Electronic Absorption Spectra and Redox Properties of C Type Cytochromes in Living Microbes

Shewanella is an electrogenic microbe that has significant content of c type cytochromes (ca. 0.5 mM ). This feature allows the optical absorption spectra of the cell‐membrane‐associated proteins to be monitored in vivo in the course of extracellular respiratory electron‐transfer reactions. The results show significant differences to those obtained in vitro with purified proteins.

     

微生物电化学系统电子中介体

电化学活性微生物与电极之间的胞外电子传递在微生物电化学系统(microbial electrochemical systems,MESs)产能、生物修复等功能的实现中起着关键作用.目前,研究者对微生物胞外电子传递机理了解有限,限制了MESs的应用.相比于需要微生物功能蛋白与电极接触才能发生的直接电子传递,间接电子传递可通过具有可逆氧化还原活性的电子中介体(electron transfer mediators,ETMs)实现电子的传递,从而有效提高微生物胞外电子传递效率.在间接电子转移过程中,ETMs起着中间电子受体和中间电子供体的作用,即被还原后可将电子传递给最终电子受体并被重新还原;理论上每个ETMs分子可以循环数千次,因此ETMs对特定环境下终端氧化物(如铁离子)的循环有着极其显著的作用.本文系统总结了MESs中ETMs及间接电子传递机制近年来的研究进展,并且在此基础上探讨了ETMs在MESs中的研究趋势,以期推动MESs在生物修复、能源生产方面的实际应用.     

Wettability‐Regulated Extracellular Electron Transfer from the Living Organism of Shewanella loihica PV‐4

C‐type cytochromes located on the outer membrane (OMCs) of genus Shewanella act as the main redox‐active species to mediate extracellular electron transfer (EET) from the inside of the outer membrane to the external environment: the central challenge that must be met for successful EET. The redox states of OMCs play a crucial role in dictating the rate and extent of EET. Here, we report that the surface wettability of the electrodes strongly influences the EET activity of living organisms of Shewanella loihica PV‐4 at a fixed external potential: the EET activity on a hydrophilic electrode is more than five times higher than that on a hydrophobic one. We propose that the redox state of OMCs varies significantly at electrodes with different wettability, resulting in different EET activities.     

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。     

Formation of Silver Nanoparticles by Electron Transfer in Peptides and c-Cytochromes

The reduction of Ag⁺ ions to Ag⁰ atoms is a highly endergonic reaction step, only the aggregation to Ag_n clusters leads to an exergonic process. These elementary chemical reactions play a decisive role if Ag nanoparticles (AgNPs) are generated by electron transfer (ET) reactions to Ag⁺ ions. We studied the formation of AgNPs in peptides by photoinduced ET, and in c-cytochromes by ET from their Fe²⁺/hemes. Our earlier photoinduced experiments in peptides had demonstrated that histidine prevents AgNP formation. We have now observed that AgNPs can be easily synthesized with less-efficient Ag⁺-binding amino acids, and the rate increases in the order lysine<asparagine<aspartate<serine. The ability of Fe²⁺/hemes of c-cytochromes to reduce Ag⁺ to AgNPs was studied in an enzymatic experiment and with living bacteria Geobacter sulfurreducens (Gs).     

革兰氏阳性电活性菌的电子传递及其应用

电活性菌将电子从胞内转移至胞外电子受体或者将胞外电子转移至胞内的过程为胞外电子传递,其在微生物群落间的电子传递及元素的地球化学循环过程中发挥重要作用。电活性菌的胞外电子传递研究前期主要集中于革兰氏阴性菌,由于革兰氏阳性菌与革兰氏阴性菌的膜结构/厚度明显不同,因此二者的电子跨膜传递途径差异明显。革兰氏阳性菌因分布广泛且可在高温、低pH、高pH和高盐等环境中生存,其电活性和电子传递机制也逐渐引起关注。本文归纳总结了革兰氏阳性电活性菌的电子传递类型,基于厚壁菌门、放线菌门和绿弯菌门的分类阐述胞外电子传递的研究进展,分析了革兰氏阳性电活性菌在污染物降解、生物能源和工业制品合成等方面的应用,并展望了未来的发展方向。     

Organic Electron Donors as Powerful Single‐Electron Reducing Agents in Organic Synthesis

One‐electron reduction is commonly used in organic chemistry for the formation of radicals by the stepwise transfer of one or two electrons from a donor to an organic substrate. Besides metallic reagents, single‐electron reducers based on neutral organic molecules have emerged as an attractive novel source of reducing electrons. The past 20 years have seen the blossoming of a particular class of organic reducing agents, the electron‐rich olefins, and their application in organic synthesis. This Review gives an overview of the different types of organic donors and their specific characteristics in organic transformations.     

基于电活性菌群的生物电催化体系的有效构筑及其强化胞外电子传递过程的应用

传统的电活性微生物(Electro-Active Bacteria,EAB)主导的胞外电子传递(Extracellular Electron Transfer,EET)效率较低,极大程度地限制了微生物电催化在环境及工业中的应用。为打破这一瓶颈,近年来多国科学家尝试开发先进的催化材料以强化生物电催化体系(Bio-Electrocatalytic System,BES)中的电子传递效能。借用材料科学、电微生物学及合成生物学技术等多学科手段尝试将传统无机催化材料及电活性微生物进行理性优化,将有望强化电子的传递通量和效率。这种优化升级推动了传统单一的无机催化材料向活体生物催化材料过渡,并有望朝着向更精细化、智能可控的先进材料升级改造,也为拓展先进材料的规模化应用提供更有利的技术支撑。本文对现阶段几种强化EET的有效手段用以有效构筑BES展开综述,包括了微生物-石墨烯改性复合材料、原位杂化光催化半导体材料自组装微生物、核/壳装配的生物材料及接种基因工程菌等内容,最后总结了微生物活体生物材料所面临的挑战及未来在环境应用中所面临的机遇。     

Electron tunneling in proteins program

We developed a unique integrated software package (called Electron Tunneling in Proteins Program or ETP) which provides an environment with different capabilities such as tunneling current calculation, semi‐empirical quantum mechanical calculation, and molecular modeling simulation for calculation and analysis of electron transfer reactions in proteins. ETP program is developed as a cross‐platform client‐server program in which all the different calculations are conducted at the server side while only the client terminal displays the resulting calculation outputs in the different supported representations. ETP program is integrated with a set of well‐known computational software packages including Gaussian, BALLVIEW, Dowser, pKip, and APBS. In addition, ETP program supports various visualization methods for the tunneling calculation results that assist in a more comprehensive understanding of the tunneling process. © 2016 Wiley Periodicals, Inc.     

电化学联用技术研究微生物的胞外电子传递机制

胞外电子传递（EET）是指氧化还原反应所产生的电子在微生物细胞内和细胞外的电子受体/电子供体之间互相转移的过程,这一过程伴随着能量和物质的转化。阐明EET机制是提高微生物能量和物质转化效率的基础,为元素的生物地球化学循环、金属防腐以及生物电化学系统的应用等提供理论支撑。电化学技术作为研究电极/溶液界面电子转移的简便、有效方法,在研究微生物的直接电子传递和间接电子传递机制中发挥了重要的作用,也促进了EET机制的研究从宏观层面到微观层面不断深入。本文综述了研究微生物EET机制所涉及的电化学联用技术（包括微电极、扫描电化学显微镜、电化学联用光学显微镜和光谱电化学等）;详细介绍了这些电化学联用技术的功能和优势;重点阐述了这些电化学联用技术如何推动着EET机制的研究,从宏观的生物膜层面到微观的单个微生物细胞、蛋白和分子层面不断深入;展望了新的电化学联用技术在EET研究领域的应用前景。     

Gold(II) Porphyrins in Photoinduced Electron Transfer Reactions

In the context of solar-to-chemical energy conversion, inspired by natural photosynthesis, the synthesis, electrochemical properties and photoinduced electron-transfer processes of three novel zinc(II)-gold(III) bis(porphyrin) dyads [Zn^II(P)–Au^III(P)]⁺ are presented (P: tetraaryl porphyrin). Time-resolved spectroscopic studies indicated ultrafast dynamics (k >10¹⁰ s⁻¹) after visible-light excitation, which finally yielded a charge-shifted state [Zn^II(P ^{⋅ +})–Au^II(P)]⁺ featuring a gold(II) center. The lifetime of this excited state is quite long due to a comparably slow charge recombination (k ≈3×10⁸ s⁻¹). The [Zn^II(P ^{⋅ +})–Au^II(P)]⁺ charge-shifted state is reductively quenched by amines in bimolecular reactions, yielding the neutral zinc(II)–gold(II) bis(porphyrin) Zn^II(P)–Au^II(P). The electronic nature of this key gold(II) intermediate, prepared by chemical or photochemical reduction, is elucidated by UV/Vis, X-band EPR, gold L₃-edge X-ray absorption near edge structure (XANES) and paramagnetic ¹H NMR spectroscopy as well as by quantum chemical calculations. Finally, the gold(II) site in Zn^II(P)–Au^II(P) is thermodynamically and kinetically competent to reduce an aryl azide to the corresponding aryl amine, paving the way to catalytic applications of gold(III) porphyrins in photoredox catalysis involving the gold(III/II) redox couple.     

Charge Transfer and Electron Pairing in Fullerenes

Electron transfer is a common characteristic in fullerene complexes and brings about an optoelectronic effect in a polymer-C₆₀ composite and superconductivity in alkali-metal doped C₆₀. This paper reports that the concept of self-trapping of the transferred electron in C₆₀ can explain the main features of photoinduced electron transfer in a polymer-CC₆₀ composite and electron pairing in alkali-metal doped C₆₀.     

Photoinduced Electron vs. Concerted Proton Electron Transfer Pathways in SnIV (l-Tryptophanato)2 Porphyrin Conjugates

Aromatic amino acids such as l -tyrosine and l -tryptophan are deployed in natural systems to mediate electron transfer (ET) reactions. While tyrosine oxidation is always coupled to deprotonation (proton-coupled electron-transfer, PCET), both ET-only and PCET pathways can occur in the case of the tryptophan residue. In the present work, two novel conjugates 1 and 2 , based on a Sn^IV tetraphenylporphyrin and Sn^IV octaethylporphyrin, respectively, as the chromophore/electron acceptor and l -tryptophan as electron/proton donor, have been prepared and thoroughly characterized by a combination of different techniques including single crystal X-ray analysis. The photophysical investigation of 1 and 2 in CH₂Cl₂ in the presence of pyrrolidine as a base shows that different quenching mechanisms are operating upon visible-light excitation of the porphyrin component, namely photoinduced electron transfer and concerted proton electron transfer (CPET), depending on the chromophore identity and spin multiplicity of the excited state. The results are compared with those previously described for metal-mediated analogues featuring Sn^IV porphyrin chromophores and l -tyrosine as the redox active amino acid and well illustrate the peculiar role of l -tryptophan with respect to PCET.     

Electron Transfer and Multi‐Electron Accumulation in ExBox4+

Molecules capable of accepting and storing multiple electrons are crucial components of artificial photosynthetic systems designed to drive catalysts, such as those used to reduce protons to hydrogen. ExBox⁴⁺, a boxlike cyclophane comprising two π‐electron‐poor extended viologen units tethered at both ends by two p‐xylylene linkers, has been shown previously to accept an electron through space from a photoexcited guest. Herein is an investigation of an alternate, through‐bond intramolecular electron‐transfer pathway involving ExBox⁴⁺ using a combination of transient absorption and femtosecond stimulated Raman spectroscopy (FSRS). Upon photoexcitation of ExBox⁴⁺, an electron is transferred from one of the p‐xylylene linkers to one of the extended viologen units in ca. 240 ps and recombines in ca. 4 ns. A crystal structure of the doubly reduced species ExBox²⁺ was obtained.