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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >What spectroscopy reveals concerning the Mn oxidation levels in the oxygen evolving complex of photosystem II: X-ray to near infra-red
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What spectroscopy reveals concerning the Mn oxidation levels in the oxygen evolving complex of photosystem II: X-ray to near infra-red

机译：光谱学揭示了与光系统II的放氧复合物中的Mn氧化水平有关：X射线至近红外

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Photosystem II (PS II), found in oxygenic photosynthetic organisms, catalyses the most energetically demanding reaction in nature, the oxidation of water to molecular oxygen and protons. The water oxidase in PS II contains a Mn _4Ca cluster (oxygen evolving complex, OEC), whose catalytic mechanism has been extensively investigated but is still unresolved. In particular the precise Mn oxidation levels through which the cluster cycles during functional turnover are still contentious. In this, the first of several planned parts, we examine a broad range of published data relating to this question, while considering the recent atomic resolution PS II crystal structure of Umena et al. (Nature, 2011, 473, 55). Results from X-ray, UV-Vis and NIR spectroscopies are considered, using an approach that is mainly empirical, by comparison with published data from known model systems, but with some reliance on computational or other theoretical considerations. The intention is to survey the extent to which these data yield a consistent picture of the Mn oxidation states in functional PS II - in particular, to test their consistency with two current proposals for the mean redox levels of the OEC during turnover; the so called 'high' and 'low' oxidation state paradigms. These systematically differ by two oxidation equivalents throughout the redox accumulating catalytic S state cycle (states S _0?S _3). In summary, we find that the data, in total, substantially favor the low oxidation proposal, particularly as a result of the new analyses we present. The low oxidation state scheme is able to resolve a number of previously 'anomalous' results in the observed UV-Visible S state turnover spectral differences and in the resonant inelastic X-ray spectroscopy (RIXS) of the Mn pre-edge region of the S _1 and S _2 states. Further, the low oxidation paradigm is able to provide a 'natural' explanation for the known sensitivity of the OEC Mn cluster to cryogenic near infra-red (NIR) induced turnover to alternative spin/redox states in S _2 and S _3.
机译：在含氧光合生物中发现的光系统II（PS II）催化自然界中最耗能的反应，即水氧化为分子氧和质子。 PS II中的水氧化酶包含一个Mn _4Ca簇（放氧络合物，OEC），其催化机理已被广泛研究，但仍未解决。尤其是在功能转换过程中簇循环所通过的精确的Mn氧化水平仍然是有争议的。在本文中，这是计划中的第一个部分，我们考虑了Umena等人最近的原子分辨率PS II晶体结构，研究了与此问题有关的广泛公开数据。 （自然，2011，473，55）。通过与主要模型的已发布数据进行比较，使用主要是经验性的方法，对X射线，UV-Vis和NIR光谱学的结果进行了考虑，但是在一定程度上依赖于计算或其他理论上的考虑。目的是调查这些数据在多大程度上产生功能性PS II中Mn氧化态的一致图像，尤其是要检验它们与当前两个有关OEC平均氧化还原水平的建议的一致性。所谓的“高”和“低”氧化态范例。这些在整个氧化还原积累的催化S状态循环（状态S _0？S _3）中系统地相差两个氧化当量。总而言之，我们发现这些数据总体上完全有利于低氧化提议，尤其是由于我们提出了新的分析结果。低氧化态方案能够解决所观察到的紫外可见S状态转换光谱差异以及S的Mn前缘区域的共振非弹性X射线光谱（RIXS）中许多先前的“异常”结果。 _1和S _2状态。此外，低氧化范式能够为OEC Mn团簇对低温近红外（NIR）诱导的S_2和S_3交替自旋/氧化还原态转换的敏感性提供“自然”的解释。

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