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

这个子项目是许多利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 配体K边XAS是配体金属键合的直接探针。我们已经发展了这种方法来研究模型复合物的电子结构和蛋白质活性位点的Cu-S和Fe-S团簇。我们以前的研究结果表明，改变一个本地化的还原Fe 2S 2簇的<$2-S-硫桥到<$-3-S-硫桥减少反铁磁耦合相互作用，导致离域的基态在Fe 3S 4和Fe 4S 4集群。我们已经发现，有一个显着减少的Fe-S键的共价性在所有的蛋白质活性位点相对于模型，这可以归因于蛋白质中的氢键。特别地，在HiPIP中的四核[Fe 4S 4]簇的共价性与在铁氧还蛋白中的非常不同。该方法已被扩展到定义的非无辜性质的二硫纶配体在确定一系列经典的Ni-二硫纶配合物的氧化还原性质。我们计划评估HiPIP和铁氧化还原蛋白之间的差异的一般性，并系统地研究氢键，溶剂相互作用和改变这些集群周围的介电场的影响，使用良好的特征模型复合物和蛋白质。 我们将利用现有的[Fe_3S_4]团簇的研究结果来理解[MFe_3S_4]配合物的电子结构，这些配合物是固氮酶、CODH等杂原子团簇活性中心的模型。我们将评估Cys->Ser突变对单核、双核和四核团簇电子结构的影响。超氧化物还原酶和腈水合酶的非血红素铁活性位点将使用S K-边进行研究，以了解活性位点中存在的Fe-S键的氧化水平及其对调节反应性的贡献。我们还将探讨P450型活性位点和底物结合对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.