Siegbahn Per E M
Department of Physics, Stockholm University, AlbaNova University Center, Stockholm Center for Physics, Astronomy and Biotechnology, 10691 Stockholm, Sweden.
Chemistry. 2006 Dec 13;12(36):9217-27. doi: 10.1002/chem.200600774.
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.
基于近期光系统II中析氧复合物的X射线结构，已对数千种结构进行了量子化学几何优化，以阐明双氧形成的机制。这些计算的许多结果此前已发表。本研究采用了S(4)态能量上最稳定的结构，来研究该结构中O—O键形成的几乎所有可能方式。S(4)态一个此前已强调的关键特征是存在一个氧自由基配体而非Mn(V)态。先前的研究表明，这个氧自由基可通过第二配位层中水分子的进攻形成O—O键。目前的系统研究得出了一种新型机制，该机制比之前的机制明显更具优势。此机制的计算过渡态能垒为12.5 kcal mol⁻¹，而之前最好的结果为18 - 20 kcal mol⁻¹。还提出了低能垒对自旋排列的要求。
