LIGAND K-EDGE STUDIES OF IRON-SULFUR PROTEINS AND MODEL COMPLEXES

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心机构，不一定为研究者机构。从我们以前的研究中，它被确定，配体K-边缘可以用来定量开壳金属离子的共价。首先，进行了一系列金属四氯化物的Cl K-边缘。利用多重理论和不可约张量方法对d-流形中含有多个空穴的金属位进行了分析。然后将分析扩展到一系列金属四硫醇盐和单体和二聚体Fe-S蛋白和模型络合物。结果发现，在蛋白质中的H-键合的效果相比，模型中可以检测到的S前边缘功能的强度和硫醇盐和硫化物的贡献可以解决由于有效的核电荷的配体的差异。在此基础上，进一步将分析扩展到四核和三核Fe-S模型配合物和蛋白质、异金属立方烷和固氮酶的FeMoco。硫键的变化，从二聚体的Fe-S簇到四聚体的Fe-S簇的影响在混合价形式的离域行为将被研究。将评价对H-键合的影响及其对HIPIP与4Fe铁氧还蛋白的还原电位的影响。此外，还研究了C.巴氏杆菌在混合价形式中的离域性将通过S K边XAS来检查。进一步分析了异金属离子对[Fe 3S 4]电子结构的影响，为固氮酶FeMoco的分析奠定了基础。这些研究将用于了解生物无机系统的共价性和电子结构，并评估其对功能的贡献。

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. From our previous studies it was determined that ligand K-edges could be used to quantitate covalency in open-shell metal ions. Initially, the Cl K-edge of a series metal tetrachlorides was performed. The analysis of metal sites with more than one hole in the d-manifold was performed using multiple theory and the irreducible tensor method. The analysis was then extended to a series of metal tetrathiolates and monomeric and dimeric Fe-S proteins and model complexes. It was found that the effect of H-bonding in the proteins in comparison to the models can be detected in the intensity of the S pre-edge feature and that the contributions of thiolate and sulfide can be resolved due to differences in effective nuclear charge of the ligands. Based on these results, the analysis will be extended to tetra and trinuclear Fe-S model complexes and proteins, heterometal cubanes and the FeMoco of nitrogenase. The change of the sulfide bonding by going from the dimeric Fe-S clusters to the tetrameric Fe-S cluster which affects the delocalization behavior in the mixed valent forms will be studied. The effect on H-bonding and its effect on the reduction potential of HIPIP vs. 4Fe ferredoxin will be evaluated. Also the effect of the serine to cysteine mutation in 2Fe ferredoxin of C. pasteurianum on delocalization in the mixed valent form will be examined by S K-edge XAS. Further the effect of a heterometal on the electronic structure of [Fe3S4] will be analyzed and the results will build the basis for analysis of FeMoco from nitrogenase. These studies will be used to understand covalency and electronic structure of bioinorganic systems and evaluate their contributions to function.