The Mechanism of Water Splitting and Oxygen Evolution in Photosynthesis

在高等植物和蓝藻中，水被氧化成分子氧是与光合作用有关的一种特征反应。光量子产生光系统的激发，导致电子一次一个地转移，直到四个电子从两个水分子中被移走以产生O2。Sauer博士和Klein博士正在对参与电子转移和储存产生O2所需的氧化当量的化学中间体进行投资。锰参与了水解酶，他们正在使用X射线吸收光谱来确定锰周围的氧化状态、连接和局部结构。结合EPR谱的研究，他们的结果证实了锰的氧化态变化直接参与了水的分解过程。这项建议旨在通过X射线吸收光谱、电子-核光谱和电子-电子双共振谱进一步表征所涉及的四个锰原子、基本辅因子、抑制剂和蛋白质配体的结构。他们希望了解，最重要的是，在氧气最终形成和释放之前，水是如何融入水分解酶的。对这一过程的了解将对开发利用太阳能将水转化为分子氧和氢燃料的人工系统最为有用。

The oxidation of water to molecular oxygen is a characteristic reaction associated with photosynthesis in higher plants and cyanobacteria. Light quanta producing excitation of the photosystem results in the transfer of electrons one at a time until four electrons are removed from two water molecules to produce O2. Drs. Sauer and Klein are investing the chemical intermediates involved in this transfer of electrons and in the storing of the oxidizing equivalents needed to yield O2. Manganese is involved in the water-splitting enzyme, and they are using X-ray absorption spectroscopy to determine the oxidation states, ligation and local structure around the Mn. Together with studies using EPR spectroscopy, their results have verified the direct participation of Mn oxidation state changes in the water-splitting process. This proposal aims to characterize further the structure of the quartet of Mn atoms involved, the essential cofactors, inhibitors and protein ligands through the use of X-ray absorption spectroscopy, electron-nuclear and electron-electron double resonance spectroscopies. They hope to learn, most importantly, how water becomes incorporated into the water-splitting enzyme prior to the final formation and release of O2. Knowledge of this process will be most useful in development artificial systems whereby solar energy can be used to convert water into molecular oxygen and hydrogen fuel.