Synthetic Models of the Oxygen Evolving Complex of Photosystem II

描述（由申请人提供）：生物双氧产生发生在蓝细菌和植物的光系统II（PSII）内。负责这种转化的活性位点，即释氧复合物（OEC），由嵌入在大蛋白质复合物中的Mn 4CaOn簇组成。由于水裂解产生分子氧的广泛的基本兴趣和潜在的应用，该簇的结构和催化机制一直是许多光谱学，计算，合成，晶体学和生物化学研究的主题。尽管取得了重大进展，但氧气产生的机制仍然没有得到很好的理解。确切的锰氧化态沿着的催化循环和O-O键形成的网站仍有争议。大的蛋白质基质使OEC活性位点的直接研究变得复杂，并且精确的小分子模型的合成受到簇的复杂性的阻碍。我们的目标包括开发MnxMOn模型（x=3，4; M=Ca，Mn，其他金属）的OEC的合成路线，并进行机理研究，这将允许更深入地了解不同成分（金属，辅助和氧代配体，质子化状态）对簇的化学和物理性质的影响，以实现高氧化态和影响O2的产生。为此，我们将测试有关电子，氧原子和质子转移和配体取代在这些复杂的系统与集群的组装和O-O键形成的影响的假设。除了少数例外，可预测的氧化锰簇合物的合成一直受到氧代配体桥接和形成复杂的低聚结构的倾向的阻碍。我们的方法来克服这个问题是使用相对较小，但刚性的有机框架，以支持三锰络合物，已制定了网站分化的金属氧簇，包括Mn 3CaO 4部分。这些结构模型将允许光谱基准（EPR，XES，XAS）与生物系统进行比较。我们在合成复合物上的工作将通过允许系统的结构-反应性研究来补充对蛋白质进行的研究，以揭示控制这些簇的性质和催化机制的化学特征。

DESCRIPTION (provided by applicant): Biological dioxygen generation occurs within Photosystem II (PSII) in cyanobacteria and plants. The active site responsible for this transformation, the Oxygen Evolving Complex (OEC), consists of a Mn4CaOn cluster embedded in a large protein complex. Given the broad fundamental interest and potential applications of water splitting to make dioxygen, the structure of this cluster and the mechanism of catalysis have been the subject of many spectroscopic, computational, synthetic, crystallographic and biochemical studies. Despite significant advances, the mechanism of oxygen production is still not well understood. The exact Mn oxidation states along the catalytic cycle and the site of O-O bond formation continue to be debated. The large protein matrix has complicated direct studies of the OEC active site and the synthesis of accurate small-molecule models has been hampered by the complexity of the cluster. Our goals include developing synthetic routes to MnxMOn models (x=3, 4; M=Ca, Mn, other metals) of the OEC and undertaking mechanistic studies that will allow a deeper understanding of the effects different constituents (metals, ancillary and oxo ligands, protonation state) have on the chemical and physical properties of the cluster relevant to achieving high oxidation states and effecting O2 production. To that end, we will test hypotheses regarding electron, oxygen-atom and proton transfers and ligand substitution in these complex systems with implications for the assembly of the clusters and O-O bond formation. With few exceptions, the synthesis of predictable manganese oxide clusters has been frustrated by the propensity of oxo ligands to bridge and form complicated oligomeric structures. Our approach to overcoming this problem is to use relatively small, but rigid organic frameworks to support trimanganese complexes that have been elaborated to site-differentiated metal-oxo clusters, including a Mn3CaO4 moiety. These structural models will allow for spectroscopic benchmarking (EPR, XES, XAS) in comparison with the biological system. Our work on synthetic complexes will complement the studies performed on the protein by allowing systematic structure- reactivity studies to uncover the chemical features that control the properties of these clusters and the mechanism of catalysis.