Resonance Raman and electrochemical investigations of primary electron transfer species in photosynthesis

The primary electron-transfer species in photosynthesis were studied in an attempt to improve the understanding of their role in the highly efficient photoinduced charge-separation processes. A brief review of the electron-transfer processes which occur in the reaction centers of both green plants and bacteria is presented. The subsequent chapters describe electrochemical and resonance Raman investigations of the primary electron donor and acceptor. Electrochemical techniques were used to study the effect of various solvents on the heterogeneous electron-transfer kinetics of bacteriochlorophyll $a$ and bacteriopheophytin $a$ at gold and platinum electrodes. The electron-transfer rate constant was found to be highly solvent dependent decreasing by tenfold with decreasing solvent dielectric constant. The solvent reorganization energy, as predicted from Marcus theory, appears to account for this change. Resonance Raman spectroscopy was used to investigate the primary electron donor and acceptor in photosystem II of green plants, chlorophyll $a$ cation radical and pheophytin $a$ anion radical, respectively. Large frequency bandshifts in the carbonyl region of these spectra with respect to the neutral spectra suggest that the C$\sb9$ keto group of both of these molecules has a role in the physiological electron-transfer process. In the final chapter, a preliminary resonance Raman and surface-enhanced resonance Raman investigation of the intact photosystem II reaction center is described. The results of this study demonstrate that resonance Raman spectroscopy and especially surface-enhanced resonance Raman spectroscopy hold great promise for the study of these complicated biological systems