Oxygen evolution catalysis by a dimanganese complex and its relation to photosynthetic water oxidation
Oxygen evolution catalysis by a dimanganese complex and its relation to photosynthetic water oxidation
复制标题
DOI：
10.1021/ic062218d
复制
发表时间：
2008-03-17
影响因子：
4.6
通讯作者：
Brudvig, Gary W.
中科院分区：
文献类型：
--
作者：
Tagore, Ranitendranath;Crabtree, Robert H.;Brudvig, Gary W.
[Mn-2(III/IV)(mu-O)(2)(terpy)(2)(OH2)(2)](NO3)(3) (1，其中 terpy = 2,2':6'2"-terpyridine) 充当水氧化催化剂，以 HSO5- 作为水溶液中的主要氧化剂，因此为光系统 II 的析氧复合物提供了模型系统（Limburg, J.；等人，2015）。 J. Am. Soc. 2001, 123, 423-430) 在此反应过程中，大部分起始 [Mn-2(III/IV)(mu-O)(2)](3+) 络合物转化为 [Mn-2(IV/IV)(mu-O)(2)](4+) 形式 (Chen, H.; et al. Inorg. Chem. 2007)。 46, 34-43）在此，我们使用停流紫外-可见光谱来监测随着 HSO5- 转化为 2 的紫外-可见光吸光度变化。模型的术语涉及 HSO5- 对 1 进行双电子氧化，然后双电子氧化中间体与另一个 1 分子快速反应，得到两个 2 分子。为了合理化低 [HSO5-] 下的双相行为，我们提出了与Mn-III 和 Mn-IV 位点的动力学差异使我们能够估计这些位点之间的分子内电子转移和末端配体交换速率的上限，并根据这些结果讨论了 1 作为水氧化催化剂的优化。
[Mn-2(III/IV)(mu-O)(2)(terpy)(2)(OH2)(2)](NO3)(3) (1, where terpy = 2,2':6'2"-terpyridine) acts as a water-oxidation catalyst with HSO5- as the primary oxidant in aqueous solution and, thus, provides a model system for the oxygen-evolving complex of photosystem II (Limburg, J.; et al. J. Am. Chem. Soc. 2001, 123, 423-430). The majority of the starting [Mn-2(III/IV)(mu-O)(2)](3+)complex is converted to the[Mn-2(IV/IV)(mu-O)(2)](4+) form (2) during this reaction (Chen, H.; et al. Inorg. Chem. 2007, 46, 34-43). Here, we have used stopped-flow UV-visible spectroscopy to monitor UV-visible absorbance changes accompanying the conversion of I to 2 by HSO5-. With excess HSO5-, the rate of absorbance change was found to be first-order in [1] and nearly zero-order in [HSO5-]. At relatively low [HSO5-], the change of absorbance with time is distinctly biphasic. The observed concentration dependences are interpreted in terms of a model involving the two-electron oxidation of 1 by HSO5-, followed by the rapid reaction of the two-electron-oxidized intermediate with another molecule of 1 to give two molecules of 2. In order to rationalize biphasic behavior at low [HSO5-], we propose a difference in reactivity of the [Mn-2(III/IV)(mu-O)(2)](3+) complex upon binding of HSO5- to the MnIII site as compared to the reactivity upon binding HSO5- to the Mn-IV site. The kinetic distinctness of the Mn-III and Mn-IV sites allows us to estimate upper limits for the rates of intramolecular electron transfer and terminal ligand exchange between these sites. The proposed, mechanism leads to insights on the optimization of 1 as a water-oxidation catalyst. The rates of terminal ligand exchange and electron transfer between oxo-bridged Mn atoms in the oxygen-evolving complex of photosystem II are discussed in light of these results.