ELECTRONIC STRUCTURE OF IRON ENZYME INTERMEDIATES FROM HIGH-RESOLUTION RIXS

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。 这项研究的目标是开发1s2p共振非弹性X射线散射(RIXS)，作为研究酶中间体的通用和定量工具。我们以前在上海同步辐射实验室使用了金属L边光谱来扩展金属-配体共价性的概念，表明L边带形可以用来量化配体与不同对称性的金属d轨道之间的相互作用，即差分轨道共价性。DOC方法允许对化学中的基本概念进行实验确定。然而，金属L边缘光谱是在超高真空中用软X射线进行的，一般不能用于酶中间体。1s2p RIXS包括从1s3d(h~7.1keV)激发和监测随后的2p 1s光子发射(H2~6.4keV)。这个共振过程的终态是2p53dn1，与L边实验的终态相同。1s2p RIXS使用硬X射线，不需要超高真空，因此可以在原位条件下获得L类边光谱。我们的新贡献是使用DOC分析对能量转移(h-H2)方向的RIXS光谱进行了定量分析。2p空穴的长寿命导致了尖锐和特征丰富的光谱，可以使用包括配置相互作用的参数化多重态模型进行精确拟合。随后从理论模型中提取了包括DOC在内的电子结构。该方法将用于研究激活惰性C？H键的高价酶中间体；血红素化合物I和II，SyrB2中的非血红素铁氧基中间体，以及双核铁酶甲烷单加氧酶中的中间体Q。RIXS提供了一种新的工具来研究C？H键激活的要求，也可以解释血红素酶和非血红素酶之间反应活性的差异。

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. The goal of the proposed research is to develop 1s2p resonant inelastic x-ray scattering (RIXS) as a general and quantitative tool for studying enzyme intermediates. We have previously used metal L-edge spectroscopy at SSRL to extend the concept of metal-ligand covalency by showing that the L-edge band shape can be used to quantify interactions between ligands and metal d-orbitals of different symmetry, i.e., differential orbital covalency (DOC). The DOC method allows for experimental determination of basic concepts in chemistry. However, metal L-edge spectroscopy is performed with soft x-rays in ultra-high vacuum and cannot in general be used for enzyme intermediates. 1s2p RIXS involves excitation from 1s 3d (h ~ 7.1 keV) and monitoring of the subsequent 2p 1s photon emission (h2 ~ 6.4 keV). The final state in this resonance process is 2p53dn+1, the same final state as for the L-edge experiment. 1s2p RIXS uses hard x-rays and does not require ultra-high vacuum, and can therefore be used to obtain L-edge-like spectra under in situ conditions. Our new contribution is a quantitative analysis of RIXS spectra in the energy transfer (h - h2) direction using the DOC analysis. The long life time of the 2p hole results in a sharp and feature-rich spectrum that can be accurately fitted using a parameterized multiplet model that includes configuration interaction. The electronic structure, including the DOC, is subsequently extracted from the theoretical model. The method will be used to study high-valent enzyme intermediates that activate inert C?H bonds; heme compounds I and II, the non-heme ferrryl-oxo intermediate in SyrB2 and intermediate Q in the binuclear iron enzyme methane monooxygenase. RIXS provides a new tool to investigate the requirements for C?H bond activation, but also to explain differences in reactivity between heme and non-heme enzymes.