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排序方式: 共有329条查询结果,搜索用时 15 毫秒
321.
Proton-coupled electron transfers currently attract considerable attention in view of their likely involvement in many natural processes. Electrochemistry, through techniques such as cyclic voltammetry, is an efficient way of investigating the reaction mechanism of these reactions, and deciding whether proton and electron transfers are concerted or occur in a stepwise manner. The oxidation of an ortho-substituted 4,6-di (tert-butyl)-phenol in which the phenolic hydrogen atom is transferred during the reaction to the nitrogen atom of a nearby amine is taken as illustrative example. A careful analysis of the cyclic voltammetric responses obtained with this compound and its OD derivative allows, after estimation of the various thermodynamic parameters, ruling out the occurrence of the square scheme mechanism involving the proton-electron and electron-proton sequences. Simulation and comparison of the rate constant and H/D kinetic isotope effect with theoretical predictions show that the experimental value of the preexponential factor is ca. 1 order of magnitude larger than the theoretical value. Detailed calculations suggest that an electric field effect is responsible for this discrepancy. 相似文献
322.
α-Acyloxynitroso derivatives are a class of heterodienophiles leading to valuable 3,6-dihydro-1,2-oxazines or the corresponding aminoalcohols in good yields. The discovery that a β-oxygenated moiety led to a domino [4+2] cycloaddition/σN-O bond cleavage in the presence of a catalytic amount of Lewis acid was investigated in detail, through kinetic profiling of the reaction both in the absence and presence of a promoter. These studies showed that the role of the Lewis acid was to accelerate the σN-O bond cleavage thereby promoting a highly reproducible sequence. In addition, our preliminary results on an asymmetric version of this domino sequence are reported. 相似文献
323.
Lucas Fortier Dr. Cyrille Gosset Dr. Corentin Lefebvre Dr. Sylvain Pellegrini Prof. Lydie Pélinski Dr. Till Bousquet 《European journal of organic chemistry》2023,26(4):e202201247
An efficient organophotocatalyzed protocol was developed for the preparation of 3-substituted phthalides. The presented transformation was performed under particularly mild conditions within 6 h and was ultimately applied to a precursor of the herbaric acid. 相似文献
324.
Dr. Bertrand Reuillard Prof. Dr. Cyrille Costentin Dr. Vincent Artero 《Angewandte Chemie (International ed. in English)》2023,62(36):e202302779
Nickel bisdiphosphine complexes bearing pendant amines form a unique series of catalysts (so-called DuBois’ catalysts) capable of bidirectional/reversible electrocatalytic oxidation and production of dihydrogen. This unique behaviour is directly linked to the presence of proton relays installed close to the metal center. We report here for the arginine derivative [Ni(P2CyN2Arg)2]6+ on a mechanistic model and its kinetic treatment that may apply to all DuBois’ catalysts and show that it allows for a good fit of experimental data measured at different pH values, catalyst concentrations and partial hydrogen pressures. The bidirectionality of catalysis results from balanced equilibria related to hydrogen uptake/evolution on one side and (metal)-hydride installation/capture on the other side, both controlled by concentration effects resulting from the presence of proton relays and connected by two square schemes corresponding to proton-coupled electron transfer processes. We show that the catalytic bias is controlled by the kinetic of the H2 uptake/evolution step. Reversibility does not require that the energy landscape be flat, with redox transitions occurring at potentials up to 250 mV away for the equilibrium potential, although such large deviations from a flat energy landscape can negatively impacts the rate of catalysis when coupled with slow interfacial electron transfer kinetics. 相似文献
325.
Camilla Russo Dr. Matthew C. Leech Jamie M. Walsh Dr. Joe I. Higham Lisa Giannessi Emmanuelle Lambert Cyrille Kiaku Dr. Darren L. Poole Dr. Joseph Mason Dr. Charles A. I. Goodall Dr. Perry Devo Dr. Mariateresa Giustiniano Dr. Marco Radi Dr. Kevin Lam 《Angewandte Chemie (International ed. in English)》2023,62(38):e202309563
Hydrogenation reactions are staple transformations commonly used across scientific fields to synthesise pharmaceuticals, natural products, and various functional materials. However, the vast majority of these reactions require the use of a toxic and costly catalyst leading to unpractical, hazardous and often functionally limited conditions. Herein, we report a new, general, practical, efficient, mild and high-yielding hydrogen-free electrochemical method for the reduction of alkene, alkyne, nitro and azido groups. Finally, this method has been applied to deuterium labelling. 相似文献
326.
Mathematical Programming - The approximate Carathéodory theorem states that given a compact convex set $${\mathcal {C}}\subset {\mathbb {R}}^n$$ and $$p\in [2,+\infty [$$ , each point $$x^*\in... 相似文献
327.
Kenny Lee Nathaniel Corrigan Cyrille Boyer 《Angewandte Chemie (International ed. in English)》2023,62(44):e202307329
Polymerization induced microphase separation (PIMS) is a strategy used to develop unique nanostructures with highly useful morphologies through the microphase separation of emergent block copolymers during polymerization. In this process, nanostructures are formed with at least two chemically independent domains, where at least one domain is composed of a robust crosslinked polymer. Crucially, this synthetically simple method is readily used to develop nanostructured materials with the highly coveted co-continuous morphology, which can also be converted into mesoporous materials by selective etching of one domain. As PIMS exploits a block copolymer microphase separation mechanism, the size of each domain can be tightly controlled by modifying the size of block copolymer precursors, thus providing unparalleled control over nanostructure and resultant mesopore sizes. Since its inception 11 years ago, PIMS has been used to develop a vast inventory of advanced materials for an extensive range of applications including biomedical devices, ion exchange membranes, lithium-ion batteries, catalysis, 3D printing, and fluorescence-based sensors, among many others. In this review, we provide a comprehensive overview of the PIMS process, summarize latest developments in PIMS chemistry, and discuss its utility in a wide variety of relevant applications. 相似文献
328.
Isabelle Morfin Ferenc Horkay Peter J. Basser Françoise Bley Françoise Ehrburger-Dolle Anne-Marie Hecht Cyrille Rochas Erik Geissler 《Macromolecular Symposia》2003,200(1):227-234
Anomalous small angle X-ray scattering is used to determine the distribution of divalent ions in a neutralized polyelectrolyte gel of sodium polyacrylate in the vicinity of the volume transition. At the five different energies of the incident beam used to vary the contrast, the scattering curves have similar shapes, and are separated only by constant multiplying factors. This result, in conjunction with SANS results from the same sample, indicates that the divalent ion (strontium) is confined on the polymer backbone. 相似文献
329.
Françoise Ehrburger-Dolle Françoise Bley Erik Geissler Frédéric Livet Isabelle Morfin Cyrille Rochas 《Macromolecular Symposia》2003,200(1):157-168
Elastomers are soft materials that can be reinforced by dispersing into them nanosized solid particles. Common examples of the latter are silica or carbon black aggregates. However, the mechanism of reinforcement is still not yet fully understood. Our work consists in investigating by small-angle X-ray scattering (SAXS) the structure of the aggregate network spreading throughout the matrix in the initial sample and its modification during and after straining (elongation). The goal is to relate the macroscopic mechanical behaviour with the structure of the aggregate network. The present paper is a qualitative overview of recent results obtained on well defined composites. 相似文献