X-RAY EMISSION SPECTROSCOPY OF THE PHOTOSYNTHETIC MN4CA COMPLEX

这个子项目是许多利用资源的研究子项目之一 由NIH/NCRR资助的中心拨款提供。子项目的主要支持 而子项目的主要调查员可能是由其他来源提供的， 包括其它NIH来源。 列出的子项目总成本可能 代表子项目使用的中心基础设施的估计数量， 而不是由NCRR赠款提供给子项目或子项目工作人员的直接资金。 氧气，支持所有的有氧生命，在大气中是丰富的，因为它不断再生的光合作用水氧化的绿色植物，藻类和蓝藻。该光反应由与光系统II（PS II）相关的Mn 4Ca簇催化。考虑到PS II在维持生物圈生命和可再生能源经济未来愿景中的作用，阐明Mn 4Ca催化剂的结构和机制至关重要，Mn 4Ca催化剂有时被称为？心脏？水的氧化过程。虽然，Mn 4Ca水裂解催化剂的电子和几何结构已被广泛研究，该催化剂的精确结构和机制迄今为止一直回避通过X射线衍射，EXAFS和其他光谱技术测定的所有尝试。高分辨率吸收和发射X射线光谱，包括RIXS，Kb交叉发射，和时间分辨XES的新方法的发展是提供重要的新信息的关键，这将有助于阐明不仅复杂的结构，而且光合水氧化过程的机制。本提案建立在过去的实验基础上，并提出了X射线发射光谱在PS II中Mn络合物的一些新应用，如下所示：B）原子间Mn Kb 2，5光谱，其将是Mn的配体原子的探针，特别是用于确定PS II中Mn的氧代/羟基桥配体的状态，提出了参与O-O形成，以及c）发展能量色散XES方法以时间分辨的方式研究Mn 4Ca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.