IRON L-EDGE XAS OF HEME, HIGH-VALENT OXYGEN INTERMEDIATES, AND BINUCLEAR MODELS

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。 在我们之前的提议中进行的研究中，发展了一种新的方法来分析和解释用总轨道共价性(DOC)和微分轨道共价性(DOC)来解释铁原子边缘跃迁强度分布。结果表明，铁L边的积分强度可以用来计算络合物的总共价性。此外，还发展了一种投影方法，允许根据L边多重态强度分布实验确定单个对称性相关轨道集和DOC的共价性。前面的研究是本文提出的一系列研究的基础。在前人对低自旋血红素络合物反键研究的基础上，一系列高自旋血红素络合物将被理解为L边多重态结构。这项工作，结合低自旋血红素的L边缘，将被用来帮助从光谱上解决长期存在的涉及O2与血红蛋白结合的问题。然后，这些血红素研究将被应用于确定一系列作为细胞色素c氧化酶模型的络合物的电子结构。这些模型的共价性和DOC的测定将有助于深入了解该酶的电子结构以及与O-O键断裂相关的差异。接下来，由于许多非血红素铁酶的酶周转被认为涉及高价Fe(IV)=O中间体，我们将利用对铁的L边的理解来观察一系列已知的执行H原子抽象的S=1和S=2Fe(IV)=O模型络合物。然后，我们将把这些研究扩展到一系列高价双核模型络合物，目的是从机理上深入了解甲烷单加氧酶的活性部位。最后，我们将使用Fe Ledge XAS来了解Fe-NO键的性质，即NO与O2反应的关系。

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. In studies performed during our previous proposals, a new methodology was developed for analyzing and interpreting iron Ledge transition intensity distributions in terms of the total and differential orbital covalency (DOC). It was found that the integrated iron L-edge intensity could be used to obtain the total covalency of the complex. Furthermore, a projection methodology was developed which allows the covalency of the individual symmetry-related sets of orbitals and the DOC to be experimentally determined from the L-edge multiplet intensity distribution. The previous study serves as a foundation for the series of studies proposed here. Building on previous studies of back-bonding in low-spin heme complexes, a series of high-spin heme complexes will be understood in terms of the L-edge multiplet structure. This work, combined with the L-edge of low-spin heme, will be used to help spectroscopally resolve long-standing issues involving the binding of O2 to hemoglobin. These heme studies will then be applied to determining the electronic structure in a series of complexes that serve as models of the enzyme cytochrome c oxidase. The determination of covalency and DOC of these models will provide insight into the electronic structure of this enzyme and differences related to the O-O bond cleavage. Next, because the enzymatic turnover in many non-heme iron enzymes is thought to involve a highvalent Fe(IV)=O intermediate, our understanding of the iron L-edge will be use to look at a series of S=1 and S=2 Fe(IV)=O model complexes known to perform H-atom abstraction. We will then extend these studies to series of high-valent binuclear model complexes with the goal of obtaining mechanistic insight into the active site methane monooxygenase. Finally we will use iron Ledge XAS to understand the nature of the Fe-NO bond as NO in relation to reactions with O2.