XAS OF MANGANESE IN THE PHOTOSYNTHETIC OXYGEN-EVOLVING COMPLEX

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 研究中心，而研究中心不一定是研究者所在的机构。 地球上支持有氧生命的大气中的大部分氧气是由植物和蓝细菌通过光诱导水氧化成分子氧产生的。 这是生物圈中大规模发生的最重要的化学过程之一。 光合作用器的放氧复合物（OEC）催化这一反应，它包含一个四个Mn原子的簇。 光系统II（PS II）中的水氧化是一个逐步的过程，其中由反应中心吸收的4个连续光子中的每一个都为OEC通过S-态中间体S 0-S4的前进提供动力。在达到假设的S4状态时，复合物释放O2并返回到S 0。 与此过程相关的关键问题是锰络合物的氧化态和结构变化，因为OEC通过S-态循环进行，以及锰络合物从两个水分子中除去四个电子以产生O2分子的机制。 人们普遍认为，锰簇是水氧化的活性部位，但实现这一点的化学机制是不充分的理解。 除了Mn之外，Cl-和Ca 2+是活性所需的重要辅因子，但其确切的结构和功能作用尚不清楚。 Mn络合物和供体络合物的部分氧化的中间体（Mn-OEC的S-态（S 0-S3））的结构和化学已经成为强烈兴趣和研究的主题。锰X射线光谱研究提供了直接的信息的复杂的微观结构和锰原子的氧化态在S 0，S1，S2和S3状态的OEC。 很少有其他光谱技术提供这样的特异性研究锰的结构在OEC，目前这是唯一的方法适合监测锰在S-状态。

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. Most of the oxygen in the atmosphere which supports aerobic life on earth is generated by plants and cyanobacteria by the photoinduced oxidation of water to dioxygen. This is one of the most important chemical processes occurring on such a large scale in the biosphere. The oxygen-evolving complex (OEC), of the photosynthetic apparatus that catalyzes this reaction contains a cluster of four Mn atoms. Water oxidation in photosystemII (PS II) is a stepwise process wherein each of 4 sequential photons absorbed by the reaction center powers the advance of the OEC through the S-state intermediates S0-S4. Upon reaching the hypothesized S4 state, the complex releases O2 and returns to S0. The critical questions related to this process are the oxidation state and structural changes in the Mn complex as the OEC proceeds through the S-state cycle, and the mechanism by which four electrons are removed from two water molecules by the Mn complex to produce an O2 molecule. It is generally accepted that the Mn cluster is the active site for water oxidation, but the chemical mechanism by which this is achieved is inadequately understood. In addition to Mn, Cl- and Ca2+ are essential cofactors that are required for activity, but their exact structural and functional role is not yet clear. The structure and chemistry of the Mn complex and the partially oxidized intermediates of the donor complex, the S-states of the Mn-OEC(S0-S3),have been the subject of intense interest and study. Mn X-ray spectroscopy studies provide direct information on the microstructure of the complex and on the oxidation states of the Mn atoms in the S0, S1, S2 and S3 states of the OEC. Few other spectroscopic techniques provide such specificity for studying the structure of Mn in the OEC, and at present this is the only method suitable to monitor Mn in the S-states.