Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
Proc Natl Acad Sci U S A. 2010 Apr 20;107(16):7225-9. doi: 10.1073/pnas.1001132107. Epub 2010 Apr 1.
As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H(2)O --> O(2) + 4e(-) + 4H(+)) is key, but it imposes a significant mechanistic challenge with requirements for both 4e(-)/4H(+) loss and O-O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as Ru(Mebimpy)(bpy)(OH(2)) [Mebimpy = 2,6-bis(1-methylbenzimidazol-2-yl)pyridine; bpy = 2,2'-bipyridine]. When oxidized from to Ru(V) = O(3+), these complexes undergo O-O bond formation by O-atom attack on a H(2)O molecule, which is often the rate-limiting step. Microscopic details of O-O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom-proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation.
作为光系统 II 的终末步骤，以及人工光合作用的潜在半反应，水氧化（2H2O --> O2 + 4e- + 4H+）是关键，但它提出了一个重大的机制挑战，需要同时失去 4e-和 4H+以及形成 O-O 键。最近，通过使用单原子 Ru 金属配合物催化剂，如[Ru（Mebimpy）（bpy）（OH2）]（2+）[Mebimpy = 2,6-双（1-甲基苯并咪唑-2-基）吡啶；bpy = 2,2'-联吡啶]，在水氧化催化方面取得了重大进展。当从 Ru(V) = O(3+)氧化时，这些配合物通过 O 原子对 H2O 分子的攻击形成 O-O 键，这通常是速率限制步骤。通过量子力学/分子力学（QM/MM）模拟探索了 O-O 键形成的微观细节，结果提供了对机制的详细了解，并提出了提高催化速率的策略。它利用添加的碱作为质子受体，并通过与质子转移到碱（B）协同进行协同原子-质子转移（APT），同时将 O 原子转移到水分子的 O 原子上。在溶液中和通过附着的膦酸化金属配合物催化剂衍生的氧化物电极表面都观察到了碱催化的 APT 反应性。这些结果对催化、电催化和光电催化水氧化具有重要意义。
