The Mechanism of Water Splitting and Oxygen Evolution in Photosynthesis

水氧化为分子氧是高等植物光合作用的一个特征反应。产生光系统激发的光量子导致电子一次一个地转移，直到从两个水分子中除去四个电子以产生氧气。目前正在研究以高还原电位转移电子和储存生成氧气所需的氧化等价物的化学中间体。锰参与了水分解酶，斯坦福同步辐射实验室的x射线光谱学被用来确定锰周围的氧化状态、结合力和局部结构。结合EPR光谱的研究，证实了Mn氧化态的变化直接参与了水的分解过程。该建议旨在表征锰结合位点的性质，首先通过鉴定所涉及的蛋白质，然后确定为锰提供配体所涉及的特定氨基酸。在不久的将来，希望通过使用电子-核和电子-电子双共振来表征所涉及的分子种类。以及x射线光谱学，以及在氧气最终形成和释放之前，水与分解水的酶结合的方式的本质。这一过程的知识将是最有用的开发人工系统，其中太阳能可以用来将水转化为分子氧和氢燃料

The oxidation of water to molecular oxygen is a characteristic reaction associated with photosynthesis in higher plants. Light quanta producing excitation of the photosystem result in the transfer of electrons one at a time until four electrons are removed from two water molecules to produce oxygen. The chemical intermediates involved in transferring electrons at high reduction potentials and in storing the oxiding equivalents needed to yield oxygen are being investigated. Manganese is involved in the water-splitting enzyme, and X-ray spectroscopy at the Stanford Synchrotron Radiation Laboratory is being used to determine the oxidation state, ligation and local structure around the Mn. Together with studies using EPR spectroscopy, results have verified the direct participation of Mn oxidation state changes in the water-splitting process. This proposal aims to characterize the nature of the manganese binding site, first by identifying the proteins involved and then in determining the specific amino acids involved in providing ligands to the manganese., In the near future it is hoped to characterize the molecular species involved, through the use of electron-nuclear and electron-electron double resonance, and X-ray spectroscopy as well the nature of the way in which water becomes incorporated into the water-splitting enzyme prior to the final formation and release of oxygen. Knowledge of this process will be most useful in developing artificial systems whereby solar energy can be used to convert water into molecular oxygen and hydrogen fuel.***