Factors Influencing Coordinated Ni(II) Cysteinate Basicity and Redox Potentials

在这项由美国国家科学基金会化学部化学结构、动态和机理B计划资助的项目中，内华达大学化学系的Jason Sheeller教授将继续进行研究，旨在了解硫酸盐连接的过渡金属中心如何促进质子耦合电子转移(PCET)反应。PCET反应涉及氢原子的净转移，在化学和生物学中具有重要意义。尽管这些反应很重要，但这些反应的细节仍然是一个激烈辩论和研究的主题。本项目的重点是了解质子化的硫酸盐配体与还原的晚期第一排过渡金属中心(R-S(H+)-M)配位在此类反应中的作用。由R-S(H+)-M部分支持的反应在许多生物系统中具有潜在的重要性，从促进氢气产生到远程电子转移到底物还原。因此，PCET反应的这一子集在开发与氢经济和工业催化(底物氧化还原化学)相关的新的生物启发技术方面具有潜在的应用。除了设计和生产能够促进R-S(H+)-M介导的PCET反应的小分子体系外，该项目还将研究这些体系的基本物理性质如何对整个PCET反应做出贡献。学生培训和开发新的科学技术将适用于这一倡议所进行的具体研究之外，这是该项目的基本方面。一个质子和一个电子的几乎同时转移是一个基本重要的化学过程。有强有力的证据表明，质子化的硫代配体以低氧化态(R-S(H+)-M；M=Fe-Ni)与第一排过渡金属配位，可以通过PCET过程还原底物。该项目的总体目标是a)了解此类反应的普遍性，b)探索它们在重要的生物和化学过程中的适用性(即制氢、远程电子转移和底物还原)。具体地说，这项研究试图了解R-S(H+)-Ni催化还原反应的基本方面，使用还原的硫酸盐连接的含镍(II)和镍(I)的络合物和金属多肽。特别强调了解金属酶镍超氧化物歧化酶，它可能利用半胱氨酸-S(H+)-镍部分促进氧阴离子还原。质子化的硫代镍络合物的几何结构、物理性质(R-S(H+)-镍的酸性、氧化还原电位)和电子结构将与它们进行PCET反应的能力相关联。还将注意整个PCET过程的基本细节(即区分协调的PCET与顺序的PCET与氢原子转移反应)。

In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the NSF Division of Chemistry, Professor Jason Shearer of the Department of Chemistry at the University of Nevada, Reno will pursue research aimed at understanding how thiolate ligated transition metal centers facilitate proton coupled electron transfer (PCET) reactions. PCET reactions involve the net transfer of a hydrogen atom, and are of fundamental importance in chemistry and biology. Despite their importance, the details of such reactions are still a subject of intense debate and study. This project focuses on understanding the role of protonated thiolate ligands coordinated to reduced late first-row transition metal centers (R-S(H+)-M) in such reactions. Reactions supported by the R-S(H+)-M moiety have potential importance in many biological systems ranging from those that facilitate hydrogen production to long-range electron transfer to substrate reduction. As such, this subset of PCET reactions have potential applications in the development of new bioinspired technologies with relevance to the hydrogen economy and industrial catalysis (substrate redox chemistry). In addition to the design and production of small molecule systems that can facilitate R-S(H+)-M mediated PCET reactions, the project will also examine how the fundamental physical properties of these systems contribute to the overall PCET reaction. Student training and the development of new scientific techniques that will be applicable beyond the specific research pursued under this initiative are fundamental aspects of this project.The near simultaneous transfer of a proton and an electron is a fundamentally important chemical process. There is strong evidence that protonated thiolate ligands coordinated to late first-row transition metals in low oxidation states (R-S(H+)-M; M = Fe - Ni) can reduce substrates through PCET processes. The overall goals of this project are to a) understand how general such reactions are, and b) explore their applicability to important biological and chemical processes (i.e. hydrogen production, long range electron transfer, and substrate reduction). Specifically, this research seeks to understand the fundamental aspects of R-S(H+)-Ni mediated reduction reactions using reduced thiolate ligated Ni(II) and Ni(I) containing complexes and metallopeptides. Special emphasis will be given to understanding the metalloenzyme nickel superoxide dismutase, which likely utilizes a Cys-S(H+)-Ni moiety to facilitate oxygen anion reduction. The geometric structure, physical properties (R-S(H+)-Ni acidity, redox potentials), and electronic structure of protonated nickel-thiolate complexes with their ability to perform PCET reactions will be correlated. Attention will also be given to the fundamental details of the overall PCET process (i.e. distinguishing between concerted vs. sequential PCET vs. hydrogen atom transfer reactions).