Mechanisms of Proton Coupled Electron Transfer

Thomas J.Meyer博士，北卡罗来纳大学教堂山分校化学系，由化学部无机化学、生物无机化学和有机金属化学项目支持，研究质子耦合电子转移(PCET)反应的机理。具体地说，这项研究将针对一种特殊类型的PCET反应，即电子质子转移(EPT)，在这种反应中，电子-质子从施主上的轨道分离位置发生协同电子-质子转移到一个或多个受体上的轨道分离位置。尽管EPT比电子转移和质子转移复杂，反之亦然，但EPT可以通过避免高能中间体来控制PCET的反应活性。光驱动或光学EPT将被研究分子内、氢键缔合络合物内以及配体桥联的混合价络合物中的电荷转移。这项工作将利用光谱测量和动态测量相结合的方法来表征光学EPT，包括超快测量。我们的目标是展示光学EPT现象的广度，并使用光谱和动态信息结合理论来深入了解EPT，其水平可与我们目前对电子转移的理解相媲美。此外，还将探索一种基于EPT猝灭和耦合质子转移的新型金属络合物激发态反应性。EPT猝灭和反向反应将利用瞬时吸收、发射和红外技术进行研究，以跟踪交换的质子，并建立KH/KD动力学同位素效应和自由能依赖关系。大多数重要的能量相关和/或生物相关的能量转换反应涉及催化的多电子、多质子变化。例如，在生物反应中，催化剂的活化通常在空间分离的位置上一次一个电子地发生。这个项目将研究电子和质子在这些过程中如何转移的详细机制，从而揭示电子转移反应实际上发生的重要程度。除了科学贡献外，该项目还将提供综合和测量之间的交叉，并应用理论为本科生和研究生以及博士后研究员的参与和培训创造良好的环境。

Dr. Thomas J. Meyer, Chemistry Department, University of North Carolina - Chapel Hill, is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry Program of the Chemistry Division for studies of the mechanism of proton coupled electron transfer (PCET) reactions. Specifically, this study will target a particular type of PCET reactions, Electron Proton Transfer (EPT) in which concerted electron-proton transfer occurs from orbitally separated sites on the donor to orbitally separated sites on an acceptor or acceptors. Although more complex than electron transfer followed by proton transfer or vice versa, EPT can dominate PCET reactivity by avoiding high energy intermediates. Light-driven or optical EPT will be investigated for charge transfer within molecules, within H-bonded association complexes, and in ligand-bridged mixed valence complexes. This work will utilize a combination of spectroscopic and dynamic measurements to characterize optical EPT, including ultrafast measurements. The goal is to demonstrate the breadth of optical EPT phenomena and to use spectroscopic and dynamic information combined with theory to gain insight about EPT at a level comparable to our current understanding of electron transfer. Additionally, a new type of metal complex excited state reactivity based on EPT quenching with coupled proton transfer will be explored. EPT quenching and back reactions will be investigated using transient absorption, emission, and infrared techniques to follow the exchanging proton and to establish kH/kD kinetic isotope effects and free energy dependences in the normal and inverted regions.Most important energy related and/or biologically relevant reactions for energy conversion involve catalyzed multi electron, multi proton changes. For example, in biological reactions, catalyst activation typically occurs one electron at a time at spatially separated sites. This project will examine the detailed mechanism of how electrons and protons are transferred in such processes and, thus, will shed light on how important electron transfer reactions actually occur. In addition to the scientific contributions, this project will provide a cross over between synthesis and measurements with application of theory creating an excellent environment for engaging and training undergraduates and graduate students, and postdoctoral research fellows.