Water Deprotonation via Oxo-Bridge Hydroxylation and 18O-Exchange in Free Tetra-Manganese Oxide Clusters
Water Deprotonation via Oxo-Bridge Hydroxylation and 18O-Exchange in Free Tetra-Manganese Oxide Clusters
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DOI：
10.1021/jp5106532
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发表时间：
2015-05-21
影响因子：
3.7
通讯作者：
Landman, Uzi
中科院分区：
文献类型：
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作者：
Lang, Sandra M.;Fleischer, Irene;Landman, Uzi
基本的生物反应之一，催化活化的水分解，发生在一个无机的四锰五氧一钙（Mn 4CaO 5）簇，它与其蛋白质配体一起形成植物，藻类和蓝藻的膜结合色素蛋白光系统II（13511）的析氧复合物（OEC）。在一个新的分层的方法来探测水裂解反应的基本概念的第一步，我们提出了一个孤立的四锰氧化物簇离子，Mn 4 O 4+，作为简化模型的OEC的气相制备。在气相离子阱实验中用（D_2O）-O-16和（H_2O）-O-18进行的反应性研究揭示了团簇中的氧原子与水氧原子的交换。这为Mn 4 O 4+通过氧桥的羟基化解离水的能力提供了直接的实验证据。自由团簇中的氧交换速率与光系统II中基质水向O-2的转化速率一致，从而支持桥氧原子参与该过程。第一性原理自旋密度泛函理论计算揭示了水去质子化和氧桥交换的分子机理。
One of the fundamental biological reactions, the catalytically activated water-splitting, takes place at an inorganic tetra-manganese monocalcium penta-oxygen (Mn4CaO5) cluster which together with its protein ligands forms the oxygen evolution complex (OEC) of the membrane-bound pigment protein photosystem II (13511) of plants, algae, and cyanobacteria. In the first step of a new hierarchical approach to probe fundamental concepts of the water-splitting reactions, we present the gas-phase preparation of an isolated tetra-manganese oxide cluster ion, Mn4O4+, as a simplified model of the OEC. Reactivity studies with (D2O)-O-16 and (H2O)-O-18 in a gas-phase ion trap experiment reveal the exchange of the oxygen atoms of the cluster with water oxygen atoms. This provides direct experimental evidence for the ability of Mn4O4+ to dissociate water via hydroxylation of the oxo-bridges. The rate of oxygen exchange in the free cluster agrees well with the conversion rate of substrate water to O-2 in photosystem II, thus supporting the involvement of bridging oxygen atoms in this process. First-principles spin density functional theory calculations reveal the molecular mechanism of the water deprotonation and oxo-bridge exchange.