Coherent Multidimensional Spectroscopy of the Oxygen Evolving Complex in Photosystem II

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The Chemical Measurement and Imaging and the Chemical Structure, Dynamics and Mechanisms Programs of the Chemistry Division have funded Professor John C. Wright of the University of Wisconsin to develop laser spectroscopy methods for measuring complex molecular systems with quantum state resolution. The methods are analogous to the brain's ability to distinguish colors from the response of the three types of retinal cone cells. The laser methods use three different laser beam colors to simultaneously excite three quantum states of specific molecules that proceed to drive photosynthesis. The methods provide the key for discovering how plants make oxygen by resolving the quantum states actually involved in photosynthesis. The primary research goal is applying the new laser methods to understanding the mechanism of oxygen evolution in photosynthesis. Oxygen is created at the oxygen evolution center (OEC) in photosystem II (PS II). The OEC contains Mn, O, and Ca ions and amino acid ligands. The laser beam colors will excite different combinations of vibrational and electronic states of the OEC that distinguish it from the much larger number of molecules in PS II. Different transition metal coordination complexes cobalamin will serve as model systems for testing and developing the methods. The project will resolve the quantum state changes as the OEC progresses through its different oxidation states. The changes will be correlated with those measured by the Biology with X-ray lasers NSF-STC program. The impact of this research is broadened by the participation of under-represented minorities; the development of strategies, materials, and the educational infrastructure required to implement active learning in college classrooms; and the dissemination of the research through different communication channels. The broadest impact is providing a model for how to efficiently collect and use solar energy for our energy future.