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尤利娅·普什卡博士研究光合作用的详细机制，光合作用是植物从二氧化碳、水和阳光中产生糖等物质的过程。对这一关键生命过程的了解，可以通过设计更好的能够进行人工光合作用的水分解催化剂来推动替代能源的开发。这项工作使用各种物理测量来实时确定这一重要过程的分子细节，因此处于物理、化学和生物科学的交界处。因此，这项研究的更广泛影响还包括生物无机化学和分子生物物理学等几个科学领域。此外，这项工作通过研究小组参与设计高中科学教师可以采用和使用的关于光合作用的课程模块，对高中一级的科学教育产生了影响。结合研究结果的探究式教学模块是为“绿叶物理”项目开发的。本研究主要研究光系统II中放氧复合体(OEC)的光诱导功能。放氧复合体中的Mn4Ca簇的光诱导分解水是维持生物圈的基本生物学过程。采用激光泵浦、X射线探测、时间分辨X射线发射和X射线吸收光谱等手段，实时监测催化过程中OEC电子结构的变化。利用超快冷冻猝灭法捕获光系统II蛋白中的瞬时中间产物，并用扩展X射线吸收精细结构(EXAFS)方法对其结构进行表征。研究的目的是确定电子结构变化的动力学和锰团簇的几何形状，并结合密度泛函理论计算，提供催化裂水机理的详细信息。

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.