Department of Physics, ALBA NOVA, SE-106 91, Stockholm, Sweden.
Dalton Trans. 2009 Dec 7(45):10063-8. doi: 10.1039/b909470a. Epub 2009 Aug 18.
Recent reviews on quantum chemical studies of water oxidation in photosystem II have focused on the energetics of O-O bond formation, including the energies of the different S-states. In the present paper, this is extended by discussing the release pathways for dioxygen and protons from the oxygen evolving complex. Based on recent X-ray structures, the effect of adding chloride has also been investigated. Unlike most earlier suggestions, a small, but probably significant, electrostatic effect of adding chloride is found for the higher S-states. For releasing dioxygen in the S4-state, entropy plays a major role. The suggested pathway for proton release in the S1 to S2 transition involves key roles of an outside water and the motion of Asp170. An electron transfer between manganese centra during proton release is also found to be important for a low barrier.
最近关于光合作用系统 II 中水分子氧化的量子化学研究综述集中在 O-O 键形成的能量学上，包括不同 S 态的能量。在本文中，通过讨论从氧释放复合物中释放氧气和质子的途径来扩展这一研究。基于最近的 X 射线结构，还研究了添加氯离子的影响。与大多数早期的建议不同，发现添加氯离子对较高 S 态有一个小但可能重要的静电效应。对于 S4 态中氧气的释放，熵起着主要作用。在 S1 到 S2 转变过程中质子释放的建议途径涉及到外部水和 Asp170 运动的关键作用。还发现质子释放过程中锰中心之间的电子转移对于低势垒也很重要。
