X-RAY EMISSION SPECTROSCOPY OF THE PHOTOSYNTHETIC MN4CA COMPLEX

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 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，但这种催化剂的精确结构和机理至今未能通过X射线衍射、EXAFS和其他光谱技术进行确定。发展高分辨率吸收和发射X射线光谱的新方法，包括RIXS、KB交叉发射和时间分辨XES，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制。本提议建立在过去实验的基础上，并阐述了x射线发射光谱在PS II中的一些新的应用，如：a)RIXS光谱将解决Mn络合物的电子结构，b)原子间的Mn Kb2，5光谱将成为Mn的配体原子的探针，特别是确定在PS II中参与O-O形成的Mn的氧/羟桥配体的状态，以及c)发展能量色散XES方法以时间分辨的方式研究Mn4Ca团簇。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. 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, EXAFS and other spectroscopic techniques. The development of new methods of high resolution absorption and emission x-ray spectroscopy, including RIXS, Kb crossover emission, and time-resolved XES 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) RIXS spectroscopy that will address the electronic structure of the Mn complex, b) Interatomic Mn Kb2,5 spectra that will be a probe for the ligand atoms of Mn, especially to ascertain the state of the oxo/hydroxo bridge ligands of Mn in PS II, which are proposed to be involved in the O-O formation, and c) Develop energy-dispersive XES methodology to investigate the Mn4Ca cluster in a time-resolved manner.