HIGH RESOLUTION MN X-RAY EMISSION SPECTROSCOPY OF THE OXYGEN-EVOLVING COMPLEX

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。所列机构为中心机构，不一定为研究者机构。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和蓝藻。这种需要光的反应由与光系统II（PS II）相关的Mn 4Cacluster催化。在我们正在进行的锰氧化态变化，结构和相关的辅因子Ca和Cl以及水氧化机制的研究中，我们正在BioCAT探索高分辨率吸收和发射X射线光谱的新方法。这些包括a）X射线拉曼光谱，B）范围扩展EXAFS和c）位置选择性X射线光谱。a）我们已经公布了S1和S2态样品以及Mn模型化合物的X射线拉曼（RIXS）结果。在过去的一年里，我们已经完成了从S 0状态的数据收集，数据分析正在进行中，这有望解决Mn（II）是否存在于这种状态的问题。B）我们已经证明了扩展EXAFS方法的可行性，并且收集的数据没有样品中Fe的干扰。k空间数据和FT的改进是惊人的。我们现在可以分辨出S1和S2态的两个短的Mn-Mn距离;而以前我们只能分辨出一个~2.7 <$m的距离。我们还收集了使用定向PS II膜的范围扩展EXAFS数据，很明显，不均匀性更明显; Mn-Mn距离为~2.7或2.8，取决于X射线e矢量与膜法线的角度。

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 and cyanobacteria. This light-requiring reaction is catalyzed by a Mn4Cacluster associated with photosystem II (PS II). In our ongoing investigations of the Mn oxidation-state changes, the structure and the associated cofactors Ca and Cl and the mechanism of water oxidation, we are exploring new methods of high resolution absorption and emission X-ray spectroscopy at the BioCAT. These include a) X-ray Raman spectroscopy, b) range extended EXAFS and c) site-selective X-ray spectroscopy. a) We have published X-ray Raman (RIXS) results from samples in the S1 and S2 states and Mn model compounds. Over the last year, we have completed collection of data from the S0 state, and data analysis is underway which promises to resolve the question of whether Mn(II) is present in this state. b) We have shown the feasibility of the range-extended EXAFS method and collected data without interference from Fe in the sample. The improvement in the k-space data and the FT is striking. We can now resolve two short Mn-Mn distances in the S1 and S2 states; while earlier we could discern only one distance of ~2.7 ¿. We have also collected range-extended EXAFS data using oriented PS II membranes, and it is quite clear that the heterogeneity is more obvious; the Mn-Mn distance is ~2.7 ¿ or 2.8 ¿ depending on the angle the X-ray e-vector makes with the membrane normal.