CAREER: Time-resolved Studies of the Oxygen Evolving Complex of Photosystem II

生命过程化学计划和分子生物物理计划正在资助普渡大学的Yulia Pushkar博士研究光合作用的详细机制，这是植物从二氧化碳，水和阳光中产生糖等物质的过程。对这一关键生命过程的理解可以通过设计更好的水分解催化剂来促进替代能源的开发，从而实现人工光合作用。这项工作采用各种物理测量来确定真实的时间中这一重要过程的分子细节，因此，它是物理学、化学和生物科学的接口。因此，该研究的更广泛影响也涉及到几个科学领域，包括生物无机化学和分子生物物理学。此外，这项工作在高中水平的科学教育的影响，通过参与的研究小组在光合作用，高中科学教师可以采用和使用的课程模块的设计。为“绿色叶子的物理学”方案开发了基于调查的教育模块，其中纳入了研究结果。本论文主要研究光系统II中放氧复合物（OEC）的光诱导功能。光诱导的水分解的Mn4Ca簇的氧进化复杂的是一个基本的生物过程，维持我们的生物圈。激光泵浦X射线探针时间分辨X射线发射和X射线吸收光谱用于监测催化过程中真实的时间内OEC电子结构的变化。光系统II蛋白质中的瞬时中间体被超快冷冻猝灭捕获，其结构使用扩展X射线吸收精细结构（EXAFS）方法进行表征。研究的目的是确定锰簇的电子结构和几何形状的变化的动力学方面，并结合DFT计算，提供催化水裂解的机制的细节。

The Chemistry of Life Processes Program and the Molecular Biophysics Program are funding Dr. Yulia Pushkar of Purdue University for research towards a detailed mechanism for photosynthesis, the process by which plants produce substances such as sugars from carbon dioxide, water and sunlight. The understanding of this key life process can advance the development of alternative energy sources through the design of better water-splitting catalysts that enable artificial photosynthesis. The work employs various physical measurements to determine the molecular details of this important process in real time and, as such, is at the interface of physics, chemistry and the biological sciences. Consequently, the broader impact of the research is also on several scientific areas including bioinorganic chemistry and molecular biophysics. Additionally, the work has consequences on science education at the high school level through the involvement of the research team in the design of lesson modules about photosynthesis that high school science teachers can adopt and use. Inquiry-based educational modules that incorporate the results of the research are developed for the "Physics of the Green Leaf" program. The research is focused on the study of the light-induced function of the oxygen evolving complex (OEC) in Photosystem II. The light-induced water splitting by the Mn4Ca cluster of the oxygen evolving complex is a fundamental biological process that sustains our biosphere. Laser pump X-ray probe time-resolved X-ray emission and X-ray absorption spectroscopy are used to monitor changes in the electronic structure of the OEC in real time during catalysis. Transient intermediates in Photosystem II protein are trapped by ultra-fast freeze-quenching and their structure is characterized using the extended X-ray absorption fine structure (EXAFS) method. The research aims are to determine aspects of both the dynamics of the change in electronic structure and the geometry of the manganese cluster and, when combined with DFT calculations, to provide details of the mechanism of catalytic water splitting.