PES/DFT STUDIES ON ELECTRONIC STRUCTURE CONTRIBUTIONS TO ELECTRON TRANSFER

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。我们的主要研究重点是应用可变能量光电子能谱（PES）结合x射线吸收边缘光谱（XAS）来定义生物系统中电子转移（ET）的电子结构贡献。PES提供了一种直接的方法来研究无机氧化还原过程和电子弛豫对氧化还原性质的贡献（E¿¿，HAB, l）。核心和价态PES数据中存在的振荡卫星结构可以与价键构型相互作用（VBCI）模型结合使用，以实验方式量化电子弛豫（即金属配合物在氧化时电子结构的变化）及其对ET还原电位和动力学的贡献。可变能量PES实验提供了一种机制，可以最大化金属而最小化配体对价带区的贡献横截面效应（延迟最大值和库珀最小值）和共振增强。我们基于同步加速器的简单模型体系[FeX4]2-/1 （X=Cl-, - sr）的研究提供了定义电子结构及其氧化还原变化的实验结果。在密度泛函理论（DFT）计算的补充下，这些研究提供了对电子松弛的深入了解，并允许扩展到金属蛋白位点。使用在[FeX4]2-/1研究中开发的方法，我们现在正在检查模型血红素复合物。血红素模型的数据与DFT计算相结合，也应该允许扩展和定义细胞色素中ET的超交换途径。我们还将这些PES/DFT研究扩展到模拟4Fe铁氧化还原蛋白和HiPIPs（高电位铁蛋白）的[Fe4S4(SR)4]系统，这将深入了解电子弛豫及其对铁氧化还原蛋白和HiPIPs中ET的动力学和途径的贡献。

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, l). 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.