Ultrafast Studies of Electron Transfer in Photosystem II

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9418390 Sension A proper understanding of the primary energy transfer and electron transfer processes in photosynthetic systems is one of the keys to a complete understanding of natural solar energy conversion. In this research project state-of-the-art ultrafast spectroscopic techniques will be uqed to study the primary electron transfer processes in photosystem II. Several types of experiments will be performed to try to elucidate the time-scale and mechanism for primary charge separation in PSII. These include the following: The ultrafast kinetics will be measured using various reaction center preparations to determine whether the method of preparation can affect either the energy relaxation kinetics or the rate of primary charge separation. Larger PSII complexes will be prepared in order to study the electron transfer rate in active centers and set to rest any speculation as to whether or not the D1-D2-Cyt b559 complex retains the native reaction center structure and dynamics. Transient absorption measurements will be made with ultrashort (50 fs) pulses to explore the possible involvement of coherent protein motion in the initial dynamics of PSII. Resonance Raman measurements will be attempted to probe the production of the initial charge separated state directly, overcoming the limitation of highly overlapping electronic absorption features. Combining the slight differences in the electronic spectra with the selectivity introduced by resonance enhancement and the differences in the vibrational spectra of the charged and neutral pigments, it should be possible to detect the charge separated state with much less ambiguity. %%% A rigorous understanding of the primary electron transfer reactions in biological photosynthetic systems is one of the keys to a complete understanding of natural solar energy conversion. The protein complex referred to as photosystem II (PSII) is responsible for the ability of green plants to utilize light energy to fuel the pr oduction of oxygen from water. The PSII protein complex works in conjunction with a second complex, photosystem I (PSI), to form carbohydrates from carbon dioxide. In this research project, state-of-the-art laser technology will be used to study the light initiated electron transfer reactions of photosystem II (PSII). The overall goal of this investigation is to obtain a detailed understanding of the factors that control the efficiency and robustness of photosynthesis in green plants. ***