Time Resolved Studies of Fundamental Mechanisms in Natural Photosynthesis

在化学系生命过程化学项目的支持下，普渡大学的尤利娅·普什卡教授将研究光系统II的放氧复合体(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解成质子、电子和氧分子，提供了地球大气中的大部分氧气。将光谱方法应用于催化循环的研究将有助于深入了解锰和钙离子及其蛋白质环境在光驱动的二氧化碳形成中的作用。从长远来看，在这个项目中研究大自然的OEC所获得的洞察力有可能使设计出新的二氧化碳中性能源生产方法成为可能。计划的教育和辅导活动范围从高中生的实际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生物物理学课程中，该课程将在普渡大学多个系的研究生和本科生水平上提供。普什卡教授将为本科生创造研究机会，并为他们提供建议，包括那些参加斯隆基金会公平路径计划的本科生，为STEM(科学、技术、工程和数学)的小规模学生提供研究指导合作伙伴。普什卡教授还积极参加普渡大学的女性物理学项目和女性科学项目。本项目的研究将集中在光系统II的放氧复合体(OEC)及其在O-O键形成中的功能的全面振动分析和时间分辨振动光谱研究。低频红外光谱能够检测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团簇中的Mn-O振动具有较高的红外活性。低频红外光谱和同位素标记将被用来确定光系统II及其异构体的S3态的分子同一性。近红外共振拉曼光谱将用于选择性地检测Mn4OCa团簇在KOK循环期间的振动和分子结构的变化。实验结果将在现有的OEC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中所提议的化学转变的能量分布。总而言之，这项对OEC的光谱/计算研究有望为这种非常高效的天然锰基分水机的机理提供新的见解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.