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首页> 外文期刊>Chemistry: A European journal >Structural, magnetic coupling and oxidation state trends in models of the CaMn4 cluster in photosystem II
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Structural, magnetic coupling and oxidation state trends in models of the CaMn4 cluster in photosystem II

机译：光系统II中CaMn4团簇模型的结构，磁耦合和氧化态趋势

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Density functional theory calculations are reported on a set of isomeric structures I, II and III that share the structural formula [CaMn4C9H10N2O16](q+)center dot(H2O)(3) (q = -1, 01 1: 2 3). Species I has a skeletal structure, which has been previously identified as a close match to the ligated CaMn4 cluster in Photosystem II, as characterized in the most recent 3.0 angstrom crystal structure. Structures II and III are rearrangements of I, which largely retain that model's bridging ligand framework, but feature metal atom positions broadly consistent with, respectively, the earlier 3.5 and 3.2 angstrom crystal structures for the Photosystem II water-oxidising complex (WOC). Our study explores the influence of the cluster charge state (and hence S state) on several important properties of the model structures; including the relative energies of the three models, their interconversion, trends in the individual Mn oxidation states, preferred hydration sites and favoured modes of magnetic coupling between the manganese atoms. We find that, for several of the explored cluster charge states, modest differences in the bridging-ligand geometry exert a powerful influence over the individual manganese oxidation states, but throughout these states the robustness of the tetrahedron formed by the Ca and three of the Mn atoms remains a significant feature and contrasts with the positional flexibility of the fourth Mn atom. Although structure I is lowest in energy for most S states, the energy differences between structures for a given S state are not large. Overall, structure II provides a better match for the EXAFS derived metal-metal distance parameters for the earlier S states (S-0 to S-2), but not for S-3 in which a significant structural change is observed experimentally. In this S state structure III provides a closer fit. The implications of these results, for the possible action of the WOC, are discussed.
机译：在一组具有相同结构式[CaMn4C9H10N2O16]（q +）中心点（H2O）（3）（q = -1，01 1：2 3）的异构结构I，II和III上报告了密度泛函理论计算。物种I具有骨骼结构，该结构先前已被确定为与Photosystem II中连接的CaMn4簇紧密匹配，以最近的3.0埃晶体结构为特征。结构II和III是I的重排，在很大程度上保留了该模型的架桥配体骨架，但金属原子的位置分别与Photosystem II水氧化复合物（WOC）的早期3.5和3.2埃晶体结构大致一致。我们的研究探索了簇电荷状态（以及S状态）对模型结构几个重要属性的影响;包括三个模型的相对能量，它们的相互转化，各个Mn氧化态的趋势，优选的水合位点以及锰原子之间的磁耦合的有利模式。我们发现，对于一些探索的团簇电荷态，桥联配体几何结构的适度差异对各个锰的氧化态具有强大的影响，但在所有这些态中，由Ca和三个Mn形成的四面体的稳健性原子仍然是一个重要特征，并且与第四个Mn原子的位置柔性形成对照。尽管对于大多数S状态，结构I的能量最低，但是对于给定的S状态，结构之间的能量差并不大。总体而言，结构II为EXAFS导出的早期S状态（S-0至S-2）的金属-金属距离参数提供了更好的匹配，但对于实验观察到显着结构变化的S-3，则没有提供更好的匹配。在此S状态下，结构III提供了更紧密的配合。讨论了这些结果对WOC可能采取的行动的影响。

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