Angewandte Chemie International Edition

General Synthesis of Nano-Metal Phosphides Embedded N-doped Porous Carbon Nanofibers for Enhanced Hydrogen Evolution at All pH Values ()
We innovatively developed an electrospinning-based reduction approach to in situ bunch tiny nickel phosphides nanoparticles in N-doped porous carbon nanofibers (Ni2P@NPCNFs), which protects nano-Ni2P from irreversible fusion and aggregation in a high temperature pyrolysis process. It is very exciting that the resistivity of Ni2P@NPCNFs (5.34 Ω*cm) was greatly decreased 104 times than that of Ni2P (>104 Ω*cm) due to the incorporation of N-doped carbon nanofibers. As an electrocatalyst for HER, Ni2P@NNPCNFs reveal remarkable performance compared to other previously reported catalysts in acidic media. Additionally, it offers excellent catalytic ability and durability in both neutral and basic media. Encouraged by the excellent electrocatalytic performance of Ni2P@NPCNFs, a series of pea-like MxP@NPCNFs, including Fe2P@NPCNFs, Co2P@NPCNFs, and Cu3P@NPCNFs, were also be synthesized by the same method.
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Pleading for a Dual Molecular-Orbital/Valence-Bond Culture ()
The history of the two main theories of chemical bonding, Valence Bond and Molecular Orbital theories, with their respective localized and delocalized visions of the electron pairs, is briefly recalled with an emphasis on their equivalence at comparable computational levels. The delocalized/localized alternative also exists in the very framework of MO theory, since localized MOs can be obtained through unitary transformations which leave Slater determinants invariant. In particular, the use of hybrid orbitals in chemical interpretations is thus perfectly justified. It is argued that a dual knowledge of both theories and their interconnections is of great help to get a complete understanding of the nature of bonding in molecules. Other means of switching from the delocalized to localized representations are also shown to be quite insightful in, e.g., hydrogen-bonding around water molecules, or conformational analysis of propene and many other unsaturated acyclic systems. It is shown that playing with such equivalent readings of the same wave function of dicarbon provides a very clear bonding picture for this enigmatic molecule, whereas the original untransformed wave function is ambiguous. The localized orbital representations of water, ethylene and dicarbon are shown to basically provide the same picture as the analysis of electron density maps as provided by the Maximum Probability Domains method and by the Dynamic Voronoi Metropolis Sampling method. Some current misconceptions are falsified, like the supposed existence of some unique "real" set of orbitals for a molecule, or the belief that the localized lone pair orbitals of water, the famous "rabbit-ear" hybrid orbitals, are in conflict with photoelectron spectroscopy.
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Synthesis of Phenols: Organophotoredox/Ni Dual Catalytic Hydroxylation of Aryl Halides with Water ()
A highly effective hydroxylation reaction of aryl halides with water under the synergistic merger of organophotoredox and nickel-catalysis is reported. The OH group of phenols originates from water following deprotonation facilitated by an intramolecular base group on the ligand. Significantly, aryl bromides as well as less reactive aryl chlorides can also serve as effective substrates, affording phenols with a wide range of functional groups. Using no strong inorganic bases and no expensive noble metal catalysts, this process can be applied to the efficient preparation of diverse phenols and enables the hydroxylation of several multifunctional pharmaceutical aryl halides.
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First End-deck Cyclo-P4 Fe complex: Synthesis and Reactivity. ()
Reduction of the FeII complex [(PhPP2Cy)FeCl2] (2) generates an electron rich and unsaturated Fe0 which is reacted with white phosphorus. The new complex obtained, [(PhPP2Cy)Fe(η4-P4)] (3), is the first iron cyclo-P4 complex and the only known stable end deck cyclo-P4 complex outside of group V. Complex 3 bears a FeII center as shown by Mössbauer spectroscopy, associated to a P42- fragment. Analysis of the molecular orbitals rationalizes the distinct reactivity of complex 3. Reaction of complex 3 with H+ affords the unstable complex [(PhPP2Cy)Fe(η4-P4)(H)]+ (4), whereas with CuCl and BCF the complexes [(PhPP2Cy)Fe(η4:η1-P4)(μ-CuCl)]2 (5) and [(PhPP2Cy)Fe(η4:η1-P4)B(C6F5)3] (6) are formed.
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Mesomeric effect of thiazolium to non-Kekulé diradicals in transketolase of Pichia stipitis ()
Given energetic carbene and uneven electronegativity, thiazolium that mesomerizes to congeners other than carbene in the low effective dielectric binding site is theoretically plausible but never reported. Here we report 9 subatomic-resolution crystal structures of TKps from Pichia stipitis, where thiazolium displays an extraordinary ring-bending effect. These bent thiazolium congeners are correlated to non-Kekulé diradicals due to no gain/loss of electrons. In conjunction with biophysical/biochemical analyses, we conclude that the ring bending is a result of tautomerization of thiazolium with its non-Kekulé diradicals exclusively in the binding site of TKps. The unique chemophysical properties of these thiazolium mesomers may account for the great variety of reactivities carried out by ThDP-containing enzymes. Additionally, the stability of ThDP in living systems may be regulated by the levels of both substrates and hydration/dehydration vs. diradical-mediated oxidative degradation.
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Synthesis and Reactivity of the Phosphorus Analogues of Cyclopentadienone, Tricyclopentanone, and Housene ()
The phosphorus analogues of cyclopentadienone, tricyclopentanone and housene were accessed from bis(cyclopropenyl)diphosphetanedione 3, that was prepared by mixing 1,2,3-tris-tert-butylcyclopropenium tetrafluoroborate (1) and sodium phosphaethynolate [Na(OCP)(dioxane)n]. While photolysis of 3 results in decarbonylation yielding bis(cyclopropenyl)diphosphene 4 and after rearrangement diphosphahousene 5, thermolysis of 3 leads to phosphatricyclo[2.1.0.0]pentanone 7. Metal-mediated valence isomerization of 7 and subsequent demetallation provides access to phosphacyclopentadienone 12.
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Taking Photochromism Beyond Visible: Direct One-Photon NIR Photoswitches Operating in the Biological Window ()
The success of photopharmacology is inevitably tied to the availability of photoswitches, which can be operated within the biological window (650-1450 nm) to maximize penetration in tissue. We have devised a general design strategy and report here on a dihydropyrene derivative, which displays negative T-type photochromism allowing for efficient and nearly quantitative (95%) switching induced by NIR light > 800 nm. The thermal half-life of the decolored ring-open meta-cyclophanediene isomer ranges from minutes to hours, depending on the solvent polarity and hence serves as a probe of the local environment. Due to the rather subtle geometrical differences between the two isomers, suitably modified NIR photoswitches are potential candidates for switching when bound in the pocket of the biological target, in principle allowing for reversible light-induced inhibitor deactivation as an alternative approach to externally regulate biological functions.
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Achilles' Heel of Li-Air Batteries: Li2CO3 ()
Lithium-air battery (LAB) is envisaged as an ultimate energy storage device because of its highest theoretical specific energy among all known battery chemistries. However, parasitic reactions bring about vexing issues on the efficiency and longevity of LAB, among which the formation and decomposition of lithium carbonate, Li_2 CO_3, is of paramount importance. The discovery of Li_2 CO_3 as the main discharge product in carbonate-based electrolytes once brought researchers to 'the end of the idyll' in the early 2010s. In the past few years, tremendous efforts have been made to understand the formation and decomposition mechanisms of Li_2 CO_3, as well as to conceive novel chemical/material strategies to suppress the Li_2 CO_3 formation and to facilitate the Li_2 CO_3 decomposition. Moreover, the study on Li_2 CO_3 in LABs is opening up a new research field of the Li-CO_2 battery. Considering the rapid development and innumerous emerging issues, it is timely to recapitulate the current understandings, define the ambiguities and scientific gaps, and discuss the topics of high priority for future research, which are the aims of this Minireview.
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Evidence for Dynamic Chemical Kinetics at Individual Ruthenium Catalysts ()
Catalytic cycles are typically depicted as possessing time-invariant steps with fixed rates. Yet the true behavior of individual catalysts with respect to time is unknown, hidden by the ensemble averaging inherent to bulk measurements. Herein, focused on a ring-opening metathesis polymerization reaction catalyzed by the second-generation Grubbs' ruthenium catalyst, we show evidence for variable chemical kinetics at individual catalysts with fluorescence microscopy possessing sufficient sensitivity for the detection of single chemical reactions. Insertion reactions in submicron regions likely occur at groups of many (not single) catalysts, yet not so many that their unique kinetic behavior is ensemble averaged.
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A Breathing ATRP: Fully Oxygen Tolerant Polymerization Inspired by Aerobic Respiration of Cells ()
The first well-controlled aqueous atom transfer radical polymerization (ATRP) conducted in the open air was enabled by the continuous conversion of oxygen to carbon dioxide catalyzed by glucose oxidase (GOx), with glucose and sodium pyruvate as sequential sacrificial substrates. Controlled initiators for continuous activator regeneration (ICAR) ATRP of oligo(ethylene oxide) methyl ether methacrylate (OEOMA, Mn=500), yielded polymers with low dispersity (1.09≤Đ ≤1.29) and molecular weights (MW) close to theoretical with pyruvate. Without pyruvate, lower MW were due to generation of new chains by H2O2 formed by reaction of O2 with GOx. Successful chain extension of POEOMA500 macroinitiator with OEOMA300 confirmed a well-controlled polymerization (Đ≤1.3). A "grafting from" polymerization from ATRP initiators covalently attached to Bovine Serum Albumin (BSA) was achieved with low amounts of catalyst (ppm vs. monomer) and short reaction time (≤ 2 hours).
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Photoinduced Co-CF3 Bond Activation Enables Arene C-H Trifluoromethylation ()
Visible light capture activates a thermodynamically inert CoIII-CF3 bond for direct C-H trifluoromethylation of arenes and heteroarenes. New trifluoromethylcobalt(III) complexes supported by a redox-active [OCO] pincer ligand were prepared. Coordinating solvents, such as MeCN, afford quasi-octahedral [(SOCO)CoIII(CF3)(MeCN)2] (2), but in non-coordinating solvents the complex is square pyramidal [(SOCO)CoIII(CF3)(MeCN)] (3). Both are thermally stable, and 2 is stable in light. But exposure of 3 to low-energy light results in facile homolysis of the CoIII-CF3 bond, releasing ●CF3 radical, which is trapped by TEMPO● or (hetero)arenes. The homolytic aromatic substitution reactions do not require a sacrificial or substrate-derived oxidant because the CoII byproduct of CoIII-CF3 homolysis produces H2. The photophysical properties of 2 and 3 provide a rationale for the disparate light stability. Design principles for photoactivation of other strong M-CF3 complexes for catalysis are discussed.
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Bioorthogonal cycloadditions with sub-millisecond intermediates ()
Tetrazine- and sydnone-based click chemistries have emerged as important bioconjugation strategies with fast kinetics and N2 or CO2 as the only by-product. Mechanistic studies of these reactions have focused on the initial rate-determining cycloaddition steps. The subsequent N2 or CO2 release from the bicyclic intermediates has been approached mainly through computational studies, which have predicted lifetimes of femtoseconds. In the present study, bioorthogonal cycloadditions involving N2 or CO2 extrusion have been examined experimentally at the single-molecule level by using a protein nanoreactor. At the resolution of this approach, the reactions appeared to occur in a single step, which places an upper limit on the lifetimes of the intermediates of ~80 μs, consistent with the computational work.
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Reductive Amination by Photoredox Catalysis via Polarity-Matched Hydrogen Atom Transfer ()
Excitation of a Ru(II) photosensitizer in presence of ascorbic acid leads to reduction of iminium ions to electron-rich alpha-aminoalkyl radical intermediates that are rapidly converted to reductive amination products via thiol-mediated hydrogen atom transfer (HAT). As a result, reductive amination of carbonyl compounds with amines via photoredox catalysis proceeds in good to excellent yields and with broad substrate scope, as illustrated by 16 different examples including detailed mechanistic studies. The three key novelties of this work are: (i) the rapid interception of electron-rich radical intermediates by polarity-matched HAT in a photoredox reaction, (ii) the method of reductive amination by photoredox catalysis itself, and (iii) the application of this new method for temporally and spatially controlled reactions on a solid support, as demonstrated by attachment of a fluorescent dye on an activated cellulose support via photoredox-catalyzed reductive amination.
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Enantioselective Iridium Catalyzed Phthalide Formation via Internal Redox Allylation of Phthalaldehydes ()
An Inside Job. Enantioselective phthalide synthesis is achieved through internal redox allylation of o-phthalaldehydes. Oxidative esterification is balanced by reductive carbonyl addition to achieve an overall redox neutral process. Using this method, formal syntheses of ent-spirolaxine methyl ether and CJ-12,954 are achieved.
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The Otherwise Inactive Keggin Polyoxometalate becomes Active towards Electrocatalytic Water Oxidation in Neutral pH: POM@ZIF-8, an Efficient and Robust Electrocatalyst ()
Keggin type of polyoxometalate anions, [XM12O40]n‒, are as versatile as their applications in interdisciplinary areas. We have shown that Keggin anion [CoW12O40]6‒ turns into an efficient and robust electrocatalyst upon its confinement in the well-defined void space of ZIF-8, a metal organic framework (MOF). We have demonstrated that [H6CoW12O40]@ZIF-8 is so stable to water oxidation, that it retains its initial activity even after 1000 catalytic cycles. The catalyst shows turnover frequency (TOF) of 10.8 mol O2(mol Co)-1s-1. To the best of our knowledge, this is one of the highest TOF for electrocatalytic oxygen evolution at neutral pH. Controlled experiments rule out the chances of formation and participation of CoOx in the present electrocatalyic water oxidation.
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Bis(perchlorocatecholato)silane - A neutral silicon Lewis super acid ()
No neutral silicon Lewis super acids are known to date. We report on the synthesis of bis(perchlorocatecholato)silane and verify its Lewis super acidity by computation (DLPNO-CCSD(T)) and experiment (fluoride abstraction from SbF₆-). The exceptional affinity towards donors is further demonstrated by e.g. the characterization of an unprecedented SiO₄F₂ dianion and applied in the first hydrodefluorination reaction catalyzed by a neutral silicon Lewis acid. Given the strength and convenient access to this new Lewis acid, versatile applications might be foreseen.
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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. A subsequent oxidation or protodeborylation leads to valuable α-chiral ketones and chiral alkanes with excellent enantiopurity.
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Bimetallic Ag-Pt sub-nanometer supported clusters as highly efficient and robust oxidation catalysts ()
A combined experimental and theoretical investigation of Ag-Pt sub-nanometer clusters as heterogeneous catalysts in the COCO2 reaction (COox) is presented. Ag9Pt2 and Ag9Pt3 clusters are size-selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and via first-principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters neither sinter nor deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano-aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O2, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species.
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The molecular structure of gauche-1,3-butadiene: Experimental proof of non-planarity ()
The planarity of the second stable conformer of 1,3-butadiene - the archetypal diene for the Diels- Alder reaction, in which a planar conjugated diene and a dienophile combine to form a ring - is not established. The most recent high level calculations predict the species to adopt a twisted, gauche structure due to steric interactions between the inner terminal hydrogens rather than a planar, cis structure favored by the conjugation of the doubled bonds. Here we unambiguously prove experimentally that the structure cis-1,3-butadiene is indeed gauche with a substantial dihedral angle of 34°, in excellent agreement with theory. Observation of two tunneling components indicates that the molecule undergoes facile interconversion between two equivalent enantiomeric forms. Comparison of experimentally determined structures for gauche-and trans-butadiene provides an opportunity to examine the effects of conjugation and steric interactions.
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Smart Solid Electrolyte Interphase Layer for Long Life Lithium Metal Anodes ()
Lithium (Li) metal is a promising anode material for high-energy density batteries. However, the unstable and static solid electrolyte interphase (SEI) can be destroyed by the dynamic Li plating/stripping behavior on the Li anode surface, leading to side reactions and Li dendrites growth. Herein, we design a smart Li polyacrylic acid (LiPAA) SEI layer with high stretchability to address the dynamic Li plating/stripping processes by the self-adapting interface regulation, which is demonstrated by in situ AFM process. With the high binding ability and excellent stability of LiPAA polymer, the smart SEI can significantly reduce the side reactions and improve the safety property markedly. The stable cycling of 700 h is achieved in the LiPAA-Li|LiPAA-Li symmetrical cell. The innovative strategy of self-adapting SEI design is broadly applicable, conceptually providing admirable opportunities for Li metal anodes.
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Dynamic Covalent Chemistry within Biphenyl Scaffolds: Reversible Covalent Bonding, Control of Selectivity, and Chirality Sensing with One Single System ()
Axial chirality is a prevalent and important phenomenon in chemistry. Herein we report a combination of dynamic covalent chemistry and axial chirality for the development of a universal platform toward binding and chirality sensing of multiple classes of mononucleophiles. An equilibrium between open aldehyde and its cyclic hemiaminal within biphenyl derivatives enables the dynamic incorporation of a broad range of alcohols, thiols, primary amines, and secondary amines with high efficiency. The selectivity toward different classes of nucleophiles was also achieved by regulating the distinct reactivity of the system with external stimuli. Through induced helicity as a result of central-to-axial chirality transfer the handedness and enantiomeric excess values of chiral monoalcohol and monoamine analytes can be reported via circular dichroism. The generality of the strategies introduced herein should find applications in many aspects, including assembly, sensing, and labeling.
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Controlling the polymer microstructure in anionic polymerization by compartmentalization ()
An ideal random anionic copolymerization is forced to 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 both monomers upon dilution of the continuous phase from ideal random to adjustable gradients by simple dilution. This model system will allow the preparation of copolymer libraries in the future in a one-pot, one-shot reaction, without any sequential monomer addition.
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Artificial Cysteine S-Glycosylation Induced by Per-O-Acetylated Unnatural Monosacharides during Metabolic Glycan Labeling ()
Here we report an unexpected, non-enzymatic cysteine S-glycosylation induced by per-O-acetylated monosaccharides and their clickable analogs on various proteins. This artificial S-glycosylation broadly compromises the specificity and validity of metabolic glycan labeling in living cells using per-O-acetylated azido and alkynyl sugars, which has been overlooked in the field for decades. We demonstrate that free unnatural sugars can avoid the artifacts and by using N-azidoactylgalactosamine, we provide a corrected list of O-GlcNAcylated proteins and O-GlcNAc sites in HeLa cells.
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A New Mechanism for β-Lactamases: Class D Enzymes Degrade 1β-Methyl Carbapenems via Lactone Formation ()
β-Lactamases threaten the clinical use of carbapenems, considered antibiotics of last resort. The classical mechanism of serine carbapenemase activity proceeds via hydrolysis of an acyl-enzyme intermediate. We show that class D β-lactamases also degrade clinically used 1β-methyl-substituted carbapenems via the unprecedented formation of a carbapenem-derived β-lactone. β-Lactone formation results from the nucleophilic attack of the carbapenem hydroxyethyl side chain onto the ester carbonyl of the acyl-enzyme intermediate. The carbapenem-derived lactone products inhibit both serine β-lactamases (particularly class D) and metallo-β-lactamases. These results define a new mechanism for the class D carbapenemases, in which a hydrolytic water molecule is not required.
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Isolation of a Reactive Tricoordinate alpha-Oxo Gold Carbene Complex ()
The [(P,P)Au=C(Ph)CO2Et]+ complex 3 [where (P,P) is an o-carboranyl diphosphine ligand] was prepared by diazo decomposition at -40°C. It is the first alpha-oxo gold carbene complex to be characterized. Its crystallographic structure was determined and DFT calculations have been performed, unraveling the key influence of the chelating (P,P) ligand. The gold center is tricoordinate and the electrophilicity of the carbene center is reduced. Complex 3 mimics transient alpha-oxo gold carbenes in a series of catalytic transformations, and enables to support the critical role of electrophilicity in the chemoselectivity of phenol functionalization (O-H vs C-H insertion).
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Electrobiorefineries: Unlocking the synergy of electrochemical and microbial conversions ()
Lead-in: An integrated biobased economy urges an alliance of the two realms "chemical production" and "electric power". The concept of electrobiorefineries provides a blueprint for such an alliance agreement. Joining the forces of microbial and electrochemical conversions in electrobiorefineries allows interfacing the production, storage, and exploitation of electricity as well as biobased chemicals. Electrobiorefineries are a technological evolution of biorefineries by means of the addition of (bio)electrochemical transformations. This interfacing of microbial and electrochemical conversions will result in synergies affecting the whole process line, like enlarging the product portfolio, increasing the productivity, or exploiting new feedstock. A special emphasis is given to the utilization of oxidative and reductive electroorganic reactions of microbially produced intermediates that may serve as privileged building blocks.
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The Ideal Ionic Liquid Salt Bridge for the Direct Determination of Gibbs Energies of Transfer of Single Ions, Part I: The Concept ()
We describe 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). We discuss the specific requirements for the IL with regard to the procedure, ensuring that the Liquid Junction Potentials (LJP) at both ends of the ILSB cancel largely. The remaining parts of the LJPs can be determined by separate emf measurements. No extrathermodynamic assumptions are necessary for this procedure. The accuracy of the measurements depends amongst others on the "ideality" of the used IL, as shown in our companion paper Part II.
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Direct asymmetric Michael reaction of α,β-unsaturated aldehydes and ketones catalyzed by two secondary amine catalysts ()
Direct asymmetric Michael reaction of α,β-unsaturated aldehydes and ketones proceeds in the presence of two pyrrolidine-type catalysts, such as diphenylprolinol silyl ether and hydroxyproline, to afford synthetically useful δ-keto aldehydes with excellent diastereo- and enantioselectivities. Although there are several iminium ions and enamines in the reaction mixture, an iminium ion generated from the former catalyst reacts preferentially with an enamine generated from the latter catalyst.
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The Ideal Ionic Liquid Salt Bridge for the 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, S1 > S2) 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 - one with nearly identical diffusion of anion and cation. This holds for [N2225]+[NTf2]- in the pure IL, but also in water and acetonitrile solution. Emf measurements of solvate cells between S1 and S2 gave Nernstian behavior for Ag+-concentration cells and constant like cell potentials for solutions with five tested Ag+-counterions.
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Co(II)-Based Metalloradical Activation of 2-(Diazomethyl)pyridines for Radical Transannulation and Cyclopropanation ()
A new catalytic method for the denitrogenative transannulation/cyclopropanation of in-situ generated 2-(diazomethyl)pyridines is described via a cobalt-catalyzed radical activation mechanism. The method has been developed by taking advantage of the inherent property of Co(III)-carbene radical intermediate. This is the first report for the denitrogenative transannulation/cyclopropanation via radical activation mechanism, which is supported by various control experiments. For synthetic application of this metalloradical approach, it has been showcased by the short total synthesis of ()-monomorine.
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CO oxidation on metal-supported monolayer oxide films: Do we know which phase (interface) is active? ()
Ultrathin ("monolayer") films of transition metal oxides grown on metal substrates have recently received considerable attention as promising catalytic materials, in particular for low-temperature CO oxidation. The reaction rate on such systems often increases when the film only partially covers the support, and the effect is commonly attributed to the formation of active sites at the metal/oxide boundary. By studying the structure and reactivity of FeO(111) films on Pt(111), here we show that, independently of the film coverage, CO oxidation takes place at the interface between reduced and oxidized phases in the oxide film formed under reaction conditions. The promotional role of a metal support is to ease formation of the reduced phase via reaction between CO adsorbed on metal and oxygen at the oxide island edge.
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Surface Molding of Microscale Hydrogels with Microactuation Functionality ()
This work describes the fabrication of numerous hydrogel microstructures, μ-gels, via a process called "surface molding"—chemically patterned elastomeric assembly substrates were used to organize and manipulate the geometry of liquid prepolymer microdroplets, which, following photo-initiated crosslinking, maintained the desired morphology. By adjusting the state of strain during the crosslinking process, a continua of structures could be created using one pattern. These arrays of μ-gels have stimuli-responsive properties that are directly applicable to actuation where the basis shape and array geometry of the μ-gels can be used to rationally generate microactuators with programmed motions. As a method, "surface molding," represents a powerful addition to the soft lithographic toolset that can be readily applied to the simultaneous synthesis of large numbers of geometrically and functionally distinct polymeric microstructures.
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Selective C-H Halogenations with a Highly Fluorinated Manganese Porphyrin ()
Selective C-H functionalizations of aliphatic molecules remain a challenge in organic synthesis. While radical chain halogenations provide an efficient way to access many halogenated molecules, application of typical protocols to selectively halogenate electron-deficient and strained aliphatic molecules are rare. Herein, we report selective C-H chlorinations and fluorinations that use an electron-deficient manganese pentafluorophenyl porphyrin catalyst, Mn(TPFPP)Cl. This catalyst displays superior properties for aliphatic halogenations of recalcitrant, electron-deficient and strained substrates with unique regio- and stereoselectivity. In operando UV-vis analyses indicate that an oxoMn(V) species is responsible for hydrogen atom abstraction. The observed stereoselectivity results from steric interactions between the bulky porphyrin ligand and the intermediate substrate radical in the halogen rebound step.
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Kinetic Dearomatization Strategy for an Expedient Biomimetic Route to the Bielschowskysin Skeleton. ()
Bielschowskysin (1), the flagship of the furanocembranoid-derived diterpene family has attracted attention from chemists owing to its intriguing and daunting polycyclic architecture and medicinal potential against lung cancer. The high level of functionalization of 1 poses a considerable challenge to synthesis. Herein a stereoselective furan dearomatization strategy of furanocembranoids was achieved via the intermediacy of chlorohydrins. The stereochemical course of the kinetic dearomatization was established and the C-3 configuration of the resulting exo-enol ether intermediates proved to be essential to complete the late-stage transannular [2+2] photocycloaddition. Overall, this biomimetic strategy starting from the natural product acerosolide (9) featured an unprecedented regio- and highly stereoselective furan dearomatization which enabled a rapid access to the pivotal exo-enol ethers en route to the intricate bielschowskyane skeleton.
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Catalytic Asymmetric Synthesis of Trifluoromethylated γ-Amino Acids via Umpolung Addition of Trifluoromethyl Imines to Carboxylic Acid Derivatives ()
Enabled by the discovery of novel cinchona alkaloid-derived chiral phase-transfer catalysts, highly chemo-, regio-, diastereo- and enantioselective umpolung additions of trifluoromethyl imines to α, β-unsaturated N-acylpyrroles were realized. With a catalyst loading ranging from 0.2 to 5.0 mol%, this new catalytic asymmetric transformation provides facile and high-yield access to highly enantiomerically enriched chiral trifluoromethylated γ-amino acids and γ-lactams.
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Electron-Precise Actinide-Pnictide (An-Pn) Bonds Spanning Non-Metal, Metalloid, and Metal Combinations (An = U, Th; Pn = P, As, Sb, Bi) ()
We report the synthesis and characterisation of the compounds [An(TrenDMBS){Pn(SiMe3)2}] and [An(TrenTIPS){Pn(SiMe3)2}] [TrenDMBS = N(CH2CH2NSiMe2But)3, An = U, Pn = P, As, Sb, Bi; An = Th, Pn = P, As; TrenTIPS = N(CH2CH2NSiPri3)3, An = U, Pn = P, As, Sb; An = Th, Pn = P, As, Sb]. The U-Sb and Th-Sb moieties are unprecedented examples of any kind of An-Sb molecular bond, and the U-Bi bond is the first electron-precise one. The Th-Bi combination was too unstable to isolate, underscoring the fragility of these linkages. However, the U-Bi complex is the heaviest electron-precise pairing of two elements involving an actinide on a macroscopic scale under ambient conditions, and this is exceeded only by An-An pairings prepared under cryogenic matrix isolation conditions. Thermolysis and photolysis experiments suggest that the U-Pn bonds degrade by hemolytic bond cleavage, whereas the more redox robust thorium compounds engage in an acid-base/dehydrocoupling route.
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Encapsulation of Homogeneous Catalysts in Mesoporous Materials Using Diffusion-Limited Atomic Layer Deposition ()
The heterogenization of homogeneous metal complex catalysts has attracted great attention. Herein, we report the encapsulation of metal complexes into nanochannels of mesoporous materials by coating metal oxides at/near the pore entrance via diffusion-limited atomic layer deposition (ALD) to produce a "hollow plug". The pore size of the hollow plug is precisely controlled on the sub-nanometer scale by the number of ALD cycles to fit various metal complexes with different molecular sizes. Typically, Co or Ti complexes are successfully encapsulated into the nanochannels of SBA-15, SBA-16 and MCM-41. The encapsulated Co and Ti catalysts show excellent catalytic activity and reusability in the hydrolytic kinetic resolution of epoxides and asymmetric cyanosilylation of carbonyl compounds, respectively. This ALD-assisted encapsulation method can be extended to the encapsulation of other homogeneous catalysts into different mesoporous materials for various heterogeneous reactions.
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CO2 to terpenes - autotrophic and electroautotrophic α-humulene production with Cupriavidus necator ()
Herein, we demonstrate that CO2 can be converted by an engineered "Knallgas" bacterium (Cupriavidus necator) to the terpene α-humulene. Heterologous expression of the mevalonate pathway and α-humulene synthase resulted in a production of approx. 10 mg α-humulene per gram cell dry mass (CDM) under heterotrophic conditions. This first example of chemolithoautotrophic production of a terpene from carbon dioxide, hydrogen and oxygen is a promising starting point for the production of different high value terpene compounds from abundant and simple raw materials. Furthermore, the production system was used to produce 17 mg α-humulene per gram CDM from CO2 and electrical energy in microbial electrosynthesis (MES) mode. Due to the fact that the system can convert CO2 by using electrical energy from solar energy it opens a new route to artificial photosynthetic systems.
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pH resistant monodispersed polymer-lipid nanodiscs ()
Polymer lipid nanodiscs have provided an invaluable system for structural and functional studies of membrane proteins in their near-native environment. In spite of the recent advances in the development and usage of polymer lipid nanodisc systems, lack of control over size and poor tolerance to pH and divalent metal ions are major limitations for further applications. Here we report a facile modification of a low molecular weight styrene maleic acid copolymer to form monodispersed lipid bilayer nanodiscs that show ultra-stability towards a pH range of 2.5 to 10 and divalent metal ion concentration. The macro-nanodiscs (>20 nm diameter) show magnetic-alignment properties that can be exploited for high-resolution structural studies of membrane proteins using well-established solid-state NMR techniques. As demonstrated in this study, the new polymer, SMA-QA, is a robust membrane mimetic tool that offers significant advantages over currently reported nanodisc systems.
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The Catalytic Asymmetric Mukaiyama-Michael Reaction of Silyl Ketene Acetals with α,β-Unsaturated Methyl Esters ()
α,β-Unsaturated esters are readily available but challenging substrates to activate in asymmetric catalysis. We now describe an efficient, general, and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with α,β-unsaturated methyl esters, catalyzed by a silylium imidodiphosphorimidate (IDPi) Lewis acid.
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Introducing Chiral Bifunctional Phosphine-Carboxylate Ligands for Palladium(0)-Catalyzed Enantioselective C-H Arylation ()
Previous enantioselective Pd0-catalyzed C-H activation reactions proceeding via the concerted metalation-deprotonation mechanism employed either a chiral ancillary ligand, a chiral base, or a bimolecular mixture thereof. This study describes the development of new chiral bifunctional ligands based on a binaphthyl scaffold and incorporating both a phosphine and a carboxylic acid moiety. The optimal ligand provided high yields and enantioselectivities for the desymmetrizing C(sp2)-H arylation leading to 5,6-dihydrophenanthridines, whereas the corresponding monofunctional ligands showed low enantioselectivities. The bifunctional system proved applicable to a range of substituted dihydrophenanthridines, and allowed the parallel kinetic resolution of racemic substrates.
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Copper-Catalyzed Enantioselective Markovnikov Protoboration of α-Olefins Enabled by a Buttressed NHC Ligand ()
We report herein a highly enantioselective copper-catalyzed Markovnikov protoboration of unactivated terminal alkenes. A variety of simple and abundant feedstock α-olefins bearing a diverse array of functional groups and heterocyclic substituents can be applied in this process, which proceeds under mild conditions at ambient temperature to provide expedient access to enantioenriched alkylboronic esters in good regioselectivity and with excellent enantiocontrol. Critical to the success of the protocol was the development and application of a novel, sterically hindered N-heterocyclic carbene, (R,R,R,R)-ANIPE, as the ligand for copper.
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Visualization of Heterogeneous Oxygen Storage Behavior in Three-Way Catalyst Pt/Ce2Zr2Ox Particles by Hard X-ray Spectro-Ptychography ()
The cerium density and valence in micrometer-size Pt/Ce2Zr2Ox (x=7-8) three-way catalyst particles were successfully mapped by hard X-ray spectro-ptychography (ptychographic-XAFS). The analysis of correlation between the Ce density and valence in ptychographic-XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce2Zr2Ox particles. Ptychographic-XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.
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Interfacial nanoprecipitation toward stable and responsive microbubbles and their use as a resuscitative fluid ()
Abstract: We report a new approach to prepare stable microbubbles (MBs) via interfacial nanoprecipitation of bioabsorbable polymers at air/liquid interface. This facile method offers robust control over MBs morphology and chemo-physical properties by simple chemical modifications. This approach is amenable to large-scale manufacturing, and is useful to develop functional MBs for advanced biomedical applications. To demonstrate this, we created a MB-based intravenous oxygen carrier that undergoes pH-triggered self-elimination. Intravenous injection of past MBs increase the risk of pulmonary vascular obstruction. However, we show, for the first time, that our current design supersedes previous MBs, as they 1) yielded no evidence of acute risks in rodents, and 2) improved the survival in a disease model of asphyxial cardiac arrest (from 0 to 100%), a condition that affects more than 100,000 in-hospital patients, carrying a ~90% mortality.
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Emissive synthetic cofactors: enzymatic interconversions of tzA analogues of ATP, NAD+, NADH, NADP+ and NADPH ()
A series of enzymatic transformations, which generate visibly emissive isofunctional cofactors based on an isothiazolo[4,3-d]pyrimidine analogue of adenosine (tzA), is described. Nicotinamide adenylyl transferase condenses nicotinamide mononucleotide and tzATP to yield NtzAD+, which can be enzymatically phosphorylated by NAD+ kinase and ATP or tzATP to the corresponding NtzADP+. The latter can be engaged in NADP-specific coupled enzymatic transformations involving conversion to NtzADPH by glucose-6-phosphate dehydrogenase and reoxidation to NtzADP+ by glutathione reductase. The NtzADP+/NtzADPH cycle can be monitored in real time by fluorescence spectroscopy.
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Transition-Metal-Catalyzed Selective Functionalization of C(sp3)-H Bonds in Natural Products ()
Direct functionalization of natural products is important for studying structure-activity and structure-property relationships of these molecules. Recent advances in transition-metal-catalyzed functionalizations of C(sp3)-H bonds, the most abundant yet inert bonds in natural products, have been shown to create natural product derivatives selectively. Strategies to achieve such transformation are reviewed.
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A bioresistant nitroxide spin label for in-cell EPR spectroscopy: in vitro and in oocytes protein structural dynamics studies. ()
Approaching proteins structural dynamics and protein-protein interactions in the cellular environment is a fundamental challenge. Due to its absolute sensitivity and to its selectivity to paramagnetic species, Site-Directed Spin Labeling (SDSL) combined with Electron Paramagnetic Resonance (EPR) has the potential to evolve into an efficient method to follow conformational changes in proteins directly inside cells. Until now, the use of nitroxyde-based spin labels for in-cell studies has represented a major hurdle because of their short persistence in the cellular context. In this work we present the design and synthesis of the first maleimido-proxyl-based spin label (M-TETPO) resistant towards reduction and being efficient to probe protein dynamics by continuous wave and pulsed EPR. In particular, the extended lifetime of M-TETPO enabled the study of structural features of a chaperone in the absence and presence of its binding partner at endogenous concentration directly inside cells.
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Building Organic/Inorganic Hybrid Interphases for Fast Interfacial Transport in Rechargeable Metal Batteries ()
We report a facile, in-situ synthesis to create durable, hybrid Solid-electrolyte interphases (SEI) on metal anodes. Composed of Si-interlinked molecules that host LiCl salt, the hybrid SEI exhibit fast charge-transfer kinetics and high exchange current densities. By means of electrochemical analysis and direct optical visualization of Li and Na deposition in symmetric Li/Li and Na/Na cells, it is further shown that the hybrid SEI enables excellent morphological control at relatively high current densities (3-5 mA/cm2) and even for notoriously unstable Na metal anodes. We investigate benefits of the fast interfacial transport attributes of the SEI in Li-S cells. It is found that stable electrochemical cycling is achieved in galvanostatic studies at rates as high as 2 C. Our work provides a promising path towards rational design of multi-functional, elastic SEI that overcomes the most serious limitations of spontaneously formed interphases on high-capacity metal anodes.
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Light-driven C-H Oxygenation of Methane into Methanol and Formic Acid by Molecular Oxygen Using Perfluorinated Solvent ()
Chlorine dioxide radical (ClO2*) was found to act as an efficient oxidizing agent in the aerobic oxygenation of methane to methanol and formic acid under photoirradiation. Photochemical oxygenation of methane occurred in a two-phase system comprising perfluorohexane and water under ambient conditions (298 K, 1 atm). The yields of methanol and formic acid were 14% and 85%, respectively, with a methane conversion of 99% without formation of the further oxygenated products such as CO2 and CO. Ethane was also photochemically converted into ethanol (19%) and acetic acid (78%). The methane oxygenation is initiated by the photochemical Cl-O bond cleavage of ClO2* to generate Cl* and O2. The produced Cl* reacts with CH4 to form a methyl radical (CH3*). Finally, the oxygenated products such as methanol and formic acid were given by the radical chain reaction. A fluorous solvent plays an important role of inhibiting the deactivation of reactive radical species such as Cl* and CH3*.
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ortho-Directing Chromium Arene Complexes as Efficient Mediators for Enantiospecific sp2-sp3 Cross-Coupling Reactions ()
A new strategy for the coupling of a broad scope of electronically diverse aromatics to boronic esters is reported. The coupling sequence, which relies on the directed ortho-lithiation of chromium arene complexes followed by boronate formation and oxidation, occurs with complete ortho-selectivity and enantiospecificity to give the coupling products in excellent yields and with high functional group tolerance. An intermediate chromium arene boronate complex was characterized by X-ray, NMR and IR to elucidate the reaction mechanism.
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Enantio- and Diastereoselective Cyclopropanation of 1-Alkenylboronates: Synthesis of 1-boryl-2,3-disubstituted Cyclopropanes ()
A novel, highly enantio- and diastereoselective synthesis of 1-boryl-2,3-disubstituted cyclopropanes has been developed by means of the cyclopropanation of alkenylboronates with ethyl diazoacetate in the presence of catalytic amounts of a chiral copper-(I) complex. The products can also be directly accessed from alkynes through an operationally simple sequential hydroboration-cyclopropanation protocol. The resulting enantioenriched 1-boryl-2,3-disubstituted-cyclopropanes are versatile synthetic intermediates through further transformations at the carbon-boron bonds
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Thioketone Directed Palladium(II)-Catalyzed C-H Arylation of Ferrocenes with Aryl Boronic Acids ()
A palladium(II)-catalyzed thioketone-chelation-assisted C-H direct arylation of ferrocenes is described. With thioketone as an efficient directing group, various mono- and di-aryl-substituted thiocarbonylferrocenes were obtained via Pd-catalyzed C-H direct functionalization reaction in high yields under mild and base-free conditions. Furthermore, the arylated thiocarbonylferrocene could undergo diverse transformations.
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Dicarboxylic Acid Separation by Dynamic and Size-Matched Recognition in Solution and in the Solid State ()
Bis(trimethylammonium) alkane diiodides dynamically encapsulate dicarboxylic acids through intermolecular hydrogen bonds between the hosts' I- anions and the guests' carboxylic OH groups. A selective recognition is realized when the size of the I-∙∙∙HOOC-(CH2/CF2)n-COOH∙∙∙I- superanion matches the dication alkyl chain length. Dynamic recognition is demonstrated also in solution, where the presence of the size-matching organic salt boosts acid solubility profile thus allowing efficient mixture separation.
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Photocatalytic Aerobic Phosphatation of Alkenes ()
A catalytic regime for the direct phosphatation of simple, non-polarized alkenes, using ordinary, non-activated phosphoric acid diesters as the phosphate source and O2 as the terminal oxidant, has been devised. The title method allows for the direct and highly econo-mic construction of a diverse range of allylic phosphate esters. From a conceptual viewpoint, the aerobic phosphatation is entirely complementary to traditional protocols for phosphate ester formation, which predominantly rely on the use of pre-functionalized or pre-activated reactants, such as alcohols and phosphoryl halides. The title transformation is enabled by the dual interplay of a photoredox- and a selenium-π-acid catalyst involving a sequence of single-electron-transfer processes.
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Nanosheet Catalysis of Carbon Dioxide Photoreduction: Fundamentals and Challenges ()
Transformation of CO2 into fuels and chemicals by using photocatalysis is a promising strategy to provide a long-term solution to mitigating global warming and energy supply problems. Achievements in photocatalysis during the last decade have sparked increased interest in using sunlight to reduce CO2. Traditional semiconductors used in photocatalysis (e.g. TiO2), are not suitable for the use in natural sunlight, and even under UV irradiation their performance is not sufficient. Some two-dimensional (2D) materials have recently been designed for catalytic reduction of CO2. These materials still require significant modification, which remains a challenge for photocatalytic process design. An overarching aim of this article is to summarize the literature reported on photocatalytic conversion of CO2 by various 2D materials in the liquid phase, with special attention given to development of novel 2D photocatalyst materials, to provide a basis to suggest improved materials.
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The common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium ()
Understanding the pathways of catalyst degradation during the oxygen evolution reaction is a cornerstone in development of efficient and stable electrolyzers, since even for most promising Ir based anodes the destined harsh conditions are detrimental. The dissolution mechanism has a complex nature and the correlation to the oxygen evolution reaction itself is still poorly understood. Here, hyphening a scanning flow cell with inductively coupled plasma and online electrochemical mass spectrometers, we in-situ monitor the oxygen evolution and degradation products of Ir and Ir-oxides. We show that at high anodic potentials several dissolution routes become possible, including formation of gaseous IrO3. On the basis of our experimental data possible pathways of oxygen evolution triggered dissolution of Ir are proposed, and the role of common intermediates for these reactions is discussed.
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Palladium-Catalyzed Intramolecular Trost-Oppolzer-Type Alder-Ene Reaction of Dienyl Acetates to Cyclopentadienes ()
A new approach for the synthesis of highly substituted cyclopentadienes, indenes and cyclopentene-fused heteroarenes via the Pd-catalyzed Trost-Oppolzer-type intramolecular Alder-ene reaction of 2,4-pentadienyl acetates is described. This unprecedented transformation combines the electrophilic features of the Tsuji-Trost reaction with the nucleophilic features of the Alder-ene reaction. The overall outcome can be perceived as a hitherto unknown 'acid-free' iso-Nazarov-type cyclization. The versatility of this strategy was further demonstrated via the formal synthesis of paucifloral F, a resveratrol-based natural product.
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Solar hydrogen generation from lignocellulose ()
Photocatalytic reforming of lignocellulosic biomass is an emerging approach to produce renewable H2. This process combines photo-oxidation of aqueous biomass with photocatalytic hydrogen evolution at ambient temperature and pressure. Biomass conversion is less energy demanding than water splitting and generates high-purity H2 without O2 production. Direct photoreforming of raw, unprocessed biomass has the potential to provide affordable, clean energy across the globe from locally sourced materials.
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Reversing Conventional Reactivity of Mixed Oxo/Alkyl Rare Earth Complexes: Non-Redox Oxygen Atom Transfer ()
The preferential substitution of oxo ligands over alkyl ones of rare earth complexes is commonly considered as "impossible" due to the high oxophilicity of metal centers. Now, it has been shown that simply assembling mixed methyl/oxo rare earth complexes to a rigid trinuclear cluster framework can not only enhance the activity of the Ln-oxo bond, but also protect the highly reactive Ln-alkyl bond, thus providing a previously unrecognized opportunity to selectively manipulate the oxo ligand in the presence of numerous reactive functionalities. Such trimetallic cluster has proved to be a suitable platform for developing the unprecedented non-redox rare earth-mediated oxygen atom transfer from ketones to CS2 and PhNCS. Controlled experiments and computational studies shed light on the driving force for these reactions, emphasizing the importance of the sterical accessibility and multimetallic effect of the cluster framework in promoting reversal of reactivity of rare earth oxo complexes.
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Single-cell Mass Spectrometry Approaches to Explore Cellular Heterogeneity ()
Compositional diversity is a fundamental property in cell populations that is responsible for evolutionary adaptation and resilience. Single-cell analysis promises new insights into this cellular heterogeneity and the corresponding subpopulations on the genomic, transcriptomic, proteomic, and metabolomic levels. Mass spectrometry (MS) is a label-free technique that enables the multiplexed analysis of proteins, peptides, lipids, and metabolites in individual cells. The abundances of these molecular classes are correlated with the physiological states and environmental responses of the cells. In this Minireview, we discuss recent advances in single-cell MS techniques with an emphasis on sampling and ionization methods developed for volume-limited samples. Strategies for sample treatment, separation methods, and data analysis require special considerations for single cells. Ongoing analytical challenges include the need for high-throughput, high molecular coverage, minimal perturbation, subcellular heterogeneity, and non-normal statistical distributions of cellular properties. The insights obtained by single-cell MS techniques inform fundamental cell biology, immunology, and individualized medicine.
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In Situ Spatial Complementation of Aptamer-Mediated Recognition Enables Live-Cell Imaging of Native RNA Transcripts in Real Time ()
Direct cellular imaging of the localization and dynamics of biomolecules helps to understand their function and reveals novel mechanisms at the single-cell resolution. In contrast to routine fluorescent-protein-based protein imaging, technology for RNA imaging remains less well explored because of the lack of enabling technology. Herein, we report the development of an aptamer-initiated fluorescence complementation (AiFC) method for RNA imaging by engineering a green fluorescence protein (GFP)-mimicking turn-on RNA aptamer, Broccoli, into two split fragments that could tandemly bind to target mRNA. When genetically encoded in cells, endogenous mRNA molecules recruited Split-Broccoli and brought the two fragments into spatial proximity, which formed a fluorophore-binding site in situ and turned on fluorescence. Significantly, we demonstrated the use of AiFC for high-contrast and real-time imaging of endogenous RNA molecules in living mammalian cells. We envision wide application and practical utility of this enabling technology to in vivo single-cell visualization and mechanistic analysis of macromolecular interactions. Let's split! An aptamer-initiated fluorescence complementation (AiFC) method was developed for RNA imaging by engineering a green fluorescence protein (GFP)-mimicking turn-on RNA aptamer into two split fragments that could tandemly bind to target mRNA. The use of AiFC enables the non-invasive, high-contrast real-time imaging of endogenous RNA molecules in living mammalian cells.
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A Sterically Constrained Tricyclic PC3 Phosphine—Coordination Behavior and Insertion of Chalcogen Atoms into P−C Bonds ()
A tricyclic phosphine has been generated that has a rigid molecular backbone with the P atoms exclusively bound to C(sp2) atoms as well as a very large Tolman angle and buried volume. It is an interesting new ligand in coordination chemistry (Au, Pd complexes) and shows unusual insertion reactions into its endocyclic P−C bonds facilitated by its inherent molecular strain. Give it a tri: A trilithium compound reacted with PCl3 to afford a new tricyclic and sterically highly shielded phosphine that has a large Tolman angle, and ligand basicity comparable to that of PPh3. Ring strain results in a promising reactivity, as demonstrated by the insertion of S or Se atoms into the P−C bonds.
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Two Distinct Substrate Binding Modes for the Normal and Reverse Prenylation of Hapalindoles by the Prenyltransferase AmbP3 ()
The cyanobacterial prenyltransferase AmbP3 catalyzes the reverse prenylation of the tetracyclic indole alkaloid hapalindole U at its C-2 position. Interestingly, AmbP3 also accepts hapalindole A, a halogenated C-10 epimer of hapalindole U, and catalyzes normal prenylation at its C-2 position. The comparison of the two ternary crystal structures, AmbP3-DMSPP/hapalindole U and AmbP3-DMSPP/hapalindole A, at 1.65–2.00 Å resolution revealed two distinct orientations for the substrate binding that define reverse or normal prenylation. The tolerance of the enzyme for these altered orientations is attributed to the hydrophobicity of the substrate binding pocket and the plasticity of the amino acids surrounding the allyl group of the prenyl donor. This is the first study to provide the intimate structural basis for the normal and reverse prenylations catalyzed by a single enzyme, and it offers novel insight into the engineered biosynthesis of prenylated natural products. One Way or Another: AmbP3 is a prenyltransferase that catalyzes both reverse and regular prenylation depending on the substrate. X-ray crystal structure analysis of AmbP3 in complex with reverse and regular prenylation substrates elucidates the structural basis of its surprising plasticity in catalyzing two types of prenylation.
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Stereochemical Definition of the Natural Product (6R,10R,13R, 14R,16R,17R,19S,20S,21R,24S,25S,28S,30S,32R,33R,34R,36S,37S,39R)-Azaspiracid-3 by Total Synthesis and Comparative Analyses ()
The previously accepted structure of the marine toxin azaspiracid-3 is revised based upon an original convergent and stereoselective total synthesis of the natural product. The development of a structural revision hypothesis, its testing, and corroboration are reported. Synthetic (6R,10R,13R,14R,16R,17R,19S,20S,21R,24S,25S,28S,30S,32R, 33R,34R,36S,37S,39R)-azaspiracid-3 chromatographically and spectroscopically matched naturally occurring azaspiracid-3, whereas the previously assigned 20R epimer did not. A convergent and stereodefined total synthesis of the marine toxin azaspiracid-3 (AZA3) enabled direct comparison with the natural product that redefines the structure of AZA3. Comparative data indicate that AZA1-AZA10 and AZA34 share the (19S*,20S*) relative stereochemistry.
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Three-Dimensional Architectures Constructed from Transition-Metal Dichalcogenide Nanomaterials for Electrochemical Energy Storage and Conversion ()
Transition-metal dichalcogenides (TMDs) have attracted considerable attention in recent years because of their unique properties and promising applications in electrochemical energy storage and conversion. However, the limited number of active sites as well as blocked ion and mass transport severely impair their electrochemical performance. The construction of three-dimensional (3D) architectures from TMD nanomaterials has been proven to be an effective strategy to solve the aforementioned problems as a result of their large specific surface areas and short ion and mass transport distances. This Review summarizes the commonly used routes to build 3D TMD architectures and highlights their applications in electrochemical energy storage and conversion, including batteries, supercapacitors, and electrocatalytic hydrogen evolution. The challenges and outlook in this research area are also discussed. Electrochemistry in 3D: Three-dimensional transition-metal dichalcogenide architectures have shown great promise for electrochemical energy storage and conversion. This Review summarizes the commonly used strategies for the construction of such architectures, as well as their application in rechargeable batteries, supercapacitors, and electrocatalytic hydrogen evolution.
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Crystal-Field Tuning of Photoluminescence in Two-Dimensional Materials with Embedded Lanthanide Ions ()
Lanthanide (Ln) group elements have been attracting considerable attention owing to the distinct optical properties. The crystal-field surroundings of Ln ions in the host materials can determine their energy level splitting, which is of vital importance to tailor their optical properties. 2D MoS2 single crystals were utilized as the host material to embed Eu3+ and energy-level splitting was achieved for tuning its photoluminescence (PL). The high anisotropy of the 2D host materials makes them distort the degenerate orbitals of the Ln ions more efficiently than the symmetrical bulk host materials. A significant red-shift of the PL peak for Eu3+ was observed. The strategy for tailoring the energy level splitting of Ln ions by the highly designable 2D material crystal field provides a new method to extend their optical properties. Tuning the crystal set: Two-dimensional MoS2 single crystals were utilized as the host material to embed Eu3+ for achieving the energy level splitting. A significant red-shift of the photoluminescence peak compared with the situation when employing bulk or nanoparticle host materials was observed.
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Synthesis and Stability of Lanthanum Superhydrides ()
Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen-rich simple compounds having new clathrate-like structures and remarkable electronic properties including room-temperature superconductivity. X-ray diffraction and optical studies demonstrate that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty-two hydrogen atoms surrounding each La atom. Upon decompression, the fcc-based structure undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H−H distances of about 1.1 Å, which are close to predictions for solid atomic metallic hydrogen at these pressures. With stability below 200 GPa, the superhydride is thus the closest analogue to solid atomic metallic hydrogen yet to be synthesized and characterized. Superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to about 1000 K. The X-ray diffraction and optical studies match the predicted cubic metallic phase of LaH10 having cages of thirty-two hydrogen atoms surrounding each La atom. With stability below 200 GPa, the superhydride is thus the closest analogue to solid atomic metallic hydrogen yet to be synthesized and characterized.
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FHBC, a Hexa-peri-hexabenzocoronene–Fluorene Hybrid: A Platform for Highly Soluble, Easily Functionalizable HBCs with an Expanded Graphitic Core ()
Materials based upon hexa-peri-hexabenzocoronenes (HBCs) show significant promise in a variety of photovoltaic applications. There remains the need, however, for a soluble, versatile, HBC-based platform, which can be tailored by incorporation of electroactive groups or groups that can prompt self-assembly. The synthesis of a HBC–fluorene hybrid is presented that contains an expanded graphitic core that is highly soluble, resists aggregation, and can be readily functionalized at its vertices. This new HBC platform can be tailored to incorporate six electroactive groups at its vertices, as exemplified by a facile synthesis of a representative hexaaryl derivative of FHBC. Synthesis of new FHBC derivatives, containing electroactive functional groups that can allow controlled self-assembly, may serve as potential long-range charge-transfer materials for photovoltaic applications. A fluorene–HBC (hexa-peri-hexabenzocoronene) hybrid with a large graphitic core was synthesized. It was found to be highly soluble and easily functionalized at its six vertices.
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Nagoya Gold and Silver Medals/Prelog Medal and Lectureship for Stephen B. H. Kent/And also in the News ()

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Uncatalyzed, Regioselective Oxidation of Saturated Hydrocarbons in an Ambient Corona Discharge ()
Atmospheric pressure chemical ionization (APCI) in air or in nitrogen with just traces of oxygen is shown to yield regioselective oxidation, dehydrogenation, and fragmentation of alkanes. Ozone is produced from ambient oxygen in situ and is responsible for the observed ion chemistry, which includes partial oxidation to ketones and C−C cleavage to give aldehydes. The mechanism of oxidation is explored and relationships between ionic species produced from individual alkanes are established. Unusually, dehydrogenation occurs by water loss. Competitive incorporation into the hydrocarbon chain of nitrogen versus oxygen as a mode of ionization is also demonstrated. No pressure: Atmospheric pressure corona discharge ionization (APCI) in air, or in the presence of trace amounts of oxygen, is shown to yield regioselective oxidation, dehydrogenation, and fragmentation. The chemistry of oxidation is explored and relationships between the ionic species, produced from single analytes, are established. Ozone is produced from ambient oxygen in situ and dehydration is responsible for the observed dehydrogenated ketones.
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A Hierarchical MFI Zeolite with a Two-Dimensional Square Mesostructure ()
A conceptual design and synthesis of ordered mesoporous zeolites is a challenging research subject in material science. Several seminal articles report that one-dimensional (1D) mesostructured lamellar zeolites are possibly directed by sheet-assembly of surfactants, which collapse after removal of intercalated surfactants. However, except for one example of two-dimensional (2D) hexagonal mesoporous zeolite, no other zeolites with ordered 2D or three-dimensional (3D) mesostructures have been reported. An ordered 2D mesoporous zeolite can be templated by a cylindrical assembly unit with specific interactions in the hydrophobic part. A template molecule with azobenzene in the hydrophobic tail and diquaternary ammonium in the hydrophilic head group directs hierarchical MFI zeolite with a 2D square mesostructure. The material has an elongated octahedral morphology, and quaternary, ordered, straight, square channels framed by MFI thin sheets expanded along the a–c planes and joined with 90° rotations. The structural matching between the cylindrical assembly unit and zeolite framework is crucial for mesostructure construction. Be there or be square: A surfactant with a hydrophobic tail and a diquaternary ammonium head group assembles into cylindrical units that can be used for template synthesis of an ordered 2D mesoporous MFI zeolite. The resultant zeolite possesses tetragonal morphology and quaternary, ordered, straight, square channels framed by thin zeolite sheets.
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Shape-Controllable and Fluorescent Supramolecular Organic Frameworks Through Aqueous Host–Guest Complexation ()
Two kinds of shape-controllable and fluorescent supramolecular organic frameworks (cuboid or spheroid) are constructed hierarchically from CB[8] and tetraphenylethylene derivatives through host–guest interaction in water. These two fluorescent SOFs exhibit intriguing and varied photophysical properties, including large red-shifts (up to 82 nm) and stimuli-responsive behavior to competitive guest by binding with CB[8], the turn-on fluorescence of which is applied in cellular imaging. Controlling the shapes: Shape-controllable supramolecular organic frameworks (cuboids and spheroids) were constructed hierarchically using the supramolecular assembly between CB[8] and tetraphenylethene derivatives with different linkers. Significantly, these supramolecular organic frameworks exhibit stimuli-responsive turn-on fluorescence, which is used for potential application in cell imaging.
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Quaternary β2,2-Amino Acids: Catalytic Asymmetric Synthesis and Incorporation into Peptides by Fmoc-Based Solid-Phase Peptide Synthesis ()
β-Amino acid incorporation has emerged as a promising approach to enhance the stability of parent peptides and to improve their biological activity. Owing to the lack of reliable access to β2,2-amino acids in a setting suitable for peptide synthesis, most contemporary research efforts focus on the use of β3- and certain β2,3-amino acids. Herein, we report the catalytic asymmetric synthesis of β2,2-amino acids and their incorporation into peptides by Fmoc-based solid-phase peptide synthesis (Fmoc-SPPS). A quaternary carbon center was constructed by the palladium-catalyzed decarboxylative allylation of 4-substituted isoxazolidin-5-ones. The N−O bond in the products not only acts as a traceless protecting group for β-amino acids but also undergoes amide formation with α-ketoacids derived from Fmoc-protected α-amino acids, thus providing expeditious access to α-β2,2-dipeptides ready for Fmoc-SPPS. A beta way to better peptides: The incorporation of β-amino acids can enhance the stability of parent peptides and improve their biological activity. A method based on catalytic asymmetric allylation has now been developed for the synthesis of otherwise inaccessible β2,2-amino acids in a setting suitable for peptide synthesis. The products were used for the solid-phase synthesis of hybrid α/β peptides (see picture).
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Mono- and Bis(imidazolidinium ethynyl) Cations and Reduction of the Latter To Give an Extended Bis-1,4-([3]Cumulene)-p-carboquinoid System ()
An extended π-system containing two [3]cumulene fragments separated by a p-carboquinoid and stabilized by two capping N-heterocyclic carbenes (NHCs) has been prepared. Mono- and bis(imidazolidinium ethynyl) cations have also been synthesized from the reaction of an NHC with phenylethynyl bromide or 1,4-bis(bromoethynyl)benzene. Cyclic voltammetry coupled with synthetic and structural studies showed that the dication is readily reduced to a neutral, singlet bis-1,4-([3]cumulene)-p-carboquinoid as a result of the π-accepting properties of the capping NHCs. Accumulating cumulenes: Two-electron reduction of a bis(imidazolidinium ethynyl) dication derived from an N-heterocyclic carbene (NHC) and 1,4-bis(bromoethynyl)benzene gave the extended bis-1,4-([3]cumulene)-p-carboquinoid 1 with no change in the overall distance between the NHC moieties. Cyclic voltammetry coupled with synthetic and structural studies showed that the π-accepting properties of the capping NHCs may play a role in the reduction of the dication.
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Martin Pumera ()

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Molecular Magnesium Hydrides ()
Solid magnesium hydride [MgH2]∞ has been pursued as a potential hydrogen-storage material. Organic chemists were rather interested in soluble magnesium hydride reagents from mid-20th century. It was only in the last two decades that molecular magnesium hydride chemistry received a major boost from organometallic chemists with a series of structurally well-characterized examples that continues to build a whole new class of compounds. More than 40 such species have been isolated, ranging from mononuclear terminal hydrides to large hydride clusters with more than 10 magnesium atoms. They provide not only insights into the structure and bonding of Mg−H motifs, but also serve as models for hydrogen-storage materials. Some of them are also recognized to participate in catalytic transformations, such as hydroelementation. Herein, an overview of these molecular magnesium hydrides is given, focusing on their synthesis and structural characterization. Searching for the right size: Molecular magnesium hydrides, including larger clusters have been studied as potential hydrogen-storage materials. An overview of structurally well-defined molecular magnesium hydrides including larger clusters are compiled with emphasis on their synthesis, characterization, and properties.
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Alkene 1,2-Difunctionalization by Radical Alkenyl Migration ()
Transition-metal-free radical α-perfluoroalkylation with the accompanying vicinal β-alkenylation of unactivated alkenes is presented. These radical cascades proceed by means of 1,4- or 1,5-alkenyl migration by electron catalysis on readily accessed allylic alcohols. The reactions comprise a regioselective perfluoroalkyl radical addition with subsequent alkenyl migration and concomitant deprotonation to generate a ketyl radical anion that sustains the chain as a single-electron-transfer reducing reagent. Electron-catalyzed transition-metal-free β-alkenylation-α-perfluoroalkylation of unactivated alkenes by radical 1,4- or 1,5-alkenyl migration is presented. Remote radical alkenyl migration is currently not established in synthetic methodology and this communication documents its potential. DABCO=1,4-diazabicyclo[2.2.2]octane; DCE=dichloroethane.
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General and Facile Route to Isomerically Pure Tricyclic Peptides Based on Templated Tandem CLIPS/CuAAC Cyclizations ()
We report a one-pot ligation/cyclization technology for the rapid and clean conversion of linear peptides into tricyclic peptides that is based on using tetravalent scaffolds containing two benzyl bromide and two alkyne moieties. These react via CLIPS/CuAAC reactions with cysteines and azides in the peptide. Flexibility in the scaffolds is key to the formation of isomerically pure products as the flexible scaffolds T41 and T42 mostly promote the formation of single isomeric tricycles while the rigid scaffolds T43 and T44 do not yield clean products. There seems to be no limitation to the number and types of amino acids present as 18 canonical amino acids were successfully implemented. We also observed that azides at the peptide termini and cysteine residues in the center gave better results than compounds with the functional groups placed the other way round. Rotatable tetravalent scaffolds containing two bromomethyl and two alkyne moieties are reported that enable the locking of linear peptides containing two cysteine and two azidohomoalanine (Aha) residues into tricyclic topologies via one-pot ligation/cyclization (CLIPS=chemical linkage of peptides onto scaffolds).
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Hierarchical Hollow Nanoprisms Based on Ultrathin Ni-Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution ()
The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water-splitting cells and metal–air batteries. Ni-Fe layered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes. The rational design of advanced nanostructures for Ni-Fe LDHs is highly desirable to optimize their electrocatalytic performance. Herein, we report a facile self-templated strategy for the synthesis of novel hierarchical hollow nanoprisms composed of ultrathin Ni-Fe LDH nanosheets. Tetragonal nanoprisms of nickel precursors were first synthesized as the self-sacrificing template. Afterwards, these Ni precursors were consumed during the hydrolysis of iron(II) sulfate for the simultaneous growth of a layer of Ni-Fe LDH nanosheets on the surface. The resultant Ni-Fe LDH hollow prisms with large surface areas manifest high electrocatalytic activity towards the OER with low overpotential, small Tafel slope, and remarkable stability. A self-templated strategy enables the synthesis of hierarchical hollow nanoprisms composed of ultrathin Ni-Fe layered double hydroxide (LDH) nanosheets. During the hydrolysis of iron(II) sulfate, prism-like Ni precursors are dissolved and converted into a shell of Ni-Fe LDH on their surface. Owing to structural and compositional advantages, these hollow nanoprisms display enhanced electrochemical activity in the oxygen evolution reaction.
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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.
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Jan C. M van Hest ()

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Near-Infrared Light-Driven Hydrogen Evolution from Water Using a Polypyridyl Triruthenium Photosensitizer ()
The evolution of H2 by near-infrared light irradiation is an unprecedented phenomenon that makes use of an extended wavelength range of the solar spectrum. In their Communication (DOI: 10.1002/anie.201708996), K. Sakai et al. report photocatalytic H2 evolution using a polypyridyl triruthenium photosensitizer with light-harvesting properties. The photosensitizer promotes H2 evolution under light irradiation at 700–800 nm.
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Integrated Transmission Electron and Single-Molecule Fluorescence Microscopy Correlates Reactivity with Ultrastructure in a Single Catalyst Particle ()
Two “superheroes” in high-resolution chemical imaging, namely single-molecule fluorescence microscopy and transmission electron microscopy, have been combined in the same set-up to facilitate correlative analysis. In their Communication (DOI: 10.1002/anie.201709723), H. C. Gerritsen, B. M. Weckhuysen et al. show the validity of this approach by studying structure–activity relationships in a single catalyst particle. Differences in reactivity exist among active components with identical structural features.
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Microtubular Self-Assembly of Covalent Organic Frameworks ()
Despite significant progress in the synthesis of covalent organic frameworks (COFs), reports on the precise construction of template-free nano- and microstructures of such materials have been rare. In the quest for dye-containing porous materials, a novel conjugated framework DPP-TAPP-COF with an enhanced absorption capability up to λ=800 nm has been synthesized by utilizing reversible imine condensations between 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) and a diketopyrrolopyrrole (DPP) dialdehyde derivative. Surprisingly, the obtained COF exhibited spontaneous aggregation into hollow microtubular assemblies with outer and inner tube diameters of around 300 and 90 nm, respectively. A detailed mechanistic investigation revealed the time-dependent transformation of initial sheet-like agglomerates into the tubular microstructures. Rolling up the COFs: Tetraphenylporphyrins and diketopyrrolopyrroles have been incorporated as functional dye components in covalent organic frameworks by means of reversible imine condensations. Upon formation, these crystalline polymers spontaneously self-assemble to form hollow microtubes.
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Abderrahmane Amgoune ()

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A π-Conjugation Extended Viologen as a Two-Electron Storage Anolyte for Total Organic Aqueous Redox Flow Batteries ()
Extending the conjugation of viologen by a planar thiazolo[5,4-d]thiazole (TTz) framework and functionalizing the pyridinium with hydrophilic ammonium groups yielded a highly water-soluble π-conjugation extended viologen, 4,4′-(thiazolo[5,4-d]thiazole-2,5-diyl)bis(1-(3-(trimethylammonio)propyl)pyridin-1-ium) tetrachloride, [(NPr)2TTz]Cl4 , as a novel two-electron storage anolyte for aqueous organic redox flow battery (AORFB) applications. Its physical and electrochemical properties were systematically investigated. Paired with 4-trimethylammonium-TEMPO (NMe-TEMPO) as catholyte, [(NPr)2TTz]Cl4 enables a 1.44 V AORFB with a theoretical energy density of 53.7 Wh L−1. A demonstrated [(NPr)2TTz]Cl4/NMe-TEMPO AORFB delivered an energy efficiency of 70 % and 99.97 % capacity retention per cycle. On the fast track: A highly water-soluble π-conjugation extended viologen has been developed as a novel two-electron storage anolyte to enable a 1.44 V total organic neutral aqueous redox flow battery.
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Martin D. Smith ()

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Solubility-Parameter-Guided Solvent Selection to Initiate Ostwald Ripening for Interior Space-Tunable Structures with Architecture-Dependent Electrochemical Performance ()
Despite significant advancement in preparing various hollow structures by Ostwald ripening, one common problem is the intractable uncontrollability of initiating Ostwald ripening due to the complexity of the reaction processes. Here, a new strategy on Hansen solubility parameter (HSP)-guided solvent selection to initiate Ostwald ripening is proposed. Based on this comprehensive principle for solvent optimization, N,N-dimethylformamide (DMF) was screened out, achieving accurate synthesis of interior space-tunable MoSe2 spherical structures (solid, core–shell, yolk-shell and hollow spheres). The resultant MoSe2 structures exhibit architecture-dependent electrochemical performances towards hydrogen evolution reaction and sodium-ion batteries. This pre-solvent selection strategy can effectively provide researchers great possibility in efficiently synthesizing various hollow structures. This work paves a new pathway for deeply understanding Ostwald ripening. Hollow inorganic structures: Solubility-parameter-guided solvent selection to initiate Ostwald ripening has been used to achieve accurate synthesis of interior space-tunable MoSe2 hollow structures in N,N-dimethylformamide. The resultant MoSe2 structures show closely architecture-dependent electrochemical performances towards hydrogen evolution reaction and sodium-ion batteries.
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The Narrowest Band Gap Ever Observed in Molecular Ferroelectrics: Hexane-1,6-diammonium Pentaiodobismuth(III) ()
Narrow band gaps and excellent ferroelectricity are intrinsically paradoxical in ferroelectrics as the leakage current caused by an increase in the number of thermally excited carriers will lead to a deterioration of ferroelectricity. A new molecular ferroelectric, hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5), was now developed through band gap engineering of organic–inorganic hybrid materials. It features an intrinsic band gap of 1.89 eV, and thus represents the first molecular ferroelectric with a band gap of less than 2.0 eV. Simultaneously, low-temperature solution processing was successfully applied to fabricate high-quality ferroelectric thin films based on HDA-BiI5, for which high-precision controllable domain flips were realized. Owing to its narrow band gap and excellent ferroelectricity, HDA-BiI5 can be considered as a milestone in the exploitation of molecular ferroelectrics, with promising applications in high-density data storage and photovoltaic conversion. The molecular ferroelectric hexane-1,6-diammonium pentaiodobismuth displays a narrow band gap of 1.89 eV. Low-temperature solution processing enabled the fabrication of high-quality flexible ferroelectric thin films.
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Nanoscale Trimetallic Metal–Organic Frameworks Enable Efficient Oxygen Evolution Electrocatalysis ()
Metal–organic frameworks (MOFs) are a class of promising materials for diverse heterogeneous catalysis, but they are usually not directly employed for oxygen evolution electrocatalysis. Most reports focus on using MOFs as templates to in situ create efficient electrocatalysts through annealing. Herein, we prepared a series of Fe/Ni-based trimetallic MOFs (Fe/Ni/Co(Mn)-MIL-53 accordingly to the Material of Institute Lavoisier) by solvothermal synthesis, which can be directly adopted as highly efficient electrocatalysts. The Fe/Ni/Co(Mn)-MIL-53 shows a volcano-type oxygen evolution reaction (OER) activity as a function of compositions. The optimized Fe/Ni2.4/Co0.4-MIL-53 can reach a current density of 20 mA cm−2 at low overpotential of 236 mV with a small Tafel slope of 52.2 mV dec−1. In addition, the OER performance of these MOFs can be further enhanced by directly being grown on nickel foam (NF). Multimetallic MOFs with modulated compositions have been successfully synthesized and directly adopted as efficient oxygen evolution reaction (OER) catalysts (MOFs=metal–organic frameworks). The Fe/Ni/Co/(Mn)-MIL-53 catalyst exhibits a volcano-type OER activity as a function of compositions. The optimized Fe/Ni/Mn0.4-MIL-53/NF catalyst is highly active and ultrastable towards OER catalysis.
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Total Synthesis of (6R,10R,13R,14R,16R,17R,19S,20R,21R,24S, 25S,28S,30S,32R,33R,34R,36S,37S,39R)-Azaspiracid-3 Reveals Non-Identity with the Natural Product ()
A convergent and stereoselective total synthesis of the previously assigned structure of azaspiracid-3 has been achieved by a late-stage Nozaki–Hiyama–Kishi coupling to form the C21−C22 bond with the C20 configuration unambiguously established from l-(+)-tartaric acid. Postcoupling steps involved oxidation to an ynone, modified Stryker reduction of the alkyne, global deprotection, and oxidation of the resulting C1 primary alcohol to the carboxylic acid. The synthetic product matched naturally occurring azaspiracid-3 by mass spectrometry, but differed both chromatographically and spectroscopically. A convergent and stereospecific total synthesis of the previously assigned structure of the marine neurotoxin azaspiracid-3 reveals non-identity with the natural product. Therefore structural revision of the primary azaspiracids is necessary.
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Ronald Breslow (1931–2017) ()
Ronald Breslow, Samuel Latham Mitchill Professor of Chemistry at Columbia University, passed away on October 25, 2017, at the age of 86. Breslow made remarkable contributions to the fields of physical-organic and bioorganic chemistry, including biological and biomimetic transformations, and the use of molecular recognition to control reaction selectivity.
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Evidence for Triplet Sensitization in the Visible-Light-Induced [2+2] Photocycloaddition of Eniminium Ions ()
Εniminium ions were prepared from the corresponding α,β-unsaturated carbonyl compounds (enones and enals), and were found to be promoted to their respective triplet states by energy transfer. The photoexcited intermediates underwent intra- or intermolecular [2+2] photocycloaddition in good yields (50–78 %) upon irradiation at λ=433 nm or λ=457 nm. Iridium or ruthenium complexes with a sufficiently high triplet energy were identified as efficient catalysts (2.5 mol % catalyst loading) for the reaction. The intermolecular [2+2] photocycloaddition of an eniminium ion derived from a chiral secondary amine proceeded with high enantioselectivity (88 % ee). The energy is the limit: The [2+2] photocycloaddition of iminium ions 1 is catalyzed by iridium or ruthenium complexes and proceeds via triplet energy transfer. The intermediate iminium ions 2 are hydrolyzed to the respective carbonyl compounds such as aldehyde 3, which was formed in 78 % yield from a chiral eniminium ion precursor.
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Total Synthesis of (+)-Sarcophytin ()
A total synthesis of the cembranoid (+)-sarcophytin is presented, featuring a Diels–Alder cycloaddition of an enone as the dienophile with an ester-derived dienoate. The study highlights a peculiar geometric preference for the Z dienoate to furnish the cycloadduct. The endgame involves a reaction cascade, including lactone opening, alcohol oxidation, and ketone epimerization to complete an efficient synthesis. A salient feature of the synthesis is the resulting reassignment of the absolute configuration, which corrects the previously reported nominal structure. All right now: A total synthesis of the cembranoid (+)-sarcophytin is presented, featuring a Diels–Alder cycloaddition of an enone and Z dienoate. A reaction cascade, including lactone opening, alcohol oxidation, and ketone epimerization, completes an efficient synthesis. Reassignment of the absolute configuration of the natural product corrects the previously reported nominal structure.
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Live-Cell Protein Sulfonylation Based on Proximity-driven N-Sulfonyl Pyridone Chemistry ()
The development of bioorthogonal approaches for labeling of endogenous proteins under the multimolecular crowding conditions of live cells is highly desirable for the analysis and engineering of proteins without using genetic manipulation. N-Sulfonyl pyridone (SP) is reported as a new reactive group for protein sulfonylation. The ligand-directed SP chemistry was able to modify not only purified proteins in vitro, but also endogenous ones on the surface of and inside live cells selectively and rapidly, which allowed to convert endogenous proteins to FRET-based biosensors in situ. Ligand-directed N-sulfonyl pyridone chemistry afforded the specific sulfonylation of endogenous proteins without disturbing their original nature. This chemical strategy allowed the simple conversion of endogenous proteins in live cell habitats into semisynthetic FRET biosensors for the analysis of the dynamic process in protein–ligand (small molecule) interactions.
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Ultrathin Graphdiyne Nanosheets Grown In Situ on Copper Nanowires and Their Performance as Lithium-Ion Battery Anodes ()
A method is presented for the scalable preparation of high-quality graphdiyne nanotubes and ultrathin graphdiyne nanosheets (average thickness: ca. 1.9 nm) using Cu nanowires as a catalyst. For the storage of Li+ ions, the graphdiyne nanostructures show a high capacity of 1388 mAh g−1 and high rate performance (870 mA h g−1 at 10 A g−1, and 449.8 mA h g−1 at 20 A g−1) with robust stability, demonstrating outstanding overall potential for its applications. A copper nanowire was used for large-scale preparation of ultrathin graphdiyne nanosheets (1.9 nm), and the growth properties were investigated. The ability of the ultrathin graphdiyne nanosheets to store lithium ions was impressive (1380 mAh g−1). Diffusion: in-plane (blue arrow), out-of-plane (red).
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CO Hydrogenation on Cobalt-Based Catalysts: Tin Poisoning Unravels CO in Hollow Sites as a Main Surface Intermediate ()
Site poisoning is a powerful method to unravel the nature of active sites or reaction intermediates. The nature of the intermediates involved in the hydrogenation of CO was unraveled by poisoning alumina-supported cobalt catalysts with various concentrations of tin. The rate of formation of the main reaction products (methane and propylene) was found to be proportional to the concentration of multi-bonded CO, likely located in hollow sites. The specific rate of decomposition of these species was sufficient to account for the formation of the main products. These hollow-CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions used here, while linear CO are mostly spectators. Site poisoning by tin was used to reveal the nature of the intermediates involved in CO hydrogenation on alumina-supported cobalt catalysts. The rate of formation of methane and propylene was proportional to the concentration of multiply bonded CO, likely located in hollow sites. These CO are proposed to be main reaction intermediates in the hydrogenation of CO under the reaction conditions, while linear CO are mostly spectators.
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Photoactivated N-Acyliminoiodinanes Applied to Amination: an ortho-Methoxymethyl Group Stabilizes Reactive Precursors ()
N-Acyliminoiodinanes were characterized for the first time by X-ray structural analysis. The ortho-methoxymethyl group and the carbonyl oxygen coordinate to the iodine atom of the iminoiodinane. Activation of the N-acyliminoiodinane was achieved by photoirradiation at 370 nm, thereby enabling reaction with various silyl enol ethers to give α-aminoketone derivatives in good to high yield. N-sulfonyliminoiodinanes bearing ortho substituents were used in photoinduced amination. N-Acyliminoiodinanes stabilized by an ortho-methoxymethyl group are activated toward reactivity with various silyl enol ethers upon photoirradiation (370 nm), and produce α-aminoketone derivatives in good to high yield. The photoinduced amination reaction extends to N-sulfonyliminoiodinanes bearing ortho substituents. PG=protecting group.
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Hierarchical Hollow Nanoprisms Based on Ultrathin Ni-Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution ()
Ni-Fe layered double hydroxides (LDHs) are promising oxygen evolution reaction (OER) electrocatalysts in alkaline electrolytes. In their Communication (DOI: 10.1002/anie.201710877), X. W. Lou and co-workers report a facile self-templated strategy for the synthesis of hierarchical hollow nanoprisms composed of ultrathin Ni-Fe LDH nanosheets. These hollow prisms with large surface areas display high electrocatalytic activity towards the OER, with a low overpotential, a small Tafel slope, and remarkable stability.
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Stephan Irle ()

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A Metal–Organic Framework with Exceptional Activity for C−H Bond Amination ()
The development of catalysts capable of fast, robust C−H bond amination under mild conditions is an unrealized goal despite substantial progress in the field of C−H activation in recent years. A Mn-based metal–organic framework (CPF-5) is described that promotes the direct amination of C−H bonds with exceptional activity. CPF-5 is capable of functionalizing C−H bonds in an intermolecular fashion with unrivaled catalytic stability producing >105 turnovers. A Mn-based MOF (metal–organic framework) with a unique active site catalyzes C−H amination under mild conditions. Importantly, the catalyst displays an exceptional and unprecedented TON of >120 000, which is about 4 orders of magnitude greater than any other state-of-the-art C−H amination catalysts.
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Three-Component Enantioselective Cyclization Reaction Catalyzed by an Unnatural Amino Acid Derivative ()
A new diastereo- and enantioselective three-component cyclization reaction is described. The reaction takes place between a ketone, a carboxylic acid, and a nitroalkene to yield a bicyclic octahydro-2H-indol-2-one scaffold possessing three chiral centers. This reaction involves a rearrangement of the nitro group under simple thermal conditions. A plausible mechanism is proposed for this new reaction based on DFT calculations and isotope-labeling experiments. A new concise enantioselective synthesis of the alkaloid (+)-pancracine is presented as an example of the potential of this novel organocatalytic cyclization reaction in the synthesis of natural products. Brand new cycle: The unnatural and densely substituted l-proline ester XL catalyzes the formation of bicyclic γ-lactams possessing three new chiral centers. This new reaction has no equivalent in organocatalytic, enzymatic, or organometallic chemistry and can be used in the synthesis of complex natural products.
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The Chemical Record Lectureship for Michael Grätzel / Baizer Award for Flavio Maran / And also in the News ()

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A General Synthesis of Porous Carbon Nitride Films with Tunable Surface Area and Photophysical Properties ()
Graphitic carbon nitride (g-CN) has emerged as a promising material for energy-related applications. However, exploitation of g-CN in practical devices is still limited owing to difficulties in fabricating g-CN films with adjustable properties and high surface area. A general and simple pathway is reported to grow highly porous and large-scale g-CN films with controllable chemical and photophysical properties on various substrates using the doctor blade technique. The growth of g-CN films, ascribed to the formation of a supramolecular paste, comprises g-CN monomers in ethylene glycol, which can be cast on different substrates. The g-CN composition, porosity, and optical properties can be tuned by the design of the supramolecular paste, which upon calcination results in a continuous porous g-CN network. The strength of the porous structure is demonstrated by high electrochemically active surface area, excellent dye adsorption and photoelectrochemical and photodegradation properties. An efficient, easy, and general method for growing highly porous and large-scale carbon nitride (g-CN) networks on various substrates using the doctor blade technique is introduced. The g-CN films have high electrochemical active surface area, excellent dye adsorption, and good photoelectrochemical and photodegradation properties. This method opens opportunities for exploitation of g-CN in electronic and photoelectronic devices.
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Ion–Solvent Complexes Promote Gas Evolution from Electrolytes on a Sodium Metal Anode ()
Lithium and sodium metal batteries are considered as promising next-generation energy storage devices due to their ultrahigh energy densities. The high reactivity of alkali metal toward organic solvents and salts results in side reactions, which further lead to undesirable electrolyte depletion, cell failure, and evolution of flammable gas. Herein, first-principles calculations and in situ optical microscopy are used to study the mechanism of organic electrolyte decomposition and gas evolution on a sodium metal anode. Once complexed with sodium ions, solvent molecules show a reduced LUMO, which facilitates the electrolyte decomposition and gas evolution. Such a general mechanism is also applicable to lithium and other metal anodes. We uncover the critical role of ion–solvent complexation for the stability of alkali metal anodes, reveal the mechanism of electrolyte gassing, and provide a mechanistic guidance to electrolyte and lithium/sodium anode design for safe rechargeable batteries. Safe rechargeable batteries: Ion–solvent complexes in alkali metal batteries have been studied by first-principles calculations and in situ optical microscopy. The ion–solvent complexes have low LUMOs and are readily reduced on an alkali metal anode. A general mechanism for organic electrolyte decomposition and gas evolution was discovered.
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A Six-Oxidase Cascade for Tandem C−H Bond Activation Revealed by Reconstitution of Bicyclomycin Biosynthesis ()
As a commercial antibiotic, bicyclomycin (BCM) is currently the only known natural product targeting the transcription termination factor rho. It belongs to a family of highly functionalized diketopiperazine (DKP) alkaloids and bears a unique O-bridged bicyclo[4.2.2]piperazinedione ring system, a C1 triol, and terminal exo-methylene groups. We have identified and characterized the BCM biosynthetic pathway by heterologous biotransformations, in vitro biochemical assays, and one-pot enzymatic synthesis. A tRNA-dependent cyclodipeptide synthase guides the heterodimerization of leucine and isoleucine to afford the DKP precursor; subsequently, six redox enzymes, including five α-ketoglutarate/Fe2+-dependent dioxygenases and one cytochrome P450 monooxygenase, regio- and stereoselectively install four hydroxy groups (primary, secondary, and two tertiary), an exo-methylene moiety, and a medium-sized bridged ring through the functionalization of eight unactivated C−H bonds. Enzymatic characterization of the biosynthesis of the antibiotic bicyclomycin revealed a tRNA-dependent cyclodipeptide synthase for the heterodimerization of Leu and Ile to afford the diketopiperazine precursor. Subsequently, six redox enzymes activate eight unactivated C−H bonds through regio- and stereoselective hydroxylation, alkenylation, heterocyclization, and desaturation/epoxidation.
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Can Coordination-Driven Supramolecular Self-Assembly Reactions Be Conducted from Fully Aliphatic Linkers? ()
The reaction between a preassembled CuI bimetallic molecular clip with a short intermetallic distance and a series of fully aliphatic cyano-capped ditopic linkers with increasing lengths was investigated. It is shown that, depending on the length of the ditopic linkers, the rational design of unprecedented supramolecular compact metallacycles containing fully aliphatic walls is possible. The specific preorganized molecular arrangement of the molecular clip used favors stabilizing interlinker London dispersion interactions, which allow, as the length of the linkers increases, the selective formation of discrete compact metallacycles at the expense of 1D coordination polymers. The generalizability of this approach was demonstrated by the reaction of fully aliphatic cyano-capped linkers with two other types of preassembled CuI bimetallic molecular clips that also had short intermetallic distances. Give them a sense of direction: Cyano-capped fully aliphatic linkers underwent supramolecular assembly with preorganized CuI dimers with short intermetallic distances to form different types of metallacycles and 1D coordination polymers depending on the length of the linkers (see picture). Stabilizing London dispersion interactions between the methylene units made the selective self-assembly of such linkers with nondirectional backbones possible.
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Asymmetric Synthesis of 2H-Azirines with a Tetrasubstituted Stereocenter by Enantioselective Ring Contraction of Isoxazoles ()
Highly strained 2H-azirines with a tetrasubstituted stereocenter were synthesized by the enantioselective isomerization of isoxazoles with a chiral diene–rhodium catalyst system. The effect of ligands and the coordination behavior support the proposed catalytic cycle in which the coordination site is fixed in favor of efficient enantiodiscrimination by a bulky substituent of the ligand. In silico studies also support the existence of a rhodium–imido complex as a key intermediate for enantiodiscrimination. Coping well under the strain: Highly strained 2H-azirines with tetrasubstituted stereocenters were synthesized with high enantioselectivity by the N−O bond-cleaving isomerization of isoxazoles in the presence of a chiral diene–rhodium catalyst (see scheme). This asymmetric ring contraction of isoxazoles proceeded under mild reaction conditions to give 2-alkoxycarbonyl 2H-azirines with various substituents, including halogen groups.
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Distal Weak Coordination of Acetamides in Ruthenium(II)-Catalyzed C−H Activation Processes ()
C−H activations with challenging arylacetamides were accomplished by versatile ruthenium(II) biscarboxylate catalysis. The distal C−H functionalization offers ample scope—including twofold oxidative C−H functionalizations and alkyne hydroarylations—through facile base-assisted internal electrophilic-type substitution (BIES) C−H ruthenation by weak O-coordination. From a distance: A versatile RuII-catalyzed method permits facile distal C−H activation of weakly O-coordinating arylacetamides via a six-membered ruthenacycle intermediate. The scope of the reaction includes primary, secondary, and tertiary amides.
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Enantioselective Synthesis of N,S-Acetals by an Oxidative Pummerer-Type Transformation using Phase-Transfer Catalysis ()
Reported is the first enantioselective oxidative Pummerer-type transformation using phase-transfer catalysis to deliver enantioenriched sulfur-bearing heterocycles. This reaction includes the direct oxidation of sulfides to a thionium intermediate, followed by an asymmetric intramolecular nucleophilic addition to form chiral cyclic N,S-acetals with moderate to high enantioselectivites. Deuterium-labelling experiments were performed to identify the stereodiscrimination step of this process. Further analysis of the reaction transition states, by means of multidimensional correlations and DFT calculations, highlight the existence of a set of weak noncovalent interactions between the catalyst and substrate that govern the enantioselectivity of the reaction. Aye, aye, CAPT: The first catalytic enantioselective Pummerer-type transformation has been developed employing chiral-anion phase-transfer catalysis (CAPT). This chemical transformation allows facile construction of a wide variety of enantioenriched cyclic N,S-acetal motifs which were previously difficult to access.
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On the Use of Polyelectrolytes and Polymediators in Organic Electrosynthesis ()
Although organic electrosynthesis is generally considered to be a green method, the necessity for excess amounts of supporting electrolyte constitutes a severe drawback. Furthermore, the employment of redox mediators results in an additional separation problem. In this context, we have explored the applicability of soluble polyelectrolytes and polymediators with the TEMPO-mediated transformation of alcohols into carbonyl compounds as a test reaction. Catalyst benchmarking based on cyclic voltammetry studies indicated that the redox-active polymer can compete with molecularly defined TEMPO species. Alcohol oxidation was also highly efficient on a preparative scale, and our polymer-based approach allowed for the separation of both mediator and supporting electrolyte in a single membrane filtration step. Moreover, we have shown that both components can be reused multiple times. Combining electrosynthesis with membrane filtration: The attachment of a TEMPO mediator and a supporting electrolyte to soluble polymers enables the selective anodic conversion of alcohols into carbonyl compounds and allows for efficient recovery/recycling of the mediator and the salt by membrane filtration.
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Desktop NMR and Its Applications From Materials Science To Organic Chemistry ()
NMR spectroscopy is an indispensable method of analysis in chemistry, which until recently suffered from high demands for space, high costs for acquisition and maintenance, and operational complexity. This has changed with the introduction of compact NMR spectrometers suitable for small-molecule analysis on the chemical workbench. These spectrometers contain permanent magnets giving rise to proton NMR frequencies between 40 and 80 MHz. The enabling technology is to make small permanent magnets with homogeneous fields. Tabletop instruments with inhomogeneous fields have been in use for over 40 years for characterizing food and hydrogen-containing materials by relaxation and diffusion measurements. Related NMR instruments measure these parameters in the stray field outside the magnet. They are used to inspect the borehole walls of oil wells and to test objects nondestructively. The state-of-the-art of NMR spectroscopy, imaging and relaxometry with compact instruments is reviewed. NMR spectroscopy is known not only for its outstanding analytical power but also for the large size and costs of the instruments. In recent years, the family of instruments with bulky superconducting magnets has been complemented with compact tabletop and portable devices suitable for small-molecule analysis and nondestructive materials testing. The state of the art of compact NMR instruments is reviewed and illustrated with selected examples.
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Computational Chemistry: The Fate of Current Methods and Future Challenges ()
“Where do we go from here?” is the underlying question regarding the future (perhaps foreseeable) developments in computational chemistry. Although this young discipline has already permeated practically all of chemistry, it is likely to become even more powerful with the rapid development of computational hard- and software.
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Macrolide Synthesis through Intramolecular Oxidative Cross-Coupling of Alkenes ()
A RhIII-catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized reaction conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This method provides an efficient approach to synthesize macrocyclic compounds containing a 1,3-conjugated diene structure. Two pair: A RhIII-catalyzed intramolecular oxidative cross-coupling between double bonds for the synthesis of macrolides is described. Under the optimized conditions, macrocycles containing a diene moiety can be formed in reasonable yields and with excellent chemo- and stereoselectivity. This provides efficient access to macrocyclic compounds containing 1,3-conjugated dienes.
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Highly Branched Polymers with Layered Structures that Mimic Light-Harvesting Processes ()
Hyperbranched polymers (HBPs) with decorated donor and acceptor chromophores in different domains were constructed to demonstrate the function of light harvesting in a polymeric nanostructure. Taking advantage of our recently developed chain-growth copper-catalyzed azide–alkyne cycloaddition polymerization, two structural parameters in the HBPs, for example, the molar ratio of the acceptor Coumarin 343 in the core to the donor Coumarin 2 on the periphery, and the average distance between these two layers, could be independently varied in a one-pot synthesis. The results demonstrated an efficient energy transfer from the excited Coumarin 2 to the ground-state Coumarin 343 in the core, with the efficiency of the energy transfer reaching as high as 98 %. The excited Coumarin 343, after receiving energy from donor Coumarin 2 emitted higher fluorescence intensity than when directly excited, indicating an observed light concentration effect from the periphery dye to the central dye in one polymer structure. Hyperbranched polymers (HBPs) with decorated donor (Coumarin 2, C2) and acceptor (Coumarin 343, C343) chromophores in different domains were constructed by chain-growth copper-catalyzed azide–alkyne cycloaddition polymerization (CuAACP) to demonstrate the function of light harvesting in a polymeric nanostructure. The efficiency of the energy transfer extended up to 98 %.
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Triple Bonds Between Iron and Heavier Group 15 Elements in AFe(CO)3− (A=As, Sb, Bi) Complexes ()
Heteronuclear transition-metal–main-group-element carbonyl complexes of AsFe(CO)3−, SbFe(CO)3−, and BiFe(CO)3− were produced by a laser vaporization supersonic ion source in the gas phase, and were studied by mass-selected IR photodissociation spectroscopy and advanced quantum chemistry methods. These complexes have C3v structures with all of the carbonyl ligands bonded on the iron center, and feature covalent triple bonds between bare Group 15 elements and Fe(CO)3−. Chemical bonding analyses on the whole series of AFe(CO)3− (A=N, P, As, Sb, Bi, Mc) complexes indicate that the valence orbitals involved in the triple bonds are hybridized 3d and 4p atomic orbitals of iron, leading to an unusual (dp–p) type of transition-metal–main-group-element multiple bonding. The σ-type three-orbital interaction between Fe 3d/4p and Group 15 np valence orbitals plays an important role in the bonding and stability of the heavier AFe(CO)3− (A=As, Sb, Bi) complexes. Going for the triple: IR photodissociation spectroscopy and quantum chemical calculations were performed on the complexes AFe(CO)3− (A=As, Sb, Bi). These studies reveal that the complexes contain a (dp–p) type of A−Fe triple bonding.
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Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate ()
The magnetic actuation of deposited drops has mainly relied on volume forces exerted on the liquid to be transported, which is poorly efficient with conventional diamagnetic liquids such as water and oil, unless magnetosensitive particles are added. Herein, we describe a new and additive-free way to magnetically control the motion of discrete liquid entities. Our strategy consists of using a paramagnetic liquid as a deformable substrate to direct, using a magnet, the motion of various floating liquid entities, ranging from naked drops to liquid marbles. A broad variety of liquids, including diamagnetic (water, oil) and nonmagnetic ones, can be efficiently transported using the moderate magnetic field (ca. 50 mT) produced by a small permanent magnet. Complex trajectories can be achieved in a reliable manner and multiplexing potential is demonstrated through on-demand drop fusion. Our paramagnetofluidic method advantageously works without any complex equipment or electric power, in phase with the necessary development of robust and low-cost analytical and diagnostic fluidic devices. Playing drops and marbles: Small magnets are used to precisely drive the motion of floating drops and liquid marbles, made of water, oil or nonmagnetic fluids, and without the use of magnetosensitive particles for the first time. Digital microfluidic operations such as transport along complex trajectories and programmed drop fusion are demonstrated.
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para-Xylene Ultra-selective Zeolite MFI Membranes Fabricated from Nanosheet Monolayers at the Air–Water Interface ()
The control of membrane morphology and microstructure is crucial to improve the separation performance of molecular-sieve membranes. This can be enabled by making thin, dense, and uniform seed-crystal coatings, which are then intergrown into continuous membranes. Herein, we show a novel and simple floating particle coating method can give closely packed monolayers of zeolite nanosheets on nonporous or porous supports. The zeolite nanosheet monolayer is formed at the air–water interface in a conical Teflon trough. As the water in the trough is drained, the monolayer is deposited on a support placed below. Membranes prepared by gel-free secondary growth of the nanosheets deposited by this method show unprecedented ultra-selective performance for separation of para- from ortho-xylene (separation factor >10 000). The membrane drain: A uniform and dense MFI nanosheet monolayer from an air–water interface is transferred onto a porous support by a new monolayer deposition method using a conical trough which drains. The high-coverage nanosheet seed coating, and subsequent intergrowth gives a thin, oriented, and low-defect-density membrane, which exhibits ultra-selective (separation factor >10 000) performance for xylene isomer separation.
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Magnetic Actuation of Drops and Liquid Marbles Using a Deformable Paramagnetic Liquid Substrate ()
Like the flow of water from a fountain, the local deformation of a paramagnetic substrate enables the gravity-driven transport of a liquid. In their Communication (DOI: 10.1002/anie.201710668), D. Baigl et al. show that, using a magnet, the deformation of the substrate (illustrated by the deformed text) allows the manipulation of drops and liquid marbles (the dots of the letters “i”). This method does not rely on magnetosensitive particles and can be used with most conventional liquids such as water or oil.
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Conformational Selection of Dimethylarginine Recognition by the Survival Motor Neuron Tudor Domain ()
Tudor domains bind to dimethylarginine (DMA) residues, which are post-translational modifications that play a central role in gene regulation in eukaryotic cells. NMR spectroscopy and quantum calculations are combined to demonstrate that DMA recognition by Tudor domains involves conformational selection. The binding mechanism is confirmed by a mutation in the aromatic cage that perturbs the native recognition mode of the ligand. General mechanistic principles are delineated from the combined results, indicating that Tudor domains utilize cation–π interactions to achieve ligand recognition. The House of Tudor: The Tudor domain of the human survival motor neuron protein selectively recognizes stereoisomers of dimethylarginine residues within its aromatic ligand-binding cage using cation–π interactions. Stereoselectivity can be modulated by a single point mutation.
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Cover Picture: Efficient Encapsulation of Fluorinated Drugs in the Confined Space of Water-Dispersible Fluorous Supraparticles (Angew. Chem. Int. Ed. 51/2017) ()
A Passion for Fluorine transport of fluorinated drugs in aqueous environments requires stable, water-dispersible carriers. In their Communication on page 16186 ff., P. Metrangolo and F. Baldelli Bombelli et al. describe a passionfruit-like supraparticle filled with fluorinated gold nanoparticles, which is coated by the vegetable protein hydrophobin II. The fluorous confined space of the supraparticle permits encapsulation of millions of fluorinated drug molecules.
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Inside Cover: Sorting of C4 Olefins with Interpenetrated Hybrid Ultramicroporous Materials by Combining Molecular Recognition and Size-Sieving (Angew. Chem. Int. Ed. 51/2017) ()
The sorting of C4 olefins is possible with a combination of molecular recognition and size-sieving effects. In their Communication on page 16282 ff. H. B. Xing and co-workers report anion-pillared hybrid interpenetrated porous materials with finely tuned cavities (the bridge tunnel) and functional sites (flowers) arranged at 0.2 Å increments. These materials exhibit outstanding performance for the separation of C4 olefins.
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Inside Back Cover: A Supramolecular Capsule for Reversible Polysulfide Storage/Delivery in Lithium-Sulfur Batteries (Angew. Chem. Int. Ed. 51/2017) ()
A supramolecular capsule that is similar to an octopus in the ocean makes possible reversible polysulfide storage and delivery in a working battery. In their Communication on page 16223 ff., Q. Zhang et al. report the introduction of cucurbit[6]uril capsules that confer high stability and high efficiency to lithium–sulfur batteries and enable high sulfur loading.
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Back Cover: The MOF+ Technique: A Significant Synergic Effect Enables High Performance Chromate Removal (Angew. Chem. Int. Ed. 51/2017) ()
Metal–organic frameworks (MOFs) used as chromium(VI) adsorbent are mainly restricted by their low adsorption capacity. F. Luo et al. show in their Communication on page 16376 ff. that the so-called MOF+ method, which relies on the surface rather than the pores of MOFs, enables ultrahigh CrVI removal of up to 796 Cr mg g−1, which is mainly due to a significant synergic effect between MOF and FeSO4.
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Frontispiece: Facile Supramolecular Processing of Carbon Nanotubes and Polymers for Electromechanical Sensors ()
Supramolecular Gels A supramolecular, non-volatile eutectic liquid can form bucky gels with carbon nanotubes upon grinding. In their Communication on page 16180 ff. S. Lee, S.-K. Lee, C. Park show the resulting viscoelastic conductor behaves as a self-healing electromechanical sensor.
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Graphical Abstract: Angew. Chem. Int. Ed. 51/2017 ()

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Corrigendum: Trace H2O2-Assisted High-Capacity Tungsten Oxide Electrochromic Batteries with Ultrafast Charging in Seconds ()

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Corrigendum: Copper-Catalyzed Synthesis of γ-Amino Acids Featuring Quaternary Stereocenters ()

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Spotlights on our sister journals: Angew. Chem. Int. Ed. 51/2017 ()

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Sensuke Ogoshi ()
“My favorite place on earth is Parker Ridge Trail in the Rocky Mountains. If I were not a scientist, I would be a lawyer ...” This and more about Sensuke Ogoshi can be found on page 16118.
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Fellows of the Electrochemical Society: C. Amatore, K. Amine, P. Atanassov, C. P. Grey, Y. Shao-Horn, and N. Wu / Priestley Medal: G. Richmond / Förderungspreis der Stadt Wien: N. Maulide ()

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Chiral Imprinting in the Gas Phase ()
Undoing the twist: Recent successful attempts to change the relative populations of two otherwise identical enantiomers of a large gas-phase molecule using resonant microwave fields are highlighted. Specifically, the population of a specific enantiomer of a chiral terpene could be enhanced relative to the other enantiomer by the application of a sequence of microwave pulses in a phase- and polarization-controlled manner.
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The Quest for Mononuclear Gold(II) and Its Potential Role in Photocatalysis and Drug Action ()
The chemistry of gold strongly focuses on the ubiquitous oxidation states +I and +III. The intermediate oxidation state +II is generally avoided in mononuclear gold species. In recent years, gold(II) has been increasingly suggested as a key intermediate in artificial photosynthesis systems, with gold(III) moieties acting as electron acceptors, as well as in gold-catalyzed photoredox catalysis and radical chemistry. This Minireview provides a concise summary of confirmed and characterized mononuclear open-shell gold(II) complexes. Recent findings on structural motifs and reactivity patterns will be discussed. Exciting developments in the fields of photosynthesis, photocatalysis, and potential roles in medicinal chemistry will be outlined. Gold(II) plays a key role in artificial photosynthesis systems, with gold(III) moieties acting as electron acceptors, as well as in gold photoredox catalysis and radical chemistry. This Minireview provides a concise summary of unambiguously characterized mononuclear gold(II) complexes along with evolving structural motifs and reactivity patterns. Developments in the fields of photosynthesis, photocatalysis, and potential modes of action of anticancer drugs are outlined.
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Selected Copper-Based Reactions for C−N, C−O, C−S, and C−C Bond Formation ()
Metal-catalyzed cross-coupling reactions belong to the most important transformations in organic synthesis. Copper catalysis has received great attention owing to the low toxicity and low cost of copper. However, traditional Ullmann-type couplings suffer from limited substrate scopes and harsh reaction conditions. The introduction of several bidentate ligands, such as amino acids, diamines, 1,3-diketones, and oxalic diamides, over the past two decades has totally changed this situation as these ligands enable the copper-catalyzed coupling of aryl halides and nucleophiles at both low reaction temperatures and catalyst loadings. The reaction scope has also been greatly expanded, rendering this copper-based cross-coupling attractive for both academia and industry. In this Review, we have summarized the latest progress in the development of useful reaction conditions for the coupling of (hetero)aryl halides with different nucleophiles. Additionally, recent advances in copper-catalyzed coupling reactions with aryl boronates and the copper-based trifluoromethylation of aromatic electrophiles will be discussed. Recent advances in copper/ligand-catalyzed cross-couplings of (hetero)aryl halides and nucleophiles, copper-catalyzed coupling reactions with aryl boronates, and copper-enabled trifluoromethylations of aromatic electrophiles are discussed in this Review.
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Facile Supramolecular Processing of Carbon Nanotubes and Polymers for Electromechanical Sensors ()
We herein report a facile, cost-competitive, and scalable method for producing viscoelastic conductors via one-pot melt-blending using polymers and supramolecular gels composed of carbon nanotubes (CNTs), diphenylamine (DP), and benzophenone (BP). When mixed, a non-volatile eutectic liquid (EL) produced by simply blending DP with BP (1:1 molar ratio) enabled not only the gelation of CNTs (EL-CNTs) but also the dissolution of a number of commodity polymers. To make use of these advantages, viscoelastic conductors were produced via one-pot melt-blending the EL and CNTs with a model thermoplastic elastomer, poly(styrene-b-butadiene-b-styrene) (SBS, styrene 30 wt %). The resulting composites displayed an excellent electromechanical sensory along with re-mendable properties. This simple method using cost-competitive EL components is expected to provide an alternative to the use of expensive ionic liquids as well as to facilitate the fabrication of novel composites for various purposes. Sense of gel: A supramolecular, non-volatile eutectic liquid (EL), consisting of diphenylamine and benzophenone, can not only dissolve many commodity polymers but also form bucky gels with CNTs upon grinding. A viscoelastic conductor composed of the EL, CNTs, and polymers was prepared by one-pot melt-blending. The resulting viscoelastic conductor behaves as a highly sensitive, self-healing electromechanical sensor.
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Efficient Encapsulation of Fluorinated Drugs in the Confined Space of Water-Dispersible Fluorous Supraparticles ()
Fluorophobic-driven assemblies of gold nanomaterials were stabilized into water-dispersible fluorous supraparticles by the film-forming protein hydrophobin II. The strategy makes use of fluorous nanomaterials of different dimensions to engineer size and inner functionalization of the resulting confined space. The inner fluorous compartments allow efficient encapsulation and transport of high loadings of partially fluorinated drug molecules in water. Fluorous supraparticles: The film-forming protein hydrophobin II stabilizes fluorophobic-driven assemblies of gold nanomaterials in water. Using nanomaterials of different dimensions, the size and inner functionalization of the resulting confined space can be engineered. Partially fluorinated drug molecules are encapsulated efficiently and can be transported in water.
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Transition-Metal-Free Catalytic Hydrodefluorination of Polyfluoroarenes by Concerted Nucleophilic Aromatic Substitution with a Hydrosilicate ()
A transition-metal-free catalytic hydrodefluorination (HDF) reaction of polyfluoroarenes is described. The reaction involves direct hydride transfer from a hydrosilicate as the key intermediate, which is generated from a hydrosilane and a fluoride salt. The eliminated fluoride regenerates the hydrosilicate to complete the catalytic cycle. Dispersion-corrected DFT calculations indicated that the HDF reaction proceeds through a concerted nucleophilic aromatic substitution (CSNAr) process. A simple but artful combination: Transition-metal-free catalytic hydrodefluorination (HDF) of polyfluoroarenes was enabled by a hydrosilicate catalyst formed in situ from a hydrosilane and a fluoride ion. The reaction involves direct hydride transfer from the hydrosilicate through concerted nucleophilic aromatic substitution (CSNAr; see scheme).
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One-Pot Synthesis of Cyclopropane-Fused Cyclic Amidines: An Oxidative Carbanion Cyclization ()
A novel and efficient one-pot method has been developed for the synthesis of cyclopropane-fused bicyclic amidines on the basis of a CuBr2-mediated oxidative cyclization of carbanions. The usefulness of this unique multicomponent strategy has been demonstrated by the use of a wide variety of substrates to furnish novel cyclopropane-containing amidines with a quaternary center in very good yields. This ketenimine-based approach provides straightforward access to biologically active and pharmaceutically important 3-azabicyclo[n.1.0]alkane frameworks under mild conditions. The synthetic power of this methodology is exemplified in the concise synthesis of the pharmaceutically important antidepressant drug candidate GSK1360707 and key intermediates for the synthesis of amitifadine, bicifadine, and narlaprevir. No stopping! An efficient one-pot multistep process enabled the synthesis of novel cyclopropane-fused cyclic amidines with a quaternary center in good yields (see scheme). This method provides ready access to the 3-azabicyclo[n.1.0]alkane framework. The synthetic utility of the CuBr2-mediated oxidative cyclization was demonstrated by a short (four-step) synthesis of the antidepressant drug candidate GSK1360707.
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High-Magnesium Calcite Mesocrystals: Formation in Aqueous Solution under Ambient Conditions ()
Mesocrystals of high-magnesian calcites are commonly found in biogenic calcites. Under ambient conditions, it remains challenging to prepare mesocrystals of high-magnesian calcite in aqueous solution. We report that mesocrystals of calcite with magnesium content of about 20 mol % can be obtained from the phase transformation of magnesian amorphous calcium carbonate (Mg-ACC) in lipid solution. The limited water content on the Mg-ACC surface would reduce the extent of the dissolution–reprecipitation process and bias the phase transformation pathway toward solid-state reaction. We infer from the selected area electron diffraction patterns and the dark-field transmission electron microscopic images that the formation of Mg-calcite mesocrystals occurs through solid-state secondary nucleation, for which the phase transformation is initiated near the mineral surface and the crystalline phase propagates gradually toward the interior part of the microspheres of Mg-ACC. Mesocrystals of high-Mg calcites are prepared in aqueous solution using phospholipids as additives. The dark-field images originating from the (104) diffraction spot indicate that a large collection of the nanocrystallites of Mg-calcites have the same orientation.
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Room-Temperature-Phosphorescence-Based Dissolved Oxygen Detection by Core-Shell Polymer Nanoparticles Containing Metal-Free Organic Phosphors ()
The highly sensitive optical detection of oxygen including dissolved oxygen (DO) is of great interest in various applications. We devised a novel room-temperature-phosphorescence (RTP)-based oxygen detection platform by constructing core–shell nanoparticles with water-soluble polymethyloxazoline shells and oxygen-permeable polystyrene cores crosslinked with metal-free purely organic phosphors. The resulting nanoparticles show a very high sensitivity for DO with a limit of detection (LOD) of 60 nm and can be readily used for oxygen quantification in aqueous environments as well as the gaseous phase. Gl-O2-w!: A dissolved oxygen (DO)-detection platform based on core–shell nanoparticles with a water-soluble polymethyloxazoline shell and oxygen-permeable polystyrene core crosslinked with metal-free purely organic phosphors is reported. The resulting nanoparticles show a very high sensitivity and can be used for oxygen quantification in a variety of environments.
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Breaking Bonds and Forming Nanographene Diradicals with Pressure ()
New anthanthrone-based polycyclic scaffolds possessing peripheral crowded quinodimethanes have been prepared. While the compounds adopt a closed-shell butterfly-shaped structure in the ground state, a curved-to-planar fluxional inversion is accessible with a low energy barrier through a biradicaloid transition state. Inversion is primarily driven by the release of strain associated with steric hindrance at the peri position of the anthanthrone core; a low-lying diradical state is accessible through planarization of the core, which is attained in solution at moderate temperatures. The most significant aspect of this transformation is that planarization is also achieved by application of mild pressure in the solid state, wherein the diradical remains kinetically trapped. Complementary information from quantum chemistry, 1H NMR, and Raman spectroscopies, together with magnetic experiments, is consistent with the formation of a nanographene-like structure that possesses radical centers localized at the exo-anthanthrone carbons bearing phenyl substituents. Breaking a π bond with your bare hands: Quinodimethane nanographenes with a closed-shell structure display a curve-to-planar fluxional inversion, which passes through a diradical intermediate. The diradical can be trapped kinetically and is characterized by a low-energy lying triplet. Key: pressure (P), solvent (S).
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Liver-Targeted Small-Molecule Inhibitors of Proprotein Convertase Subtilisin/Kexin Type 9 Synthesis ()
Targeting of the human ribosome is an unprecedented therapeutic modality with a genome-wide selectivity challenge. A liver-targeted drug candidate is described that inhibits ribosomal synthesis of PCSK9, a lipid regulator considered undruggable by small molecules. Key to the concept was the identification of pharmacologically active zwitterions designed to be retained in the liver. Oral delivery of the poorly permeable zwitterions was achieved by prodrugs susceptible to cleavage by carboxylesterase 1. The synthesis of select tetrazole prodrugs was crucial. A cell-free in vitro translation assay containing human cell lysate and purified target mRNA fused to a reporter was used to identify active zwitterions. In vivo PCSK9 lowering by oral dosing of the candidate prodrug and quantification of the drug fraction delivered to the liver utilizing an oral positron emission tomography 18F-isotopologue validated our liver-targeting approach. A liver-targeting strategy was developed for a small-molecule drug candidate that inhibits PCSK9 synthesis at the human ribosome. Chemistry enabling the synthesis of N1 tetrazole prodrugs and a companion PET tracer were essential to validating the approach.
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A Supramolecular Capsule for Reversible Polysulfide Storage/Delivery in Lithium-Sulfur Batteries ()
Supramolecular materials, in which small organic molecules are assembled into regular structures by non-covalent interactions, attract tremendous interests because of their highly tunable functional groups and porous structure. Supramolecular adsorbents are expected to fully expose their abundant adsorptive sites in a dynamic framework. In this contribution, we introduced cucurbit[6]uril as a supramolecular capsule for reversible storage/delivery of mobile polysulfides in lithium-sulfur (Li-S) batteries to control undesirable polysulfide shuttle. The Li-S battery equipped with the supramolecular capsules retains a high Coulombic efficiency and shows a large increase in capacity from 300 to 900 mAh g−1 at a sulfur loading of 4.2 mg cm−2. The implementation of supramolecular capsules offers insights into intricate multi-electron-conversion reactions and manifests as an effective and efficient strategy to enhance Li-S batteries and analogous applications that involve complex transport phenomena and intermediate manipulation. Smart energy storage: Solutions for effectively managing the transport of polysulfides in Li-S batteries address the shuttle. A supramolecular capsule with the ability to reversibly store/deliver polysulfides was introduced to Li-S batteries.
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Temperature-Mediated Template Release: Facile Growth of Copper(I) Mixed Ethynediide/Isopropylethynide Nanoclusters ()
In the comproportionation reaction of CuIIX2 and Cu0 with isopropylacetylene (iPr−C≡C−H), the ethynediide species C22− is generated via concomitant C−H/C−C bond cleavage of the iPr−C≡C−H precursor under moderate temperature to direct the formation of CuI mixed ethynediide/isopropylethynide nanoclusters (potentially explosive). The active ethynediide dianion C22− exhibits chameleon-like templating behavior to form C2@Cum (m=6 (3, 4), 7 (2, 4), 8 (1)) central structural units for successive formation of {C22−⊂Cu24} (1, 2), {6 C22−⊂Cu48} (3), and {18 C22−⊂Cu92} (4) complexes. Bearing the highest C22− content, complex 4 features an unprecedented nanoscale Cu2C2 kernel. Furthermore, 1–3 exhibit structure-controlled photoluminescence in the solid state. Template release: Temperature variation triggers the release of ethynediide C22− from isopropylacetylene through concomitant C−H/C−C bond cleavage, leading to formation of CuI mixed ethynediide/alkynide nanoclusters. Synthesis of {C22−⊂Cu24}, {6 C22−⊂Cu48}, and {18 C22−⊂Cu92} establishes a class of tunable nanostructures where the increasing number of ethynediide bestows nuclearity expansion and structural diversity.
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Functional Cellular Mimics for the Spatiotemporal Control of Multiple Enzymatic Cascade Reactions ()
Next-generation therapeutic approaches are expected to rely on the engineering of biomimetic cellular systems that can mimic specific cellular functions. Herein, we demonstrate a highly effective route for constructing structural and functional eukaryotic cell mimics by loading pH-sensitive polymersomes as membrane-associated and free-floating organelle mimics inside the multifunctional cell membrane. Metabolism mimicry has been validated by performing successive enzymatic cascade reactions spatially separated at specific sites of cell mimics in the presence and absence of extracellular organelle mimics. These enzymatic reactions take place in a highly controllable, reproducible, efficient, and successive manner. Our biomimetic approach to material design for establishing functional principles brings considerable enrichment to the fields of biomedicine, biocatalysis, biotechnology, and systems biology. Metabolism mimicry in cell mimics: Multicompartmentalized systems containing pH-responsive Ada-polymersomes as organelle mimics were developed. These systems were employed as cell mimics to mimic metabolism by incorporating various stimuli for regulating enzymatic cascade reactions and for controlling the simultaneous and/or subsequent release of the encapsulated (therapeutic) molecules.
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Supramolecular Radical Anions Triggered by Bacteria In Situ for Selective Photothermal Therapy ()
A supramolecular complex that can be selectively reduced to radical anions in situ by facultative anaerobic bacteria is reported. To this end, a water-soluble bifunctional monomer bearing perylene diimide was synthesized, and its supramolecular complex with cucurbit[7]uril was fabricated on the basis of host–guest complexation, which could be reduced to forming radical anions in the presence of E. coli. It was found that this supramolecular complex could display different ability of generating radical anions by facultative anaerobic and aerobic bacteria in terms of their various reductive abilities. The selective antibacterial activity of the supramolecular complex could be realized by the photothermal performance of the radical anions under near-infrared irradiation. It is anticipated that this method may lead to a novel bacteria-responsive photothermal therapy to regulate balance of bacterial flora. Photothermal therapy: A supramolecular complex of a perylene diimide derivative and cucurbit[7]uril shows different possibilities of generating radical anions by facultative anaerobic and aerobic bacteria. The selective antibacterial activity of the supramolecular complex is based on the photothermal effect of the radical anions that convert optical energy into heat under near-infrared illumination.
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Adsorption-Induced Structural Phase Transformation in Nanopores ()
We report a new type of structural transformation occurring in methane adsorbed in micropores. The observed methane structures are defined by probability distributions of molecular positions. The mechanism of the transformation has been modeled using Monte Carlo method. The transformation is totally determined by a reconstruction of the probability distribution functions of adsorbed molecules. The methane molecules have some freedom to move in the pore but most of the time they are confined to the positions around the high probability adsorption sites. The observed high-probability structures evolve as a function of temperature and pressure. The transformation is strongly discontinuous at low temperature and becomes continuous at high temperature. The mechanism of the transformation is influenced by a competition between different components of the interaction and the thermal energy. The methane structure represents a new state of matter, intermediate between solid and liquid. Between solid and liquid: New type of structural transformation has been observed in a model of methane molecules adsorbed in micropores of the IRMOF-1 metal–organic framework (MOF). The mechanism of the transformation is defined by a probability distribution function. The methane structure in the pore is characterized by limited mobility, and represents a new state of matter, intermediate between solid and liquid.
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Synthesis of a Phlorin from a Meso-Fused Anthriporphyrin by a Diels–Alder Strategy ()
An anthracene-containing meso-fused carbaporphyrin, which has extended π-conjugation pathways as compared to the corresponding naphthalene-containing carbaporphyrin, has been synthesized. The weak global aromaticity of the anthriporphyrin also allowed its use as the diene for a Diels–Alder reaction with dimethyl acetylenedicarboxylate (DMAD). The resulting phlorin contains an interesting bicyclic structure. Moreover, to the best of our knowledge, this phlorin is the first Diels–Alder adduct of a diene forming part of the global π-conjugation pathway of an aromatic porphyrinoid. Expanding horizons: An anthracene-containing meso-fused carbaporphyrin with weak aromaticity was synthesized as a diene for a Diels–Alder reaction and thus further expanded into a meso-fused phlorin (see scheme). The metal-coordination chemistry of the anthriporphyrin and the novel phlorin was investigated by the synthesis of palladium(II) complexes.
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Microporous Cyclic Titanium-Oxo Clusters with Labile Surface Ligands ()
By using ethylene glycol and monocarboxylic acid as surface ligands, a series of cyclic Ti-oxo clusters (CTOC) with permanent microporosity are successfully synthesized. With a cyclic {Ti32O16} backbone made of eight connected Ti4 tetrahedral cages that are arranged in a zigzag fashion, the clusters have a “donut” shape with an inner diameter of 8.3 Å, outer diameter of 26.9 Å and height of 10.4 Å. While both inner and outer walls of the “donut” clusters are modified by double-deprotonated ethylene glycolates, their upper and lower surfaces are bound by carboxylates and mono-deprotonated ethylene glycolates. The clusters are readily packed into one-dimensional tubes which are further arranged in two different modes into crystalline microporous solids with surface areas over 660 m2 g−1, depending on the surface carboxylates. The solid with olefin-bearing carboxylates exhibits a superior CO2 adsorption capacity of 40 cm3 g−1 at 273 K under 1 atm. Moreover, the mono-deprotonated ethylene glycolates on the clusters are demonstrated to be highly exchangeable by other alcohols, providing a nice platform for creating microporous solids or films with a wide variety of surface functionalities. Microporous materials: A strategy based on the surface ligands ethylene glycol and monocarboxylic acid has been successfully implemented to prepare macrocyclic Ti-oxo clusters (TOCs). The donut TOCs interlock with each other into one-dimensional nanotubes which form microporous solids. The labile surface ligands also make it possible to generate microporous TOCs with a wide variety of surface functionalities.
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On the Non-Metallicity of 2.2 nm Au246(SR)80 Nanoclusters ()
The transition from molecular to plasmonic behaviour in metal nanoparticles with increasing size remains a central question in nanoscience. We report that the giant 246-gold-atom nanocluster (2.2 nm in gold core diameter) protected by 80 thiolate ligands is surprisingly non-metallic based on UV/Vis and femtosecond transient absorption spectroscopy as well as electrochemical measurements. Specifically, the Au246 nanocluster exhibits multiple excitonic peaks in transient absorption spectra and electron dynamics independent of the pump power, which are in contrast to the behaviour of metallic gold nanoparticles. Moreover, a prominent oscillatory feature with frequency of 0.5 THz can be observed in almost all the probe wavelengths. The phase and amplitude analysis of the oscillation suggests that it arises from the wavepacket motion on the ground state potential energy surface, which also indicates the presence of a small band-gap and thus non-metallic or molecular-like behaviour. When is a metal not a metal? The ultrafast electron and phonon dynamics of Au246(SR)80 nanoclusters reveal that Au246 is still non-metallic despite its large size (2.2 nm in diameter). A prominent oscillatory feature with frequency of 0.5 THz is observed indicating the presence of a small band-gap and thus non-metallic or molecular-like behaviour.
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Ligand-controlled Regiodivergent C−H Alkenylation of Pyrazoles and its Application to the Synthesis of Indazoles ()
Regioselective C4-, C5-, and di-alkenylations of pyrazoles were achieved. An electrophilic Pd catalyst generated by trifluoroacetic acid (TFA) and 4,5-diazafluoren-9-one (DAF) leads to C4-alkenylation, whereas KOAc and mono-protected amino acid (MPAA) ligand Ac-Val-OH give C5-alkenylation. A combination of palladium acetate, silver carbonate, and pivalic acid affords dialkenylation products. Annulation through sequential alkenylation, thermal 6π-electrocyclization, and oxidation gives functionalized indazoles. This comprehensive strategy greatly expands the range of readily accessible pyrazole and indazole derivatives, enabling useful regiodivergent C−H functionalization of pyrazoles and other heteroaromatic systems. A regioselective C−H functionalization of pyrazoles was developed to provide C4-, C5-, and di-alkenyl pyrazoles using three distinctive Pd catalytic systems. The systematic preparation of alkenyl pyrazoles enabled the synthesis of multifunctionalized indazoles and π-extended pyrazoles from readily available, inexpensive pyrazoles and olefins.
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Controlled and Reversible Stepwise Growth of Linear Copper(I) Chains Enabled by Dynamic Ligand Scaffolds ()
Reversible stepwise chain growth in linear CuI assemblies can be achieved by using the dynamic, unsymmetric naphthyridinone-based ligand scaffolds L1 and L2. With the same ligand scaffolds, the length of the linear copper chain can be varied from two to three and four copper atoms, and the nuclearity of the complex is easily controlled by the stepwise addition of a CuI precursor to gradually increase the chain length, or by the reductive removal of Cu atoms to decrease the chain length. This represents a rare example of a stepwise controlled chain growth in extended metal atom chains (EMACs). All complexes are formed with excellent selectivity, and the mutual transformations of the complexes of different nuclearity were found to be fast and reversible. These unusual rearrangements of metal chains of different nuclearities were achieved by a stepwise “sliding” movement of the naphthyridinone bridging fragment along the metal chain. Copper chain traffic control: The stepwise growth of copper(I) linear chain complexes was achieved with dynamic ligand scaffolds. Complexes containing the same ligand and one, two, three, or four CuI atoms interconvert reversibly in a process that is controlled by the stoichiometry, solvent polarity, and redox transformations.
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Controlling the Host–Guest Interaction Mode through a Redox Stimulus ()
A proof-of-concept related to the redox-control of the binding/releasing process in a host–guest system is achieved by designing a neutral and robust Pt-based redox-active metallacage involving two extended-tetrathiafulvalene (exTTF) ligands. When neutral, the cage is able to bind a planar polyaromatic guest (coronene). Remarkably, the chemical or electrochemical oxidation of the host–guest complex leads to the reversible expulsion of the guest outside the cavity, which is assigned to a drastic change of the host–guest interaction mode, illustrating the key role of counteranions along the exchange process. The reversible process is supported by various experimental data (1H NMR spectroscopy, ESI-FTICR, and spectroelectrochemistry) as well as by in-depth theoretical calculations performed at the density functional theory (DFT) level. Stimuli-responsive metallacages: A self-assembled, redox-active platinum cage constructed from an extended-tetrathiafulvalene ligand can be reversibly oxidized to its stable tetracationic state. The reversible control of the cavity charge from 0 to 4+ makes it possible to tune the binding and releasing of a polyaromatic.
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Aqueous Bismuth Titanium–Oxo Sulfate Cluster Speciation and Crystallization ()
Inorganic aqueous metal–oxo clusters are both functional “molecular metal oxides” and intermediates to understand metal oxide growth from water. There has been a recent surge in discovery of aqueous Ti-oxo clusters but without extensive solution characterization. We use small-angle and total X-ray scattering, dynamic light scattering, transmission electron microscopy, and a single-crystal X-ray structure to show that heterometals such as bismuth stabilize labile Ti–oxo sulfate clusters in aqueous solution.[Ti22Bi7O41(OH)(OH2)30(SO4)12]2+ features edge-sharing between the Ti and Bi polyhedra, in contrast to the dominant corner-linking of Ti-oxo clusters. Bi stabilizes the Ti-polyhedra, which are synergistically stabilized by the bidentate sulfates. Gained stability and potential functionality from heterometals is an incentive to develop more broadly the landscape of heterometallic Ti–oxo clusters. Disassembly, re-assembly: Titanium oxysulfate immediately self-assembles into monodisperse polynuclear clusters upon dissolution in water. According to X-ray scattering, these clusters are highly labile without distinct internal order. They are disassembled stepwise by adding nitric acid and BiIII; a solution that yields a heterometallic Ti–oxo cluster.
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Sorting of C4 Olefins with Interpenetrated Hybrid Ultramicroporous Materials by Combining Molecular Recognition and Size-Sieving ()
C4 olefin separations present one of the great challenges in hydrocarbon purifications owing to their similar structures, thus a single separation mechanism often met with limited success. Herein we report a series of anion-pillared interpenetrated copper coordination for which the cavity and functional site disposition can be varied in 0.2 Å scale increments by altering the anion pillars and organic linkers (GeFSIX-2-Cu-i (ZU-32), NbFSIX-2-Cu-i (ZU-52), GeFSIX-14-Cu-i (ZU-33)), which enable selective recognition of different C4 olefins. In these materials the rotation of the organic linkers is controlled to create a contracted flexible pore window that enables the size-exclusion of specific C4 olefins, while still adsorbing significant amounts of 1,3-butadiene (C4H6) or 1-butene (n-C4H8). Combining the molecular recognition and size-sieving effect, these materials unexpectedly realized the sieving of C4H6/n-C4H8, C4H6/iso-C4H8, and n-C4H8/iso-C4H8 with high capacity. Separate ways: Three anion-pillared interpenetrated copper coordination networks were prepared for the highly efficient separation of C4 olefins by combining targeted molecular recognition and size-sieving effects. These dual-functional materials are varied by altering the anions and organic linkers to change the shape and functionality, and are able to distinguish the multiple differences between hydrocarbon isomers therefore maximize the separation efficiency.
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Record High-Nuclearity Polyoxoniobates: Discrete Nanoclusters {Nb114}, {Nb81}, and {Nb52}, and Extended Frameworks Based on {Cu3Nb78} and {Cu4Nb78} ()
A series containing the highest nuclearity polyoxoniobate (PONb) nanoclusters, ranging from dimers to tetramers, has been obtained. They include one 114-nuclear {Li8⊂Nb114O316}, one 81-nuclear {Li3K⊂Nb81O225}, and one 52-nuclear {H4Nb52O150}. The Nb nuclearity of these PONbs is remarkably larger than those of all known high-nuclearity PONbs (≤32). Furthermore, the introduction of 3d Cu2+ ions can lead to the generation of extended inorganic–organic hybrid frameworks built from novel, high-nuclearity, nanoscale heterometallic PONb building blocks {H3Cu3Nb78O222} or {H3Cu4(en)Nb78O222}. These building blocks also contain the largest number of Nb centers of any heterometallic PONbs reported to date. The synthesis of new-type PONbs has long been a challenging subject in PONb chemistry. Big, bigger, biggest: A series of record high-nuclearity PONbs, ranging from 52-nuclear {Nb52}, 81-nuclear {Nb81} to 114-nuclear {Nb114}, is made. The introduction of 3d Cu2+ ions allows the construction of extended inorganic–organic hybrid PONb frameworks based on giant heterometallic nanoclusters {Cu3Nb78} and {Cu4Nb78}.
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Asymmetric Synthesis of Less Accessible α-Tertiary Amines from Alkynyl Z-Ketimines ()
A highly stereoselective synthesis of hitherto less accessible chiral α-tertiary amines with multiple structurally similar linear carbon chains was achieved through chiral auxiliary mediated addition of organolithium reagents to the geometrically well-controlled alkynyl Z-ketimines. This stereoselective nucleophilic addition offers a general approach to the asymmetric synthesis of nitrogen-containing chiral materials. One-sided: Geometrically well-controlled alkynyl Z-ketimines were prepared and successfully employed in the asymmetric synthesis of less accessible α-tertiary amines bearing multiple linear carbon chains through chiral auxiliary mediated nucleophilic addition of organolithium reagents.
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An in situ Dynamic Continuum of Supramolecular Phosphoglycopeptides Enables Formation of 3D Cell Spheroids ()
Higher-order assemblies of proteins, with a structural and dynamic continuum, is an important concept in biology, but these insights have yet to be applied in designing biomaterials. Dynamic assemblies of supramolecular phosphoglycopeptides (sPGPs) transform a 2D cell sheet into 3D cell spheroids. A ligand–receptor interaction between a glycopeptide and a phosphopeptide produces sPGPs that form nanoparticles, which transform into nanofibrils upon partial enzymatic dephosphorylation. The assemblies form dynamically and hierarchically in situ on the cell surface, and interact with the extracellular matrix molecules and effectively abolish contact inhibition of locomotion (CIL) of the cells. Integrating molecular recognition, catalysis, and assembly, these active assemblies act as a dynamic continuum to disrupt CIL, thus illustrating a new kind of biomaterial for regulating cell behavior. Sphere we go: Enzymatically formed dynamic biomaterials in the cell milieu modulate intercellular interactions to generate three-dimensional cell spheroids.
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Cyclic Triimidazole Derivatives: Intriguing Examples of Multiple Emissions and Ultralong Phosphorescence at Room Temperature ()
The performance of solid luminogens depends on both their inherent electronic properties and their packing status. Intermolecular interactions have been exploited to achieve persistent room-temperature phosphorescence (RTP) from organic molecules. However, the design of organic materials with bright RTP and the rationalization of the role of interchromophoric electronic coupling remain challenging tasks. Cyclic triimidazole has been shown to be a promising scaffold for such purposes owing to its crystallization-induced room-temperature ultralong phosphorescence (RTUP), which has been associated with H-aggregation. Herein, we report three triimidazole derivatives as significant examples of multifaceted emission. In particular, dual fluorescence, RTUP, and phosphorescence from the molecular and supramolecular units were observed. H-aggregation is responsible for the red RTUP, and Br substituents favor yellow molecular phosphorescence while halogen-bonded Br⋅⋅⋅Br tetrameric units are involved in the blue-green phosphorescence. Three triimidazole derivatives were synthesized that display multiple emissions covering dual fluorescence, room-temperature ultralong phosphorescence (RTUP), and phosphorescence from the molecular and supramolecular units. H-aggregation is responsible for the red RTUP, Br substituents favor yellow molecular phosphorescence, and halogen-bonded Br⋅⋅⋅Br tetrameric units are involved in the blue-green phosphorescence.
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Organocatalytic Atroposelective Arylation of 2-Naphthylamines as a Practical Approach to Axially Chiral Biaryl Amino Alcohols ()
The first phosphoric acid catalyzed direct arylation of 2-naphthylamines with iminoquinones for the atroposelective synthesis of axially chiral biaryl amino alcohols has been developed. This reaction constitutes a highly functional-group-tolerant route for the rapid construction of enantioenriched axially chiral biaryl amino alcohols, and is a rare example of 2-naphthylamines acting as nucleophiles in an organocatalytic enantioselective transformation. Furthermore, the products, which feature various halogen atoms, provide access to structurally diverse axially chiral amino alcohols through further transformations. The phosphoric acid catalyzed direct arylation of 2-naphthylamines with iminoquinones enables the atroposelective synthesis of axially chiral biaryl amino alcohols. Many functional groups are tolerated in this reaction, and it is a rare example of 2-naphthylamines acting as nucleophiles in an organocatalytic enantioselective transformation.
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Three-Dimensional Anionic Cyclodextrin-Based Covalent Organic Frameworks ()
Three-dimensional covalent organic frameworks (3D COFs) are promising crystalline materials with well-defined structures, high porosity, and low density; however, the limited choice of building blocks and synthetic difficulties have hampered their development. Herein, we used a flexible and aliphatic macrocycle, namely γ-cyclodextrin (γ-CD), as the soft struts for the construction of a polymeric and periodic 3D extended network, with the units joined via tetrakis(spiroborate) tetrahedra with various counterions. The inclusion of pliable moieties in the robust open framework endows these CD-COFs with dynamic features, leading to a prominent Li ion conductivity of up to 2.7 mS cm−1 at 30 °C and excellent long-term Li ion stripping/plating stability. Exchanging the counterions within the pores can effectively modulate the interactions between the CD-COF and CO2 molecules. Three-dimensional anionic covalent organic frameworks (COFs) were constructed from aliphatic and flexible macrocyclic γ-cyclodextrin (γ-CD) units joined via spiroborate linkages with various counterions. The CD-COF with Li+ is a good Li ion conductor, and different counterions within the framework lead to different interactions with CO2.
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Enantiospecific sp2–sp3 Coupling of ortho- and para-Phenols with Secondary and Tertiary Boronic Esters ()
The coupling of ortho- and para-phenols with secondary and tertiary boronic esters has been explored. In the case of para-substituted phenols, after reaction of a dilithio phenolate species with a boronic ester, treatment with Ph3BiF2 or Martin's sulfurane gave the coupled product with complete enantiospecificity. The methodology was applied to the synthesis of the broad spectrum antibacterial natural product (−)-4-(1,5-dimethylhex-4-enyl)-2-methyl phenol. For ortho-substituted phenols, initial incorporation of a benzotriazole on the phenol oxygen atom was required. Subsequent ortho-lithiation and borylation gave the coupled product, again with complete stereospecificity. The coupling of ortho- and para-phenols with boronic esters has been explored. In the case of para-bromophenols, after reaction of the dilithio aryl species with the boronic ester, treatment with Ph3BiF2 or Martin's sulfurane gave the coupled product with complete enantiospecificity. For ortho-phenols, initial incorporation of a benzotriazole on the phenol oxygen atom was required.
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Enantioselective and Collective Total Syntheses of Xanthanolides ()
An enantioselective synthesis of (+)-8-epi-xanthatin hinging on a chiral phosphoric acid catalyzed tandem allylboration/lactonization reaction is reported. With (+)-8-epi-xanthatin as the precursor, the collective synthesis of a series of synthetically challenging xanthanolides was also accomplished. Among them, xanthipungolide, one of the most complex xanthanolide monomers, was accessed through a bioinspired tandem double-bond isomerization/6π electronic cyclization/intramolecular Diels–Alder reaction, and pungiolides A, B, D, E, and L–N, a group of xanthanolide dimers, were assembled through a bioinspired Diels–Alder dimerization followed by late-stage diversification. The more the merrier: The enantioselective synthesis of (+)-8-epi-xanthatin from readily available fragments was completed in seven steps (longest linear sequence) and 15 % overall yield. A further 1–3 steps were required for the collective total synthesis of various synthetically challenging xanthanolide monomers and dimers (see scheme) on the basis of a series of intriguing bioinspired transformations.
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Development of an Efficient Biosensor for the In Vivo Monitoring of Cu+ and pH in the Brain: Rational Design and Synthesis of Recognition Molecules ()
An efficient biosensor was created for the ratiometric monitoring of Cu+ and pH in the brain using both current and potential outputs. A series of N,N-bis(2-[2-(ethylthio)ethyl])-based (NS4s) derivatives was designed for the specific recognition of Cu+. After systematically evaluating the electrochemical parameters of Cu+ oxidation by tuning alkyl chain length, polyaromatic structure, and substitute group site of NS4, N,N-bis(2-[2-(ethylthio)ethyl])-2-naphthamide (NS4-C1) was finally optimized for Cu+ detection as it showed the most negative potential and the largest current density. At the same time, 9,10-anthraquinone was used as a selective pH sensor with 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) as an internal reference. This single biosensor with both current and potential signal outputs can simultaneously determine Cu+ concentrations from 0.5 to 9.5 μm and pH values ranging from 6.0 to 8.0. The efficient biosensor was applied to the simultaneous detection of Cu+ and pH in the live brain. The average levels of Cu+ were reported for the first time in the cortex, hippocampus, and striatum in a mouse model of Alzheimer's disease. The cuprous ion (Cu+) and pH play vital roles in the physiological and pathological events of brain. An efficient biosensor, using two types of electrical signal outputs, was created for the ratiometric monitoring of Cu+ and pH in a mouse model of Alzheimer's disease (AD). The average levels of Cu+ were reported in the cortex, hippocampus, and striatum in the mouse model of AD.
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In-Situ Microfluidic Study of Biphasic Nanocrystal Ligand-Exchange Reactions Using an Oscillatory Flow Reactor ()
Oscillatory flow reactors provide a surface energy-driven approach for automatically screening reaction conditions and studying reaction mechanisms of biphasic nanocrystal ligand-exchange reactions. Sulfide and cysteine ligand-exchange reactions with as-synthesized CdSe quantum dots (QDs) are chosen as two model reactions. Different reaction variables including the new-ligand-to-QD ratio, the size of the particles, and the original ligand type are examined systematically. Based on the in situ-obtained UV/Vis absorption spectra during the reaction, we propose two different exchange pathways for the sulfide exchange reaction. Oscillatory flow reactors were used to automatically screen reaction kinetics and study the reaction mechanisms of biphasic nanocrystal ligand-exchange reactions with CdSe quantum dots (QDs). Based on the UV/Vis absorption spectra obtained in situ during the reaction, two different reaction pathways are proposed.
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Consecutive Transformations of Tetrafluoropropenes: Hydrogermylation and Catalytic C−F Activation Steps at a Lewis Acidic Aluminum Fluoride ()
Functionalization reactions of the refrigerants HFO-1234yf (2,3,3,3-tetrafluoropropene) and HFO-1234ze (1,3,3,3-tetrafluoropropene) were developed. The selectivity and reactivity towards CF3 groups of C−F activation reactions can be controlled by employing either a germane or a silane as the hydrogen source. Unique transformations were designed to accomplish consecutive hydrogermylation and C−F activation steps. This allowed for an unprecedented transformation of an olefinic C−F bond into a C−H bond by heterogeneous catalysis. These reactions are catalyzed by nanoscopic aluminum chlorofluoride (ACF) under very mild conditions. Functionalizations of tetrafluoropropenes such as HFO-1234yf were developed. The transformation of the CF3 group into an olefinic CF2 group was achieved at nanoscopic aluminum chlorofluoride (ACF) with silane. Consecutive hydrogermylation and C−F activation steps enabled the transformation of an olefinic C−F into a C−H bond.
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Nucleophilic Arylation of N,O-Ketene Acetals with Triaryl Aluminum Reagents: Access to α-Aryl Amides through an Umpolung Process ()
A novel approach for the umpolung α-arylation of amides is presented. By the nucleophilic phenylation of O-silyl N,O-ketene acetals, generated in situ from N-alkoxy amides, a phenyl group can be introduced onto the α-carbon atom of amides through N−O bond cleavage in a two-step, one-pot process. The asymmetric synthesis of α-aryl amides through the diastereoselective arylation of a chiral N,O-ketene acetal is also described. Changing the rules to win the game: By means of an umpolung strategy involving the generation of O-silyl N,O-ketene acetals in situ from N-alkoxyamides, a phenyl group could be introduced onto the α-carbon center of amides through N−O bond cleavage in a two-step, one-pot process (see scheme). The asymmetric synthesis of α-aryl amides through the diastereoselective arylation of a chiral N,O-ketene acetal is also described.
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Supramolecular Recognition Allows Remote, Site-Selective C−H Oxidation of Methylenic Sites in Linear Amines ()
Site-selective C−H functionalization of aliphatic alkyl chains is a longstanding challenge in oxidation catalysis, given the comparable relative reactivity of the different methylenes. A supramolecular, bioinspired approach is described to address this challenge. A Mn complex able to catalyze C(sp3)-H hydroxylation with H2O2 is equipped with 18-benzocrown-6 ether receptors that bind ammonium substrates via hydrogen bonding. Reversible pre-association of protonated primary aliphatic amines with the crown ether selectively exposes remote positions (C8 and C9) to the oxidizing unit, resulting in a site-selective oxidation. Remarkably, such control of selectivity retains its efficiency for a whole series of linear amines, overriding the intrinsic reactivity of C−H bonds, no matter the chain length. Remote control: Supramolecular recognition of protonated primary amines on 18-crown-6 receptors exposes specific, remote methylenes to the Mn active site. Linear alkyl chains can thus be selectively oxidized on C8 and C9 positions with H2O2, overriding the intrinsic reactivity of C−H bonds.
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Enantioselective Rhodium-Catalyzed Coupling of Arylboronic Acids, 1,3-Enynes, and Imines by Alkenyl-to-Allyl 1,4-Rhodium(I) Migration ()
A chiral rhodium complex catalyzes the highly enantioselective coupling of arylboronic acids, 1,3-enynes, and imines to give homoallylic sulfamates. The key step is the generation of allylrhodium(I) species by alkenyl-to-allyl 1,4-rhodium(I) migration. A chiral rhodium complex catalyzes the highly enantioselective coupling of arylboronic acids, 1,3-enynes, and imines to give homoallylic sulfamates. The key step is the generation of allylrhodium(I) species by alkenyl-to-allyl 1,4-rhodium(I) migration. tAm=tert-amyl.
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Formation of Polymeric Nanocubes by Self-Assembly and Crystallization of Dithiolane-Containing Triblock Copolymers ()
Template-free fabrication of non-spherical polymeric nanoparticles is desirable for various applications, but has had limited success owing to thermodynamic favorability of sphere formation. Herein we present a simple way to prepare cubic nanoparticles of block copolymers by self-assembly from aqueous solutions at room temperature. Nanocubes with edges of 40–200 nm are formed spontaneously on different surfaces upon water evaporation from micellar solutions of triblock copolymers containing a central poly(ethylene oxide) block and terminal trimethylene carbonate/dithiolane blocks. These polymers self-assemble into 28±5 nm micelles in water. Upon drying, micelle aggregation and a kinetically controlled crystallization of central blocks evidently induce solid cubic particle formation. An approach for preserving the structures of these cubes in water by thiol- or photo-induced crosslinking was developed. The ability to solubilize a model hydrophobic drug, curcumin, was also explored. Polymers cubed: Cubic polymeric nanoparticles are prepared simply by self-assembly from aqueous solutions at room temperature. Cubes with edges of 40–200 nm are formed spontaneously upon drying from micellar solutions of triblock copolymers containing a central poly(ethylene oxide) block and terminal trimethylene carbonate/dithiolane blocks. An approach for preserving the cube structure by dithiolane crosslinking is developed.
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Magnesium Boryl Reactivity with 9-BBN and Ph3B: Rational B−B′ Bond Formation and Diborane Isomerization ()
Reactions of a magnesium-based pinacolatoboryl nucleophile with the electrophilic organoboranes, 9-BBN and Ph3B, provide facile B−B′ single bond formation. Although the Ph3B derivative is thermally stable, when heated, the unsymmetrical diborane(5) anion derived from 9-BBN is found to isomerize to two regioisomeric species via a proposed mechanism involving dehydroboration of the borabicyclo[3.3.1]nonane and syn-diboration of the resultant alkenyl carbocycle. B-B King: Reactions of a magnesium-based pinacolatoboryl nucleophile with electrophilic organoboranes, 9-BBN or Ph3B, provide facile B−B′ single bond formation.
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Cobalt-Catalyzed Suzuki Biaryl Coupling of Aryl Halides ()
Readily accessed cobalt pre-catalysts with N-heterocyclic carbene ligands catalyze the Suzuki cross-coupling of aryl chlorides and bromides with alkyllithium-activated arylboronic pinacolate esters. Preliminary mechanistic studies indicate that the cobalt species is reduced to Co0 during the reaction. Co-ming of age: Simple cobalt N-heterocyclic-carbene-based catalysts allow facile Suzuki cross-coupling of aryl chloride and bromide substrates.
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Cooperative Multifunctional Catalysts for Nitrone Synthesis: Platinum Nanoclusters in Amine-Functionalized Metal–Organic Frameworks ()
Nitrones are key intermediates in organic synthesis and the pharmaceutical industry. The heterogeneous synthesis of nitrones with multifunctional catalysts is extremely attractive but rarely explored. Herein, we report ultrasmall platinum nanoclusters (PtNCs) encapsulated in amine-functionalized Zr metal–organic framework (MOF), UiO-66-NH2 (Pt@UiO-66-NH2) as a multifunctional catalyst in the one-pot tandem synthesis of nitrones. By virtue of the cooperative interplay among the selective hydrogenation activity provided by the ultrasmall PtNCs and Lewis acidity/basicity/nanoconfinement endowed by UiO-66-NH2, Pt@UiO-66-NH2 exhibits remarkable activity and selectivity, in comparison to Pt/carbon, Pt@UiO-66, and Pd@UiO-66-NH2. Pt@UiO-66-NH2 also outperforms Pt nanoparticles supported on the external surface of the same MOF (Pt/UiO-66-NH2). To our knowledge, this work demonstrates the first examples of one-pot synthesis of nitrones using recyclable multifunctional heterogeneous catalysts. In tandem: Platinum nanoclusters (PtNCs) encapsulated in amine-functionalized UiO-66-NH2 (Pt@UiO-66-NH2) act as a multifunctional catalyst in the one-pot tandem synthesis of nitrones. By the cooperative interplay between the selective hydrogenation activity provided by PtNCs and Lewis acidity/basicity/nanoconfinement provided by the MOF, Pt@UiO-66-NH2 exhibits remarkable activity and selectivity.
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The MOF+ Technique: A Significant Synergic Effect Enables High Performance Chromate Removal ()
A significant synergic effect between a metal–organic framework (MOF) and Fe2SO4, the so-called MOF+ technique, is exploited for the first time to remove toxic chromate from aqueous solutions. The results show that relative to the pristine MOF samples (no detectable chromate removal), the MOF+ method enables super performance, giving a 796 Cr mg g−1 adsorption capacity. The value is almost eight-fold higher than the best value of established MOF adsorbents, and the highest value of all reported porous adsorbents for such use. The adsorption mechanism, unlike the anion-exchange process that dominates chromate removal in all other MOF adsorbents, as unveiled by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), is due to the surface formation of Fe0.75Cr0.25(OH)3 nanospheres on the MOF samples. A pause from pores: Relying on the surface rather than the pores of metal–organic frameworks (MOFs), the MOF+ method enables an ultrahigh chromate removal in aqueous solution of up to 796 Cr mg g−1, exceeding any porous material for this kind use. The hexavalent chromate is reduced by FeSO4 to generate FeIII and CrIII ions, the MOF surface then induces the formation of Fe0.75Cr0.25(OH)3 nanospheres.
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Solid-State Structure of Protonated Ketones and Aldehydes ()
Protonated carbonyl compounds have been invoked as intermediates in many acid-catalyzed organic reactions. To gain key structural and electronic data about such intermediates, oxonium salts derived from five representative examples of ketones and aldehydes are synthesized in the solid state, and characterized by X-ray crystallography and Raman spectroscopy for the first time. DFT calculations were carried out on the cations in the gas phase. Whereas an equimolar reaction of the carbonyl compounds, acetone, cyclopentanone, adamantanone, and acetaldehyde, with SbF5 in anhydrous HF yielded mononuclear oxonium cations, the same stoichiometry in a reaction with benzaldehyde resulted in formation of a hemiprotonated, hydrogen-bridged dimeric cation. Hemiprotonated acetaldehyde was obtained when a 2:1 ratio of aldehyde and SbF5 was used. Experimental and NBO analyses quantify the significant increase in electrophilicity of the oxonium cations compared to that of the parent ketones/aldehydes. Reactive intermediates: Solid-state structures of protonated carbonyl compounds are presented. Whereas protonation of ketones (acetone, cyclopentanone and adamantanone) in superacidic solution yielded the mononuclear oxonium ions, hemiprotonated hydrogen-bridged dinculear structures were observed in the crystal structure obtained from reactions of benzaldehyde or acetaldehyde with HF/SbF5.
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Spata-13,17-diene Synthase—An Enzyme with Sesqui-, Di-, and Sesterterpene Synthase Activity from Streptomyces xinghaiensis ()
A terpene synthase from the marine bacterium Streptomyces xinghaiensis has been characterised, including a full structure elucidation of its products from various substrates and an in-depth investigation of the enzyme mechanism by isotope labelling experiments, metal cofactor variations, and mutation experiments. The results revealed an interesting dependency of Mn2+ catalysis on the presence of Asp-217, a residue that is occupied by a highly conserved Glu in most other bacterial terpene synthases. On active duty: A terpene synthase from Streptomyces xinghaiensis with sesqui-, di-, and sesterterpene synthase activity has been identified. The enzyme mechanism was investigated by isotope labelling experiments. Site-directed mutagenesis uncovered several previously unrecognised highly conserved residues that are important for catalysis. One of these residues was linked to the requirement of a Mg2+ or Mn2+ cofactor.
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Preparation of Functionalized Diaryl- and Diheteroaryllanthanum Reagents by Fast Halogen–Lanthanum Exchange ()
Aryl and heteroaryl halides (X=Br, I) undergo a fast and convenient halogen–lanthanum exchange with nBu2LaMe, which leads to functionalized diaryl- and diheteroaryllanthanum derivatives. Subsequent trapping reactions with selected electrophiles, such as ketones, aldehydes, or amides, proceeded smoothly at −50 °C in THF, affording polyfunctionalized alcohols and carbonyl derivatives. Kinetic competition experiments revealed a similar reactivity trend as for Br/Mg exchange, but 106-times higher rates, making it comparable to Br/Li exchange. Lanthanum as a lithium alternative: Aryl and heteroaryl halides (X=Br, I) undergo a fast and convenient halogen–lanthanum exchange with nBu2LaMe, which leads to functionalized diaryl- and diheteroaryllanthanum derivatives. Trapping reactions with ketones, aldehydes, or amides proceeded smoothly at −50 °C, affording polyfunctionalized alcohols and carbonyl derivatives.
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Are There Carbenes in N-Heterocyclic Carbene Organocatalysis? ()
Azolium cations are widely employed in organocatalysis to catalyse highly valuable synthetic processes in the presence of a base. These reactions are called “N-heterocyclic carbene catalysis”, based on the assumption that they are initiated by the formation of a free carbene through deprotonation, which can then react with the substrates and thereby affect their reactivity to obtain the desired products. However, we herein provide evidence that an electrophilic aromatic substitution mechanism is energetically more favourable, in which the azolium cation reacts directly with the substrate, avoiding the formation of the free carbene in solution. Another alternative: A novel reaction pathway for N-heterocyclic carbene organocatalysis has been identified. In this process, proton transfer and the binding of the substrate to the catalyst occur simultaneously in a single elementary reaction step, without the formation of a free carbene molecule in the reaction mixture.
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O2 Activation on Ceria Catalysts—The Importance of Substrate Crystallographic Orientation ()
An atomic-level understanding of dioxygen activation on metal oxides remains one of the major challenges in heterogeneous catalysis. By performing a thorough surface-science study of all three low-index single-crystal surfaces of ceria, probably the most important redox catalysts, we provide a direct spectroscopic characterization of reactive dioxygen species at defect sites on the reduced ceria (110) and (100) surfaces. Surprisingly, neither of these superoxo and peroxo species was found on ceria (111), the thermodynamically most stable surface of this oxide. Applying density functional theory, we could relate these apparently inconsistent findings to a sub-surface diffusion of O vacancies on (111) substrates, but not on the less-closely packed surfaces. These observations resolve a long standing debate concerning the location of O vacancies on ceria surfaces and the activation of O2 on ceria powders. A puzzle is solved: The first infrared reflection–absorption spectroscopy (IRRAS) data of dioxygen activation on an oxide single-crystal surface show, in conjunction with theory, the formation of various superoxo and peroxo species on reduced CeO2(110) and (100) surfaces, but not on CeO2(111). This inconsistency originates from a subsurface diffusion of O vacancies.
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Overcoming the Lack of Oral Availability of Cyclic Hexapeptides: Design of a Selective and Orally Available Ligand for the Integrin αvβ3 ()
A highly systematic approach for the development of both orally bioavailable and bioactive cyclic N-methylated hexapeptides as high affinity ligands for the integrin αvβ3 is based on two concepts: a) screening of systematically designed libraries with spatial diversity and b) masking of the peptide charge with a lipophilic protecting group. The key steps of the method are 1) initial design of a combinatorial library of N-methylated analogues of the stem peptide cyclo(d-Ala-Ala5); 2) selection of cyclic peptides with the highest intestinal permeability; 3) design of sublibraries with the bioactive RGD sequence in all possible positions; 4) selection of the best ligands for RGD-recognizing integrin subtypes; 5) fine-tuning of the affinity and selectivity by additional Ala to Xaa substitutions; 6) protection of the charged functional groups according to the prodrug concept to regain intestinal and oral permeability; 7) proof of biological effects in mice after oral administration. The oral bioavailability of peptides is mainly limited by their transport through epithelial cells into the blood stream. The development of both orally bioavailable and bioactive cyclic N-methylated hexapeptides by a systematic approach involving screening permeable peptide libraries with spatial diversity and masking the peptides with lipophilic protecting groups led to orally active ligands for the integrin subtype αvβ3.
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Oxidation of Organic Molecules with a Redox-Active Guanidine Catalyst ()
Herein, we report the first examples of the use of redox-active guanidines as catalysts in the green oxidation of organic molecules with dioxygen. In one half-reaction, the oxidized form of the redox-active guanidine is converted into the reduced, protonated state, thereby enabling dehydrogenative oxidation of the substrate (3,5-di-tert-butylcatecholortho-benzoquinone, benzoinbenzil, and 2,4-di-tert-butylphenolbiphenol). In the other half-reaction, efficient re-oxidation of the guanidine to the oxidized state is achieved with dioxygen in the presence of a copper catalyst. These results pave the way for the broader use of redox-active guanidines as oxidation catalysts. Green and organic: Owing to the combination of high Brønsted basicity and electron-donor properties, redox-active guanidines are superior organic redox catalysts, as herein shown for the first catalytic oxidation reactions of 3,5-di-tert-butylcatechol, benzoin, and 2,4-di-tert-butylphenol with dioxygen.
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