Hide Menu
Hide Menu   Home   |     About Us   |   Contact   |   Imprint   |   Privacy   |   Sitemap
Hide Menu   Chemistry Index   |   Chemicals   |   Elemente
Hide Menu   Lab Instruments   |  
Hide Menu   Job Vacancies   |  
Hide Menu   Chemistry Forum   |  
Chemistry A - Z
Equipment for Lab and Industry
Chemicals and Compounds
Job Vacancies
Imprint, Contact
Chemistry Forum


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.

The publisher is Wiley. The copyright and publishing rights of specialized products listed below are in this publishing house. This is also responsible for the content shown.

To search this web page for specific words type "Ctrl" + "F" on your keyboard (Command + "F" on a Mac). Then: type the word you are searching for in the window that pops up!

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

 - Chemical Communications, ChemComm,

 - Chemical Monthly,

 - The Chemical Record,

 - Chemistry Central Journal,

 - Chemistry Letters,

 - Journal of the American Chemical Society,

 - Nature Chemistry.

Angewandte Chemie International Edition - Abstracts

Li2B12 and Li3B12: Prediction of the smallest tubular and cage-like boron structures

We report an intriguing structural transition from the quasi-planar form of B12 cluster upon the interaction with lithium atoms. High-level computations show that the lowest energy structures of LiB12, Li2B12, and Li3B12 have quasi-planar (Cs), tubular (D6d), and cage-like (Cs) geometries, respectively. The energetic cost of distorting the B12 quasi-planar fragment is overcompensated by an enhanced electrostatic interaction between the Li cations and the tubular or cage-like B12 fragments, which is the main reason of such drastic structural changes, resulting in the smallest tubular (Li2B12) and cage-like (Li3B12) boron structures reported until now.
Datum: 23.02.2018

Metal-Free Dehydrogenation of N-Heterocycles by Ternary h-BCN Nanosheets with Visible Light

An efficient metal-free catalytic system has been developed using hexagon boron carbon nitride (h-BCN) nanosheets for the dehydrogenations of N-heterocycles with visible light, while releasing hydrogen gas (H2), and thus no proton acceptor is needed. This acceptorless dehydrogenation of hydroquinolines, hydroisoquinolines or indolines to the corresponding aromatic N-heterocycles has been achieved with excellent yield by visible light irradiation under the ambient temperature. With h-BCN as the photocatalyst and water as the solvent, this protocol shows broad substitution tolerance, environment benign and high efficiency. This metal-free photoredox catalytic system for organic synthesis expands our knowledge of chemical reactivity and enables new environmentally friendly synthetic protocols.
Datum: 23.02.2018

Fluoride-Catalyzed Deblocking as a New Route to Polymeric Urethanes

We report a fluoride-catalyzed deblocking of urethanes as "blocked" isocyanates. Organic and inorganic sources of fluoride ion proved effective for deblocking urethanes and for converting polyurethanes to small molecules. Distinct from conventional deblocking chemistry involving organometallic compounds and high temperatures, the method we describe is metal-free and operates at or slightly above room temperature. The use of fluorescent blocking agents enabled visual and spectroscopic monitoring of blocking/deblocking reactions, and the selected conditions proved applicable to urethanes containing a variety of blocking groups. The method additionally enabled a one pot deblocking and polymerization with diols. Overall, this deblocking/polymerization strategy offers a convenient and efficient solution to problems that have limited the breadth of applications of polyurethane chemistry.
Datum: 23.02.2018

Chaotropic Monovalent Anion Induced Rectification Inversion at Polyimidazolium Brushes Modified Nanopipettes

Here we report a nonintuitive observation of monovalent anion-induced ion current rectification inversion at polyimidazolium brush (PimB) modified nanopipettes. The rectification inversion degree is found to be strongly dependent on the concentration and species of monovalent anions. For chaotropic anions , the rectification inversion is easily observed at a low concentration (5 mM), while there is no rectification inversion observed for kosmotropic anions (e.g., Cl-) even at a high concentration (1 M). Moreover, at the specific concentration (e.g., 10 mM), the variation of rectification ratio on the type of anions is ranged by Hofmeister series. Estimation of the electrokinetic charge density demonstrates that rectification inversion is originated from the charge inversion due to the over-adsorption of chaotropic monovalent anion. To qualitatively understand this phenomenon, the concentration-dependent adsorption mechanism is proposed and discussed.
Datum: 23.02.2018

Design, Synthesis and Application of Novel Chiral C2-symmetric Spiroketal-containing Ligands in Transition Metal Catalysis

We present an expedient and economical route to a new spiroketal-based C2-symmetric chiral scaffold termed SPIROL. Based on this spirocyclic scaffold, several chiral ligands were generated and successfully employed in an array of stereoselective transformations including Ir-catalyzed hydroarylation (up to 95% ee), Pd-catalyzed allylic alkylation (up to 97% ee), intermolecular Pd-catalyzed Heck reaction (up to 95% ee), and Rh-catalyzed hydrogenations of dehydroalanine (up to 93% ee).
Datum: 23.02.2018

Spectroscopic and computational characterization of DTPA-transplutonium chelates: evidencing heterogeneity in the heavy actinide(III) series

The chemistry of trivalent transplutonium ions (Am3+, Cm3+, Bk3+, Cf3+, Es3+) is usually perceived as monotonic and parallel to that of the trivalent lanthanide series. Herein, we present the first extended X-ray absorption fine structure (EXAFS) study performed on a series of aqueous heavy actinide chelates, extending past Cm. The results obtained on diethylenetriaminepentaacetic acid (DTPA) complexes of trivalent Am, Cm, Bk, and Cf show a break to a much shorter metal-oxygen nearest-neighbor bond lengths in the case of Cf3+. Corroborating those results, density functional theory calculations, extended to Es3+, suggest that the shorter Cf-O and Es-O bonds could arise from the departure of the coordinated water molecule and contraction of the ligand around the metal relative to the other [MIIIDTPA(H2O)]2- (M = Am, Cm, Bk) complexes. Taken together, these results demonstrate inhomogeneity within the trivalent transplutonium series that has been insinuated and debated in recent years.
Datum: 23.02.2018

Electron Transfer around a Molecular Corner

The distance dependence of electron transfer (ET) is commonly investigated in linear rigid rod-like compounds, but studies of molecular wires with integrated corners imposing 90° angles are very rare. By using spirobifluorene as a key bridging element and by substituting it at different positions, two isomeric series of donor-bridge-acceptor compounds with either nearly linear or angled geometries were obtained. Photoinduced ET in both series is dominated by rapid through-bond hole hopping across oligo-fluorenes over distances of up to 70 Å. Despite considerable conformational flexibility, direct through-space and through-solvent ET is negligible even in the angled series. The independence of the ET rate constant on the total number of fluorene units in the angled series is attributed to a rate-limiting tunneling step through the spirobifluorene corner. This finding is relevant for multi-dimensional ET systems and grids in which individual molecular wires are interlinked at 90° angles.
Datum: 22.02.2018

Gene Expression on DNA Biochips Patterned with Strand Displacement Lithography

Lithographic patterning of DNA molecules enables spatial organization of cell-free genetic circuits under well-controlled experimental conditions. Here, we present a biocompatible, DNA-based resist termed "Bephore" based on commercially available components, which can be patterned by both photo- and electron beam lithography. The patterning mechanism is based on cleavage of a chemically modified DNA hairpin by ultraviolet light or electrons, and a subsequent strand displacement reaction. All steps are performed in aqueous solution and do not require chemical development of the resist, which makes the lithographic process robust and biocompatible. Bephore is well suited for multi-step lithographic processes, enabling immobilization of different types of DNA molecules with micrometer precision. As an application, we demonstrate compartmentalized, on-chip gene expression from three sequentially immobilized DNA templates, leading to three spatially resolved protein expression gradients.
Datum: 22.02.2018

Nanobody-enabled reverse pharmacology on GPCRs

The conformational complexity of G protein-coupled receptor (GPCR) transmembrane signaling is a central hurdle for the design of screens for receptor agonists. In their basal states, GPCRs have lower affinities for agonists compared to their G protein-bound active state conformations. Moreover, different agonists can stabilize distinct active receptor conformations and do not uniformly activate all cellular signaling pathways linked to a given receptor (agonist bias). Herein, comparative fragment screens were performed on a β2 adrenoreceptor-Nanobody fusion locked in its active state conformation by a G protein mimicking Nanobody, and the same receptor in its basal state conformation. This simple biophysical assay allowed the identification and ranking of multiple novel agonists and permitted to classify the efficacy of each hit in agonist, antagonist, or inverse agonist categories, opening doors to Nanobody-enabled reverse pharmacology.
Datum: 22.02.2018

Rational tuning of fluorobenzene probes for cysteine-selective protein modification

Fluorobenzene probes for protein profiling through selective cysteine labeling have been developed by rational reactivity tuning. Tuning was achieved by selecting an electron-withdrawing para-substituent combined with variation of the number of fluorine substituents. Optimized probes chemo-selectively arylated cysteine residues in proteins under aqueous conditions. Probes linked to azide, biotin or a fluorophore were applicable to labeling of eGFP and albumin. Selective inhibition of cysteine proteases was also demonstrated with the probes. Additionally, probes were tuned for site selective labeling among cysteine residues and for activity based protein profiling in cell lysates.
Datum: 22.02.2018

Covalent Functionalization of Black Phosphorus with Conjugated Polymer for Information Storage

Major disadvantages of black phosphorus (BP) are its poor air-stability and poor solubility in common organic solvents. The best way to solve this problem is to incorporate BP into a polymer backbone or a polymer matrix to form novel functional materials that can provide both challenges and opportunities for new innovation in e.g., optoelectronic and photonic applications. As a proof-of concept application, we synthesized in situ the first highly soluble conjugated polymer-covalently functionalized BP derivative (PDDF-g-BP) which was used to fabricate a resistive random access memory (RRAM) device with a configuration of Au/PDDF-g-BP/ITO. In contrast to PDDF without memory effect, PDDF-g-BP-based device exhibits a nonvolatile rewritable memory performance, with a turn-on and turn-off voltages of +1.95V and -2.34V, and an ON/OFF current ratio of 10000. The current through the device in both the ON and OFF states is still kept unchanged even at 200th switching cycle. The PDDF/BP blends show a very unstable memory performance with a very small ON/OFF current ratio.
Datum: 22.02.2018

Electrochemical Dynamics of a Single Platinum Nanoparticle Collision Event for the Hydrogen Evolution Reaction

Chronoamperometry was used to study the dynamics of Pt nanoparticle (NP) collision with an inert ultramicroelectrode via electrocatalytic amplification (ECA) in the hydrogen evolution reaction. ECA and dynamic light scattering (DLS) results reveal that the NP colloid remains stable only at low proton concentrations (1.0 mm) under a helium (He) atmosphere, ensuring that the collision events occur at genuinely single NP level. Amperometry of single NP collisions under a He atmosphere shows that each discrete current profile of the collision event evolves from spike to staircase at more negative potentials, while a staircase response is observed at all of the applied potentials under hydrogen-containing atmospheres. The particle size distribution estimated from the diffusion-controlled current in He agrees well with electron microscopy and DLS observations. These results shed light on the interfacial dynamics of the single nanoparticle collision electrochemistry. Evolution or stability? Under a helium atmosphere, the electrochemical catalytic current profile of the hydrogen evolution reaction on a single platinum nanoparticle (Pt NP) evolves from a spike to a staircase at more negative potentials on the underlying inert ultramicroelectrode (UME). Under a hydrogen atmosphere, the current profile stabilizes as a staircase at all polarized potentials but at least 5 times lower than that in helium.
Datum: 22.02.2018

The Binding Mode of a Tau Peptide with Tubulin

The microtubule-associated protein Tau promotes the polymerization of tubulin and modulates the function of microtubules. As a consequence of the dynamic nature of the Tau–tubulin interaction, the structural basis of this complex has remained largely elusive. By using NMR methods optimized for ligand–receptor interactions in combination with site-directed mutagenesis we demonstrate that the flanking domain downstream of the four microtubule-binding repeats of Tau binds competitively to a site on the α-tubulin surface. The binding process is complex, involves partial coupling of different interacting regions, and is modulated by phosphorylation at Y394 and S396. This study strengthens the hypothesis of an intimate relationship between Tau phosphorylation and tubulin binding and highlights the power of the INPHARMA NMR method to characterize the interaction of peptides derived from intrinsically disordered proteins with their molecular partners. The interaction of Tau protein with soluble tubulin has been dissected by using NMR methods optimized for ligand–receptor interactions. These methods reveal a complex, phosphorylation-dependent binding mode of the flanking domain downstream of the four microtubule-binding repeats of Tau to α-tubulin.
Datum: 22.02.2018

Zirconium–Porphyrin-Based Metal–Organic Framework Hollow Nanotubes for Immobilization of Noble-Metal Single Atoms

Single atoms immobilized on metal–organic frameworks (MOFs) with unique nanostructures have drawn tremendous attention in the application of catalysis but remain a great challenge. Various single noble-metal atoms have now been successfully anchored on the well-defined anchoring sites of the zirconium porphyrin MOF hollow nanotubes, which are probed by aberration-corrected scanning transmission electron microscopy and synchrotron-radiation-based X-ray absorption fine-structure spectroscopy. Owing to the hollow structure and excellent photoelectrochemical performance, the HNTM-Ir/Pt exhibits outstanding catalytic activity in the visible-light photocatalytic H2 evolution via water splitting. The single atom immobilized on MOFs with hollow structures are expected to pave the way to expand the potential applications of MOFs. Single noble metal atoms can be successfully immobilized on the well-defined anchoring sites of zirconium–porphyrin MOF hollow nanotubes. Owing to the hollow structure and excellent photoelectrochemical performance, HNTM-Ir/Pt exhibits outstanding catalytic activity in the visible-light photocatalytic H2 evolution via water splitting.
Datum: 22.02.2018

Small Molecules Targeting Mycobacterium tuberculosis Type II NADH Dehydrogenase Exhibit Antimycobacterial Activity

The generation of ATP through oxidative phosphorylation is an essential metabolic function for Mycobaterium tuberculosis (Mtb), regardless of the growth environment. The type II NADH dehydrogenase (Ndh-2) is the conduit for electrons into the pathway, and is absent in the mammalian genome, thus making it a potential drug target. Herein, we report the identification of two types of small molecules as selective inhibitors for Ndh-2 through a multicomponent high-throughput screen. Both compounds block ATP synthesis, lead to effects consistent with loss of NADH turnover, and importantly, exert bactericidal activity against Mtb. Extensive medicinal chemistry optimization afforded the best analogue with an MIC of 90 nm against Mtb. Moreover, the two scaffolds have differential inhibitory activities against the two homologous Ndh-2 enzymes in Mtb, which will allow precise control over Ndh-2 function in Mtb to facilitate the assessment of this anti-TB drug target. A tale of two inhibitors: A high-throughput screen against the Mycobacterium tuberculosis (Mtb) oxidative phosphorylation pathway led to the identification of two inhibitors of the type II NADH dehydrogenase (Ndh-2). The inhibitors show differential inhibitory activities against one or both of the Ndh-2 isozymes. Treatment of Mtb with these compounds leads to shutdown of ATP synthesis and bacterial killing.
Datum: 22.02.2018

Titanium Phosphonate Based Metal–Organic Frameworks with Hierarchical Porosity for Enhanced Photocatalytic Hydrogen Evolution

Photocatalytic hydrogen production is crucial for solar-to-chemical conversion process, wherein high-efficiency photocatalysts lie in the heart of this area. A photocatalyst of hierarchically mesoporous titanium phosphonate based metal–organic frameworks, featuring well-structured spheres, a periodic mesostructure, and large secondary mesoporosity, are rationally designed with the complex of polyelectrolyte and cathodic surfactant serving as the template. The well-structured hierarchical porosity and homogeneously incorporated phosphonate groups can favor the mass transfer and strong optical absorption during the photocatalytic reactions. Correspondingly, the titanium phosphonates exhibit significantly improved photocatalytic hydrogen evolution rate along with impressive stability. This work can provide more insights into designing advanced photocatalysts for energy conversion and render a tunable platform in photoelectrochemistry. A multi-structured photocatalyst: A metal–organic framework (MOF) nanostructure synthesized by a surfactant-directed strategy features a stable framework of titanium phosphates, a well-defined sphere, and hierarchical nanopores. These features ensure competitive photoactivity in evolving hydrogen under both visible light and full-spectrum simulator irradiation, along with high durability.
Datum: 22.02.2018

Silicon-Based Dielectric Metamaterials: Focus on the Current Synthetic Challenges

Metamaterials have optical properties that are unprecedented in nature. They have opened new horizons in light manipulation, with the ability to bend, focus, completely reflect, transmit, or absorb an incident wave front. Optically active metamaterials in particular could be used for applications ranging from 3D information storage to photovoltaic cells. Silicon (Si) particles are some of the most promising building blocks for optically active metamaterials, with high scattering efficiency coupled to low light absorption for visible frequencies. However, to date ideal Si building blocks cannot be produced by bulk synthesis techniques. The key is to find a synthetic route to produce Si building blocks between 75–200 nm in diameter of uniform size and shape, that are crystalline, have few impurities, and little to no porosity. This Review provides a theoretical background on Si optical properties for metamaterials, an overview of current synthetic methods and gives direction towards the most promising routes to ideal Si particles for metamaterials. The silicon spectrum: All-dielectric metamaterials are expected to revolutionize optics technologies, provided chemists overcome a few key challenges. Submicronic silicon particles are promising candidates for the manufacturing of such all-dielectric metamaterials, active across the visible spectrum. The requirements, possibilities and the state-of-the art of silicon particles for optical metamaterials are explored.
Datum: 22.02.2018

The [2+2] Cycloaddition-Retroelectrocyclization (CA-RE) Click Reaction: Facile Access to Molecular and Polymeric Push-Pull Chromophores

The [2+2] cycloaddition-retroelectrocyclization (CA-RE) reaction between electron-rich alkynes and electron-deficient alkenes is an efficient procedure to create nonplanar donor–acceptor (D-A) chromophores in both molecular and polymeric platforms. They feature attractive properties including intramolecular charge-transfer (ICT) bands, nonlinear optical properties, and redox activities for use in next-generation electronic and optoelectronic devices. This Review summarizes the development of the CA-RE reaction, starting from the initial reports with organometallic compounds to the extension to purely organic systems. The structural requirements for rapid, high-yielding transformations with true click chemistry character are illustrated by examples that include the broad alkyne and alkene substitution modes. The CA-RE click reaction has been successfully applied to polymer synthesis, with the resulting polymeric push-pull chromophores finding many interesting applications. Only a click away: Nonplanar donor–acceptor (D-A) chromophores can be prepared by click synthesis through [2+2] cycloaddition-retroelectrocyclization (CA-RE). This is a powerful method for producing functional molecular and polymeric systems for use in next-generation electronic and optoelectronic devices.
Datum: 22.02.2018

Fire-retardant and thermally insulating phenolic-silica aerogels

Energy efficient buildings require materials with a low thermal conductivity and a high fire resistance. Traditional organic insulation materials are limited by a poor fire resistance and inorganic insulation materials display a high thermal conductivity. Here we report a mechanically resilient organic/inorganic composite aerogel with a thermal conductivity significantly lower than expanded polystyrene and excellent fire resistance. Co-polymerization and nanoscale phase separation of the phenol-formaldehyde-resin (PFR) and silica generate a binary network with domain sizes below 20 nm. The PFR/SiO2 aerogel can resist high-temperature flame without disintegration and prevents the temperature on the non-exposed side to increase above temperature critical for collapse of reinforced concrete structures. Integration of the fire resistant organic/inorganic composite aerogels with architectural materials could be of interest to improve the appearance and energy efficiency of older building.
Datum: 22.02.2018

Total Synthesis of (−)-Enigmazole A

Total synthesis of (−)-enigmazole A, a marine macrolide natural product with cytotoxic activity, has been accomplished. The tetrahydropyran moiety was constructed by means of a domino olefin cross-metathesis/intramolecular oxa-Michael addition of a δ-hydroxy olefin. After coupling of advanced intermediates, the macrocycle was forged via a gold-catalyzed rearrangement of a propargylic benzoate, followed by a ring-closing metathesis of the resultant α,β-unsaturated ketone.
Datum: 22.02.2018

Molecular recognition by a short partial peptide of adrenergic receptor - Bottom-up approach

Receptor-neurotransmitter molecular recognition is key of neurotransmission. Although crystal structures of the receptors are known, the mechanism for recognition is not clear. At present, the trial-and-error approach is the only sure method to identify ligands (e.g. drugs) that trigger the receptor. Here, we report the ultraviolet and infrared spectra of complexes between a partial peptide SIVSF, the binding motif of a catechol ring in the adrenergic receptor, and various ligands. The ultraviolet spectra show that two isomers coexist in the complex of SIVSF with properly recognized ligands, such as protonated adrenaline (adrenalineH+). From infrared spectra, they are assigned to catechol-bound and ammonium-bound structures. The catechol-bound structure is not observed when the ligand is replaced by non-proper molecules, such as noradrenalineH+. The results suggest that SIVSF not only recognizes the catechol ring but can distinguish differences in the amine side-chain. This suggests a new possibility for screening molecules as potential therapeutics that activate the receptor.
Datum: 22.02.2018

Selective Reductive Elimination at Alkyl Palladium(IV) by Dissociative Ligand Ionization: Catalytic C(sp3)−H Amination to Azetidines

A palladium(II)-catalyzed γ-C−H amination of cyclic alkyl amines to deliver highly substituted azetidines is reported. The use of a benziodoxole tosylate oxidant in combination with AgOAc was found to be crucial for controlling a selective reductive elimination pathway to the azetidines. The process is tolerant of a range of functional groups, including structural features derived from chiral α-amino alcohols, and leads to the diastereoselective formation of enantiopure azetidines. Crucial combo: A PdII-catalyzed γ-C−H amination of cyclic alkyl amines delivers highly substituted azetidines. The use of a benziodoxole tosylate oxidant in combination with AgOAc was crucial for controlling the selective reductive elimination pathway to the azetidines. The process is tolerant of a range of functional groups, including structural features derived from chiral α-amino alcohols, and leads to the diastereoselective formation of enantiopure azetidines.
Datum: 22.02.2018

Sensor Technologies Empowered by Materials and Molecular Innovations

Functional synthetic designer materials can impact many advanced technologies, and the chemical sensor area is intimately reliant on these new chemical innovations. The transduction of chemical and biological signals is necessary for low cost omnipresent chemical sensing and will be realized by chemical designs of new transduction materials. We are poised for many new innovations to empower new generations of sensor technologies. Materials innovations promise to expand the capabilities of present hardware, drive down the cost, and ensure broad implementation of these methods. Sensing materials make sense: The transduction of chemical and biological signals is necessary for low cost omnipresent chemical sensing and will be realized by chemical designs of new transduction materials. Materials innovations promise to expand the capabilities of present hardware, drive down the cost, and ensure broad implementation of these methods.
Datum: 22.02.2018

Direct Room-Temperature Conversion of Methane into Protonated Formaldehyde: The Gas-Phase Chemistry of Mercury among the Zinc Triad Oxide Cations

In thermal reactions of methane with diatomic metal oxides [MO].+ of the zinc triad (M=Zn, Cd, Hg), protonated formaldehyde [CH2OH]+ is generated as the major product only for the [HgO].+/CH4 couple. Mechanistic insight is provided by high-level quantum-chemical calculations, and relativistic effects are suggested to be the root cause for the unexpected thermal production of [CH2OH]+ from [HgO].+/CH4. The strong relativistic effects of the mercury atom lead to a very high ionization energy IE [Hg] as well as to rather small bond dissociation energies BDE [Hg−O]+ and BDE [Hg−H].. These thermodynamic properties facilitate the [HgO].+-mediated thermal conversion of methane into protonated formaldehyde.
Datum: 22.02.2018

RNA Cloaking by Reversible Acylation

We describe a selective and mild chemical approach for controlling RNA hybridization, folding, and enzyme interactions. Reaction of RNAs in aqueous buffer with an azide-substituted acylating agent (100–200 mm) yields several 2′-OH acylations per RNA strand in as little as 10 min. This poly-acylated (“cloaked”) RNA is strongly blocked from hybridization with complementary nucleic acids, from cleavage by RNA-processing enzymes, and from folding into active aptamer structures. Importantly, treatment with a water-soluble phosphine triggers a Staudinger reduction of the azide groups, resulting in spontaneous loss of acyl groups (“uncloaking”). This fully restores RNA folding and biochemical activity. Chemical switch for RNA: A simple selective chemical approach for the control of RNA function is described. Polyacylation of 2′-OH groups with a nicotinyl-imidazole reagent (cloaking) switches off structure and molecular recognition. RNA function is switched on again (uncloaking) by Staudinger reductions that remove the acyl groups.
Datum: 22.02.2018

Small Molecules Drive Big Improvements in Immuno-Oncology Therapies

Immuno-oncology therapies have the potential to revolutionize the armamentarium of available cancer treatments. To further improve clinical response rates, researchers are looking for novel combination regimens, with checkpoint blockade being used as a backbone of the treatment. This Review highlights the significance of small molecules in this approach, which holds promise to provide increased benefit to cancer patients. Kiss of death: There are many ways to kill a tumor cell. With an emphasis on clinically relevant compounds, this Review demonstrates how small molecules can support T-cells in their mission against cancer.
Datum: 22.02.2018

Glass and Alchemy in Early Modern Europe: An Analytical Study of Glassware from the Oberstockstall Laboratory in Austria

Glass distillation equipment from an early modern alchemical laboratory was analyzed for its technology of manufacture and potential origin. Chemical data show that the assemblage can be divided into sodium-rich, colorless distillation vessels made with glass from Venice or its European imitation, and potassium-rich dark-brown non-specialized forms produced within the technological tradition of forest glass typical for central and north-western Europe. These results complete our understanding of the supply of technical apparatus at one of the best-preserved alchemical laboratories and highlight an early awareness of the need for high-quality instruments to guarantee the successful outcome of specialized chemical operations. This study demonstrates the potential of archaeological science to inform historical research around the practice of early chemistry and the development of modern science. What sort of operations did alchemists carry out in their laboratories? What tools did they use? Can answering similar questions help us better understand the development of science and technology in the Renaissance? It is shown that the information gained through archaeometric analysis of artefacts from laboratories can be a powerful tool in exploring how alchemy was practiced in early modern Europe.
Datum: 22.02.2018

Dye-incorporated Polynaphthalenediimide Acceptor for Additive-free High-performance All-polymer Solar Cells

All-polymer solar cells (all-PSCs) can offer unique advantages for applications in flexible devices, and naphthalene diimide (NDI)-based polymer acceptors are the widely used polymer acceptors. However, their power conversion efficiency (PCE) still lags behind that of state-of-the-art polymer solar cells, due to low light absorption, suboptimal energy levels and the strong aggregation of the NDI-based polymer acceptor. In this work, by means of simple random copolymerization, a rhodanine-based dye molecule was introduced into the NDI-based polymer acceptor and showed an improved light absorption coefficient, an up-shifted lowest unoccupied molecular orbital level and reduced crystallization. Consequently, additive-free all-PSCs demonstrated a high PCE of 8.13%, which is one of the highest performance characteristics reported for all-PSCs to date. These results indicate that incorporating dye into the n-type polymer yields insights into the precise design of high-performance polymer acceptors for all-PSCs.
Datum: 22.02.2018

A Crosslinked Nucleic Acid Nanogel for Effective siRNA Delivery and Antitumor Therapy

Functional siRNAs are employed as cross-linkers to direct the self-assembly of DNA-grafted polycaprolactone (DNA-g-PCL) brushes to form spherical and nanosized hydrogels via nucleic acid hybridization in which small interfering RNAs (siRNAs) are fully embedded and protected for systemic delivery. Owing to the existence of multivalent mutual crosslinking events inside, the crosslinked nanogels with tunable size exhibit not only good thermostability, but also remarkable physiological stability that can resist the enzymatic degradation. As a novel siRNA delivery system with spherical nucleic acid (SNA) architecture, the crosslinked nanogels can assist the delivery of siRNAs into different cells without any transfection agents and achieve the gene silencing effectively both in vitro and in vivo, through which a significant inhibition of tumor growth is realized in the anticancer treatment. Functional siRNA is employed as a cross-linker to direct the self-assembly of DNA-grafted polycaprolactone (DNA-g-PCL) brushes to form a spherical and nanosized hydrogel by nucleic acid hybridization in which siRNAs are fully embedded and protected for systemic delivery. The nanogel can assist the delivery of siRNA into cells without any transfection agents and achieve gene silence effectively.
Datum: 22.02.2018

Van der Waals Heterostructures Comprised of Ultrathin Polymer Nanosheets for Efficient Z-Scheme Overall Water Splitting

Inspired by natural photosynthesis, Z-scheme photocatalytic systems are very appealing for achieving efficient overall water splitting. Developing metal-free Z-scheme photocatalysts for overall water splitting, however, still remains challenging. The construction of polymer-based van der Waals heterostructures as metal-free Z-scheme photocatalytic systems for overall water splitting is described using aza-fused microporous polymers (CMP) and C2N ultrathin nanosheets as O2- and H2-evolving catalysts, respectively. Although neither polymer is able to split pure water using visible light, a 2:1 stoichiometric ratio of H2 and O2 was observed when aza-CMP/C2N heterostructures were used. A solar-to-hydrogen conversion efficiency of 0.23 % was determined, which could be further enhanced to 0.40 % by using graphene as the solid electron mediator to promote the interfacial charge-transfer process. This study highlights the potential of polymer photocatalysts for overall water splitting. After all, you′re my van der Waal: A metal-free Z-scheme photocatalytic system was prepared for efficient overall water splitting. 2D van der Waals heterostructures composed of ultrathin polymer nanosheets facilitate charge separation and consequently enhance the lifetime and density of photogenerated excitons.
Datum: 22.02.2018

Universality of the Sodium Ion Binding Mechanism in Class A G-Protein-Coupled Receptors

The allosteric modulation of G-protein-coupled receptors (GPCRs) by sodium ions has received significant attention as crystal structures of several receptors show Na+ ions bound to the inactive conformations at the conserved Asp2.50. To date, structures from 24 families of GPCRs have been determined, though mechanistic insights into Na+ binding to the allosteric site are limited. We performed hundreds-of-microsecond long simulations of 18 GPCRs and elucidated their Na+ binding mechanism. In class A GPCRs, the Na+ ion binds to the conserved residue 2.50 whereas in class B receptors, it binds at 3.43b, 6.53b, and 7.49b. Using Markov state models, we obtained the free energy profiles and kinetics of Na+ binding to the allosteric site, which reveal a conserved mechanism of Na+ binding for GPCRs and show the residues that act as major barriers for ion diffusion. Furthermore, we also show that the Na+ ion can bind to GPCRs from the intracellular side when the allosteric site is inaccessible from the extracellular side. The free energy barriers for Na+ ion binding to the allosteric site of 18 G-protein-coupled receptors were calculated using Markov state models. Receptors from different classes and families follow a conserved Na+ ion binding mechanism but they exhibit large differences in the kinetics of the ion binding process. For PAR1 and P2Y12, ion binding occurs from the intracellular side.
Datum: 22.02.2018

Efficient CO2 Removal for Ultra-Pure CO Production by Two Hybrid Ultramicroporous Materials

Removal of CO2 from CO gas mixtures is a necessary but challenging step during production of ultra-pure CO as processed from either steam reforming of hydrocarbons or CO2 reduction. Herein, two hybrid ultramicroporous materials (HUMs), SIFSIX-3-Ni and TIFSIX-2-Cu-i, which are known to exhibit strong affinity for CO2, were examined with respect to their performance for this separation. The single-gas CO sorption isotherms of these HUMs were measured for the first time and are indicative of weak affinity for CO and benchmark CO2/CO selectivity (>4000 for SIFSIX-3-Ni). This prompted us to conduct dynamic breakthrough experiments and compare performance with other porous materials. Ultra-pure CO (99.99 %) was thereby obtained from CO gas mixtures containing both trace (1 %) and bulk (50 %) levels of CO2 in a one-step physisorption-based separation process. Benchmark CO2/CO selectivity under ambient conditions has been observed in two hybrid ultramicroporous materials, thanks to much weaker interactions towards CO versus CO2. Ultra-pure CO (>99.99 %) can thereby be produced efficiently from gas mixtures containing CO2 impurities (1 % and 50 %) in a one-step separation process using a fixed-bed column of adsorbent.
Datum: 22.02.2018

Palladium-Catalyzed Regioselective Aromatic Extension of Internal Alkynes through a Norbornene-Controlled Reaction Sequence

A regioselective aromatic π-extension reaction of internal alkynes is reported. The proposed method employs three easily available components, namely aryl halides, 2-haloarylcarboxylic acids, and disubstituted acetylenes. The transformation is driven by a controlled reaction sequence of C−H activation, decarboxylation, and annulation to give poly(hetero)aromatic compounds in a site-selective fashion. Unlike in previously reported palladium-catalyzed three-component annulations, alkyne carbopalladation is the last step of this tandem reaction. The right way round: A regioselective multicomponent reaction of aryl halides, 2-haloarylcarboxylic acids, and disubstituted acetylenes proceeds through C−H activation, decarboxylation, and annulation to give poly(hetero)aromatic compounds by aromatic extension. Alkyne carbopalladation is the last step of this tandem reaction.
Datum: 22.02.2018

Cytochrome-P450-Induced Ordering of Microsomal Membranes Modulates Affinity for Drugs

Although membrane environment is known to boost drug metabolism by mammalian cytochrome P450s, the factors that stabilize the structural folding and enhance protein function are unclear. In this study, we use peptide-based lipid nanodiscs to “trap” the lipid boundaries of microsomal cytochrome P450 2B4. We report the first evidence that CYP2B4 is able to induce the formation of raft domains in a biomimetic compound of the endoplasmic reticulum. NMR experiments were used to identify and quantitatively determine the lipids present in nanodiscs. A combination of biophysical experiments and molecular dynamics simulations revealed a sphingomyelin binding region in CYP2B4. The protein-induced lipid raft formation increased the thermal stability of P450 and dramatically altered ligand binding kinetics of the hydrophilic ligand BHT. These results unveil membrane/protein dynamics that contribute to the delicate mechanism of redox catalysis in lipid membrane. Redox catalysis in the lipid membrane: A novel application of peptide nanodiscs shows that cytochrome P450 2B4 is able to induce the formation of lipid raft domains in a biomimetic compound of the endoplasmic reticulum (ER). The protein-induced lipid rafts increase the thermal stability cytochrome P450 and dramatically alter the ligand-binding kinetics of the hydrophilic ligand BHT.
Datum: 22.02.2018

Isolation of a Cationic Platinum(II) σ-Silane Complex

The platinum complex [Pt(ItBuiPr′)(ItBuiPr)][BArF] interacts with tertiary silanes to form stable (<0 °C) mononuclear PtII σ-SiH complexes [Pt(ItBuiPr′)(ItBuiPr)(η1-HSiR3)][BArF]. These compounds have been fully characterized, including X-ray diffraction methods, as the first examples for platinum. DFT calculations (including electronic topological analysis) support the interpretation of the coordination as an unusual η1-SiH. However, the energies required for achieving a η2-SiH mode are rather low, and is consistent with the propensity of these derivatives to undergo Si−H cleavage leading to the more stable silyl species [Pt(SiR3)(ItBuiPr)2][BArF] at room temperature. Cationic platinum(II) σ-SiH complexes are sufficiently stable for isolation at temperatures below 0 °C. The most stable coordination mode is η1, but the energetic cost to reach the η2 mode is very low. These complexes evolve at room temperature, through cleavage of the Si−H bond, thus leading to platinum(II) silyl 14-electron species.
Datum: 22.02.2018

Supramolecular Nanostructures of Structurally Defined Graphene Nanoribbons in the Aqueous Phase

Structurally well-defined graphene nanoribbons (GNRs) have attracted great interest because of their unique optical, electronic, and magnetic properties. However, strong π–π interactions within GNRs result in poor liquid-phase dispersibility, which impedes further investigation of these materials in numerous research areas, including supramolecular self-assembly. Structurally defined GNRs were synthesized by a bottom-up strategy, involving grafting of hydrophilic poly(ethylene oxide) (PEO) chains of different lengths (GNR-PEO). PEO grafting of 42–51 % percent produces GNR-PEO materials with excellent dispersibility in water with high GNR concentrations of up to 0.5 mg mL−1. The “rod–coil” brush-like architecture of GNR-PEO resulted in 1D hierarchical self-assembly behavior in the aqueous phase, leading to the formation of ultralong nanobelts, or spring-like helices, with tunable mean diameters and pitches. In aqueous dispersions the superstructures absorbed in the near-infrared range, which enabled highly efficient conversion of photon energy into thermal energy. Supramolecular nanostructures of structurally well-defined graphene nanoribbons grafted with hydrophilic poly(ethylene oxide) chains present excellent dispersibility in the aqueous phase. Aqueous dispersions of graphene nanoribbon superstructures absorb in the near-infrared range, thereby enabling highly efficient conversion of photon energy into thermal energy.
Datum: 22.02.2018

Iron-Catalyzed Reductive Ethylation of Imines with Ethanol

The borrowing hydrogen strategy has been applied to the ethylation of imines with an air-stable iron complex as precatalyst. This approach opens new perspectives in this area as it enables the synthesis of unsymmetric tertiary amines from readily available substrates and ethanol as a C2 building block. A variety of imines bearing electron-rich aryl or alkyl groups at the nitrogen atom could be efficiently reductively alkylated without the need for molecular hydrogen. The mechanism of this reaction, which shows complete selectivity for ethanol over other alcohols, has been studied experimentally and by means of DFT computations. The borrowing hydrogen strategy was applied to the ethylation of imines with an air-stable iron complex as precatalyst. This approach enables the synthesis of unsymmetric tertiary amines from readily available substrates and ethanol as a C2 building block. The reductive alkylation of imines bearing electron-rich aryl or alkyl groups at the N atom is thus possible in the absence of molecular hydrogen.
Datum: 22.02.2018

Capacitance for Carbon Capture

Metal recycling: A sustainable, capacitance-assisted carbon capture and sequestration method can turn scrap metal and CO2 into metal carbonates at an attractive energy cost.
Datum: 22.02.2018

Discovery of a Fungal Multicopper Oxidase That Catalyzes the Regioselective Coupling of a Tricyclic Naphthopyranone To Produce Atropisomers.

Atropisomer dinapinones (DP) A1 and A2 were isolated from a culture of Talaromyces pinophilus FKI-3864. Monapinone coupling enzyme (MCE), which dimerizes naphthopyranone monapinone (MP) A, was purified from a cell-free extract of T. pinophilus FKI-3864. MCE uses MPA as a substrate and regioselectively dimerizes it at the 8,8' positions to synthesize the atropisomers DPA1 and DPA2 at a ratio of approximately 1:2.5 without a cofactor. The optimal pH and temperature for MCE were 4.0 and 50°C, and the apparent Km and Vmax values for MPA were 72.7±23.2 μM and 1.21±0.170 μmol/min/mg protein, respectively. The MCE polypeptide is significantly homologous with multicopper oxidases. Heterologous expression of MCE and functional analysis confirmed that MCE catalyzes the regioselective coupling reaction of MPA to produce DPA. This is the first report that a fungal multicopper oxidase can catalyze the regioselective intermolecular oxidative phenol coupling to produce naphthopyranone atropisomers.
Datum: 22.02.2018

The Cyclic Hydrogen-Bonded 6-Azaindole Trimer and Its Prominent Excited-State Triple Proton Transfer Reaction

We report a previously unrecognized feature in that 6-azaindole undergoes self-assembling via N(1)-H...N(6) hydrogen bond (H-bond) formation, forming a cyclic, triply H-bonded trimer. The 6-azaindole trimer formation is visualized by the scanning tunnelling microscopy. Remarkably, this H-bonded trimer undergoes excited-state triple proton transfer (ESTPT), resulting in a proton-transfer tautomer emission maximized at 435 nm (cf. 325 nm of the normal emission) in cyclohexane. Computational approaches further affirm the thermodynamically favourable H-bonded trimer formation and the associated ESTPT reaction. Thus, nearly half century after Michael Kasha discovered the double H-bonded dimer of 7-azaindole and its associated excited-state double proton transfer reaction[3], we demonstrate the triply H-bonded trimer formation of 6-azaindole and its ESTPT reaction.
Datum: 22.02.2018

The Fourth Alloying Mode by Way of Anti-Galvanic Reaction

Anti-galvanic reaction (AGR) not only defies classic galvanic theory but also is a promising method for tuning noble metal nanoparticles' compositions, structures and properties. In particular, employing AGR for the preparation of alloy nanoparticles has recently received extensive interest. Herein, we report on a unprecedented alloying mode by way of AGR, in which the foreign atoms induce the structural transformation of the mother nanoparticles and enter the novel nanoparticles in a non-replacement fashion. A novel, active metal-doped, gold nanoparticle was facilely synthesized by this novel alloying mode, and its structure was resolved by single-crystal X-ray crystallography. Surprisingly, one CdSH motif was found in the protecting staples of the novel bimetal nanoparticle for the first time. The density functional theory (DFT) calculations revealed that the Au20Cd4(SH)(SR)19 is a 8e superatom cluster. Furthermore, although the Cd-doping does not essentially alter the absorption of the mother nanocluster, it distinctly enhances the stability and catalytic selectivity of the mother nanoclusters.
Datum: 22.02.2018

Readily production of flow reactor cartridges by 3D printing of thermostable enzymes

Compartmentalization of chemical reactions is an essential principle of life that provides a major source of innovation for the development of novel approaches in biocatalysis. To implement spatially controlled biotransformations, rapid manufacturing methods are needed for the production of biocatalysts applicable in flow systems. While three-dimensional (3D) printing techniques offer high throughput manufacturing capability, they are not usually compatible with the delicate nature of enzymes, which call for physiological processing parameters. We here demonstrate the utility of thermostable enzymes to realize biocatalytic agarose-based inks for a simple temperature-controlled 3D printing process. As examples we utilized an esterase and an alcohol dehydrogenase from thermophilic organisms as well as a decarboxylase, which has been thermostabilized by directed protein evolution. We applied the resulting 3D printed parts for a continuous, two-step sequential biotransformation in a fluidic setup.
Datum: 21.02.2018

Revealing Transient Concentration of CO2 in a Mixed Matrix Membrane by IR Microimaging and Molecular Modeling

Through IR microimaging the spatially and temporally resolved development of the CO2 concentration in a ZIF-8@6FDA-DAM mixed matrix membrane was visualized during transient adsorption. By recording the evolution of the CO2 concentration, it is observed that the CO2 molecules propagate from the ZIF-8 filler, which acts as a transport "highway", towards the surrounding polymer. A high-CO2-concentration layer is formed at the MOF/polymer interface, which becomes more pronounced at higher CO2 gas pressures. A microscopic explanation of the origins of this phenomenon is suggested by means of molecular modeling. By applying a computational methodology combining quantum and force-field based calculations, the formation of microvoids at the MOF/polymer interface is predicted. Grand Canonical Monte Carlo simulations further demonstrate that CO2 tends to preferentially reside in these microvoids, which is expected to facilitate CO2 accumulation at the interface.
Datum: 21.02.2018

Literally green chemical synthesis of artemisinin from plant extracts

Active pharmaceutical ingredients are either extracted from biological sources - where they are synthesized in complex, dynamic environments - or prepared via step-wise chemical syntheses by reacting pure reagents and catalysts under controlled conditions. A combination of these two approaches, where plant extracts containing reagents and catalysts are utilized in intensified chemical syntheses, creates expedient and sustainable processes. We illustrate the principle by reacting crude plant extract, oxygen, acid, and light to produce artemisinin, a key active pharmaceutical ingredient of the most powerful anti-malaria drugs. The traditionally discarded extract of Artemisia annua plants contains dihydroartemisinic acid - the final biosynthetic precursor - as well as chlorophyll, which acts as a photosensitizer. Efficient illumination with visible light in a continuous flow setup produces artemisinin in high yield, and the artificial biosynthetic process outperforms syntheses using pure reagents.
Datum: 21.02.2018

Classical N-Heterocyclic Carbenes Derived Crystalline Radicals

One electron reduction of C2-arylated 1,3-imidazoli(ni)um salts (IPrAr)Br (Ar = Ph, 3a; 4-DMP, 3b; 4-DMP = 4-Me2NC6H4) and (SIPrAr)I (Ar = Ph, 4a; 4-Tol, 4b) derived from classical NHCs (IPr = :C{N(2,6-iPr2C6H3)}2CHCH, 1; SIPr = :C{N(2,6- iPr2C6H3)}2CH2CH2, 2) gives radicals [(IPrAr)]* (Ar = Ph, 5a; 4-DMP, 5b) and [(SIPrAr)]* (Ar = Ph, 6a; 4-Tol, 6b). Each of 5a,b and 6a,b exhibits a doublet EPR signal, a characteristic of monoradical species. The first solid-state characterization of NHC-derived carbon-centered radicals 6a,b by single crystal X-ray diffraction is reported. DFT calculations indicate that the unpaired electron is mainly located at the original carbene carbon atom and stabilized by partial delocalization over the adjacent aryl group.
Datum: 21.02.2018

Incorporation of Non-canonical Amino Acids into 2,5-Diketopiperazines by Cyclodipeptide Synthases

The manipulation of natural product biosynthetic pathways is a powerful means of expanding the chemical diversity of bioactive molecules. 2,5-diketopiperazines (2,5-DKPs) have been widely developed by medicinal chemists, but their biological production is yet to be exploited. We introduce an in vivo method for incorporating non-canonical amino acids (ncAAs) into 2,5-DKPs using cyclodipeptide synthases (CDPSs), the enzymes responsible for scaffold assembly in many 2,5-DKP biosynthetic pathways. CDPSs use aminoacyl-tRNAs as substrates. We exploited the natural ability of aminoacyl-tRNA synthetases to load ncAAs onto tRNAs. We found 26 ncAAs to be usable as substrates by CDPSs, leading to the enzymatic production of approximately 200 non-canonical cyclodipeptides. CDPSs constitute an efficient enzymatic tool for the synthesis of highly diverse 2,5-DKPs. Such diversity could be further expanded, for example, by using various cyclodipeptide-tailoring enzymes found in 2,5-DKP biosynthetic pathways. It takes two: Cyclodipeptide synthases (CDPSs) are a family of enzymes that divert aminoacyl-tRNAs from the translational apparatus to produce cyclodipeptides. By making use of the natural promiscuity of aminoacyl-tRNA synthetases, CDPSs were shown to tolerate a wide range of non-canonical amino acids as substrates and the biosynthesis of around 200 cyclodipeptides containing non-canonical amino acids was achieved.
Datum: 21.02.2018

Reversible Clustering of Gold Nanoparticles under Confinement

A limiting factor of solvent-induced nanoparticle self-assembly is the need for constant sample dilution in assembly/disassembly cycles. Changes in the nanoparticle concentration alter the kinetics of the subsequent assembly process, limiting optical signal recovery. Herein, we show that upon confining hydrophobic nanoparticles in permeable silica nanocapsules, the number of nanoparticles participating in cyclic aggregation remains constant despite bulk changes in solution, leading to highly reproducible plasmon band shifts at different solvent compositions. Changes in the nanoparticle concentration during solvent-induced nanoparticle self-assembly alter the kinetics of the assembly process. Upon confining hydrophobic nanoparticles in permeable silica nanocapsules, the number of nanoparticles participating in cyclic aggregation remains constant despite bulk changes in solution, leading to highly reproducible plasmon band shifts at different solvent compositions.
Datum: 21.02.2018

Epoxy-functionalized Porous Organic Polymers via the Diels–Alder Cycloaddition Reaction for Atmospheric Water Capture

The synthesis of highly microporous, epoxy-functionalized porous organic polymers (ep-POPs) by a one-pot, catalyst-free Diels–Alder cycloaddition polymerization is reported. The high oxygen content of ep-POPs offer efficient hydrogen-bonding sites for water molecules, thus leading to high water-uptake capacities up to 39.2–42.4 wt % under a wide temperature range of 5–45 °C, which covers the span of climatic conditions and manufacturing applications in which such materials might be used. Importantly, ep-POPs demonstrated regeneration temperatures as low as 55 °C, as well as excellent water stability, recyclability, and high specific surface areas up to 852 m2 g−1. Thirsty polymers: Porous organic polymers incorporating epoxy moieties were synthesized by a one-pot, catalyst-free Diels–Alder cycloaddition polymerization. The hydrogen bonding between epoxy groups and water molecules optimizes binding affinity, thus balancing between high water uptake and low regeneration temperature.
Datum: 21.02.2018

Mono-allyloxylated Cucurbit[7]uril Acts as an Unconventional Amphiphile to Form Light-Responsive Vesicles

Serendipitously, mono-allyloxylated cucurbit[7]uril (AO1CB[7]) was discovered to act as an unconventional amphiphile which self-assembles into light-responsive vesicles (AO1CB[7]VC) in water. Although the mono-allyloxy group, directly tethered on the periphery of CB[7], is much shorter (C4) than the hydrophobic tails of conventional amphiphiles, it played an important role in vesicle formation. Light-activated transformation of the allyloxy group by conjugation with glutathione was exploited as a remote tool to disrupt the vesicle. The vesicle showed on-demand release of cargo upon irradiation by a laser, after they were internalized into cancer cells. This result demonstrated the potential of AO1CB[7]VC as a new type of light-responsive intracellular delivery vehicle for the release of therapeutic cargo, within cells, on demand. Serendipitous amphiphilicity: Mono-allyloxylated cucurbit[7]uril acts as an unconventional amphiphile which self-assembles into light-responsive vesicles in water, despite only having a short hydrophobic chain. These vesicles were used for two-photon activated on-demand drug delivery into cancer cells.
Datum: 21.02.2018

Ultrathin Palladium Nanomesh for Electrocatalysis

An ordered mesh of palladium with a thickness of about 3 nm was synthesized by a solution-based oxidative etching. The ultrathin palladium nanomeshes have an interconnected two-dimensional network of densely arrayed, ultrathin quasi-nanoribbons that form ordered open holes. The unique mesoporous structure and high specific surface area make these ultrathin Pd nanomeshes display superior catalytic performance for ethanol electrooxidation (mass activity of 5.40 Am g−1 and specific activity of 7.09 mA cm−2 at 0.8 V vs. RHE). Furthermore, the regular mesh structure can be applied to support other noble metals, such as platinum, which exhibits extremely high hydrogen evolution reaction (HER) activity and durability. Meshing around: A novel ultrathin Pd nanomesh with a densely arrayed, ultrathin quasi-nanoribbons and regular open holes was transformed from a Pd nanosheet by a solution-based free corrosion, which exhibits exceptional electrocatalytic performance.
Datum: 21.02.2018

Two Diterpene Synthases for Spiroalbatene and Cembrene A from Allokutzneria albata

Two bacterial diterpene synthases from the actinomycete Allokutzneria albata were investigated, resulting in the identification of the structurally unprecedented compound spiroalbatene from the first and cembrene A from the second enzyme. Both enzymes were thoroughly investigated in terms of their mechanisms by isotope labeling experiments, site-directed mutagenesis, and variation of the metal cofactors and pH value. For spiroalbatene synthase, the pH- and Mn2+-dependent formation of the side product thunbergol was observed, which is biosynthetically linked to spiroalbatene. Two diterpene synthases from Allokutzneria albata were investigated in terms of their products, which resulted in the identification of the structurally complex compound spiroalbatene and cembrene A. The enzyme mechanisms were studied by isotope labeling experiments, through mutations, and by variation of the incubation conditions. For spiroalbatene synthase, a change in the incubation conditions resulted in the formation of thunbergol.
Datum: 21.02.2018

Synthesis and Electronic Structure of Boron-Graphdiyne with an sp-Hybridized Carbon Skeleton and Its Application in Sodium Storage

Boron-graphdiyne (BGDY), which has a unique π-conjugated structure comprising an sp-hybridized carbon skeleton and evenlydistributed boron heteroatoms in a well-organized 2D molecular plane, is prepared through a bottom-up synthetic strategy. Excellent conductivity, a relatively low band gap and a packing mode of the planar BGDY are observed. Notably, the unusual bonding environment of the all sp-carbon framework and the electron-deficient boron centers generates affinity to metal atoms, and thus provides extra binding sites. Furthermore, the expanded molecule pores of the BGDY molecular plane can also facilitate the transfer of metal ions in the perpendicular direction. The practical effect of the all sp-carbon structure and boron heteroatoms on the properties of BGDY are demonstrated in its performance as the anode in sodium-ion batteries. The Bs needs: Boron-graphdiyne (BGDY) is prepared through a bottom-up chemical strategy. BGDY has a unique structure with molecular pores decorated with boron atoms. The pure sp-hybridized-carbon skeleton and boron heteroatoms can stabilize the metal atoms intercalated in the BGDY framework. As a result of this unique structure, BGDY shows remarkable electrochemical performance in sodium-ion half cells.
Datum: 21.02.2018

Conformation-Enabled Total Syntheses of Ohmyungsamycins A and B and Structural Revision of Ohmyungsamycin B

The first total syntheses of the bioactive cyclodepsipeptides ohmyungsamycin A and B are described. Key features of our synthesis include the concise preparation of a linear cyclization precursor that consists of N-methyl amides and non-proteinogenic amino acids, and its macrolactamization from a bent conformation. The proposed structure of ohmyungsamycin B was revised based on its synthesis. The cyclic core of the ohmyungsamycins was shown to be responsible for the excellent antituberculosis activity, and ohmyungsamycin variants with truncated chains were evaluated for their biological activity. Turn by turn: The first total syntheses of the bioactive cyclodepsipeptide ohmyungsamycin A and the proposed structure of ohmyungsamycin B are based on the concise preparation of a linear cyclization precursor followed by macrocyclization. In addition, the proposed structure of ohmyungsamycin B was revised, and the correct position of the additional methyl group was elucidated.
Datum: 21.02.2018

Copper-Catalyzed Highly Stereoselective Trifluoromethylation and Difluoroalkylation of Secondary Propargyl Sulfonates

It is challenging to stereoselectively introduce a trifluoromethyl group (CF3) into organic molecules. To date, only limited strategies involving direct asymmetric trifluoromethylation have been reported. Herein, we describe a new strategy for direct asymmetric trifluoromethylation through the copper-catalyzed stereospecific trifluoromethylation of optically active secondary propargyl sulfonates. The reaction enables propargylic trifluoromethylation with high regioselectivity and stereoselectivity. The reaction could also be extended to stereospecific propargylic difluoroalkylation. Transformations of the resulting enantiomerically enriched fluoroalkylated alkynes led to a variety of chiral fluoroalkylated compounds, thus providing a useful protocol for applications in the synthesis of fluorinated complexes. Just the beginning: The title reaction enables propargylic trifluoromethylation and difluoroalkylation with high regioselectivity and stereoselectivity (see scheme) to provide versatile building blocks that undergo a wide variety of transformations. Inversion of configuration was observed for the copper-catalyzed process, thus demonstrating that SN2-type oxidative addition of copper to the secondary propargyl sulfonate may be involved in the reaction.
Datum: 21.02.2018

Supramolecular Nested Microbeads as Building Blocks for Macroscopic Self-Healing Scaffolds

The ability to construct self-healing scaffolds that are injectable and capable of forming a designed morphology offers the possibility to engineer sustainable materials. Herein, we introduce supramolecular nested microbeads that can be used as building blocks to construct macroscopic self-healing scaffolds. The core–shell microbeads remain in an “inert” state owing to the isolation of a pair of complementary polymers in a form that can be stored as an aqueous suspension. An annealing process after injection effectively induces the re-construction of the microbead units, leading to supramolecular gelation in a preconfigured shape. The resulting macroscopic scaffold is dynamically stable, displaying self-recovery in a self-healing electronic conductor. This strategy of using the supramolecular assembled nested microbeads as building blocks represents an alternative to injectable hydrogel systems, and shows promise in the field of structural biomaterials and flexible electronics. Self-healable scaffolds: Supramolecular nested microbeads that are capable of isolating a pair of complementary polymers were developed for the construction of macroscopic self-healing scaffolds. This protocol promotes the polymer flowability for injection while retaining self-healing behaviour on account of the dynamic molecular interactions.
Datum: 21.02.2018

Metal-Free and Alkali-Metal-Catalyzed Synthesis of Isoureas from Alcohols and Carbodiimides

The first addition of alcohols to carbodiimides catalyzed by transition-metal-free compounds employs 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and its alkali metal salts. Isoureas are obtained in short reaction times and high yields when TBDK is used as the catalyst. Control of the coordination sphere of potassium with exogenous chelating ligands, in combination with mechanistic DFT calculations, demonstrated the role and positive influence of the alkali-metal cation on the kinetics. The addition of alcohols to carbodiimides is catalyzed by transition-metal-free compounds such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and its alkali-metal salts. Isoureas are obtained in short reaction times and high yields when TBDK is used as the catalyst.
Datum: 21.02.2018

Catalytic CO Oxidation by O2 Mediated by Noble-Metal-Free Cluster Anions Cu2VO3–5−

Catalytic CO oxidation by molecular O2 is an important model reaction in both the condensed phase and gas-phase studies. Available gas-phase studies indicate that noble metal is indispensable in catalytic CO oxidation by O2 under thermal collision conditions. Herein, we identified the first example of noble-metal-free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu2VO3–5− for CO oxidation by O2. The reactions were characterized by mass spectrometry, photoelectron spectroscopy, and density functional calculations. The dynamic nature of the Cu−Cu unit in terms of the electron storage and release is the driving force to promote CO oxidation and O2 activation during the catalysis. Noble-metal-free heteronuclear oxide cluster catalysts, the copper–vanadium bimetallic oxide clusters Cu2VO3–5− for CO oxidation by O2, have been experimentally identified. The catalysis is driven by the electron cycling on the Cu−Cu unit in Cu2VO3–5− clusters.
Datum: 21.02.2018

Direct Observation of an Imidoylnitrene: Photochemical Formation of PhC(=NMe)−N and Me−N from 1-Methyl-5-phenyltetrazole

The imidoylnitrene 8, N-methyl-C-phenylimidoylnitrene, has been generated by laser photolysis of 1-methyl-5-phenyltetrazole 6 at 5 K and characterized by its ESR spectrum (|D/hc|=0.9602, |E/hc|=0.0144 cm−1). In addition, the triplet excited states of 6 and of 2-methyl-5-phenyltetrazole 11 were also observed by ESR spectroscopy in the 5 K matrices (6: |D/hc|=0.123 cm−1, E/hc=0.0065 cm−1, 11: |D/hc|=0.126 cm−1, |E/hc|=0.0056 cm−1). The imidoylnitrene 8 is unstable both thermally (disappearing at 80 K) and photochemically (disappearing on continued irradiation at 266 nm). Methyl(phenyl)carbodiimide is the end product of photolysis. Trapped in the cold: N-methyl-C-phenylimidoylnitrene (3) has been generated together with methylnitrene (1) and characterized in its triplet ground state by ESR spectroscopy at 5 K (|D/hc|=0.9602, |E/hc|=0.0144 cm−1). Furthermore, the ESR spectra of the triplet excited states of its precursor, 1-methyl-5-phenyltetrazole (2) as well as 2-methyl-5-phenyltetrazole, were also observed.
Datum: 21.02.2018

Dicationic E4 Chains (E=P, As, Sb, Bi) Embedded in the Coordination Sphere of Transition Metals

The oxidation chemistry of the complexes [{CpMo(CO)2}2(μ,η2:η2-E2)] (E=P (A), As (B), Sb (C), Bi (D)) is compared. The oxidation of A–D with [Thia]+ (=[C12H8S2]+) results in the selective formation of the dicationic E4 complexes [{CpMo(CO)2}4(μ4,η2:η2:η2:η2-E4)]2+ (E=P (1), As (2), Sb (3), Bi (4)), stabilized by four [CpMo(CO)2] fragments. The formation of the corresponding monocations [A]+, [C]+, and [D]+ could not be detected by cyclic voltammetry, EPR, or NMR spectroscopy. This finding suggests that dimerization is fast and that there is no dissociation in solution, which was also predicted by DFT calculations. However, EPR measurements of 2 confirmed the presence of small amounts of the radical cation [B]+ in solution. Single-crystal X-ray diffraction revealed that the products 1 and 2 feature a zigzag E4 chain in the solid state while 3 and 4 bear a central E4 cage with a distorted “butterfly-like” geometry. Additionally, 1 can be easily and reversibly converted into a symmetric and an unsymmetric form. Unprecedented dicationic E4 chains and cages (E=pnictogen) are obtained by the oxidation of [{CpMo(CO)2}2(μ,η2:η2-E2)] complexes through E−E bond formation. The dicationic cores are free of organic substituents and are stabilized in the coordination sphere of molybdenum atoms.
Datum: 21.02.2018

An Intracellular H2O2-Responsive AIEgen for the Peroxidase-Mediated Selective Imaging and Inhibition of Inflammatory Cells

Inflammatory cells have gained widespread attention because inflammatory diseases increase the risk for many types of cancer. Therefore, it is urgent and important to implement detection and treatment methods for inflammatory cells. Herein, we constructed a theranostic probe with aggregation-induced emission (AIE) characteristics, in which tetraphenylethene (TPE) was modified with two tyrosine (Tyr) moieties. Owing to the H2O2-dependent, enzyme-catalyzed dityrosine formation, Tyr-containing TPE (TT) molecules crosslink through dityrosine linkages to induce the formation of hydrophobic aggregates, activating the AIE process in inflammatory cells that contain H2O2 and overexpress myeloperoxidase. The emission turn-on resulting from the crosslinking of TT molecules could be used to distinguish between inflammatory and normal cells. Moreover, the massive TT aggregates induced mitochondria damage and cell apoptosis. This study demonstrates that the H2O2-responsive peroxidase-activated AIEgen holds great promise for inflammatory-cell selective imaging and inhibition. Aggregate therapy: An intracellular H2O2-responsive and peroxidase-mediated therapeutic strategy with AIEgens has been developed. The method described provides a theranostic tool for inflammatory-cell selective imaging and inhibition to achieve the precise detection and treatment.
Datum: 21.02.2018

Nitrogen-Based Lewis Acids: Synthesis and Reactivity of a Cyclic (Alkyl)(Amino)Nitrenium Cation

A room-temperature-stable crystalline cyclic (alkyl)(amino)nitrenium cation 2 features cationic nitrogen atom with a smaller HOMO–LUMO gap compared to that of a 1,2,3-triazolium 5 (an N-heterocyclic nitrenium cation). The low-lying LUMO of 2 results in an enhanced electrophilicity, which allowed for the formation of Lewis adducts with neutral Lewis bases, such as Me3P, nBu3P, and IiPr. The N-based Lewis acid 2 also forms an FLP with tBu3P but subsequently reacts with (PrS)2 to cleave the S−S bond. Both experimental and theoretical results suggest that the Lewis acidity of 2 is stronger than its N3 analogues. The room-temperature-stable crystalline cyclic (alkyl)(amino) nitrenium features a cationic nitrogen atom and exhibits enhanced electrophilicity, yielding Lewis adducts with Me3P, nBu3P, and IiPr and an FLP with tBu3P.
Datum: 21.02.2018

Potassium-Zincate-Catalyzed Benzylic C−H Bond Addition of Diarylmethanes to Styrenes

Direct functionalization of the benzylic C−H bond of diarylmethanes is an important strategy for the synthesis of diarylmethine-containing compounds. However, the methods developed to date for this purpose require a stoichiometric amount (usually more) of either a strong base or an oxidant. Reported here is the first catalytic benzylic C−H bond addition of diarylmethanes to styrenes and conjugated dienes. A potassium zincate complex, generated from potassium benzyl and zinc amide, acts as a catalyst and displays good activity and chemoselectivity. Considering the atom economy of the reaction and the ready availability of the catalyst, this reaction constitutes a practical, efficient method for diarylalkane synthesis. ‘Zinc’ into it: The catalytic addition of the benzylic carbon center of diarylmethanes to styrenes and conjugated dienes was achieved for the first time by using a potassium zincate catalyst. The reaction demonstrates wide scope and high yields.
Datum: 21.02.2018

Contra-Thermodynamic, Photocatalytic EZ Isomerization of Styrenyl Boron Species: Vectors to Facilitate Exploration of Two-Dimensional Chemical Space

Designing strategies to access stereodefined olefinic organoboron species is an important synthetic challenge. Despite significant advances, there is a striking paucity of routes to Z-α-substituted styrenyl organoborons. Herein, this strategic imbalance is redressed by exploiting the polarity of the C(sp2)−B bond to activate the neighboring π system, thus enabling a mild, traceless photocatalytic isomerization of readily accessible E-α-substituted styrenyl BPins to generate the corresponding Z-isomers with high fidelity. Preliminary validation of this contra-thermodynamic EZ isomerization is demonstrated in a series of stereoretentive transformations to generate Z-configured trisubstituted alkenes, as well as in a concise synthesis of the anti-tumor agent Combretastatin A4. It's EZ: Exploitation of the polarity of the C(sp2)−B bond to activate the neighboring π system enables a mild, traceless photocatalytic isomerization of readily accessible E-α-substituted styrenyl BPins to generate the corresponding Z-isomers with high fidelity. The method is used for a series of stereoretentive transformations to generate Z-configured trisubstituted alkenes, as well as in a concise synthesis of the anti-tumor agent combretastatin A4.
Datum: 21.02.2018

N-Carboxyanhydride Polymerization of Glycopolypeptides that Activate Antigen-Presenting Cells through Dectin-1 and Dectin-2

The C-type lectins dectin-1 and dectin-2 contribute to innate immunity against microbial pathogens by recognizing their foreign glycan structures. These receptors are promising targets for vaccine development and cancer immunotherapy. However, currently available agonists are heterogeneous glycoconjugates and polysaccharides from natural sources. Herein, we designed and synthesized the first chemically defined ligands for dectin-1 and dectin-2. They comprised glycopolypeptides bearing mono-, di-, and trisaccharides and were built through polymerization of glycosylated N-carboxyanhydrides. Through this approach, we achieved glycopolypeptides with high molecular weights and low dispersities. We identified structures that elicit a pro-inflammatory response through dectin-1 or dectin-2 in antigen-presenting cells. With their native proteinaceous backbones and natural glycosidic linkages, these agonists are attractive for translational applications. Causing a response: The first chemically defined ligands for dectin-1 and dectin-2 were designed and synthesized. These consisted of glycopolypeptides built through the polymerization of glycosylated N-carboxyanhydrides. Structures that elicit a proinflammatory response through dectin-1 or dectin-2 in antigen-presenting cells were identified.
Datum: 21.02.2018

Highly Efficient Artificial Light-Harvesting Systems Constructed in Aqueous Solution Based on Supramolecular Self-Assembly

Highly efficient light-harvesting systems were successfully fabricated in aqueous solution based on the supramolecular self-assembly of a water-soluble pillar[6]arene (WP6), a salicylaldehyde azine derivative (G), and two different fluorescence dyes, Nile Red (NiR) or Eosin Y (ESY). The WP6-G supramolecular assembly exhibits remarkably improved aggregation-induced emission enhancement and acts as a donor for the artificial light-harvesting system, and NiR or ESY, which are loaded within the WP6-G assembly, act as acceptors. An efficient energy-transfer process takes place from the WP6-G assembly not only to NiR but also to ESY for these two different systems. Furthermore, both of the WP6-G-NiR and WP6-G-ESY systems show an ultrahigh antenna effect at a high donor/acceptor ratio. Light-harvesting systems were fabricated in aqueous solution by supramolecular self-assembly of a water-soluble pillar[6]arene (WP6), a salicylaldehyde azine derivative (G, acting as donor), and two different fluorescence dyes, Nile Red or Eosin Y, which is loaded within the WP6-G assembly, acts as acceptor.
Datum: 21.02.2018

Isolation of an Eleven-Atom Polydentate Carbon-Chain Chelate Obtained by Cycloaddition of a Cyclic Osmium Carbyne with an Alkyne

Carbon ligands have long played an important role in organometallic chemistry. However, previous examples of all-carbon chelating ligands are limited. Herein, we present a novel complex with an eleven-atom carbon chain as a polydentate chelating ligand. This species was formed by the [2+2+2] cycloaddition reaction of two equivalents of an alkyne with an osmapentalyne that contains the smallest carbyne bond angle (127.9°) ever observed. Density functional calculations revealed that electron-donating groups play a key role in the stabilization of this polydentate carbon-chain chelate. This process is also the first [2+2+2] cycloaddition reaction of an alkyne with a late-transition-metal carbyne complex. This study not only enriches the chemistry of polydentate carbon-chain chelates, but also deepens our understanding of the chelating ability of carbon ligands. Polydentate carbon ligands: The first organometallic compound with an eleven-atom carbon chain as a polydentate chelating ligand was obtained by [2+2+2] cycloaddition of an alkyne with a late-transition-metal carbyne complex, and provides further insight into the coordinating ability of carbon ligands.
Datum: 21.02.2018

Highly Stable Lithium Metal Batteries Enabled by Regulating the Li+ Solvation in Nonaqueous Electrolyte

Safe and rechargeable lithium (Li) metal batteries have been hindered by the uncontrollable Li dendrites, where nonaqueous electrolyte always plays a significant role in practical batteries. Herein an emerging electrolyte based on a simple solvation strategy was proposed for highly stable Li metal anodes in both coin and pouch cells. Fluoroethylene carbonate (FEC) and lithium nitrate (LiNO3) were concurrently introduced into electrolyte, altering the solvation sheath of Li ions and then forming uniform solid electrolyte interphase (SEI) with abundant LiF and LiNxOy on a working Li metal anode that contributes to dendrite-free Li deposition. Ultrahigh Coulombic efficiency (99.96%) and long lifespans (1000 cycles) were achieved when FEC/LiNO3 electrolyte was applied in working batteries. The solvation chemistry of electrolyte was further explored by molecular dynamics simulations and first-principles calculations. This work provides a fruitful insight on understanding the critical role of the solvation of Li ions in forming SEI and delivers an effective route to optimize electrolytes for safe Li metal batteries.
Datum: 21.02.2018

Site-Specific Studies of Nucleosome Interactions by Solid-State NMR

Chromatin function depends on a dense network of interactions between nucleosomes and wide range of proteins. A detailed description of these protein-nucleosome interactions is required to reach a full molecular understanding of chromatin function in both genetics and epigenetics. Here, we show that the structure, dynamics and interactions of nucleosomes can be interrogated in a residue-specific manner using state-of-the-art solid-state NMR. Using sedimented nucleosomes, high-resolution spectra are obtained for both flexible histone tails and the non-mobile histone core. Through co-sedimentation of a nucleosome-binding peptide, we demonstrate that protein binding sites on the nucleosome surface can be determined. We believe that this approach holds great promise as it is generally applicable, extendable to include the structure and dynamics of the bound proteins, and scalable to interactions of proteins with higher-order chromatin structures, including isolated or cellular chromatin.
Datum: 21.02.2018

An αv-RGD Integrin Inhibitor Toolbox: Drug Discovery Insight, Challenges and Opportunities

There is a requirement for efficacious and safe medicines to treat diseases with high unmet need. The resurgence in αv-RGD integrin inhibitor drug discovery is poised to contribute to this requirement. However, drug discovery in the αv integrin space is notoriously difficult due to the receptors being structurally very similar as well as the polar zwitterionic nature of the pharmacophore. This Review aims to guide drug discovery research in this field through an αv inhibitor toolbox, consisting of small molecules and antibodies. Small-molecule αv tool compounds with extended profiles in αvβ1, 3, 5, 6 and 8 cell adhesion assays, with key physicochemical properties, have been collated to assist in the selection of the right tool for the right experiment. This should also facilitate an understanding of partial selectivity profiles of compounds generated in different assays across research institutions. Prospects for further αv integrin research and the critical importance of target validation are discussed, where increased knowledge of the selectivity for individual RGD αv integrins is key. Insights into the design of small-molecule RGD chemotypes for topical or oral administration are provided and clinical findings on advanced molecules are examined. Integrins are transmembrane proteins that link the extracellular matrix with the cytoskeleton of cells and function as receptors for signalling. This Review aims to guide drug discovery in the αv integrin space through an αv inhibitor toolbox, consisting of small molecules and antibodies.
Datum: 21.02.2018

Bioorthogonal Catalytic Activation of Platinum and Ruthenium Anticancer Complexes by FAD and Flavoproteins

Flavins and flavoproteins have been employed as photocatalysts for the activation of metal-based prodrugs. In their Communication (DOI: 10.1002/anie.201800288), F. López-Gallego, L. Salassa, and co-workers show how these photocatalysts convert PtIV and RuII complexes into potentially toxic PtII or RuII−OH2 species in the presence of electron donors and low doses of blue light. The flavoproteins miniSOG and NADH oxidase catalytically activate PtIV prodrugs with bioorthogonal selectivity. Unconventionally, metal complexes act as substrates in these reactions.
Datum: 21.02.2018

Silica-Supported Pentamethylcyclopentadienyl Cyclopentadienyl Ytterbium(II) and Samarium(II) Sites: Ultrahigh Molecular Weight Polyethylene without Co-Catalyst

Designing highly active supported ethylene polymerization catalysts that do not require a co-catalyst to generate electrophilic metal alkyl species is still a challenge despite its industrial relevance. Described herein is the synthesis and characterization of well-defined silica-supported cyclopentadienyl LnII sites (Ln=Yb and Sm) of general formula [(≡SiO)LnCp*]. These well-defined surface species are highly activite towards ethylene polymerization in the absence of added co-catalyst. Initiation is proposed to occur by single electron transfer. Ready, SET, Go: Well-defined silica-supported lanthanocene(II) [(≡SiO)LnCp*] (Ln=Yb, Sm) were synthesized and fully characterized by extended X-ray absorption fine structure, infrared spectroscopy, solid-state NMR spectroscopy, and elemental analysis. These catalysts demonstrated very high activity for ethylene polymerization, the initiation of which is postulated to occur through a single electron transfer.
Datum: 21.02.2018

Revealing active species for aerobic alcohol oxidation using stoichiometrically uniform supported Pd catalysts

Supported metal catalysts are one of the foundations of modern chemical industry. The active species in such catalysts are always elusive to identify, and in the meanwhile large quantities of inert species can cause significant waste. Herein, using a stoichiometrically precise synthetic method, we prepare atomically dispersed palladium-cerium oxide (Pd1/CeO2) and hexapalladium cluster-cerium oxide (Pd6/CeO2), as confirmed by spherical-aberration-corrected transmission electron microscopy and X-ray absorption fine structure spectroscopy. We discover that, for aerobic alcohol oxidation, Pd1/CeO2 shows extremely high catalytic activity with a TOF of 6739 h-1 and satisfactory selectivity (almost 100% for benzaldehyde), while Pd6/CeO2 is inactive, indicating that the true active species are single Pd atoms. Theoretical simulations reveal that the bulkier Pd6 clusters hinder the interactions between hydroxyl groups and the CeO2 surface, thus suppressing synergy of Pd-Ce perimeter. This work provides a new way to maximize material utilization and reduce waste in supported metal catalysts.
Datum: 21.02.2018

Cobalt-Bridged Ionic Liquid Polymer on a Carbon Nanotube for Enhanced Oxygen Evolution Reaction Activity

By taking inspiration from the catalytic properties of single-site catalysts and the enhancement of performance through ionic liquids on metal catalysts, we exploited a scalable way to place single cobalt ions on a carbon-nanotube surface bridged by polymerized ionic liquid. Single dispersed cobalt ions coordinated by ionic liquid are used as heterogeneous catalysts for the oxygen evolution reaction (OER). Performance data reveals high activity and stable operation without chemical instability. Co-operating: A scalable method was developed to get single cobalt ions on CNT surface with polymerized ionic liquid. The polymerized ionic liquid can adjust the electron structure of the atomically dispersed Co which is favorable for the oxygen evolution reaction. The tangled polymerized ionic liquid, as counter ion, make the Co ion stable on CNT surface.
Datum: 21.02.2018

Broadening the Scope for Fluoride-Free Synthesis of Siliceous Zeolites

Siliceous zeolites are ideally suited for emerging applications in gas separations, sensors, and the next generation of low-k dielectric materials, but the use of fluoride in the synthesis significantly hinders their commercialization. Herein, we show that the dry gel conversion (DGC) technique can overcome this problem. Fluoride-free synthesis of two siliceous zeolites—AMH-4 (CHA-type) and AMH-5 (STT-type), has been achieved for the first time using the method. Siliceous *BEA-, MFI-, and *MRE-type zeolites have also been synthesized to obtain insights into the crystallization process. Charge-balancing interactions between the inorganic cation, organic structure-directing agent (OSDA), and Si−O− defects are found to be an essential aspect. We quantify this factor in terms of the “OSDA charge/silica ratio” of the as-made zeolites and demonstrate that the DGC technique is broadly applicable and opens up new avenues for fluoride-free siliceous zeolite synthesis. No F required: Fluoride-free synthesis of siliceous zeolites remains highly challenging—of the 234 recognized zeolite framework structures, less than 25 have been made in purely siliceous form without using fluoride. The dry gel conversion technique has been used to synthesize two new fluoride-free siliceous zeolites. Systematic studies and analysis reveal mechanistic insights into fluoride-free siliceous zeolite synthesis.
Datum: 21.02.2018

Super-chelators for advanced protein labeling in living cells

Live-cell labeling, super-resolution microscopy, single-molecule applications, protein localization or chemically induced assembly are emerging approaches, which require specific and very small interaction pairs. The minimal disturbance of protein function is essential to derive unbiased insights into cellular processes. Here, we define a new class of hexavalent N-nitrilotriacetic acid (hexaNTA) chelators, displaying the highest affinity and stability of all NTA-based small interaction pairs described so far. Coupled to bright organic fluorophores with fine-tuned photo-physical properties, these super-chelator probes were delivered into human cells by chemically gated nanopores. These super-chelators permit kinetic profiling, multiplexed labeling of His6 and His12-tagged proteins as well as single-molecule based super-resolution imaging.
Datum: 21.02.2018

Odorant receptor 7D4 activation dynamics

Deciphering how an odorant activates an odorant receptor (OR) and how changes in specific OR residues affect its responsiveness are central to understanding how we smell. A joint approach combining site-directed mutagenesis and functional assays with computational modeling has been used to explore the signaling mechanics of OR7D4. In this OR, a genetic polymorphism affects our perception of androstenone. A total of 0.12 ms molecular simulations predicted that, similarly to observations from other G protein-coupled receptors with known experimental structures, an activation pathway connects the ligand and G protein binding site. The 3D model activation mechanism correlates with in vitro data and notably predicts that the OR7D4 WM variant does not activate. Upon activation, an OR-specific sequence motif is the convergence point of the mechanism. Our study suggests that robust homology modeling can serve as a powerful tool to capture OR dynamics related to smell perception.
Datum: 20.02.2018

O2 sensitivity of [Fe]-hydrogenase in the Presence of Reducing Substrates

[Fe]-hydrogenase reversibly catalyzes the transfer of a hydride ion from H2 to methenyl-tetrahydromethanopterin (methenyl-H4MPT+) to form methylene-H4MPT. Its iron-guanylylpyridinol (FeGP) cofactor plays a key role in H2 activation. Here, we show that [Fe]-hydrogenase becomes O2-sensitive under turnover conditions in the presence of the reducing-substrates, methylene-H4MPT or methenyl-H4MPT+/H2. Only then, H2O2 is generated and decomposes the FeGP cofactor as demonstrated by spectroscopic analyses and the crystal structure of the inactivated enzyme. O2 reduction to H2O2 requires a reductant, which can be a catalytic intermediate transiently formed during the [Fe]-hydrogenase reaction. The most probable candidate is an iron-hydride species; its presence has already been predicted by theoretical studies of the catalytic reaction. Our finding supported the prediction because the same type of reduction reaction is described for ruthenium hydride complexes that hydrogenate polar compounds.
Datum: 20.02.2018

Customizing the Electrochemical Properties of Carbon Nanodots with Quinones in Bottom-Up Syntheses

We show how the redox potentials of Carbon Nanodots (CNDs) can be modulated by employing quinones as electroactive precursors during the microwave-assisted synthetic step. We prepared and characterized a redox library of CNDs, demonstrating that this approach can promote the use of carbon nanodots for ad-hoc applications, including photocatalysis.
Datum: 20.02.2018

Chiral 1,3,2-Diazaphospholenes as Catalytic Molecular Hydrides for Enantioselective Conjugate Reductions

Secondary 1,3,2-diazaphospholenes have a polarized P‒H bond and are emerging as molecular hydrides. A class of chiral conformationally restricted methoxy-1,3,2-diazaphospholene catalysts is reported. We demonstrate their catalytic potential in enantioselective 1,4-reduction of α,β-unsaturated carbonyl derivatives comprising enones, acyl pyrroles and amides in enantioselectivities of up to 95.5:4.5 er.
Datum: 20.02.2018

Enzymatic or in vivo installation of propargyl groups in combination with click chemistry enables enrichment and detection of methyltransferase target sites in RNA

m6A is the most abundant internal modification in eukaryotic mRNA. It is introduced by METTL3-METTL14 and tunes mRNA metabolism, impacting cell differentiation and development. Precise transcriptome-wide assignment of m6A sites is of utmost importance. However, m6A does not interfere with Watson-Crick base pairing making polymerase-based detection challenging. We developed a chemical-biology approach for the precise mapping of methyltransferase (MTase) target sites based on the introduction of a bioorthogonal propargyl group in vitro and in cells. We show that propargyl can be introduced enzymatically by wild-type METTL3-METTL14. Reverse transcription terminated up to 65 % at m6A sites after bioconjugation and purification, hence enabling detection of METTL3-METTL14 target sites by next generation sequencing. Importantly, we implemented metabolic propargyl labeling of RNA MTase target sites in vivo based on propargyl-L-selenohomocysteine and validated different types of known rRNA methylation sites.
Datum: 20.02.2018

Unprecedented Dearomatized Spirocyclopropane in a Sequential Rh(III)-catalyzed C-H Activation and Rearrangement Reaction

An unprecedented dearomatized spirocyclopropane intermediate was discovered in a sequential Cp*Rh(III)-catalyzed C-H activation and Wagner-Meerwein-type rearrangement reaction. How the oxidative O-N bond is cleaved and the role of HOAc were uncovered in this study. Furthermore, a Cp*Rh(III)-catalyzed dearomatization reaction of N-(naphthalen-1-yloxy)acetamide with strained olefins was developed, affording a variety of spirocyclopropanes.
Datum: 20.02.2018

One-Pot Tandem Photoredox and Cross-Coupling Catalysis with a Single Pd-Carbodicarbene Complex

The combination of conventional transition metal-catalyzed coupling (2e- process) and photoredox catalysis (1e- process) has emerged as a powerful approach to catalyze difficult cross-coupling reactions under mild conditions. We report a Pd-carbodicarbene (CDC) complex that mediates both Suzuki-Miyaura coupling and photoredox catalysis for C-N bond formation upon visible-light irradiation. These two catalytic pathways can be further merged to promote both conventional transition-metal-catalyzed coupling and photoredox catalysis to mediate C-H arylation under ambient conditions with a single component catalyst in an efficient one-pot process.
Datum: 20.02.2018

Lewis Acid Catalyzed Enantioselective Desymmetrization of Donor-Acceptor Meso-Diaminocyclopropanes

The first example of Lewis acid catalyzed enantioselective ring-opening desymmetrization of donor-acceptor meso-diaminocyclopropanes is reported herein. A copper(II)-catalyzed Friedel-Crafts alkylation of indoles and a pyrrole with an unprecedented meso-diaminocyclopropane delivered enantioenriched diastereomerically pure urea products, which are structurally related to natural and synthetic bioactive compounds. The development of a new ligand through the investigation of an underexplored subclass of BOX ligands was essential for obtaining high enantiomeric ratios.
Datum: 20.02.2018

Direct formation of C-C triple bonded structural motifs by on-surface dehalogenative homocoupling of tribromomethyl molecules

On-surface synthesis shows significant potential in constructing novel nanostructures/nanomaterials, which has been intensely studied over the recent years. The formation of acetylenic scaffoldings provides an important route to the fabrication of emerging carbon nanostructures including carbyne, graphyne and graphdiyne, which involve the chemically vulnerable sp-hybridized carbons. Herein, we designed and synthesized a tribromomethyl group, by using the combination of high-resolution scanning tunneling microscopy and non-contact atomic force microscopy imaging and density functional theory calculations, we demonstrated that it is feasible to achieve the direct formation of C-C triple bonded structural motifs via on-surface dehalogenative homocoupling reactions. Correspondingly, we are able to convert the sp3 hybridized state to sp hybridized state of carbon atoms, i.e., from an alkyl group to an alkynyl one. Moreover, we successfully achieved the formation of dimer structures, one-dimensionalmolecular wires and two-dimensional molecular networks on Au(111) surface,which would inspire further studies towards the two-dimensional graphyne structures.
Datum: 20.02.2018

Iron-Catalyzed Cross-Coupling in the Synthesis of Pharmaceuticals: In Pursuit of Sustainability

The scarcity of precious metals has given raise to the development of sustainable strategies for metal-catalyzed cross-coupling reactions. The establishment of new catalytic methods using iron is attractive due to low cost, abundance, ready availability and very low toxicity of iron. In the last few years sustainable methods for iron-catalyzed cross-couplings have entered the critical area of pharmaceutical research. Most notably, iron is one of the very few metals that have been successfully field tested as highly effective base-metal catalysts in practical, kilogram-scale industrial cross-couplings, thus validating the potential and promise of iron-catalysis to address the challenge of sustainability for chemical synthesis. In this minireview, we critically discuss the strategic benefits of using iron catalysis as a green and sustainable alternative to precious metals in cross-coupling applications for the synthesis of pharmaceuticals. The minireview provides an essential introduction to the fundamental aspect of practical iron catalysis, highlights areas for improvement and identifies new fields to explore.
Datum: 20.02.2018

NiH-Catalyzed Reductive Relay Hydroalkylation: A Strategy for Remote sp3 C-H Alkylation of Alkenes

The terminal-selective, remote sp3 C-H alkylation of alkenes was achieved by a NiH-catalyzed reductive, chainwalking and sequential alkylation relay process. This method allows the construction of unfunctionalized C(sp3)-C(sp3) bonds, under mild conditions from two simple feedstock chemicals, olefins and alkyl halides. The practical value of this transformation is further demonstrated by the large-scale and regioconvergent alkylation of isomeric mixtures of olefins with low catalyst loading.
Datum: 20.02.2018

Phosphoric Acid Catalyzed Asymmetric [2+2] Cyclization/Penicillin-penillonic Acid Rearrangement

The first example of asymmetric penicillin-penillonic acid (PPA) rearrangement was reported that is based on the first [2+2] cyclization followed by acid-catalyzed asymmetric rearrangement. In the presence of a phosphoric acid catalyst, the reaction of azlactones with β-carbolines generates α-amino-β-lactams, which undergo PPA rearrangement with high selectivities. This process represents the first [2+2] cyclization of azlactones with imines and the first PPA rearrangement, which are linked together by the phosphoric acid catalyst.
Datum: 20.02.2018

Atomically dispersed metal sites in MOF-based materials for electrocatalytic and photocatalytic energy conversion

Metal sites play an essential role for both electrocatalytic and photocatalytic energy conversion applications. The highly ordered arrangements of the organic linkers and metal nodes and the well-defined pore structures of metal-organic frameworks (MOFs) make them ideal substrates to support atomically dispersed metal sites (ADMSs) located in their metal nodes, linkers, and pores. Besides, porous carbon materials doped with ADMSs can be derived from these ADMS-incorporated MOF precursors through controlled treatments. These ADMSs incorporated in pristine MOFs and MOF-derived carbon materials possess unique merits over the molecular or the bulk metal-based catalysts, bridging the gap between homogeneous and heterogeneous catalysts for energy conversion applications. In this review, recent progress and perspective of design and incorporation of ADMSs in pristine MOFs and MOF-derived materials for energy conversion applications are highlighted, which will hopefully promote further developments of advanced MOF-based catalysts in foreseeable future.
Datum: 20.02.2018

Counting the Clicks in Fluorescent Polymer Networks

We introduce a fluorescence-based methodology enabling the quantification of ligation points in photochemically prepared polymer networks, addressing the vexed question of quantifying the number of linkages within networks. Well-defined α,ω-tetrazole-capped polymer strands prepared via RAFT polymerization are crosslinked under UV irradiation by a trimaleimide via nitrile imine-mediated tetrazole-ene cycloaddition. Thus, for each linkage point a fluorescent pyrazoline ring is formed, resulting fluorescent networks, which are degradable by aminolysis of the trithiocarbonate functionalities, resulting in soluble fragments. The fluorescence emission of the soluble network fragments correlates directly with the number of pyrazoline moieties originally present in the network, thus providing a direct measure of the elusive number of ligation points constituting the network. The herein introduced strategy based on a fluorescence readout is a powerful yet simple approach to quantify network formation processes applicable to a wide class of polymers accessible via RAFT.
Datum: 20.02.2018

Visible-Light Photocatalysis: Does it make a difference in Organic Synthesis?

Visible light photocatalysis has evolved over the last decade into a widely used method in organic synthesis. For many important transformations, such as cross-coupling reactions, alpha-amino functionalizations, cycloadditions, ATRA reactions, or fluorinations, photocatalytic variants have been reported. In this review, we try to compare classical and photocatalytic procedures for selected classes of reactions and highlight their advantages and limitations. In many cases, the photocatalytic reactions proceed at milder reaction conditions, typically at room temperature, and stoichiometric reagents are replaced by simple oxidants or reductants, like air oxygen or amines. This way, besides providing alternative protocols for established transformations that allow a broadening of the substrate scope, also new transformations become possible, especially by merging photocatalysis with organo- or metal catalysis. Does visible light photocatalysis make a difference in organic synthesis? The prospect to shuttle electrons back and forth to substrates and intermediates or to selectively transfer energy through a visible light absorbing photocatalyst holds the promise to improve current protocols in radical chemistry and to open up new avenues by accessing reactive species hitherto unknown.
Datum: 19.02.2018

A Stable Metal-Organic Framework Featuring Local Buffer Environment for Carbon Dioxide Fixation

A majority of metal-organic frameworks (MOFs) fail to preserve their physical and chemical properties after exposure to acidic, neutral, or alkaline aqueous solutions, therefore limiting their practical applications in many areas. The strategy demonstrated herein is the design and synthesis of an organic ligand that behaves as a buffer to drastically boost the aqueous stability of a porous MOF (JUC-1000), which maintains its structural integrity at low and high pH values. The local buffer environment resulting from the weak acid-base pairs of the custom-designed organic ligand also greatly facilitates the performance of JUC-1000 in the chemical fixation of carbon dioxide under ambient conditions, outperforming a series of benchmark catalysts.
Datum: 19.02.2018

Promoted Fixation of Molecular Nitrogen with Surface Oxygen Vacancies on Plasmon-Enhanced TiO2 Photoelectrodes

A hundred years on energy-intensive Haber-Bosch process continuously turn the nitrogen in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The urgency of mitigating climate change motivates people to progress towards a more sustainable way in fixing nitrogen based on clean energy. Surface oxygen vacancies (surface Ovac) hold great potential for N2 adsorption and activation, but introducing Ovac on the very surface without affecting bulk properties remains a great challenge. This communication describes the promotional role of surface OVac in outer layers of amorphous TiO2 thin films in the adsorption and activation of nitrogen. This facilitates nitrogen reduction to ammonia by excited electrons from ultraviolet-light-driven rutile TiO2 nanorod arrays and visible-light-driven Au surface plasmons. This demonstration contributes to the ongoing efforts of developing new approaches for nitrogen fixation under ambient conditions. (i.e., room temperature, atmospheric pressure).
Datum: 19.02.2018

Postsynthetic Functionalization of Three-Dimensional Covalent Organic Framework for Selective Extraction of Lanthanide Ions

Chemical Functionalization of covalent organic frameworks (COFs) is critical to tune their properties and broaden their potential applications. However, the introduction of functional groups especially in three-dimensional (3D) COFs still remains largely unexplored. Here we report a general strategy for generating a 3D carboxyl-functionalized COF through postsynthetic modification of a hydroxyl COF, and for the first time explore the carboxyl COF for selective extraction of lanthanide ions. The obtained COF shows high crystalllinity, good chemical stability, and large specific surface area. Furthermore, the carboxyl COF displays high metal loading capacities together with excellent adsorption selectivity for Nd3+ over Sr2+ and Fe3+ confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens the route to their environmental related applications.
Datum: 19.02.2018

Peter J. Dunn Award / International Solvay Chair in Chemistry for Gernot Frenking / Max Born Prize for Angel Rubio / Terrae Rarae Prize for Rhett Kempe / Frontiers in Chemical Energy Science Award for Karsten Reuter / And also in the News

Datum: 19.02.2018

Dual input regulation and positional control in hybrid oligonucleotide-discotic supramolecular wires

The combination of oligonucleotides and synthetic supramolecular systems allows for novel and long needed modes of regulation of the self-assembly of both molecular elements. Discotic molecules were conjugated with short oligonucleotides and their assembly into responsive supramolecular wires studied. The self-assembly of the discotics provides additional stability for DNA-duplex formation due to a cooperative effect. Reversely, the appended oligonucleotides allow for positional control of the discotic elements within the supramolecular wire. The programmed assembly of these hybrid architecture can be modulated via the DNA, e.g. by changing the number of base pairs or salt concentration, and via the discotic platform by the addition of discotics without oligonucleotide handles. These hybrid supramolecular-DNA structures allow for advanced levels of control over 1-D dynamic platforms with responsive regulatory elements at the interface with biological systems.
Datum: 19.02.2018

Towards structural studies of self-assembled subviral particles: combining cell-free expression with 100 kHz MAS NMR

Viral membrane proteins are prime targets in the combat against infection. Still, their structure determination remains a challenge, both with respect to sample preparation, and the need for structural methods allowing analysis in a native-like lipid environment. Cell-free protein synthesis and solid-state NMR are promising approaches in this context, one with respect to its high potential of native expression of complex proteins, and the other for its ability to analyze membrane proteins in lipids. We here show that milligram amounts of the small envelope protein of the duck hepatitis B virus (DHBV) can be produced using cell-free expression, and that the protein self-assembles into subviral particles. 2D proton-detected NMR spectra recorded at 110 kHz magic angle spinning on < 500 μg protein show a number of isolated peaks with linewidths comparable to model membrane proteins, paving the way for structural studies this homologous protein to a potential drug target in HBV infection.
Datum: 19.02.2018

Designed Long-Lived Emission from CdSe Quantum Dots through Reversible Electronic Energy Transfer with a Surface-Bound Chromophore

The size-tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface-bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self-assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer. Extended play: The first examples of delayed luminescence involving CdSe quantum dots are reported, with by emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to analogous parent compounds. The mechanism involves unprecedented reversible quantum dot to organic chromophore electronic energy transfer.
Datum: 19.02.2018

Stimuli-Responsive Dual-Color Photon Upconversion: A Singlet-to-Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane

Reversible emission color switching of TTA-UC (triplet–triplet annihilation-based photon upconversion) has been achieved, as shown by N. Yanai, N. Kimizuka et al. in their Communication (DOI: 10.1002/anie.201712644). An Os complex sensitizer displays large anti-Stokes shift by direct singlet-to-triplet NIR excitation, and the combination with a luminescent cyclophane emitter allows thermally reversible upconversion color switching between the green-emissive crystalline state and yellow-emissive nematic state.
Datum: 19.02.2018

Porphyrin-Based Symmetric Redox-Flow Batteries towards Cold-Climate Energy Storage

Electrochemical energy storage with redox-flow batteries (RFBs) under subzero temperature is of great significance for the use of renewable energy in cold regions. However, RFBs are generally used above 10 °C. Herein we present non-aqueous organic RFBs based on 5,10,15,20-tetraphenylporphyrin (H2TPP) as a bipolar redox-active material (anode: [H2TPP]2−/H2TPP, cathode: H2TPP/[H2TPP]2+) and a Y-zeolite–poly(vinylidene fluoride) (Y-PVDF) ion-selective membrane with high ionic conductivity as a separator. The constructed RFBs exhibit a high volumetric capacity of 8.72 Ah L−1 with a high voltage of 2.83 V and excellent cycling stability (capacity retention exceeding 99.98 % per cycle) in the temperature range between 20 and −40 °C. Our study highlights principles for the design of RFBs that operate at low temperatures, thus offering a promising approach to electrochemical energy storage under cold-climate conditions. Hot stuff when it gets chilly: Redox-flow batteries (RFBs) for energy storage at subzero temperatures would facilitate the use of renewable energy in cold regions. Such non-aqueous RFBs with high volumetric capacity, high voltage, and excellent cycling stability between 20 and −40 °C have been developed with the porphyrin H2TPP as a bipolar redox-active material and a Y-zeolite–poly(vinylidene fluoride) ion-selective membrane.
Datum: 19.02.2018

Total Synthesis of Astellatol

Chinese paper cutting is a long-standing tradition in China, and often used to decorate doors and windows during the Spring Festival. The Chinese character 福 means blessing and happiness and the character 春 means spring. With this backdrop, J. Xu et al. present in their Communication (DOI: 10.1002/anie.201800167) the first enantiospecific synthesis for a three-decade-old synthetic challenge, astellatol.
Datum: 19.02.2018

A C=O⋅⋅⋅Isothiouronium Interaction Dictates Enantiodiscrimination in Acylative Kinetic Resolutions of Tertiary Heterocyclic Alcohols

A combination of experimental and computational studies have identified a C=O⋅⋅⋅isothiouronium interaction as key to efficient enantiodiscrimination in the kinetic resolution of tertiary heterocyclic alcohols bearing up to three potential recognition motifs at the stereogenic tertiary carbinol center. This discrimination was exploited in the isothiourea-catalyzed acylative kinetic resolution of tertiary heterocyclic alcohols (38 examples, s factors up to >200). The reaction proceeds at low catalyst loadings (generally 1 mol %) with either isobutyric or acetic anhydride as the acylating agent under mild conditions. Test your resolve: Experimental and computational studies have identified a C=O⋅⋅⋅isothiouronium interaction as key to efficient enantiodiscrimination in the kinetic resolution of tertiary heterocyclic alcohols with up to three potential recognition motifs at the stereogenic tertiary carbinol center. The kinetic resolution of a range of such alcohols was achieved with an isothiourea catalyst and either isobutyric or acetic anhydride.
Datum: 19.02.2018

Isotope Substitution of Promiscuous Alcohol Dehydrogenase Reveals the Origin of Substrate Preference in the Transition State

The origin of substrate preference in promiscuous enzymes was investigated by enzyme isotope labelling of the alcohol dehydrogenase from Geobacillus stearothermophilus (BsADH). At physiological temperature, protein dynamic coupling to the reaction coordinate was insignificant. However, the extent of dynamic coupling was highly substrate-dependent at lower temperatures. For benzyl alcohol, an enzyme isotope effect larger than unity was observed, whereas the enzyme isotope effect was close to unity for isopropanol. Frequency motion analysis on the transition states revealed that residues surrounding the active site undergo substantial displacement during catalysis for sterically bulky alcohols. BsADH prefers smaller substrates, which cause less protein friction along the reaction coordinate and reduced frequencies of dynamic recrossing. This hypothesis allows a prediction of the trend of enzyme isotope effects for a wide variety of substrates. Take the bad with the good: The origin of substrate preference in promiscuous enzymes was investigated by enzyme isotope labelling of the alcohol dehydrogenase from BsADH. The results show that “good” substrates induce fewer recrossing events along the antisymmetric reaction coordinate due to efficient electrostatic preorganization. In contrast, “bad” substrates cause substantial active-site reorganization, and electrostatic preorganization is suboptimal.
Datum: 19.02.2018

Accessing Tetravalent Transition-Metal Nitridophosphates through High-Pressure Metathesis

Advancing the attainable composition space of a compound class can lead to fascinating materials. The first tetravalent metal nitridophosphate, namely Hf9−xP24N52−4xO4x (x≈1.84), was prepared by high-pressure metathesis. The Group 4 nitridophosphates are now an accessible class of compounds. The high-pressure metathesis reaction using a multianvil setup yielded single crystals that were suitable for structure analysis. Magnetic properties of the compound indicate Hf in oxidation state +IV. Optical measurements show a band gap in the UV region. The presented route unlocks the new class of Group 4 nitridophosphates by significantly improving the understanding of this nitride chemistry. Hf9−xP24N52−4xO4x (x≈1.84) is a model system and its preparation is the first step towards a systematic exploration of the transition-metal nitridophosphates. Working under pressure: A tetravalent transition-metal nitridophosphate, namely Hf9−xP24N52−4xO4x (x≈1.84), was prepared by high-pressure metathesis. Its preparation highlights the systematic access to transition-metal nitridophosphates, which is potentially granted by high-pressure metathesis.
Datum: 19.02.2018

Carbon Atom Hybridization Matters: Ultrafast Humidity Response of Graphdiyne Oxides

Graphdiyne (GDY), a new kind of 2D carbon allotrope consisting of sp- and sp2-hybridized carbon atoms, has been envisaged to be promising in fundamental studies and various applications due to their unique atomic arrangement and electronic structure as well as surface chemistry. We herein for the first time find that graphdiyne oxide (GDO) exhibits an ultrafast humidity response with an unprecedented response speed (~ 7 ms), which is considered to benefit from the unique carbon hybridization of GDO that contains acetylenic bonds with stronger electron-withdrawing property than ethylenic bonds in GO. The GDO-based humidity sensor shows an ultrafast response speed, good selectivity and high sensitivity. These properties well validate the sensor to monitor the respiration rate change of human and hypoxic rats. This study not only demonstrates the unprecedented humidity-sensing capability of GDO but also provides new insight into the structure-property relationship of 2D carbon materials.
Datum: 19.02.2018

Features of protonation of the simplest weakly basic molecules, SO2, CO, N2O, CO2, and others, by solid carborane superacids

Experimental study on protonation of simple weakly basic molecules (L) by the strongest solid superacid, H(CHB11F11), showed that basicity of SO2 is high enough (during attachment to the acidic H atoms at partial pressure of 1 atm) to break the bridged H-bonds of the polymeric acid and to form a mixture of solid mono- and disolvates, LH+‧‧‧An˗ and L-H+-L. With a decrease in the basicity of L = CO (via C), N2O, and CO (via O), only proton monosolvates are formed, which approach L-H+-An species with convergence of the strengths of bridged H-bonds. The molecules with the weakest basicity, such as CO2 and weaker, when attached to the proton, cannot break the bridged H-bond of the polymeric superacid, and the interaction stops at stage of physical adsorption. It is shown here that under the conditions of acid monomerization, it is possible to protonate such weak bases as CO2, N2, and Xe.
Datum: 19.02.2018

Spotlights on our sister journals: Angew. Chem. Int. Ed. 9/2018

Datum: 19.02.2018

Frontispiece: Enantio- and Diastereoselective Cyclopropanation of 1-Alkenylboronates: Synthesis of 1-Boryl-2,3-Disubstituted Cyclopropanes

Asymmetric Cyclopropanation A. Caballero, P. Pérez et al. describe in their Communication on page 2334 ff. a method for the highly selective conversion of terminal alkynes into 2,3-disubstituted 1-borylcyclopropanes.
Datum: 19.02.2018

Graphical Abstract: Angew. Chem. Int. Ed. 9/2018

Datum: 19.02.2018

The Dewar isomer of 1,2-dihydro-1,2-azaborinines: Isolation, fragmentation, and energy storage

The photochemistry of 1,2-dihydro-1,2-azaborinine derivatives was studied under matrix isolation conditions and in solution. Photoisomerization occurs exclusively to the Dewar valence isomers upon irradiation with UV light (> 280 nm) with high quantum yield (46 %). Further photolysis with UV light (254 nm) results in the formation of cyclobutadiene and iminoborane. The thermal electrocyclic ring opening reaction of the Dewar valence isomer back to the 1,2-dihydro-1-tert-butyldimethylsilyl-2-mesityl-1,2-azaborinine has an activation barrier of 27.0 ± 1.2 kcal·mol-1. In the presence of Wilkinson's catalyst, the ring opening occurs rapidly and exothermically (H = -48 ± 1 kcal·mol-1) at room temperature.
Datum: 19.02.2018

Tailored microstructured hyperpolarizing matrices for optimal magnetic resonance imaging

Tailoring the physical features and the porous network architecture of silica-based hyperpolarizing solids containing TEMPO radicals, known as HYPSO (HYbrid Polarizing SOlids), enable unprecedented performance of dissolution Dynamic Nuclear Polarization (d-DNP). High polarization values up to P(1H) = 99 % were reached for samples impregnated with a mixture of H2O:D2O and loaded in a 6.7 T polarizer at temperatures around 1.2 K. These HYPSO materials combine the best performance of homogeneous DNP formulations with the advantages of solid polarizing matrices which provide hyperpolarized solutions free of any - potentially toxic - additives (radicals and glass-forming agents). The hyperpolarized solutions can be expelled from the porous solids, filtered and rapidly transferred either to a Nuclear Magnetic Resonance (NMR) spectrometer or to a Magnetic Resonance Imaging (MRI) system.
Datum: 19.02.2018

On the Upper Limits of Oxidation States in Chemistry

The concept of oxidation state (OS) is based on the concept of Lewis electron pairs, in which the bonding electrons are assigned to the more electronegative element. This approach is useful for keeping track of the electrons, predicting chemical trends, and guiding syntheses. Experimental and quantum-chemical results reveal a limit near +8 for the highest OS in stable neutral chemical substances under ambient conditions. OS=+9 was observed for the isolated [IrO4]+ cation in vacuum. The prediction of OS=+10 for isolated [PtO4]2+ cations is confirmed computationally for low temperatures only, but hasn't yet been experimentally verified. For high OS species, oxidation of the ligands, for example, of O−2 with formation of .O−1 and O−O bonds, and partial reduction of the metal center may be favorable, possibly leading to non-Lewis type structures. The highest oxidation state (OS) of elements in compounds is limited not only by the number and the ionization energies of their valence electrons, but also by the electronic properties of the ligands. Spontaneous oxidation of the ligand and reduction of the metal center results in strongly correlated, open-shell, multicenter bonds. A joint theoretical–experimental case study of PtO42+ isomers reveals a maximum OS near +8 for chemical substances under ambient conditions.
Datum: 19.02.2018

A Non-Heme Iron Photocatalyst for Light-Driven Aerobic Oxidation of Methanol

Non-heme (L)FeIII and (L)FeIII-O-FeIII(L) complexes (L=1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)ethan-1-amine) underwent reduction under irradiation to the FeII state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge-transfer excitation of a FeIII−μ-O−FeIII complex to generate [(L)FeIV=O]2+ (observed transiently during irradiation in acetonitrile), and an equivalent of (L)FeII. Under aerobic conditions, irradiation accelerates reoxidation from the FeII to the FeIII state with O2, thus closing the cycle of methanol oxidation to methanal. Cut out the middlecat: Non-heme (L)FeIII and (L)FeIII−O−FeIII(L) complexes were reduced under irradiation to the FeII state (see scheme) with concomitant oxidation of methanol to methanal, without a photosensitizer. Spectroscopic and DFT studies support a mechanism involving charge-transfer excitation of a FeIII−μ-O−FeIII complex to generate [(L)FeIV=O]2+ and (L)FeII. Irradiation accelerates reoxidation of FeII with O2 to close the catalytic cycle.
Datum: 19.02.2018

Palladium-Catalyzed C−H Silylation through Palladacycles Generated from Aryl Halides

A highly efficient palladium-catalyzed disilylation reaction of aryl halides through C−H activation has been developed for the first time. The reaction has broad substrate scope. A variety of aryl halides can be disilylated by three types of C−H activation, including C(sp2)−H, C(sp3)−H, and remote C−H activation. In particular, the reactions are also unusually efficient. The yields are essentially quantitative in many cases, even in the presence of less than 1 mol % catalyst and 1 equivalent of the silylating reagent under relatively mild conditions. The disilylated biphenyls can be converted into disiloxane-bridged biphenyls. Choice of three: A palladium-catalyzed disilylation reaction of aryl halides has been developed through C−H activation. The reaction has broad substrate scope and is unusually efficient. A variety of aryl halides can be disilylated by three types of C−H activation, including C(sp2)−H, C(sp3)−H, and remote C−H activation, in excellent yields. The method is scalable and features high atom economy.
Datum: 19.02.2018

From Linear to Angular Isomers: Achieving Tunable Charge Transport in Single Crystal Indolocarbazoles via Delicate Synergetic CH/NH···Pi Interactions

Four five fused-ring isomers were rationally designed and synthesized to investigate the isomeric influence of linear and angular shapes in affecting their molecular packing and resultant electronic properties. Single-crystal field-effect transistors showed mobility order of 5,7-ICZ (3.61 cm2 V-1 s-1) > 5,11-ICZ (0.55 cm2 V-1 s-1) > 5,12-ICZ (~10-5 cm2 V-1 s-1) and 11,12-ICZ (~10-6 cm2 V-1 s-1). Theoretical calculations based on density functional theory (DFT) and polaron transport model revealed that 5, 7-ICZ can reach higher mobilities than the others thanks to relatively higher hole transfer integral that links to stronger intermolecular interaction due to the presence of multiple NH···pi and CH···pi(py) interactions with energy close to common NH···N hydrogen bonds, as well as overall lower hole-vibrational coupling owing to the absence of coupling of holes to low frequency modes due to better pi conjugation.
Datum: 19.02.2018

Electrochemical Exfoliation of Pillared-layer Metal-Organic Framework for Boosting the Oxygen Evolution Reaction

Having high surface areas and fully exposed active sites, two-dimensional (2D) materials and ultrathin nanosheets are advantageous for elevating the catalysis performance and elucidating the catalysis mechanism. 2D materials are mostly restricted to inorganic or organic materials based on covalent bonds, because strong bonding within two dimensions and weak interactions in the third dimension are beneficial to stabilize the 2D structure. Here, we report an electrochemical exfoliation strategy for synthesizing metal-organic 2D materials based on coordination bonds. A catechol functionalized ligand is used as the redox active pillar to construct a pillared-layer framework. As an electrocatalyst for water oxidation, the pillar ligand can be in-situ oxidized and removed to yield ultrathin (2 nm) nanosheets, giving extraordinary catalytic activity at pH = 13 with overpotential as low as 211 mV at 10 mA cm^-2 and turnover frequency as high as 34 s^-1 at an overpotential of 300 mV.
Datum: 19.02.2018

Tracking the Dynamic Folding and Unfolding of RNA G-Quadruplexes in Live Cells

Due to the absence of methods for tracking RNA G-quadruplex dynamics, especially the folding and unfolding of this attractive structure in live cells, understanding of the biological roles of RNA G-quadruplexes is so far limited. Here we reported a new red-emitting fluorescent probe, QUMA-1, for a selective, continuous and real-time visualization of RNA G-quadruplexes in live cells. The applications of QUMA-1 in several previously intractable applications, including live-cell imaging of the dynamic folding, unfolding and movement of RNA G-quadruplexes and visualizing the unwinding of RNA G-quadruplexes by RNA helicase have been demonstrated. Notably, our real-time results revealed the complexity of the dynamics of RNA G-quadruplexes in live cells. We anticipate that the further application of QUMA-1 in combination with appropriate biological and imaging methods to explore the dynamics of RNA G-quadruplexes will uncover more information about the biological roles of RNA G-quadruplexes.
Datum: 17.02.2018

Lewis Acid Catalyzed Stereoselective Dearomative Coupling of Indolylboron Ate Complexes with D-A Cyclopropanes and Alkyl Halides

Indolylboron ate complexes readily generated from 2-lithio indoles and boronic esters undergo multicomponent dearomative coupling with D-A cyclopropanes and alkyl halides in the presence of Sc(OTf)3 as a catalyst. Reactions proceed with complete diastereoselectivity and excellent stereospecificity to provide indolines bearing three contiguous stereocenters. The valuable boronic ester moiety remains in the product and allows for subsequent functionalization.
Datum: 17.02.2018

N-Heterocyclic Carbene-Treated Gold Surfaces in Pentacene Organic Field-Effect Transistors: Improved Stability and Contact at the Interface

N-Heterocyclic carbene (NHC) molecules, which reacted with the surface of Au electrodes, have been successfully applied in the pentacene transistors. With the application of NHCs, the charge carrier mobility of pentacene transistors increased by five times, while the contact resistance at the pentacene-Au interface reduced down to 85%. Even after annealing the NHC-Au electrodes at 200 oC for two hours before pentacene deposition, the charge carrier mobility of the pentacene transistors did not decrease. The distinguished performance renders the NHCs as excellent alternatives to thiols as metal modifiers for the application in organic field-effect transistors (OFETs).
Datum: 17.02.2018

Nucleopeptide Assemblies Selectively Sequester ATP in Cells

Here we report that assemblies of nucleopeptides selectively sequestrate ATP in complex conditions (e.g., serum and cytosol). We develop assemblies of nucleopeptides that selectively sequester ATP over ADP. Counteracting enzymes interconvert ATP and ADP to modulate the nanostructures formed by the nucleopeptides and the nucleotides. The nucleopeptides, sequestering ATP effectively in cells, slow down efflux pumps in multidrug resistance cancer cells, thus boosting the efficacy of an anticancer drug. Examining additional 11 nucleopeptides (including D- and L-enantiomers) yields five more nucleopeptides that differentiate ATP and ADP via either precipitation or gelation. As the first example of using assemblies of nucleopeptides for interacting with ATP and disrupting intracellular ATP dynamics, this work illustrates the use of supramolecular assemblies to interact with small and essential biological molecules for controlling cell behaviors
Datum: 16.02.2018

One-Step Synthesis of Hybrid Core-Shell Metal-Organic Frameworks

Epitaxial growth of MOF-on-MOF composite is an evolving research topic. In current methods, the core-shell MOFs are synthesized via a stepwise strategy which involves growing the shell-MOFs on top of the preformed core-MOFs with matched lattice parameters. However, the inconvenient stepwise synthesis and the strict lattice-matching requirement have limited the development of core-shell MOFs. Herein, we demonstrate that hybrid core-shell MOFs with mismatching lattices can be synthesized under the guidance of nucleation kinetics. A series of MOF composites with mesoporous core and microporous shell were constructed and characterized by optical microscopy, powder X-ray diffraction, gas sorption measurement, and scanning electron microscopy. Isoreticular expansion of microporous shells and orthogonal modification of the core was realized to produce multifunctional MOF composites, which acted as size selective catalysts for olefin epoxidation with high activity and selectivity.
Datum: 16.02.2018

Direct Measurement of Charge Regulation in Metalloprotein Electron Transfer

Quantifying how a protein regulates its net electrostatic charge during electron transfer (ET) is a means of directly measuring factors that contribute to either redox potential and/or reorganization energy. Charge regulation by proteins during ET has never been measured because few tools exist to measure the net charge of a folded protein in solution at different oxidation states. Here, by using protein charge ladders and capillary electrophoresis, we determined that the net charge of myoglobin, cytochrome c, and azurin changed by 0.62 ± 0.06, 1.19 ± 0.02, and 0.51 ± 0.04 units upon single ET. Computational analysis predicts that these fluctuations in charge arise from changes in the pKa of multiple non-coordinating residues (predominantly histidine) and require between 0.42-0.90 eV. These results suggest that ionizable residues can tune the reactivity of redox centers via charge regulation.
Datum: 16.02.2018

Enhanced Photodynamic Therapy by Reduced Intracellular Glutathione Levels Employing Nano-MOF with Cu (II) as Active Center

In photodynamic therapy (PDT), the level of reactive oxygen species (ROS) produced in the cell directly determines therapeutic effect. Therefore, the development of photosensitizers combining the ability of reducing GSH levels through synergistically improving ROS concentration to strengthen the efficacy of PDT for tumor is important. We report a nano-metal-organic framework based on Cu (II) as active center for PDT. This MOF-2 is readily uptaken by breast cancer cells, and high-level ROS is generated under light irradiation. Meanwhile, intracellular GSH is considerably decreased owing to absorption on MOF-2, synergistically increasing ROS concentration and accelerating apoptosis, thereby enhancing the effect of PDT. Notably, through the direct adsorption of GSH, MOF-2 showed comparable effect with commercial antitumor drug camptothecin in mouse breast cancer treatment. This work provides strong evidence for MOF-2 as a promising new PDT candidate and anti-cancer drug.
Datum: 16.02.2018

Selective sp3 C-H Aerobic Oxidation enabled by Deca-tungstate Photocatalysis in Flow

A mild and selective sp3 C-H aerobic oxidation enabled by deca-tungstate photocatalysis has been developed. The reaction can be significantly improved in a microflow reactor enabling the safe use of oxygen and the enhanced irradiation of the reaction mixture. Our method allows for the oxidation of both activated and unactivated C-H bonds (30 examples). The ability to selectively oxidize natural scaffolds, such as (-)-ambroxide, pregnenolone acetate, (+)-sclareolide and artemisinin exemplifies the utility of this new method.
Datum: 16.02.2018

ADUC Prizes: U.-P. Apfel, P. Heretsch, O. Hollóczki / Carl Duisberg Memorial Award: B. Morandi / Elected to the Académie des Sciences: E. Charpentier, J. Cossy, I. Marek / Max Delbrück Junior Prize: S. Disch / Novartis Early Career Award: B. Morandi and R. R. Knowles

Datum: 16.02.2018

The Enantioselective Total Synthesis of Bisquinolizidine Alkaloids: A Modular “Inside-Out” Approach

Bisquinolizidine alkaloids are characterized by a chiral bispidine core (3,7-diazabicyclo[3.3.1]nonane) to which combinations of an α,N-fused 2-pyridone, an endo- or exo-α,N-annulated piperidin(on)e, and an exo-allyl substituent are attached. We developed a modular “inside-out” approach that permits access to most members of this class. Its applicability was proven in the asymmetric synthesis of 21 natural bisquinolizidine alkaloids, among them more than ten first enantioselective total syntheses. Key steps are the first successful preparation of both enantiomers of C2-symmetric 2,6-dioxobispidine by desymmetrization of a 2,4,6,8-tetraoxo precursor, the construction of the α,N-fused 2-pyridone by using an enamine-bromoacrylic acid strategy, and the installation of endo- or, optionally, exo-annulated piperidin(on)es. All in one sweep: A diversity-driven, modular “inside-out” approach to natural bisquinolizidine alkaloids was developed. Its versatility was confirmed in the enantioselective total synthesis of 21 alkaloids of this class. Key steps are a desymmetrization, permitting access to C2-symmetric 2,6-dioxobispidine in both enantiomeric forms, and the annulation of 2-pyridone and endo- or exo-fused piperidines to this chiral core building block.
Datum: 12.02.2018

Carbohydrate-Responsive Surface Adhesion Based on the Dynamic Covalent Chemistry of Phenylboronic Acid- and Catechol-Containing Polymer Brushes

A glue, based on dynamic covalent chemistry, with a strong adhesion (2.38 kg cm−2), water resistance and carbohydrate responsive reversibility is presented. Using surface initiated atom transfer radical polymerization (SI-ATRP), glass and silicon surfaces were coated with copolymers functionalized with phenylboronic acids and catechols. In combination with microcontact printing (μCP) these polymer brushes give access to a carbohydrate responsive “supramolecular Velcro”. Glue and release: A supramolecular glue is prepared through the combination of atom-transfer radical polymerization and the dynamic covalent chemistry of phenyl boronic acids and catechols. The glue shows strong adhesion (2.38 kg cm−2), is water resistant, can be reused multiple times, and releases in the presence of a carbohydrate.
Datum: 09.02.2018

Disilenyl Silylene Reactivity of a Cyclotrisilene

The highly reactive silicon congeners of cyclopropene, cyclotrisilenes (c-Si3R4), typically undergo either π-addition to the Si=Si double bond or σ-insertion into the Si−Si single bond. In contrast, treatment of c-Si3Tip4 (Tip=2,4,6-iPr3C6H2) with styrene and benzil results in ring opening of the three-membered ring to formally yield the [1+2]- and [1+4] cycloaddition product of the isomeric disilenyl silylene to the C=C bond and the 1,2-diketone π system, respectively. At elevated temperature, styrene is released from the [1+2]-addition product leading to the thermodynamically favored housane species after [2+2] cycloaddition of styrene and c-Si3Tip4. Speed is of the essence to ring-open the peraryl-substituted cyclotrisilene (R=2,4,6-iPr3C6H2) and coax disilenyl silylene reactivity towards benzil and styrene from it. In the case of styrene, the kinetic product with a residual R2Si=SiR substituent is transformed into the saturated thermodynamic product by the re-detachment of the styrene reagent at elevated temperature, as confirmed by a control experiment under vacuum.
Datum: 08.02.2018

Highly Fluorescent Chiral N-S-Doped Carbon Dots from Cysteine: Affecting Cellular Energy Metabolism

Cysteine-based chiral optically active carbon dots (CDs) and their effects on cellular energy metabolism, which is vital for essential cellular functions, have been barely reported. A green and effective synthesis strategy for chiral N-S-doped CDs (fluorescence quantum yield ca. 41.26 %) based on hydrothermal treatment of l- or d-cysteine at as low as 60 °C has been developed. This suggested that cysteine was instable in aqueous solutions and acts as a warning for high-temperature synthesis of nanomaterials using cysteine as stabilizer. Human bladder cancer T24 cells treated with l-CDs showed up-regulated glycolysis, while d-CDs had no similar effects. In contrast, no disturbance to the basal mitochondrial aerobic respiration of T24 cells was caused by either chiral CD. A green and effective synthesis has been developed for chiral CDs (fluorescence quantum yield ca. 41.26 %) based on hydrothermal treatment of small-molecule l- or d-cysteine at temperatures as low as 60 °C. The l-CDs showed chirality-dependent enhancement in cellular glycolysis, but did not influence the cellular ATP levels of T24 cells.
Datum: 08.02.2018

The Ideal Ionic Liquid Salt Bridge for Direct Determination of Gibbs Energies of Transfer of Single Ions, Part II: Evaluation of the Role of Ion Solvation and Ion Mobilities

An important intermediate goal to evaluate our concept for the assumption-free determination of single-ion Gibbs transfer energies ΔtrG°(i, S1S2) is presented. We executed the crucial steps a) and b) of the methodology, described in Part I of this treatise, exemplarily for Ag+ and Cl- with S1 being water and S2 being acetonitrile. The experiments showed that virtually all parts of the liquid junction potentials (LJPs) at both ends of a salt bridge cancel, if the bridge electrolyte is an “ideal” ionic liquid, that is, one with nearly identical diffusion of anion and cation. This ideality holds for [N2225]+[NTf2]- in the pure IL, but also in water and acetonitrile solution. Electromotive force measurements of solvation cells between S1 and S2 demonstrated Nernstian behavior for Ag+ concentration cells and constant like cell potentials for solutions with five tested Ag+ counterions. It′s ideal: A step towards measuring single-ion Gibbs transfer energies without extra-thermodynamic assumptions is described. In elementary open-circuit potential experiments utilizing an ideal ionic liquid salt bridge, virtually all parts of the liquid junction potential between different solvents could be circumvented for Ag+-based systems because of the nearly identical diffusion of [N2225]+ and [NTf2]− within the salt bridge and in the medium.
Datum: 07.02.2018

Design of Metal-Free Polymer Carbon Dots: A New Class of Room-Temperature Phosphorescent Materials

Polymer carbon dots (PCDs) are proposed as a new class of room-temperature phosphorescence (RTP) materials. The abundant energy levels in PCDs increase the probability of intersystem crossing (ISC) and their covalently crosslinked framework structures greatly suppress the nonradiative transitions. The efficient methods allow the manufacture of PCDs with unique RTP properties in air without additional metal complexation or complicated matrix composition. They thus provide a route towards the rational design of metal-free RTP materials that may be synthesized easily. Furthermore, we find that RTP is associated with a crosslink-enhanced emission (CEE) effect, which provides further routes to design improved PCDs with diverse RTP performance. Our results show the potential of PCDs as a universal route to achieve effective metal-free RTP. Room-temperature phosphorescence: Polymer carbon dots (PCDs) showing metal-free room-temperature phosphorescence (RTP) have been constructed by using a facile method. The contribution of the cross-link-enhanced emission effect to the generation of RTP is verified and proposed as a guideline to forecast and synthesize a series of PCDs with diverse RTP performance (ISC=intersystem crossing).
Datum: 06.02.2018

Discovery and Enumeration of Organic-Chemical and Biomimetic Reaction Cycles within the Network of Chemistry

Analysis of the chemical-organic knowledge represented as a giant network reveals that it contains millions of reaction sequences closing into cycles. Without realizing it, independent chemists working at different times have jointly created examples of cyclic sequences that allow for the recovery of useful reagents and for the autoamplification of synthetically important molecules, those that mimic biological cycles, and those that can be operated one-pot. NOC-ing on heaven′s door: Big-data analysis of the network of organic chemistry (NOC) reveals that, over many decades, chemists have created—unknowingly—millions of cyclic reaction sequences including those that recover valuable substrates, those that amplify useful chemicals, or those that mimic biological cycles. The image shows a special type of a cycle (the so-called clique) in which any member can be made from any other one in one step. Colors correspond to years in which a reaction was first reported.
Datum: 06.02.2018

Palladium-Catalyzed Asymmetric Aminohydroxylation of 1,3-Dienes

A PdII-catalyzed asymmetric aminohydroxylation of 1,3-dienes with N-tosyl-2-aminophenols was developed by making use of a chiral pyridinebis(oxazoline) ligand. The highly regioselective reaction provides direct and efficient access to chiral 3,4-dihydro-2H-1,4-benzoxazines in high yield and enantioselectivity (up to 96:4 e.r.). The reaction employs readily available N-tosyl-2-aminophenols as a unique aminohydroxylation reagent and is complementary to known asymmetric aminohydroxylation methods. Give me a ring: A palladium-catalyzed asymmetric aminohydroxylation reaction of 1,3-dienes with N-tosyl-2-aminophenols was developed by employing a chiral pyridinebis(oxazoline) ligand. This reaction furnishes optically active 3,4-dihydro-2H-1,4-benzoxazines in high yields and with high levels of regio- and stereoselectivity.
Datum: 06.02.2018

Active Molybdenum-Based Anode for Dehydrogenative Coupling Reactions

A new and powerful active anode system that can be operated in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) has been discovered. In HFIP the molybdenum anode forms a compact, conductive, and electroactive layer of higher-valent molybdenum species. This system can replace powerful but stoichiometrically required MoV reagents for the dehydrogenative coupling of aryls. This electrolytic reaction is more sustainable and allows the conversion of a broad scope of activated arenes. Electrochemically driven and with a reactivity comparable to that of MoV reagents, a novel active anode system based on 1,1,1,3,3,3-hexafluoro-2-propanol and molybdenum mediates the dehydrogenative coupling of arenes.
Datum: 05.02.2018

Orientation Control of Molecularly Functionalized Surfaces Applied to the Simultaneous Alignment and Sorting of Carbon Nanotubes

Self-assembly has been relied upon for molecular alignment in many advanced technological applications. However, although effective, it is inherently limited in its capability for optimization. Despite the potential benefits, the seemingly fundamental strategy of external orientation control has yet to be realized. Herein we demonstrate an approach that allows control of the orientation of small molecules covalently bound to a surface. The method exploits an alignment relay technique, passing alignment information through a liquid-crystal medium to small molecules to control surface functionalization events. The method is technically simple and can be carried out on a bench top without the need for specialized equipment. Moreover, we demonstrate the utility of the resulting surfaces to address two long-standing problems in nanoscience: the sorting and alignment of single-walled carbon nanotubes. This new method enabled significant alignment of the nanotubes as well as length and diameter sorting. The ART of science: An alignment relay technique (ART) has been developed for the alignment of organic molecules covalently bound to a surface. The resulting functionalized surface was used to promote the simultaneous alignment and length and diameter sorting of single-walled carbon nanotubes (see picture).
Datum: 05.02.2018

Fe2Si5N8: Access to Open-Shell Transition-Metal Nitridosilicates

Highly condensed nitridosilicates doped with Eu2+ or Ce3+ play an important role in saving energy by converting the blue light of (In,Ga)N-LEDs. Although nitridosilicates are known for great structural variety based on covalent anionic Si-N networks, elemental variety is restricted. Presenting a significant extension of the latter, this work describes a general access to open-shell transition-metal nitridosilicates. As a proof-of-principle, the first iron nitridosilicate, namely Fe2Si5N8, was prepared by exchanging Ca2+ in α-Ca2Si5N8 applying a FeCl2 melt (salt metathesis). The title compound was analyzed by powder X-ray diffraction, EDX, ICP-OES, combustion analysis, TG/DSC, Mössbauer spectroscopy and magnetic susceptibility measurements. Furthermore, the structure of α-Ca2Si5N8 was determined at 1073 and 1173 K confirming the anionic network of α-Ca2Si5N8 providing possible migration pathways for the ion-exchange reaction. Cation exchange is possible in nitridosilicates by applying salt melts. Application of this strategy led to the first iron nitridosilicate Fe2Si5N8, which represents a significant extension in elemental variety for nitridosilicates. Motivated by experimental results, the mechanism of the ion exchange was elucidated by identifying possible migration channels for divalent cations in α-Ca2Si5N8.
Datum: 05.02.2018

Manipulating Band Structure through Reconstruction of Binary Metal Sulfide for High-Performance Thermoelectrics in Solution-Synthesized Nanostructured Bi13S18I2

Reconstructing canonical binary compounds by inserting a third agent can significantly modify their electronic and phonon structures. Therefore, it has inspired the semiconductor communities in various fields. Introducing this paradigm will potentially revolutionize thermoelectrics as well. Using a solution synthesis, Bi2S3 was rebuilt by adding disordered Bi and weakly bonded I. These new structural motifs and the altered crystal symmetry induce prominent changes in electrical and thermal transport, resulting in a great enhancement of the figure of merit. The as-obtained nanostructured Bi13S18I2 is the first non-toxic, cost-efficient, and solution-processable n-type material with z T=1.0. Bi2S3 was rebuilt by adding disordered Bi and weakly bonded I in a solution synthesis. The new structural motifs and the altered crystal symmetry induce prominent changes in electrical and thermal transport. The as-obtained nanostructured Bi13S18I2 is a non-toxic, cost-efficient, and solution-processable n-type thermoelectric material with z T=1.0.
Datum: 05.02.2018

Mechanochemical Activation of Iron Cyano Complexes: A Prebiotic Impact Scenario for the Synthesis of α-Amino Acid Derivatives

Mechanochemical activation of iron cyano complexes by ball milling results in the formation of HCN, which can be trapped and incorporated into α-aminonitriles. This prebiotic impact scenario can be extended by mechanochemically transforming the resulting α-aminonitriles into α-amino amides using a chemical route related to early Earth conditions. Prebiotic-impact chemistry: Mechanochemistry enabled the study of a prebiotic impact scenario for the formation α-amino acid derivatives under ball milling conditions. Ball milling iron cyano complexes results in the formation of HCN, which can be trapped and incorporated into α-aminonitriles.
Datum: 05.02.2018

Cover Picture: The Enantioselective Total Synthesis of Bisquinolizidine Alkaloids: A Modular “Inside-Out” Approach (Angew. Chem. Int. Ed. 9/2018)

A modular “inside-out” approach to 21 natural bisquinolizidine alkaloids, among them more than ten first enantioselective total syntheses, is reported by M. Breuning et al. in their Communication on page 2432 ff. Key was the successful preparation of both enantiomers of C2-symmetric 2,6-dioxobispidine by desymmetrization and the successive α,N-annulation of a 2-pyridone and endo- or exo-fused piperidines to the chiral core building block.
Datum: 05.02.2018

The Ideal Ionic Liquid Salt Bridge for the Direct Determination of Gibbs Energies of Transfer of Single Ions, Part I: The Concept

Described is a procedure for the thermodynamically rigorous, experimental determination of the Gibbs energy of transfer of single ions between solvents. The method is based on potential difference measurements between two electrochemical half cells with different solvents connected by an ideal ionic liquid salt bridge (ILSB). Discussed are the specific requirements for the IL with regard to the procedure, thus ensuring that the liquid junction potentials (LJP) at both ends of the ILSB are mostly canceled. The remaining parts of the LJPs can be determined by separate electromotive force measurements. No extra-thermodynamic assumptions are necessary for this procedure. The accuracy of the measurements depends, amongst others, on the ideality of the IL used, as shown in our companion paper Part II. Extra-free! Can single-ion Gibbs transfer energies be determined without extra-thermodynamic assumptions? So far, the answer to this question has been no. A procedure based on straightforward potentiometric measurements is presented, thus making the answer a yes. Experimental proof for this claim is presented in the following Communication.
Datum: 05.02.2018

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 the development of efficient and stable electrolyzers, since even for the most promising Ir based anodes the harsh reaction conditions are detrimental. The dissolution mechanism is complex and the correlation to the oxygen evolution reaction itself is still poorly understood. Here, by coupling a scanning flow cell with inductively coupled plasma and online electrochemical mass spectrometers, we monitor the oxygen evolution and degradation products of Ir and Ir oxides in situ. It is shown that at high anodic potentials several dissolution routes become possible, including formation of gaseous IrO3. On the basis of experimental data, possible pathways are proposed for the oxygen-evolution-triggered dissolution of Ir and the role of common intermediates for these reactions is discussed. Possible routes of Ir dissolution are proposed based on the detection of a common intermediate in the oxygen evolution reaction. At least three dissolution pathways are possible depending on the nature of the electrode and potential. At high current densities two reactions proceed via formation of volatile IrO3. Hindering IrO3 hydrolysis can be a strategy to improve electrode stability in the oxygen evolution reaction.
Datum: 05.02.2018

MoP Nanoparticles Supported on Indium-Doped Porous Carbon: Outstanding Catalysts for Highly Efficient CO2 Electroreduction

Electrochemical reduction of CO2 into value-added product is an interesting area. MoP nanoparticles supported on porous carbon were synthesized using metal–organic frameworks as the carbon precursor, and initial work on CO2 electroreduction using the MoP-based catalyst were carried out. It was discovered that MoP nanoparticles supported on In-doped porous carbon had outstanding performance for CO2 reduction to formic acid. The Faradaic efficiency and current density could reach 96.5 % and 43.8 mA cm−2, respectively, when using ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate as the supporting electrolyte. The current density is higher than those reported up to date with very high Faradaic efficiency. The MoP nanoparticles and the doped In2O3 cooperated very well in catalyzing the CO2 electroreduction. MoP nanoparticles supported on In-doped porous carbon show outstanding performance for CO2 reduction to formate. The Faradaic efficiency and current density reach 96.5 % and 43.8 mA cm−2, respectively, when using an ionic liquid as the supporting electrolyte. MoP and In-doped carbon support show an excellent synergistic effect for promoting this reaction.
Datum: 02.02.2018

Seeded Polymerization through the Interplay of Folding and Aggregation of an Amino-Acid-based Diamide

Amino acid based diamides are widely used as a substructure in supramolecular polymers and are also key components of polypeptides that help to understand protein folding. The interplay of folding and aggregation of a diamide was used to achieve seed-initiated supramolecular polymerization. For that purpose, a pyrene-substituted diamide was synthesized in which pyrene is used as a tracer to monitor the supramolecular polymerization. Thermodynamics and time-dependent studies revealed that the folding of the diamide moiety, via the formation of intramolecular hydrogen bonds, effectively prevents a spontaneous nucleation that leads to supramolecular polymerization. Under such out-of-equilibrium conditions, the addition of seeds successfully initiates the supramolecular polymerization. These results demonstrate the utility of such amino acid based diamides in programmable supramolecular polymerizations. Seeded polymerization: The hydrogen-bond-directed folding of a diamide group effectively prevents the spontaneous nucleation in the supramolecular polymerization of extended diamides. The seeded polymerization of pyrene, as an example of luminescent π-conjugated systems, was accomplished under out-of-equilibrium conditions in these coupled equilibria.
Datum: 02.02.2018

Keiji Morokuma (1934–2017)

Keiji Morokuma, William Henry Emerson Professor Emeritus of Emory University and Research Leader at the Fukui Institute for Fundamental Chemistry, Kyoto University, passed away at the age of 83 on November 27, 2017. Morokuma made numerous contributions to theoretical methodologies for the determination of reaction mechanisms and the understanding of intermolecular interactions.
Datum: 02.02.2018

Back Cover: Seeded Polymerization through the Interplay of Folding and Aggregation of an Amino-Acid-based Diamide (Angew. Chem. Int. Ed. 9/2018)

The utility of an amino acid based diamide in seeded supramolecular polymerization is demonstrated by S. Ogi, K. Matsumoto, and S. Yamaguchi in their Communication on page 2339 ff. The spontaneous aggregation (right pathway) of diamides in an extended form is effectively retarded by folding of the diamide moiety through intramolecular hydrogen bonding. Under such out-of-equilibrium conditions, the time course of the self-assembly was successfully regulated through a seeding approach (left pathway).
Datum: 02.02.2018

Inside Cover: Dual Ligand-Enabled Nondirected C−H Olefination of Arenes (Angew. Chem. Int. Ed. 9/2018)

How many ligands does it take to change a bond? The oxidative C−H arylation of olefins (the Fujiwara–Moritani reaction) has been plagued by low efficiency and the need for excess amounts of valuable arene starting materials. In their Communication on page 2497, M. van Gemmeren and co-workers report a dual ligand strategy for optimizing the palladium catalyst for this reaction.
Datum: 02.02.2018

Inside Back Cover: Cationic Metallo-Polyelectrolytes for Robust Alkaline Anion-Exchange Membranes (Angew. Chem. Int. Ed. 9/2018)

Cationic polyelectrolytes are widely used as anion-exchange membranes (AEMs) in alkaline fuel cells for converting fuels into electricity. In their Communication on page 2388 ff., C. Tang et al. report a class of metallo-polyelectrolytes that are conceptualized for chemically inert AEMs under highly basic conditions. The AEMs exhibit excellent thermal, chemical, and mechanical stability, as well as high ion conductivity.
Datum: 31.01.2018

RuBisCO-Inspired CO2 Activation and Transformation by an Iridium(I) Complex

The synthesis of a new iridium(I) complex containing an enamido phosphine anion (dbuP−) and its unique reactivity with CO2 is reported. The complex binds two equivalents of CO2 and initiates a highly selective reaction cascade. The reaction leads to the reversible cleavage of CO2 and the enamido ligand as well. Computational analysis points to the existence of a relatively stable Ir-CO2 complex as a reaction intermediate prior to CO2 cleavage, which was confirmed experimentally. The observed transformation resembles several aspects of enzymatic CO2 fixation by RuBisCO. COO-peration: The highly selective binding and transformation of CO2 by an iridium complex clearly shows cooperative effects between the two CO2 molecules involved. The reversible transformation resembles some aspects of CO2 fixation by the RuBisCO enzyme.
Datum: 29.01.2018

Hot Water Generates Crystalline Organic Materials

In hot water: Hydrothermal crystallization was recently used to transform amporphous polymer networks into amide-linked, stable covalent–organic frameworks. This work is highlighted in the context of the synthesis and especially crystallization of organic materials by using high-temperature water.
Datum: 29.01.2018

Increasing Catalyst Efficiency in C−H Activation Catalysis

C−H activation reactions with high catalyst turnover numbers are still very rare in the literature and 10 mol % is a common catalyst loading in this field. We offer a representative overview of efficient C−H activation catalysis to highlight this neglected aspect of catalysis development and inspire future effort towards more efficient C−H activation. Examples ranging from palladium catalysis, Cp*RhIII- and Cp*CoIII-catalysis, the C−H borylation and silylation to methane C−H activation are presented. In these reactions, up to tens of thousands of catalyst turnovers have been observed. Go, catalyst, go! C−H activation reactions with high catalyst turnover numbers are still very rare in the literature and 10 mol % is a common catalyst loading in this field. A representative overview of efficient C−H activation catalysis is presented here to highlight this neglected aspect of catalysis development and inspire future effort towards more efficient C−H activation.
Datum: 29.01.2018

Direct Transformation of Esters into Heterocyclic Fluorophores

Despite the manifold use of heterocyclic fluorophores, only a fraction of the desired dye diversity can be accessed by contemporary synthetic approaches. Herein, we describe a modular method that converts various carboxylic acid esters directly into a broad spectrum of heteroanthrylium fluorophores. The double addition of heteroatom-bridged 1,5-bifunctional organomagnesium reagents to esters leads to the formation of acridinium, xanthylium, and SiR fluorophores after dehydrative acidic work-up. This one-step synthetic method provides access to organophotoredox catalysts for dual catalysis with nickel and dyes amenable to fluorescence enhancement. The spectrum of esters: Heteroatom-bridged 1,5-bifunctional organomagnesium reagents enable the direct transformation of carboxylic acid esters into acridinium, xanthylium, and SiR dyes. Owing to the high diversity of esters, the chemical, photophysical, and electrochemical properties of the fluorophores can be ideally modulated to provide organophotoredox catalysts for dual catalysis with nickel and dyes amenable to fluorescence enhancement.
Datum: 29.01.2018

Dual Ligand-Enabled Nondirected C−H Olefination of Arenes

The application of the Pd-catalyzed oxidative C−H olefination of arenes, also known as the Fujiwara–Moritani reaction, has traditionally been limited by the requirement for directing groups on the substrate or the need to use the arene in large excess, typically as a (co)solvent. Herein the development of a catalytic system is described that, through the combined action of two complementary ligands, makes it possible to use directing-group-free arenes as limiting reagents for the first time. The reactions proceed under a combination of both steric and electronic control and enable the application of this powerful reaction to valuable arenes, which cannot be utilized in excess. How many ligands does it take to change a bond? The Pd-catalyzed C−H olefination of arenes as the limiting reagents is reported. The combined action of two ligands, N-acetylglycine and a pyridine, enables this Fujiwara–Moritani reaction under steric/electronic control; traditionally this reaction required use of arenes as (co)solvents or of directing groups on the substrate.
Datum: 26.01.2018

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 that is catalyzed by a silylium imidodiphosphorimidate (IDPi) Lewis acid. A reaction half-life of over 35 million years without catalysis: Cinnamate esters belong to the least electrophilic Michael acceptors and react extremely slowly even with strong nucleophiles such as silyl ketene acetals if no catalysis is applied. Extremely active silylium imidodiphosphorimidate (IDPi) Lewis acid catalysts now enable highly efficient Mukaiyama–Michael reactions at low catalyst loadings and with excellent enantio- and diastereocontrol.
Datum: 26.01.2018

Nanobodies: Chemical Functionalization Strategies and Intracellular Applications

Nanobodies can be seen as next-generation tools for the recognition and modulation of antigens that are inaccessible to conventional antibodies. Due to their compact structure and high stability, nanobodies see frequent usage in basic research, and their chemical functionalization opens the way towards promising diagnostic and therapeutic applications. In this Review, central aspects of nanobody functionalization are presented, together with selected applications. While early conjugation strategies relied on the random modification of natural amino acids, more recent studies have focused on the site-specific attachment of functional moieties. Such techniques include chemoenzymatic approaches, expressed protein ligation, and amber suppression in combination with bioorthogonal modification strategies. Recent applications range from sophisticated imaging and mass spectrometry to the delivery of nanobodies into living cells for the visualization and manipulation of intracellular antigens. Nano-bodybuilding: Small antigen-recognizing proteins such as nanobodies are powerful tools in the life sciences. By taking advantage of chemical functionalization strategies, they can be used to visualize and manipulate intracellular targets.
Datum: 26.01.2018

Optical Control of a Biological Reaction–Diffusion System

Patterns formed by reaction and diffusion are the foundation for many phenomena in biology. However, the experimental study of reaction–diffusion (R–D) systems has so far been dominated by chemical oscillators, for which many tools are available. In this work, we developed a photoswitch for the Min system of Escherichia coli, a versatile biological in vitro R–D system consisting of the antagonistic proteins MinD and MinE. A MinE-derived peptide of 19 amino acids was covalently modified with a photoisomerizable crosslinker based on azobenzene to externally control peptide-mediated depletion of MinD from the membrane. In addition to providing an on–off switch for pattern formation, we achieve frequency-locked resonance with a precise 2D spatial memory, thus allowing new insights into Min protein action on the membrane. Taken together, we provide a tool to study phenomena in pattern formation using biological agents. Leading light: Optical control over the Min system, a biological reaction–diffusion system found in many bacteria, was achieved in vitro with the help of an azobenzene-cross-linked peptide derived from MinE. This system opens up new ways to study pattern formation in biology.
Datum: 26.01.2018

Rapid Capture and Release of Nucleic Acids through a Reversible Photo-Cycloaddition Reaction in a Psoralen-Functionalized Hydrogel

Reversible immobilization of DNA and RNA is of great interest to researchers who seek to manipulate DNA or RNA in applications such as microarrays, DNA hydrogels, and gene therapeutics. However, there is no existing system that can rapidly capture and release intact nucleic acids. To meet this unmet need, we developed a functional hydrogel for rapid DNA/RNA capture and release based on the reversible photo-cycloaddition of psoralen and pyrimidines. The functional hydrogel can be easily fabricated through copolymerization of acrylamide with the synthesized allylated psoralen. The psoralen-functionalized hydrogel exhibits effective capture and release of nucleic acids spanning a wide range of lengths in a rapid fashion; over 90 % of the capture process is completed within 1 min, and circa 100 % of the release process is completed within 2 min. We observe no deleterious effects on the hybridization to the captured targets. Reversible capture scaffold for DNA and RNA: A polyacrylamide gel can be modified through copolymerization of acrylamide with allylated psoralen to form an efficient DNA/RNA capture scaffold. Reversible photo-cycloaddition of psoralen and pyrimidine allows DNA/RNA capture in 1 min and release in 2 min under UV irradiation. The capture and release applies to a wide range of DNA/RNA target lengths and is compatible with hybridization.
Datum: 24.01.2018

Controlling the Polymer Microstructure in Anionic Polymerization by Compartmentalization

An ideal random anionic copolymerization is forced to produce gradient structures by physical separation of two monomers in emulsion compartments. One monomer (M) is preferably soluble in the droplets, while the other one (D) prefers the continuous phase of a DMSO-in-cyclohexane emulsion. The living anionic copolymerization of two activated aziridines is thus confined to the DMSO compartments as polymerization occurs selectively in the droplets. Dilution of the continuous phase adjusts the local concentration of monomer D in the droplets and thus the gradient of the resulting copolymer. The copolymerizations in emulsion are monitored by real-time 1H NMR kinetics, proving a change of the reactivity ratios of the two monomers upon dilution of the continuous phase from ideal random to adjustable gradients by simple dilution. The selective solubility of two monomers in a DMSO/cyclohexane emulsion forces the production of controllable gradient copolymers.
Datum: 18.01.2018

Reductive Amination by Photoredox Catalysis and Polarity-Matched Hydrogen Atom Transfer

The excitation of a RuII photosensitizer in the presence of ascorbic acid leads to the reduction of iminium ions to electron-rich α-aminoalkyl radical intermediates, which are rapidly converted into reductive amination products by thiol-mediated hydrogen atom transfer (HAT). As a result, the reductive amination of carbonyl compounds with amines by photoredox catalysis proceeds in good to excellent yields and with broad substrate scope and good functional group tolerance. The three key features of this work are 1) the rapid interception of electron-rich α-aminoalkyl radical intermediates by polarity-matched HAT in a photoredox reaction, 2) the method of reductive amination by photoredox catalysis itself, and 3) the application of this new method for temporally and spatially controlled reactions on a solid support, as demonstrated by the attachment of a fluorescent dye on an activated cellulose support by photoredox-catalyzed reductive amination. Light instead of hydride: A photoredox process for reductive amination is reported, alongside substrate scope studies and in-depth mechanistic investigations. With this new method, reductive amination reactions can be conducted in a temporally and spatially controlled fashion, for example, on solid supports.
Datum: 18.01.2018

Electrochemical C−H/N−H Activation by Water-Tolerant Cobalt Catalysis at Room Temperature

Electrochemistry enabled C−H/N−H functionalizations at room temperature by external oxidant-free cobalt catalysis. Thus, the sustainable cobalt electrocatalysis manifold proceeds with excellent levels of chemoselectivity and positional selectivity, and with ample scope, thus allowing electrochemical C−H activation under exceedingly mild reaction conditions at room temperature in water. Electro Co: Cobalt-catalyzed C−H/N−H functionalizations were accomplished in H2O at 23 °C without toxic metal oxidants by using electricity. This sustainable cobalt electrocatalysis manifold proceeds with excellent levels of chemoselectivity and positional selectivity, and with ample scope.
Datum: 17.01.2018

Lanthanide Complexes Supported by a Trizinc Crown Ether as Catalysts for Alternating Copolymerization of Epoxide and CO2: Telomerization Controlled by Carboxylate Anions

A new family of heterometallic catalysts based on trimetalated macrocyclic tris(salen) ligands and rare-earth metals was prepared and structurally characterized. The LaZn3 system containing anionic ligands such as acetate plays a critical role in catalyzing the alternating copolymerization of cyclohexene oxide (CHO) and CO2 with a high proportion of carbonate linkages. Among the lanthanide metals, the CeZn3 system exhibits high catalytic activity with a turnover frequency (TOF) of over 370 h−1. NMR analysis of the complex and end-group analysis of the polymer suggest that the acetate ligands are rapidly exchanged, not only among coordinated acetates, but also between coordinated acetates and added carboxylate anions. These unique properties make this the first example of telomerization for the copolymerization of CHO and CO2. Homogeneous heterometallic complexes based on the trizincated macrocycle trisaloph and a rare-earth metal showed high catalytic activity for the alternating copolymerization of cyclohexene oxide and CO2 with a high proportion of carbonate repeat units. The carboxylate anion of the ammonium salt initiates the telomerization, providing the polycarbonate with the corresponding carboxylate.
Datum: 17.01.2018

Photocatalytic Aerobic Phosphatation of Alkenes

A catalytic regime for the direct phosphatation of simple, non-polarized alkenes has been devised that is based on using ordinary, non-activated phosphoric acid diesters as the phosphate source and O2 as the terminal oxidant. The title method enables the direct and highly economic construction of a diverse range of allylic phosphate esters. From a conceptual viewpoint, the aerobic phosphatation is entirely complementary to traditional methods for phosphate ester formation, which predominantly rely on the use of prefunctionalized or preactivated reactants, such as alcohols and phosphoryl halides. The title transformation is enabled by the interplay of a photoredox and a selenium π-acid catalyst and involves a sequence of single-electron-transfer processes. Once in a blue moon: The aerobic dehydrogenative coupling of simple hydrogen phosphates with non-activated alkenes generates a diverse range of allylic phosphates through the catalytic interplay of a photosensitizer (PS) and a chalcogen Lewis acid (Se). In addition to its operational simplicity and high chemoselectivity, the title reaction also enables the facile consecutive redox alkylation of olefins with organocuprates.
Datum: 17.01.2018

Enzymatic Electrosynthesis of Alkanes by Bioelectrocatalytic Decarbonylation of Fatty Aldehydes

An enzymatic electrosynthesis system was created by combining an aldehyde deformylating oxygenase (ADO) from cyanobacteria that catalyzes the decarbonylation of fatty aldehydes to alkanes and formic acid with an electrochemical interface. This system is able to produce a range of alkanes (octane to propane) from aldehydes and alcohols. The combination of this bioelectrochemical system with a hydrogenase bioanode yields a H2/heptanal enzymatic fuel cell (EFC) able to simultaneously generate electrical energy with a maximum current density of 25 μA cm−2 at 0.6 V and produce hexane with a faradaic efficiency of 24 %. The combination of an aldehyde deformylating oxygenase that catalyzes the decarbonylation of fatty aldehydes to alkanes and formic acid with an electrochemical interface yields an enzymatic electrosynthesis system that produces various alkanes from aldehydes and alcohols. Combining this bioelectrochemical system with a hydrogenase bioanode yields a H2/heptanal enzymatic fuel cell that generates electrical energy while producing hexane.
Datum: 16.01.2018

Synthesis and Structure Revision of Dichrocephones A and B

Herein, we report the first enantioselective synthesis of dichrocephones A and B, which are cytotoxic triquinane sesquiterpenes with a dense array of stereogenic centers within a strained polycyclic environment. Key features include the application of a catalytic asymmetric Wittig reaction, followed by stereoselective functionalization of the propellane core into a pentacyclic intermediate. Double reductive ring cleavage yielded the proposed structure of dichrocephone A. Mismatched spectroscopic data for our synthetic material compared to the natural isolate led us to revise the previously proposed configuration based on biosynthetic considerations and NMR calculations. Implementation of these findings culminated in the synthesis of dichrocephones A and B. Cyclize and revise: Total synthesis of the densely functionalized dichrocephones A and B is described. Key features include a catalytic asymmetric Wittig reaction, followed by stereoselective functionalization of the propellane core into a pentacyclic intermediate. Mismatched spectroscopic data for the initial synthetic product compared to the natural isolate led to a revision of the previously proposed configuration.
Datum: 16.01.2018

Synthesis of α-Chiral Ketones and Chiral Alkanes Using Radical Polar Crossover Reactions of Vinyl Boron Ate Complexes

Vinyl boron ate complexes of enantioenriched secondary alkyl pinacolboronic esters undergo stereospecific radical-induced 1,2-migration in radical polar crossover reactions. In this three-component process various commercially available alkyl iodides act as radical precursors and light is used for chain initiation. Subsequent oxidation and protodeborylation leads to valuable α-chiral ketones and chiral alkanes, respectively, with excellent enantiopurity. Radical and polar! Various chiral vinyl boron ate complexes, readily generated from the corresponding pinacolboronic esters and vinyllithium, react in a radical polar crossover cascade to produce secondary alkyl boronic esters that are either oxidized to valuable α-chiral ketones or protodeborylated to the corresponding alkanes. Products are isolated in good overall yields and excellent stereospecificity. Pin=pinacolate.
Datum: 16.01.2018

All-in-One Cellulose Nanocrystals for 3D Printing of Nanocomposite Hydrogels

Cellulose nanocrystals (CNCs) with >2000 photoactive groups on each can act as highly efficient initiators for radical polymerizations, cross-linkers, as well as covalently embedded nanofillers for nanocomposite hydrogels. This is achieved by a simple and reliable method for surface modification of CNCs with a photoactive bis(acyl)phosphane oxide derivative. Shape-persistent and free-standing 3D structured objects were printed with a mono-functional methacrylate, showing a superior swelling capacity and improved mechanical properties. All-rounder: Multifunctional cellulose nanocrystals were achieved by facile surface immobilization of photoactive groups. They serve as highly efficient visible light photoinitiators, cross-linkers and covalently embedded nanofillers for 3D printing of nanocomposite hydrogels, using a mono-functional methacrylate as monomer without any conventional cross-linkers.
Datum: 16.01.2018

Photocontrolled Release of Chemicals from Nano- and Microparticle Containers

A benzoin-derived diol linker was synthesized and used to generate biocompatible polyesters that can be fully decomposed on demand upon UV irradiation. Extensive structural optimization of the linker unit was performed to enable the defined encapsulation of diverse organic compounds in the polymeric structures and allow for a well-controllable polymer cleavage process. Selective tracking of the release kinetics of encapsulated model compounds from the polymeric nano- and microparticle containers was performed by confocal laser scanning microscopy in a proof-of-principle study. The physicochemical properties of the incorporated and released model compounds ranged from fully hydrophilic to fully hydrophobic. The demonstrated biocompatibility of the utilized polyesters and degradation products enables their use in advanced applications, for example, for the smart packaging of UV-sensitive pharmaceuticals, nutritional components, or even in the area of spatially selective self-healing processes. Chemicals on demand: Biocompatible polyesters were synthesized that can be fully decomposed by UV irradiation. The formation of nano- and microparticles allows for the defined encapsulation of structurally diverse organic compounds and a controllable cleavage process. These particles can be used for the smart packaging of UV-sensitive pharmaceuticals or for spatially selective self-healing processes.
Datum: 16.01.2018

Cationic Metallo-Polyelectrolytes for Robust Alkaline Anion-Exchange Membranes

Chemically inert, mechanically tough, cationic metallo-polyelectrolytes were conceptualized and designed as durable anion-exchange membranes (AEMs). Ring-opening metathesis polymerization (ROMP) of cobaltocenium-containing cyclooctene with triazole as the only linker group, followed by backbone hydrogenation, led to a new class of AEMs with a polyethylene-like framework and alkaline-stable cobaltocenium cation for ion transport. These AEMs exhibited excellent thermal, chemical and mechanical stability, as well as high ion conductivity. Ring-opening metathesis polymerization of cobaltocenium-containing cyclooctene with triazole as the only linker group, followed by backbone hydrogenation, has led to a new class of anion-exchange membranes (AEMs) with a polyethylene-like framework and alkaline-stable cobaltocenium cations for the ion transport. The AEMs show excellent thermal, chemical and mechanical stability, as well as high ion conductivity.
Datum: 16.01.2018

Lessons To Be Learned: The Molecular Basis of Kinase-Targeted Therapies and Drug Resistance in Non-Small Cell Lung Cancer

The treatment of non-small cell lung cancer (NSCLC) is currently experiencing a revolution. Over the last decade, the knowledge gained about the biochemical features of biomarkers and their predictive abilities has led to the development of targeted small-molecule inhibitors that present an alternative to harsh chemotherapy. The use of these new therapies has improved the quality of life and increased the survival of patients. The occurrence of inevitable drug resistance requires the constant development of precision medicine. The detailed understanding of the target biology and the search for innovative chemical approaches has encouraged investigations in this field. Herein, we review selected aspects of the molecular targets and present an overview of current topics and challenges in the rational development of small molecules to target NSCLC. An alternative to chemotherapy: The knowledge gained over the last decade about biomarkers and their predictive abilities has led to the development of precision medicine, which has improved the quality of life and increased the survival of patients. This Minireview highlights selected aspects of the molecular targets and presents an overview of current topics and challenges in targeting lung cancer (NSCLC).
Datum: 12.01.2018

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 that undergo further transformations at the carbon–boron bond. Useful handles: 1-Boryl-2,3-disubstituted cyclopropanes can be prepared in high yield and high diastereo- and enantioselectivity from alkenylboronates and ethyl diazoacetate in the presence of catalytic amounts of a copper(I) bisoxazoline species. The resulting cyclopropanes are versatile synthetic intermediates that can undergo further transformations at the carbon–boron bond.
Datum: 02.01.2018

Cristina Nevado

“My favorite way to spend a holiday is diving in warm waters. Looking back over my career, I still feel I am at the outset and the last ten years went by way too fast! ...” This and more about Cristina Nevado can be found on page 2285.
Datum: 20.12.2017

Driving Chemistry and Europe

“… Mobility that favors individual exchanges between researchers is extremely important for the scientific community. The merging of scientific publications within a consortium of European journals and the creation of the European Chemistry Congresses have been major successes …” Read more in the Guest Editorial by Gilberte Chambaud.
Datum: 14.12.2017

Shunai Che

“The secret of being a successful scientist is to question any known results and conclusions. My favorite molecule is DNA, with the most beautiful structures and amazing functionalities ...” This and more about Shunai Che can be found on page 2284.
Datum: 17.11.2017


Category: Current Chemistry Research

Last update: 04.01.2018.

© 1996 - 2018 Internetchemistry

I agree!

This site uses cookies. By using this website, you agree to the use of cookies! Learn more ...