Influence of the Electron Transfer Rate on Electrochemically Controlled Hydrogen Bonding

Hydrogen bonding is an essential interaction in natural and artificial systems. Its strength can be modulated by employing process known as Electrochemically Controlled Hydrogen bonding (ECHB). Although these processes are assumed to operate under thermodynamic control no experimental evidence for kinetic control exists. In this work, ECHB processes where studied using electrogenerated radical anions from 5-nitroimidazole derivatives as receptor molecules and 1,3-diethylurea as hydrogen bond donor species. Results revealed that kinetic control occurs due to an increase in the internal reorganization energy of the receptor molecule, which cause a decrease in electron transfer rate. Electronic structure calculations and experimental K_b values suggested that kinetic limitations were the product of a competition between intra and intermolecular hydrogen bonding formation during the global process.     

Flavin Redox Bifurcation as a Mechanism for Controlling the Direction of Electron Flow during Extracellular Electron Transfer

The iron‐reducing bacterium Shewanella oneidensis MR‐1 has a dual directional electronic conduit involving 40 heme redox centers in flavin‐binding outer‐membrane c‐type cytochromes (OM c‐Cyts). While the mechanism for electron export from the OM c‐Cyts to an anode is well understood, how the redox centers in OM c‐Cyts take electrons from a cathode has not been elucidated at the molecular level. Electrochemical analysis of live cells during switching from anodic to cathodic conditions showed that altering the direction of electron flow does not require gene expression or protein synthesis, but simply redox potential shift about 300 mV for a flavin cofactor interacting with the OM c‐Cyts. That is, the redox bifurcation of the riboflavin cofactor in OM c‐Cyts switches the direction of electron conduction in the biological conduit at the cell–electrode interface to drive bacterial metabolism as either anode or cathode catalysts.     

S‐Click Reaction for Isotropic Orientation of Oxidases on Electrodes to Promote Electron Transfer at Low Potentials

Electrochemical sensors are essential for point‐of‐care testing (POCT) and wearable sensing devices. Establishing an efficient electron transfer route between redox enzymes and electrodes is key for converting enzyme‐catalyzed reactions into electrochemical signals, and for the development of robust, sensitive, and selective biosensors. We demonstrate that the site‐specific incorporation of a novel synthetic amino acid (2‐amino‐3‐(4‐mercaptophenyl)propanoic acid) into redox enzymes, followed by an S‐click reaction to wire the enzyme to the electrode, facilitates electron transfer. The fabricated biosensor demonstrated real‐time and selective monitoring of tryptophan (Trp) in blood and sweat samples, with a linear range of 0.02–0.8 mm . Further developments along this route may result in dramatic expansion of portable electrochemical sensors for diverse health‐determination molecules.     

Interconversion of Phosphinyl Radical and Phosphinidene Complexes by Proton Coupled Electron Transfer

The isolable complex [Os(PHMes*)H(PNP)] (Mes*=2,4,6‐^tBu₃C₆H₃; PNP=N{CHCHP^tBu₂}₂) exhibits high phosphinyl radical character. This compound offers access to the phosphinidene complex [Os(PMes*)H(PNP)] by P?H proton coupled electron transfer (PCET). The P?H bond dissociation energy (BDE) was determined by isothermal titration calorimetry and supporting DFT computations. The phosphinidene product exhibits electrophilic reactivity as demonstrated by intramolecular C?H activation.     

Birch‐Type Photoreduction of Arenes and Heteroarenes by Sensitized Electron Transfer

The direct reduction of arenes and heteroarenes by visible‐light irradiation remains challenging, as the energy of a single photon is not sufficient for breaking aromatic stabilization. Shown herein is that the energy accumulation of two visible‐light photons allows the dearomatization of arenes and heteroarenes. Mechanistic investigations confirm that the combination of energy‐transfer and electron‐transfer processes generates an arene radical anion, which is subsequently trapped by hydrogen‐atom transfer and finally protonated to form the dearomatized product. The photoreduction converts planar aromatic feedstock compounds into molecular skeletons that are of use in organic synthesis.     

电子穿梭体介导的微生物胞外电子传递:机制及应用

厌氧条件下微生物将电子传递给胞外电子受体的现象非常普遍,电子穿梭体(electron shuttle,ES)是介导胞外电子传递过程的重要途径之一,但其具体的机制尚未明晰。一部分微生物自身能分泌一些物质作为内生ES,另一部分微生物能利用天然存在或人工合成的某些物质作为外生ES,并将其携带的电子传递至微生物胞外电子受体。ES介导微生物胞外电子传递的基本过程为:氧化态电子穿梭体(ES_ox)接受电子变成还原态(ES_red),ES_red传递电子给胞外电子受体,自身再次氧化成ES_ox,从而循环往复。本文重点介绍不同种类ES及其电子穿梭机制,以及ES的分子扩散、氧化还原电势及电子转移能力对胞外电子传递过程的影响。ES介导的胞外电子传递过程直接影响污染物转化和微生物产电,因此在污染修复及生物能源等方面具有重要的应用前景。     

A Photophysical Study of Sensitization-Initiated Electron Transfer: Insights into the Mechanism of Photoredox Activity

The development of photocatalytic reactions has provided many novel opportunities to expand the scope of synthetic organic chemistry. In parallel with progress towards uncovering new reactivity, there is consensus that efforts focused on providing detailed mechanistic insight in order to uncover underlying excited-state reactions are essential to maximise formation of desired products. With this in mind, we have investigated the recently reported sensitization-initiated electron transfer (SenI-ET) reaction for the C−H arylation of activated aryl halides. Using a variety of techniques, and in particular nanosecond transient absorption spectroscopy, we are able to distinguish several characteristic signals from the excited-state species involved in the reaction, and subsequent kinetic analysis under various conditions has facilitated a detailed insight into the likely reaction mechanism.     

Light‐Triggered,Spatially Localized Chemistry by Photoinduced Electron Transfer

It is of immense interest to exert spatial and temporal control of chemical reactions. It is now demonstrated that irradiation can trigger reactions specifically at the surface of a simple colloidal construct, obtained by adsorbing polyethyleneimine on fluorescent colloidal particles. Exciting the fluorescent dye in the colloid affords photoinduced electron transfer to spatially proximal amine groups on the adsorbed polymer to form free radical ions. It is demonstrated that these can be harnessed to polymerize acrylic acid monomer at the particle surface, or to break up colloidal assemblies by cleaving a cross‐linked polymer mesh. Formation of free radical ions is not a function of the size of the colloid, neither is it restricted to a specific fluorophore. Fluorophores with redox potentials that allow photoinduced electron transfer with amine groups show formation of free radical ions.