.2017


Enzyme Activity by Design: An Artificial Rhodium Hydroformylase for Linear Aldehydes

Artificial metalloenzymes (ArMs) are hybrid catalysts that offer a unique opportunity to combine the superior performance of natural protein structures with the unnatural reactivity of transition-metal catalytic centers. Therefore, they provide the prospect of highly selective and active catalytic chemical conversions for which natural enzymes are unavailable. Herein, we show how by rationally combining robust site-specific phosphine bioconjugation methods and a lipid-binding protein (SCP-2L), an artificial rhodium hydroformylase was developed that displays remarkable activities and selectivities for the biphasic production of long-chain linear aldehydes under benign aqueous conditions. Overall, this study demonstrates that judiciously chosen protein-binding scaffolds can be adapted to obtain metalloenzymes that provide the reactivity of the introduced metal center combined with specifically intended product selectivity. Artificial metalloenzymes are hybrid catalysts that offer a unique opportunity to combine the superior performance of natural protein structures with the unnatural reactivity of transition-metal catalytic centers. An artificial rhodium hydroformylase has been developed that displays remarkable activities and selectivities in the biphasic production of long-chain linear aldehydes.
Datum: 13.09.2017


Molecular Dynamics of Hexamethylbenzene at Low Temperatures: Evidence of Unconventional Magnetism Based on Rotational Motion of Protons

The types of magnetism known to date are all mainly based on contributions from electron motion. We show how rotational motion of protons (H+) within the methyl groups in hexamethylbenzene (C6(CH3)6) also contribute significantly to the magnetic susceptibility. Starting from below 118 K, as the rotational motion of the methyl groups set in, an associated magnetic moment positive in nature due to charge of the protons renders the susceptibility to become anomalously dependent on temperature. Starting from 20 K, the susceptibility diverges with decreasing temperature indicative of spin–spin interactions between methyl groups aligned in a previously unclassified type of anti-ferromagnetic configuration. Complementary dielectric constant measurements also show the existence of magneto-dielectric coupling. Our findings allow for the study of strongly correlated systems that are based on a species that possesses much slower dynamics. A strongly correlated system: A previously unidentified type of magnetism based on the rotational motion of protons within methyl groups is shown to occur in hexamethylbenzene. At lower temperatures spin–spin interactions exist between methyl groups aligned in a previously unclassified type of antiferromagnetic configuration.
Datum: 07.09.2017


A Pyrene-Linked Cavity within a β-Barrel Protein Promotes an Asymmetric Diels–Alder Reaction

A unique π-expanded reaction cavity tethering a polycyclic moiety which provides a platform for substrate binding was constructed within the robust β-barrel structure of nitrobindin (NB). NB variants with cavities of different sizes and shapes are coupled with N-(1-pyrenyl)maleimide (Pyr) to prepare a series of NB-Pyr conjugates. The orientation of the pyrene moiety is fixed within the cavity by the coupling reaction. The fluorescent quenching analysis of NB-Pyr indicates that azachalcone (aza), which is a dienophile for a Diels–Alder (DA) reaction, is efficiently incorporated within the pyrene-linked reaction cavity by the aromatic interaction. The DA reaction between aza and cyclopentadiene proceeds within the reaction cavity of NB-Pyr in the presence of CuII ion in high yield and high enantio- and regioselectivity. Selectivity by the barrel-load: A reaction cavity with a tethered polycyclic pyrene moiety, which acts as a platform to provide aromatic interactions, is constructed within the rigid scaffold of the β-barrel nitrobindin protein. An asymmetric Diels–Alder reaction between azachalcone and cyclopentadiene proceeds within the reaction cavity of the pyrene-linked nitrobindin with high stereoselectivity.
Datum: 31.08.2017


Olefins from Natural Gas by Oxychlorination

Ethylene and propylene are the key building blocks of the chemical industry, but current processes are unable to close the growing gap between demand and manufacture. Reported herein is an exceptional europium oxychloride (EuOCl) catalyst for the selective (≥95 %) production of light olefins from ethane and propane by oxychlorination chemistry, thus achieving yields of ethylene (90 %) and propylene (40 %) unparalleled by any existing olefin production technology. Moreover, EuOCl is able to process mixtures of methane, ethane, and propane to produce the olefins, thereby reducing separation costs of the alkanes in natural gas. Finally, the EuOCl catalyst was supported on suitable carriers and evaluated in extrudate form, and preserves performance for >150 h under realistic process conditions. Gas up: Ethylene and propylene can be generated from ethane and propane, respectively, or from methane/ethane/propane mixtures, over a europium oxychloride catalyst. The reaction proceeds by oxychlorination with yields surpassing those of any existing technologies for alkene production. Its performance is preserved in technical form, and testifies to the practical relevance of this technology for the manufacture of light olefins.
Datum: 23.08.2017


Potential-Cycling Synthesis of Single Platinum Atoms for Efficient Hydrogen Evolution in Neutral Media

Single-atom catalysts (SACs) have exhibited high activities for the hydrogen evolution reaction (HER) electrocatalysis in acidic or alkaline media, when they are used with binders on cathodes. However, to date, no SACs have been reported for the HER electrocatalysis in neutral media. We demonstrate a potential-cycling method to synthesize a catalyst comprising single Pt atoms on CoP-based nanotube arrays supported by a Ni foam, termed PtSA-NT-NF. This binder-free catalyst is centimeter-scale and scalable. It is directly used as HER cathodes, whose performances at low and high current densities in phosphate buffer solutions (pH 7.2) are comparable to and better than, respectively, those of commercial Pt/C. The Pt mass activity of PtSA-NT-NF is 4 times of that of Pt/C, and its electrocatalytic stability is also better than that of Pt/C. This work provides a large-scale production strategy for binder-free Pt SAC electrodes for efficient HER in neutral media. Singles suitable for HER: Large-area single Pt atoms on CoP-based nanotube arrays supported by Ni foams were synthesized by potential cycling. These binder-free electrocatalysts are centimeter-scale and can be scaled up further. They exhibit unparalleled performance when catalyzing the hydrogen evolution reaction in neutral media.
Datum: 23.08.2017


Highly Fluorescent Pyridinium Betaines for Light Harvesting

We report the findings of our experimental and theoretical investigations into the properties of pyridinium enolates and their potential utility in light-harvesting applications, such as in luminescent solar concentrators (LSCs). We present the synthesis, structures, photophysical characterization, and wavefunction-based quantum-chemical studies of five cyclobetaines. The performance of an LSC device incorporating one of these cyclobetaines is shown to be comparable to state-of-the-art devices. Experiment and theory: Pyridinium enolates and their potential utility in light-harvesting applications, such as in luminescent solar concentrators, were studied experimentally and theoretically. The synthesis, structures, photophysical properties, and wavefunction-based quantum-chemical studies of five cyclobetaines are presented.
Datum: 21.08.2017


Precisely Assembled Cyclic Gold Nanoparticle Frames by 2D Polymer Single-Crystal Templating

In recent decades, extensive studies have been devoted to assembling nanoparticles (NPs) into various ordered structures to achieve novel optical properties. However, it still remains a challenging task to assemble NPs into cyclic one-dimensional (1D) shapes, such as rings and frames. Herein, we report a directed assembly method to precisely assemble NPs into well-defined, free-standing frames using polymer single crystals (PSCs) as the template. Preformed poly(ethylene oxide) (PEO) single crystals were used as the template to direct the crystallization of block copolymer (BCP) poly(ethylene oxide)-b-poly(4-vinylpyridine) (PEO-b-P4VP), which directs the gold NPs (AuNPs) to form AuNP frames. By controlling the PSC growth, we were able to, for the first time, precisely tune both the size and width of the AuNP frame. These novel AuNP frames topologically resemble NP nanorings and cyclic polymer chains, and show unique surface plasmon resonance (SPR) behaviors. Frame: Free-standing gold nanoparticle (AuNP) frame structures are formed by directed assembly of AuNPs on polymer single-crystal templates. The size and width of the frames are precisely controllable and easily tunable. These frames resemble NP nanorings and 1D cyclic polymer chains, and have intriguing optical properties similar to Au nanorods.
Datum: 18.08.2017


Spotlights on our sister journals: Angew. Chem. Int. Ed. 44/2017


Datum: 19.07.2017


Yasujiro Murata

“If I were a car I would be a red Porsche 911. If I could be anyone for a day, I would be the conductor of an orchestra ...” This and more about Yasujiro Murata can be found on page 13562.
Datum: 12.07.2017


Silver-Catalyzed Stereoselective Aminosulfonylation of Alkynes

A silver-catalyzed intermolecular aminosulfonylation of terminal alkynes with sodium sulfinates and TMSN3 is reported. This three-component reaction proceeds through sequential hydroazidation of the terminal alkyne and addition of a sulfonyl radical to the resultant vinyl azide. The method enables the stereoselective synthesis of a wide range of β-sulfonyl enamines without electron-withdrawing groups on the nitrogen atom. These enamines are found to be suitable for a variety of further transformations. Controllable assembly: The first intermolecular aminosulfonylation of terminal alkynes with sodium sulfinates and TMSN3 is reported. This three-component coupling, which shows excellent functional group tolerance, proceeds through sequential hydroazidation of the terminal alkyne and addition of a sulfonyl radical to the resultant vinyl azide. This enables the stereoselective synthesis of a wide range of β-sulfonyl N-unprotected enamines.
Datum: 07.07.2017






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