X-RAY EMISSON SPECTROSCOPY OF THE PHOTOSYNTHETIC MN4CA COMPLEX

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。 支持所有有氧生命的氧气在大气中是丰富的，因为它通过绿色植物、藻类和蓝藻的光合作用水氧化不断地再生。这种需要光的反应是由与光系统II(PS II)相关的Mn4Ca簇催化的。考虑到PS II在维持生物圈生命方面的作用和未来可再生能源经济的愿景，阐明Mn4Ca催化剂的结构和机理至关重要，它有时被称为心脏？对水氧化过程的影响。尽管人们对Mn4Ca水裂化催化剂的电子结构和几何结构进行了广泛的研究，但该催化剂的精确结构和机理至今仍未能通过X射线衍射(XRD)、扩展X射线吸收精细结构(EXAFS)和其他光谱技术进行确定。发展高分辨吸收和发射X射线光谱的新方法，包括X射线拉曼光谱、射程扩展EXAFS和位置选择X射线光谱，对于提供重要的新信息至关重要，这些信息不仅有助于阐明络合物的结构，而且有助于阐明光合作用水氧化过程的机理。本建议建立在过去实验的基础上，并解决了x射线发射光谱在PS II中的一些新的应用，如：a)X射线拉曼光谱或RIXS光谱将解决Mn络合物的电子结构，b)Kβ发射和位选择性光谱将选择性地探测Mn络合物中的不同的锰位或不同的氧化态，c)高分辨率的MnKalpha探测EXAFS，它将使我们能够收集超出Fe K边缘的EXAFS，从而提高分辨率和d)原子间的Mn Kbeta2，5光谱将成为锰的配体原子的探针，特别是确定氯化物是否为PS II中的锰的配体。

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. Oxygen, that supports all aerobic life, is abundant in the atmosphere because of its constant regeneration by photosynthetic water oxidation by green plants, algae and cyanobacteria. This light-requiring reaction is catalyzed by a Mn4Ca cluster associated with photosystem II (PS II). Given the role of PS II in maintaining life on the biosphere and the future visions of a renewable energy economy, it is vital to elucidate the structure and mechanism of the Mn4Ca catalyst, which is sometimes referred to as the ?heart? of the water oxidation process. Although, the electronic and geometric structure of the Mn4Ca water-splitting catalyst has been extensively investigated, the precise structure and mechanism of this catalyst has so far eluded all attempts of determination by x-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS) and other spectroscopic techniques. The development of new methods of high resolution absorption and emission x-ray spectroscopy, including x-ray Raman spectroscopy, range-extended EXAFS and site-selective X-ray spectroscopy are critical for providing important new information, that will help in elucidating not only the structure of the complex, but also the mechanism of the photosynthetic water oxidation process. The present proposal builds on the past experiments and addresses some new applications of x-ray emission spectroscopy to the Mn complex in PS II as follows: a) X-ray Raman or RIXS spectroscopy that will address the electronic structure of the Mn complex, b) Kbeta emission and site selective spectroscopy that will selectively probe different Mn sites or different oxidation states in the Mn complex, c) High resolution Mn Kalpha detection of EXAFS that will allow us to collect EXAFS beyond the Fe K-edge thus improving resolution and d) Interatomic Mn Kbeta2,5 spectra that will be a probe for the ligand atoms of Mn, especially to ascertain whether chloride is a ligand of Mn in PS II.