Pecoraro Vincent L, Hsieh Wen-Yuan
Department of Chemistry and Biophysics, The University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
Inorg Chem. 2008 Mar 17;47(6):1765-78. doi: 10.1021/ic7017488.
Significant progress in the understanding of biological water oxidation has occurred during the past 25 years. Today we have a somewhat clearer description of the structure of the Mn4Ca cluster and an idea of the appropriate oxidation states for the enzyme during catalysis. At issue is the mechanism of water oxidation. Depending on one's belief of the manganese ion oxidation levels at the catalytically active S4 configuration, one can invoke a variety of different processes that could lead to water oxidation. We have suggested that the most likely process is the nucleophilic attack of a water bound to calcium (or manganese) onto a highly electrophilic Mn(V)=O center. In this Article, we explore the difficulties of preparing Mn(V) in dimeric systems and the even more arduous task of definitively assigning oxidation states to such highly reactive species.
在过去25年里，我们对生物水氧化的理解取得了重大进展。如今，我们对Mn4Ca簇的结构有了更清晰的描述，并且对酶在催化过程中合适的氧化态也有了一定的认识。目前的问题是水氧化的机制。根据人们对催化活性S4构型下锰离子氧化水平的看法，可以提出多种不同的过程，这些过程可能导致水氧化。我们认为最有可能的过程是与钙（或锰）结合的水对高度亲电的Mn(V)=O中心进行亲核攻击。在本文中，我们探讨了在二聚体系统中制备Mn(V)的困难，以及确定此类高反应性物种氧化态这一更艰巨的任务。
