Time Resolved Studies of Fundamental Mechanisms in Natural Photosynthesis

在化学部门生命过程化学项目的支持下，普渡大学的Yulia Pushkar教授将研究光系统II的析氧复合体（OEC），这是一种含有锰和钙离子的蛋白质。这种蛋白质利用太阳光的能量催化水分子分裂成质子、电子和氧分子，提供了地球大气中的大部分氧气。光谱学方法在催化循环研究中的应用将有助于深入了解锰离子和钙离子及其蛋白质环境在光驱动形成双氧中的作用。从长远来看，在该项目中对自然OEC的研究中获得的见解有可能使设计生产二氧化碳中性能源的新方法成为可能。计划的教育和指导活动范围从高中生的动手研究参与到博士后研究员的培训。光系统II研究的新成果将被整合到普渡大学多个系研究生和本科生的生物物理学课程中。Pushkar教授将为本科生创造研究机会，并为他们提供建议，包括参与斯隆基金会公平途径项目的本科生，该项目为STEM（科学、技术、工程和数学）领域的少数族裔学生提供研究指导。Pushkar教授还积极参与普渡大学的女性物理学和女性科学项目。本项目的研究将集中于光系统II的氧演化复合物（OEC）及其在O-O键形成中的功能的综合振动分析和时间分辨振动光谱研究。低频IR（红外）光谱能够检测到OEC中的Mn-O振动，即使在大蛋白质存在的情况下也是如此。这是由于Mn4OCa簇中Mn-O振动的高红外活性所致。低频红外光谱和同位素标记将用于确定S3状态的光系统II和它的异构体的分子身份。近红外共振拉曼光谱将并行用于选择性检测Mn4OCa团簇振动和团簇分子结构在Kok周期中的变化。实验结果将在OEC现有结构模型的框架内进行解释。将进行互补密度泛函理论（DFT）计算，以监测OEC中拟议化学转化的能量分布。这种对OEC的光谱/计算结合研究有望为这种非常高效的天然锰基水分解机器的机制提供新的见解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemistry of Life Processes Program of the Chemistry Division, Professor Yulia Pushkar of Purdue University will study the oxygen evolving complex (OEC) of photosystem II, a protein that contains manganese and calcium ions. This protein, which uses the energy of sunlight to catalyze the splitting of water molecules into protons, electrons, and oxygen molecules, provides the majority of oxygen in the Earth’s atmosphere. Application of spectroscopic methods to the study of the catalytic cycle will provide insight into the roles of the manganese and calcium ions and their protein environment in the light-driven formation of dioxygen. In the longer term, insights gained in the study of Nature's OEC in this project have the potential to enable the design of new methods for the production of energy that is CO2-neutral. The planned educational and mentoring activities range from hands-on research involvement of high school students to the training of postdoctoral fellows. New results from photosystem II research will be integrated into the biophysics curriculum that is delivered across multiple Purdue Departments at both the graduate and undergraduate levels. Professor Pushkar will create research opportunities for and advise undergraduate students including those participating in the Sloan Foundation Equitable Pathways Program Partnering in Research Mentoring for Minoritized Students in STEM (science, technology, engineering and mathematics). Professor Pushkar also actively participates in Purdue’s Women in Physics and Women in Science Programs. Research in this project will be focused upon a comprehensive vibrational analysis and time-resolved vibrational spectroscopic study of the oxygen-evolving complex (OEC) of photosystem II and its functions in the O-O bond formation. Low-frequency IR (infrared) spectroscopy is capable of detecting Mn-O vibrations in the OEC, even in the presence of the large protein. This is due to high IR activity of the Mn-O vibrations in Mn4OCa clusters. Low-frequency IR spectroscopic and isotopic labeling will be used to determine the molecular identity of the S3 state of photosystem II and its proposed isomers. Near-IR resonance Raman spectrascopy will be used in a parallel for the selective detection of Mn4OCa cluster vibrations and changes in the molecular structure of the cluster during the Kok cycle. The experimental results will be interpreted within the framework of currently available structural models of the OEC. Complementary density functional theory (DFT) calculations will be conducted to monitor the energy profile of the proposed chemical transformations in the OEC. Together this combined spectroscopic/computational study of the OEC is expected to provide new insights into the mechanism of this remarkably efficient, natural Mn-based water splitting machine.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.