PES/DFT STUDIES ON ELECTRONIC STRUCTURE CONTRIBUTIONS TO ELECTRON TRANSFER

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 我们的研究重点是将变能光电子能谱(PES)与X射线吸收边能谱(XAS)相结合来确定生物体系中电子结构对电子转移(ET)的贡献。PES为研究无机氧化还原过程和电子弛豫对氧化还原性质(E、HAB、λ)的贡献提供了直接方法。核心和价态PES数据中存在的震荡卫星结构可以与价键组态相互作用(VBCI)模型相结合来实验量化电子弛豫(即氧化后金属络合物电子结构的变化)及其对ET还原电位和动力学的贡献。变能质子交换实验提供了一种机制，通过截面效应(延迟最大值和库珀最小值)和共振增强来最大化金属，同时最小化配体对价带区域的贡献。我们对简单模型体系[FeX4]2-/1(X=Cl-，-SR)的同步加速器研究提供了定义电子结构及其在氧化还原过程中的变化的实验结果。在密度泛函理论(DFT)计算的补充下，这些研究提供了对电子弛豫的洞察，并允许扩展到金属蛋白质位置。使用在[FeX4]2-/1的研究中开发的方法，我们现在正在检查模型血红素络合物。血红素模型上的数据结合密度泛函计算也应该允许扩展和定义细胞色素中ET的超交换途径。我们还将把这些PES/DFT研究扩展到[Fe4S4(SR)4]模拟4Fe铁还蛋白和HIPIPS(高势铁蛋白)的体系，这将提供对电子松弛及其对铁还蛋白和HIPIPS中ET的动力学和途径的贡献的洞察力。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The major emphasis of our research is to apply variable energy photoelectron spectroscopy (PES) combined with X-ray absorption edge spectroscopy (XAS) to define electronic structure contributions to electron transfer (ET) in biological systems. PES provides a direct method to study inorganic redox processes and the contribution of electronic relaxation to redox properties (E¿, HAB, lambda). The shake-up satellite structure present in core and valence PES data can be used in combination with a valence bond configuration interaction (VBCI) model to experimentally quantify electronic relaxation (i.e. the change in electronic structure of metal complexes upon oxidation) and its contributions to reduction potentials and kinetics of ET. Variable-energy PES experiments provide a mechanism to maximize the metal while minimizing the ligand contributions to the valence band region through cross section effects (delayed maximum and Cooper minimum) and resonance enhancement. Our synchrotron-based studies on simple model systems [FeX4]2-/1 (X=Cl-, -SR) have afforded experimental results that define electronic structure and its changes upon redox. Complemented by density functional theory (DFT) calculations, these studies provide insight into electronic relaxation and allow extension to the metalloprotein sites. Using the methodology developed in the studies on [FeX4]2-/1, we are now examining model heme complexes. The data on the heme models combined with DFT calculations should also allow extention to and define the superexchange pathways for ET in the cytochromes. We will also extend these PES/DFT studies to [Fe4S4(SR)4] systems modeling the 4Fe ferredoxins and HiPIPs (high potential iron proteins), which will provide insight into electronic relaxation and its contributions to the kinetics and pathways for ET in the ferredoxins and HiPIPS.