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

本子项目是利用由NIH/NCRR资助的中心赠款提供的资源的众多研究子项目之一。子项目和研究者（PI）可能已经从另一个NIH来源获得了主要资金，因此可以在其他CRISP条目中表示。列出的机构是中心的，不一定是研究者的机构。支持所有需氧生命的氧气在大气中是丰富的，因为它通过绿色植物和蓝藻的光合作用不断再生。这种需要光的反应是由与光系统II （PS II）相关的mn4簇催化的。在对锰的氧化态变化、结构及其伴生因子Ca和Cl以及水氧化机理的研究中，我们正在探索在BioCAT上进行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)我们发表了S1态和S2态样品和Mn模型化合物的x射线拉曼（RIXS）结果。在过去的一年里，我们已经完成了对S0状态的数据收集，并且正在进行数据分析，这有望解决Mn（II）是否存在于该状态的问题。b)我们已经证明了扩展范围的EXAFS方法的可行性，并且在没有样品中Fe干扰的情况下收集了数据。k空间数据和FT的改进是惊人的。我们现在可以在S1和S2状态下解析两个短的Mn-Mn距离；而早先我们只能分辨出~2.7°的距离。我们还使用定向PS II膜收集了扩展范围的EXAFS数据，很明显，异质性更明显；Mn-Mn距离为~2.7¿或2.8¿，取决于x射线e向量与膜法线的夹角。

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.