O-O bond formation in the S4 state of the oxygen-evolving complex in photosystem II
O-O bond formation in the S4 state of the oxygen-evolving complex in photosystem II
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DOI：
10.1002/chem.200600774
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发表时间：
2006-12-13
影响因子：
4.3
通讯作者：
Siegbahn, Per E. M.
中科院分区：
文献类型：
--
作者：
Siegbahn, Per E. M.
基于光系统 II 中释氧络合物的最新 X 射线结构，对数千个结构进行了量子化学几何优化，以阐明分子氧形成的机制。这些计算的许多结果之前已经介绍过。本研究已使用能量上最稳定的 S-4 态结构来研究在该结构中形成 O-O 键的所有可能方式。前面强调的 S-4 态的一个关键特征是存在氧自由基配体而不是 Mn-V 态。先前的研究表明，该氧自由基可以通过第二配位层中水分子的攻击形成O-O键。目前的系统研究产生了一种新型机制，它比以前的机制明显受到青睐。计算出该机制的过渡态势垒为 12.5 kcal mol(-1)，而之前最好的结果为 18-20 kcal mol(-1)。制定了低势垒的自旋对准要求。
Based on recent X-ray structures of the oxygen-evolving complex in photosystem II, quantum chemical geometry optimizations of several thousand structures have been performed in order to elucidate the mechanism for dioxygen formation. Many of the results of these calculations have been presented previously. The energetically most stable structure of the S-4 state has been used in the present study to investigate essentially all the possible ways the O-O bond can be formed in this structure. A key feature, emphasized previously, of the S-4 state is that an oxygen radical ligand is present rather than an Mn-V state. Previous studies have indicated that this oxygen radical can form an O-O bond by an attack from a water molecule in the second coordination shell. The present systematic investigation has led to a new type of mechanism that is significantly favored over the previous one. A calculated transition-state barrier of 12.5 kcal mol(-1) was found for this mechanism, whereas the best previous results gave 18-20 kcal mol(-1). A requirement on the spin alignment for a low barrier is formulated.