ABSTRACT
The electron transfer reactions reveal a directional specificity whose origin is not obvious from the crystal structure. The biological importance of photosynthesis lends special significance to the goal of understanding how the reaction centre captures the energy of sunlight with a quantum yield of essentially 100%. This chapter discusses the electron transfer reactions that occur in the reaction centres of purple, non-sulphur photosynthetic bacteria. It focuses mainly on the kinetic and thermodynamic properties of the transient radical pair states that participate in the initial steps of photochemical charge separation. The chapter emphasizes the importance of the free energies of the reaction centre’s radical pair states for controlling the rate and reversibility of the charge separation and recombination reactions. It provides information on how free energies are obtained. The chapter also discusses approaches that have been used to explore the kinetics, mechanism and specificity of the reaction.
