DETERMINATION OF ELECTRONIC AND GEOMETRIC STRUCTURES OF NOVEL FE-S SYSTEMS

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。 为了绘制铁-S相图随长度尺度(微米和纳米)、合成(表面/束流、蛋白质笼控制合成)和制备条件(曝光时间、温度、pH、其他离子的存在)的函数关系，提出了改性铁-S矿物表面和纳米粒子的多边X射线吸收光谱研究。我们假设，利用能量(表面/束流)和结构(蛋白质笼或病毒衣壳)控制的Fe-S体系的合成，可以获得用常规合成方法不可能获得的Fe-S相图区域。最近获得的初步数据已经表明，黄铁矿存在一种以前没有观察到的还原状态，这种状态是通过将原始的[100]黄铁矿表面暴露在氢原子/氢气等离子体中而制备的。我们将利用XAS数据在Fe K边、Fe L边和S K边的互补性。最近在BL4-3上开发的光束线允许收集硫EXAFS，与铁EXAFS相结合，可以为难以表征中间体或过渡态的化合物提供更可靠的几何结构。XANES分析了Fe的L边和S K边的前缘和上升边特征，提供了金属/配体中心的有效核电荷、轨道组成、金属中心的配位场分裂和配体的非无辜行为的电子结构信息。拟议实验的结构见解对Fe-S体系作为生物前代谢催化剂的作用产生了影响(美国国家航空航天局天体生物学研究所支持密歇根大学的研究计划)，以及从丰富的Fe-S中提出新型工业催化剂的潜力，这些材料含有活化小分子如氮气或氢气的材料。

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. Multi-edge x-ray absorption spectroscopic investigations of modified Fe-S mineral surfaces and nanoparticles are proposed in order to map the Fe-S phase diagrams as a function of length scale (micrometer vs. nanometer), synthesis (surface/beam, protein-cage controlled synthesis), and preparation conditions (exposure time, temperature, pH, presence of other ions). We hypothesize that using energy- (surface/beam) and structure- (protein cage or viral capsid) controlled synthesis of Fe-S systems, areas of Fe-S phase diagrams can be accessed that would not be possible by conventional synthetic methods. Recently obtained preliminary data already indicate the existence of a previously unobserved reduced state of pyrite, which was prepared by exposing pristine [100] pyrite surface to hydrogen atom/hydrogen gas plasma. We will take advantage of the complementarity of XAS data at the Fe K-edge, Fe L-edge, and S K-edge. Recent beamline development at BL4-3 now allows for collection of sulfur EXAFS, which in combination with iron EXAFS can provide more reliable fits of geometric structure for hard to characterize intermediates or transition states. XANES analysis of preedge and rising-edge features of Fe L-edge and S K-edge spectra provides electronic structural information about effective nuclear charges of metal/ligand centers, orbital compositions, ligand-field splitting of metal centers, and non-innocent behavior of ligands. Structural insights from the proposed experiments have an impact on the role of Fe-S systems as pre-biotic metabolic catalysts (NASA Astrobiology Institute supported research program at MSU), as well as, potential in proposing novel industrial catalysts from abundant Fe-S containing materials for activation of small molecules such as dinitrogen or dihydrogen.