SITE SELECTIVE EXAFS AND RIXS OF FE-ONLY HYDROGENASE AND RELATED MODELS

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来源获得了主要资金，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。这一提议是我们对关键金属酶FeFe氢化酶及其催化二氢活化机理研究的一部分：2 H ++2e- = H2。 我们建议使用我们的高分辨率发射光谱仪BioCAT上测量纯化的酶以及简单的无机“模型”化合物的XES的位点选择性EXAFS。FeFe] H2酶是已知的最有效的H2催化剂之一，Kcat值高达6000 H2 s-1，尽管有优异的晶体结构和广泛的光谱研究，但对分子和电子结构的许多问题仍然知之甚少。(1)在活化和催化过程中，团簇的结构和构象发生了什么变化？(2)二聚铁子位的氧化态和自旋态是什么？这更有利于氢键结合？如果是这样，怎么做，为什么？XES应该能让我们解决氧化态的问题。我们以前的H-团簇模型表明其低自旋Fe（I）的性质，并且价区域对团簇氧化态和/或桥连CO的存在敏感。我们建议进一步研究模型化合物，并将研究扩展到纯化的蛋白质，从而解决氧化态问题。 对纯化蛋白质的位点选择性EXAFS也有助于解决结构和构象问题。由于立方烷4Fe几乎肯定是高自旋的，2Fe子位是低自旋的，因此选择性EXAFS应该在结构上表征低自旋2Fe子位与4Fe立方烷的预期动态变化。

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. This proposal is part of our study on the critical metalloenzyme FeFe hydrogenase, and its mechanism of catalytic dihydrogen activation: 2H+ + 2e- = H2. We propose to use our high-resolution emission spectrometer on BioCAT to measure both site-selective EXAFS on purified enzyme as well as XES on simple inorganic "model" compounds. FeFe] H2ases are among the most efficient H2 catalysts known, with Kcat values up to 6000 H2 s-1 Despite the availability of excellent crystal structures and extensive spectroscopic study many questions about the molecular and electronic structure are still poorly understood. (1) What are the structural and conformational changes in the cluster during activation and catalysis?. (2) What are the oxidation states and spin-states of the dimeric Fe sub-sites. this more favorable towards hydrogen binding? If so how, and why? XES should allow us to resolve the oxidation state problem. Our previous on H-cluster models showed their low-spin Fe(I) nature, and that the valance region is sensitive to cluster oxidation state and/or the presence of a bridging CO. We propose to study further model compounds and extend the studies to purified protein, thus resolving the oxidation state issue. Site-selective EXAFS on purified protein should also help resolve the structural and conformational issues. As the cubane 4Fe are almost certainly high-spin, and the 2Fe subsite is low-spin, site-selective EXAFS should structurally characterize the expected dynamic changes of the low-spin 2Fe subsite separately from the 4Fe cubane.