Primary processes in photosynthesis: what do we learn from high-field EPR spectroscopy?

Primary photosynthesis is the biological electron transfer process by which green plants and certain bacteria convert the energy of sunlight into electrochemical energy. Light-induced charge separation is achieved by (bacterio) chlorophyll donor and quinone acceptor cofactors in the transmembrane reaction center protein complexes. Thereby transient radical ions are formed creating weakly coupled radical pairs. Time-resolved high-field EPR spectroscopy is ideally suited to study such short-lived species in their working states. It provides detailed information on the structure and dynamics of the cofactors in their binding sites and on hydrogen bond interaction with the protein. Thereby, our understanding of primary photosynthesis on the molecular level is improved.