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

Board Of Regents, Nshe, Obo University Of Nevada, Reno, Reno NV

Investigators

Abstract

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).