Angewandte Chemie International Edition

Current research reports and chronological list of recent articles.


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

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

 - Chemical Communications, ChemComm,

 - Chemical Monthly,

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 - Chemistry Central Journal,

 - Chemistry Letters,

 - Journal of the American Chemical Society,

 - Nature Chemistry.



Angewandte Chemie International Edition - Abstracts



Catalytic Asymmetric Synthesis of Trifluoromethylated γ-Amino Acids via Umpolung Addition of Trifluoromethyl Imines to Carboxylic Acid Derivatives

Enabled by the discovery of novel cinchona alkaloid-derived chiral phase-transfer catalysts, highly chemo-, regio-, diastereo- and enantioselective umpolung additions of trifluoromethyl imines to α, β-unsaturated N-acylpyrroles were realized. With a catalyst loading ranging from 0.2 to 5.0 mol%, this new catalytic asymmetric transformation provides facile and high-yield access to highly enantiomerically enriched chiral trifluoromethylated γ-amino acids and γ-lactams.
Datum: 12.12.2017


Electron-Precise Actinide-Pnictide (An-Pn) Bonds Spanning Non-Metal, Metalloid, and Metal Combinations (An = U, Th; Pn = P, As, Sb, Bi)

We report the synthesis and characterisation of the compounds [An(TrenDMBS){Pn(SiMe3)2}] and [An(TrenTIPS){Pn(SiMe3)2}] [TrenDMBS = N(CH2CH2NSiMe2But)3, An = U, Pn = P, As, Sb, Bi; An = Th, Pn = P, As; TrenTIPS = N(CH2CH2NSiPri3)3, An = U, Pn = P, As, Sb; An = Th, Pn = P, As, Sb]. The U-Sb and Th-Sb moieties are unprecedented examples of any kind of An-Sb molecular bond, and the U-Bi bond is the first electron-precise one. The Th-Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U-Bi complex is the heaviest electron-precise pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An-An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U-Pn bonds degrade by hemolytic bond cleavage, whereas the more redox robust thorium compounds engage in an acid-base/dehydrocoupling route.
Datum: 12.12.2017


Encapsulation of Homogeneous Catalysts in Mesoporous Materials Using Diffusion-Limited Atomic Layer Deposition

The heterogenization of homogeneous metal complex catalysts has attracted great attention. Herein, we report the encapsulation of metal complexes into nanochannels of mesoporous materials by coating metal oxides at/near the pore entrance via diffusion-limited atomic layer deposition (ALD) to produce a "hollow plug". The pore size of the hollow plug is precisely controlled on the sub-nanometer scale by the number of ALD cycles to fit various metal complexes with different molecular sizes. Typically, Co or Ti complexes are successfully encapsulated into the nanochannels of SBA-15, SBA-16 and MCM-41. The encapsulated Co and Ti catalysts show excellent catalytic activity and reusability in the hydrolytic kinetic resolution of epoxides and asymmetric cyanosilylation of carbonyl compounds, respectively. This ALD-assisted encapsulation method can be extended to the encapsulation of other homogeneous catalysts into different mesoporous materials for various heterogeneous reactions.
Datum: 12.12.2017


CO2 to terpenes - autotrophic and electroautotrophic α-humulene production with Cupriavidus necator

Herein, we demonstrate that CO2 can be converted by an engineered "Knallgas" bacterium (Cupriavidus necator) to the terpene α-humulene. Heterologous expression of the mevalonate pathway and α-humulene synthase resulted in a production of approx. 10 mg α-humulene per gram cell dry mass (CDM) under heterotrophic conditions. This first example of chemolithoautotrophic production of a terpene from carbon dioxide, hydrogen and oxygen is a promising starting point for the production of different high value terpene compounds from abundant and simple raw materials. Furthermore, the production system was used to produce 17 mg α-humulene per gram CDM from CO2 and electrical energy in microbial electrosynthesis (MES) mode. Due to the fact that the system can convert CO2 by using electrical energy from solar energy it opens a new route to artificial photosynthetic systems.
Datum: 12.12.2017


pH resistant monodispersed polymer-lipid nanodiscs

Polymer lipid nanodiscs have provided an invaluable system for structural and functional studies of membrane proteins in their near-native environment. In spite of the recent advances in the development and usage of polymer lipid nanodisc systems, lack of control over size and poor tolerance to pH and divalent metal ions are major limitations for further applications. Here we report a facile modification of a low molecular weight styrene maleic acid copolymer to form monodispersed lipid bilayer nanodiscs that show ultra-stability towards a pH range of 2.5 to 10 and divalent metal ion concentration. The macro-nanodiscs (>20 nm diameter) show magnetic-alignment properties that can be exploited for high-resolution structural studies of membrane proteins using well-established solid-state NMR techniques. As demonstrated in this study, the new polymer, SMA-QA, is a robust membrane mimetic tool that offers significant advantages over currently reported nanodisc systems.
Datum: 12.12.2017


Three-Component Enantioselective Cyclization Reaction Catalyzed by an Unnatural Amino Acid Derivative

A new diastereo- and enantioselective three-component cyclization reaction is described. The reaction takes place between a ketone, a carboxylic acid, and a nitroalkene to yield a bicyclic octahydro-2H-indol-2-one scaffold possessing three chiral centers. This reaction involves a rearrangement of the nitro group under simple thermal conditions. A plausible mechanism is proposed for this new reaction based on DFT calculations and isotope-labeling experiments. A new concise enantioselective synthesis of the alkaloid (+)-pancracine is presented as an example of the potential of this novel organocatalytic cyclization reaction in the synthesis of natural products. Brand new cycle: The unnatural and densely substituted l-proline ester XL catalyzes the formation of bicyclic γ-lactams possessing three new chiral centers. This new reaction has no equivalent in organocatalytic, enzymatic, or organometallic chemistry and can be used in the synthesis of complex natural products.
Datum: 12.12.2017


The Chemical Record Lectureship for Michael Grätzel / Baizer Award for Flavio Maran / And also in the News


Datum: 12.12.2017


A General Synthesis of Porous Carbon Nitride Films with Tunable Surface Area and Photophysical Properties

Graphitic carbon nitride (g-CN) has emerged as a promising material for energy-related applications. However, exploitation of g-CN in practical devices is still limited owing to difficulties in fabricating g-CN films with adjustable properties and high surface area. A general and simple pathway is reported to grow highly porous and large-scale g-CN films with controllable chemical and photophysical properties on various substrates using the doctor blade technique. The growth of g-CN films, ascribed to the formation of a supramolecular paste, comprises g-CN monomers in ethylene glycol, which can be cast on different substrates. The g-CN composition, porosity, and optical properties can be tuned by the design of the supramolecular paste, which upon calcination results in a continuous porous g-CN network. The strength of the porous structure is demonstrated by high electrochemically active surface area, excellent dye adsorption and photoelectrochemical and photodegradation properties. An efficient, easy, and general method for growing highly porous and large-scale carbon nitride (g-CN) networks on various substrates using the doctor blade technique is introduced. The g-CN films have high electrochemical active surface area, excellent dye adsorption, and good photoelectrochemical and photodegradation properties. This method opens opportunities for exploitation of g-CN in electronic and photoelectronic devices.
Datum: 12.12.2017


Ion–Solvent Complexes Promote Gas Evolution from Electrolytes on a Sodium Metal Anode

Lithium and sodium metal batteries are considered as promising next-generation energy storage devices due to their ultrahigh energy densities. The high reactivity of alkali metal toward organic solvents and salts results in side reactions, which further lead to undesirable electrolyte depletion, cell failure, and evolution of flammable gas. Herein, first-principles calculations and in situ optical microscopy are used to study the mechanism of organic electrolyte decomposition and gas evolution on a sodium metal anode. Once complexed with sodium ions, solvent molecules show a reduced LUMO, which facilitates the electrolyte decomposition and gas evolution. Such a general mechanism is also applicable to lithium and other metal anodes. We uncover the critical role of ion–solvent complexation for the stability of alkali metal anodes, reveal the mechanism of electrolyte gassing, and provide a mechanistic guidance to electrolyte and lithium/sodium anode design for safe rechargeable batteries. Safe rechargeable batteries: Ion–solvent complexes in alkali metal batteries have been studied by first-principles calculations and in situ optical microscopy. The ion–solvent complexes have low LUMOs and are readily reduced on an alkali metal anode. A general mechanism for organic electrolyte decomposition and gas evolution was discovered.
Datum: 12.12.2017


A Six-Oxidase Cascade for Tandem C−H Bond Activation Revealed by Reconstitution of Bicyclomycin Biosynthesis

As a commercial antibiotic, bicyclomycin (BCM) is currently the only known natural product targeting the transcription termination factor rho. It belongs to a family of highly functionalized diketopiperazine (DKP) alkaloids and bears a unique O-bridged bicyclo[4.2.2]piperazinedione ring system, a C1 triol, and terminal exo-methylene groups. We have identified and characterized the BCM biosynthetic pathway by heterologous biotransformations, in vitro biochemical assays, and one-pot enzymatic synthesis. A tRNA-dependent cyclodipeptide synthase guides the heterodimerization of leucine and isoleucine to afford the DKP precursor; subsequently, six redox enzymes, including five α-ketoglutarate/Fe2+-dependent dioxygenases and one cytochrome P450 monooxygenase, regio- and stereoselectively install four hydroxy groups (primary, secondary, and two tertiary), an exo-methylene moiety, and a medium-sized bridged ring through the functionalization of eight unactivated C−H bonds. Enzymatic characterization of the biosynthesis of the antibiotic bicyclomycin revealed a tRNA-dependent cyclodipeptide synthase for the heterodimerization of Leu and Ile to afford the diketopiperazine precursor. Subsequently, six redox enzymes activate eight unactivated C−H bonds through regio- and stereoselective hydroxylation, alkenylation, heterocyclization, and desaturation/epoxidation.
Datum: 12.12.2017


Can Coordination-Driven Supramolecular Self-Assembly Reactions Be Conducted from Fully Aliphatic Linkers?

The reaction between a preassembled CuI bimetallic molecular clip with a short intermetallic distance and a series of fully aliphatic cyano-capped ditopic linkers with increasing lengths was investigated. It is shown that, depending on the length of the ditopic linkers, the rational design of unprecedented supramolecular compact metallacycles containing fully aliphatic walls is possible. The specific preorganized molecular arrangement of the molecular clip used favors stabilizing interlinker London dispersion interactions, which allow, as the length of the linkers increases, the selective formation of discrete compact metallacycles at the expense of 1D coordination polymers. The generalizability of this approach was demonstrated by the reaction of fully aliphatic cyano-capped linkers with two other types of preassembled CuI bimetallic molecular clips that also had short intermetallic distances. Give them a sense of direction: Cyano-capped fully aliphatic linkers underwent supramolecular assembly with preorganized CuI dimers with short intermetallic distances to form different types of metallacycles and 1D coordination polymers depending on the length of the linkers (see picture). Stabilizing London dispersion interactions between the methylene units made the selective self-assembly of such linkers with nondirectional backbones possible.
Datum: 12.12.2017


Asymmetric Synthesis of 2H-Azirines with a Tetrasubstituted Stereocenter by Enantioselective Ring Contraction of Isoxazoles

Highly strained 2H-azirines with a tetrasubstituted stereocenter were synthesized by the enantioselective isomerization of isoxazoles with a chiral diene–rhodium catalyst system. The effect of ligands and the coordination behavior support the proposed catalytic cycle in which the coordination site is fixed in favor of efficient enantiodiscrimination by a bulky substituent of the ligand. In silico studies also support the existence of a rhodium–imido complex as a key intermediate for enantiodiscrimination. Coping well under the strain: Highly strained 2H-azirines with tetrasubstituted stereocenters were synthesized with high enantioselectivity by the N−O bond-cleaving isomerization of isoxazoles in the presence of a chiral diene–rhodium catalyst (see scheme). This asymmetric ring contraction of isoxazoles proceeded under mild reaction conditions to give 2-alkoxycarbonyl 2H-azirines with various substituents, including halogen groups.
Datum: 12.12.2017


Distal Weak Coordination of Acetamides in Ruthenium(II)-Catalyzed C−H Activation Processes

C−H activations with challenging arylacetamides were accomplished by versatile ruthenium(II) biscarboxylate catalysis. The distal C−H functionalization offers ample scope—including twofold oxidative C−H functionalizations and alkyne hydroarylations—through facile base-assisted internal electrophilic-type substitution (BIES) C−H ruthenation by weak O-coordination. From a distance: A versatile RuII-catalyzed method permits facile distal C−H activation of weakly O-coordinating arylacetamides via a six-membered ruthenacycle intermediate. The scope of the reaction includes primary, secondary, and tertiary amides.
Datum: 12.12.2017


The Catalytic Asymmetric Mukaiyama-Michael Reaction of Silyl Ketene Acetals with α,β-Unsaturated Methyl Esters

α,β-Unsaturated esters are readily available but challenging substrates to activate in asymmetric catalysis. We now describe an efficient, general, and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with α,β-unsaturated methyl esters, catalyzed by a silylium imidodiphosphorimidate (IDPi) Lewis acid.
Datum: 12.12.2017


Introducing Chiral Bifunctional Phosphine-Carboxylate Ligands for Palladium(0)-Catalyzed Enantioselective C-H Arylation

Previous enantioselective Pd0-catalyzed C-H activation reactions proceeding via the concerted metalation-deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold and incorporating both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for the desymmetrizing C(sp2)-H arylation leading to 5,6-dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities. The bifunctional system proved applicable to a range of substituted dihydrophenanthridines, and allowed the parallel kinetic resolution of racemic substrates.
Datum: 12.12.2017


Enantioselective Synthesis of N,S-Acetals by an Oxidative Pummerer-Type Transformation using Phase-Transfer Catalysis

Reported is the first enantioselective oxidative Pummerer-type transformation using phase-transfer catalysis to deliver enantioenriched sulfur-bearing heterocycles. This reaction includes the direct oxidation of sulfides to a thionium intermediate, followed by an asymmetric intramolecular nucleophilic addition to form chiral cyclic N,S-acetals with moderate to high enantioselectivites. Deuterium-labelling experiments were performed to identify the stereodiscrimination step of this process. Further analysis of the reaction transition states, by means of multidimensional correlations and DFT calculations, highlight the existence of a set of weak noncovalent interactions between the catalyst and substrate that govern the enantioselectivity of the reaction. Aye, aye, CAPT: The first catalytic enantioselective Pummerer-type transformation has been developed employing chiral-anion phase-transfer catalysis (CAPT). This chemical transformation allows facile construction of a wide variety of enantioenriched cyclic N,S-acetal motifs which were previously difficult to access.
Datum: 12.12.2017


On the Use of Polyelectrolytes and Polymediators in Organic Electrosynthesis

Although organic electrosynthesis is generally considered to be a green method, the necessity for excess amounts of supporting electrolyte constitutes a severe drawback. Furthermore, the employment of redox mediators results in an additional separation problem. In this context, we have explored the applicability of soluble polyelectrolytes and polymediators with the TEMPO-mediated transformation of alcohols into carbonyl compounds as a test reaction. Catalyst benchmarking based on cyclic voltammetry studies indicated that the redox-active polymer can compete with molecularly defined TEMPO species. Alcohol oxidation was also highly efficient on a preparative scale, and our polymer-based approach allowed for the separation of both mediator and supporting electrolyte in a single membrane filtration step. Moreover, we have shown that both components can be reused multiple times. Combining electrosynthesis with membrane filtration: The attachment of a TEMPO mediator and a supporting electrolyte to soluble polymers enables the selective anodic conversion of alcohols into carbonyl compounds and allows for efficient recovery/recycling of the mediator and the salt by membrane filtration.
Datum: 12.12.2017


Desktop NMR and Its Applications From Materials Science To Organic Chemistry

NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small-molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen-containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state-of-the-art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed. NMR spectroscopy is known not only for its outstanding analytical power but also for the large size and costs of the instruments. In recent years, the family of instruments with bulky superconducting magnets has been complemented with compact tabletop and portable devices suitable for small-molecule analysis and nondestructive materials testing. The state of the art of compact NMR instruments is reviewed and illustrated with selected examples.
Datum: 12.12.2017


Computational Chemistry: The Fate of Current Methods and Future Challenges

“Where do we go from here?” is the underlying question regarding the future (perhaps foreseeable) developments in computational chemistry. Although this young discipline has already permeated practically all of chemistry, it is likely to become even more powerful with the rapid development of computational hard- and software.
Datum: 12.12.2017


Macrolide Synthesis trough Intramolecular Oxidative Cross-Coupling of Alkenes

A RhIII-catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized reaction conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This method provides an efficient approach to synthesize macrocyclic compounds containing a 1,3-conjugated diene structure. Two pair: A RhIII-catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This provides efficient access to macrocyclic compounds containing 1,3-conjugated dienes.
Datum: 12.12.2017


Highly Branched Polymers with Layered Structures that Mimic Light-Harvesting Processes

Hyperbranched polymers (HBPs) with decorated donor and acceptor chromophores in different domains were constructed to demonstrate the function of light harvesting in a polymeric nanostructure. Taking advantage of our recently developed chain-growth copper-catalyzed azide–alkyne cycloaddition polymerization, two structural parameters in the HBPs, for example, the molar ratio of the acceptor Coumarin 343 in the core to the donor Coumarin 2 on the periphery, and the average distance between these two layers, could be independently varied in a one-pot synthesis. The results demonstrated an efficient energy transfer from the excited Coumarin 2 to the ground-state Coumarin 343 in the core, with the efficiency of the energy transfer reaching as high as 98 %. The excited Coumarin 343, after receiving energy from donor Coumarin 2 emitted higher fluorescence intensity than when directly excited, indicating an observed light concentration effect from the periphery dye to the central dye in one polymer structure. Hyperbranched polymers (HBPs) with decorated donor (Coumarin 2, C2) and acceptor (Coumarin 343, C343) chromophores in different domains were constructed by chain-growth copper-catalyzed azide–alkyne cycloaddition polymerization (CuAACP) to demonstrate the function of light harvesting in a polymeric nanostructure. The efficiency of the energy transfer extended up to 98 %.
Datum: 12.12.2017


Copper-Catalyzed Enantioselective Markovnikov Protoboration of α-Olefins Enabled by a Buttressed NHC Ligand

We report herein a highly enantioselective copper-catalyzed Markovnikov protoboration of unactivated terminal alkenes. A variety of simple and abundant feedstock α-olefins bearing a diverse array of functional groups and heterocyclic substituents can be applied in this process, which proceeds under mild conditions at ambient temperature to provide expedient access to enantioenriched alkylboronic esters in good regioselectivity and with excellent enantiocontrol. Critical to the success of the protocol was the development and application of a novel, sterically hindered N-heterocyclic carbene, (R,R,R,R)-ANIPE, as the ligand for copper.
Datum: 12.12.2017


Visualization of Heterogeneous Oxygen Storage Behavior in Three-Way Catalyst Pt/Ce2Zr2Ox Particles by Hard X-ray Spectro-Ptychography

The cerium density and valence in micrometer-size Pt/Ce2Zr2Ox (x=7-8) three-way catalyst particles were successfully mapped by hard X-ray spectro-ptychography (ptychographic-XAFS). The analysis of correlation between the Ce density and valence in ptychographic-XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce2Zr2Ox particles. Ptychographic-XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.
Datum: 12.12.2017


Interfacial nanoprecipitation toward stable and responsive microbubbles and their use as a resuscitative fluid

Abstract: We report a new approach to prepare stable microbubbles (MBs) via interfacial nanoprecipitation of bioabsorbable polymers at air/liquid interface. This facile method offers robust control over MBs morphology and chemo-physical properties by simple chemical modifications. This approach is amenable to large-scale manufacturing, and is useful to develop functional MBs for advanced biomedical applications. To demonstrate this, we created a MB-based intravenous oxygen carrier that undergoes pH-triggered self-elimination. Intravenous injection of past MBs increase the risk of pulmonary vascular obstruction. However, we show, for the first time, that our current design supersedes previous MBs, as they 1) yielded no evidence of acute risks in rodents, and 2) improved the survival in a disease model of asphyxial cardiac arrest (from 0 to 100%), a condition that affects more than 100,000 in-hospital patients, carrying a ~90% mortality.
Datum: 12.12.2017


Emissive synthetic cofactors: enzymatic interconversions of tzA analogues of ATP, NAD+, NADH, NADP+ and NADPH

A series of enzymatic transformations, which generate visibly emissive isofunctional cofactors based on an isothiazolo[4,3-d]pyrimidine analogue of adenosine (tzA), is described. Nicotinamide adenylyl transferase condenses nicotinamide mononucleotide and tzATP to yield NtzAD+, which can be enzymatically phosphorylated by NAD+ kinase and ATP or tzATP to the corresponding NtzADP+. The latter can be engaged in NADP-specific coupled enzymatic transformations involving conversion to NtzADPH by glucose-6-phosphate dehydrogenase and reoxidation to NtzADP+ by glutathione reductase. The NtzADP+/NtzADPH cycle can be monitored in real time by fluorescence spectroscopy.
Datum: 11.12.2017


Transition-Metal-Catalyzed Selective Functionalization of C(sp3)-H Bonds in Natural Products

Direct functionalization of natural products is important for studying structure-activity and structure-property relationships of these molecules. Recent advances in transition-metal-catalyzed functionalizations of C(sp3)-H bonds, the most abundant yet inert bonds in natural products, have been shown to create natural product derivatives selectively. Strategies to achieve such transformation are reviewed.
Datum: 11.12.2017


A bioresistant nitroxide spin label for in-cell EPR spectroscopy: in vitro and in oocytes protein structural dynamics studies.

Approaching proteins structural dynamics and protein-protein interactions in the cellular environment is a fundamental challenge. Due to its absolute sensitivity and to its selectivity to paramagnetic species, Site-Directed Spin Labeling (SDSL) combined with Electron Paramagnetic Resonance (EPR) has the potential to evolve into an efficient method to follow conformational changes in proteins directly inside cells. Until now, the use of nitroxyde-based spin labels for in-cell studies has represented a major hurdle because of their short persistence in the cellular context. In this work we present the design and synthesis of the first maleimido-proxyl-based spin label (M-TETPO) resistant towards reduction and being efficient to probe protein dynamics by continuous wave and pulsed EPR. In particular, the extended lifetime of M-TETPO enabled the study of structural features of a chaperone in the absence and presence of its binding partner at endogenous concentration directly inside cells.
Datum: 11.12.2017


Building Organic/Inorganic Hybrid Interphases for Fast Interfacial Transport in Rechargeable Metal Batteries

We report a facile, in-situ synthesis to create durable, hybrid Solid-electrolyte interphases (SEI) on metal anodes. Composed of Si-interlinked molecules that host LiCl salt, the hybrid SEI exhibit fast charge-transfer kinetics and high exchange current densities. By means of electrochemical analysis and direct optical visualization of Li and Na deposition in symmetric Li/Li and Na/Na cells, it is further shown that the hybrid SEI enables excellent morphological control at relatively high current densities (3-5 mA/cm2) and even for notoriously unstable Na metal anodes. We investigate benefits of the fast interfacial transport attributes of the SEI in Li-S cells. It is found that stable electrochemical cycling is achieved in galvanostatic studies at rates as high as 2 C. Our work provides a promising path towards rational design of multi-functional, elastic SEI that overcomes the most serious limitations of spontaneously formed interphases on high-capacity metal anodes.
Datum: 11.12.2017


Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3− (A=As, Sb, Bi) Complexes

Heteronuclear transition-metal–main-group-element carbonyl complexes of AsFe(CO)3−, SbFe(CO)3−, and BiFe(CO)3− were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass-selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)3−. Chemical bonding analyses on the whole series of AFe(CO)3− (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp–p) type of transition-metal–main-group-element multiple bonding. The σ-type three-orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)3− (A=As, Sb, Bi) complexes. Going for the triple: IR photodissociation spectroscopy and quantum chemical calculations were performed on the complexes AFe(CO)3− (A=As, Sb, Bi). These studies reveal that the complexes contain a (dp–p) type of A−Fe triple bonding.
Datum: 11.12.2017


Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate

The magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water and oil, unless magnetosensitive particles are added. Herein, we describe a new and additive-free way to magnetically control the motion of discrete liquid entities. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. A broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones, can be efficiently transported using the moderate magnetic field (ca. 50 mT) produced by a small permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on-demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment or electric power, in phase with the necessary development of robust and low-cost analytical and diagnostic fluidic devices. Playing drops and marbles: Small magnets are used to precisely drive the motion of floating drops and liquid marbles, made of water, oil or nonmagnetic fluids, and without the use of magnetosensitive particles for the first time. Digital microfluidic operations such as transport along complex trajectories and programmed drop fusion are demonstrated.
Datum: 11.12.2017


para-Xylene Ultra-selective Zeolite MFI Membranes Fabricated from Nanosheet Monolayers at the Air–Water Interface

The control of membrane morphology and microstructure is crucial to improve the separation performance of molecular-sieve membranes. This can be enabled by making thin, dense, and uniform seed-crystal coatings, which are then intergrown into continuous membranes. Herein, we show a novel and simple floating particle coating method can give closely packed monolayers of zeolite nanosheets on nonporous or porous supports. The zeolite nanosheet monolayer is formed at the air–water interface in a conical Teflon trough. As the water in the trough is drained, the monolayer is deposited on a support placed below. Membranes prepared by gel-free secondary growth of the nanosheets deposited by this method show unprecedented ultra-selective performance for separation of para- from ortho-xylene (separation factor >10 000). The membrane drain: A uniform and dense MFI nanosheet monolayer from an air–water interface is transferred onto a porous support by a new monolayer deposition method using a conical trough which drains. The high-coverage nanosheet seed coating, and subsequent intergrowth gives a thin, oriented, and low-defect-density membrane, which exhibits ultra-selective (separation factor >10 000) performance for xylene isomer separation.
Datum: 11.12.2017


Light-driven C-H Oxygenation of Methane into Methanol and Formic Acid by Molecular Oxygen Using Perfluorinated Solvent

Chlorine dioxide radical (ClO2*) was found to act as an efficient oxidizing agent in the aerobic oxygenation of methane to methanol and formic acid under photoirradiation. Photochemical oxygenation of methane occurred in a two-phase system comprising perfluorohexane and water under ambient conditions (298 K, 1 atm). The yields of methanol and formic acid were 14% and 85%, respectively, with a methane conversion of 99% without formation of the further oxygenated products such as CO2 and CO. Ethane was also photochemically converted into ethanol (19%) and acetic acid (78%). The methane oxygenation is initiated by the photochemical Cl-O bond cleavage of ClO2* to generate Cl* and O2. The produced Cl* reacts with CH4 to form a methyl radical (CH3*). Finally, the oxygenated products such as methanol and formic acid were given by the radical chain reaction. A fluorous solvent plays an important role of inhibiting the deactivation of reactive radical species such as Cl* and CH3*.
Datum: 11.12.2017


ortho-Directing Chromium Arene Complexes as Efficient Mediators for Enantiospecific sp2-sp3 Cross-Coupling Reactions

A new strategy for the coupling of a broad scope of electronically diverse aromatics to boronic esters is reported. The coupling sequence, which relies on the directed ortho-lithiation of chromium arene complexes followed by boronate formation and oxidation, occurs with complete ortho-selectivity and enantiospecificity to give the coupling products in excellent yields and with high functional group tolerance. An intermediate chromium arene boronate complex was characterized by X-ray, NMR and IR to elucidate the reaction mechanism.
Datum: 11.12.2017


Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate

Like the flow of water from a fountain, the local deformation of a paramagnetic substrate enables the gravity-driven transport of a liquid. In their Communication (DOI: 10.1002/anie.201710668), D. Baigl et al. show that, using a magnet, the deformation of the substrate (illustrated by the deformed text) allows the manipulation of drops and liquid marbles (the dots of the letters “i”). This method does not rely on magnetosensitive particles and can be used with most conventional liquids such as water or oil.
Datum: 11.12.2017


Enantio- and Diastereoselective Cyclopropanation of 1-Alkenylboronates: Synthesis of 1-boryl-2,3-disubstituted Cyclopropanes

A novel, highly enantio- and diastereoselective synthesis of 1-boryl-2,3-disubstituted cyclopropanes has been developed by means of the cyclopropanation of alkenylboronates with ethyl diazoacetate in the presence of catalytic amounts of a chiral copper-(I) complex. The products can also be directly accessed from alkynes through an operationally simple sequential hydroboration-cyclopropanation protocol. The resulting enantioenriched 1-boryl-2,3-disubstituted-cyclopropanes are versatile synthetic intermediates through further transformations at the carbon-boron bonds
Datum: 11.12.2017


Thioketone Directed Palladium(II)-Catalyzed C-H Arylation of Ferrocenes with Aryl Boronic Acids

A palladium(II)-catalyzed thioketone-chelation-assisted C-H direct arylation of ferrocenes is described. With thioketone as an efficient directing group, various mono- and di-aryl-substituted thiocarbonylferrocenes were obtained via Pd-catalyzed C-H direct functionalization reaction in high yields under mild and base-free conditions. Furthermore, the arylated thiocarbonylferrocene could undergo diverse transformations.
Datum: 11.12.2017


Dicarboxylic Acid Separation by Dynamic and Size-Matched Recognition in Solution and in the Solid State

Bis(trimethylammonium) alkane diiodides dynamically encapsulate dicarboxylic acids through intermolecular hydrogen bonds between the hosts' I- anions and the guests' carboxylic OH groups. A selective recognition is realized when the size of the I-∙∙∙HOOC-(CH2/CF2)n-COOH∙∙∙I- superanion matches the dication alkyl chain length. Dynamic recognition is demonstrated also in solution, where the presence of the size-matching organic salt boosts acid solubility profile thus allowing efficient mixture separation.
Datum: 11.12.2017


Photocatalytic Aerobic Phosphatation of Alkenes

A catalytic regime for the direct phosphatation of simple, non-polarized alkenes, using ordinary, non-activated phosphoric acid diesters as the phosphate source and O2 as the terminal oxidant, has been devised. The title method allows for the direct and highly econo-mic construction of a diverse range of allylic phosphate esters. From a conceptual viewpoint, the aerobic phosphatation is entirely complementary to traditional protocols for phosphate ester formation, which predominantly rely on the use of pre-functionalized or pre-activated reactants, such as alcohols and phosphoryl halides. The title transformation is enabled by the dual interplay of a photoredox- and a selenium-π-acid catalyst involving a sequence of single-electron-transfer processes.
Datum: 08.12.2017


Nanosheet Catalysis of Carbon Dioxide Photoreduction: Fundamentals and Challenges

Transformation of CO2 into fuels and chemicals by using photocatalysis is a promising strategy to provide a long-term solution to mitigating global warming and energy supply problems. Achievements in photocatalysis during the last decade have sparked increased interest in using sunlight to reduce CO2. Traditional semiconductors used in photocatalysis (e.g. TiO2), are not suitable for the use in natural sunlight, and even under UV irradiation their performance is not sufficient. Some two-dimensional (2D) materials have recently been designed for catalytic reduction of CO2. These materials still require significant modification, which remains a challenge for photocatalytic process design. An overarching aim of this article is to summarize the literature reported on photocatalytic conversion of CO2 by various 2D materials in the liquid phase, with special attention given to development of novel 2D photocatalyst materials, to provide a basis to suggest improved materials.
Datum: 08.12.2017


The common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium

Understanding the pathways of catalyst degradation during the oxygen evolution reaction is a cornerstone in development of efficient and stable electrolyzers, since even for most promising Ir based anodes the destined harsh conditions are detrimental. The dissolution mechanism has a complex nature and the correlation to the oxygen evolution reaction itself is still poorly understood. Here, hyphening a scanning flow cell with inductively coupled plasma and online electrochemical mass spectrometers, we in-situ monitor the oxygen evolution and degradation products of Ir and Ir-oxides. We show that at high anodic potentials several dissolution routes become possible, including formation of gaseous IrO3. On the basis of our experimental data possible pathways of oxygen evolution triggered dissolution of Ir are proposed, and the role of common intermediates for these reactions is discussed.
Datum: 08.12.2017


Conformational Selection of Dimethylarginine Recognition by the Survival Motor Neuron Tudor Domain

Tudor domains bind to dimethylarginine (DMA) residues, which are post-translational modifications that play a central role in gene regulation in eukaryotic cells. NMR spectroscopy and quantum calculations are combined to demonstrate that DMA recognition by Tudor domains involves conformational selection. The binding mechanism is confirmed by a mutation in the aromatic cage that perturbs the native recognition mode of the ligand. General mechanistic principles are delineated from the combined results, indicating that Tudor domains utilize cation–π interactions to achieve ligand recognition. The House of Tudor: The Tudor domain of the human survival motor neuron protein selectively recognizes stereoisomers of dimethylarginine residues within its aromatic ligand-binding cage using cation–π interactions. Stereoselectivity can be modulated by a single point mutation.
Datum: 08.12.2017


Stability of Residual Oxides in Oxide-Derived Copper Catalysts for Electrochemical CO2 Reduction Investigated with 18O Labeling

Oxide-derived (OD) Cu catalysts have high selectivity towards the formation of multi-carbon products (C2/C3) for aqueous electrochemical CO2 reduction (CO2R). It has been proposed that a large fraction of the initial oxide can be surprisingly resistant to reduction, and these residual oxides play a crucial catalytic role. The stability of residual oxides was investigated by synthesizing 18O-enriched OD Cu catalysts and testing them for CO2R. These catalysts maintain a high selectivity towards C2/C3 products (ca. 60 %) for up to 5 h in 0.1 m KHCO3 at −1.0 V vs. RHE. However, secondary-ion mass spectrometry measurements show that only a small fraction (<1 %) of the original 18O content remains, showing that residual oxides are not present in significant amounts during CO2R. Furthermore, we show that OD Cu can reoxidize rapidly, which could compromise the accuracy of ex situ methods for determining the true oxygen content. Residual oxides in oxide-derived Cu catalysts are not stable under strongly reducing potentials during electrochemical CO2 reduction. This is demonstrated with the use of 18O labeled oxide-derived Cu catalysts.
Datum: 08.12.2017


Highly Selective Manganese(I)/Lewis Acid Cocatalyzed Direct C−H Propargylation Using Bromoallenes

A manganese(I)/Lewis acid cocatalyzed direct C−H propargylation with high selectivity has been developed. BPh3 was discovered to not only promote the reactivity, but also enhance the selectivity. Secondary, tertiary, and even quaternary carbon centers at the propargylic position could be directly constructed. Both internal and terminal alkynes are easily accessible. The chirality was successfully transferred from an axially chiral allene to central chirality. The reactivity of the manganese catalyst in this reaction was found to be unique among transition metal catalysts. Proper(gylation)! In a highly selective manganese(I)/Lewis acid cocatalyzed direct C−H propargylation, BPh3 not only promotes the reactivity, but also enhances the selectivity. Secondary, tertiary, and even quaternary carbon centers at the propargylic position could be directly constructed. The reactivity of the manganese catalyst in this reaction is unique among transition metal catalysts.
Datum: 08.12.2017


Benjamin List


Datum: 08.12.2017


Intramolecular Acetyl Transfer to Olefins by Catalytic C−C Bond Activation of Unstrained Ketones

A rhodium-catalyzed intramolecular acetyl-group transfer has been achieved through a “cut and sew” process. The challenge arises from the existence of different competitive pathways. Preliminary success has been achieved with unstrained enones that contain a biaryl linker. The use of an electron-rich N-heterocycilc carbene (NHC) ligand is effective to inhibit undesired β-hydrogen elimination. Various 9,10-dihydrophenanthrene derivatives can be prepared with excellent functional-group compatibility. The 13C-labelling study suggests that the reaction begins with cleavage of the unstrained C−C bond, followed by migratory insertion and reductive elimination. Cross-stitch: A rhodium-catalyzed intramolecular acetyl-group transfer has been achieved by a cut and sew process. By using unstrained enones that contain a biaryl linker, C−C activation occurs with the assistance of a temporary directing group. Various 9,10-dihydrophenanthrene derivatives can be prepared with excellent functional-group compatibility.
Datum: 08.12.2017


A Chiral Halogen-Bonding [3]Rotaxane for the Recognition and Sensing of Biologically Relevant Dicarboxylate Anions

The unprecedented application of a chiral halogen-bonding [3]rotaxane host system for the discrimination of stereo- and E/Z geometric isomers of a dicarboxylate anion guest is described. Synthesised by a chloride anion templation strategy, the [3]rotaxane host recognises dicarboxylates through the formation of 1:1 stoichiometric sandwich complexes. This process was analysed by molecular dynamics simulations, which revealed the critical synergy of halogen and hydrogen bonding interactions in anion discrimination. In addition, the centrally located chiral (S)-BINOL motif of the [3]rotaxane axle component facilitates the complexed dicarboxylate species to be sensed via a fluorescence response. The discrimination between dicarboxylate stereo- and geometric isomers by a chiral halogen-bonding [3]rotaxane can be monitored in terms of the fluorescence response. Computational modelling studies revealed the critical synergy between the axle of the rotaxane host and macrocycle components in achieving dicarboxylate guest selectivity.
Datum: 08.12.2017


A Step Closer to Metal-Free Dinitrogen Activation: A New Chapter in the Chemistry of Frustrated Lewis Pairs

The end of the metal age: Recent developments in small-molecule activation and chemical transformations of main-group species pose the question as to whether metal catalysts could be avoided altogether in the activation of dinitrogen. A ground-breaking study by Stephan and co-workers clearly implies that the metal-free activation of N2 with frustrated Lewis pairs may be achievable in the not-too-distant future.
Datum: 08.12.2017


Rhodium-Catalyzed Cyclization of O,ω-Unsaturated Alkoxyamines: Formation of Oxygen-Containing Heterocycles

O,ω-Unsaturated N-tosyl alkoxyamines undergo unexpected RhIII-catalyzed intramolecular cyclization by oxyamination to produce oxygen-containing heterocycles. Mechanistic studies show that an aziridine intermediate seems to be responsible for the formation of the heterocycles, possibly via a RhV species. Unexpected reactivity: Functionalized tetrahydrofurans were unexpectedly obtained instead of the intended isoxazolidines. The reaction proceeds from N-tosyl O,ω-unsaturated alkoxyamines and a known rhodium(III)-catalyzed allylic C−H activation protocol. The scope and limitations of this surprising reaction are described. A mechanism, involving a rhodium(V) nitrenoid and an aziridination step, is discussed.
Datum: 08.12.2017


Nickel(0)-Catalyzed Hydroarylation of Styrenes and 1,3-Dienes with Organoboron Compounds

A Ni-catalyzed hydroarylation of styrenes and 1,3-dienes with organoboron compounds has been developed. The reaction offers a highly selective approach to diarylalkanes and allylarenes under redox-neutral conditions. In this hydroarylation reaction, a new strategy that uses the proton of methanol to generate the active catalyst species Ni−H was developed. The Ni-catalyzed hydroarylation, combined with a Ir-catalyzed C−H borylation, affords a very efficient and straightforward access to a retinoic acid receptor agonist. OH yeah: A nickel(0)-catalyzed hydroarylation of alkenes with organoboron reagents using an alcohol OH group as the H-atom source is reported. The reaction offers a highly selective approach to diarylalkanes and allylarenes under redox-neutral conditions.
Datum: 08.12.2017


Purely Physisorption-Based CO-Selective Gate-Opening in Microporous Organically Pillared Layered Silicates

Separation of gas molecules with similar physical and chemical properties is challenging but nevertheless highly relevant for chemical processing. By introducing the elliptically shaped molecule, 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane, into the interlayer space of a layered silicate, a two-dimensional microporous network with narrow pore size distribution is generated (MOPS-5). The regular arrangement of the pillar molecules in MOPS-5 was confirmed by the occurrence of a 10 band related to a long-range pseudo-hexagonal superstructure of pillar molecules in the interlayer space. Whereas with MOPS-5 for CO2 adsorption, gate-opening occurs at constant volume by freezing pillar rotation, for CO the interlayer space is expanded at gate-opening and a classical interdigitated layer type of gate-opening is observed. The selective nature of the gate-opening might be used for separation of CO and N2 by pressure swing adsorption. MOPS (microporous organically pillared layered silicates) are capable of discriminating two, physically very similar gases (CO/N2) by a simple selective gate-opening process. More importantly, gate-opening seems to be a general feature of MOPS, and selectivity may be easily tuned by the highly modular design of MOPS.
Datum: 08.12.2017


Thermally Activated Delayed Fluorescence in a Y3N@C80 Endohedral Fullerene: Time-Resolved Luminescence and EPR Studies

The endohedral fullerene Y3N@C80 exhibits luminescence with reasonable quantum yield and extraordinary long lifetime. By variable-temperature steady-state and time-resolved luminescence spectroscopy, it is demonstrated that above 60 K the Y3N@C80 exhibits thermally activated delayed fluorescence with maximum emission at 120 K and a negligible prompt fluorescence. Below 60 K, a phosphorescence with a lifetime of 192±1 ms is observed. Spin distribution and dynamics in the triplet excited state is investigated with X- and W-band EPR and ENDOR spectroscopies and DFT computations. Finally, electroluminescence of the Y3N@C80/PFO film is demonstrated opening the possibility for red-emitting fullerene-based organic light-emitting diodes (OLEDs). Delayed on the cage: Efficient thermally activated delayed fluorescence is found in the endohedral fullerene Y3N@C80. Predominant localization of the exciton on the carbon cage is confirmed by ENDOR spectroscopy.
Datum: 08.12.2017


Controlled Sol–Gel Transitions of a Thermoresponsive Polymer in a Photoswitchable Azobenzene Ionic Liquid as a Molecular Trigger

Producing ionic liquids (ILs) that function as molecular trigger for macroscopic change is a challenging issue. Photoisomerization of an azobenzene IL at the molecular level evokes a macroscopic response (light-controlled mechanical sol–gel transitions) for ABA triblock copolymer solutions. The A endblocks, poly(2-phenylethyl methacrylate), show a lower critical solution temperature in the IL mixture containing azobenzene, while the B midblock, poly(methyl methacrylate), is compatible with the mixture. In a concentrated polymer solution, different gelation temperatures were observed in it under dark and UV conditions. Light-controlled sol–gel transitions were achieved by a photoresponsive solubility change of the A endblocks upon photoisomerization of the azobenzene IL. Therefore, an azobenzene IL as a molecular switch can tune the self-assembly of a thermoresponsive polymer, leading to macroscopic light-controlled sol–gel transitions. Photoswitchable sol–gel transitions: An ABA triblock copolymer with thermoresponsive A endblocks was dissolved in a mixture of conventional and photoresponsive ionic liquid (IL). The azobenzene IL can tune the affinities between the A blocks and the solvent: the polymer is soluble in the trans-IL and insoluble in the cis-IL. Thus, a molecular-level switch evokes a reversible macroscopic sol–gel transition.
Datum: 08.12.2017


Crochelins: Siderophores with an Iron-Chelating Moiety from the Nitrogen-Fixing Bacterium Azotobacter chroococcum

Microbes use siderophores to access essential iron resources in the environment. Over 500 siderophores are known, but they utilize a small set of common moieties to bind iron. Azotobacter chroococcum expresses iron-rich nitrogenases, with which it reduces N2. Though an important agricultural inoculant, the structures of its iron-binding molecules remain unknown. Here, the “chelome” of A. chroococcum is examined using small molecule discovery and bioinformatics. The bacterium produces vibrioferrin and amphibactins as well as a novel family of siderophores, the crochelins. Detailed characterization shows that the most abundant member, crochelin A, binds iron in a hexadentate fashion using a new iron-chelating γ-amino acid. Insights into the biosynthesis of crochelins and the mechanism by which iron may be removed upon import of the holo-siderophore are presented. This work expands the repertoire of iron-chelating moieties in microbial siderophores. New ways to bind iron: Crochelin A, the founding member of a family of siderophores with an unprecedented iron-ligating substructure, has been discovered from the agricultural inoculant Azotobacter chroococcum. It binds iron with an unusual γ-amino acid (see picture, red). Insights into its iron-binding capability and biosynthesis are obtained from experimental and bioinformatic studies.
Datum: 08.12.2017


Manganese Complexes for (De)Hydrogenation Catalysis: A Comparison to Cobalt and Iron Catalysts

The sustainable use of the resources on our planet is essential. Noble metals are very rare and are diversely used in key technologies, such as catalysis. Manganese is the third most abundant transition metal of the Earth's crust and based on the recently discovered impressive reactivity in hydrogenation and dehydrogenation reactions, is a potentially useful noble-metal “replacement”. The hope of novel selectivity profiles, not possible with noble metals, is also an aim of such a “replacement”. The reactivity of manganese complexes in (de)hydrogenation reactions was demonstrated for the first time in 2016. Herein, we summarize the work that has been published since then and especially discuss the importance of homogeneous manganese catalysts in comparison to cobalt and iron catalysts. A latecomer worth waiting for: In the last two years manganese complexes have been identified as highly active catalysts for diverse hydrogenation and dehydrogenation reactions. The results in this field are summarized and discussed and compared to iron and cobalt catalysts.
Datum: 08.12.2017


Quantum Refinement Does Not Support Dinuclear Copper Sites in Crystal Structures of Particulate Methane Monooxygenase

Particulate methane monooxygenase (pMMO) is one of the few enzymes that can activate methane. The metal content of this enzyme has been highly controversial, with suggestions of a dinuclear Fe site or mono-, di-, or trinuclear Cu sites. Crystal structures have shown a mono- or dinuclear Cu site, but the resolution was low and the geometry of the dinuclear site unusual. We have employed quantum refinement (crystallographic refinement enhanced with quantum-mechanical calculations) to improve the structure of the active site. We compared a number of different mono- and dinuclear geometries, in some cases enhanced with more protein ligands or one or two water molecules, to determine which structure fits two sets of crystallographic raw data best. In all cases, the best results were obtained with mononuclear Cu sites, occasionally with an extra water molecule. Thus, we conclude that there is no crystallographic support for a dinuclear Cu site in pMMO. Two crystal structures of particulate methane monooxygenase (pMMO) were studied with quantum refinement. For the putative active site, several different mono- and dinuclear geometries, in some cases with more protein ligands or one or two water molecules, were compared to determine which structure fits the crystallographic raw data best. The results indicate that there is no crystallographic support for a dinuclear Cu site in pMMO.
Datum: 08.12.2017


Temperature-Directed Biocatalysis for the Sustainable Production of Aromatic Aldehydes or Alcohols

The biosynthesis of aromatic aldehydes and alcohols from renewable resources is currently receiving considerable attention because of an increase in demand, finite fossil resources, and growing environmental concerns. Here, a temperature-directed whole-cell catalyst was developed by using two novel enzymes from a thermophilic actinomycete. Ferulic acid, a model lignin derivative, was efficiently converted into vanillyl alcohol at a reaction temperature at 30 °C. However, when the temperature was increased to 50 °C, ferulic acid was mainly converted into vanillin with a productivity of 1.1 g L−1 h−1. This is due to the fact that the redundant endogenous alcohol dehydrogenases (ADHs) are not active at this temperature while the functional enzymes from the thermophilic strain remain active. As the biocatalyst could convert many other renewable cinnamic acid derivatives into their corresponding aromatic aldehydes/alcohols, this novel strategy may be extended to generate a vast array of valuable aldehydes or alcohols. By using two novel enzymes from a thermophilic actinomycete, a whole-cell catalyst was constructed for the sustainable production of aromatic aldehydes or alcohols from renewable cinnamic acid derivatives. Ferulic acid was converted into vanillyl alcohol at 30 °C whereas the same reaction mainly gave vanillin at 50 °C because the endogenous alcohol dehydrogenases are not active at this temperature.
Datum: 08.12.2017


Palladium-Catalyzed Intramolecular Trost-Oppolzer-Type Alder-Ene Reaction of Dienyl Acetates to Cyclopentadienes

A new approach for the synthesis of highly substituted cyclopentadienes, indenes and cyclopentene-fused heteroarenes via the Pd-catalyzed Trost-Oppolzer-type intramolecular Alder-ene reaction of 2,4-pentadienyl acetates is described. This unprecedented transformation combines the electrophilic features of the Tsuji-Trost reaction with the nucleophilic features of the Alder-ene reaction. The overall outcome can be perceived as a hitherto unknown 'acid-free' iso-Nazarov-type cyclization. The versatility of this strategy was further demonstrated via the formal synthesis of paucifloral F, a resveratrol-based natural product.
Datum: 08.12.2017


Solar hydrogen generation from lignocellulose

Photocatalytic reforming of lignocellulosic biomass is an emerging approach to produce renewable H2. This process combines photo-oxidation of aqueous biomass with photocatalytic hydrogen evolution at ambient temperature and pressure. Biomass conversion is less energy demanding than water splitting and generates high-purity H2 without O2 production. Direct photoreforming of raw, unprocessed biomass has the potential to provide affordable, clean energy across the globe from locally sourced materials.
Datum: 08.12.2017


Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare Earth Complexes: Non-Redox Oxygen Atom Transfer

The preferential substitution of oxo ligands over alkyl ones of rare earth complexes is commonly considered as "impossible" due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare earth complexes to a rigid trinuclear cluster framework can not only enhance the activity of the Ln-oxo bond, but also protect the highly reactive Ln-alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non-redox rare earth-mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare earth oxo complexes.
Datum: 08.12.2017


Single-cell Mass Spectrometry Approaches to Explore Cellular Heterogeneity

Compositional diversity is a fundamental property in cell populations that is responsible for evolutionary adaptation and resilience. Single-cell analysis promises new insights into this cellular heterogeneity and the corresponding subpopulations on the genomic, transcriptomic, proteomic, and metabolomic levels. Mass spectrometry (MS) is a label-free technique that enables the multiplexed analysis of proteins, peptides, lipids, and metabolites in individual cells. The abundances of these molecular classes are correlated with the physiological states and environmental responses of the cells. In this Minireview, we discuss recent advances in single-cell MS techniques with an emphasis on sampling and ionization methods developed for volume-limited samples. Strategies for sample treatment, separation methods, and data analysis require special considerations for single cells. Ongoing analytical challenges include the need for high-throughput, high molecular coverage, minimal perturbation, subcellular heterogeneity, and non-normal statistical distributions of cellular properties. The insights obtained by single-cell MS techniques inform fundamental cell biology, immunology, and individualized medicine.
Datum: 08.12.2017


Quantum machine learning in chemical compound space

Rather than numerically solving the computationally demanding equations of quantum or statistical mechanics, machine learning methods can infer approximate solutions, interpolating previously acquired property data sets of molecules and materials. The case is made for quantum machine learning: An inductive molecular modeling approach which can be applied to quantum chemistry problems.
Datum: 07.12.2017


A Cesium Rare-Earth Silicate Cs3RESi6O15 (RE = Dy-Lu, Y, In): The "Parent" of an Unusual Structural Class Featuring a Remarkable 57 Å Unit Cell Axis

A new structural member of the broad class of A3RESi6O15 compounds has been discovered for the formula Cs3RESi6O15, where RE = Dy-Lu,Y,In. The structure is unusual in that it contains octahedrally coordinated rare earth ions whose relative orientation dictates the structure as they rotate about the c-axis supported by the cyclic Si6O15 framework. The repeat unit of the rotation is eight units generating a very long, ~57 Å, unit cell axis. This unusual repeat unit is created by the structural flexibility of the hexasilicate ring, which is in turn affected by the size of the rare earth ion as well as the size of alkali ion residing within the silicate layers. The products described here are prepared as large, high quality single crystals using a high temperature (650˚C) hydrothermal method with CsOH and F- mineralizers. The presence of fluoride is essential to the formation of the product, as reactions without fluoride do not form these products.
Datum: 07.12.2017


New views of head-to-middle and cis- head-to-tail prenyltransferases: Structure of isosesquilavandulyl diphosphate synthase

We report the first X-ray crystallographic structure of the "head-to-middle" prenyltransferase, isosesquilavandulyl diphosphate synthase, involved in biosynthesis of the merochlorin class of antibiotics. The protein adopts the ζ or cis-prenyl transferase fold but remarkably, unlike tuberculosinol adenosine synthase and other cis-prenyl transferases (e.g. cis-farnesyl, decaprenyl, undecaprenyl diphosphate synthases), the large, hydrophobic side-chain does not occupy a central hydrophobic tunnel. Instead, it occupies a surface pocket oriented at ~90º to the hydrophobic tunnel. Product chain-length control is achieved by squeezing out the ligand from the conventional allylic S1 binding site, with proton abstraction being achieved via a diphosphate-Asn-Ser relay. The structures revise and unify our thinking as to the mechanism of action of many other prenyl transferases and may also be of use in engineering new merochlorin-class antibiotics.
Datum: 07.12.2017


A Zero-Dimensional Organic Seesaw-Shaped Tin Bromide with Highly Efficient Strongly Stokes-Shifted Deep-Red Emission

We report the synthesis and characterization of (C9NH20)2SnBr4, a novel organic metal halide hybrid with a zero-dimensional (0D) structure, in which individual seesaw-shaped tin (II) bromide anions (SnBr42-) are co-crystallized with 1-butyl-1-methylpyrrolidinium cations (C9NH20+). Upon photoexcitation, the bulk crystals exhibit a highly efficient broadband deep-red emission peaked at 695 nm, with a large Stokes shift of 332 nm and a high quantum efficiency of around 46%. The unique photophysical properties of this hybrid material are attributed to two major factors, (i) the 0D structure allowing the bulk crystals to exhibit the intrinsic properties of individual SnBr42- species, and (ii) the seesaw structure enabling a pronounced excited state structural deformation as confirmed by density functional theory (DFT) calculations.
Datum: 07.12.2017


Deuterated Molecular Ruby with Record Luminescence Quantum Yield

The recently reported luminescent chromium(III) complex [Cr(ddpd)2]3+ shows exceptionally strong near-IR emission in water under ambient conditions (QY 11 %) with a microsecond lifetime. In the absence of energy acceptors such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these oscillators in the excited state deactivation. Addressing these energy transfer pathways in the first and second coordination sphere furnishes a record 30 % quantum yield and a 2.3 millisecond lifetime for a metal complex with an earth abundant metal ion in solution at room temperature. The combined fundamental insights will pave the way for selective design strategies in the field of luminescent complexes with earth-abundant metal ions.
Datum: 07.12.2017


Polymer film dewetting by water/surfactant/good solvent mixtures: a mechanistic insight and its implications for the conservation of Cultural Heritage

Aqueous nanostructured fluids (NSFs) have been proposed in the recent past to remove polymer coatings from the surfaces of works of art; this process usually involves film dewetting. Here we report on a major advancement in the study of NSFs cleaning mechanisms using several complementary techniques that are employed to get a mechanistic insight on the interaction of a methacrylic/acrylic copolymer (Paraloid B72®) film laid on glass surfaces and several NSFs, based on two different solvents, i.e. propylene carbonate (PC) and 2-butanone (MEK), and two different surfactants, i.e. a nonionic alcohol ethoxylate (C9-11E6) and sodium dodecylsulfate (SDS). The experimental results provide a detailed picture of the dewetting process, where the role of each component is elucidated. These findings open new perspectives in the formulation of cleaning systems in the field of cultural heritage conservation, as well as coatings and detergency.
Datum: 07.12.2017


Triplet Tellurophene-based Acceptors for Organic Solar Cells

Triplet materials have been employed to achieve high performing OSCs, while the triplet nonfullerene acceptor materials have never been reported for bulk heterojunction OSCs. Herein, for the first time, three triplet molecular acceptors based on tellurophene with different extent of ring fusing were designed and synthesized for OSCs. Significantly, these molecules possess long exciton lifetime and diffusion length, leading to efficient power conversion efficiency (7.52%), which is the highest values for tellurophene based OSCs. Moreover, the influence of the extent of ring fusing on molecular geometry and OSCs performance was investigated to show the PCEs continuously increased along with increasing the extent of ring fusing. This contribution demonstrated a novel method to design high performing nonfullerene acceptors for OSCs and provided new insights for understanding the relationship between molecular geometry and OSCs performances.
Datum: 07.12.2017


Photochemical Creation of Fluorescent Quantum Defects in Semiconducting Carbon Nanotube Hosts

Quantum defects are an emerging class of synthetic single photon emitters that hold potential for near-infrared imaging, chemical sensing, materials engineering, and quantum information processing. Herein, we show it is possible to optically direct the synthetic creation of molecularly tunable fluorescent quantum defects in semiconducting single-walled carbon nanotube hosts through photochemical reactions. By exciting the host semiconductor with light that resonates with its electronic transition, we find that halide-containing aryl groups can covalently bond to the sp2 carbon lattice. The reaction is independent of temperature but correlates strongly with the photon energy used to drive the reaction, suggesting a photochemical mechanism rather than photothermal effects. This type of photochemical reactions opens the possibility to control the synthesis of quantum defects using light and may enable lithographic patterning of quantum emitters with electronic and molecular precision.
Datum: 07.12.2017


A Vinyl Sulfone-Based Fluorogenic Probe Capable of Selective Labeling of PHGDH in Live Mammalian Cells

Chemical probes are powerful tools for interrogating small molecule-target interactions. With additional fluorescence Turn-ON functionality, such probes might enable direct measurements of target engagement in live mammalian cells. DNS-pE (and its terminal alkyne-containing version DNS-pE2) is the first small molecule that can selectively label endogenous 3-phosphoglycerate dehydrogenase (PHGDH) from various mammalian cells. Endowed with an electrophilic vinyl sulfone moiety that possesses fluorescence-quenching properties, DNS-pE/DNS-pE2 became highly fluorescent only upon irreversible covalent modification of PHGDH. With an inhibitory property (in vitro Ki=7.4 μm) comparable to that of known PHGDH inhibitors, our probes thus offer a promising approach to simultaneously image endogenous PHGDH activities and study its target engagement in live-cell settings. Turn-ON the label: A fluorogenic probe that selectively and covalently labels endogenous PHGDH from various live mammalian cells was developed based on a vinyl sulfone-containing dansyl fluorophore. This enables simultaneous live-cell imaging of PHGDH activities and studies of its active-site engagement.
Datum: 07.12.2017


Engineering of a DNA Polymerase for Direct m6A Sequencing

Methods for the detection of RNA modifications are of fundamental importance for advancing epitranscriptomics. N6-methyladenosine (m6A) is the most abundant RNA modification in mammalian mRNA and is involved in the regulation of gene expression. Current detection techniques are laborious and rely on antibody-based enrichment of m6A-containing RNA prior to sequencing, since m6A modifications are generally “erased” during reverse transcription (RT). To overcome the drawbacks associated with indirect detection, we aimed to generate novel DNA polymerase variants for direct m6A sequencing. Therefore, we developed a screen to evolve an RT-active KlenTaq DNA polymerase variant that sets a mark for N6-methylation. We identified a mutant that exhibits increased misincorporation opposite m6A compared to unmodified A. Application of the generated DNA polymerase in next-generation sequencing allowed the identification of m6A sites directly from the sequencing data of untreated RNA samples. Deliberate error: A KlenTaq DNA polymerase variant with elevated error rates opposite m6A but not unmodified A in an RNA template was evolved by using a primer-extension-based screening assay. The identified mutant was applied in a next-generation sequencing (NGS) library preparation method and m6A sites could be directly identified in the sequencing data as mutational hotspots.
Datum: 07.12.2017


Maximizing the Catalytic Activity of Nanoparticles through Monolayer Assembly on Nitrogen-Doped Graphene

We report a facile method for assembly of a monolayer array of nitrogen-doped graphene (NG) and nanoparticles (NPs) and the subsequent transfer of two layers onto a solid substrate (S). Using 3 nm NiPd NPs as an example, we demonstrate that NiPd-NG-Si (Si=silicon wafer) can function as a catalyst and show maximum NiPd catalysis for the hydrolysis of ammonia borane (H3NBH3, AB) with a turnover frequency (TOF) of 4896.8 h−1 and an activation energy (Ea) of 18.8 kJ mol−1. The NiPd-NG-S catalyst is also highly active for catalyzing the transfer hydrogenation from AB to nitro compounds, leading to the green synthesis of quinazolines in water. Our assembly method can be extended to other graphene and NP catalyst materials, providing a new 2D NP catalyst platform for catalyzing multiple reactions in one pot with maximum efficiency. A versatile catalyst: A simple method was developed for the assembly of nanoparticles and nitrogen-doped graphene (NG) monolayers onto a solid substrate. The as-prepared NiPd-NG-Si material (Si=silicon wafer) serves as a robust and highly efficient catalyst for the hydrolysis of ammonia borane and for the following tandem reactions that lead to the high-yield synthesis of quinazolines in water.
Datum: 07.12.2017


MoB/g-C3N4 Interface Materials as a Schottky Catalyst to Boost Hydrogen Evolution

Proton adsorption on metallic catalysts is a prerequisite for efficient hydrogen evolution reaction (HER). However, tuning proton adsorption without perturbing metallicity remains a challenge. A Schottky catalyst based on metal–semiconductor junction principles is presented. With metallic MoB, the introduction of n-type semiconductive g-C3N4 induces a vigorous charge transfer across the MoB/g-C3N4 Schottky junction, and increases the local electron density in MoB surface, confirmed by multiple spectroscopic techniques. This Schottky catalyst exhibits a superior HER activity with a low Tafel slope of 46 mV dec−1 and a high exchange current density of 17 μA cm−2, which is far better than that of pristine MoB. First-principle calculations reveal that the Schottky contact dramatically lowers the kinetic barriers of both proton adsorption and reduction coordinates, therefore benefiting surface hydrogen generation. Schottky catalyst: The hydrogen evolution activity of a metallic MoB catalyst can be significantly promoted by enhancing the surface charge density across a Schottky contact with an n-type semiconductor.
Datum: 07.12.2017


Photoinduced Pedalo-Type Motion in an Azodicarboxamide-Based Molecular Switch

Well-defined structural changes of molecular units that can be triggered by light are crucial for the development of photoactive functional materials. Herein, we report on a novel switch that has azodicarboxamide as its photo-triggerable element. Time-resolved UV-pump/IR probe spectroscopy in combination with quantum-chemical calculations shows that the azodicarboxamide functionality, in contrast to other azo-based chromophores, does not undergo trans–cis photoisomerization. Instead, a photoinduced pedalo-type motion occurs, which because of its volume-conserving properties enables the design of functional molecular systems with controllable motion in a confined space. Motion without volume change: By combining time-resolved infrared spectroscopy with quantum-mechanical calculations, a volume-conserving pedalo-type motion was studied in a molecular switch. These azodicaboxamide-based systems have the potential to open a new realm in the achievement of motion in a confined space.
Datum: 07.12.2017


Transition-Metal π-Ligation of a Tetrahalodiborane

The reaction of tetraiododiborane (B2I4) with trans-[Pt(BI2)I(PCy3)2] gives rise to the diplatinum(II) complex [{(Cy3P)(I2B)Pt}2(μ2:η3:η3-B2I4)], which is supported by a bridging diboranyl dianion ligand [B2I4]2−. This complex is the first transition-metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B2X4 (X=halide) unit of any type to a metal center. Million dollar BB: The reaction of tetraiododiborane with trans-[Pt(BI2)I(PCy3)2] gives rise to a diplatinum(II) complex supported by a bridging [B2I4] unit. This complex is the first transition-metal complex of a diboranyl dianion, as well as the first example of intact coordination of a B2X4 (X=halide) unit of any type to a metal center.
Datum: 07.12.2017


Electrochemical Synthesis of Aryl Iodides by Anodic Iododesilylation

An electrochemical access to iodinated aromatic compounds starting from trimethylsilyl-substituted arenes is presented. By design of experiments, highly efficient and mild conditions were identified for a wide range of substrates. A functional group stability test and the synthesis of an important 3-iodobenzylguanidine radiotracer illustrate the scope of this process. Get me out of here: An electrochemical access to iodinated aromatic compounds starting from trimethylsilyl-substituted arenes is presented. By design of experiments, highly efficient and mild conditions were identified for a wide range of substrates. A functional group stability test and the synthesis of an important 3-iodobenzylguanidine radiotracer illustrate the scope of this process.
Datum: 07.12.2017


A Bottom-Up Proteomic Approach to Identify Substrate Specificity of Outer-Membrane Protease OmpT

Peptide arrays are used to identify highly active substrates for the OmpT protease, as described by M. Mrksich, B. Liedberg, et al. in their Communication (DOI: 10.1002/anie.201707535). By preparing the peptide arrays on self-assembled monolayers, mass spectrometry (the SAMDI method) was used to characterize the extent of cleavage of each peptide. A commonly used mutant form of the protease, although regarded as having identical activity, instead had an altered specificity for its substrates.
Datum: 07.12.2017


Ruthenium(II)-catalyzed C-H Difluoromethylation of Ketoxime: Tuning the Regioselectivity from meta to para Position

A highly para-selective CAr-H difluoromethylation of ketoxime ether using a ruthenium catalyst has been developed. A wide variety of ketoxime ethers are compatible in the reaction, leading to the corresponding para-selective difluorometylated products in moderate to good yield. A mechanistic study clearly shows that chelation-assisted cycloruthenation is the key factor in achieving the para-selective difluoromethylation of ketoxime ethers. The density functional theory (DFT) method was used to gain a theoretical understanding of the para-selectivity.
Datum: 07.12.2017


Integration of Plasmonic Effect and Schottky Junction into Metal-Organic Framework Composites: Steering Charge Flow for Enhanced Visible-Light Photocatalysis

A wide range of light absorption and rapid electron-hole separation are desired for efficient photocatalysis. Herein, on the basis of a semiconductor-like metal-organic framework (MOF), the rationally designed Pt@MOF/Au catalyst with two types of metal-MOF interfaces integrates the surface plasmon resonance excitation of Au nanorods with Pt-MOF Schottky junction, which not only extends the light absorption of the MOF from UV to visible region but also greatly accelerates charge transfer. The spatial separation of Pt and Au particles by the MOF further steers the formation of charge flow and expedites the charge migration. As a result, the Pt@MOF/Au presents an exceptionally high photocatalytic H2 production rate by water splitting under visible light irradiation, far superior to Pt/MOF/Au, MOF/Au and other counterparts with similar Pt or Au contents, highlighting the important role of each component and the Pt location in the catalyst.
Datum: 07.12.2017


Restoration of Ribozyme Tertiary Contact and Function by Using a Molecular Glue for RNA

Some RNA classes require folding into the proper higher-order structures to exert their functions. Hammerhead ribozyme (HHR) requires a folding conformation stabilized by tertiary interaction for full activity. A rationally engineered HHR was developed that was inactive, but could be activated by a synthetic RNA-binding ligand, naphthyridine carbamate tetramer with Z-stilbene linker (Z-NCTS). Binding of Z-NCTS could induce the formation of an active folding structure and thereby restore ribozyme activity, where Z-NCTS acts as a molecular glue to bring two isolated RNA loops into contact with each other. Next, we designed a Z-NCTS-responsive genetic switch using the HHR sequence inserted into the 3′ untranslated region as a cis-acting element. We demonstrated that the rationally designed ribozyme switch enabled regulation of gene expression by Z-NCTS and was functional in mammalian cells. A hammerhead ribozyme was designed that was inactive, but could be activated by a synthetic ligand function as a molecular glue for RNA. Molecular glue could bring two RNA loops into contact leading to restoration of the active tertiary structure. The rationally designed ribozyme switch enabled regulation of gene expression by Z-NCTS and was functional in mammalian cells.
Datum: 07.12.2017


Ruthenium(II)-Catalyzed Synthesis of Spirobenzofuranones by a Decarbonylative Annulation Reaction

The first decarbonylative insertion of an alkyne through C−H/C−C activation of six-membered compounds is reported. The Ru-catalyzed reaction of 3-hydroxy-2-phenyl-chromones with alkynes works most efficiently in the presence of the ligand PPh3 to provide spiro-indenebenzofuranones. Unlike previously reported metal-catalyzed decarbonylative annulation reactions, in the present decarbonylative annulation reaction, the annulation occurs before extrusion of carbon monoxide. Ruthenium(II)-catalyzed C−H/C−C activation, alkyne insertion, and decarbonylation reactions of 3-hydroxy-2-phenyl chromones and disubstituted alkynes afforded good yields of spiro-indenebenzofuranones.
Datum: 07.12.2017


A General Approach Towards Triazole-linked Adenosine Diphosphate Ribosylated Peptides and Proteins

Current chemistries to prepare Adenosine Diphosphate ribosylated (ADPr) peptides are not generally applicable due to the labile nature of this post-translational modification and its incompatibility with strong acidic conditions used in standard solid phase peptide synthesis protocols. We present a general strategy to prepare ADPr peptide analogues based on a copper catalysed click reaction between an azide modified peptide and an alkyne modified ADPr counterpart. We expand the scope of this approach to proteins by preparing two ADPr Ubiquitin analogues carrying the biological relevant α-glycosidic linkage. Biochemical validation using Legionella effector enzyme SdeA shows that clicked Ub-ADPr is well tolerated and highlights the potential of this strategy to prepare ADPr proteins.
Datum: 07.12.2017


A Glowing Trajectory between Bio- and Chemiluminescence: From Luciferin-Based Probes to Triggerable Dioxetanes

Bioluminescent and chemiluminescent probes are widely used for noninvasive imaging applications because of their high sensitivity and the simplicity of the equipment required to perform the measurement. Synthetic luciferin-analogue probes with in vivo imaging performance better than that of luciferin are now available. In addition, caged luciferin-based bioluminogenic probes have been emerged as a general tool for the visualization of different enzymes and analytes in vivo. Recent discoveries have led to development of highly efficient chemiluminescent probes that are extremely bright under physiological conditions. As discussed in this Minireview, chemiluminescence is ready to realize its potential as a valuable tool for imaging in living systems. Light-emitting compounds for bioimaging: In the last decade, chemists have significantly expanded the toolbox of imaging agents by preparing new bio- and chemiluminescence compounds. These developments include synthetic analogues of luciferin, caged luciferin-based bioluminogenic probes, and the recently emerging highly bright chemiluminescence dioxetane probes.
Datum: 07.12.2017


Sulfamate Esters Guide Selective Radical-Mediated Chlorination of Aliphatic C−H Bonds

Masked alcohols are particularly appealing as directing groups because of the ubiquity of hydroxy groups in organic small molecules. Herein, we disclose a general strategy for aliphatic γ-C(sp3)−H functionalization guided by a masked alcohol. Specifically, we determine that sulfamate ester derived nitrogen-centered radicals mediate 1,6-hydrogen-atom transfer (HAT) processes to guide γ-C(sp3)−H chlorination. This reaction proceeds through a light-initiated radical chain-propagation process and is capable of installing chlorine atoms at primary, secondary, and tertiary centers. Guiding light: Aliphatic γ-C(sp3)−H chlorination is guided by a sulfamate ester masked alcohol. This reaction involves light-initiated N−Cl bond homolysis, followed by an unusual radical-mediated 1,6-hydrogen-atom abstraction with subsequent chlorination enabled by a chain propagation process. This method allows chlorine atoms to be selectively installed at primary, secondary, and tertiary centers with predictable selectivity.
Datum: 07.12.2017


Gram-Scale Synthesis of the (−)-Sparteine Surrogate and (−)-Sparteine

An 8-step, gram-scale synthesis of the (−)-sparteine surrogate (22 % yield, with just 3 chromatographic purifications) and a 10-step, gram-scale synthesis of (−)-sparteine (31 % yield) are reported. Both syntheses proceed with complete diastereocontrol and allow access to either antipode. Since the syntheses do not rely on natural product extraction, our work addresses long-term supply issues relating to these widely used chiral ligands. Supply and demand: The first gram-scale synthesis of the (−)-sparteine surrogate and (−)-sparteine has been achieved. A convergent approach to the two diamines is reported, with (−)-sparteine being obtained through a resolution/recombination strategy. This work addresses long-term supply issues relating to these widely used chiral ligands.
Datum: 07.12.2017


Microemulsions, Micelles and Functional Gels. How Colloid and Soft Matter Preserve Works of Art

Colloid Science provides fundamental knowledge to fields such as pharmaceutical, detergency, paint and food industry. An exciting application is art conservation, which poses a challenge owing to the complex range of interfacial interactions involved in restoring artefacts. Currently, the majority of the most performing and environmentally safe cleaning and consolidation agents for artworks belong to soft matter and colloids. We report here on the development and application of increasingly complex systems, from microemulsions to semi-interpenetrating hydrogels containing such fluids. These systems have been used on diverse artefacts, from Renaissance frescos to works by Picasso and Pollock. Chemical design can be implemented to meet the requirements of curators, and knowledge of the colloids structure and dynamics can overcome serendipitous approaches of traditional conservation practice. Finally, we summarize future perspectives that soft matter and colloid science can disclose in the field of cultural heritage preservation.
Datum: 07.12.2017


Visible Light-Driven Iminyl Radical-Mediated C-C Single Bond Cleavage/Radical Addition Cascade of Oxime Esters

A room temperature, visible light-driven N-centered iminyl radical-mediated and redox-neutral C-C single bond cleavage/radical addition cascade reaction of oxime esters and unsaturated systems has been accomplished. The strategy tolerates a wide range of O-acyl oximes and unsaturated systems such as alkenes, silyl enol ethers, alkynes, and isonitrile, enabling highly selective formation of various chemical bonds. This protocol thus provides an efficient approach to various diversely substituted cyano-containing alkenes, ketones, carbocycles and heterocycles.
Datum: 07.12.2017


Incorporation of 2,6-Connected Azulene Units into the Backbone of Conjugated Polymers towards High-Performance Organic Optoelectronic Materials

Azulene is considered to be a promising candidate for constructing optoelectronic materials. We present herein an effective strategy to obtain high performance conjugated polymers by incorporating 2,6-connected azulene units into the polymeric backbone, and two conjugated copolymers P(TBAzDI-TPD) and P(TBAzDI-TFB) are designed and synthesized based on this strategy. They are the first two examples for 2,6-connected azulene-based conjugated polymers and exhibit unipolar n-type transistor performance with an electron mobility of up to 0.42 cm2 V-1 s-1, which is among the highest values for n-type polymeric semiconductors in bottom-gate top-contact organic field effect transistors. Besides, preliminary all-polymer solar cell devices with P(TBAzDI-TPD) as the electron acceptor and PTB7-Th as the electron donor display a power conversion efficiency of 1.82%.
Datum: 07.12.2017


Direct Dehydroxytrifluoromethoxylation of Alcohols

The first example of a direct dehydroxytrifluoromethoxylation of alcohols has been developed. This method generated an alkyl fluoroformate in situ from alcohols, followed by nucleophilic trifluoromethoxylation with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent. The reaction is operationally simple and scalable, and it proceeds under mild reaction conditions to provide access to a wide range of trifluoromethyl ethers from alcohols. In addition, this method is suitable for the late-stage trifluoromethoxylation of complex small molecules. Short and simple: A direct dehydroxytrifluoromethoxylation of alcohols with trifluoromethyl arylsulfonate (TFMS) as the trifluoromethoxylation reagent is reported. The reaction is operationally simple and amenable to gram-scale synthesis. Preliminary mechanistic studies suggest that the reaction may proceed through an alkyl fluoroformate intermediate that subsequently undergoes nucleophilic trifluoromethoxylation.
Datum: 07.12.2017


Cryo-EM Revolutionizes the Structure Determination of Biomolecules

Freeze frame: The Nobel Prize in Chemistry 2017 was jointly awarded to Jacques Dubochet, Joachim Frank, and Richard Henderson for “developing cryo-electron microscopy (cryo-EM) for the high-resolution structure determination of biomolecules in solution”. This Highlight describes how the field of cryo-EM developed from the first transmission electron microscope in 1931 to the sophisticated technique of today.
Datum: 07.12.2017


A Gold-Catalyzed Domino Cyclization Enabling Rapid Construction of Diverse Polyheterocyclic Frameworks

We report herein an efficient gold(I)-catalyzed post-Ugi domino dearomatization/ipso-cyclization/Michael sequence that enables access to libraries of diverse (hetero)arene-annulated tricyclic heterocycles. This process affords novel complex polycyclic scaffolds in moderate to good yields from readily available acyclic precursors with excellent chemo-, regio-, and diastereoselectivity. The power of this strategy has been demonstrated by the rapid synthesis of 40 highly functionalized polyheterocycles bearing indole, pyrrole, (benzo)furan, (benzo)thiophene, pyrazole, and electron-rich arene groups in two operational steps. Two-stride synthesis: A post-Ugi gold(I)-catalyzed domino dearomatization/ipso-cyclization/Michael sequence enabled facile access to diverse (hetero)arene-annulated tricyclic heterocycles from readily available precursors. The power of this strategy was demonstrated by the rapid synthesis of 40 highly functionalized polyheterocycles containing indole, pyrrole, (benzo)furan, (benzo)thiophene, pyrazole, and electron-rich arene groups.
Datum: 07.12.2017


Initial Steps of Amyloidogenic Peptide Assembly Revealed by Cold-Ion Spectroscopy

The early stages of fibril formation are difficult to capture in solution. We use cold-ion spectroscopy to examine an 11-residue peptide derived from the protein transthyretin and clusters of this fibre-forming peptide containing up to five units in the gas phase. For each oligomer, the UV spectra exhibit distinct changes in the electronic environment of aromatic residues in this peptide compared to that of the monomer and in the bulk solution. The UV spectra of the tetra- and pentamer are superimposable but differ significantly from the spectra of the monomer and trimer. Such a spectral evolution suggests that a common structural motif is formed as early as the tetramer. The presence of this stable motif is further supported by the low conformational heterogeneity of the tetra- and pentamer, revealed from their IR spectra. From comparison of the IR-spectra in the gas and condensed phases, we propose putative assignments for the dominant motif in the oligomers. It’s cold and ion-a go home: The early stages of amyloid formation of an 11-residue peptide derived from the protein transthyretin have been studied in the gas phase by means of UV and IR cold-ion spectroscopy. Spectral evolution suggests that a common structural motif is formed as early as the trimer of the peptide.
Datum: 07.12.2017


A Redox-Activated G-Quadruplex DNA Binder Based on a Platinum(IV)–Salphen Complex

There has been increasing interest in the development of small molecules that can selectively bind to G-quadruplex DNA structures. The latter have been associated with a number of key biological processes and therefore are proposed to be potential targets for drug development. Herein, we report the first example of a reduction-activated G-quadruplex DNA binder. We show that a new octahedral platinum(IV)–salphen complex does not interact with DNA in aqueous media at pH 7.4; however, upon addition of bioreductants such as ascorbic acid or glutathione, the compound is readily reduced to the corresponding square planar platinum(II) complex. In contrast to the parent platinum(IV) complex, the in situ generated platinum(II) complex has good affinity for G-quadruplex DNA. Be there and be square: A reduction-activated G-quadruplex DNA binder is reported. The new octahedral platinum(IV)–salphen complex does not interact with DNA in aqueous media at pH 7.4. However, upon addition of bioreductants such as ascorbic acid or glutathione, the compound is readily reduced to the corresponding square planar platinum(II) complex, which binds to G-quadruplex DNA with high affinity.
Datum: 07.12.2017


Catalytic Three-Component Machinery: Control of Catalytic Activity by Machine Speed

Three supramolecular slider-on-deck systems DS1–DS3 were obtained as two-component aggregates from the sliders S1–S3 and deck D with its three zinc porphyrin (ZnPor) binding sites. The binding of the two-footed slider to the deck varies with the donor qualities of and the steric hindrance at the pyridine/pyrimidine (pyr) feet, and was effected by two NpyrZnPor interactions. Accordingly, the sliders move over the three zinc porphyrins in the deck at different speeds, namely with 32.2, 220, and 440 kHz at room temperature. The addition of N-methylpyrrolidine as an organocatalyst to DS1–DS3 generates catalytic three-component machineries. By using a conjugate addition as a probe reaction, we observed a correlation between the operating speed of the slider-on-deck systems and the yields of the catalytic reaction. As the thermodynamic binding of the slider decreases, both the frequency of the sliding motion and the yield of the catalytic reaction increase. It's the engine speed! The coupling of an output (here catalysis) to the speed of a mechanical motion is a characteristic feature of machinery. With increasing sliding speed of the three-component machinery, the catalysis of an organic transformation is enhanced. The effect may be explained by a dynamic neighboring-group participation.
Datum: 07.12.2017


Boosting Electrochemical Water Oxidation with Metal Hydroxide Carbonate Templated Prussian Blue Analogues

Development of efficient and stable catalyst systems with low cost, abundant and non-toxic materials is the primary demand for the electrochemical water oxidation. Here, we report a unique method for the syntheses of metal hydroxide carbonate templated Prussian blue analogues (PBAs) on carbon cloth and their outstanding water oxidation activities in alkaline medium. The best water oxidation activity is obtained with cobalt hydroxide carbonate templated t-CoII-CoIII with overpotential as low as 240 mV to reach the current density 10 mA cm-2 and produces constant current over 48 h in chronoamperometric measurements. Moreover, the catalysts outperform the activities of the PBAs prepared without any template and even the noble metal catalyst RuO2. Spectroscopic and microscopic studies clearly prove that the PBAs are transformed into layered hydroxide-oxyhydroxide structures during electrochemical process and provide the active sites for the water oxidation.
Datum: 07.12.2017


Chemicals on demand: Photo-induced release from nano- and microparticle containers

A benzoin-derived diol linker was synthesized and used to create biocompatible polyesters, which can be fully decomposed on demand triggered by UV light. Extensive structural optimization of the linker unit was performed to enable a defined encapsulation of structurally diverse organic compounds in polymeric structures and a well-controllable polymer cleavage process. Selective tracking of release kinetics of encapsulated model compounds from the polymeric nano- and microparticle containers was enabled by confocal laser scanning microscopy as a proof-of-principle for desired applications. The model compounds comprised physico-chemical properties from fully hydrophilic to fully hydrophobic. Demonstrated biocompatibility of the utilized polyesters and degradation products enables advanced applications, e.g. for smart packaging of UV sensitive pharmaceuticals or nutrition components, or even in the area of spatially-selective self-healing processes.
Datum: 07.12.2017


Breaking Unstrained C-C Bond in Acenes by Boron and Light: Transformation of Naphthalene to Benzoborepin

Naphthalene and acenaphthene with peri 2-py and BMes2 (Mes = mesityl) substituents have been found to undergo facile phototransformation, cleaving a C-C bond of naphthalene and forming 2-py-bound benzoborepins as the major products. Mechanistic pathways of this new photoreaction are established by examining both excited and ground states using CASSCF and CASPT2 methods with DFT and TD-DFT. The Mes to py-naphthyl charge transfer transition and the Mes migration from boron to naphthyl drive this unprecedented C-C bond cleavage and boron insertion reaction.
Datum: 06.12.2017


Heterotelechelic polymers via ring opening metathesis and regioselective chain transfer

Heterotelechelic polymers were synthesized via a kinetic telechelic ring opening metathesis polymerization method relying on the regioselective cross metathesis of the propagating Grubbs' first generation catalyst with cinnamyl alcohol derivatives. This procedure allowed the synthesis of hetero-bis-end-functional polymers in a one-pot setup. The molecular weight of the polymers could be controlled by varying the ratio between cinnamyl alcohol derivatives and monomer. The end functional groups can be changed using different aromatically substituted cinnamyl alcohol derivatives. Different monomers were investigated and the presence of the functional groups was shown by NMR spectroscopy and MALDI-ToF mass spectrometry. Labeling experiments with dyes were conducted to demonstrate the orthogonal addressability of both chain ends of the heterotelechelic polymers obtained.
Datum: 06.12.2017


Fabrication of defined polydopamine nanostructures by DNA origami-templated polymerization

A versatile, bottom-up approach allows the controlled fabrication of polydopamine (PD) nanostructures on DNA origami. PD is a biosynthetic polymer that has been investigated as an adhesive and promising surface coating material. However, the control of dopamine polymerization is challenged by the multistage-mediated reaction mechanism and diverse chemical structures in PD. DNA origami decorated with multiple horseradish peroxidase-mimicking DNAzyme motifs was used to control the shape and size of PD formation with nanometer resolution. These fabricated PD nanostructures can serve as "supramolecular glue" for controlling DNA origami conformations. Facile liberation of the PD nanostructures from the DNA origami templates has been achieved in acidic medium. This presented DNA origami-controlled polymerization of a highly crosslinked polymer provides a unique access towards anisotropic PD architectures with distinct shapes that were retained even in the absence of the DNA origami template
Datum: 06.12.2017


Cross-Coupling of Sodium Sulfinates with Aryl, Heteroaryl and Vinyl Halides by Nickel/photoredox dual catalysis

An efficient photoredox/nickel dual catalyzed sulfonylation reaction of aryl, heteroaryl, and vinyl halides has been achieved for the first time. This newly developed sulfonylation protocol provides a versatile method for the synthesis of diverse aromatic sulfones at room temperature and shows excellent functional group tolerance. The electrophilic coupling partners are not limited to aryl, heteroaryl and vinyl bromides but also less reactive aryl chlorides are suitable substrates for this transformation.
Datum: 06.12.2017


Visible-light Emulsion Photopolymerization of Styrene

The photopolymerization of styrene in emulsion is achieved in a conventional double wall reactor equipped with a LED ribbon coiled around the external glass wall. Styrene mixed to acridine orange is added to the water phase containing sodium dodecyl sulfate, a water-soluble N-heterocyclic carbene-borane and disulfide, and irradiated. Highly stable latexes are obtained, with particles up to a diameter of 300 nm. The ability to reach such large particles sizes via a photochemical process in a dispersed medium is due to the use of visible light: the photons in the visible range are less scattered by larger objects and thus penetrate and initiate better the polymerizations. They are also greener and cheaper to produce via LEDs, and much safer than UVs. The method presented does not require any specific glassware; it works at lower temperature and delivers larger particles compared to thermal processes at similar solids contents and surfactant concentrations.
Datum: 06.12.2017


Dynamic Cross-Exchange in Halophosphonium Species: Direct Observation of Stereochemical Inversion in the Course of an SN2 Process

The complex fluxional interconversions between otherwise very similar phosphonium bromides and chlorides R3PX+X− (R=Alk, Ar, X=Cl or Br) were studied by NMR techniques. Their energy barriers are typically ca. 11 kcal mol−1, but rise rapidly as bulky groups are attached to phosphorus, revealing the importance of steric factors. In contrast, electronic effects, as measured by Hammett analysis, are modest (ρ 1.46) but still clearly indicate negative charge flow towards phosphorus in the transition state. Most significantly, detailed analysis of the exchange pathways unequivocally, and for the first time in any such process, shows that nucleophilic attack of the nucleophilic anion on the tetrahedral centre results in inversion of configuration. Double lift: The energy barrier to halogen exchange in halophosphonium species rises rapidly when either bulky substituents or electron-donating groups are present. When degeneracy is lifted twice (see picture), measurement of diastereomeric cross-exchange provides direct observation of stereochemical inversion in the course of an SN2 process.
Datum: 06.12.2017


Insights into the Dual Activity of a Bifunctional Dehydratase-Cyclase Domain

Oxygen-containing heterocycles are a common structural motif in polyketide natural products and contribute significantly to their biological activity. Here, we report structural and mechanistic investigations on AmbDH3, a polyketide synthase domain with dual activity as dehydratase (DH) and pyran-forming cyclase in ambruticin biosynthesis. AmbDH3 is similar to monofunctional DH domains, using H51 and D215 for dehydration. V173 was confirmed as a diagnostic residue for cyclization activity by a mutational study and enzymatic in vitro experiments. Similar motifs were observed in the seemingly monofunctional AmbDH2, which also shows an unexpected cyclase activity. Our results pave the way for mining of hidden cyclases in biosynthetic pathways. They also open interesting prospects for the generation of novel biocatalysts for chemoenzymatic synthesis and pyran-polyketides by combinatorial biosynthesis. The crystal structure of the bifunctional dehydratase-cyclase AmbDH3 from ambruticin biosynthesis was solved at 1.17 Å resolution. Bioinformatic analysis and molecular modeling revealed an active-site Y-to-V mutation that is essential for cyclase activity. A mutational study combined with enzymatic activity assays in vitro confirmed the central role of V173.
Datum: 06.12.2017


Isoindigo-3,4-Difluorothiophene Polymer Acceptors Yield “All-Polymer” Bulk-Heterojunction Solar Cells with over 7 % Efficiency

Poly(isoindigo-alt-3,4-difluorothiophene) (PIID[2F]T) analogues used as “polymer acceptors” in bulk-heterojunction (BHJ) solar cells achieve >7 % efficiency when used in conjunction with the polymer donor PBFTAZ (model system; copolymer of benzo[1,2-b:4,5-b′]dithiophene and 5,6-difluorobenzotriazole). Considering that most efficient polymer-acceptor alternatives to fullerenes (e.g. PC61BM or its C71 derivative) are based on perylenediimide or naphthalenediimide motifs thus far, branched alkyl-substituted PIID[2F]T polymers are particularly promising non-fullerene candidates for “all-polymer” BHJ solar cells. Light work for polymers: Poly(isoindigo-alt-3,4-difluorothiophene) (PIID[2F]T) analogues can serve as fullerene alternatives in “all-polymer” bulk-heterojunction (BHJ) solar cells. Employing PIID[2F]T with a wide-band-gap polymer donor yields efficiencies as high as 7.3%, and some of the best open-circuit voltage figures (ca. 1.0 V) reported for BHJ solar cells.
Datum: 06.12.2017


Synthesis and Reactivity of Nickel-Stabilised μ2:η2,η2-P2, As2 and PAs Units

The reactivity of two paramagnetic nickel(I) compounds, CpNi(NHC) (where Cp=cyclopentadienyl; NHC=1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) or 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)), towards [Na(dioxane)x][PnCO] (Pn=P, As) is described. These reactions afford symmetric bimetallic compounds (μ2:η2,η2-Pn2){Ni(NHC)(CO)}2. Several novel intermediates en route to such species are identified and characterised, including a compound containing the PCO− anion in an unprecedented μ2:η2,η2-binding mode. Ultimately, on treatment of the (μ2:η2,η2-Pn2){Ni(IMes)(CO)}2 compounds with carbon monoxide, the Pn2 units can be released, affording P4 in the case of the phosphorus-containing species, and elemental arsenic in the case of (μ2:η2,η2-As2){Ni(IMes)(CO)}2. The butterfly effect: The reactivity of two paramagnetic nickel(I) compounds, CpNi(NHC) (where Cp=cyclopentadienyl; NHC=N-heterocyclic carbene), towards [Na(dioxane)x][PnCO] (Pn=P, As) is described.
Datum: 06.12.2017


Biocatalytic Oxidative Cascade for the Conversion of Fatty Acids to α-Ketoacids via Internal H2O2 Recycling

The functionalization of bio-based chemicals is essential to allow valorization of natural carbon sources. An atom-efficient biocatalytic oxidative cascade was developed for the conversion of saturated fatty acids to α-ketoacids. Employment of P450 monooxygenase in the peroxygenase mode for regioselective α-hydroxylation of fatty acids combined with enantioselective oxidation by α-hydroxyacid oxidase(s) resulted in internal recycling of the oxidant H2O2, thus minimizing degradation of ketoacid product and maximizing biocatalyst lifetime. The O2-dependent cascade relies on catalytic amounts of H2O2 and releases water as sole by-product. Octanoic acid was converted under mild conditions in aqueous buffer to 2-oxooctanoic acid in a simultaneous one-pot two-step cascade in up to >99 % conversion without accumulation of hydroxyacid intermediate. Scale-up allowed isolation of final product in 91 % yield and the cascade was applied to fatty acids of various chain lengths (C6:0 to C10:0). An atom-efficient biocatalytic oxidative cascade that combines a P450 monooxygenase in the peroxygenase mode with α-hydroxyacid oxidase(s) was developed for the conversion of saturated fatty acids to α-ketoacids and resulted in the internal recycling of the oxidant H2O2. Overall, the O2-dependent cascade relies on catalytic amounts of H2O2 and releases water as the sole by-product.
Datum: 06.12.2017


Exploiting the Strong Hydrogen Bond Donor Properties of a Borinic Acid Functionality for Fluoride Anion Recognition

Borinic acids have typically not been considered as hydrogen bond donor groups in molecular recognition. Described herein is a bifunctional borane/borinic acid derivative (2) in which the two functionalities are connected by a 1,8-biphenylenediyl backbone. Anion binding studies reveal that 2 readily binds a fluoride anion by formation of a unique B−F⋅⋅⋅H−O−B hydrogen bond. This hydrogen bond is characterized by a short H-F distance of 1.79(3) Å and a large coupling constant (1JHF) of 57.2 Hz. The magnitude of this interaction, which has also been investigated computationally, augments the fluoride anion binding properties of 2, thus making it compatible with aqueous environments. A Brønsted and Lewis handshake: The borinic acid functionality of a new diboron electrophilic host reaches across the binding pocket to engage a borane-bound fluoride anion in a strong hydrogen-bonding interaction. The resulting B−F⋅⋅⋅H−O−B interaction stabilizes the complex in aqueous solutions, thereby illustrating the role that borinic acids may play as hydrogen bond donor groups.
Datum: 06.12.2017


Structure Re-Determination and Superconductivity Observation of Bulk 1T MoS2

2H MoS2 has been intensively studied because of layer-dependent electronic structures and novel physical properties. Though the metastable 1T MoS2 with the [MoS6] octahedron was observed from the microscopic area, the true crystal structure of 1T phase has not been determined strictly. Moreover, the true physical properties have not been demonstrated from experiments due to the challenge for the preparation of pure 1T MoS2 crystals. Here, we successfully synthesized the 1T MoS2 single crystals and re-determined the crystal structure of 1T MoS2 from single-crystal X-ray diffraction. 1T MoS2 crystalizes in space group P-3m1 with a cell of a = b = 3.190(3) Å and c = 5.945(6) Å. The individual MoS2 layer consists of MoS6 octahedron sharing edge with each other. More surprisingly, the bulk 1T MoS2 crystals undergo a superconducting transition of Tc = 4 K, which is the first observation of superconductivity in pure 1T MoS2 phase.
Datum: 06.12.2017


Total Synthesis of Bryostatin 8 via an Organosilane-Based Strategy

Convergent total synthesis of bryostatin 8 has been accomplished via an organosilane-based strategy. The C ring is constructed stereoselectively through geminal bis(silane)-based [1,5]-Brook rearrangement, and the B ring through geminal bis(silane)-based Prins cyclization, efficiently joining the northern and southern parts of the molecule.
Datum: 06.12.2017


Catalytic Dibenzocyclooctene Synthesis via Cobalt(III)–Carbene Radical and ortho-Quinodimethane Intermediates

The metalloradical activation of ortho-benzallylaryl N-tosyl hydrazones with [Co(TPP)] (TPP=tetraphenylporphyrin) as the catalyst enabled the controlled exploitation of the single-electron reactivity of the redox non-innocent carbene intermediate. This method offers a novel route to prepare eight-membered rings, using base metal catalysis to construct a series of unique dibenzocyclooctenes through selective Ccarbene−Caryl cyclization. The desired eight-membered-ring products were obtained in good to excellent yields. A large variety of aromatic substituents are tolerated. The proposed reaction mechanism involves intramolecular hydrogen atom transfer (HAT) to CoIII–carbene radical intermediates followed by dissociation of an ortho-quinodimethane that undergoes 8π cyclization. The mechanism is supported by DFT calculations, and the presence of radical-type intermediates was confirmed by trapping experiments. Metalloradical activation of the shown N-tosyl hydrazones with [Co(TPP)] provides an effective method for the construction of a series of unique dibenzocyclooctenes in good to excellent yields. The proposed reaction mechanism involves intramolecular hydrogen atom transfer to the key CoIII–carbene radical followed by dissociation of an ortho-quinodimethane, which then undergoes 8π cyclization.
Datum: 06.12.2017


Molecular pillar approach to grow vertical covalent organic framework nanosheets on graphene: new hybrid materials for energy storage

Hybrid 2D-2D materials composed by perpendicularly oriented covalent organic frameworks (COFs) and graphene were prepared and tested for energy storage applications. Diboronic acid molecules covalently attached to graphene oxide (GO) were used as nucleation sites for directing vertical growth of COF-1 nanosheets (v-COF-GO). The hybrid material shows forest of COF-1 nanosheets with thickness of ~3 to 15 nm in edge-on orientation relative to GO. The same reaction performed in absence of molecular pillars resulted in uncontrollable growth of thick COF-1 platelets parallel to the surface of GO. The v-COF-GO was converted into conductive carbon material preserving the nanostructure of precursor with ultrathin porous carbon nanosheets grafted to graphene in edge-on orientation. It was demonstrated as high-performance electrode material for supercapacitors. The molecular pillar approach can be used for preparation of many other 2D-2D materials with control of their relative orientation.
Datum: 06.12.2017


Protection Group Effects during α,γ-Diol Lignin Stabilization Promote High-Selectivity Monomer Production

Protection groups were introduced during biomass pretreatment to stabilize lignin's α,γ-diol group during its extraction and prevent its condensation. Acetaldehyde and propionaldehyde stabilized the α,γ-diol without any aromatic ring alkylation, which significantly increased final product selectivity. The subsequent hydrogenolysis catalyzed by Pd/C, generated lignin monomers at near-theoretical yields based on Klason lignin (48% from birch, 20% from spruce, 70% from high-syringyl transgenic poplar) with - in the case of the poplar - high selectivity to a single 4-n-propanolsyringol product (80%). Unlike direct hydrogenation of native wood, hydrogenolysis of protected lignin with Ni/C also led to high selectivity to this single product (78%), paving the way to high-selectivity lignin upgrading with base metal catalysts. The use of extracted lignin facilitated valorization of biomass's polysaccharides, leading to high yields of all three major biomass polymers to a single product.
Datum: 06.12.2017


"Dumbbell"- and "Clackers"-Shaped Dimeric Derivatives of Monocarba-closo-dodecaborate

We designed, synthesized and characterized two types of dimeric forms of monocarba-closo-dodecaborate, namely, a "dumbbell"-shaped dianion having a C-C bond and a "clackers"-shaped monoanion having an iodonium linker. The unique architectures of these anionic molecules were established by X-ray analysis. Spectroscopic analysis, DFT calculations, and reactivity experiments revealed high anionic and chemical stability of both anions, which are crucial properties for weakly coordinating anions.
Datum: 06.12.2017


Spotlights on our sister journals: Angew. Chem. Int. Ed. 50/2017


Datum: 06.12.2017


Graphical Abstract: Angew. Chem. Int. Ed. 50/2017


Datum: 06.12.2017


Frontispiece: Orientation-Induced Adsorption of Hydrated Protons at the Air–Water Interface

Air–Water Interface In their Communication on page 15846; ff., D. J. Bonthuis et al. describe the calculation of surface tensions and ionic surface propensities at air–water interfaces by molecular dynamics simulations.
Datum: 06.12.2017


A 30 nm Nanopore Electrode: Facile Fabrication and Direct Revealing of the Intrinsic Feature in Single Nanoparticle Collision

Clarifying the hidden but intrinsic feature of single nanoparticles by nanoelectrochemistry could help understand its potential for diverse applications. The uncontrolled interface and bandwidth limitation in the electrochemical measurement put the obstacle in single particle collision. Here, we demonstrate a well-defined 30 nm nanopore electrode with a rapid chemical-electrochemical fabrication method which provides a high reproducibility in both size and nanoelectrode performance. A capacitance-based detection mechanism is demonstrated to achieve a high current resolution of 0.6 pA ± 0.1 pA (RMS) and a high the temporal resolution of 0.01 ms. By utilizing this electrode, the dynamic interactions of every single particle in the mixture could be directly read during the collision process. The collision frequency is two orders of magnitude higher than previous reports, which helps reveal the hidden features of nanoparticles during the complex and multidimensional interaction processes.
Datum: 06.12.2017


Environmental-Friendly Solid Synthesis of Fe-N-C Electrocatalyst with Fe Exclusively in Atomically Dispersed Fe-N4 Moieties for High-Power Proton Exchange Membrane Fuel Cells

Environmental-friendly synthesis of highly active Fe-N-C electrocatalyst for proton exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. Herein, we report a green, simple and scalable method to fabricate Fe(II)-doped ZIF-8, which can be further pyrolyzed into Fe-N-C with 3 wt.% of Fe exclusively in Fe-N4 active moieties. Significantly, this Fe-N-C derived acidic PEMFC exhibits an unprecedented current density of 1.65 A cm-2 at 0.6 V and the highest power density of 1.14 W cm-2 compared with previously reported NPMCs. The excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe-N4 active moieties on the small and uniform catalyst nanoparticles.
Datum: 06.12.2017


Selective Nascent Polymer Catch and Release Enables Scalable Isolation of Multi-Kilobase Single-Stranded DNA

Scalable methods currently are lacking for isolation of long ssDNA, an important material for numerous biotechnological applications. Conventional biomolecule purification strategies achieve target capture using solid supports, which are limited in scale and susceptible to contamination due to nonspecific adsorption and desorption on the substrate surface. We herein disclose Selective Nascent Polymer Catch and Release (SNAPCAR), a method that utilizes the reactivity of growing poly(acrylamide-co-acrylate) chains to capture acrylamide-labeled molecules in free solution. The copolymer acts as a stimuli-responsive anchor that can be precipitated on demand to pull down the target from solution. SNAPCAR enabled scalable isolation of multi-kilobase ssDNA with high purity and 50-70% yield. The ssDNA products were used to fold various DNA origami. SNAPCAR-produced ssDNA will expand the scope of applications in nanotechnology, gene editing, and DNA library construction.
Datum: 06.12.2017


Hydrophilicity and microsolvation of an organic molecule resolved on the sub-molecular level by scanning tunneling microscopy

We used low-temperature scanning tunneling microscopy to follow the formation of a solvation shell around an adsorbed functionalized azo dye from the attachment of the first water molecule to a fully solvated molecule. Specific functional groups bind initially one water molecule each, which act as anchor points for additional water molecules. Further water attachment occurs in areas close to these functional groups even when the functional groups themselves are already saturated. In contrast, water molecules surround the hydrophobic parts of the molecule only, when the two-dimensional solvation shell closes around them. Our study thus traces hydrophilic and hydrophobic properties of an organic molecule down to a sub molecular length scale.
Datum: 05.12.2017


A Permselective CeOx Coating Improves the Stability of Oxygen Evolution Electrocatalysts

Highly active NiFeOx electrocatalysts for the oxygen evolution reaction (OER) suffer gradual deactivation with time due to the loss of Fe species from the active sites into solution during catalysis. Here, we describe the anodic deposition of a CeOx layer that prevents the loss of such Fe species from the OER catalysts, achieving a highly stable performance. The CeOx layer does not affect the OER activity of the catalyst underneath but exhibits unique permselectivity, allowing the permeation of OH− and O2 through while preventing the diffusion of redox ions through the layer to function as a selective O2-evolving electrode. The use of such permselective protective layer provides a new strategy for improving the durability of electrocatalysts.
Datum: 05.12.2017


Solventless and Metal-Free Synthesis of High Molecular Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines

The solventless reaction of diisopropylaminoborane with n-butylamine, at room temperature, leads to a mixture of well identified B(sp2)H, B(sp3)H2 and B(sp3)H3 boron containing species. At low temperature, the reaction outcome is completely modified leading selectively to the formation of high mass polybutylaminoborane. Extended to a variety of primary amines under solventless conditions and at low temperature, this reaction provides a new, efficient and direct metal-free access to high molecular mass polyaminoboranes in good to high yield, in very mild conditions.
Datum: 05.12.2017


Diversity-Oriented Synthesis of Furo[3,2-c]coumarins and Benzofuranyl Chromenones via Chemoselective Acylation/Wittig Reaction

A highly efficient and chemoselective one-pot protocol for the diversity-oriented synthesis of two coumarin-based formal cross-coupling adducts, viz. furo[3,2-c]coumarins and 3-benzofuranyl chromenones is described. Key attributes of the methodology comprise an initial chemoselective acylation of functionalized phosphorus zwitterions followed by chemoselective intramolecular Wittig reaction that preferentially resulted in one of the two coumarin derivatives in high yields, depending on relative reactivities and addition sequence of acylating agents.
Datum: 05.12.2017


Conversion of Olefins to Ketones by an Iron-Catalyzed Wacker-type Oxidation Using Oxygen as Sole Oxidant

We describe a mild and operationally simple protocol for the oxidation of olefins to ketones. The reaction is catalyzed by the hexadecafluorinated iron-phthalocyanine complex FePcF16 using stoichiometric amounts of triethylsilane as additive under oxygen to give ketones in good to high yields with excellent chemoselectivity and functional group tolerance. Up to 95 % yield and 100 % regioselectivity for ketone formation are obtained, while the corresponding alcohol was observed as a by-product.
Datum: 05.12.2017


Back Cover: Three-Dimensional Printing with Biomass-Derived PEF for Carbon-Neutral Manufacturing (Angew. Chem. Int. Ed. 50/2017)

The synthesis of bioplastic from plants and its use in a 3D printing process are reported by V. P. Ananikov et al. in their Communication on page 15931 ff. Biomass-derived, easily accessible poly(ethylene-2,5-furandicarboxylate) was used for fused deposition modeling 3D printing. The suggested approach extends additive manufacturing processes to carbon-neutral materials and opens up new avenues for sustainable development.
Datum: 30.11.2017


Bilateral Awards from European Chemical Societies


Datum: 23.11.2017


The Effect of Methylammonium Iodide on the Supersaturation and Interfacial Energy of the Crystallization of Methylammonium Lead Triiodide Single Crystals

It is very important to study the crystallization of hybrid organic–inorganic perovskites because their thin films are usually prepared from solution. The investigation on the growth of perovskite films is however limited by their polycrystallinity. In this work, methylammonium lead triiodide single crystals grown from solutions with different methylammonium iodide (MAI):lead iodide (PbI2) ratios were investigated. We observed a V-shaped dependence of the crystallization onset temperature on the MAI:PbI2 ratio. This is attributed to the MAI effects on the supersaturation of precursors and the interfacial energy of the crystal growth. At low MAI:PbI2 ratio (<1.7), more MAI leads to the supersaturation of the precursors at lower temperature. At high MAI:PbI2 ratio, the crystal growing plans change from (100)-plane dominated to (001)-plane dominated. The latter have higher interfacial energy than the former, leading to a higher crystallization onset temperature. Growing planes: The methylammonium iodide (MAI):PbI2 ratio significantly affects the supersaturation of precursors and the interfacial energy of the crystal growth. As a result, it has an effect on both the crystallization onset temperature (see picture) and the shape of perovskite single crystals.
Datum: 23.11.2017


Rhodium(II)- or Copper(I)-Catalyzed Formal Intramolecular Carbene Insertion into Vinylic C(sp2)−H Bonds: Access to Substituted 1H-Indenes

A rhodium(II)- or copper(I)-catalyzed formal intramolecular carbene insertion into vinylic C(sp2)−H bonds is reported herein. This method provides straightforward access to 1H-indenes with high efficiency and excellent functional-group compatibility. Mechanistically, the reaction is proposed to involve the following sequence: metal carbene formation, intramolecular nucleophilic addition of the double bond to the electron-deficient carbene carbon atom, dearomatization, and finally a 1,5-H shift. Get into vinyl! A rhodium(II)- or copper(I)-catalyzed formal carbene insertion into vinylic C−H bonds has been developed as a straightforward method for the synthesis of 1H-indenes with high efficiency and good functional-group compatibility (see scheme). The reaction is proposed to follow a stepwise mechanism involving nucleophilic addition of the double bond to the metal carbene and dearomatization/aromatization processes.
Datum: 22.11.2017


Bifurcated Nickel-Catalyzed Functionalizations: Heteroarene C−H Activation with Allenes

A unified strategy for nickel(0)-catalyzed C−H allylations, alkenylations, and dienylations has been realized through versatile hydroarylations of allenes with ample scope. Thus, an inexpensive nickel catalyst modified with a N-heterocyclic carbene ligand enabled the direct transformation of C−H bonds of biologically relevant imidazole and purine derivatives with full control of regio- and chemoselectivity. Facile C−H activation: Bifurcated nickel(0)-catalyzed C−H allylations, alkenylations, and dienylations have been accomplished by versatile hydroarylations of allenes with full control of regio- and chemoselectivity. The scope of the reaction covers a variety of imidazole and purine derivatives.
Datum: 22.11.2017


Site-Specific Pre-Swelling-Directed Morphing Structures of Patterned Hydrogels

Morphing materials have promising applications in various fields, yet how to program the self-shaping process for specific configurations remains a challenge. Herein we show a versatile approach to control the buckling of individual domains and thus the outcome configurations of planar-patterned hydrogels. By photolithography, high-swelling disc gels were positioned in a non-swelling gel sheet; the swelling mismatch resulted in out-of-plain buckling of the disc gels. To locally control the buckling direction, masks with holes were used to guide site-specific swelling of the high-swelling gel under the holes, which built a transient through-thickness gradient and thus directed the buckling during the subsequent unmasked swelling process. Therefore, various configurations of an identical patterned hydrogel can be programmed by the pre-swelling step with different masks to encode the buckling directions of separate domains. A swell idea: Morphing structures of photo-lithographically patterned hydrogels were programmed by selective pre-swelling of the regions with a high-swelling capacity. This step built a transient through-thickness gradient and directed the buckling direction. Different combinations of localized buckling led to different morphing structures from identically patterned hydrogels.
Datum: 22.11.2017


A Tunable and Enantioselective Hetero-Diels–Alder Reaction Provides Access to Distinct Piperidinoyl Spirooxindoles

The active complexes of chiral N,N′-dioxide ligands with dysprosium and magnesium salts catalyze the hetero-Diels–Alder reaction between 2-aza-3-silyloxy-butadienes and alkylidene oxindoles to selectively form 3,3′- and 3,4′-piperidinoyl spirooxindoles, respectively, in very high yields and with excellent enantioselectivities. The exo-selective asymmetric cycloaddition successfully regaled the construction of sp3-rich and highly substituted natural-product-based spirooxindoles supporting many chiral centers, including contiguous all-carbon quaternary centers. Tuned to ring! DyIII and MgII salts with an N,N′-dioxide ligand catalyze enantioselective hetero-Diels–Alder reactions of silyloxy-2-azadienes with alkylidene oxindoles to selectively form 3,3′- and 3,4′-piperidinoyl-spirooxindoles, respectively, in excellent yields with excellent enantiomeric ratios. Boc=tert-butoxycarbonyl, TBS=tert-butyldimethylsilyl, Tf=trifluoromethanesulfonyl.
Datum: 22.11.2017


Jan-E. Bäckvall

“I like refereeing because it keeps me updated and it forces me to read recent interesting work in a critical manner. What I look at first in a publication are the abstract and the conclusion ...” This and more about Jan-E. Bäckvall can be found on page 15796.
Datum: 22.11.2017


Polyproline as a Minimal Antifreeze Protein Mimic That Enhances the Cryopreservation of Cell Monolayers

Tissue engineering, gene therapy, drug screening, and emerging regenerative medicine therapies are fundamentally reliant on high-quality adherent cell culture, but current methods to cryopreserve cells in this format can give low cell yields and require large volumes of solvent “antifreezes”. Herein, we report polyproline as a minimum (bio)synthetic mimic of antifreeze proteins that is accessible by solution, solid-phase, and recombinant methods. We demonstrate that polyproline has ice recrystallisation inhibition activity linked to its amphipathic helix and that it enhances the DMSO cryopreservation of adherent cell lines. Polyproline may be a versatile additive in the emerging field of macromolecular cryoprotectants. No culture shock: Polyproline is introduced as a mimic of antifreeze proteins, with ice recrystallisation inhibition activity linked to its amphipathic helix. These polymers are shown to enhance the cryopreservation of cultured cell monolayers. Polyproline can be obtained by synthetic and biosynthetic methods, making it an appealing macromolecular cryopreservative for storing donor cells and tissue.
Datum: 22.11.2017


Microwave-Assisted Synthesis of Heterocycles by Rhodium(III)-Catalyzed Annulation of N-Methoxyamides with α-Chloroaldehydes

α-Chloroaldehydes have been used as alkyne equivalents in rhodium-catalyzed syntheses of isoquinolones and 3,4-dihydroisoquinolins starting from N-methoxyamides. Compared to the existing technology, a complementary regioselectivity is achieved. Mechanistic investigations have been performed, and it was found that steric effects of both substrate and additive determine the product selectivity. Various other heterocycles, such as isoquinolines and lactones, can be prepared by transformation of the obtained products. Pinch of salt: α-Chloroaldehydes are used as equivalents of terminal alkynes, thus allowing preparation of isoquinolones, 2-pyridones, and 3,4-dihydroisoquinolines with regioselectivity complementary to that of known processes. Such products proved valuable for approaching other heterocycles. The anion of an added sodium salt presumably supports an ester enolate generation, or stabilizes assemblies induced by hydrogen-bond interactions.
Datum: 22.11.2017


Cyclic (Amino)(Phosphonium Bora-Ylide)Silanone: A Remarkable Room-Temperature-Persistent Silanone

A silanone substituted by bulky amino and phosphonium bora-ylide substituents has been isolated in crystalline form. Thanks to the exceptionally strong electron-donating phosphonium bora-ylide substituent, the lifetime at room temperature of the silanone is dramatically extended (t1/2=4 days) compared to the related (amino)(phosphonium ylide)silanone VI (t1/2=5 h), allowing easier manipulation and its use as precursor of new valuable silicon compounds. The interaction of silanone with a weak Lewis acid such as MgBr2 increases further its stability (no degradation after 3 weeks at room temperature). A silanone substituted with bulky amino and phosphonium bora-ylide substituents has been synthesized and isolated in crystalline form. Thanks to the exceptionally strong electron-donating phosphonium-bora-ylide substituent, the lifetime is dramatically extended (t1/2=4 days). The interaction with a weak Lewis acid such as MgBr2 increases further its stability, and no degradation of silanone was observed after 3 weeks at room temperature.
Datum: 22.11.2017


Understanding LiOH Chemistry in a Ruthenium-Catalyzed Li–O2 Battery

Non-aqueous Li–O2 batteries are promising for next-generation energy storage. New battery chemistries based on LiOH, rather than Li2O2, have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru-catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e− oxygen reduction reaction, the H in LiOH coming solely from added H2O and the O from both O2 and H2O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li2O2, LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long-lived battery. An optimized metal-catalyst–electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals. Labeling the events: Ru-catalyzed LiOH formation and decomposition reactions are demonstrated in a Li–O2 battery with added water. Its mechanism was revealed via isotopic labeling.
Datum: 21.11.2017


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

To date, it has not been possible to combine the high optical quality of silver particles with the good chemical stability and synthetic convenience in a fully aqueous system, while simultaneously allowing chemical surface functionalization. We present a synthetic pathway for future developments in information, energy and medical technology where strong optical/electronic properties are crucial. Therefore, the advantages inherent to gold are fused with the plasmonic properties of silver in a fully aqueous Au/Ag/Au core–shell shell system. These nanoparticles inherit low dispersity from their masked gold cores, yet simultaneously exhibit the strong plasmonic properties of silver. Protecting the silver surface with a thin gold layer enables oxidant stability and functionality without altering the Ag-controlled optical properties. This combines both worlds—optical quality and chemical stability—and is not limited to a specific particle shape. Optical quality and chemical stability: A general nanoparticle synthesis enables low dispersity and well-defined shape to be inherited from the masked gold cores, yet simultaneously allows the strong plasmonic properties of silver to be exhibited. Protecting the silver with a thin gold layer enables oxidant stability and surface functionality of this system without altering the silver-based optical properties.
Datum: 21.11.2017


GOx@ZIF-8(NiPd) Nanoflower: An Artificial Enzyme System for Tandem Catalysis

We report a facile approach to prepare an artificial enzyme system for tandem catalysis. NiPd hollow nanoparticles and glucose oxidase (GOx) were simultaneously immobilized on the zeolitic imidazolate framework 8 (ZIF-8) via a co-precipitation method. The as-prepared GOx@ZIF-8(NiPd) nanoflower not only exhibited the peroxidase-like activity of NiPd hollow nanoparticles but also maintained the enzymatic activity of GOx. A colorimetric sensor for rapid detection of glucose was realized through the GOx@ZIF-8(NiPd) based multi-enzyme system. Moreover, the GOx@ZIF-8(NiPd) modified electrode showed good bioactivity of GOx and high electrocatalytic activity for the oxygen reduction reaction (ORR), which could also be used for electrochemical detection of glucose. Flower power: NiPd hollow nanoparticles and glucose oxidase (GOx) were simultaneously immobilized on a ZIF-8 metal–organic framework via a co-precipitation method. The resulting artificial enzyme system maintains the GOx activity and also has oxygen reduction reaction (ORR) reactivity, building a bridge between nanozymes and natural enzymes.
Datum: 20.11.2017


Gold-Catalyzed Asymmetric Intramolecular Cyclization of N-Allenamides for the Synthesis of Chiral Tetrahydrocarbolines

Highly enantioselective gold-catalyzed intramolecular cyclization of N-allenamides was implemented by utilizing a designed chiral sulfinamide phosphine ligand (PC-Phos). This represents the first example of highly enantioselective intramolecular cyclization of N-allenamides. The practicality of this reaction was validated in the total synthesis of (R)-desbromoarborescidine A and formal synthesis of (R)-desbromoarborescidine C and (R)-deplancheine. Moreover, the catalyst system PC-Phos/AuNTf2 proved to be specifically efficient to promote the desymmetrization of N-allenamides in excellent yields with satisfactory ee values. Ringing the changes: The first example of highly enantioselective gold-catalyzed intramolecular cyclization of N-allenamides was implemented by utilizing PC-Phos ligands. The utility of this reaction was validated by the total synthesis of (R)-desbromoarborescidine A.
Datum: 20.11.2017


Efficient Water Reduction with sp3-sp3 Diboron(4) Compounds: Application to Hydrogenations, H–D Exchange Reactions, and Carbonyl Reductions

A series of crystalline sp3-sp3 diboron(4) compounds were synthesized and shown to promote the facile reduction of water with dihydrogen formation. The application of these diborons as simple and effective dihydrogen and dideuterium sources was demonstrated by conducting a series of selective reductions of alkynes and alkenes, and hydrogen–deuterium exchange reactions using two-chamber reactors. Finally, as the water reduction reaction generates an intermediate borohydride species, a range of aldehydes and ketones were reduced by using water as the hydride source. (B)reaking (B)ad: The reported sp3-sp3 diboron(4) compounds are capable of reducing water to dihydrogen. The produced gas has been utilized in a variety of reductive transformations. Furthermore, a selection of aldehydes and ketones can be reduced in the presence of such diboron compounds in water via an intermediary borohydride species.
Datum: 17.11.2017


Ring-Size-Modulated Reactivity of Putative Dicobalt-Bridging Nitrides: C−H Activation versus Phosphinimide Formation

Dicobalt complexes supported by flexible macrocyclic ligands were used to target the generation of the bridging nitrido species [(nPDI2)Co2(μ-N)(PMe3)2]3+ (PDI=2,6-pyridyldiimine; n=2, 3, corresponding to the number of catenated methylene units between imino nitrogen atoms). Depending on the size of the macrocycle and the reaction conditions (solution versus solid-state), the thermolysis of azide precursors yielded bridging phosphinimido [(2PDI2)Co2(μ-NPMe3)(PMe3)2]3+, amido [(nPDI2)Co2(μ-NH2)(PMe3)2]3+ (n=2, 3), and C−H amination [(3PDI2*-μ-NH)Co2(PMe3)2]3+ products. All results are consistent with the initial formation of [(nPDI2)Co2(μ-N)(PMe3)2]3+, followed by 1) PMe3 attack on the nitride, 2) net hydrogen-atom transfer to form N−H bonds, or 3) C−H amination of the alkyl linker of the nPDI2 ligand. The products of C−H amination, hydrogen-atom transfer, and phosphinimide formation were obtained following the thermal activation of dicobalt-bridging azides bound by flexible macrocyclic ligands. The size of the macrocycle was found to influence the product distribution.
Datum: 17.11.2017


Dual Functionalization of White Phosphorus: Formation, Characterization, and Reactivity of Rare-Earth-Metal Cyclo-P3 Complexes

The [3+1] fragmentation reaction of rare-earth metallacyclopentadienes 1 a–c with 0.5 equivalents of P4 affords a series of rare-earth metal cyclo-P3 complexes 2 a–c and a phospholyl anion 3. 2 a–c demonstrate an unusual η3 coordination mode with one P−P bond featuring partial π-bonding character. 2 a–c are the first cyclo-P3 complexes of rare-earth metals, and also the first organo-substituted polyphosphides in the category of Group 3 and f-block elements. Rare-earth metallacyclopentadienes play a dual role in the combination of aromatization and Diels–Alder reaction. Compounds 2 a–c can coordinate to one or two [W(CO)5] units, yielding 4 a–c or 5 c, respectively. Furthermore, oxidation of 2 a with p-benzoquinone produces its corresponding phospholyllithium and regenerated P4. Fragmentation of P4 mediated by a rare-earth metal gives a series of rare-earth-metal cyclo-P3 complexes. The cyclo-P3 complexes demonstrate an unusual η3 coordination mode with one P−P bond featuring partial π-bonding character. Oxidation of the cyclo-P3 complex with p-benzoquinone can produce the phospholyl anion and regenerate P4.
Datum: 17.11.2017


Access to α-Amino Acid Esters through Palladium-Catalyzed Oxidative Amination of Vinyl Ethers with Hydrogen Peroxide as the Oxidant and Oxygen Source

A novel and convenient palladium catalytic system for the synthesis of α-amino acid esters from simple starting materials is reported. Hydrogen peroxide not only acts as the green oxidant, but also as the oxygen source. This strategy for the conversion of amines and vinyl ethers into highly functionalized and structurally diverse α-amino acid esters is characterized by the simplicity of the experimental procedure, mild reaction conditions, high atom economy, scalability, and practicability. Start simple: Readily available amines and vinyl ethers were converted into highly functionalized and structurally diverse α-amino acid esters by the use of a convenient palladium catalytic system in which hydrogen peroxide acted as both a green oxidant and an oxygen-atom source (see scheme). This versatile strategy is characterized by the simplicity of the experimental procedure, mild reaction conditions, and high atom economy.
Datum: 17.11.2017


Polycyclic Polyprenylated Acylphloroglucinols: An Emerging Class of Non-Peptide-Based MRSA- and VRE-Active Antibiotics

In the past 20 years, peptide-based antibiotics, such as vancomycin, teicoplanin, and daptomycin, have often been considered as second-line antibiotics. However, in recent years, an increasing number of reports on vancomycin resistance in pathogens appeared, which forces researchers to find novel lead structures for potent new antibiotics. Herein, we report the total synthesis of a defined endo-type B PPAP library and their antibiotic activity against multiresistant S. aureus and various vancomycin-resistant Enterococci. Four new compounds that combine high activities and low cytotoxicity were identified, indicating that the PPAP core might become a new non-peptide-based lead structure in antibiotic research. A defined endo-type B PPAP library was synthesized, and antibiotic activity against methicillin-resistant S. aureus (MRSA) and various vancomycin-resistant Enterococci (VRE) was evaluated. Four new compounds with high activity and low cytotoxicity were identified, indicating that the PPAP core might become a new non-peptide-based lead structure in antibiotic research. PPAP=polycyclic polyprenylated acylphloroglycinol.
Datum: 17.11.2017


Localized Supramolecular Peptide Self-Assembly Directed by Enzyme-Induced Proton Gradients

Electrodes are ideal substrates for surface localized self-assembly processes. Spatiotemporal control over such processes is generally directed through the release of ions generated by redox reactions occurring specifically at the electrode. The so-used gradients of ions proved their effectiveness over the last decade but are in essence limited to material-based electrodes, considerably reducing the scope of applications. Herein is described a strategy to enzymatically generate proton gradients from non-conductive surfaces. In the presence of oxygen, immobilization of glucose oxidase (GOx) on a multilayer film provides a flow of protons through enzymatic oxidation of glucose by GOx. The confined acidic environment located at the solid–liquid interface allows the self-assembly of Fmoc-AA-OH (Fmoc=fluorenylmethyloxycarbonyl and A=alanine) dipeptides into β-sheet nanofibers exclusively from and near the surface. In the absence of oxygen, a multilayer nanoreactor containing GOx and horseradish peroxidase (HRP) similarly induces Fmoc-AA-OH self-assembly. The power of enzymes: A multilayer film including a bi-enzyme reaction system establishes a proton gradient going from the bottom to the top of the film, leading to the localized self-assembly of peptides that underpin a supramolecular hydrogel. This approach constitutes an alternative to an electrode surface to induce pH-sensitive self-assembly processes.
Datum: 16.11.2017


Atomically Dispersed Copper–Platinum Dual Sites Alloyed with Palladium Nanorings Catalyze the Hydrogen Evolution Reaction

Designing highly active catalysts at an atomic scale is required to drive the hydrogen evolution reaction (HER). Copper–platinum (Cu-Pt) dual sites were alloyed with palladium nanorings (Pd NRs) containing 1.5 atom % Pt, using atomically dispersed Cu on ultrathin Pd NRs as seeds. The ultrafine structure of atomically dispersed Cu-Pt dual sites was confirmed with X-ray absorption fine structure (XAFS) measurements. The Pd/Cu-Pt NRs exhibit excellent HER properties in acidic solution with an overpotential of only 22.8 mV at a current density of 10 mA cm−2 and a high mass current density of 3002 A g−1(Pd+Pt) at a −0.05 V potential. Ring in the new year: Atomically dispersed copper–platinum (Cu-Pt) dual sites alloyed with palladium (Pd) nanorings exhibit excellent performance in the hydrogen evolution reaction. Electrocatalytic activity surpasses that of commercial platinum/carbon (Pt/C) catalysts.
Datum: 15.11.2017


Activation and Deactivation of Gold/Ceria–Zirconia in the Low-Temperature Water–Gas Shift Reaction

Gold (Au) on ceria–zirconia is one of the most active catalysts for the low-temperature water–gas shift reaction (LTS), a key stage of upgrading H2 reformate streams for fuel cells. However, this catalyst rapidly deactivates on-stream and the deactivation mechanism remains unclear. Using stop–start scanning transmission electron microscopy to follow the exact same area of the sample at different stages of the LTS reaction, as well as complementary X-ray photoelectron spectroscopy, we observed the activation and deactivation of the catalyst at various stages. During the heating of the catalyst to reaction temperature, we observed the formation of small Au nanoparticles (NPs; 1–2 nm) from subnanometer Au species. These NPs were then seen to agglomerate further over 48 h on-stream, and most rapidly in the first 5 h when the highest rate of deactivation was observed. These findings suggest that the primary deactivation process consists of the loss of active sites through the agglomeration and possible dewetting of Au NPs. After the Gold Rush: Stop–start scanning transmission electron microscopy was used to track gold (Au) species formed during the low-temperature water–gas shift reaction over Au/CeZrO4. Au nanoparticles formed during the heating of the catalyst to reaction temperature agglomerate under reaction conditions. X-ray photoelectron spectroscopy reveals that catalyst deactivation is an outcome of particle agglomeration.
Datum: 15.11.2017


Access to Chiral Hydropyrimidines through Palladium-Catalyzed Asymmetric Allylic C−H Amination

A palladium-catalyzed asymmetric intramolecular allylic C−H amination controlled by a chiral phosphoramidite ligand was established for the preparation of various substituted chiral hydropyrimidinones, the precursors of hydropyrimidines, in high yields with high enantioselectivities. In particular, dienyl sodium N-sulfonyl amides bearing an arylethene-1-sulfonyl group underwent a sequential allylic C−H amination and intramolecular Diels–Alder (IMDA) reaction to produce chiral fused tricyclic tetrahydropyrimidinone frameworks in high yields and with high levels of stereoselectivity. Significantly, this method was used as the key step in an asymmetric synthesis of letermovir. Getting to the core of it: An asymmetric palladium-catalyzed intramolecular allylic C−H amination controlled by a chiral phosphoramidite ligand was used to provide efficient access various substituted chiral hydropyrimidines. This methodology was successfully applied to the asymmetric synthesis of letermovir (see scheme; IMDA=intramolecular Diels–Alder reaction).
Datum: 15.11.2017


Creation of “Rose Petal” and “Lotus Leaf” Effects on Alumina by Surface Functionalization and Metal-Ion Coordination

Functional differences between superhydrophobic surfaces, such as lotus leaf and rose petals, are due to the subtle architectural features created by nature. Mimicry of these surfaces with synthetic molecules continues to be fascinating as well as challenging. Herein, we demonstrate how inherently hydrophilic alumina surface can be modified to give two distinct superhydrophobic behaviors. Functionalization of alumina with an organic ligand resulted in a rose-petal-like surface (water pinning) with a contact angle of 145° and a high contact angle hysteresis (±69°). Subsequent interaction of the ligand with Zn2+ resulted in a lotus-leaf-like surface with water rolling behavior owing to high contact angle (165°) and low-contact-angle-hysteresis (±2°). In both cases, coating of an aromatic bis-aldehyde with alkoxy chain substituents was necessary to emulate the nanowaxy cuticular feature of natural superhydrophobic materials. A new leaf: Surface-functionalization and coordination-polymer chemistry are utilized to create metal–organic framework (MOF)-based nanoarchitectures on an alumina surface, which modify the surface's inherent superhydrophilicity to the distinctive superhydrophobic behaviors of rose petals and lotus leaves.
Datum: 15.11.2017


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

The self-assembly of a new perylene bisimide (PBI) organogelator with 1,7-dimethoxy substituents in the bay position affords non-fluorescent H-aggregates at high cooling rates and fluorescent J-aggregates at low cooling rates. Under properly adjusted conditions, the kinetically trapped “off-pathway” H-aggregates are transformed into the thermodynamically favored J-aggregates, a process that can be accelerated by the addition of J-aggregate seeds. Spectroscopic studies revealed a subtle interplay of π–π interactions and intra- and intermolecular hydrogen bonding for monomeric, H-, and J-aggregated PBIs. Multiple polymerization cycles initiated from the seed termini demonstrate the living character of this chain-growth supramolecular polymerization process. Living supramolecular polymerization: The first perylene bisimide (PBI) based multicycle living polymerization system is reported. The bay-substituted PBI organogelator forms off-pathway H-aggregates that are transformed into thermodynamically favored fluorescent J-aggregates by a living seeded polymerization.
Datum: 15.11.2017


Lead- and Iodide-Deficient (CH3NH3)PbI3 (d-MAPI): The Bridge between 2D and 3D Hybrid Perovskites

3D and 2D hybrid perovskites, which have been known for more than 20 years, have emerged recently as promising materials for optoelectronic applications, particularly the 3D compound (CH3NH3)PbI3 (MAPI). The discovery of a new family of hybrid perovskites called d-MAPI is reported: the association of PbI2 with both methyl ammonium (MA+) and hydroxyethyl ammonium (HEA+) cations leads to a series of five compounds with general formulation (MA)1−2.48x(HEA)3.48x[Pb1−xI3−x]. These materials, which are lead- and iodide-deficient compared to MAPI while retaining 3D architecture, can be considered as a bridge between the 2D and 3D materials. Moreover, they can be prepared as crystallized thin films by spin-coating. These new 3D materials appear very promising for optoelectronic applications, not only because of their reduced lead content, but also in account of the large flexibility of their chemical composition through potential substitutions of MA+, HEA+, Pb2+ and I− ions. Back on the MAPI: A family of hybrid perovskites (d-MAPI) is presented. Association of PbI2 with methylammonium (MA+) and hydroxyethylammonium (HEA+) cations leads to five compounds with the general formula (MA)1−2.48x(HEA)3.48x[Pb1−xI3−x]. These materials, which can be prepared as thin films, are lead- and iodide-deficient compared to (CH3NH3)PbI3 (MAPI). Keeping a 3D architecture, they are a bridge between 2D hybrid perovskites and MAPI.
Datum: 15.11.2017


Multi-Step Crystallization of Barium Carbonate: Rapid Interconversion of Amorphous and Crystalline Precursors

The direct observation of amorphous barium carbonate (ABC), which transforms into a previously unknown barium carbonate hydrate (herewith named gortatowskite) within a few hundred milliseconds of formation, is described. In situ X-ray scattering, cryo-, and low-dose electron microscopy were used to capture the transformation of nanoparticulate ABC into gortatowskite crystals, highly anisotropic sheets that are up to 1 μm in width, yet only about 10 nm in thickness. Recrystallization of gortatowskite to witherite starts within 30 seconds. We describe a bulk synthesis and report a first assessment of the composition, vibrational spectra, and structure of gortatowskite. Our findings indicate that transient amorphous and crystalline precursors can play a role in aqueous precipitation pathways that may often be overlooked owing to their extremely short lifetimes and small dimensions. However, such transient precursors may be integral to the formation of more stable phases. The precipitation of witherite (BaCO3) from aqueous solution involves not one, but two precursors: amorphous barium carbonate (ABC) and a crystalline barium carbonate monohydrate (gortatowskite) that crystallizes in a quasi-2D habit. Both intermediates are very short-lived and their characterization requires rapid, cryogenic, and/or low-dose in situ techniques.
Datum: 15.11.2017


Intermolecular Pummerer Coupling with Carbon Nucleophiles in Non-Electrophilic Media

A new Pummerer-type C−C coupling protocol is introduced based on turbo-organomagnesium amides, which unlike traditional Pummerer reactions, does not require strong electrophilic activators, engages a broad range of C(sp3)-, C(sp2)-, and C(sp)-nucleophiles, and seamlessly integrates with C−H and C−X magnesiation. Given the central character of sulfur compounds in organic chemistry, this protocol allows access to unrelated carbonyls, olefins, organometallics, halides, and boronic esters through a single strategy. The Pummerer coupling allows C−C bond formation to be performed in a single operation but it is limited by the need for electrophilic activators. Reported herein is an efficient and orthogonal protocol for electrophile-free Pummerer C−C coupling, which addresses the scope and limitations of traditional approaches, by using DIPAMgCl⋅LiCl.
Datum: 15.11.2017


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

The concept of a synergistic double catalytic kinetic resolution (DoCKR) as described in this article was successfully applied to racemic acyclic anti-1,3-diols, a common motif in natural products. This process takes advantage of an additive Horeau amplification involving two successive enantioselective organocatalytic acylation reactions, and leads to diesters and recovered diols with high enantiopurities. It was first developed with C2-symmetrical diols and then further extended to non-C2-symmetrical anti diols to prepare useful chiral building blocks. The protocol is highly practical as it only requires 1 mol % of a commercially available organocatalyst and leads to easily separable products. This procedure was applied to the shortest reported total synthesis of (+)-cryptocaryalactone, a natural product with anti-germinative activity. Give a second chance to your catalyst! The concept of a synergistic double catalytic kinetic resolution (DoCKR) was successfully applied to racemic acyclic anti-1,3-diols, a common motif in natural products. The organocatalyzed double acylation led to diesters and recovered diols with high enantiopurities. It was first developed with C2-symmetrical diols and then further extended to non-C2-symmetrical anti diols to prepare useful chiral building blocks.
Datum: 15.11.2017


Atom-Specific Mutagenesis Reveals Structural and Catalytic Roles for an Active-Site Adenosine and Hydrated Mg2+ in Pistol Ribozymes

The pistol RNA motif represents a new class of self-cleaving ribozymes of yet unknown biological function. Our recent crystal structure of a pre-catalytic state of this RNA shows guanosine G40 and adenosine A32 close to the G53–U54 cleavage site. While the N1 of G40 is within 3.4 Å of the modeled G53 2′-OH group that attacks the scissile phosphate, thus suggesting a direct role in general acid–base catalysis, the function of A32 is less clear. We present evidence from atom-specific mutagenesis that neither the N1 nor N3 base positions of A32 are involved in catalysis. By contrast, the ribose 2′-OH of A32 seems crucial for the proper positioning of G40 through a H-bond network that involves G42 as a bridging unit between A32 and G40. We also found that disruption of the inner-sphere coordination of the active-site Mg2+ cation to N7 of G33 makes the ribozyme drastically slower. A mechanistic proposal is suggested, with A32 playing a structural role and hydrated Mg2+ playing a catalytic role in cleavage. Smoking gun: Atom-specific mutagenesis revealed that the ribose moiety of a conserved adenosine (A32) and a hydrated Mg2+ ion in the active site of the pistol ribozyme contribute to the cleavage activity. A mechanistic proposal is suggested in which A32 plays a structural role and the hydrated Mg2+ plays a catalytic role in cleavage.
Datum: 15.11.2017


The Metal–Support Interaction Concerning the Particle Size Effect of Pd/Al2O3 on Methane Combustion

The particle size effect of Pd nanoparticles supported on alumina with various crystalline phases on methane combustion was investigated. Pd/θ, α-Al2O3 with weak metal-support interaction showed a volcano-shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ-Al2O3 increased with the particle size. Based on a structural analysis of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration-corrected scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina crystalline phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal–support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al2O3 for methane combustion. Size and phase matters: Pd/θ-Al2O3 and Pd/α-Al2O3 exhibit a different size effect from Pd/γ-Al2O3. Based on a structural analysis using spectroscopy and microscopy, the dependence of catalytic activity on size and the alumina crystalline phase was due to the fraction of step sites on the Pd particle. This difference in fraction is derived from the particle shape, which varies with Pd particle size and strength of metal–support interaction.
Datum: 15.11.2017


A Manganese Pre-Catalyst: Mild Reduction of Amides, Ketones, Aldehydes, and Esters

A new (N-phosphinoamidinate)manganese complex is shown to be a useful pre-catalyst for the hydrosilative reduction of carbonyl compounds, and in most cases at room temperature. The Mn-catalyzed reduction of tertiary amides to tertiary amines, with a useful scope, is demonstrated for the first time by use of this catalyst, and is competitive with the most effective transition-metal catalysts known for such transformations. Ketones, aldehydes, and esters were also successfully reduced under mild conditions by using this new Mn catalyst. Hey Man(ganese): A newly prepared (N-phosphinoamidinate)manganese pre-catalyst (see Scheme) has been shown to be effective for the hydrosilative reduction of a diverse scope of carbonyl compounds, and in most cases can be used at room temperature. The reaction proceeds under reaction conditions that are competitive with the most effective transition-metal catalysts known for such transformations, and thereby establishes a new class of synthetically useful Mn-catalyzed transformations.
Datum: 15.11.2017


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

An asymmetric copper-catalyzed alkylation of quinoline N-oxides with chiral Cu–alkyl species, generated by migratory insertion of a vinylarene into a chiral Cu−H complex, is reported. A variety of quinoline N-oxides and vinylarenes underwent this Cu-catalyzed enantioselective alkylation reaction, affording the corresponding chiral alkylated N-heteroarenes in high yield with high-to-excellent enantioselectivity. This enantioselective protocol represents the first general and practical approach to access a wide range of chiral alkylated quinolines. A highly enantioselective copper-catalyzed alkylation of quinoline N-oxides with vinylarenes was developed. A wide range of quinoline N-oxides and vinylarenes reacted to afford the corresponding chiral alkylated quinolines in high yield with excellent enantioselectivity.
Datum: 15.11.2017


Oxidative P−P Bond Addition to Cobalt(−I): Formation of a Low-Spin Cobalt(III) Phosphanido Complex

The first homoleptic cobalt phosphanido complex [K(thf)4][Co{1,2-(PtBu2)2C2B10H12}2] (1) was prepared by an unprecedented oxidative P−P bond addition of an ortho-carborane-substituted 1,2-diphosphetane to cobalt(−I) in [K(thf)0.2][Co(η4-cod)2)] (cod=1,5-cycloctadiene). Compound 1 is a rare distorted tetrahedral 3d6 complex with a low-spin ground state configuration. Magnetic measurements revealed that the complex is diamagnetic between 2 to 270 K in the solid state and at 298 K in [D8]THF solution. Based on DFT calculations, the unusual singlet ground state is caused by the strong σ-donor and moderate π-donor properties of the bis(phosphanido) ligand. Cobalt in a P pod: The first homoleptic cobalt phosphanido complex is formed via consecutive oxidative additions of P−P bonds to cobalt(−I). X-ray crystallography and magnetic measurements show that this new cobalt(III) compound is a rare example of a tetrahedral complex with a low-spin ground state.
Datum: 15.11.2017


High-Pressure Band-Gap Engineering in Lead-Free Cs2AgBiBr6 Double Perovskite

Novel inorganic lead-free double perovskites with improved stability are regarded as alternatives to state-of-art hybrid lead halide perovskites in photovoltaic devices. The recently discovered Cs2AgBiBr6 double perovskite exhibits attractive optical and electronic features, making it promising for various optoelectronic applications. However, its practical performance is hampered by the large band gap. In this work, remarkable band gap narrowing of Cs2AgBiBr6 is, for the first time, achieved on inorganic photovoltaic double perovskites through high pressure treatments. Moreover, the narrowed band gap is partially retainable after releasing pressure, promoting its optoelectronic applications. This work not only provides novel insights into the structure–property relationship in lead-free double perovskites, but also offers new strategies for further development of advanced perovskite devices. High pressure is adopted to modulate the crystal structure and engineer the band gap of the Cs2AgBiBr6 double perovskite. A 22.3 % band gap narrowing is achieved for the inorganic photovoltaic double perovskite. The narrowed band gap is partially retainable after releasing the pressure, promoting its optoelectronic applications.
Datum: 15.11.2017


Scandium-Catalyzed Self-Assisted Polar Co-monomer Enchainment in Ethylene Polymerization

Direct coordinative copolymerization of ethylene with functionalized co-monomers is a long-sought-after approach to introducing polyolefin functionality. However, functional-group Lewis basicity typically depresses catalytic activity and co-monomer incorporation. Finding alternatives to intensively studied group 4 d0 and late-transition-metal catalysts is crucial to addressing this long-standing challenge. Shown herein is that mono- and binuclear organoscandium complexes with a borate cocatalyst are active for ethylene + amino olefin [AO; H2C=CH(CH2)nNR2] copolymerizations in the absence of a Lewis-acidic masking reagent. Both activity (up to 4.2×102 kg mol−1⋅h−1> atm−1>) and AO incorporation (up to 12 % at 0.2 m [AO]) are appreciable. Linker-length-dependent (n) AO incorporation and mechanistic probes support an unusual functional-group-assisted enchainment mechanism. Furthermore, the binuclear catalysts exhibit enhanced AO tolerance and enhanced long chain AO incorporation. Self-assisted: Sc-catalyzed ethylene + amino olefin (AO) copolymerizations proceed with appreciable activity and AO incorporation in the absence of Lewis acid masking agents. Linker-length-dependent AO enchainment patterns and mechanistic probes support an unusual amino-group-assisted enchainment pathway. Binuclear-catalyst-mediated copolymerization rates are less sensitive to AO concentration, and incorporation patterns at large linker lengths implicate bimetallic cooperative enchainment.
Datum: 15.11.2017


Enantioselective Total Synthesis of 3β-Hydroxy-7β-kemp-8(9)-en-6-one, a Diterpene Isolated from Higher Termites

The first total synthesis of the title diterpene was accomplished starting from the Wieland–Miescher ketone. A diastereoselective sulfa-Michael addition enabled the generation of the delicate β,γ-unsaturated ketone moiety, while the tetracyclic kempane skeleton was readily constructed through domino metathesis. Sulfur helps! The first total synthesis of the title diterpene was accomplished starting from the Wieland–Miescher ketone. A diastereoselective sulfa-Michael addition enabled the generation of the delicate β,γ-unsaturated ketone moiety, while the tetracyclic kempane skeleton was readily constructed through domino metathesis.
Datum: 15.11.2017


Crossover between Tilt Families and Zero Area Thermal Expansion in Hybrid Prussian Blue Analogues

Materials in the family of Prussian blue analogues (C3H5N2)2K[M(CN)6], where C3H5N2 is the imidazolium ion and M=Fe, Co, undergo two phase transitions with temperature; at low temperatures the imidazolium cations have an ordered configuration (C2/c), while in the intermediate- and high-temperature phases (both previously reported as R3‾m ) they are dynamically disordered. We show from high-resolution powder neutron diffraction data that the high-temperature phase has zero area thermal expansion in the ab-plane. Supported by Landau theory and single-crystal X-ray diffraction data, we re-evaluate the space group symmetry of the intermediate-temperature phase to R3‾ . This reveals that the low-to-intermediate temperature transition is due to competition between two different tilt patterns of the [M(CN)6]3− ions. Controlling the relative stabilities of these tilt patterns offers a potential means to tune the exploitable electric behaviour that arises from motion of the imidazolium guest. A different tilt: A reassessment of the symmetry of two cyanide-bridged perovskite analogues reveals that phase transitions in these materials arise from competition between two different tilt patterns. Tilt engineering of the hybrid materials provides a way to access combinations of distortions that are rare or impossible among the inorganic perovskites.
Datum: 15.11.2017


Metallo-Supramolecular Gels that are Photocleavable with Visible and Near-Infrared Irradiation

A photolabile ruthenium-based complex, [Ru(bpy)2(4AMP)2](PF6)2, (4AMP=4-(aminomethyl)pyridine) is incorporated into polyurea organo- and hydrogels via the reactive amine moieties on the photocleavable 4AMP ligands. While showing long-term stability in the dark, cleavage of the pyridine–ruthenium bond upon irradiation with visible or near-infrared irradiation (in a two-photon process) leads to rapid de-gelation of the supramolecular gels, thus enabling spatiotemporal micropatterning by photomasking or pulsed NIR-laser irradiation Light as a liquidizer: Supramolecular ruthenium-based metallopolymer hydrogels undergo photocleavage and rapid de-gelation upon irradiation with visible and NIR light. They are stabile in the dark or in the absence of solvents.
Datum: 15.11.2017


Cationic Nitrogen-Doped Helical Nanographenes

Herein, we report the design and synthesis of a series of novel cationic nitrogen-doped nanographenes (CNDNs) with nonplanar geometry and axial chirality. Single-crystal X-ray analysis reveals helical and cove-edged structures. Compared to their all-carbon analogues, the frontier orbitals of the CNDNs are energetically lower lying, with a reduced optical energy gap and greater electron-accepting behavior. Cyclic voltammetry shows all the derivatives to undergo quasireversible reductions. In situ spectroelectrochemical studies prove that, depending on the number of nitrogen dopants, either neutral radicals (one nitrogen dopant) or radical cations (two nitrogen dopants) are formed upon reduction. The concept of cationic nitrogen doping and introducing helicity into nanographenes paves the way for the design and synthesis of expanded nanographenes or even graphene nanoribbons with cationic nitrogen dopants. Nitrogen plus: A new bottom-up synthetic method allows the generation of cationic nitrogen-doped nanographenes with nonplanar helical structures. The new nanographenes have interesting properties and have potential use as optical and electronic materials.
Datum: 15.11.2017


3D Laser Micro- and Nanoprinting: Challenges for Chemistry

3D printing is a powerful emerging technology for the tailored fabrication of advanced functional materials. This Review summarizes the state-of-the art with regard to 3D laser micro- and nanoprinting and explores the chemical challenges limiting its full exploitation: from the development of advanced functional materials for applications in cell biology and electronics to the chemical barriers that need to be overcome to enable fast writing velocities with resolution below the diffraction limit. We further explore chemical means to enable direct laser writing of multiple materials in one resist by highly wavelength selective (λ-orthogonal) photochemical processes. Finally, chemical processes to construct adaptive 3D written structures that are able to respond to external stimuli, such as light, heat, pH value, or specific molecules, are highlighted, and advanced concepts for degradable scaffolds are explored. It's all in print: Recent progress in micro- and nanoprinting by 3D laser lithography is highlighted and the critical chemical challenges identified. These include the design of functional photoresists for the generation of multifunctional nanostructures as well as the ability to write disparate material properties from one resist with different colors of light and the ability to conduct subdiffraction 3D lithography.
Datum: 15.11.2017


Time-Resolved Interception of Multiple-Charge Accumulation in a Sensitizer–Acceptor Dyad

Biomimetic models that contain elements of photosynthesis are fundamental in the development of synthetic systems that can use sunlight to produce fuel. The critical task consists of running several rounds of light-induced charge separation, which is required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur. Long-lived first charge-separated state and distinct electronic signatures for the sequential charge accumulated species are essential features to be able to track these events on a spectroscopic ground. Herein, we use a double-excitation nanosecond pump–pump–probe experiment to interrogate two successive rounds of photo-induced electron transfer on a molecular dyad containing a naphthalene diimide (NDI) linked to a [Ru(bpy)3]2+ (bpy=bipyridine) chromophore by using a reversible electron donor. We report an unprecedented long-lived two-electron charge accumulation (t=200 μs). A molecular dyad containing a naphthalene diimide (NDI) linked to a [Ru(bpy)3]2+ (bpy=bipyridine) chromophore by a reversible electron donor is used in a double-excitation nanosecond pump–pump–probe experiment to investigate two successive rounds of photoinduced electron transfer. An unprecedented long-lived two-electron charge accumulation occurs. css=charge-separated state.
Datum: 15.11.2017


Systemic Delivery of Bc12-Targeting siRNA by DNA Nanoparticles Suppresses Cancer Cell Growth

Short interfering RNA (siRNA) is a promising molecular tool for cancer therapy, but its clinical success is limited by the lack of robust in vivo delivery systems. Rationally designed DNA nanoparticles (DNPs) have emerged as facile delivery vehicles because their physicochemical properties can be precisely controlled. Nonetheless, few studies have used DNPs to deliver siRNAs in vivo, and none has demonstrated therapeutic efficacy. Herein, we constructed a number of DNPs of rectangular and tubular shapes with varied dimensions using the modular DNA brick method for the systemic delivery of siRNA that targets anti-apoptotic protein Bcl2. The siRNA delivered by the DNPs inhibited cell growth both in vitro and in vivo, which suppressed tumor growth in a xenograft model that specifically correlated with Bcl2 depletion. This study suggests that DNPs are effective tools for the systemic delivery of therapeutic siRNA and have great potential for further clinical translation. DNPs can deliver: DNA nanoparticles (DNPs) were utilized as vehicles for the systemic delivery of siRNA to suppress tumor growth by specifically knocking down the anti-apoptotic protein Bcl2.
Datum: 15.11.2017


Rational Design of Single Molybdenum Atoms Anchored on N-Doped Carbon for Effective Hydrogen Evolution Reaction

The highly efficient electrochemical hydrogen evolution reaction (HER) provides a promising pathway to resolve energy and environment problems. An electrocatalyst was designed with single Mo atoms (Mo-SAs) supported on N-doped carbon having outstanding HER performance. The structure of the catalyst was probed by aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption fine structure (XAFS) spectroscopy, indicating the formation of Mo-SAs anchored with one nitrogen atom and two carbon atoms (Mo1N1C2). Importantly, the Mo1N1C2 catalyst displayed much more excellent activity compared with Mo2C and MoN, and better stability than commercial Pt/C. Density functional theory (DFT) calculation revealed that the unique structure of Mo1N1C2 moiety played a crucial effect to improve the HER performance. This work opens up new opportunities for the preparation and application of highly active and stable Mo-based HER catalysts. Single Mo atoms dispersed on N-doped carbon was prepared as a catalyst. It showed high catalytic activity and stability for the hydrogen evolution reaction (HER), and its structure was characterized by electronic microscopy and XAFS measurements. The unique catalytic properties for HER were investigated by DFT calculations.
Datum: 15.11.2017


Antibacterial Narrow-Band-Gap Conjugated Oligoelectrolytes with High Photothermal Conversion Efficiency

Two conjugated oligoelectrolytes (COEs), WMG1 and WMG2, were designed with the goal of achieving near infrared absorption and high photothermal conversion efficiency. Specifically, electron-rich thiophene and electron-poor benzo[1,2-c:4,5-c′]bis[1,2,5]thiadiazole subunits were introduced into the conjugated core to modulate the optical gap and to reduce the fluorescence emission efficiency. WMG1 and WMG2 show absorption maxima at around 800 nm, which favors tissue penetration. Although relatively small in size, WMG1 and WMG2 exhibit photothermal conversion efficiencies of circa 60 % and 54 %, respectively. WMG1 shows dark toxicity to the Gram positive bacterium B. subtilis and good photothermal killing efficiency toward both B. subtilis and Gram negative E. coli, features that demonstrate the promising potential of the COE molecular design for photothermal applications. Two conjugated oligoelectrolytes (COEs), WMG1 and MWG2, that exhibit NIR absorption and high photothermal conversion efficiencies were prepared. WMG1 shows good photothermal killing efficiency toward pathogens and traditional dark toxicity to Gram positive bacteria, demonstrating the potential of COEs for photothermal applications.
Datum: 15.11.2017


Orientation-Induced Adsorption of Hydrated Protons at the Air–Water Interface

The surface tension of the air—water interface increases upon addition of inorganic salts, implying a negative surface excess of ionic species. Most acids, however, induce a decrease in surface tension, indicating a positive surface excess of hydrated protons. In combination with the apparent negative charge at pure air–water interfaces derived from electrokinetic experiments, this experimental observation has been a source of intense debate since the mid-19th century. Herein, we calculate surface tensions and ionic surface propensities at air–water interfaces from classical, thermodynamically consistent molecular dynamics simulations. The surface tensions of NaOH, HCl, and NaCl solutions show outstanding quantitative agreement with experiment. Of the studied ions, only H3O+ adsorbs to the air–water interface. The adsorption is explained by the deep potential well caused by the orientation of the H3O+ dipole in the interfacial electric field, which is confirmed by ab initio simulations. Surface tensions and ionic surface propensities at air–water interfaces were calculated by molecular dynamics simulations. The surface tensions of NaOH, HCl, and NaCl solutions agree remarkably well with experiment, and of the studied ions, only H3O+ adsorbs to the air–water interface. The adsorption is explained by the deep potential well caused by the orientation of the H3O+ dipole in the interfacial electric field.
Datum: 13.11.2017


Valence-Engineering of Quantum Dots Using Programmable DNA Scaffolds

Precise control over the valency of quantum dots (QDs) is critical and fundamental for quantitative imaging in living cells. However, prior approaches on valence control of QDs remain restricted to single types of valences. A DNA-programmed general strategy is presented for valence engineering of QDs with high modularity and high yield. By employing a series of programmable DNA scaffolds, QDs were generated with tunable valences in a single step with near-quantitative yield (>95 %). The use of these valence-engineered QDs was further demonstrated to develop 12 types of topologically organized QDs-QDs and QDs-AuNPs and 4 types of fluorescent resonance energy transfer (FRET) nanostructures. Quantitative analysis of the FRET nanostructures and live-cell imaging reveal the high potential of these nanoprobes in bioimaging and nanophotonic applications. A DNA-programmed general strategy is presented for valence engineering of quantum dots (QDs) with high modularity and high yield. By employing a series of programmable DNA scaffolds, we generated QDs with tunable valences in a single step with near-quantitative yield (>95 %). We demonstrated the use of these valence-engineered QDs to develop 12 types of topologically organized QDs-QDs and QDs-AuNPs and 4 types of FRET nanostructures.
Datum: 13.11.2017


Mesoporous Carbon@Titanium Nitride Hollow Spheres as an Efficient SeS2 Host for Advanced Li–SeS2 Batteries

The introduction of a certain proportion of selenium into sulfur-based cathodes is an effective strategy for enhancing the integrated battery performance. However, similar to sulfur, selenium sulfide cathodes suffer from poor cycling stability owing to the dissolution of reaction intermediate products. In this study, to exploit the advantages of SeS2 to the full and avoid its shortcomings, we designed and synthesized a hollow mesoporous carbon@titanium nitride (HMC@TiN) host for loading 70 wt % of SeS2 as a cathode material for Li–SeS2 batteries. Benefiting from both physical and chemical entrapment by hollow mesoporous carbon and TiN, the HMC@TiN/SeS2 cathode manifests high utilization of the active material and excellent cycling stability. Moreover, it exhibits promising areal capacity (up to 4 mAh cm−2) with stable cell performance in the high-mass-loading electrode. A double trap: A hollow mesoporous carbon@titanium nitride (HMC@TiN) host has been designed and synthesized for loading 70 wt % of SeS2 as a cathode material for Li–SeS2 batteries (see picture). As a result of both physical and chemical entrapment by the hollow mesoporous carbon and TiN, the HMC@TiN/SeS2 cathode showed high utilization of the active material and excellent cycling stability.
Datum: 13.11.2017


A Multivalent Structure-Specific RNA Binder with Extremely Stable Target Binding but Reduced Interaction with Nonspecific RNAs

By greatly enhancing binding affinities against target biomolecules, multivalent interactions provide an attractive strategy for biosensing. However, there is also a major concern for increased binding to nonspecific targets by multivalent binding. A range of charge-engineered probes of a structure-specific RNA binding protein PAZ as well as multivalent forms of these PAZ probes were constructed by using diverse multivalent avidin proteins (2-mer, 4-mer, and 24-mer). Increased valency vastly enhanced the binding stability of PAZ to structured target RNA. Surprisingly, nonspecific RNA binding of multivalent PAZ can be reduced even below that of the PAZ monomer by controlling negative charges on both PAZ and multivalent avidin scaffolds. The optimized 24-meric PAZ showed nearly irreversible binding to target RNA with negligible binding to nonspecific RNA, and this ultra-specific 24-meric PAZ probe allowed SERS detection of intact microRNAs at an attomolar level. Multivalent probe for a biosensor: An RNA binding monomer and multivalent scaffold proteins were optimized to develop a multivalent probe with near irreversible binding to target RNA and negligible binding to nonspecific RNA. The resulting ultra-specific 24-meric RNA binder allowed SERS detection of intact miRNAs at an attomolar level.
Datum: 13.11.2017


Selenium and Selenocysteine in Protein Chemistry

Selenocysteine, the selenium-containing analogue of cysteine, is the twenty-first proteinogenic amino acid. Since its discovery almost fifty years ago, it has been exploited in unnatural systems even more often than in natural systems. Selenocysteine chemistry has attracted the attention of many chemists in the field of chemical biology owing to its high reactivity and resulting potential for various applications such as chemical modification, chemical protein (semi)synthesis, and protein folding, to name a few. In this Minireview, we will focus on the chemistry of selenium and selenocysteine and their utility in protein chemistry. Se how far we've come: Since its presence in proteins was discovered over 40 years ago, the singular properties of selenocysteine (Sec) have been exploited by protein chemists for a host of different applications. This Minireview summarizes the use of selenium and selenocysteine in various protein chemistry applications, including chemical modifications, protein synthesis, and protein folding.
Datum: 08.11.2017


Inside Back Cover: An Epitope-Imprinted Biointerface with Dynamic Bioactivity for Modulating Cell–Biomaterial Interactions (Angew. Chem. Int. Ed. 50/2017)

Molecularly imprinted synthetic receptors are approaching the perfection of natural receptors! In their Communication on page 15959, G. Pan, B. Sellergren, and co-workers report an epitope imprinting strategy for reversible anchoring of the cell-adhesive peptide RGD to give controllable cell-adhesion behavior.
Datum: 07.11.2017


Cover Picture: Mild Reduction of Phosphine Oxides with Phosphites To Access Phosphines (Angew. Chem. Int. Ed. 50/2017)

In 1669, Henning Brand discovered the element phosphorus by reducing phosphate contained in urine under harsh conditions and thus started phosphorus chemistry while not knowing that he was reducing P=O bonds. In their Communication on page 15989 ff., P. Li, P. Métivier, and R. Wischert propose an efficient, mild, and inexpensive method for reducing the P=O bonds in phosphine oxides through oxygen transfer and transmutation with another phosphorus species.
Datum: 06.11.2017


Inside Cover: Ferroelasticity in an Organic Crystal: A Macroscopic and Molecular Level Study (Angew. Chem. Int. Ed. 50/2017)

Ferroelastic deformation in crystals occurs when the direction of a mechanical force is switched, thereby inducing a reversible change in macroscopic strain while transferring an interface that separates two crystal domains. In their Communication on page 15882 ff., S. Takamizawa et al. describe the macroscopic behavior, microscopic mechanism, and mechanical properties of rare organic ferroelasticity in crystals of 5-chloro-2-nitroaniline.
Datum: 06.11.2017


Ferroelasticity in an Organic Crystal: A Macroscopic and Molecular Level Study

Ferroelasticity has been relatively well-studied in mechanically robust inorganic atomic solids but poorly investigated in organic crystals, which are typically inherently fragile. The absence of precise methods for the mechanical analysis of small crystals has, no doubt, impeded research on organic ferroelasticity. The first example of ferroelasticity in an organic molecular crystal of 5-chloro-2-nitroaniline is presented, with thorough characterization by macro- and microscopic methods. The observed cyclic stress–strain curve satisfies the requirements of ferroelasticity. Single-crystal X-ray structure analysis provides insight into lattice correspondence at the twining interface, which enables substantial crystal bending by a large molecular orientational shift. This deformation represents the highest maximum strain (115.9 %) among reported twinning materials, and the associated dissipated energy density of 216 kJ m−3 is relatively large, which suggests that this material is potentially useful as a mechanical damping agent. Two of a kind: An organic single crystal of 5-chloro-2-nitroaniline presents ferroelasticity induced by mechanical twinning. Crystal structure analysis of lattices at the twinning interface reveals that a large molecular shift accompanies drastic crystal bending. Deformation generates a maximum shear strain of 115.9 % and a high dissipated strain-energy density (Ed: 216 kJ m−3), which could be relevant to mechanical damping applications.
Datum: 02.11.2017


Mild Reduction of Phosphine Oxides with Phosphites To Access Phosphines

A new method for the iodine-catalyzed reduction of phosphine oxides with phosphites at room temperature is reported. The mild reaction conditions, scalability, and simple purification requirements render it a method of choice for the large-scale production and facile regeneration of a variety of phosphines. Mechanistic studies, supported by DFT calculations of the oxygen transfer between the starting phosphine oxide and the phosphite reagent, are also presented. Such transmutations of phosphorus species were previously unknown. The facile reduction of phosphine oxides to phosphines can be achieved with inexpensive phosphites at room temperature. The mild reaction conditions, scalability, and simple purification requirements render this process a method of choice for the large-scale production and regeneration of a variety of phosphines.
Datum: 26.10.2017


Three-Dimensional Printing with Biomass-Derived PEF for Carbon-Neutral Manufacturing

Biomass-derived poly(ethylene-2,5-furandicarboxylate) (PEF) has been used for fused deposition modeling (FDM) 3D printing. A complete cycle from cellulose to the printed object has been performed. The printed PEF objects created in the present study show higher chemical resistance than objects printed with commonly available materials (acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), glycol-modified poly(ethylene terephthalate) (PETG)). The studied PEF polymer has shown key advantages for 3D printing: optimal adhesion, thermoplasticity, lack of delamination and low heat shrinkage. The high thermal stability of PEF and relatively low temperature that is necessary for extrusion are optimal for recycling printed objects and minimizing waste. Several successive cycles of 3D printing and recycling were successfully shown. The suggested approach for extending additive manufacturing to carbon-neutral materials opens a new direction in the field of sustainable development. From cellulose to the printed object: Biomass-derived poly(ethylene-2,5-furandicarboxylate) (PEF) was used as an efficient material for fused deposition modeling 3D printing. A complete cycle from cellulose to the printed object has been performed. The printed PEF objects reported in the present study show higher chemical resistance than objects printed with commonly available materials.
Datum: 19.10.2017


Palladium-Catalyzed Cross-Coupling of Nitroarenes

Pd at the crossroads: The palladium-catalyzed cross-coupling of nitroarenes has eluded chemists for decades. Recently, the first palladium-catalyzed Suzuki–Miyaura and Buchwald–Hartwig cross-couplings of nitroarenes were reported. Mechanistically, this process involves the challenging oxidative addition of LPd0 into the Ar−NO2 bond. This process features a broad substrate scope with respect to both the nitroarene and the nucleophilic coupling partners.
Datum: 19.10.2017


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

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


Theoretical Treatment of CH3NH3PbI3 Perovskite Solar Cells

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






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