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:

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 - Chemistry Central Journal,

 - Chemistry Letters,

 - Journal of the American Chemical Society,

 - Nature Chemistry.



Angewandte Chemie International Edition - Abstracts



α-Radical Phosphines: Synthesis, Structure and Reactivity

A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl-/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one-electron reduction of the corresponding cationic intermediates. Structural, spectroscopic and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α-position to the central phosphorus. The potential of these α-radical phosphines to serve as spin-labeled ligands is demonstrated through the preparation of several Au(I) derivatives, which were also structurally characterized by single-crystal X-ray diffraction.
Datum: 23.05.2017


Frontispiece: The Structure of the Elusive Simplest Dipeptide Gly-Gly

Dipeptide Structures In their Communication on page 6420 ff., J. L. Alonso et al. provide the first experimental information on the structure of the simplest dipeptide Gly-Gly by using laser ablation of solid samples combined with FT microwave spectroscopy in a supersonic expansion.
Datum: 23.05.2017


Graphical Abstract: Angew. Chem. Int. Ed. 23/2017


Datum: 23.05.2017


Spotlights on our sister journals: Angew. Chem. Int. Ed. 23/2017


Datum: 23.05.2017


Absolute Minimal Sampling of Homonuclear 2D NMR TOCSY Spectra for High-Throughput Applications of Complex Mixtures

Modern applications of 2D NMR spectroscopy to diagnostic screening, metabolomics, quality control, and other high-throughput applications are often limited by the time-consuming sampling requirements along the indirect time domain t1. 2D Total Correlation Spectroscopy (TOCSY) provides unique spin-connectivity information for the analysis of a large number of compounds in complex mixtures, but standard methods typically require >100 t1-increments for an accurate spectral reconstruction, rendering these experiments ineffective for high-throughput applications. Here, we demonstrate for a complex metabolite mixture how absolute minimal sampling (AMS), based on direct fitting of resonance frequencies and amplitudes in the time domain, yields an accurate spectral reconstruction of TOCSY spectra using as few as 16 t1-points. This permits the rapid collection of homonuclear 2D NMR experiments at high resolution with measurement times that previously were the realm of 1D experiments only.
Datum: 23.05.2017


Synthesis of Aldehydes by Organocatalytic Formylation Reactions of Boronic Acids with Glyoxylic Acid

We report a conceptually novel organocatalytic strategy for formylation of boronic acids, in which a new reactivity is engineered into the α-amino acid forming Petasis reaction occurring between aryl boron acids, amines and glyoxylic acid. The feasibility and preparative power of the protocol was demonstrated by its use to prepare aldehydes from broadly accessible aryl and alkenyl boronic acids, glyoxylic acid, and the cheap N-alkylaniline derivatives, tetrahydroquinoline and indoline, as catalysts. Furthermore, the operational simplicity of the process, which is performed by simply mixing these reagents under ambient conditions, and its ability to generate structurally diverse and valued aryl, heteroaryl and α,β-unsaturated aldehydes containing a wide array of functional groups, demonstrates the practical utility of the newly unveiled synthetic strategy.
Datum: 23.05.2017


Crystalline Hollow Microrods for Site-Selective Enhancement of Nonlinear Photoluminescence

A class of one-dimensional hollow microstructure is described, which was formed by a kinetically controlled crystal growth process. A hexagonal-phase NaYbF4 microrod comprising isolated holes along the longitudinal axis was synthesized by a one-pot hydrothermal method with the assistance of citrate ligands. The structural void feature modulates light intensity across the microrods as a result of interference arising from light scattering and reflection by the inner walls. A single crystal comprising a structural void was doped with upconverting lanthanide ions. Upon near-infrared excitation of the doped crystal spatially resolvable optical codes were produced. Hollow-structured microcrystals of hexagonal phase NaYbF4 produce nonlinear photoluminescence upon illumination with near-infrared light. Light scattering and reflection by the inner walls of the microrod modulate light intensity across the structure. Spatially resolved optical codes are attained when the irradiated material is doped with upconverting lanthanide ions.
Datum: 23.05.2017


Common Fibril Structures Imply Systemically Conserved Protein Misfolding Pathways In Vivo

Systemic amyloidosis is caused by the misfolding of a circulating amyloid precursor protein and the deposition of amyloid fibrils in multiple organs. Chemical and biophysical analysis of amyloid fibrils from human AL and murine AA amyloidosis reveal the same fibril morphologies in different tissues or organs of one patient or diseased animal. The observed structural similarities concerned the fibril morphology, the fibril protein primary and secondary structures, the presence of post-translational modifications and, in case of the AL fibrils, the partially folded characteristics of the polypeptide chain within the fibril. Our data imply for both analyzed forms of amyloidosis that the pathways of protein misfolding are systemically conserved; that is, they follow the same rules irrespective of where inside one body fibrils are formed or accumulated. Never break the chain: Polypeptide chains form the same amyloid fibril structures in different tissues of the same body, indicating that the pathways of protein misfolding are conserved in vivo.
Datum: 23.05.2017


Sulfation of the Human Cytomegalovirus Protein UL22A Enhances Binding to the Chemokine RANTES

UL22A is an 83 amino acid chemokine-binding protein produced by human cytomegalovirus that likely assists the virus in dampening the host antiviral response. We proposed that UL22A is sulfated on two tyrosine residues and tested this hypothesis through the chemical synthesis of a small library of differentially sulfated protein variants. The (sulfo)proteins were efficiently prepared using a novel β-selenoleucine motif to facilitate one-pot ligation–deselenization chemistry. Tyrosine sulfation of UL22A proved critical for RANTES binding, with the doubly sulfated variant exhibiting an improvement in binding of 2.5 orders of magnitude compared to the unmodified protein. Modifications matter: The chemokine-binding protein UL22A was predicted to be post-translationally sulfated on two tyrosine residues. A library of sulfated UL22A proteins was constructed through a one-pot synthesis using a novel β-selenoleucine-mediated peptide ligation reaction followed by deselenization chemistry. Binding experiments showed that sulfation of the tyrosine residues substantially enhances the binding affinity for the chemokine RANTES.
Datum: 23.05.2017


Structure and Biosynthesis of Crocagins: Polycyclic Postranslationally Modified Ribosomal Peptides from Chondromyces crocatus

Secondary metabolome mining efforts in the myxobacterial multiproducer of natural products, Chondromyces crocatus Cm c5, resulted in the isolation and structure elucidation of crocagins, which are novel polycyclic peptides containing a tetrahydropyrrolo[2,3-b]indole core. The gene cluster was identified through an approach combining genome analysis, targeted gene inactivation in the producer, and in vitro experiments. Based on our findings, we developed a biosynthetic scheme for crocagin biosynthesis. These natural products are formed from the three C-terminal amino acids of a precursor peptide and thus belong to a novel class of ribosomally synthesized and post-translationally modified peptides (RiPPs). We demonstrate that crocagin A binds to the carbon storage regulator protein CsrA, thereby inhibiting the ability of CsrA to bind to its cognate RNA target. Ribosomally synthesized and post-translationally modified peptides (RiPPs) were isolated from a myxobacterial producer. The unusual tetracyclic peptide scaffold of these crocagins turned out to originate from a ribosomally assembled precursor peptide. Isolation, structure elucidation, mutagenesis of the producer, and in vitro experiments are presented.
Datum: 23.05.2017


Surface Modification of Two-Dimensional Metal-Organic Layers Creates Biomimetic Catalytic Microenvironments for Selective Oxidation

Microenvironments in enzymes play crucial roles in controlling the activities and selectivities of reaction centers. Herein we report the tuning of the catalytic microenvironments of metal-organic layers (MOLs), a two-dimensional version of metal-organic frameworks (MOFs) with thickness down to a monolayer, to control product selectivities. By modifying the secondary building units (SBUs) of MOLs with monocarboxylic acids such as gluconic acid, we successfully changed the hydrophobicity/hydrophilicity around the active sites and fine-tuned the selectivity in photocatalytic oxidation of tetrahydrofuran (THF) to exclusively afford butyrolactone (BTL), likely via prolonging residence time of reaction intermediates in the hydrophilic microenvironment of catalytic centers. Our work highlights new opportunities in using functional MOLs as highly tunable and selective two-dimensional catalytic materials.
Datum: 23.05.2017


A Designed Approach to Enantiodivergent Enamine Catalysis

The rational design and implementation of enantiodivergent enamine catalysis is reported. A simple secondary amine catalyst, 2-methyl-L-proline, and its tetrabutylammonium salt function as an enantiodivergent catalyst pair delivering opposite enantiomers of α-functionalized aldehyde products in excellent enantioselectivities. This novel concept of 'designed enantiodivergence' is applied to the enantioselective α-amination, aldol and α-aminoxylation/α-hydroxyamination reactions of aldehydes.
Datum: 23.05.2017


Multiple hydrogen bonding enables the self-healing of sensors for human-machine interaction

Despite its widespread use in signal collection, flexible sensor has been rarely used in human-machine interaction due to its indistinguishable signal, poor reliability and stability when suffered from unavoidable scratches and/or mechanical cuts. Here, we demonstrate a highly sensitive and self-healing sensor enabled by multiple hydrogen bonding network and nanostructured conductive network. The nanostructured supramolecular sensor displays extremely fast (~15 s) and repeatable self-healing ability with high healing efficiency (93% after the 3rd healing process). It can precisely detect tiny human motions, demonstrating highly distinguishable and reliable signals even after cutting-healing and bending over 20000 cycles. Furthermore, a human-machine interaction system is integrated to develop a facial expression control system and an electronic larynx, aiming to control the robot to assist the patient's daily life and help the dumb to realize real-time speaking.
Datum: 23.05.2017


Frozen Acrylamide Gels as Dynamic Nuclear Polarization Matrices.

We show that aqueous acrylamide gels can be used to provide dynamic nuclear polarization (DNP) NMR signal enhancements of around 200 at 9.4 T and 100 K. The enhancements are shown to increase with cross linker concentration and low concentrations of the AMUPol biradical. We show that this DNP matrix can be used in situations where conventional incipient wetness methods fail, such as to obtain DNP surface enhanced NMR spectra from inorganic nanoparticles. In particular, we obtain 113Cd spectra from CdTe-COOH NPs in minutes. The spectra clearly indicate a highly-disordered cadmium rich surface.
Datum: 23.05.2017


SERS- and Electrochemically-Active 3D Plasmonic Liquid Marble for Molecular-Level Spectroelectrochemical Investigation of Microliter Reaction

Liquid marbles are emerging microreactors due to their isolated environment and flexibility of materials used. Herein, we demonstrate plasmonic liquid marble (PLM) as the smallest spectroelectrochemical microliter-scale reactor for concurrent spectro- and electrochemical analyses. We exploit PLM's three-dimensional Ag shell as bifunctional surface-enhanced Raman scattering (SERS) platform and working electrode for redox process modulation. The combination of SERS and electrochemistry (EC) capability enable in situ molecular read-out of transient electrochemical species, and elucidation of potential-dependent and multi-step reaction dynamics. The 3D configuration of our PLM-based EC-SERS system exhibits 2-fold and 10-fold superior electrochemical and SERS performance than conventional 2D platforms. The rich molecular-level electrochemical insights and excellent EC-SERS capabilities offered by our 3D spectroelectrochemical system is pertinent in charge transfer processes.
Datum: 23.05.2017


DNA barcoding meets nanotechnology: development of a smart universal tool for food authentication

Food trade globalization and the growing demand for selected food varieties have led to the intensification of adulteration cases, especially in the form of species substitution/mixing with cheaper taxa. This phenomenon acquired huge economic impact and sometimes even public health implications. DNA barcoding represents a well-proven molecular tool to assess the authenticity of food items, although its diffusion is hampered by analytical constraints and timeframes that are often prohibitive for food market. To address such issues, we have introduced a new technology, named NanoTracer, which allows for rapid and naked-eye molecular traceability of any food, employing limited instrumentation and cost-effective reagents. Moreover, unlike sequencing, this method allows to identify not only the substitution of a fine ingredient, but also its dilution with cheaper ones.
Datum: 23.05.2017


Total Synthesis of (±)-Corymine

The first total synthesis of the hexacyclic indole alkaloid (±)-corymine is described. Starting from the readily available N-protected tryptamine, the title compound was achieved in 21 steps in 3.4 % overall yield. Key steps of the synthesis include: a) the addition of a malonate to a 3-bromooxindole to afford 3,3-disubstituted oxindole, b) the formation of a 12-membered cyclic enol ether by intramolecular O-propargylation, immediately followed by propargyl Claisen rearrangement to provide the α-allenyl ketone stereospecifically, c) DMDO oxidation to install a hydroxy group in a highly stereoselective manner, and d) the SmI2-mediated reductive C−O bond cleavage to remove the α-keto carboxyl group. To the cor(ymine): The first total synthesis of (±)-corymine has been accomplished in 21 steps starting from N-nosyl-protected tryptamine. The synthesis features the intramolecular O-propargylation to generate a 12-membered cyclic enol ether, and subsequent propargyl Claisen rearrangement to provide, stereospecifically, the corresponding 3-vinylideneazocane as a key intermediate.
Datum: 23.05.2017


Enantioselective Dearomative Difunctionalization of Indoles by Palladium-Catalyzed Heck/Sonogashira Sequence

Palladium-catalyzed enantioselective dearomative arylalkynylation of N-substituted indoles, through a Heck/Sonogashira sequence, was established using a new BINOL-based phosphoramidite as the chiral ligand. A wide range of 2,3-disubstituted indolines, bearing vicinal quaternary and tertiary stereocenters, were efficiently constructed in one step with excellent enantioselectivities (up to 97 % ee) and diastereoselectivities (>20:1). Double the function: A highly enantioselective dearomative arylalkynylation of N-substituted indoles with alkynes has been established by using palladium and a BINOL-based phosphoramidite as the chiral ligand. A wide range of 2,3-disubstituted indolines, bearing vicinal tertiary and quaternary stereocenters, were constructed in one step with excellent enantio- and diastereoselectivities.
Datum: 23.05.2017


Induced-fit recognition of CCG trinucleotide repeats by a nickel chromomycin complex results in large-scale DNA deformation

Small-molecule compounds targeting trinucleotide repeats in DNA have considerable potential as therapeutic or diagnostic agents against many neurological diseases. NiII(Chro)2 (Chro = chromomycin A3) was found to bind specifically to the minor groove of (CCG)n repeats in duplex DNA, with unique fluorescence features that may serve as a probe for disease detection. Crystallographic studies have revealed that the specificity originates from the large-scale spatial rearrangement of the DNA structure, including extrusion of consecutive bases and backbone distortions, with a sharp bending of the duplex accompanied by conformational changes in the Ni(II) chelate itself. The DNA deformation of CCG repeats upon binding forms a GGCC tetranucleotide tract, which is recognized by NiII(Chro)2. The extruded cytosine and last guanine nucleotides form water-mediated hydrogen bonds which aid in ligand recognition. The recognition can be accounted for by the classic induced-fit paradigm.
Datum: 23.05.2017


Total Synthesis of (±)-Waihoensene

The first total synthesis of waihoensene, a tetracyclic diterpene containing an angular triquinane and a six-membered ring, with four contiguous quaternary carbon atoms, was achieved through the tandem cycloaddition reaction of an allenyl diazo substrate containing a six-membered ring via trimethylenemethane (TMM) diyl intermediate.
Datum: 23.05.2017


An Unsaturated Quinolone N-Oxide of Pseudomonas aeruginosa Modulates Growth and Virulence of Staphylococcus aureus

Chemical interactions of competing bacteria have major implications for health and disease of their human host. In their Communication (DOI: 10.1002/anie.201702944), D. Szamosvári and T. Böttcher report an unsaturated quinolone N-oxide produced by Pseudomonas aeruginosa with unprecedented efficacy and activity against Staphylococcus aureus affecting both growth and virulence. These results provide insight into a major metabolite by which P. aeruginosa modulates growth and behavior of its competitors.
Datum: 23.05.2017


Total Synthesis of Aplydactone by a Conformationally Controlled C−H Functionalization

A concise, protecting-group-free total synthesis of the unusual brominated sesquiterpene aplydactone is described. Our synthesis features a [2+2] photocycloaddition, a Wolff ring contraction, an unusual remote C−H functionalization to establish the highly strained tetracyclic core, and a hydrogen-atom transfer (HAT) reaction to access the bromine-containing stereocenter. A finely tuned conformation of the α-diazoketone precursor is the key for the success of the late-stage transannular C−H insertion to deliver a bridged six-membered ring and a quaternary stereocenter (C6) between two quaternary carbon atoms (C1 and C7). HAT in hand: A concise, protecting-group-free total synthesis of aplydactone has been achieved. The synthesis features a transannular six-membered-ring C−H insertion and a hydrogen atom transfer (HAT) reaction. A finely tuned conformation, as supported by theoretical calculations, is key to the success of the challenging C−H insertion.
Datum: 23.05.2017


Modified Tetrathiafulvalene as an Organic Conductor for Improving Performances of Li−O2 Batteries

Large over-potentials owing to the sluggish kinetics of battery reactions have always been the drawbacks of Li−O2 batteries, which lead to short cycle life. Although redox mediators have been intensively investigated to overcome this issue, side-reactions are generally induced by the solvated nature of redox mediators. Herein, we report an alternative method to achieve more efficient utilization of tetrathiafulvalene (TTF) in Li−O2 batteries. By coordinating TTF+ with LiCl during charging, an organic conductor TTF+Clx− precipitate covers Li2O2 to provide an additional electron-transfer pathway on the surface, which can significantly reduce the charge over-potential, improve the energy efficiency of Li−O2 batteries, and eliminate side-reactions between the lithium metal anode and TTF+. When a porous graphene electrode is used, the Li−O2 battery combined with TTF and LiCl shows an outstanding performance and prolonged cycle life. A pinch of salt: TTF+Clx− precipitates on the surface of the Li2O2 discharge product upon the addition of LiCl to tetrathiafulvalene-containing electrolytes during charging. This efficiently reduces the risk of side-reactions and enhances the cycling performances of Li−O2 batteries.
Datum: 23.05.2017


Rapid Production of High-Purity Hydrogen Fuel through Microwave-Promoted Deep Catalytic Dehydrogenation of Liquid Alkanes with Abundant Metals

Hydrogen as an energy carrier promises a sustainable energy revolution. However, one of the greatest challenges for any future hydrogen economy is the necessity for large scale hydrogen production not involving concurrent CO2 production. The high intrinsic hydrogen content of liquid-range alkane hydrocarbons (including diesel) offers a potential route to CO2-free hydrogen production through their catalytic deep dehydrogenation. We report here a means of rapidly liberating high-purity hydrogen by microwave-promoted catalytic dehydrogenation of liquid alkanes using Fe and Ni particles supported on silicon carbide. A H2 production selectivity from all evolved gases of some 98 %, is achieved with less than a fraction of a percent of adventitious CO and CO2. The major co-product is solid, elemental carbon. Stop CO2! Microwave-promoted, catalytic deep dehydrogenation of liquid alkanes using the abundant metals iron and nickel as catalysts produces CO2-free hydrogen, signaling a route to the decarbonization of fossil fuels.
Datum: 23.05.2017


Biocatalytic Friedel–Crafts Acylation and Fries Reaction

The Friedel–Crafts acylation is commonly used for the synthesis of aryl ketones, and a biocatalytic version, which may benefit from the chemo- and regioselectivity of enzymes, has not yet been introduced. Described here is a bacterial acyltransferase which can catalyze Friedel–Crafts C-acylation of phenolic substrates in buffer without the need of CoA-activated reagents. Conversions reach up to >99 %, and various C- or O-acyl donors, such as DAPG or isopropenyl acetate, are accepted by this enzyme. Furthermore the enzyme enables a Fries-like rearrangement reaction of resorcinol derivatives. These findings open an avenue for the development of alternative and selective C−C bond formation methods. Order up on Fries: The biocatalytic acylation of resorcinol substrates, catalyzed by an acyltransferase, leads to C-acylated products. The Friedel–Crafts bio-C-acylation allows use of simple activated esters, such as isopropenyl acetate, as an acyl source. Additionally the enzyme enables a Fries-like rearrangement reaction.
Datum: 23.05.2017


Facile Access to NaOC≡As and Its Use as an Arsenic Source to Form Germylidenylarsinidene Complexes

A facile, one-pot synthesis of [Na(OC≡As)(dioxane)x] (x=2.3–3.3) in 78 % yield is reported through the reaction of arsine gas with dimethylcarbonate in the presence of NaOtBu and 1,4-dioxane. It has been employed for the synthesis of the first arsaketenyl-functionalized germylene [LGeAsCO] (2, L=CH[CMeN(Dipp)]2; Dipp=2,6-iPr2C6H3) from the reaction with LGeCl (1). Upon exposure to ambient light, 2 undergoes CO elimination to form the 1,3-digerma-2,4-diarsacyclobutadiene [L2Ge2As2] (3), which contains a symmetric Ge2As2 ring with ylide-like Ge=As bonds. Remarkably, the CO ligand located at the arsenic center of 2 can be exchanged with PPh3 or an N-heterocyclic carbene iPrNHC donor (iPrNHC=1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) to afford the novel germylidenylarsinidene complexes [LGe-AsPPh3] (4) and [LGe-As(iPrNHC)] (5), respectively, demonstrating transition-metal-like ligand substitution at the arsinidene-like As atom. The formation of 2–5 and their electronic structures have been studied by DFT calculations. Germanium meets arsenic: A convenient, one-pot synthesis of Na(OC≡As) starts from arsine as an arsenic source. This reagent reacts straightforwardly with a chloro-β-diketiminato germylene to form the first arsaketenyl-functionalized germylene 1. Compound 1 undergoes CO release to afford, via the arsagermyne intermediate 2, the unprecedented isolable 1,3-digerma-2,4-diarsacyclobutadiene 3 with ylide-like Ge=As bonds.
Datum: 23.05.2017


Self-Optimization of the Active Site of Molybdenum Disulfide by an Irreversible Phase Transition during Photocatalytic Hydrogen Evolution

The metallic 1T-MoS2 has attracted considerable attention as an effective catalyst for hydrogen evolution reactions (HERs). However, the fundamental mechanism about the catalytic activity of 1T-MoS2 and the associated phase evolution remain elusive and controversial. Herein, we prepared the most stable 1T-MoS2 by hydrothermal exfoliation of MoS2 nanosheets vertically rooted into rigid one-dimensional TiO2 nanofibers. The 1T-MoS2 can keep highly stable over one year, presenting an ideal model system for investigating the HER catalytic activities as a function of the phase evolution. Both experimental studies and theoretical calculations suggest that 1T phase can be irreversibly transformed into a more active 1T′ phase as true active sites in photocatalytic HERs, resulting in a “catalytic site self-optimization”. Hydrogen atom adsorption is the major driving force for this phase transition. An irreversible phase transition of MoS2 during the photocatalytic hydrogen evolution was decrypted. Hydrogen atom adsorption is the driving force for this phase transition. The distorted structure could be stabilized by both strain and S vacancies. This phase-transition-induced catalytic activity improvement was defined as a “self-optimization” mechanism.
Datum: 23.05.2017


Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene

Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra-long aliphatic α,ω-difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω-dicarboxylic fatty acid self-metathesis products is shifted selectively to the statistically much-disfavored α,β-position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co-reagents, yields ultra-long-chain α,ω-difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self-assembly to polyethylene-like single crystals. Double the fun: Common monounsaturated fatty acids are used to provide ultra-long aliphatic α,ω-difunctional building blocks of precise chain length. A sequence of two scalable catalytic steps (isomerization and “chain doubling”) virtually double the chain length of the starting materials.
Datum: 23.05.2017


Construction of Chiral Tetrahydro-β-Carbolines: Asymmetric Pictet–Spengler Reaction of Indolyl Dihydropyridines

A highly efficient synthesis of the enantioenriched tetrahydro-β-carbolines was developed by using a chiral phosphoric acid catalyzed Pictet–Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro-β-carbolines in good to excellent yields (up to 96 %) and high enantioselectivities (up to 99 % ee). With this method, a formal synthesis of tangutorine and a total synthesis of deplancheine were achieved in a highly efficient manner. New twist, old reaction: A highly efficient synthesis of the enantioenriched title compounds was developed by using a chiral phosphoric acid (CPA) catalyzed Pictet–Spengler reaction of indolyl dihydropyridines. The reaction proceeds under mild reaction conditions to afford the desired chiral tetrahydro-β-carbolines in good to excellent yields and high enantioselectivities. The method was used in the formal synthesis of tangutorine and a total synthesis of deplancheine.
Datum: 23.05.2017


Base-Selective Five- versus Six-Membered Ring Annulation in Palladium-Catalyzed C–C Coupling Cascade Reactions: New Access to Electron-Poor Polycyclic Aromatic Dicarboximides

Palladium-catalyzed base-selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross-coupling and direct C−H arylation afforded a series of new five- and six-membered ring annulated electron-poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs2CO3) as auxiliary base in these C−C coupling cascade reactions led exclusively to six-membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five-membered ring annulated products. This base-dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X-ray analysis of the respective five- and six-membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry. Polycycles: Depending on the auxiliary bases applied in Pd-catalyzed C−C coupling reactions electron-poor polycyclic aromatic hydrocarbons are obtained by selective five- or six-membered ring annulation.
Datum: 23.05.2017


Carbon Monoxide Dehydrogenase Reduces Cyanate to Cyanide

The biocatalytic function of carbon monoxide dehydrogenase (CODH) has a high environmental relevance owing to its ability to reduce CO2. Despite numerous studies on CODH over the past decades, its catalytic mechanism is not yet fully understood. In the present combined spectroscopic and theoretical study, we report first evidences for a cyanate (NCO−) to cyanide (CN−) reduction at the C-cluster. The adduct remains bound to the catalytic center to form the so-called CN−-inhibited state. Notably, this conversion does not occur in crystals of the Carboxydothermus hydrogenoformans CODH enzyme (CODHIICh), as indicated by the lack of the corresponding CN− stretching mode. The transformation of NCO−, which also acts as an inhibitor of the two-electron-reduced Cred2 state of CODH, could thus mimic CO2 turnover and open new perspectives for elucidation of the detailed catalytic mechanism of CODH. Take-O-way: By combining spectroscopic and theoretical studies, the C-cluster of carbon monoxide dehydrogenase (CODH) was found to catalyze the reduction of cyanate to cyanide. The adduct remains bound to the catalytic center to form the so-called CN−-inhibited state. The transformation of NCO− could thus mimic CO2 turnover and open new perspectives for elucidation of the detailed catalytic mechanism of CODH.
Datum: 23.05.2017


Unexpected Direct Synthesis of N-Vinyl Amides through Vinyl Azide–Enolate [3+2] Cycloaddition

The unexpected synthesis of industrially important N-vinyl amides directly from aldehydes and α,β-unsaturated N-vinyl amides from esters is reported. This reaction probably proceeds through an initial [3+2] azide–enolate cycloaddition involving a vinyl azide generated in situ. A survey of the reaction scope and preliminary mechanistic findings supported by quantum computational analysis are reported, with implications for the future development of atom-efficient amide synthesis. Intriguingly, this study suggests that (cautious) reevaluation of azidoethene as a synthetic reagent may be warranted. Worth another look: Industrially important N-vinyl amides were synthesized directly from aldehydes/esters and 1-azido-2-iodoethane. Quantum-chemical calculations support the proposed mechanism involving [3+2] cycloaddition of the enolate derived from the aldehyde or ester with a vinyl azide generated in situ (see scheme). The results suggest that azidoethene itself may be worth (cautious) reevaluation as an atom-efficient synthetic reagent.
Datum: 23.05.2017


High-Fidelity, Narcissistic Self-Sorting in the Synthesis of Organometallic Assemblies from Poly-NHC Ligands

Highly selective, narcissistic self-sorting has been observed in the one-pot synthesis of three organometallic molecular cylinders of type [M3{L-(NHC)3}2](PF6)3 (M=Ag+, Au+; L=1,3,5-benzene, triphenylamine, or 1,3,5-triphenylbenzene) from L-(NHC)3 and silver(I) or gold(I) ions. The molecular cylinders contain only one type of tris-NHC ligand with no crossover products detectable. Transmetalation of the tris-NHC ligands from Ag+ to Au+ in a one-pot reaction with retention of the supramolecular structures is also demonstrated. High-fidelity self-sorting was also observed in the one-pot reaction of benzene-bridged tris-NHC and tetrakis-NHC ligands with Ag2O. This study for the first time extends narcissistic self-sorting in metal–ligand interactions from Werner-type complexes to organometallic derivatives. Perfect sorting! Unique narcissistic self-sorting has been observed in the one-pot reaction of three different trigonal trisimidazolium salts with Ag2O. Only three cylinder-like trinuclear complexes each bearing two identical tris-NHC ligands were obtained from this reaction. Self-sorting was also observed in the subsequent transmetalation of the tris-NHC ligands from the three silver(I) complexes to give three gold(I) complexes.
Datum: 23.05.2017


Unprecedented Carbon Signal Enhancement in Liquid-State NMR Spectroscopy

We shall overcome: As a result of efforts to overcome the sensitivity challenge of liquid-state NMR spectroscopy, a thousand-fold signal enhancement was achieved by dynamic nuclear polarization (DNP) for 13C signals at high magnetic field (3.4 T) and room temperature, thereby exceeding the predicted limitations of high-field liquid-state in situ DNP.
Datum: 23.05.2017


Self-Assembly of Conjugated Metallopolymers with Tunable Length and Controlled Regiochemistry

Self-assembled materials can be designed to express useful optoelectronic properties; however, achieving structural control is a necessary precondition for the optimization of desired properties. Here we report a simple, metal-templated polymerization process that generates helical metallopolymer strands over 75 repeat units long (28 kDa) from a single bifunctional monomer and CuI. The resulting polymer consists of a double helix of two identical conjugated organic strands enclosing a central column of metal ions. The length of this metallopolymer can be controlled by adding monofunctional subcomponents to end-cap the conjugated ligands. The use of ditopic and bulky monotopic subcomponents, respectively, allows a head-to-head or head-to-tail double helix to be generated. Spectroscopic measurements of different polymer lengths demonstrate how control over polymer length leads to control over the electronic and luminescent properties of the resulting material, thereby enabling tunable white-light emission. Polymers with a twist: The self-assembly of bifunctional subcomponents around CuI to yield long, double helical metallopolymers is reported. Terminating groups are employed that govern the regiochemistry of the two strands within the polymer. Varying the stoichiometry of monomer to terminating group alters the polymer length, thereby enabling tunable white-light emission.
Datum: 23.05.2017


Mild, Redox-Neutral Formylation of Aryl Chlorides through the Photocatalytic Generation of Chlorine Radicals

We report a redox-neutral formylation of aryl chlorides that proceeds through selective 2-functionalization of 1,3-dioxolane through nickel and photoredox catalysis. This scalable benchtop approach provides a distinct advantage over traditional reductive carbonylation in that no carbon monoxide, pressurized gas, or stoichiometric reductant is employed. The mild conditions give unprecedented scope from abundant and complex aryl chloride starting materials. Born to be mild: Aromatic aldehydes are generated from abundant aryl chlorides through nickel-photocatalyzed C−H functionalization of the inexpensive solvent 1,3-dioxolane. The mild conditions and absence of pressurized carbon monoxide or stoichiometric reductant lead to broad functional-group tolerance and scope.
Datum: 23.05.2017


Morphological Control of Heteroleptic cis- and trans-Pd2L2L′2 Cages

Control over the integrative self-sorting of metallo-supramolecular assemblies opens up possibilities for introducing increased complexity and function into a single self-assembled architecture. Herein, the relationship between the geometry of three ligand components and morphology of three self-sorted heteroleptic [Pd2L2L′2]4+ cages is examined. Pd-mediated assembly of two bis-monodentate pyridyl ligands with native bite angles of 75° and 120° affords a cis-[Pd2L2L′2]4+ cage while the same reaction with two ligands with bite angles of 75° and 60° gives an unprecedented, self-penetrating structural motif; a trans-[Pd2(anti-L)2L′2]4+ heteroleptic cage with a “doubly bridged figure eight” topology. Each heteroleptic assembly can be formed by cage-to-cage conversion of the homoleptic precursors and morphological control of [Pd2L2L′2] cages is achieved by selective ligand displacement transformations in a system of three ligands and at least six possible cage products. A doubly bridged figure eight: Integrative self-sorting of geometrically distinct ligands and cages is regulated to form new [Pd2L2L′2] structures. For one example, X-ray analysis reveals a doubly bridged figure-eight topology which is an unprecedented motif for metallo-supramolecular structures. Furthermore, morphological control of a system of cages is achieved by highly selective ligand displacement transformations.
Datum: 23.05.2017


A Structurally Characterized Fluoroalkyne

The facile synthesis of a stable and isolable compound with a fluoroalkynyl group, M−C≡CF, is reported. Reaction of [Ru(C≡CH)(η5-C5Me5)(dppe)] with an electrophilic fluorinating agent (NFSI) results in the formation of the fluorovinylidene complex [Ru(=C=CHF)(η5-C5Me5)(dppe)][N(SO2Ph)2]. Subsequent deprotonation with LiN(SiMe3)2 affords the fluoroalkynyl complex [Ru(C≡CF)(η5-C5Me5)(dppe)]. In marked contrast to the rare and highly reactive examples of fluoroalkynes that have been reported previously, this compound can be readily isolated and structurally characterized. This has allowed the structure and bonding in the CCF motif to be explored. Further electrophilic fluorination of this species yields the difluorovinylidene complex [Ru(C=CF2)(η5-C5Me5)(dppe)][N(SO2Ph)2]. Fancy a fluorine? In contrast to other fluorinated alkynes, structurally characterized {M−C≡CF} exhibits considerable long-term stability. Structural, spectroscopic and computational analyses reveal that this longevity is underpinned by kinetic stabilization by a half-sandwich ruthenium substituent. Subsequent fluorination provides facile access to a rare example of a difluorovinylidene complex.
Datum: 23.05.2017


A Membrane-Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst

Polymer electrolyte membranes employed in contemporary fuel cells severely limit device design and restrict catalyst choice, but are essential for preventing short-circuiting reactions at unselective anode and cathode catalysts. Herein, we report that nickel sulfide Ni3S2 is a highly selective catalyst for the oxygen reduction reaction in the presence of 1.0 m formate. We combine this selective cathode with a carbon-supported palladium (Pd/C) anode to establish a membrane-free, room-temperature formate fuel cell that operates under benign neutral pH conditions. Proof-of-concept cells display open circuit voltages of approximately 0.7 V and peak power values greater than 1 mW cm−2, significantly outperforming the identical device employing an unselective platinum (Pt) cathode. The work establishes the power of selective catalysis to enable versatile membrane-free fuel cells. A highly selective catalyst: Nickel sulfide (Ni3S2) selectively catalyzes the oxygen reduction reaction (ORR) in the presence of 1.0 m formate, enabling a membrane-free formate fuel cell that operates under benign neutral pH conditions. The Ni3S2–Pd fuel cell achieves higher open circuit voltage and power density than a Pt–Pd configuration.
Datum: 23.05.2017


Direct Nucleophilic Substitution Reaction of Cage B−H Bonds by Grignard Reagents: A Route to Regioselective B4-Alkylation of o-Carboranes

Direct nucleophilic substitution reaction of cage B−H bonds of o-carboranes by Grignard reagents in the absence of any transition metals has been achieved for the first time, and leads to the regioselective synthesis of a series of 4-alkyl-1,2-diaryl-o-carboranes in very high yields. The presence of two electron-withdrawing aryl groups on the cage carbon atoms is crucial to realizing the reaction. The regioselectivity is controlled by both electronic and steric factors. This work represents a new strategy for the development of methods for carborane functionalization. Rattled cage: The title reaction proceeds in the absence of transition metals and leads to 4-alkyl-1,2-diaryl-o-carboranes in high yields. The presence of two electron-withdrawing aryl groups on the cage carbon atoms is crucial for the reaction, and the regioselectivity is controlled by both electronic and steric factors.
Datum: 23.05.2017


Luminescence, Plasmonic, and Magnetic Properties of Doped Semiconductor Nanocrystals

Introducing a few atoms of impurities or dopants in semiconductor nanocrystals can drastically alter the existing properties or even introduce new properties. For example, mid-gap states created by doping tremendously affect photocatalytic activities and surface controlled redox reactions, generate new emission centers, show thermometric optical switching, make FRET donors by enhancing the excited state lifetime, and also create localized surface plasmon resonance induced low energy absorption. In addition, researchers have more recently started focusing their attention on doped nanocrystals as an important and alternative material for solar energy conversion to meet the current demand for renewable energy. Moreover, the electrical and magnetic properties of the host are also strongly altered on doping. These beneficial dopant-induced changes suggest that doped nanocrystals with proper selections of dopant–host pairs may be helpful for generating designer materials for a wide range of current technological needs. How properties relate to the doping of a variety of semiconductor nanocrystals are summarized in this Review. Doping control: Doping semiconductor nanocrystals combines properties of both the dopant ion and the quantum confinement effect of the nanocrystal. This Review presents recent advances in synthesis, luminescence, photocatalysis, photovoltaic, plasmonic, magnetic, and magneto-optic properties of doped semiconductor nanocrystals.
Datum: 23.05.2017


Antivitamin B12 Inhibition of the Human B12-Processing Enzyme CblC: Crystal Structure of an Inactive Ternary Complex with Glutathione as the Cosubstrate

B12 antivitamins are important and robust tools for investigating the biological roles of vitamin B12. Here, the potential antivitamin B12 2,4-difluorophenylethynylcobalamin (F2PhEtyCbl) was prepared, and its 3D structure was studied in solution and in the crystal. Chemically inert F2PhEtyCbl resisted thermolysis of its Co−C bond at 100 °C, was stable in bright daylight, and also remained intact upon prolonged storage in aqueous solution at room temperature. It binds to the human B12-processing enzyme CblC with high affinity (KD=130 nm) in the presence of the cosubstrate glutathione (GSH). F2PhEtyCbl withstood tailoring by CblC, and it also stabilized the ternary complex with GSH. The crystal structure of this inactivated assembly provides first insight into the binding interactions between an antivitamin B12 and CblC, as well as into the organization of GSH and a base-off cobalamin in the active site of this enzyme. Antivitamins in action: A new, chemically robust antivitamin B12 was used for biochemical analysis of the inhibition of CblC, the key B12-processing enzyme of humans. The crystal structure of the inactive enzyme complex provides detailed insight into CblC loaded with a cobalamin and its cosubstrate glutathione.
Datum: 23.05.2017


Single-Atom Electrocatalysts

Recent years have witnessed the increasing production of the sustainable and renewable energy. The limitations of electrochemical performances are closely associated with the search for highly efficient electrocatalysts with more rational control of size, shape, composition and structure. Specifically, the rapidly emerging studies on single-atom catalysts (SACs) have sparked new interests in electrocatalysis because of the unique properties such as high catalytic activity, selectivity and 100% atom utilization. In this review, we introduce the innovative synthesis and advanced characterizations of SACs and primarily focus on their electrochemical applications in oxygen reduction/evolution reaction, hydrogen evolution reaction, hydrocarbon conversion reactions for fuel cells (methanol, ethanol and formic acid electrooxidation) and other related fields. Significantly, this unique single atom-depended electrocatalytic performance together with the underlying mechanism will also be discussed. Furthermore, future research directions and challenges are proposed to further realize the ultimate goal of tailoring single-atoms for electrochemical applications.
Datum: 23.05.2017


From Extended-Nano Fluidics to an Autonomous Solar Light Driven Micro Fuel Cell Device

Autonomous micro/nano mechanical, chemical and biomedical sensors require persistent power sources scaled to their size. Realization of autonomous micro-power sources is a challenging task, as it requires combination of wireless energy supply, conversion, storage and delivery to the sensor. In this work, we realized solar light driven power source that consists of a micro fuel cell (μFC) and a photocatalytic micro fuel generator (μFG) integrated on a single microfluidic chip. The μFG produces hydrogen by photocatalytic water splitting under solar light. The hydrogen is then consumed by the μFC to generate electricity. Importantly, the byproduct water returns back to the photocatalytic μFG via recirculation loop without losses. Functionality of both devices relies on novel phenomena in extended-nano fluidic channels that ensure ultra-fast proton transport. As a proof of concept, we demonstrate that μFG/μFC source achieves remarkable energy density of ~17.2 mWh cm-2 at room temperature.
Datum: 23.05.2017


A Tunable Ionic Diode based on Biomimetic Structure-Tailorable Nanochannel

In this work, we reported a tunable ionic diode based on biomimetic structure-tailorable nanochannels, with the precise ions transport characteristics from ohmic behaviour to bidirectional rectification as well as the gating properties. The forward/reverse directions of the ionic diode and the degree of rectification can be well regulated by combining the patterned surface charge and the sophisticated structure. This system creates an ideal platform for precise transportation of ions and molecules, and anticipates to have potential applications in analytical sciences.
Datum: 23.05.2017


Rhodium-Catalyzed Enantioselective Radical Addition of CX4 Reagents to Olefins

We describe an enantioselective addition of Br-CX3 (X = Cl or Br) to terminal olefins that introduces a trihalomethyl group and generates optically active secondary bromides. Computational and experimental evidence supports an asymmetric atom transfer radical addition (ATRA) mechanism in which the stereodetermining step involves outer-sphere bromine abstraction from a (bisphosphine)Rh(II)BrCl complex by a benzylic radical intermediate. Beyond the synthetic utility, this mechanism appears unprecedented in asymmetric catalysis.
Datum: 22.05.2017


Eight-Electron Silver and Mixed Gold/Silver Nanoclusters Stabilized by Se-Donor Ligands

The first atomically and structurally precise silver-nanoclusters stabilized by Se-donor ligands, [Ag20{Se2P(OiPr)2}12] (3) and [Ag21{Se2P(OEt)2}12]+(4), have been isolated by ligand replacement reaction of [Ag20{S2P(OiPr)2}12] (1) and [Ag21{S2P(OiPr)2}12]+ (2), respectively. Further, doping reactions of 4 with Au(PPh3)Cl resulted in the formation of [AuAg20{Se2P(OEt)2}12]+, (5). Structures of 3, 4 and 5 were determined by single crystal X-ray diffraction. The anatomy of cluster 3 with an Ag20 core having C3 symmetry is very similar to that of its dithiophosphate analogue 1. Clusters 4 and 5 exhibit an Ag21 and Au@Ag20 core of Oh symmetry composed of eight silver capping atoms in a cubic arrangement and encapsulating an Ag13 and Au@Ag12 centered icosahedron, respectively. Both ligand exchange and heteroatom doping result in significant changes in optical and emissive properties for chalcogen-passivated silver nanoparticles, which have been theoretically proved as 8-electron superatoms.
Datum: 22.05.2017


Phenotypic Identification of a Novel Autophagy Inhibitor Chemotype Targeting Lipid Kinase VPS34

Autophagy is a critical regulator of cellular homeostasis and metabolism. Interference with this process is considered a new approach for the treatment of disease, in particular cancer and neurological disorders. Therefore, novel small molecule autophagy modulators are in high demand. We describe the discovery of autophinib, a potent autophagy inhibitor with a novel chemotype. Autophinib was identified by means of a phenotypic assay monitoring formation of autophagy-induced puncta indicating accumulation of lipidated cytosolic protein LC3 on the autophagosomal membrane. Target identification and validation revealed that autophinib inhibits autophagy induced by starvation or Rapamycin by targeting the lipid kinase VPS34.
Datum: 22.05.2017


Catalytic Electrophilic Alkylation of p-Quinones via a Redox Chain Reaction

Allylation and benzylation of p-quinones is achieved by an unusual redox chain reaction. Mechanistic studies suggest that the trace existence of hydroquinone initiates a redox chain reaction that consists of a Lewis acid-catalyzed Friedel-Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. Addition of Hantzsch ester as initiator improves the efficiency of the reaction.
Datum: 22.05.2017


Gold-Catalyzed Cadiot–Chodkiewicz-Type Cross-Coupling of Terminal Alkynes with Alkynyl Hypervalent Iodine Reagents: Highly Selective Synthesis of Unsymmetrical 1,3-Diynes

A new and efficient method for the synthesis of unsymmetrical 1,3-butadiynes by gold-catalyzed C(sp)–C(sp) cross-coupling of terminal alkynes with alkynyl hypervalent iodine(III) reagents has been developed. The reaction features high selectivity and efficiency, mild reaction conditions, wide substrate scope, and functional-group compatibility, and is a highly attractive complement to existing methods. Mechanistic studies reveal that formation of a phenanthrolinyl-ligated gold(I) complex is crucial for the efficiency and selectivity of the target transformation. All the hype: A new method for the title reaction has been developed. The reaction features high selectivity and efficiency, mild reaction conditions, wide substrate scope, and functional-group compatibility. Mechanistic studies reveal that the formation of a phenanthrolinyl-ligated gold(I) complex is crucial for the efficiency and selectivity of the target transformation.
Datum: 22.05.2017


A Modular Flow Design for the meta-Selective C−H Arylation of Anilines

Described herein is an effective and practical modular flow design for the meta-selective C−H arylation of anilines. The design consists of four continuous-flow modules (i.e., diaryliodonium salt synthesis, meta-selective C−H arylation, inline copper extraction, and aniline deprotection) which can be operated either individually or consecutively to provide direct access to meta-arylated anilines. With a total residence time of 1 hour, the desired product could be obtained in high yield and excellent purity without the need for column chromatography, and the residual copper content meets the standards for parenterally administered pharmaceutical substances. One by one or all in one: meta-Arylated anilines are key moieties in a variety of high-value chemicals. To access these compounds, four key flow steps were identified, including synthesis of the diaryliodonium salt, meta-selective C−H arylation, and the removal of both the copper catalyst and the directing group. Each module has great individual potential, however, combining them allowed straightforward access to meta-arylated anilines within a reasonable time scale and with good purity.
Datum: 22.05.2017


Discovery of EGF Receptor Inhibitors that are Selective for the d746-750/T790M/C797S Mutant through Structure-Based de Novo Design

Next-generation epidermal growth factor receptor (EGFR) inhibitors against the d746-750/T790M/C797S mutation were discovered through two-track virtual screening and de novo design. A number of nanomolar inhibitors were identified using 2-aryl-4-aminoquinazoline as the molecular core and the modified binding energy function involving a proper dehydration term, which provides important structural insight into the key principles for high inhibitory activities against the d746-750/T790M/C797S mutant. Furthermore, some of these EGFR inhibitors showed a greater than 1000-fold selectivity for the d746-750/T790M/C797S mutant over the wild type, as well as nanomolar activity against the mutant. Mutant selective: Next-generation epidermal growth factor receptor (EGFR) inhibitors against the d746-750/T790M/C797S mutation were discovered through two-track virtual screening and de novo design. A number of nanomolar 2-aryl-4-aminoquinazoline-based inhibitors exhibited more than 1000-fold selectivity for the triple mutant over the wild type. High inhibitory activity was achieved by strengthening the interactions in the ATP-binding site.
Datum: 22.05.2017


Catalytic Asymmetric [3+1]-Cycloaddition Reaction of Ylides with Electrophilic Metallo-enolcarbene Intermediates

The first asymmetric [3+1]-cycloaddition was successfully achieved by copper(I) triflate/double-sidearmed bisoxazoline complex catalyzed reactions of β-triisopropylsilyl-substituted enoldiazo compounds with sulfur ylides. This methodology delivered a series of chiral cyclobutenes in good yields with high enantio- and diastereoselectivities (up to 99 % ee, and >20:1 d.r.). Additionally, the [3+1]-cycloaddition of catalytically generated metallo-enolcarbenes was successfully extended to reaction with a stable benzylidene dichlororuthenium complex. Three plus one: β-Triisopropylsilyl-substituted enoldiazo compounds react with sulfur ylides in a [3+1]-cycloaddition reaction catalyzed by copper(I) triflate/double-sidearmed bisoxazoline complex (see figure) to give cyclobutenes. The asymmetric version proceeds in good yield with high enantio- and diastereoselectivity.
Datum: 22.05.2017


Redox-Sensitive Stomatocyte Nanomotors: Destruction and Drug Release in the Presence of Glutathione

The development of artificial nanomotor systems that are stimuli-responsive is still posing many challenges. Herein, we demonstrate the self-assembly of a redox-responsive stomatocyte nanomotor system, which can be used for triggered drug release under biological reducing conditions. The redox sensitivity was introduced by incorporating a disulfide bridge between the hydrophilic poly(ethylene glycol) block and the hydrophobic polystyrene block. When incubated with the endogenous reducing agent glutathione at a concentration comparable to that within cells, the external PEG shells of these stimuli-responsive nanomotors are cleaved. The specific bowl-shaped stomatocytes aggregate after the treatment with glutathione, leading to the loss of motion and triggered drug release. These novel redox-responsive nanomotors can not only be used for remote transport but also for drug delivery, which is promising for future biomedical applications. Destruction on demand: A redox-responsive stomatocyte nanomotor was developed by incorporating disulfide bridges between the hydrophilic PEG and hydrophobic PS moieties of the copolymer. When incubated in vitro with the endogenous reducing agent glutathione, the external PEG shells of the nanomotors are cleaved, which results in the loss of motion and can be used for drug release.
Datum: 22.05.2017


Oxidative Neutralization of Mustard-Gas Simulants in an On-Board Flow Device with In-Line NMR Monitoring

The fast and effective neutralization of the mustard-gas simulant 2-chloroethyl ethyl sulfide (CEES) using a simple and portable continuous flow device is reported. Neutralization takes place through a fully selective sulfoxidation by a stable source of hydrogen peroxide (alcoholic solution of urea–H2O2 adduct/MeSO3H freshly prepared). The reaction progress can be monitored with an in-line benchtop NMR spectrometer, allowing a real-time adjustment of reaction conditions. Inherent features of millireactors, that is, perfect control of mixing, heat and reaction time, allowed the neutralization of 25 g of pure CEES within 46 minutes in a 21.5 mL millireactor (tR=3.9 minutes). This device, which relies on affordable and nontoxic reagents, fits into a suitcase, and can be deployed by police/military forces directly on the attack site. Mustard-gas simulant 2-chloroethyl ethyl sulfide (CEES) was fully neutralized by selective oxidation to sulfoxide (CEESO) under continuous flow with in-line NMR monitoring. Pure CEES (25 g) has been converted almost completely into CEESO within 46 minutes in a 21.5 mL millireactor. This flow device is small enough to be moved by security forces and used directly on the site of a chemical threat.
Datum: 22.05.2017


Observation of CH⋅⋅⋅π Interactions between Methyl and Carbonyl Groups in Proteins

Protein structure and function is dependent on myriad noncovalent interactions. Direct detection and characterization of these weak interactions in large biomolecules, such as proteins, is experimentally challenging. Herein, we report the first observation and measurement of long-range “through-space” scalar couplings between methyl and backbone carbonyl groups in proteins. These J couplings are indicative of the presence of noncovalent C−H⋅⋅⋅π hydrogen-bond-like interactions involving the amide π network. Experimentally detected scalar couplings were corroborated by a natural bond orbital analysis, which revealed the orbital nature of the interaction and the origins of the through-space J couplings. The experimental observation of this type of CH⋅⋅⋅π interaction adds a new dimension to the study of protein structure, function, and dynamics by NMR spectroscopy. Don't neglect the little ones: Solution NMR spectroscopy and DFT calculations showed the existence of weak, hydrogen-bond-like C−H⋅⋅⋅π interactions in proteins between methyl donor groups and peptide-bond acceptor groups (see picture). As large numbers of C−H⋅⋅⋅πCO interactions are present in proteins, they presumably make an important cumulative contribution to protein structure, dynamics, and function.
Datum: 22.05.2017


Deprotonation of a Seemingly Hydridic Diborane(6) to Build a B−B Bond

Deprotonation of the doubly arylene-bridged diborane(6) derivative 1H2 with (Me3Si)3CLi or (Me3Si)2NK gives the B−B σ-bonded species M[1H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4′-di-tert-butyl-2,2′-biphenylylene). With nBuLi as the base, the yield of Li[1H] drops to 20 % and the 1,1-bis(9-borafluorenyl)butane Li[2H] is formed as a side product (30 %). In addition to the 1,1-butanediyl fragment, the two boron atoms of Li[2H] are linked by a μ-H bridge. In the closely related molecule Li[3H], the corresponding μ-H atom can be abstracted with (Me3Si)3CLi to afford the B−B-bonded conjugated base Li2[3] (THF, 150 °C; 15 %). Li[1H] and Li[2H] were characterized by NMR spectroscopy and X-ray crystallography. Fluid identity: A B−B bond was formed through the deprotonation of a doubly arylene-bridged diborane(6) derivative. The reaction shows that organoboranes are not necessarily hydridic and paves the way for new access routes to electron-precise diboranes.
Datum: 22.05.2017


Self-Assembled Biomimetic Chloroplast Coupled Photoenzymatic Reaction for Sustainable Synthesis of Fuel

Prototypes of biosystems provide good blueprints for the design and creation of biomimetic systems. However, mimicking both the sophisticated natural structures and their complex biological functions still remains a great challenge. Herein, biomimetic chloroplasts have been fabricated by one-step bio-inspired amino acid mineralization and simultaneous integration of catalytically active units. Hierarchically structured crystals are obtained by metal ion-directed self-assembly of cystine (the oxidized dimer form of the amino acid cysteine), with porous structure and stacking nanorods, which show similar architectural principles to chloroplasts. Porphyrin and enzyme molecules can be both encapsulated in the crystal during mineralization, endowing photocatalytic and enzymatic activity to the crystal, achieving efficient and sustainable synthesis of hydrogen and aldehyde via coupled photoenzymatic reaction.
Datum: 22.05.2017


Direct Hydroxylation of Benzene to Phenol by Cytochrome P450BM3 Triggered by Amino Acid Derivatives

Selective hydroxylation of benzene to phenol, without formation of side products resulting from overoxidation, was catalyzed by cytochrome P450BM3 (P450BM3) with the assistance of amino acid derivatives as decoy molecules. The catalytic turnover rate and the total turnover number reached 259 min-1P450BM3-1 and 40,200 P450BM3-1 when N-heptyl-L-proline modified with L-phenyl alanine (C7-L-Pro-L-Phe) was used as the decoy molecule. This work shows that amino acid derivatives that have a totally different structure from fatty acids can be used as decoy molecules for aromatic hydroxylation by wild-type P450BM3. This methodology for nonnative substrate hydroxylation by wild-type P450BM3 has the potential to expand the utility of P450BM3 for biotransformations.
Datum: 22.05.2017


Selected Copper-Based Reactions for C-N, C-O, C-S and C-C Bond Formation

The metal catalyzed cross-coupling reactions are one of the most important transformations in organic synthesis. Copper catalysis has received great attention due to its low toxicity and inexpensive nature. However, traditional Ullmann-type coupling reactions suffered from limited substrate scope and harsh reaction conditions. The introduction of some bidentate ligands such as amino acids, diamines, 1,3-diketones and oxalic diamides during the past two decades has totally changed its scenario, allowing the coupling reactions of aryl halides and nucleophiles to take place at both low reaction temperatures and catalytic loadings. The reaction scope has also been greatly expanded and makes this copper-based cross coupling attractive in both academia and industry. This review will summarize the latest progress in developing the useful reaction conditions for coupling of (hetero)aryl halides with different nucleophiles. Additionally, recent advances on Cu-catalyzed coupling reactions with aryl boronates and Cu-based trifluoromethylations of aromatic electrophiles will be introduced.
Datum: 22.05.2017


Structural basis for copper-oxygen mediated C-H bond activation by the formylglycine-generating enzyme

The formylglycine-generating enzyme (FGE) is a unique copper-protein that catalyzes oxygen-dependent C-H activation. We describe 1.66 Å- and 1.28 Å-resolution crystal structures of FGE from Thermomonospora curvata in complex with either Ag (I) or Cd (II) providing definitive evidence for a high-affinity metal-binding site in this enzyme. The structures reveal a bis-cysteine linear coordination of the monovalent metal, and tetrahedral coordination of the bivalent metal. Similar coordinational change may occur in the active enzyme as a result of Cu (I)/(II) redox cycling. Complexation of copper by two cysteines is common among copper-trafficking proteins, but is unprecedented for redox-active copper-enzymes or synthetic copper catalysts.
Datum: 22.05.2017


Reversing polarity: Carbonyl α-aminations with nitrogen nucleophiles

The synthesis of alpha-amino carbonyl compounds is an important challenge in synthesis en route to biologically essential structures. While classical approaches involve the use of enol or enolate chemistries in combination with an electrophilic source of nitrogen, those strategies usually necessitate further transformations in order to reach the desired targets. In recent years, a new approach arose involving the direct use of nucleophilic sources of nitrogen along with an oxidant. This advantageously leads in one-pot to the biologically relevant alpha-amino compounds, without further transformation required. This Minireview highlights the recent advances in the emerging field of oxidative alpha-amination reactions using nucleophilic sources of nitrogen.
Datum: 20.05.2017


Black Tungsten Nitride as Metallic Photocatalyst for Overall Water Splitting Operable at up to 765 nm

Semiconductor photocatalysts are hardly to be employed for overall water splitting beyond 700 nm, owing to both thermodynamic aspects and activation barriers. Metallic materials as photocatalysts are known to overcome this limitation through interband transitions for creating electron-hole pairs, however, the application of metallic photocatalysts for overall water splitting has never been fulfilled. Here we report, for the first time, that the black tungsten nitride can be employed as metallic photocatalyst for overall water splitting at wavelengths of up to 765 nm. Experimental and theoretical results together confirm that metallic properties play a substantial role in exhibiting photocatalytic activity under red-light irradiation for tungsten nitride. This work represents the first red-light responsive photocatalyst for overall water splitting, and may open a promising venue in searching of metallic materials as efficient photocatalysts for solar energy utilization.
Datum: 19.05.2017


Enantiopure cycloiridiated complexes bearing a pentahelicenic N-heterocyclic carbene and displaying long-lived circularly-polarized phosphorescence

A fused pi-helical N-heterocyclic (NHC) system has been prepared and examined through its diastereoisomerically pure cycloiridiated complexes. The latter display light-green phosphorescence with i) unusually long lifetimes and ii) circular polarization that depends on both the helical-NHC P/M and the iridium delta/lambda stereochemistry. These unprecedented features are attributed to extended pi-conjugation within helical carbenic ligand and efficient helicene-NHC-Ir interaction.
Datum: 19.05.2017


Methylammonium-Mediated Evolution of Mixed-Organic-Cation Perovskite Thin Films: A Dynamic Composition-Tuning Process

Methylammonium-mediated phase-evolution behavior of FA1−xMAxPbI3 mixed-organic-cation perovskite (MOCP) is studied. It is found that by simply enriching the MOCP precursor solutions with excess methylammonium cations, the MOCPs form via a dynamic composition-tuning process that is key to obtaining MOCP thin films with superior properties. This simple chemical approach addresses several key challenges, such as control over phase purity, uniformity, grain size, composition, etc., associated with the solution-growth of MOCP thin films with targeted compositions. Under control: FA1−xMAxPbI3 mixed-organic-cation iodide perovskite (MOCP) thin films have been synthesized. By simply enriching the precursor solutions with methylammonium cations, the MOCPs form via a dynamic composition-tuning process that is key to obtaining thin films with superior properties, exact composition, excellent uniformity, and extra-large grains.
Datum: 19.05.2017


Biofunctional Microgel-Based Fertilizers for Controlled Foliar Delivery of Nutrients to Plants

Foliar application of micronutrients (e.g. Fe3+) onto plants over an extended time is challenging and often not possible due to insufficient rainfastness. Smart delivery systems which enable micronutrient release over several weeks would offer innovative and sustainable options to improve plant health and food production. Herein, we report a novel foliar fertilizer delivery system based on functional pH-responsive biohybrid microgels that have orthogonal functionality as carriers of micronutrients and employ peptides (termed anchor peptides) as foliar adhesion promoters. The anchor peptides bind to hydrophobic surfaces and the waxy “islands” of plant leaves. Our system requires no auxiliaries and is loadable, storable, and applicable from aqueous dispersion. We report the synthesis and functionalization of microgels, their loading with Fe3+ ions, and a proof of concept for the biofunctional microgel-based fertilizer system is demonstrated for iron-deficient cucumber plants. Gel nourished: Foliar application of micronutrients onto plants over an extended time offers sustainable options for plant health and food production. Novel biohybrid microgels modified with iron binding ligands and anchor peptides as foliar adhesion promoters can be employed as a micronutrients carrier system. A proof of concept is presented for iron-deficient cucumber plants.
Datum: 19.05.2017


Elucidating the Role of Dissolution in CeO2 Nanoparticle Plant Uptake by Smart Radiolabeling

The identification of major uptake pathways in plants is an important factor when evaluating the fate of manufactured nanoparticles in the environment and the associated risks. Using different radiolabeling techniques we were able to show a predominantly particulate uptake for CeO2 nanoparticles in contrast to a possible uptake in the form of ionic cerium. Ce-ing and doing: Two radiolabeling techniques for CeO2 nanoparticles were developed which produce radiolabeled [139Ce]CeO2 nanoparticles with different activity release kinetics upon dissolution. Using these showed a predominantly particular uptake and translocation route of CeO2 along the water current in plants, with a slow dissolution inside the plant.
Datum: 19.05.2017


A Long-Life Lithium–Air Battery in Ambient Air with a Polymer Electrolyte Containing a Redox Mediator

Lithium–air batteries when operated in ambient air generally exhibit poor reversibility and cyclability, because of the Li passivation and Li2O2/LiOH/Li2CO3 accumulation in the air electrode. Herein, we present a Li–air battery supported by a polymer electrolyte containing 0.05 m LiI, in which the polymer electrolyte efficiently alleviates the Li passivation induced by attacking air. Furthermore, it is demonstrated that I−/I2 conversion in polymer electrolyte acts as a redox mediator that facilitates electrochemical decomposition of the discharge products during recharge process. As a result, the Li–air battery can be stably cycled 400 times in ambient air (relative humidity of 15 %), which is much better than previous reports. The achievement offers a hope to develop the Li–air battery that can be operated in ambient air. An oxygen-breathing battery: A long-life lithium–air battery in ambient air was developed by using a gel polymer electrolyte containing the redox mediator I−/I2 (see picture). The polymer electrolyte and the redox mediator alleviate lithium passivation induced by attacking air and improve the charge–discharge efficiency of the battery.
Datum: 19.05.2017


Non-Pincer-Type Manganese Complexes as Efficient Catalysts for the Hydrogenation of Esters

Ester reduction with manganese catalysis is enabled by balancing the reactivity of the Mn(I) species with simple bidentate P,N ligands and alkoxide base. In their Communication (http://doi.org/10.1002/anie.201701365), E. A. Pidko and co-workers report highly active Mn-based catalyst systems for selective ester hydrogenation. Their performance is the result of a delicate balance between the complex catalytic and deactivation paths, which depend on the choice of the solvent, base and the reaction conditions.
Datum: 19.05.2017


Mechanical Deformation Accelerates Protein Ageing

A hallmark of tissue ageing is the irreversible oxidative modification of its proteins. We show that single proteins, kept unfolded and extended by a mechanical force, undergo accelerated ageing in times scales of minutes to days. A protein forced to be continuously unfolded completely loses its ability to contract by folding, becoming a labile polymer. Ageing rates vary among different proteins, but in all cases they lose their mechanical integrity. Random oxidative modification of cryptic side chains exposed by mechanical unfolding can be slowed by the addition of antioxidants such as ascorbic acid, or accelerated by oxidants. By contrast, proteins kept in the folded state and probed over week-long experiments show greatly reduced rates of ageing. We demonstrate a novel approach whereby protein ageing can be greatly accelerated: the constant unfolding of a protein for hours to days is equivalent to decades of exposure to free radicals under physiological conditions. Time will tell: Accelerated ageing occurs when a protein is held unfolded under force for long periods of time. Maintaining a protein extended for more 20 h blocks its ability to refold. This loss of folding contraction is triggered by the exposure of cryptic side chains to the oxidative environment, and can be greatly slowed by antioxidants. This kind of oxidative damage is a hallmark of the loss of tissue elasticity that occurs during ageing.
Datum: 19.05.2017


An Aggregating Amphiphilic Squaraine: A Light-up Probe That Discriminates Parallel G-Quadruplexes

G-quadruplexes (G4s) are peculiar DNA or RNA tertiary structures that are involved in the regulation of many biological events within mammalian cells, bacteria, and viruses. Although their role as versatile therapeutic targets has been emphasized for 35 years, G4 selectivity over ubiquitous double-stranded DNA/RNA, as well as G4 differentiation by small molecules, still remains challenging. Here, a new amphiphilic dicyanovinyl-substituted squaraine, SQgl, is reported to act as an NIR fluorescent light-up probe discriminating an extensive panel of parallel G4s while it is non-fluorescent in the aggregated state. The squaraine can form an unconventional sandwich π-complex binding two quadruplexes, which leads to a strongly fluorescent (ΦF=0.61) supramolecular architecture. SQgl is highly selective against non-quadruplex and non-parallel G4 sequences without altering their topology, as desired for applications in selective in vivo high-resolution imaging and theranostics. In parallel: An amphiphilic squaraine that self-assembles into a non-fluorescent aggregated state in water has been designed as a near-infrared light-up probe with high selectivity for G-quadruplexes (G4s) with parallel topology. The strong fluorescence is based on the formation of an unconventional sandwich π-complex between the squaraine and two parallel G4s.
Datum: 19.05.2017


Significant Enhancement of C2H2/C2H4 Separation by a Photochromic Diarylethene Unit: A Temperature- and Light-Responsive Separation Switch

Adjusting adsorption selectivity and separation in photochromic metal–organic frameworks (MOFs) just by external stimuli is highly important but still rare. In their Communication (http://doi.org/10.1002/anie.201702484), F. Luo, G.-C. Guo, and co-workers employ a photochromic diarylethene unit as a light-triggered selectivity and separation regulator, leading to ultrahigh adsorption selectivity and improvement in adsorption selectivity, for example for C2H2/C2H4.
Datum: 19.05.2017


A Membrane-Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst

A membrane-free fuel cell relies on the selectivity of catalysts at both the anode and the cathode. In their Communication (DOI: 10.1002/anie.201702578), Y. Surendranath et al. show that the sulfide N3S2 selectively catalyzes the oxygen reduction reaction (ORR) in the presence of a high concentration of formate. Paired with the known formate oxidation catalyst Pd/C the selective ORR catalyst Ni3S2 enables the construction of a membrane-free formate fuel cell that operates at neutral pH and outperforms the Pt–Pd device.
Datum: 19.05.2017


Enzymatic engineering of live bacterial cell surface using butelase 1

We show that butelase-mediated ligation (BML) can be used to modify live bacterial cell surfaces with diverse cargo molecules. Surface-displayed butelase recognition motif NHV was first introduced at the C-terminal end of the anchoring protein OmpA on E. coli cells. This then served as a handle of BML for the functionalization of E. coli cell surfaces with fluorescein and biotin tags, a tumor-associated monoglycosylated peptide and mCherry protein. The cell-surface ligation reaction was achieved at low concentrations of butelase and the labeling substrates. Furthermore, the fluorescein-labeled bacterial cells were used to show the interactions with cultured HeLa cells and with macrophages in live transgenic zebrafish, capturing the latter's powerful phagocytic effect in action. Together these results highlight the usefulness of butelase 1 in live bacterial cell surface engineering for novel applications.
Datum: 19.05.2017


Tris(perfluorotolyl)borane - a Boron Lewis Superacid

Tris(tetrafluoro-4-(trifluoromethyl)phenyl)borane (BTolF) was prepared by reacting boron tribromide with tetrameric F3CC6F4-Cu(I). The latter was generated from F3CC6F4MgBr and copper(I) bromide. Lewis acidities of BTolF evaluated by the Gutmann-Beckett method and calculated fluoride ion affinities are 9 and 10%, respecttively, higher than that of tris(penta-fluorophenyl)borane (BCF) and even higher than that of SbF5. The molecular structures of BTolF and BCF were determined by gas electron diffraction, that of BTolF also by single crystal X-ray diffraction.
Datum: 19.05.2017


Solution NMR Structure of a Ligand/Hybrid-2-G-Quadruplex Complex Reveals Rearrangements that Affect Ligand Binding

Telomeric G-quadruplexes have recently emerged as drug targets in cancer research. Herein, we present the first NMR structure of a telomeric DNA G-quadruplex that adopts the biologically relevant hybrid-2 conformation in a ligand-bound state. We solved the complex with a metalorganic gold(III) ligand that stabilizes G-quadruplexes. Analysis of the free and bound structures reveals structural changes in the capping region of the G-quadruplex. The ligand is sandwiched between one terminal G-tetrad and a flanking nucleotide. This complex structure involves a major structural rearrangement compared to the free G-quadruplex structure as observed for other G-quadruplexes in different conformations, invalidating simple docking approaches to ligand–G-quadruplex structure determination. Conformation matters: G-quadruplexes are emerging drug targets in cancer research. The first NMR structure determination of a telomeric DNA G-quadruplex in the hybrid-2 conformation in complex with a ligand is reported. The structure reveals major changes in the capping regions of the G-quadruplex, highlighting the importance of obtaining a ligand-bound structure to aid rational drug design.
Datum: 19.05.2017


Double-Caging Linker for AND-Type Fluorogenic Construction of Protein/Antibody Bioconjugates and in situ Quantification

We report on in situ fluorescent quantification of the conjugation efficiency between azide-terminated synthetic polymers/ imaging probes and thiol-functionalized antibodies/proteins/peptides, by utilizing a doubly caged profluorescent and heterodifunctional core molecule (C1) as the self-sorting bridging unit. Orthogonal dual 'click' coupling of C1 with azide- and thiol-functionalized precursors leads to highly fluorescent bioconjugates, whereas single click products of C1 remain essentially nonfluorescent. This 'AND' logic gate-type fluorogenic feature also enables further integration with FRET processes. For the construction of antibody-probe conjugates from an anti-carcinoembryonic antigen and a quinone-caged profluorescent naphthalimide derivative, the dual 'click' coupling process with C1 can be conveniently monitored via emission turn-on of C1, whereas prominent changes in FRET ratios occur for antibody-probe conjugates when triggered by specific tumor-associated enzymes.
Datum: 19.05.2017


Synthesis of Highly Substituted Pyridines via Copper-Catalyzed Condensation of Oximes and α,β-Unsaturated Imines

A copper-catalyzed condensation reaction of oxime acetates and α,β-unsaturated ketimines into pyridine derivatives is reported. The reaction features mild conditions, high functional group compatibility, and high regioselectivity with respect to unsymmetrical oxime acetates, thus allowing for the preparation of a wide range of polysubstituted pyridines, many of which are not readily accessible by conventional condensation methods.
Datum: 19.05.2017


Arylative Intramolecular Allylation of Ketones with 1,3-Enynes Enabled by Catalytic Alkenyl-to-Allyl 1,4-Rhodium(I) Migration

Alkenyl-to-allyl 1,4-rhodium(I) migration enables the generation of nucleophilic allylrhodium(I) species by remote C−H activation. This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a 1,3-enyne tethered to a ketone, to give products containing three contiguous stereocenters. The products can be obtained in high enantioselectivities using a chiral sulfur-alkene ligand. On the move: The title migration enables the generation of nucleophilic allylrhodium(I) species by remote C−H activation. This new mode of reactivity was employed in the diastereoselective reaction of arylboron reagents with substrates containing a 1,3-enyne tethered to a ketone, to give products containing three contiguous stereocenters. The products can be obtained in high enantioselectivities using a chiral sulfur-alkene ligand.
Datum: 19.05.2017


Paul Hagenmuller

Paul Hagenmuller, honorary professor at the Université de Bordeaux, passed away at the age of 95 on January 7, 2017. Hagenmuller was one of the founders of solid-state chemistry at the interface between chemistry, physics, and material science, with contributions including high oxidation states in transition metal oxides, magnesium hydride for hydrogen-storage applications, and synthesis of copper perovskites.
Datum: 19.05.2017


A Long-Range Acting Dehydratase Domain as the Missing Link for C17-Dehydration in Iso-Migrastatin Biosynthesis

The dehydratase domains (DHs) of the iso-migrastatin (iso-MGS) polyketide synthase (PKS) were investigated by systematic inactivation of the DHs in module-6, -9, -10 of MgsF (i.e., DH6, DH9, DH10) and module-11 of MgsG (i.e., DH11) in vivo, followed by structural characterization of the metabolites accumulated by the mutants, and biochemical characterization of DH10 in vitro, using polyketide substrate mimics with varying chain lengths. These studies allowed us to assign the functions for all four DHs, identifying DH10 as the dedicated dehydratase that catalyzes the dehydration of the C17 hydroxy group during iso-MGS biosynthesis. In contrast to canonical DHs that catalyze dehydration of the β-hydroxy groups of the nascent polyketide intermediates, DH10 acts in a long-range manner that is unprecedented for type I PKSs, a novel dehydration mechanism that could be exploited for polyketide structural diversity by combinatorial biosynthesis and synthetic biology. Missed and found: Inactivation of dehydratase (DH) domains of iso-migrastatin polyketide synthase, followed by in vitro characterization toward substrate mimics with varying chain lengths, identified DH10 as the dedicated dehydratase for elimination of a remote hydroxy group at C17 position during the biosynthesis of iso-migrastatin. This activity was “missing” in the canonical collinear model.
Datum: 19.05.2017


Cameron Jones


Datum: 19.05.2017


Sulfone–Metal Exchange and Alkylation of Sulfonylnitriles

The first general sulfone–metal exchange is described. Treating substituted 2-pyridylsulfonylacetonitriles with either BuLi or Bu3MgLi generates metalated nitriles that efficiently intercept a variety of electrophiles to afford quaternary nitriles. The 2-pyridylsulfone is critical for the sulfone–metal exchange because chelation anchors the organometallic proximal to the electrophilic, tetrasubstituted sulfone to override complex-induced deprotonation. Alkylating commercial 2-pyridinesulfonylacetonitrile with mild bases, either K2CO3 or DBU, and subsequent sulfone–metal exchange and alkylation rapidly assembles quaternary nitriles by three alkylations, only one of which requires an organometallic reagent. Sulfones as latent organometallics: Sulfone–metal exchange of substituted 2-pyridylsulfonylacetonitriles with either BuLi or Bu3MgLi generates metalated nitriles that alkylate a variety of electrophiles to efficiently install quaternary centers.
Datum: 19.05.2017


Enantioselective Propargylation of Polyols and Desymmetrization of meso 1,2-Diols by Copper/Borinic Acid Dual Catalysis

A copper/borinic acid dual catalytic reaction enabled the enantioselective propargylation of aliphatic polyols. Readily available reagents and catalysts were used in this transformation, which displayed good to excellent chemo- and stereoselectivity for a broad array of substrates. The method was also applicable to the desymmetrization of meso 1,2-diols to furnish products with three stereogenic centers and a terminal alkyne group in one operation. Together they're strong: A copper/borinic acid dual catalytic reaction was developed for the efficient and enantioselective propargylation of polyols. Control experiments revealed the essential role of each catalyst. The transformation is amenable to the desymmetrization of meso 1,2-diols to furnish compounds with three stereogenic centers in one step (see scheme).
Datum: 19.05.2017


Entropy Drives the Formation of Salt Bridges in the Protein GB3

Salt bridges are very common in proteins. But what drives the formation of protein salt bridges is not clear. In this work, we determined the strength of four salt bridges in the protein GB3 by measuring the ΔpKa values of the basic residues that constitute the salt bridges with a highly accurate NMR titration method at different temperatures. The results show that the ΔpKa values increase with temperature, thus indicating that the salt bridges are stronger at higher temperatures. Fitting of ΔpKa values to the van't Hoff equation yields positive ΔH and ΔS values, thus indicating that entropy drives salt-bridge formation. Molecular dynamics simulations show that the protein and solvent make opposite contributions to ΔH and ΔS. Specifically, the enthalpic gain contributed from the protein is more than offset by the enthalpic loss contributed from the solvent, whereas the entropic gain originates from the desolvation effect. Out of disorder: The strengths of four salt bridges in the protein GB3 were determined by measuring the ΔpKa values of the basic residues that constitute the salt bridges with a highly accurate NMR titration method at different temperatures. Fitting of the ΔpKa values to the van't Hoff equation showed that entropy drives the formation of protein salt bridges, while the enthalpic contribution disfavors salt-bridge formation.
Datum: 19.05.2017


Tunable Self-Assembly of Diblock Copolymers into Colloidal Particles with Triply Periodic Minimal Surfaces

We herein report the tunable self-assembly of simple block copolymers, namely polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers, into porous cubosomes with inverse Im3‾m or Pn3‾m mesophases of controlled unit cell parameters as well as hexasomes with an inverse hexagonal (p6mm) structure, which have been rarely observed in polymer self-assembly. A new morphological phase diagram was constructed for the solution self-assembly of PS-b-PEO based on the volume fraction of the PS block against the initial copolymer concentration. The formation mechanisms of the cubosomes and hexasomes have also been revealed. This study not only affords a simple system for the controllable preparation and fundamental studies of ordered bicontinuous structures, but also opens up a new avenue towards porous architectures with highly ordered pores. Polymer cubosomes: The tunable self-assembly of simple polystyrene-block-poly(ethylene oxide) diblock copolymers into porous cubosomes with inverse Im3‾m or Pn3‾m mesophases and hexasomes with an inverse hexagonal (p6mm) structure is reported along with a new morphological phase diagram for the solution self-assembly of such diblock copolymers.
Datum: 19.05.2017


An Unsaturated Quinolone N-Oxide of Pseudomonas aeruginosa Modulates Growth and Virulence of Staphylococcus aureus

The pathogen Pseudomonas aeruginosa produces over 50 different quinolones, 16 of which belong to the class of 2-alkyl-4-quinolone N-oxides (AQNOs) with various chain lengths and degrees of saturation. We present the first synthesis of a previously proposed unsaturated compound that is confirmed to be present in culture extracts of P. aeruginosa, and its structure is shown to be trans-Δ1-2-(non-1-enyl)-4-quinolone N-oxide. This compound is the most active agent against S.  aureus, including MRSA strains, by more than one order of magnitude whereas its cis isomer is inactive. At lower concentrations, the compound induces small-colony variants of S. aureus, reduces the virulence by inhibiting hemolysis, and inhibits nitrate reductase activity under anaerobic conditions. These studies suggest that this unsaturated AQNO is one of the major agents that are used by P. aeruginosa to modulate competing bacterial species. Pseudomonas’ secret weapon: trans-Δ1-2-Nonenyl-4-quinolone N-oxide, the most active quinolone N-oxide produced by Pseudomonas aeruginosa against Staphylococcus aureus, was synthesized. The efficacy of this compound is also demonstrated by its ability to inhibit the hemolytic and nitrate reductase activity of S. aureus at low concentrations. These results shed new light onto how P. aeruginosa chemically modulates the growth and behavior of its competitors.
Datum: 19.05.2017


A Bifunctional Hybrid Electrocatalyst for Oxygen Reduction and Evolution: Cobalt Oxide Nanoparticles Strongly Coupled to B,N-Decorated Graphene

The electrocatalyzed oxygen reduction and evolution reactions (ORR and OER, respectively) are the core components of many energy conversion systems, including water splitting, fuel cells, and metal–air batteries. Rational design of highly efficient non-noble materials as bifunctional ORR/OER electrocatalysts is of great importance for large-scale practical applications. A new strongly coupled hybrid material is presented, which comprises CoOx nanoparticles rich in oxygen vacancies grown on B,N-decorated graphene (CoOx NPs/BNG) and operates as an efficient bifunctional OER/ORR electrocatalyst. Advanced spectroscopic techniques were used to confirm formation of abundant oxygen vacancies and strong Co−N−C bridging bonds within the CoOx NPs/BNG hybrid. Surprisingly, the CoOx NPs/BNG hybrid electrocatalyst is highly efficient for the OER with a low overpotential and Tafel slope, and is active in the ORR with a positive half-wave potential and high limiting current density in alkaline medium. The Ties That Bind: CoOx nanoparticles were coupled to B,N-decorated graphene by strong Co−N−C bonds. The hybrid material, which is rich in oxygen vacancies, is a bifunctional electrocatalyst for oxygen evolving and reduction reactions in alkaline conditions.
Datum: 19.05.2017


Identification of Multiple Druggable Secondary Sites by Fragment Screening against DC-SIGN

DC-SIGN is a cell-surface receptor for several pathogenic threats, such as HIV, Ebola virus, or Mycobacterium tuberculosis. Multiple attempts to develop inhibitors of the underlying carbohydrate–protein interactions have been undertaken in the past fifteen years. Still, drug-like DC-SIGN ligands are sparse, which is most likely due to its hydrophilic, solvent-exposed carbohydrate-binding site. Herein, we report on a parallel fragment screening against DC-SIGN applying SPR and a reporter displacement assay, which complements previous screenings using 19F NMR spectroscopy and chemical fragment microarrays. Hit validation by SPR and 1H–15N HSQC NMR spectroscopy revealed that although no fragment bound in the primary carbohydrate site, five secondary sites are available to harbor drug-like molecules. Building on key interactions of the reported fragment hits, these pockets will be targeted in future approaches to accelerate the development of DC-SIGN inhibitors. Multiple binding sites: DC-SIGN, which has been known for 15 years for its role in the HIV transinfection of T cells, is one of the most attractive targets among glycan-binding proteins. Nevertheless, drug-like effectors are sparse but its undruggable primary site might be bypassed by targeting druggable secondary sites.
Datum: 19.05.2017


Competition between Arene–Perfluoroarene and Charge-Transfer Interactions in Organic Light-Harvesting Systems

Two typical types of luminescent organic cocrystals comprising pyrene–octafluoronaphthalene (pyrene–OFN) and pyrene–1,2,4,5-tetracyanobezene (pyrene–TCNB) were developed by a simple supramolecular assembly strategy. The cocrystals exhibit distinct optical properties because of their different intermolecular interaction modes; that is, arene–perfluoroarene (AP) and charge-transfer (CT) interactions. Unexpectedly, a pyrene–TCNB system with strong CT interactions was incorporated into a pyrene–OFN host as a robust guest to generate white-light emission (WLE). In the supramolecular cocrystal system, an efficient energy-transfer process from pyrene–OFN to pyrene–TCNB occurred because of the well-matched spectra of the constituents and a desirable energy donor/acceptor (D/A) distance. The present competitive intermolecular interaction strategy could be applied to the fabrication of more complicated organic light-harvesting systems. Luminescent lightsabers: Stable white light-emitting crystals containing pyrene–octafluoronaphthalene (pyrene–OFN) cocrystals doped with pyrene–1,2,4,5- tetracyanobenzene (pyrene–TCNB) integrate competitive intermolecular charge-transfer and arene–perfluoroarene interactions. Efficient energy transfer from the charge-transfer host to the arene–perfluoroarene dopant is observed.
Datum: 19.05.2017


Kinetically Controlled Layer-by-Layer Stacking of Metal Oxide 2D Nanosheets

An efficient chemical way to finely control the layer-by-layer stacking of inorganic nanosheets (NS) is developed by tuning the type and composition of intercalant ion, and the reaction temperature for restacking process. The finely controlled stacking of NS relies on a kinetic control of the self-assembly of NS in the presence of coordinating organic cations. A critical role of organic cations in this assembly highlights the importance of the appropriate activation energy. Of prime importance is that a fine-control of the interstratification of 2D NS is highly effective not only in tailoring its pore structure but also in enhancing its electrode activity. The present study clearly demonstrates that the kinetically controlled restacking of NS provides a facile and powerful method to tailor their stacking number and functionality. How it stacks up: A facile chemical method to tailor the interstratification structure of inorganic nanosheets was developed by controlling the reaction kinetics of the process. The tuning of the type and composition of intercalant ion, and the reaction temperature, is highly effective not only in tailoring the surface area and pore structure, but also in enhancing the properties of nanosheets.
Datum: 19.05.2017


Highly Sensitive Detection of Ionizing Radiations by a Photoluminescent Uranyl Organic Framework

Precise detection of low-dose X- and γ-radiations remains a challenge and is particularly important for studying biological effects under low-dose ionizing radiation, safety control in medical radiation treatment, survey of environmental radiation background, and monitoring cosmic radiations. We report here a photoluminescent uranium organic framework, whose photoluminescence intensity can be accurately correlated with the exposure dose of X- or γ-radiations. This allows for precise and instant detection of ionizing radiations down to the level of 10−4 Gy, representing a significant improvement on the detection limit of approximately two orders of magnitude, compared to other chemical dosimeters reported up to now. The electron paramagnetic resonance analysis suggests that with the exposure to radiations, the carbonyl double bonds break affording oxo-radicals that can be stabilized within the conjugated uranium oxalate-carboxylate sheet. This gives rise to a substantially enhanced equatorial bonding of the uranyl(VI) ions as elucidated by the single-crystal structure of the γ-ray irradiated material, and subsequently leads to a very effective photoluminescence quenching through phonon-assisted relaxation. The quenched sample can be easily recovered by heating, enabling recycled detection for multiple runs. A uranium MOF dosimeter: A photoluminescent uranium–organic framework, whose intensity accurately correlates with the exposure dose of X- or γ-radiations, enables the precise and instant detection of ionizing radiations. The detection limit of 10−4 Gy represents an improvement of approximately two orders of magnitude compared to other chemical dosimeters reported up to now.
Datum: 19.05.2017


Silica-Polypyrrole Hybrids as High-Performance Metal-Free Electrocatalysts for Hydrogen Evolution Reaction in Neutral Media

Constructing inorganic-organic hybrids with high abilities of water adsorption and activation will lead to significant enhancement of electrocatalytic activity for hydrogen evolution reaction (HER) in neutral media that is environmentally benign. Here we report SiO2-polypyrrole (PPy) hybrid nanotubes supported on carbon fibers (CFs) (SiO2/PPy NTs-CFs) as low-cost and high-performance electrocatalysts for HER in neutral media. Because of the strong electronic interactions between SiO2 and PPy, SiO2 uniquely serves as the centers of water adsorption and activation, and accordingly it will obviously promote HER. SiO2/PPy NTs-CFs as metal-free electrocatalysts achieve high catalytic performance for HER in neutral media, such as low onset potential, small Tafel slope and excellent long-term durability.
Datum: 19.05.2017


Bandgap Engineering of Lead-Free Double Perovskite Cs2AgBiBr6 through Trivalent Metal Alloying

The double perovskite family, A2MIMIIIX6, represents a promising route to overcome the lead toxicity issue confronting current photovoltaic (PV) standout, CH3NH3PbI3. Given the generally large indirect bandgap within most known double perovskites, bandgap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs2AgBiBr6 as host, we demonstrate bandgap engineering through alloying of InIII/SbIII. Cs2Ag(Bi1-xMx)Br6 (M = In, Sb) accommodates up to 75% InIII with increased bandgap, and up to 37.5% SbIII with reduced bandgap—i.e., enabling ~0.41 eV bandgap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs2Ag(Bi0.625Sb0.375)Br6. Band structure calculations indicate that opposite bandgap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed.
Datum: 19.05.2017


Optochemical Control of Biological Processes in Cells and Animals

Achieving precise control of biological function represents a crucial tool for studying the mechanisms of cellular processes. Naturally, these processes occur in a strict spatially and temporally regulated fashion. In order to generate accurate models, the tools used to study these processes must also operate with high spatiotemporal resolution. To this end, the use of light as a conditional stimulus has found extensive applications for the activation and deactivation of small molecules, proteins, peptides, and oligonucleotides. Harnessing light has enabled significant advances in both research applications and holds promise toward clinical studies. This review showcases many of the most recent applications and methodology developments of optical control of biology. It focuses on the most recent developments in utilizing chemistry to optically manipulate living systems such as cells and animals.
Datum: 18.05.2017


Quantifying hydrogen-bond populations in DMSO/water mixtures

Dimethyl sulfoxide (DMSO) disrupts the hydrogen-bond networks in water. DMSO's widespread uses as a cosolvent, along with its unusual attributes, have inspired numerous studies. In this study, infrared absorption spectroscopy of the S=O stretch combined with molecular dynamics and quantum chemistry models were used to directly quantify DMSO/water hydrogen bond populations in binary mixtures. Singly H-bonded species are dominant at 10 mol%, due to strong DMSO-water interactions. We found an unexpected increase in non-hydrogen-bonded DMSO near the eutectic point (~35 mol%) which also correlates with several abnormalities in the solution's bulk properties. We find evidence for three distinct regimes: 1. Strong DMSO-water interactions (<30 mol%); 2. ideal-solution-like (30-90 mol%); 3. self-interaction, or aggregation, regime (>90 mol%). We propose a "step in" mechanism, which involves hydrogen bonding between water and the DMSO aggregate species.
Datum: 18.05.2017


Perovskite solar cells from the atomic to the film level

Organic-inorganic perovskites have made tremendous progress in recent years due to exceptional material properties such as high panchromatic absorption, charge carrier diffusion lengths and a sharp optical band edge. The combination of high-quality semiconductor with low-cost deposition techniques seems to be a match made in heaven creating great excitement and anticipation far beyond the academic ivory tower. This is particularly true for perovskite solar cells (PSCs) that have shown unprecedented gains in efficiency and stability over a time span of just 5 years. Now there are serious efforts for commercialisation with the hope that PSCs can make a major impact in generating inexpensive, sustainable solar electricity. In this review, we will focus on materials and devices from the atomic to the thin film level to highlight the remaining challenges and to anticipate the future developments of PSCs.
Datum: 18.05.2017


Asymmetric Synthesis of Secondary and Tertiary Boronic Esters

Non-racemic chiral boronic esters are recognised as immensely valuable building blocks in modern organic synthesis. Their stereospecific transformation into a variety of functional group - from amines and halides to arenes and alkynes - along with their air and moisture stability, has established them as an important target for asymmetric synthesis. Efforts towards the stereoselective synthesis of secondary and tertiary alkyl boronic esters have spanned over five decades and are underpinned by a wealth of reactivity platforms, drawing on the unique and varied reactivity of boron. This review summarizes strategies for the asymmetric synthesis of alkyl boronic esters, from the seminal hydroboration methods of H. C. Brown to the current state of the art.
Datum: 18.05.2017


Nanojunction polymer photoelectrode for efficient charge transport and separation

A novel nanojunction archiecture of metal-free photoanode, composed of B-doped carbon nitride nanolayer and bulk carbon nitride has been fabricated by a one-step construction approach. This type of nanojunction overcomes a few intrinsic drawbacks of carbon nitride film, e.g. severe bulk charge recombination and slow charge transfer. For the optium sample, the top layer of the nanojunction has a depth of ca. 100 nm and the bottom layer is ca. 900 nm. The nanojunction photoanode results into a 10 fold higher photocurrent than bulk graphitic carbon nitride and an extremely high incident photon-to-current efficiency (IPCE) of ca. 10% at 400 nm, which to the best of our knowledge is the highest for G-CN based polymer photoanodes in the absence of any sacrificial reagents. The EIS, MS and IMPS spectroscopies all prove such enhancement is mainly due to more than 10 times faster charge seperation rate and nearly 3 times higher conductivity due to the nanojunction architcutre.
Datum: 18.05.2017


Encapsulation and Polymerization of White Phosphorus Inside Single-wall Carbon Nanotubes

Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. Here, we report that white phosphorus can be filled into single-wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily to chain structures inside the SWCNT 'nanoreactors'. The energies of the possible chain structures were determined computationally highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single-stranded zig-zag chain of phosphorus atoms was observed which represents the lowest energy structure at small confinement diameters. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.
Datum: 18.05.2017


Lithium Bond Chemistry in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is a promising high-energy-density energy storage system. The strong anchoring of intermediates is widely accepted to retard the shuttle of polysulfides in a working battery. However, the understanding of the intrinsic chemistry is still deficient. Inspired by the concept of hydrogen bond, herein we focus on the Li bond chemistry in Li-S batteries through sophisticated quantum chemical calculations, in combination with 7Li nuclear magnetic resonance (NMR). Identified as Li bond, the strong dipole-dipole interaction between Li polysulfides and Li-S cathode materials originates from the electron-rich donors (e.g., pyridinic nitrogen (pN)), and enhanced by the inductive and conjugative effect of scaffold materials with π-electrons (e.g., graphene). The chemical shift of Li polysulfides in 7Li NMR, being both theoretically predicted and experimentally verified, is suggested to serve as a quantitative descriptor of Li bond strength.
Datum: 18.05.2017


High-Dimensional Neural Network Potentials for Complex Systems

Modern simulation techniques have reached a level of maturity, which allows addressing a wide range of problems in chemistry and materials science. Unfortunately, the application of first principles methods with predictive power is still limited to rather small systems, and in spite of the rapid evolution of computer hardware no fundamental change of this situation can be expected. Consequently, to reach an atomic level understanding of complex systems, the development of more efficient but equally reliable atomistic potentials has received considerable attention in recent years. A promising new development has been the introduction of machine learning (ML) methods to describe the atomic interactions. Once trained to electronic structure data, ML potentials can accelerate computer simulations by several orders of magnitude, while quantum mechanical accuracy is preserved. In this article, the methodology of an important class of ML potentials employing artificial neural networks is reviewed.
Datum: 18.05.2017


Development of Biomass-Derived Non-Noble Metal Catalysts for Selective Hydrodehalogenation of Alkyl and (Hetero)Aryl Halides

Hydrodehalogenation represents a straightforward approach for detoxifications of anthropogenic harmful organohalide based pollutants as well as removal of halide protecting groups used in multistep synthesis. A novel sustainable catalytic material has been prepared from biowaste (chitosan) in a combination with earth-abundant cobalt salt. This heterogeneous catalyst was fully characterized by means of TEM, XRD as well as XPS analysis and applied successfully for hydrodehalogenation of alkyl and (hetero)aryl halides with broad scope (>40 examples) and excellent chemoselectivity using molecular hydrogen. The general usefulness of this methodology has been proven by the successful implementation for detoxification of non-degradable pesticides and fire retardants. In addition, its use in the multistep synthesis of (±)-Peronatin B (alkaloid) as deprotection tool showed its potential applicability.
Datum: 18.05.2017


Meta-C‒H Arylation and Alkylation of Benzylsulfonamide Enabled by a Pd(II)/Isoquinoline Catalyst

Palladium(II)-catalyzed meta-C‒H arylation and alkylation of benzylsulfonamide using 2-carbomethoxynorbornene (NBE-CO2Me) as a transient mediator are realized using a newly developed electron-deficient directing group and isoquinoline as a ligand. This protocol features broad substrate scope and good functional group tolerance. The meta-substituted benyzlsulfonamide can be readily transformed to sodium sulfonate, sulfonate ester, sulfonamide, as well as styrenes via Julia-type olefination. The unique impact of the isoquinoline ligand underscores the importance of subtle matching between ligands and the directing groups.
Datum: 18.05.2017


Electrochemically-Treated BiVO4 Photoanode for Efficient Photoelectrochemical Water Splitting

BiVO4 films with (040) facet grown vertically on fluorine doped SnO2 (FTO) glass substrates are prepared by a seed-assisted hydrothermal method. A simple electrochemical treatment process drastically enhances the photocatalytic activity of BiVO4, exhibiting a remarkable photocurrent density of 2.5 mA cm-2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination, which is approximately 10 folds higher than that of the pristine one. Loading cobalt borate (CoBi) as cocatalyst, the photocurrent density of the BiVO4 photoanode can be further improved to 3.2 mA cm-2, delivering an applied bias photon-to-current efficiency (ABPE) of 1.1%. Systematic studies reveal that crystal facet orientation also synergistically boosts both charge separation and transfer efficiencies, resulting in remarkably enhanced photocurrent densities. The new findings provide a facile and effective approach for the development of efficient photoelectrodes for photoelectrochemical water splitting.
Datum: 18.05.2017


The Narrow Road to the Deep Past

The sequence of events that gave rise to the first life on our planet took place in the Earth's deep past, seemingly forever beyond our reach. Perhaps for that very reason the idea of reconstructing our ancient story is tantalizing, almost irresistible. Understanding the processes that led to synthesis of the chemical building blocks of biology and the ways in which these molecules self-assembled into cells that could grow, divide and evolve, nurtured by a rich and complex environment, seems at times insurmountably difficult. And yet, to my own surprise, simple experiments have revealed robust processes that could have driven the growth and division of primitive cell membranes. The nonenzymatic replication of RNA is more complicated and less well understood, but here too significant progress has come from surprising developments. Even our efforts to combine replicating compartments and genetic materials into a full protocell model have moved forward in unexpected ways. Fortunately, many challenges remain before we will be close to a full understanding of the origin of life, so the future of research in this field is brighter than ever!
Datum: 17.05.2017


Overcoming the instability of nanoparticle based catalyst films in alkaline electrolysers by self-assembling and self-healing films

Engineering stable electrodes using highly active catalyst nanopowders for electrochemical water splitting remains a notorious challenge. We report an innovative and general approach for attaining highly stable catalyst films with self-healing capability based on in-situ self-assembly of catalyst particles during electrolysis. The catalyst particles are added to the electrolyte forming a suspension that is pumped through the electrolyzer. Particles with negatively charged surfaces stick onto the anode, while particles with positively charged surfaces stick to the cathode. The self-assembled catalyst films possess self-healing properties as long as a sufficient amount of catalyst particles are present in the electrolyte. The proof-of-concept was demonstrated in a non-zero gap alkaline electrolyzer using NiFe LDH and NixB catalyst nanopowders for anode and cathode, respectively. Steady cell voltages were maintained for at least three weeks during continuous electrolysis at 50-100 mA cm-2
Datum: 17.05.2017


Rhodium-Catalyzed Regioselective Domino Azlactone-Alkyne Coupling/Aza-Cope Rearrangement: A Facile Access to 2-Allyl-3-oxazolin-5-ones and Trisubstituted Pyridines

A merged rhodium-catalyzed regioselective addition of azlactones to internal alkynes/aza-Cope rearrangement provides efficient atom economic access to 2-allyl-3-oxazolin-5-one derivatives. Extension to a triple domino process combining the above process with an in situ azlactone formation starting from amino acids renders this process even more attractive. A subsequent thermolysis of the 2-allyl-3-oxazolines enabled a de novo synthesis of trisubstituted pyridines.
Datum: 17.05.2017


Fragment screening against the EthR-DNA interaction by native mass spectrometry

Native nanoelectrospray ionization mass spectrometry is an underutilized technique for fragment screening. In this study, the first demonstration is provided of the use of native mass spectrometry for screening fragments against a protein-DNA interaction. EthR is a transcriptional repressor of EthA expression in Mycobacterium tuberculosis (Mtb) that reduces the efficacy of ethionamide, a second-line anti-tubercular drug used to combat multidrug resistant Mtb strains. A small-scale fragment screening campaign was conducted against the EthR-DNA interaction using native mass spectrometry, and results were compared with those from differential scanning fluorimetry, a commonly used primary screening technique. Hits were validated using surface plasmon resonance and X-ray crystallography. The screening campaign identified two new fragments that disrupt the EthR-DNA interaction in vitro (IC50 = 460 μM to 610 μM) and that bind to the hydrophobic channel of the EthR dimer.
Datum: 17.05.2017


Bioinspired Total Synthesis of Homodimericin A

Homodimericin A is a remarkable fungal metabolite, and a highly oxygenated and racemic unsaturated polyketide. It poses a significant synthetic challenge due to its sterically demanding central cage-like core bearing eight contiguous stereogenic centers (including three contiguous all-carbon quaternary stereocenters), and several carbonyl functionalities. Based on its proposed biogenetic synthesis, we designed a bioinspired total synthesis of homodimericin A that proceeds in seven steps, featuring a double Michael reaction, an intramolecular Diels-Alder reaction, and an ene reaction.
Datum: 17.05.2017


Tailored Ahp-cyclodepsipeptides as potent non-covalent serine protease inhibitors

The S1 serine protease family is one of the largest and biologically relevant protease families. Despite their biomedical significance, generic approaches to generate potent, class-specific, bioactive non-covalent inhibitors for these enzymes are still limited. Here, we demonstrate that Ahp-cyclodepsipeptides represent a suitable scaffold for generating target-tailored serine protease inhibitors. For efficient synthetic access, we developed a practical mixed solid and solution phase synthesis that we validated by the first chemical synthesis of two natural products, Tasipeptin A and B. We showcase the suitability of the Ahp-cyclodepsipeptide scaffold for tailored inhibitor synthesis by generation of the most potent human HTRA protease inhibitors to date. We anticipate that our approach may also be applied to other serine proteases, thus opening new avenues for a systematic discovery of serine protease inhibitors.
Datum: 17.05.2017


Glycan Fingerprinting using Cold-Ion Infrared Spectroscopy

The diversity of stereochemical isomers present in glycans and glycoconjugates poses a formidable challenge for comprehensive structural analysis. Typically, sophisticated mass spectrometry (MS)-based techniques are used in combination with chromatography or ion mobility separation. However, coexisting structurally similar isomers often render an unambiguous identification impossible. Other powerful techniques such as gas-phase infrared (IR) spectroscopy have been limited to smaller glycans, as conformational flexibility and thermal activation during the measurement result in poor spectral resolution. Here, we show that this limitation can be overcome using cold-ion spectroscopy. The vibrational fingerprints of cold oligosaccharide ions exhibit a wealth of well-resolved absorption features that are diagnostic for minute structural variations. The unprecedented resolution of cold-ion spectroscopy coupled with tandem MS may render this the key technology to unravel complex glycomes.
Datum: 17.05.2017


Carbon doped BN nanosheets for the oxidative dehydrogenation of ethylbenzene

Carbon-based catalysts have recently been demonstrated great potential for aerobic oxidative dehydrogenation reaction (ODH). However, its widespread application is retarded by the unavoidable deactivation due to the appearance of coking or combustion under ODH condition. Here we report the synthesis and characterization of porous structure of BCN nanosheets as well as their application as a novel catalyst for ODH. Such BCN nanosheets consist of hybridized, randomly distributed domains of h-BN and C phases, where C, B, and N were confirmed to covalent bond in the graphene-like layers. Our studies reveal that BCN exhibits both high activity and selectivity in oxidative dehydrogenation of ethylbenzene to styrene, as well as excellent oxidation resistance. The discovery of a simple chemical process to synthesize highly active BCN allows the premise of industrial-scale carbocatalysis to be explored.
Datum: 17.05.2017


Cyclic Polysiloxanes with Linked Rings

Cyclic polymer represents one important class of macromolecules, but the structural diversity on the backbone is limited. Herein we would like to report for the first time the utilization of Piers-Rubinsztajn reaction for the one-step synthesis of cyclic polysiloxanes with novel structural features. Specifically the B(C6F5)3 catalyzed coupling reaction between various organic tris(dimethylsiloxy)silane and trialkoxysilane compounds generates a series of cyclic polysiloxanes with cyclotetrasiloxane subunits. The thiolated cyclic polymer is also shown effective in directing the circular assembly gold nano particles. The presence of constrained rings on the backbone is unprecedented and may bring opportunities for novel applications of these cyclic polymers.
Datum: 17.05.2017


Catalyst-Controlled Regiodivergent Alkyne Insertion in the Context of C-H Activation and Diels-Alder Reactions: Synthesis of Fused and Bridged Cycles

Catalyst-Controlled C-H activation of indoles and coupling with 1,6-enynes is discussed. Under Rh(III) catalysis, the alkyne insertion follows 2,1-regioselectivity with subsequent type-I intramolecular Diels-Alder reaction (IMDA) to afford [6,5]-fused cycles. When catalyzed by the Co(III) congener, 1,2-insertion of alkyne is preferred, followed by rare type-II IMDA leading to bridged [3,3,1]-cycles. This selectivity of the alkyne insertion was mainly tuned by the steric sensitivity of the catalyst.
Datum: 17.05.2017


Δ-Myrtoxin-Mp1a is a helical heterodimer from the venom of the Jack Jumper ant with antimicrobial, membrane disrupting and nociceptive activities

Δ-Myrtoxin-Mp1a (Mp1a), a 49-residue heterodimeric peptide from the venom of Myrmecia pilosula is comprised of a 26-mer A chain and a 23-mer B chain connected by two disulfide bonds in an antiparallel arrangement. Combination of the individual synthetic chains via aerial oxidation remarkably resulted in the self-assembly of Mp1a as a homogenous product without the need for directed disulfide bond formation. NMR analysis revealed a well-defined, unique structure containing a pair of antiparallel α-helices. DPI analysis showed strong interaction with supported lipid bilayers and insertion within the bilayers. Mp1a caused non-specific calcium influx in SH-SY5Y cells with an EC50 of 4.3 µM. Mp1a also displayed broad-spectrum antimicrobial activity, with the highest potency against Gram-negative A. baumannii (MIC 25 nM). Intraplantar injection (10 µM) in mice elicited spontaneous pain and mechanical allodynia. Single and two chain mimetics of Mp1a revealed functionally selectivity.
Datum: 17.05.2017


Native Mass Spectrometry from Common Buffers with Salts that Mimic the Extracellular Environment

Nonvolatile salts are essential for the structures and functions of many proteins and protein complexes but can severely degrade performance of native mass spectrometry by adducting to protein and protein complex ions, thereby reducing sensitivity and mass measuring accuracy. Here, small nanoelectrospray emitters are used to form protein and protein complex ions directly from high ionic strength (>150 mM) nonvolatile buffers with salts that mimic the extracellular environment. Charge-state distributions are not obtained for proteins and protein complexes from six commonly used nonvolatile buffers and ≥150 mM Na+ with conventional sized nanoelectrospray emitter tips but are resolved with 0.5 µm tips. This method enables mass measurements of proteins and protein complexes directly from a variety of commonly used buffers with high concentrations of nonvolatile salts and eliminates the need to buffer exchange into volatile ammonium buffers traditionally used in native mass spectrometry.
Datum: 16.05.2017


Iridium-catalyzed Formyl-selective Deuteration of Aldehydes

We report the first direct catalytic method for formyl-selective deuterium labeling of aromatic aldehydes under mild conditions, using an iridium-based catalyst designed to favor formyl- over aromatic C-H activation. A good range of aromatic aldehydes is selectively labeled, and a one-pot labeling/olefination protocol is also described. Computational studies support kinetic product control over competing aromatic labeling and decarbonylation pathways.
Datum: 16.05.2017


Cucurbit[8]uril and 14-3-3 based binary bivalent supramolecular-protein assembly platform and co-crystal structure

Interactions between proteins frequently employ recognition sequences that engage in multivalent binding events. Dimeric 14-3-3 adapter proteins represent a prominent example, typically binding partner proteins in a phosphorylation-dependent mono- or bivalent manner. Here we describe the development of a cucurbit[8]uril (Q8)-based supramolecular system, which in conjunction with the 14-3-3 protein dimer acts as a binary and bivalent protein assembly platform. We fused the phenylalanine-glycine-glycine (FGG) tripeptide motif to the N-terminus of the 14-3-3-binding epitope of the estrogen receptor α (ERα), for selective binding to Q8. Q8-induced dimerization of the ERα epitope augmented its affinity towards 14-3-3 via a binary bivalent binding mode. The crystal structure of the Q8-induced ternary complex, a first of its kind, reveals molecular insights into the multiple supramolecular interactions between the protein, peptide and Q8.
Datum: 16.05.2017


Bottom Up Design of a Novel CuRu Nanoparticulate Catalyst for Low Temperature Ammonia Oxidation

A novel nanoparticulate catalyst of copper and ruthenium is designed for low temperature ammonia oxidation at near stoichiometric mixtures using a bottom up approach. A synergistic effect of the two metals is found: an optimum CuRu catalyst shows reaction rate three-fold higher than Ru and fourty-fold higher than Cu. X-ray Absorption Spectroscopy (XAS) suggests that in the most active catalyst Cu forms one or two monolayer thick patches on Ru and the catalysts are less active once 3D Cu-islands form. The good performance of Cu/Ru is attributed to the change in the electronic structure and thus the altered adsorption properties of the surface Cu sites.
Datum: 16.05.2017


An Enyne Cope Rearrangement Enables Polycycloalkane Synthesis from Abundant Starting Materials by a Simple Strategy

Cyclohexanone-derived Knoevenagel adducts (cyclohexylidenemalononitriles) and two different propargyl electrophiles serve as carbon sources for assembling diverse 6/7/5 tricycloalkanes, a common terpenoid framework. The sequence involves three unique reactions: (i.) deconjugative propargylation, (ii.) one-pot enyne Cope rearrangement/deconjugative propargylation, and (iii.) allenic-Pauson-Khand reaction.
Datum: 16.05.2017


Tricyanomethane and its Ketenimine Tautomer Generated from Different Precursors and Analyzed in Solution, Argon Matrix, and Single Crystal

Solutions of azidomethylidenemalononitrile were photolyzed at low temperatures to produce the corresponding 2H-azirine and tricyanomethane, which were analyzed by low-temperature NMR spectroscopy. The latter product was also observed after short thermolysis of the azide precursor in solution, whereas irradiation of the azide isolated in an argon matrix did not lead to tricyanomethane, but to unequivocal detection of the tautomeric ketenimine by IR spectroscopy for the first time. When the long-known "aquoethereal" greenish phase, generated from potassium tricyanomethanide, dilute sulfuric acid, and diethyl ether, was rapidly evaporated and sublimed, a mixture of hydronium tricyanomethanide and tricyanomethane was formed instead of previously claimed ketenimine tautomer. Under special conditions of sublimation, isolation of single crystals of tricyanomethane was possible and enabled analysis of the molecular structure by X-ray diffraction.
Datum: 16.05.2017


1-Substituted 2-azaspiro[3.3]heptanes: overseen motifs for drug discovery.

Spirocyclic analogues for 2-substituted piperidines have been designed, synthesized and validated in drug discovery.
Datum: 16.05.2017


IUAPC 2017 Distinguished Women in Chemistry or Chemical Engineering


Datum: 11.05.2017


Back Cover: Fluorophores for Excited-State Intramolecular Proton Transfer by an Yttrium Triflate Catalyzed Reaction of Isocyanides with Thiocarboxylic Acids (Angew. Chem. Int. Ed. 23/2017)

The one-pot synthesis of 5-amino-4-carboxamidothiazole molecules by the yttrium triflate catalyzed reaction of thiocarboxylic acids with isocyanides is reported by J. Zhu et al. in their Communication on page 6599 ff. The resulting heterocycles are novel prototypical structures for the double excited-state intramolecular proton transfer (ESIPT) process and could serve as templates for designing ESICT-to-ESIPT-coupled molecules (CT=charge transfer).
Datum: 11.05.2017


C−N Bond Activation and Ring Opening of a Saturated N-Heterocyclic Carbene by Lateral Alkali-Metal-Mediated Metalation

Combining alkali-metal-mediated metalation (AMMM) and N-heterocyclic carbene (NHC) chemistry, a novel C−N bond activation and ring-opening process is described for these increasingly important NHC molecules, which are generally considered robust ancillary ligands. Here, mechanistic investigations on reactions of saturated NHC SIMes (SIMes=[:C{N(2,4,6-Me3C6H2)CH2}2]) with Group 1 alkyl bases suggest this destructive process is triggered by lateral metalation of the carbene. Exploiting co-complexation and trans-metal-trapping strategies with lower polarity organometallic reagents (Mg(CH2SiMe3)2 and Al(TMP)iBu2), key intermediates in this process have been isolated and structurally defined. Co-lateral damage! Lateral metalation of saturated N-heterocyclic carbene [:C{N(2,4,6-Me3C6H2)CH2}2] (SIMes) triggers a destructive process, inducing C−N bond activation and ring opening of the five-membered heterocyclic ring.
Datum: 10.05.2017


Phenol-Catalyzed Discharge in the Aprotic Lithium-Oxygen Battery

Discharge in the lithium-O2 battery is known to occur either by a solution mechanism, which enables high capacity and rates, or a surface mechanism, which passivates the electrode surface and limits performance. The development of strategies to promote solution-phase discharge in stable electrolyte solutions is a central challenge for development of the lithium-O2 battery. Here we show that the introduction of the protic additive phenol to ethers can promote a solution-phase discharge mechanism. Phenol acts as a phase-transfer catalyst, dissolving the product Li2O2, avoiding electrode passivation and forming large particles of Li2O2 product—vital requirements for high performance. As a result, we demonstrate capacities of over 9 mAh cm−2areal, which is a 35-fold increase in capacity compared to without phenol. We show that the critical requirement is the strength of the conjugate base such that an equilibrium exists between protonation of the base and protonation of Li2O2. Battery balancing: Discharge in the Li-O2 battery occurs either by a desired solution mechanism or an unfavored surface mechanism, which passivates the electrode surface. The introduction of phenol promotes solution-phase discharge. Phenol acts as a phase-transfer catalyst (see scheme), dissolving the product Li2O2, avoiding electrode passivation and forming large particles of Li2O2—vital requirements for high performance.
Datum: 10.05.2017


Cover Picture: Mo2B4O9—Connecting Borate and Metal-Cluster Chemistry (Angew. Chem. Int. Ed. 23/2017)

Two fields are united in Mo2B4O9, the first borate compound incorporating transition-metal clusters into its crystal structure. It thus constitutes the hitherto unknown interface between two previously separated fields of research—borate and metal cluster chemistry. In their Communication on page 6449 ff., H. Huppertz and co-workers show how the planned reduction of a reagent in a high-pressure experiment smoothed the way to this novel substance class.
Datum: 09.05.2017


Chromatin Regulates Genome Targeting with Cisplatin

Cisplatin derivatives can form various types of DNA lesions (DNA-Pt) and trigger pleiotropic DNA damage responses. Here, we report a strategy to visualize DNA-Pt with high resolution, taking advantage of a novel azide-containing derivative of cisplatin we named APPA, a cellular pre-extraction protocol and the labeling of DNA-Pt by means of click chemistry in cells. Our investigation revealed that pretreating cells with the histone deacetylase (HDAC) inhibitor SAHA led to detectable clusters of DNA-Pt that colocalized with the ubiquitin ligase RAD18 and the replication protein PCNA. Consistent with activation of translesion synthesis (TLS) under these conditions, SAHA and cisplatin cotreatment promoted focal accumulation of the low-fidelity polymerase Polη that also colocalized with PCNA. Remarkably, these cotreatments synergistically triggered mono-ubiquitination of PCNA and apoptosis in a RAD18-dependent manner. Our data provide evidence for a role of chromatin in regulating genome targeting with cisplatin derivatives and associated cellular responses. Treatment of cancer cells with cisplatin derivatives and a histone deacetylase inhibitor leads to the production of clusters of platinated DNA lesions that synergistically activate translesion synthesis and apoptosis signaling. These findings provide evidence for a role of chromatin in regulating genome targeting with cisplatin derivatives and associated cellular responses.
Datum: 05.05.2017


Color-Change Photoswitching of an Alkynylpyrene Excimer Dye

We describe a photoswitchable DNA-based dimeric dye that visibly changes fluorescence from green to blue upon UV irradiation. A novel bis-alkyne-dependent [2+2+2] cycloaddition is proposed as a mechanism for the color change in air. The photoinduced structural switching results in spatial separation of stacked pyrene units, thereby causing selective loss of the excimer emission. We demonstrate and suggest several applications for this novel photoswitch. DNA-based photoswitch: A DNA-based dimeric dye that visibly changes color from green to blue upon UV irradiation is described. A novel bis-alkyne [2+2+2] cycloaddition with oxygen is proposed as a mechanism for the color change in air (see picture).
Datum: 05.05.2017


Total Synthesis of Rishirilide B by Organocatalytic Oxidative Kinetic Resolution: Revision of Absolute Configuration of (+)-Rishirilide B

Described herein is the enantioselective syntheses of (+)- and (−)-rishirilide B from the corresponding optically active β-substituted tetralones, which were obtained by oxidative kinetic resolution based on α-hydroxylation in the presence of a chiral guanidine-bisurea bifunctional organocatalyst. Benzylic oxidation of the tetralones at C1 followed by regioselective isomerization of the oxabenzonorbornadiene structure led to rishirilide B. Our findings lead to the revision of the previously proposed (2R,3R,4R) absolute configuration of (+)-rishirilide B to (2S,3S,4S). Reconfigured: Enantioselective synthesis of (+)- and (−)-rishirilide B has been achieved from optically active β-substituted tetralone, which was obtained by oxidative kinetic resolution using a guanidine-bisurea bifunctional organocatalyst. This synthetic studies led to revision of the previously proposed absolute configuration of (+)-rishirilide B to (2S,3S,4S).
Datum: 04.05.2017


Iron Oxide Photoelectrode with Multidimensional Architecture for Highly Efficient Photoelectrochemical Water Splitting

Nanostructured metal oxide semiconductors have shown outstanding performances in photoelectrochemical (PEC) water splitting, but limitations in light harvesting and charge collection have necessitated further advances in photoelectrode design. Herein, we propose anodized Fe foams (AFFs) with multidimensional nano/micro-architectures as a highly efficient photoelectrode for PEC water splitting. Fe foams fabricated by freeze-casting and sintering were electrochemically anodized and directly used as photoanodes. We verified the superiority of our design concept by achieving an unprecedented photocurrent density in PEC water splitting over 5 mA cm−2 before the dark current onset, which originated from the large surface area and low electrical resistance of the AFFs. A photocurrent of over 6.8 mA cm−2 and an accordingly high incident photon-to-current efficiency of over 50 % at 400 nm were achieved with incorporation of Co oxygen evolution catalysts. In addition, research opportunities for further advances by structual and compositional modifications are discussed, which can resolve the low fill factoring behavior and improve the overall performance. An anodized iron foam photoelectrode with multidimensional nano/micro-architecture leads to extremely large photocurrent generation and high Faradaic efficiency in photoelectrochemical water splitting. Morphologies of anodic iron oxides and activation of photoelectrode by phase-transition phenomena were also investigated.
Datum: 04.05.2017


Directing Reaction Pathways through Controlled Reactant Binding at Pd–TiO2 Interfaces

Recent efforts to design selective catalysts for multi-step reactions, such as hydrodeoxygenation (HDO), have emphasized the preparation of active sites at the interface between two materials having different properties. However, achieving precise control over interfacial properties, and thus reaction selectivity, has remained a challenge. Here, we encapsulated Pd nanoparticles (NPs) with TiO2 films of regulated porosity to gain a new level of control over catalyst performance, resulting in essentially 100 % HDO selectivity for two biomass-derived alcohols. This catalyst also showed exceptional reaction specificity in HDO of furfural and m-cresol. In addition to improving HDO activity by maximizing the interfacial contact between the metal and metal oxide sites, encapsulation by the nanoporous oxide film provided a significant selectivity boost by restricting the accessible conformations of aromatics on the surface. Nanoscale morphology control over active sites consisting of Pd and TiO2 specifies binding orientation of reactant molecules to provide unprecedented reaction specificity toward hydrodeoxygenation during catalytic conversion of biomass-derived aromatic alcohols/aldehydes and phenolic compounds.
Datum: 04.05.2017


Crystallinity-Modulated Electrocatalytic Activity of a Nickel(II) Borate Thin Layer on Ni3B for Efficient Water Oxidation

The exploration of new efficient OER electrocatalysts based on nonprecious metals and the understanding of the relationship between activity and structure of electrocatalysts are important to advance electrochemical water oxidation. Herein, we developed an efficient OER electrocatalyst with nickel boride (Ni3B) nanoparticles as cores and nickel(II) borate (Ni-Bi) as shells (Ni-Bi@NB) via a very simple and facile aqueous reaction. This electrocatalyst exhibited a small overpotential of 302 mV at 10 mA cm−2 and Tafel slope of 52 mV dec−1. More interestingly, it was found that the OER activity of Ni-Bi@NB was closely dependent on the crystallinity of the Ni-Bi shells. The partially crystalline Ni-Bi catalyst exhibited much higher activity than the amorphous or crystalline analogues; this higher activity originated from the enhanced intrinsic activity of the catalytic sites. These findings open up opportunities to explore nickel(II) borates as a new class of efficient nonprecious metal OER electrocatalysts, and to improve the electrocatalyst performance by modulating their crystallinity. A new winner! Crystallinity-dependent activity was demonstrated on a new efficient electrocatalyst for the oxygen evolution reaction (OER) which consists of a nickel(II) borate thin layer on nickel boride (NB) nanoparticles (Ni-Bi@NB) (see figure). The partially crystalline Ni-Bi catalyst exhibits excellent OER performance.
Datum: 04.05.2017


Discovery of Hexagonal Structured Pd–B Nanocrystals

We report on hexagonal close-packed (hcp) palladium (Pd)–boron (B) nanocrystals (NCs) by heavy B doping into face-centered cubic (fcc) Pd NCs. Scanning transmission electron microscopy–electron energy loss spectroscopy and synchrotron powder X-ray diffraction measurements demonstrated that the B atoms are homogeneously distributed inside the hcp Pd lattice. The large paramagnetic susceptibility of Pd is significantly suppressed in Pd–B NCs in good agreement with the reduction of density of states at Fermi energy suggested by X-ray absorption near-edge structure and theoretical calculations. A change in behavior: Hexagonal close-packed (hcp) Pd–B nanocrystals (NCs) are synthesized by B doping into face-centered cubic (fcc) Pd NCs. Analyses (HR-HAADF-STEM, EELS, and synchrotron PXRD) of Pd–B NCs demonstrate that B atoms are homogeneously distributed inside an hcp Pd lattice. The large paramagnetic susceptibility of Pd NCs is suppressed in Pd–B NCs, in good agreement with the reduction of density of states at Fermi energy suggested by XANES and theoretical calculations.
Datum: 04.05.2017


Synthesis of Layered Carbonitrides from Biotic Molecules for Photoredox Transformations

The construction of layered covalent carbon nitride polymers based on tri-s-triazine units has been achieved by using nucleobases (adenine, guanine, cytosine, thymine and uracil) and urea to establish a two-dimensional semiconducting structure that allows band-gap engineering applications. This biomolecule-derived binary carbon nitride polymer enables the generation of energized charge carrier with light-irradiation to induce photoredox reactions for stable hydrogen production and heterogeneous organosynthesis of C−O, C−C, C−N and N−N bonds, which may enrich discussion on chemical reactions in prebiotic conditions by taking account of the photoredox function of conjugated carbonitride semiconductors that have long been considered to be stable HCN-derived organic macromolecules in space. A prebiotic photocatalyst? Graphitic carbon nitrides synthesized from nucleobases and urea enable the photogeneration of charge carriers to induce photoredox reactions for H2 production and heterogeneous organosynthesis of C−O, C−C, C−N, and N−N bonds. The findings enrich the concept of photochemical reactions in the primordial soup.
Datum: 04.05.2017


Atroposelective Synthesis of Axially Chiral Biaryls by Palladium-Catalyzed Asymmetric C−H Olefination Enabled by a Transient Chiral Auxiliary

Atroposelective synthesis of axially chiral biaryls by palladium-catalyzed C−H olefination, using tert-leucine as an inexpensive, catalytic, and transient chiral auxiliary, has been realized. This strategy provides a highly efficient and straightforward access to a broad range of enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (95 to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (95 to >99 % ee, s-factor up to 600). No attachements: The title reaction employs tert-leucine as a transient chiral auxiliary and provides efficient access to enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (up to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (up to >99 % ee, s-factor up to 600).
Datum: 04.05.2017


Insights Into How Heme Reduction Potentials Modulate Enzymatic Activities of a Myoglobin-based Functional Oxidase

Heme-copper oxidase (HCO) is a class of respiratory enzymes that use a heme-copper center to catalyze O2 reduction to H2O. While heme reduction potential (E°′) of different HCO types has been found to vary >500 mV, its impact on HCO activity remains poorly understood. Here, we use a set of myoglobin-based functional HCO models to investigate the mechanism by which heme E°′ modulates oxidase activity. Rapid stopped-flow kinetic measurements show that increasing heme E°′ by ca. 210 mV results in increases in electron transfer (ET) rates by 30-fold, rate of O2 binding by 12-fold, O2 dissociation by 35-fold, while decreasing O2 affinity by 3-fold. Theoretical calculations reveal that E°′ modulation has significant implications on electronic charge of both heme iron and O2, resulting in increased O2 dissociation and reduced O2 affinity at high E°′ values. Overall, this work suggests that fine-tuning E°′ in HCOs and other heme enzymes can modulate their substrate affinity, ET rate and enzymatic activity. A four-electron reduction of O2 to H2O in heme-copper oxidase (HCO) requires an efficient control of electron transfer, O2 binding/dissociation rates, and O2 affinity. By employing a functional model of HCO, it is shown that the heme reduction potential plays a key role in controlling these parameters, the electronics of bound O2, and thus the overall enzymatic activity.
Datum: 04.05.2017


Different Reactivity of As4 towards Disilenes and Silylenes

The activation of yellow arsenic is possible with the silylene [PhC(NtBu)2SiN(SiMe3)2] (1) and the disilene [(Me3Si)2N(η1-Me5C5)Si=Si(η1-Me5C5)N(SiMe3)2] (3). The reaction of As4 with 1 leads to the unprecedented As10 cage compound [(LSiN(SiMe3)2)3As10] (2; L=PhC(NtBu)2) with an As7 nortricyclane core stabilized by arsasilene moieties containing silicon(II)bis(trimethylsilyl)amide substituents. In contrast, the compound [Cp*{(SiMe3)2N}SiAs]2 (4) containing a butterfly-like diarsadisilabicyclo[1.1.0]butane unit is formed by the reaction of As4 with the disilene 3. Both compounds were characterized by single-crystal X-ray diffraction analysis, NMR spectroscopy, and mass spectrometry. The reaction outcomes demonstrate the different reaction behavior of yellow arsenic (As4) compared to white phosphorus (P4) in the reactions with the corresponding silylenes and disilenes. As revealed: The reaction of yellow arsenic with the silylene [PhC(NtBu)2SiN(SiMe3)2] and the disilene [(Me3Si)2N(η1-Me5C5)Si=Si(η1-Me5C5)N(SiMe3)2] gives an As10 cage compound with a nortricyclane core and a diarsadisila-butterfly derivative, respectively. These reactions demonstrate the different reaction behavior of yellow arsenic As4 and white phosphorus P4 with the corresponding silicon derivatives.
Datum: 04.05.2017


A Short Synthesis of (±)-3-Demethoxyerythratidinone by Ligand-Controlled Selective Heck Cyclization of Equilibrating Enamines

A short, 5-step total synthesis of (±)-3-demethoxyerythratidinone from a simple pyrrole derivative is described. Features include the formation of gram quantities of a key tricylic aziridine from a challenging photochemical cascade reaction through the use of flow photochemistry. The final step involved a highly unusual Heck cyclization whereby ligand control enabled efficient formation of the natural product in 69 % yield from the minor isomer present in an equilibrating mixture of labile enamines. Five steps to success: A short total synthesis of (±)-3-demethoxyerythratidinone (1) has been completed using a combination of photochemistry and Pd-catalyzed Heck cyclization. A key feature was the ability to control the outcome of the Heck cyclization onto an equilibrating mixture of labile enamines by ligand choice.
Datum: 04.05.2017


Oligonucleotide-Addressed Covalent 3′-Terminal Derivatization of Small RNA Strands for Enrichment and Visualization

The HEN1 RNA 2′-O-methyltransferase plays important roles in the biogenesis of small non-coding RNAs in plants and proved a valuable tool for selective transfer of functional groups from cofactor analogues onto miRNA and siRNA duplexes in vitro. Herein, we demonstrate the versatile HEN1-mediated methylation and alkylation of small RNA strands in heteroduplexes with a range of complementary synthetic DNA oligonucleotides carrying user-defined moieties such as internal or 3′-terminal extensions or chemical reporter groups. The observed DNA-guided covalent functionalization of RNA broadens our understanding of the substrate specificity of HEN1 and paves the way for the development of novel chemo-enzymatic tools with potential applications in miRNomics, synthetic biology, and nanomedicine. Versatile RNA tagging: A method for addressable chemo-enzymatic labeling of miRNAs and siRNAs, which exploits the activity of HEN1 2′-O-methyltransferase to transfer functional groups to the 3′-end of the RNA strand in DNA/RNA heteroduplexes, is presented. This method permits a variety of user-defined single- or dual-reporter applications, in which one tag can be synthetically incorporated into the DNA probe and the second is covalently attached by HEN1 to the target RNA.
Datum: 04.05.2017


Activatable Singlet Oxygen Generation from Lipid Hydroperoxide Nanoparticles for Cancer Therapy

Reactive oxygen species (ROS)-induced apoptosis is a widely practiced strategy for cancer therapy. Although photodynamic therapy (PDT) takes advantage of the spatial–temporal control of ROS generation, the meticulous participation of light, photosensitizer, and oxygen greatly hinders the broad application of PDT as a first-line cancer treatment option. An activatable system has been developed that enables tumor-specific singlet oxygen (1O2) generation for cancer therapy, based on a Fenton-like reaction between linoleic acid hydroperoxide (LAHP) tethered on iron oxide nanoparticles (IO NPs) and the released iron(II) ions from IO NPs under acidic-pH condition. The IO-LAHP NPs are able to induce efficient apoptotic cancer cell death both in vitro and in vivo through tumor-specific 1O2 generation and subsequent ROS mediated mechanism. This study demonstrates the effectiveness of modulating biochemical reactions as a ROS source to exert cancer death. Singlet oxygen generation through an activatable biochemical reaction between lipid hydroperoxide and catalytic iron(II) ions from iron oxide nanoparticles was engineered as a novel cancer therapy strategy, which showed promise to exert apoptotic cancer cell death both in vitro and in vivo.
Datum: 04.05.2017


Elusive Terminal Copper Arylnitrene Intermediates

We report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β-diketiminate. Addition of N3ArX3 (ArX3=2,4,6-X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be “masked” forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene. Attempts at isolating terminal arylnitrenes [Cu]=NAr result in a dicopper diketimide (see scheme, left) formed through reversible C−C coupling at the para position of the NAr group or acetonitrile insertion to give a diazametallacyclobutene (right). Experimental and theoretical studies reveal that both intermediates serve as “masked” sources of the corresponding terminal nitrene [Cu]=NAr that undergoes nitrene transfer to PMe3, CNtBu, and benzylic C−H bonds.
Datum: 04.05.2017


Synthesis of Intrinsically Disordered Fluorinated Peptides for Modular Design of High-Signal 19F MRI Agents

19F MRI is valuable for in vivo imaging due to the only trace amounts of fluorine in biological systems. Because of the low sensitivity of MRI however, designing new fluorochemicals remains a significant challenge for achieving sufficient 19F signal. Here, we describe a new class of high-signal, water-soluble fluorochemicals as 19F MRI imaging agents. A polyamide backbone is used for tuning the proteolytic stability to avoid retention within the body, which is a limitation of current state-of-the-art perfluorochemicals. We show that unstructured peptides containing alternating N-ϵ-trifluoroacetyllysine and lysine provide a degenerate 19F NMR signal. 19F MRI phantom images provide sufficient contrast at micromolar concentrations, showing promise for eventual clinical applications. Finally, the degenerate high signal characteristics were retained when conjugated to a large protein, indicating potential for in vivo targeting applications, including molecular imaging and cell tracking. Disordered symmetry: A new class of water-soluble, peptide-based fluorochemicals as high-signal 19F MRI imaging agents is described. The design strategy utilizes an alternating sequence of positive charges and fluorinated amino acids to produce a disordered peptide with overlapping 19F resonances that give a singular intense signal for use as a 19F MRI agent.
Datum: 04.05.2017


Palladium-Catalyzed Cascade sp2 C−H Functionalization/Intramolecular Asymmetric Allylation: From Aryl Ureas and 1,3-Dienes to Chiral Indolines

A chiral PdII-catalyzed cascade sp2 C−H functionalization/intramolecular asymmetric allylation reaction is reported. A new chiral sulfoxide–oxazoline (SOX) ligand bearing single chiral center on the sulfur was identified as the optimal ligand for the reaction, being efficient both in the C−H cleavage step and the stereocontrol of the allylation step. The broad scope of this method with respect to aryl ureas and 1,3-dienes enables the rapid construction of valuable chiral indoline derivatives with high yields and enantioselectivities (up to 99 % yield, up to 95:5 e.r.). Efficiency and chirality: A chiral PdII-catalyzed cascade sp2 C−H functionalization/intramolecular asymmetric allylation reaction is described. A chiral sulfoxide–oxazoline (SOX) ligand bearing a single chiral center on the sulfur was identified as the optimal ligand for the reaction, being efficient both in the C−H cleavage step and the stereocontrol of the allylation step.
Datum: 03.05.2017


Non-Enzymatic RNA Backbone Proofreading through Energy-Dissipative Recycling

Non-enzymatic oligomerization of activated ribonucleotides leads to ribonucleic acids that contain a mixture of 2′,5′- and 3′,5′-linkages, and overcoming this backbone heterogeneity has long been considered a major limitation to the prebiotic emergence of RNA. Herein, we demonstrate non-enzymatic chemistry that progressively converts 2′,5′-linkages into 3′,5′-linkages through iterative degradation and repair. The energetic costs of this proofreading are met by the hydrolytic turnover of a phosphate activating agent and an acylating agent. With multiple rounds of this energy-dissipative recycling, we show that all-3′,5′-linked duplex RNA can emerge from a backbone heterogeneous mixture, thereby delineating a route that could have driven RNA evolution on the early earth. If at first you don't succeed, try, try again: With enzymes not available on the early Earth, energy-dissipative cycles might have contributed to the correction and recycling of ribonucleic acids, which defines a plausible scenario for the prebiotic evolution of RNA.
Datum: 03.05.2017


Inside Back Cover: Synthesis and Bowl-in-Bowl Assembly of a Geodesic Phenylene Bowl (Angew. Chem. Int. Ed. 23/2017)

A carbon-rich geodesic dome has been synthesized by linking 20 trigonal planar 1,3,5-linked phenylenes through 25 biaryl linkages. H. Isobe et al. describe in their Communication on page 6511 ff. how the geodesic, corannulenoidal combination of one pentagon and five hexagons leads to the nanometer-sized bowl. Concave–convex molecular recognition results in the formation of a bowl-in-bowl dimer in both the crystalline state and in solution.
Datum: 03.05.2017


Palladium-Catalyzed Enantioselective Redox-Relay Heck Alkynylation of Alkenols To Access Propargylic Stereocenters

An enantioselective redox-relay Heck alkynylation of di- and trisubstituted alkenols to construct propargylic stereocenters is disclosed using a new pyridine oxazoline ligand. This strategy allows direct access to chiral β-alkynyl carbonyl compounds employing allylic alcohol substrates in contrast to more traditional conjugate addition methods. Heck alkynylation: A convenient redox-relay Heck strategy to synthesize enantiomerically enriched β-alkynyl carbonyl compounds from allylic alcohols with high functional group tolerance is described. Trisubstituted allylic alcohols are also promising substrates allowing for the formation of propargylic quaternary stereocenters.
Datum: 03.05.2017


Mizoroki–Heck Cyclizations of Amide Derivatives for the Introduction of Quaternary Centers

We report non-decarbonylative Mizoroki–Heck reactions of amide derivatives. The transformation relies on the use of nickel catalysis and proceeds using sterically hindered tri- and tetrasubstituted olefins to give products containing quaternary centers. The resulting polycyclic or spirocyclic products can be obtained in good yields. Moreover, a diastereoselective variant of this method gives access to an adduct bearing vicinal, highly substituted sp3 stereocenters. These results demonstrate that amide derivatives can be used as building blocks for the assembly of complex scaffolds. Adding complexity: A non-decarbonylative Mizoroki–Heck reaction of Boc-activated amide derivatives is reported. The transformation relies on the use of nickel catalysis and proceeds using sterically hindered tri- and tetrasubstituted olefins to give products containing quaternary centers. The results demonstrate that amide derivatives can be used as building blocks for the assembly of complex scaffolds.
Datum: 03.05.2017


Copper(I)-Catalyzed Enantioselective Nucleophilic Borylation of Aliphatic Ketones: Synthesis of Enantioenriched Chiral Tertiary α-Hydroxyboronates

A new method was developed for the first catalytic enantioselective borylation of aliphatic ketones. A variety of substrates reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex catalyst to furnish optically active tertiary α-hydroxyboronates with moderate to high enantioselectivities (up to 94 % ee). Notably, the product could be converted into the chiral tertiary alcohol derivative using a stereospecific boron functionalization process. The theoretical study of the mechanism for the enantioselectivity is also described. Ketone functionalization: The first catalytic enantioselective borylation of ketones is presented. A variety of aliphatic ketones reacted efficiently with bis(pinacolato)diboron in the presence of a copper(I)/chiral N-heterocyclic carbene complex to furnish the corresponding tertiary α-hydroxyboronate esters with moderate to high enantioselectivities.
Datum: 03.05.2017


Ultrafast Delamination of Graphite into High-Quality Graphene Using Alternating Currents

To bridge the gap between laboratory-scale studies and commercial applications, mass production of high quality graphene is essential. A scalable exfoliation strategy towards the production of graphene sheets is presented that has excellent yield (ca. 75 %, 1–3 layers), low defect density (a C/O ratio of 21.2), great solution-processability, and outstanding electronic properties (a hole mobility of 430 cm2 V−1 s−1). By applying alternating currents, dual exfoliation at both graphite electrodes enables a high production rate exceeding 20 g h−1 in laboratory tests. As a cathode material for lithium storage, graphene-wrapped LiFePO4 particles deliver a high capacity of 167 mAh g−1 at 1 C rate after 500 cycles. A great alternative: A facile, cost-effective and highly efficient strategy has been developed to delaminate graphite into high-quality graphene by means of alternating currents. This procedure shows great potential to bridge the gap between laboratory-scale research and commercial applications.
Datum: 03.05.2017


A Rhodium(II)-Catalyzed Formal [4+1]-Cycloaddition toward Spirooxindole Pyrrolone Construction Employing Vinyl Isocyanates as 1,4-Dipoles

A RhII-catalyzed, formal [4+1]-cycloaddition between diazooxindoles as electrophilic C1 synthons and 1,3-heterodienes for the construction of spirooxindole pyrrolones is described. Employing vinyl isocyanates as 1,4-dipoles, the cycloannulation occurs under relatively mild conditions and provides the corresponding pyrrolones in good to excellent yields. Put a ring on it: The title reaction between diazooxindoles as electrophilic C1 synthons and 1,3-heterodienes enables the construction of spirooxindole pyrrolones. Employing vinyl isocyanates as 1,4-dipoles, the cycloannulation occurs under relatively mild conditions and provides the corresponding pyrrolones in good to excellent yields.
Datum: 03.05.2017


Enhanced Catalytic Activity of Cobalt Porphyrin in CO2 Electroreduction upon Immobilization on Carbon Materials

In a comparative study of the electrocatalytic CO2 reduction, cobalt meso-tetraphenylporphyrin (CoTPP) is used as a model molecular catalyst under both homogeneous and heterogeneous conditions. In the former case, employing N,N-dimethylformamide as solvent, CoTPP performs poorly as an electrocatalyst giving low product selectivity in a slow reaction at a high overpotential. However, upon straightforward immobilization of CoTPP onto carbon nanotubes, a remarkable enhancement of the electrocatalytic abilities is seen with CO2 becoming selectively reduced to CO (>90 %) at a low overpotential in aqueous medium. This effect is ascribed to the particular environment created by the aqueous medium at the catalytic site of the immobilized catalyst that facilitates the adsorption and further reaction of CO2. This work highlights the significance of assessing an immobilized molecular catalyst from more than homogeneous measurements alone. Heterogeneous vs. homogeneous: When cobalt meso-tetraphenylporphyrin (CoTPP) is immobilized on carbon nanotubes, a remarkably enhanced catalytic activity in CO2 electroreduction is observed, with [CoITPP]− serving as the active species. The simple approach for heterogenization enables facile screening and evaluation of molecular catalysts under heterogeneous conditions.
Datum: 03.05.2017


An Organic Semiconductor Organized into 3D DNA Arrays by “Bottom-up” Rational Design

A 3D array of organic semiconductors was assembled using a DNA scaffold. An octameric aniline molecule (“octaniline”) was incorporated into a DNA building block based on a dimeric tensegrity triangle. The construct self-assembled to form a 3D crystal. Reversible redox conversion between the pernigraniline and leucoemeraldine states of the octaniline is retained in the crystal. Protonic doping gave emeraldine salt at pH 5, corresponding to the conductive form of polyaniline. Redox cycling within the crystal was visualized by color changes and Raman microscopy. The ease of conversion between the octaniline states suggests that it is a viable electronic switch within a unique 3D structure. Foresee and see: Three decades after the prediction, molecules of an organic semiconductor (octaniline) were templated by a DNA nanostructure and self-assembled into a macroscopic crystal by rational design (see picture). The oxidation and conducting states of octaniline are readily controlled inside of the crystal and visualized by the corresponding color changes.
Datum: 03.05.2017


Enhanced Electrocatalytic Oxygen Evolution in Au–Fe Nanoalloys

Oxygen evolution reaction (OER) is the most critical step in water splitting, still limiting the development of efficient alkaline water electrolyzers. Here we investigate the OER activity of Au–Fe nanoalloys obtained by laser-ablation synthesis in solution. This method allows a high amount of iron (up to 11 at %) to be incorporated into the gold lattice, which is not possible in Au–Fe alloys synthesized by other routes, due to thermodynamic constraints. The Au0.89Fe0.11 nanoalloys exhibit strongly enhanced OER in comparison to the individual pure metal nanoparticles, lowering the onset of OER and increasing up to 20 times the current density in alkaline aqueous solutions. Such a remarkable electrocatalytic activity is associated to nanoalloying, as demonstrated by comparative examples with physical mixtures of gold and iron nanoparticles. These results open attractive scenarios to the use of kinetically stable nanoalloys for catalysis and energy conversion. Splitting water: Au–Fe nanoparticles synthesized by laser ablation in solution exhibit enhanced activity in the oxygen evolution reaction (see diagram). The results open exciting perspectives for using nanoalloys in catalysis and energy conversion.
Datum: 02.05.2017


Pressure-Induced Polymerization of Acetylene: Structure-Directed Stereoselectivity and a Possible Route to Graphane

Geometric isomerism in polyacetylene is a basic concept in chemistry textbooks. Polymerization to cis-isomer is kinetically preferred at low temperature, not only in the classic catalytic reaction in solution but also, unexpectedly, in the crystalline phase when it is driven by external pressure without a catalyst. Until now, no perfect reaction route has been proposed for this pressure-induced polymerization. Using in situ neutron diffraction and meta-dynamic simulation, we discovered that under high pressure, acetylene molecules react along a specific crystallographic direction that is perpendicular to those previously proposed. Following this route produces a pure cis-isomer and more surprisingly, predicts that graphane is the final product. Experimentally, polycyclic polymers with a layered structure were identified in the recovered product by solid-state nuclear magnetic resonance and neutron pair distribution functions, which indicates the possibility of synthesizing graphane under high pressure. From acetylene to graphane: By using neutron diffraction and theoretical calculations the domination of cis-polyacetylene in the pressure-induced polymerization of C2H2 is explained. Graphane is predicted as the final product and a layered polycyclic polymer was identified experimentally as an intermediate between polyacetylene and graphane.
Datum: 02.05.2017


Manganese(I)-Catalyzed Regioselective C−H Allenylation: Direct Access to 2-Allenylindoles

A MnI-catalyzed regioselective C−H allenylation is reported that allows a broad range of 2-allenylindoles to be synthesized regioselectively on a gram scale under simple conditions. Notably, a highly efficient chirality transfer was observed (up to 93 % ee) in this transformation. This procedure was further found to allow, for the first time, the direct preparation of ketones by MnI-catalyzed C−H activation. Mechanistic investigations revealed that the precoordination of the oxygen atom to the manganese center as well as the congested tertiary carbon atom in the propargylic carbonates play a crucial role. Magic manganese! The title reaction allows simple access to a broad range of 2-allenylindoles with efficient chirality transfer, and for the first time also allows the direct preparation of ketones by MnI-catalyzed C−H activation. The coordination of the carbonate oxygen atom to the Mn catalyst and the congested tertiary carbon atom play crucial roles in the reaction mechanism.
Datum: 02.05.2017


Fullerene C70 as a Nanoflask that Reveals the Chemical Reactivity of Atomic Nitrogen

To investigate the intrinsic reactivity of atomic nitrogen, which had previously been accomplished only by examining its decay in the gas phase using special equipment, a nitrogen atom was inserted into a series of molecule-encapsulating C60 and C70 fullerenes. Among the studied endofullerenes, H2@C70 was able to encapsulate an additional nitrogen atom within the fullerene cage under radiofrequency plasma conditions. The product was analyzed by ESR spectroscopy and mass spectrometry in solution, which revealed that the nitrogen atom with a quartet ground state does not react but weakly interact with the H2 molecule, thus demonstrating the utility of such fullerenes as “nanoflasks”. A weak interaction: Atomic nitrogen was encapsulated in a series of molecule-encapsulating endohedral C60 and C70 fullerenes in order to investigate the intrinsic reactivity of the N atom. Among the studied endofullerenes, H2@C70 accommodated an additional N atom within its fullerene cage under radiofrequency plasma conditions. The obtained product was analyzed by ESR spectroscopy and mass spectrometry in solution.
Datum: 02.05.2017


Structure-Selective Cation Exchange in the Synthesis of Zincblende MnS and CoS Nanocrystals

The ability to selectively form one crystal structure among several options in a polymorphic system is an important goal in solid-state synthesis. Nanocrystal cation exchange, which proceeds rapidly under mild conditions, can retain key structural features and yield otherwise inaccessible phases, but the extent to which crystal structure can be retained and therefore selectively targeted during such reactions has been limited. Here, we show that nanocrystals of digenite Cu2−xS transform to zincblende MnS and CoS upon cation exchange. Zincblende MnS and CoS, which are metastable in bulk, retain both the tetrahedral cation coordination and cubic close packed anion sublattice of digenite Cu2−xS. Comparison with wurtzite MnS and CoS, which have been accessed previously through analogous cation exchange of roxbyite Cu2−xS, demonstrates the selective formation of the related zincblende vs. wurtzite polymorphs by cation exchange of structurally distinct templates. This structure, not that one! The anion and cation sublattices of digenite Cu2−xS nanocrystals are retained upon cation exchange to form zincblende MnS and CoS, which are metastable compounds in bulk. Using this synthesis pathway, multiple phases in the same system can now be accessed selectively and rationally.
Datum: 02.05.2017


Enhancing Light Absorption and Charge Transfer Efficiency in Carbon Dots through Graphitization and Core Nitrogen Doping

Single-source precursor syntheses have been devised for the preparation of structurally similar graphitic carbon dots (CDs), with (g-N-CD) and without (g-CD) core nitrogen doping for artificial photosynthesis. An order of magnitude improvement has been realized in the rate of solar (AM1.5G) H2 evolution using g-N-CD (7950 μmolH2 (gCD)−1 h−1) compared to undoped CDs. All graphitized CDs show significantly enhanced light absorption compared to amorphous CDs (a-CD) yet undoped g-CD display limited photosensitizer ability due to low extraction of photogenerated charges. Transient absorption spectroscopy showed that nitrogen doping in g-N-CD increases the efficiency of hole scavenging by the electron donor and thereby significantly extends the lifetime of the photogenerated electrons. Thus, nitrogen doping allows the high absorption coefficient of graphitic CDs to be translated into high charge extraction for efficient photocatalysis. Carbon dots are investigated for solar H2 production and a number of critical structure–activity relationships are determined for the first time. Nitrogen-doping of the core structure is established as a strategy to enhance charge-transfer reactions in graphitic carbons dots, which also demonstrate strong light absorption.
Datum: 02.05.2017


Intramolecular Cross-Linking: Addressing Mechanochemistry with a Bioinspired Approach

Many of the attractive properties in polymers are a consequence of their high molecular weight and therefore, scission of chains due to mechanochemistry leads to deterioration in properties and performance. Intramolecular cross-links are systematically added to linear chains, slowing down mechanochemical degradation to the point where the chains become virtually invincible to shear in solution. Our approach mimics the immunoglobulin-like domains of Titin, whose structure directs mechanical force towards the scission of sacrificial intramolecular hydrogen bonds, absorbing mechanical energy while unfolding. The kinetics of the mechanochemical reactions supports this hypothesis, as the polymer properties are maintained while high rates of mechanochemistry are observed. Our results demonstrate that polymers with intramolecular cross-links can be used to make solutions which, even under severe shear, maintain key properties such as viscosity. Unbreakable polymers: Random covalent intramolecular cross-links in single-chain polymer nanoparticles break preferably during ultrasonication, making the polymers resistant to mechanochemistry in solution. Above a certain cross-link density, the nanoparticles become virtually invincible to shear in solution.
Datum: 02.05.2017


Preparation of Waterproof Organometal Halide Perovskite Photonic Crystal Beads

Herein, we report on an innovative method for the preparation of a series of organometal halide perovskite (OHP) photonic crystal beads with pronounced and tunable photonic stop bands by using self-assembled polystyrene spheres as a mold. After infiltration of the mold with OHP precursor solution and slow drying, the OHPs crystallized in the voids of the polystyrene arrays. By controlling the diameter of the polystyrene spheres, the photonic stop band of the OHPs could be precisely tuned. The overlap between the photonic stop band of the beads and the band gap of the OHPs enhances the light harvesting of the perovskite because of the slow photon effect, which arises from the photonic crystal beads. Moreover, the stability of the composite was greatly enhanced by coating with the transparent polymer PDMS without blocking the light propagation. The coated OHP photonic beads kept their composition even after having been in contact with water for 24 h. Waterproof organometal halide perovskite/photonic crystal bead composites were prepared. The band gap of the halide perovskite and the stop band of the photonic crystal beads can be tuned to overlap with each other, which is promising for enhancing the light harvesting under visible-light irradiation through the slow photon effect. The composite was very stable in water after coating with PDMS.
Datum: 02.05.2017


Switchable Site-Selective Catalytic Carboxylation of Allylic Alcohols with CO2

A switchable site-selective catalytic carboxylation of allylic alcohols has been developed in which CO2 is used with dual roles, both facilitating C−OH cleavage and as a C1 source. This protocol is characterized by its mild reaction conditions, absence of stoichiometric amounts of organometallic reagents, broad scope, and exquisite regiodivergency which can be modulated by the type of ligand employed. Double agent: In the title reaction, CO2 serves as both a facilitator for the C−OH cleavage and as a C1 source. This reaction is the first example of a cross-electrophile coupling of unprotected alcohols in the absence of stoichiometric amounts of organometallic species. The procedure has broad scope and an exquisite regiodivergency which can be modulated by the ligand-type employed.
Datum: 02.05.2017


Palladium-Catalyzed Regioselective Synthesis of 3-Arylindoles from N-Ts-Anilines and Styrenes

A Pd-catalyzed intermolecular oxidative annulation between N-Ts-anilines and styrenes was developed. This method offers a straightforward and robust approach to a wide range of 3-arylindoles using readily available starting materials with good functional-group tolerance and high regioselectivity and efficiency. Further elaboration of the products obtained from this process provided access to highly functionalized and structurally diverse indoles, for example, 3-(indol-3-yl)carbazoles, 1,9-dihydropyrrolo-[2,3-b]carbazoles, and 3′-aryl-3,5′-biindoles. Hello from the other side: A Pd-catalyzed intermolecular oxidative annulation for one-pot C−C/C−N bond formation was developed. In contrast to the opposite regioselectivity pattern of related methods, this method offers facile access to the synthetically valuable 3-arylindoles, which were previously inaccessible from styrenes and anilines, with high efficiency and excellent regioselectivity.
Datum: 02.05.2017


Tyrosine or Tryptophan? Modifying a Metalloradical Catalytic Site by Removal of the Cys–Tyr Cross-Link in the Galactose 6-Oxidase Homologue GlxA

The concerted redox action of a metal ion and an organic cofactor is a unique way to maximize the catalytic power of an enzyme. An example of such synergy is the fungal galactose 6-oxidase, which has inspired the creation of biomimetic copper oxidation catalysts. Galactose 6-oxidase and its bacterial homologue, GlxA, possess a metalloradical catalytic site that contains a free radical on a covalently linked Cys–Tyr and a copper atom. Such a catalytic site enables for the two-electron oxidation of alcohols to aldehydes. When the ability to form the Cys–Tyr in GlxA is disrupted, a radical can still be formed. Surprisingly, the radical species is not the Tyr residue but rather a copper second-coordination sphere Trp residue. This is demonstrated through the introduction of a new algorithm for Trp-radical EPR spectra simulation. Our findings suggest a new mechanism of free-radical transfer between aromatic residues and that the Cys–Tyr cross-link prevents radical migration away from the catalytic site. Breaking the bond is still radical: Copper radical oxidases contain an unusual Cys–Tyr redox cofactor capable of housing a stable protein radical required for their catalytic activity. Breaking the Cys–Tyr bond still yields a radical, surprisingly not on the Tyr but on the π-stacking Trp residue.
Datum: 02.05.2017


The Effect of Surface Site Ensembles on the Activity and Selectivity of Ethanol Electrooxidation by Octahedral PtNiRh Nanoparticles

Direct ethanol fuel cells are attractive power sources based on a biorenewable, high energy-density fuel. Their efficiency is limited by the lack of active anode materials which catalyze the breaking of the C−C bond coupled to the 12-electron oxidation to CO2. We report shape-controlled PtNiRh octahedral ethanol oxidation electrocatalysts with excellent activity and previously unachieved low onset potentials as low as 0.1 V vs. RHE, while being highly selective to complete oxidation to CO2. Our comprehensive characterization and in situ electrochemical ATR studies suggest that the formation of a ternary surface site ensemble around the octahedral Pt3Ni1Rhx nanoparticles plays a crucial mechanistic role for this behavior. It's the shape, that matters: The efficient and complete electrooxidation of ethanol at low overpotentials has been a prime research target for a long time. The unique combination of a ternary Pt-Ni-Rh ensemble on defined octahedral {111} facets now shows promising activity coupled with good selectivity in this transformation.
Datum: 28.04.2017


Lead-free Perovskite Materials (NH4)3Sb2IxBr9−x

A family of perovskite light absorbers (NH4)3Sb2IxBr9−x (0≤x≤9) was prepared. These materials show good solubility in ethanol, a low-cost, hypotoxic, and environmentally friendly solvent. The light absorption of (NH4)3Sb2IxBr9−x films can be tuned by adjusting I and Br content. The absorption onset for (NH4)3Sb2IxBr9−x films changes from 558 nm to 453 nm as x changes from 9 to 0. (NH4)3Sb2I9 single crystals were prepared, exhibiting a hole mobility of 4.8 cm2 V−1 s−1 and an electron mobility of 12.3 cm2 V−1 s−1. (NH4)3Sb2I9 solar cells gave an open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %. Unleaded: Lead-free perovskite materials (NH4)3Sb2IxBr9−x (0≤x≤9) were developed by using ethanol as the solvent. (NH4)3Sb2I9 single crystals were prepared and the crystal structure was analyzed. Solar cells were made by using (NH4)3Sb2IxBr9−x as the light absorbers. (NH4)3Sb2I9 solar cells gave a high open-circuit voltage of 1.03 V and a power conversion efficiency of 0.51 %.
Datum: 28.04.2017


Crack-Free, Soft Wrinkles Enable Switchable Anisotropic Wetting

Soft skin layers on elastomeric substrates are demonstrated to support mechano-responsive wrinkle patterns that do not exhibit cracking under applied strain. Soft fluoropolymer skin layers on pre-strained poly(dimethylsiloxane) slabs achieved crack-free surface wrinkling at high strain regimes not possible by using conventional stiff skin layers. A side-by-side comparison between the soft and hard skin layers after multiple cycles of stretching and releasing revealed that the soft skin layer enabled dynamic control over wrinkle topography without cracks or delamination. We systematically characterized the evolution of wrinkle wavelength, amplitude, and orientation as a function of tensile strain to resolve the crack-free structural transformation. We demonstrated that wrinkled surfaces can guide water spreading along wrinkle orientation, and hence switchable, anisotropic wetting was realized. Wrinkles without the worry: Soft fluoropolymer skin layers on elastomer substrates produced wrinkles that could undergo numerous stretch-and-release cycles without delamination or formation of cracks. A side-by-side comparison with conventional hard skin layers highlighted the integrity and robustness of wrinkles in a soft skin layer as well as their unique properties such as switchable anisotropic water spreading.
Datum: 28.04.2017


Gerd Becker (1940–2017)


Datum: 28.04.2017


Reversible Supracolloidal Self-Assembly of Cobalt Nanoparticles to Hollow Capsids and Their Superstructures

The synthesis and spontaneous, reversible supracolloidal hydrogen bond-driven self-assembly of cobalt nanoparticles (CoNPs) into hollow shell-like capsids and their directed assembly to higher order superstructures is presented. CoNPs and capsids form in one step upon mixing dicobalt octacarbonyl (Co2CO8) and p-aminobenzoic acid (pABA) in 1,2-dichlorobenzene using heating-up synthesis without additional catalysts or stabilizers. This leads to pABA capped CoNPs (core ca. 5 nm) with a narrow size distribution. They spontaneously assemble into tunable spherical capsids (d≈50–200 nm) with a few-layered shells, as driven by inter-nanoparticle hydrogen bonds thus warranting supracolloidal self-assembly. The capsids can be reversibly disassembled and reassembled by controlling the hydrogen bonds upon heating or solvent exchanges. The superparamagnetic nature of CoNPs allows magnetic-field-directed self-assembly of capsids to capsid chains due to an interplay of induced dipoles and inter-capsid hydrogen bonds. Finally, self-assembly on air–water interface furnishes lightweight colloidal framework films. Chain of CoNP capsids: In situ, template-free, and reversible supracolloidal self-assembly of superparamagnetic cobalt nanoparticles to hollow spherical capsids and their directed assembly to higher order superstructures is reported.
Datum: 28.04.2017


The Structure of the Elusive Simplest Dipeptide Gly-Gly

Among the hundreds of peptide compounds for which conformations have been determined by using different spectroscopic techniques, the structure of the simplest dipeptide glycylglycine (Gly-Gly) is conspicuously absent. Herein, for the first time, solid samples of Gly-Gly have been vaporized by laser ablation and three different structures have been revealed in a supersonic expansion by Fourier transform microwave spectroscopy. The intramolecular hydrogen bonding interactions that stabilize the observed forms have been established based on the 14N nuclear quadrupole hyperfine structure. We have illustrated how conformer interconversion distorts the equilibrium conformational distribution, giving rise to missing conformers in the conformational landscape. Exposed! Structural secrets of Gly-Gly: The conformational landscape of the simplest dipeptide glycylglycine (Gly-Gly) has been unveiled for the first time by laser ablation coupled with Fourier transform microwave spectroscopy. The three identified conformers, along with those not observed because of conformer interconversion, provide the first global structural picture of Gly-Gly, which is, to some extent, dynamic.
Datum: 28.04.2017


Biosynthesis of the β-Lactone Proteasome Inhibitors Belactosin and Cystargolide

Belactosins and cystargolides are natural product proteasome inhibitors from Actinobacteria. Both feature dipeptidic backbones and a unique β-lactone building block. Herein, we present a detailed investigation of their biosynthesis. Identification and analysis of the corresponding gene clusters indicated that both compounds are assembled by rare single-enzyme amino acid ligases. Feeding experiments with isotope-labeled precursors and in vitro biochemistry showed that the formation of the β-lactone warhead is unprecedented and reminiscent of leucine biosynthesis, and that it involves the action of isopropylmalate synthase homologues. Lactone synthesis: The biosynthesis of belactosins and cystargolides, which are peptidic β-lactone proteasome inhibitors, follows an NRPS- and PKS-independent pathway. The distinct β-lactone moiety is assembled by isopropylmalate synthase like enzymes in a process that is reminiscent of leucine metabolism. The formation of the peptidic backbones is directed by discrete amino acid ligases.
Datum: 28.04.2017


Partial Reduction and Selective Transfer of Hydrogen Chloride on Catalytic Gold Nanoparticles

HCl in solution accepts electron density from Au NPs and partially reduces at room temperature, as occurs with other simple diatomic molecules, such as O2 and H2. The activation can be run catalytically in the presence of alkynes to give exclusively E-vinyl chlorides, after the regio- and stereoselective transfer of HCl. Based also on this method, vinyl chloride monomer (VCM) can be produced in a milder and greener way than current industrial processes. A helping hand from gold: Hydrogen chloride is partially reduced by supported gold nanoparticles at room temperature. It is catalytically added to alkynes to give, regio- and stereoselectively, E-α-vinyl chlorides. This approach enabled the synthesis of vinyl chloride monomer from acetylene in continuous mode.
Datum: 28.04.2017


Direct Experimental Evidence for Halogen–Aryl π Interactions in Solution from Molecular Torsion Balances

We dissected halogen–aryl π interactions experimentally using a bicyclic N-arylimide based molecular torsion balances system, which is based on the influence of the non-bonded interaction on the equilibria between folded and unfolded states. Through comparison of balances modulated by higher halogens with fluorine balances, we determined the magnitude of the halogen–aryl π interactions in our unimolecular systems to be larger than −5.0 kJ mol−1, which is comparable with the magnitude estimated in the biomolecular systems. Our study provides direct experimental evidence of halogen–aryl π interactions in solution, which until now have only been revealed in the solid state and evaluated theoretically by quantum-mechanical calculations. Weighty evidence: Molecular torsion balances containing an N-aryl imide and an additional aromatic moiety provided direct experimental evidence for halogen–aryl π interactions in solution (see picture). The magnitude of the halogen–aryl π interactions in the unimolecular systems described herein are found to be larger than −5.0 kJ mol−1.
Datum: 28.04.2017


Inside Cover: Solvent-Assisted Metal Metathesis: A Highly Efficient and Versatile Route towards Synthetically Demanding Chromium Metal–Organic Frameworks (Angew. Chem. Int. Ed. 23/2017)

Owing to their extraordinary robustness and high porosity, chromium(III)-based metal–organic frameworks (Cr-MOFs) have great potential, but they are currently difficult to synthesize. In their Communication on page 6478 ff., J. H. Wang, X. M. Zhang et al. describe the preparation of a variety of Cr-MOFs from the corresponding Fe-MOFs under mild conditions by solvent-assisted metal metathesis. This efficient and versatile strategy constitutes a promising route for the synthesis of stable MOFs.
Datum: 28.04.2017


Amide-Directed C−H Sodiation by a Sodium Hydride/Iodide Composite

A new protocol for amide-directed ortho and lateral C−H sodiation is enabled by sodium hydride (NaH) in the presence of either sodium iodide (NaI) or lithium iodide (LiI). The transient organosodium intermediates could be transformed into functionalized aromatic compounds. New direction: An amide-directed ortho and lateral C−H sodiation is enabled by sodium hydride (NaH) in the presence of either sodium iodide (NaI) or lithium iodide (LiI). The transient organosodium intermediates could be transformed into functionalized aromatic compounds.
Datum: 27.04.2017


Anaerobic Respiration on Self-Doped Conjugated Polyelectrolytes: Impact of Chemical Structure

We probe anaerobic respiration of bacteria in the presence of conjugated polyelectrolytes (CPEs). Three different CPEs were used to probe how structural variations impact biocurrent generation from Shewanella oneidensis MR-1. For the self-doped anionic CPE only, absorption spectroscopy shows that the addition of S. oneidensis MR-1 leads to the disappearance of the polaron (radical cation) band at >900 nm and an increase in the band at 735 nm due to the neutral species, consistent with electron transfer from microbe to polymer. Microbial three-electrode electrochemical cells (M3Cs) show an increase in the current generated by S. oneidensis MR-1 with addition of the self-doped CPE relative to other CPEs and controls. These experiments combined with in situ cyclic voltammetry suggest that the doped CPE facilitates electron transport to electrodes and reveal structure–function relationships relevant to developing materials for biotic/abiotic interfaces. Building better bioelectrodes: Abiotic–biotic interfacial contact resistance remains a limiting feature in the performance of bioelectronic devices. Anionic self-doped conjugated polyelectrolytes improve bioelectricity generation from anode-respiring Shewanella oneidensis MR-1 by acting as a conductive extension of the electrode and increasing colonization.
Datum: 26.04.2017


Vesicle Origami: Cuboid Phospholipid Vesicles Formed by Template-Free Self-Assembly

Phospholipid liposomes are archetypical self-assembled structures. To minimize the surface tension, the vesicles typically are spherical. Deciphering the bilayer code, the basic physical interactions between phospholipids would allow these molecules to be utilized as building blocks for novel, non-spherical structures. A 1,2-diamidophospholipid is presented that self-assembles into a cuboid structure. Owing to intermolecular hydrogen bonding, the bilayer membranes form an exceptionally tight subgel packing, leading to a maximization of flat structural elements and a minimization of any edges. These conditions are optimized in the geometrical structure of a cube. Surprisingly, the lateral surface pressure in the membrane is only one third of the value typically assumed for a bilayer membrane, questioning a long-standing rule-of-thumb. Cuboid vesicles: A 1,2-diamidophospholipid is presented that self-assembles into the first non-template phospholipid cube. Owing to intermolecular hydrogen bonding, the bilayer membranes form an exceptionally tight subgel packing, leading to a maximization of flat structural elements and a minimization of any edges. These conditions are optimized in the geometrical structure of a cube.
Datum: 26.04.2017


Synthetic Biology—The Synthesis of Biology

Synthetic biology concerns the engineering of man-made living biomachines from standardized components that can perform predefined functions in a (self-)controlled manner. Different research strategies and interdisciplinary efforts are pursued to implement engineering principles to biology. The “top-down” strategy exploits nature's incredible diversity of existing, natural parts to construct synthetic compositions of genetic, metabolic, or signaling networks with predictable and controllable properties. This mainly application-driven approach results in living factories that produce drugs, biofuels, biomaterials, and fine chemicals, and results in living pills that are based on engineered cells with the capacity to autonomously detect and treat disease states in vivo. In contrast, the “bottom-up” strategy seeks to be independent of existing living systems by designing biological systems from scratch and synthesizing artificial biological entities not found in nature. This more knowledge-driven approach investigates the reconstruction of minimal biological systems that are capable of performing basic biological phenomena, such as self-organization, self-replication, and self-sustainability. Moreover, the syntheses of artificial biological units, such as synthetic nucleotides or amino acids, and their implementation into polymers inside living cells currently set the boundaries between natural and artificial biological systems. In particular, the in vitro design, synthesis, and transfer of complete genomes into host cells point to the future of synthetic biology: the creation of designer cells with tailored desirable properties for biomedicine and biotechnology. Exciting times for synthetic biology: Cells are being engineered to produce drugs and biofuels, entire genomes are being synthesized from scratch, proteins and DNA molecules are being equipped with unnatural functions, and recent progress in genome engineering promises to revolutionize biomedicine and biotechnology. This Review gives a comprehensive overview of different research areas in synthetic biology.
Datum: 25.04.2017


Transition-Metal-Catalyzed Utilization of Methanol as a C1 Source in Organic Synthesis

Methanol is used as a common solvent, cost-effective reagent, and sustainable feedstock for value-added chemicals, pharmaceuticals, and materials. Among the various applications, the utilization of methanol as a C1 source for the formation of carbon–carbon, carbon–nitrogen, and carbon–oxygen bonds continues to be important in organic synthesis and drug discovery. In particular, the synthesis of C-, N-, and O-methylated products is of central interest because these motifs are found in a large number of natural products as well as fine and bulk chemicals. In this Minireview, we summarize the utilization of methanol as a C1 source in methylation, methoxylation, formylation, methoxycarbonylation, and oxidative methyl ester formation reactions. Sustainable C1 source: Methanol serves as a sustainable feedstock for value-added chemicals, materials, and life science molecules. It has also been used as a C1 source in methylation, methoxylation, formylation, methoxycarbonylation, and oxidative methyl ester formation reactions for the synthesis of C-methylated products, N-methylamines, formamides, urea derivatives, ethers, esters, and heterocycles.
Datum: 25.04.2017


Mo2B4O9—Connecting Borate and Metal-Cluster Chemistry

We report on the first thoroughly characterized molybdenum borate, which was synthesized in a high-pressure/high-temperature experiment at 12.3 GPa/1300 °C using a Walker-type multianvil apparatus. Mo2B4O9 incorporates tetrahedral molybdenum clusters into an anionic borate crystal structure—a structural motif that has never been observed before in the wide field of borate crystal chemistry. The six bonding molecular orbitals of the [Mo4] tetrahedron are completely filled with 12 electrons, which are fully delocalized over the four molybdenum atoms. This finding is in agreement with the results of the magnetic measurements, which confirmed the diamagnetic character of Mo2B4O9. The two four-coordinated boron sites can be differentiated in the 11B MAS-NMR spectrum because of the strongly different degrees of local distortions. Experimentally obtained IR and Raman bands were assigned to vibrational modes based on DFT calculations. Come together: In the field of borate crystal chemistry, Mo2B4O9 is the first compound incorporating transition-metal clusters into its crystal structure. The tetrahedral molybdenum clusters and the face-capping oxygen atoms form heterocubane-like [Mo4O4] units. The reduction of a reagent in a high-pressure experiment enabled the combination of two hitherto separated fields of research and revealed an approach to this novel substance class.
Datum: 21.04.2017


Hydronium Ion Batteries: A Sustainable Energy Storage Solution

Hydronium ions have been reversibly stored for the first time in an electrode of crystalline 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). A highly reversible discharge–charge behavior of PTCDA was observed in an aqueous acidic electrolyte of 1 m H2SO4. The capacity and the operation potentials are comparable to that of Na-ion storage in the same electrode.
Datum: 18.04.2017


Oxidative Cross-Coupling Reactions. By Aiwen Lei, Wei Shi, Chao Liu, Wei Liu, Hua Zhang and Chuan He.

Wiley-VCH, Weinheim, 2016. 229 pp., hardcover, € 129.00.—ISBN 978-3527336883
Datum: 18.04.2017


Fluorophores for Excited-State Intramolecular Proton Transfer by an Yttrium Triflate Catalyzed Reaction of Isocyanides with Thiocarboxylic Acids

Discovery of new chemical reactivity of a given functional group can often result in innovative synthesis of important chemical entities that possess unprecedented properties. We designed and developed a one-step synthesis of 5-amino-4-carboxamidothiazoles 1 by an yttrium-triflate-catalyzed reaction of thiocarboxylic acids 2 with isocyanides 3. In this reaction, both reactants 2 and 3 deviated from their normal reactivities because of metal coordination. The resulting heterocycles are novel prototypical structures for the double ESIPT process. Some of them were excited by visible light irradiation and emitted fluorescence at the NIR region with large Stokes shift, high quantum yield, and strong solvatochromism. Colorful reactivity: The reaction of thiocarboxylic acids with isocyanides in the presence of a catalytic amount of yttrium triflate afforded 5-amino-4-carboxamidothiazoles in good to excellent yields. Some of these heterocycles were excited by visible light and emitted fluorescence in the near-infrared region with large Stokes shift, high quantum yield, and strong positive solvatochromism.
Datum: 13.04.2017


Synthesis and Bowl-in-Bowl Assembly of a Geodesic Phenylene Bowl

A phenylene multiring with a corannulenoidal skeleton was synthesized. Geodesic constraints over 20 phenylene panels resulted in its nanometer-sized, bowl-shaped molecular structure, which was unequivocally revealed by crystallographic analysis. The crystal structure also showed the presence of a bowl-in-bowl dimeric assembly, which was driven by entropic factors in solution. Shape sorting: Geodesic constraints arising from the coupling of trigonal planar phenylenes into a pentagon surrounded by five hexagons resulted in a nanometer-sized bowl-shaped molecule. Concave–convex molecular recognition resulted in the molecules assembling in a bowl-in-bowl fashion. The shape recognition was driven by an entropy gain for the assembly of the large 120 π-systems.
Datum: 12.04.2017


On-Chip Microsupercapacitors Based on Coordination Polymer Frameworks for Alternating Current Line-Filtering

AC line-filtering on-chip micro-supercapacitors (MSCs) based on coordination polymer frameworks were fabricated by a facile layer-by-layer method. The reported on-chip MSCs showed a low impedance phase angle of −73° at 120 Hz and a high power density of up to 1323 W cm−3 with a low relaxation time constant of 0.27 ms.
Datum: 11.04.2017


Solvent-Assisted Metal Metathesis: A Highly Efficient and Versatile Route towards Synthetically Demanding Chromium Metal–Organic Frameworks

Chromium(III)-based metal–organic frameworks (Cr-MOFs) are very attractive in a wide range of investigations because of their robustness and high porosity. However, reports on Cr-MOFs are scarce owing to the difficulties in their direct synthesis. Recently developed postsynthetic routes to obtain Cr-MOFs suffered from complicated procedures and a lack of general applicability. Herein, we report a highly efficient and versatile strategy, namely solvent-assisted metal metathesis, to obtain Cr-MOFs from a variety of FeIII-MOFs, including several well-known MOFs and a newly synthesized one, through judicious selection of a coordinating solvent. The versatility of this strategy was demonstrated by producing Cr-MIL-100, Cr-MIL-142A/C, Cr-PCN-333, and Cr-PCN-600 from their FeIII analogues and Cr-SXU-1 from a newly synthesized MOF precursor, Fe-SXU-1, in acetone as the solvent under very mild conditions. We have thus developed a general approach for the preparation of robust Cr-MOFs, which are difficult to synthesize by direct methods. Chromium exchange: An efficient and versatile strategy for the synthesis of chromium(III)-based metal–organic frameworks (Cr-MOFs) from a variety of FeIII-MOFs has been developed based on solvent-assisted metal metathesis. These transformations proceeded in a judiciously chosen coordinating solvent (acetone) under very mild conditions.
Datum: 04.04.2017


Makoto Yamashita

“I lose track of time when I am solving crystal structures. The most important thing I learned from my parents is optimism ...” This and more about Makoto Yamashita can be found on page 6372.
Datum: 16.11.2016






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