Time Resolved Studies of Fundamental Mechanisms in Natural Photosynthesis

Purdue University, West Lafayette IN

Investigators

Abstract

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.