INVESTIGATION OF ELECTRONIC STRUCTURES OF FE-S AND MO-S ACTIVE SITES AND THEIR R

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。 配体K-EDGE XAS是配体金属键合的直接探针。我们发展了这种方法来研究铜-S和铁-S团簇的模型络合物和蛋白质活性中心的电子结构。我们以前的结果表明，将局域还原的Fe2S2团簇的2-S-硫键桥改变为-3-S-硫键桥，减少了反铁磁耦合作用，导致了Fe_3S_4和Fe_4S_4团簇的离域基态。我们发现与模型相比，所有蛋白质活性中心的Fe-S键的共价性都显著降低，这可以归因于蛋白质中的氢键。特别是，HIPIP中四核[Fe4S4]团簇的共价性与铁氧还蛋白有很大不同。在确定一系列经典的镍-二硫杂环戊烯络合物的氧化还原性质时，该方法已扩展到定义二硫杂环戊烯配体的非无害性质。我们计划评估HIPIPs和铁氧还蛋白差异的普遍性，并使用表征良好的模型络合物和蛋白质系统地研究氢键、溶剂相互作用和改变这些簇周围介电场的影响。我们将利用目前关于[Fe3S4]簇合物的结果来理解[MFe3S4]络合物的电子结构，这些[MFe3S4]络合物是包括固氮酶、CODH等异核簇合物活性中心的模型。我们将评估Cys-&gt；Ser突变对单核、双核和四核簇合物电子结构的影响。利用S K边研究超氧化物还原酶和氰基水合酶的非血红素铁活性中心，以了解活性中心中铁-S键的氧化程度及其对反应活性的调节作用。我们还将探索P450类型的活性中心以及底物结合对Fe-S键的影响。

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. Ligand K-edge XAS is a direct probe of ligand metal bonding. We have developed this methodology to investigate the electronic structures of model complexes and protein active-sites of Cu-S and Fe-S clusters. Our previous results showed that changing a ¿2-S-sulfide bridge of a localized reduced Fe2S2 cluster to a ¿-3-S-sulfide bridge reduces the anti-ferromagnetic coupling interaction leading to delocalized ground states in Fe3S4 and Fe4S4 clusters. We have found that there is a significant reduction of Fe-S bond covalency in all the protein active-sites relative to the models, which can be attributed to H-bonding in the protein. Particularly, the covalency of the tetranuclear [Fe4S4] cluster in HiPIP was very different than that in ferredoxin. The method has been extended to define the non-innocent nature of the dithiolene ligands in determining the redox properties of a classic series of Ni-dithiolene complexes. We plan to evaluate the generality of the difference between HiPIPs and ferredoxins and systematically study the effect of H-bonding, solvent interaction and effect of changing dielectric field around these clusters using well-characterized model complexes and proteins. We will use current results on [Fe3S4] clusters to understand the electronic structures of [MFe3S4] complexes which are models for the active sites of heteronuclear clusters including nitrogenase, CODH, etc. The effects of Cys->Ser mutation on the electronic structures of mononuclear, binuclear and tetranuclear clusters will be evaluated. The non-heme iron active sites of superoxide reductase and nitrile hydratase will be studied using S K-edge to understand the oxidation level of the Fe-S bonds present in the active site and their contribution to tuning reactivity. We will also explore P450 type active sites and the effect of substrate binding on the Fe-S bond.