Abstract

One of the most intriguing and fundamental processes on our planet is photosynthesis, whereby light is converted into chemical energy. The first step in the chain of events is known to involve a charge-separation reaction in which a specialized chlorophyll (Chl) or bacteriochlorophyll (BChl) pigment-complex reduces a nearby pheophytin (Ph) molecule. In subsequent reactions the electron moves along a chain of acceptors and finally becomes stabilized such that the remaining potential energy can be used in metabolic reactions. It is obvious that these fundamental electron-transfer reactions have been an ongoing challenge to spectroscopists. Since the functioning pigment-protein complex was isolated in pure form (1) much progress has been made towards elucidating the architecture of the pigment complex and the optical dynamics of the system. Very recently these investigations were greatly stimulated by an X-ray structural determination of the reaction center of the photosynthetic bacterium Rhodopseudomonas viridis (2). One of the most interesting findings was that the pigments spatial arrangement was such that it contained a quasi C₂-axis with a dimer at one end. It was known from previous time-resolved experiments that this dimer played a crucial role in the initial events of the charge separation. It is apparent that with the structure at hand one can ask very specific questions about the functioning of the reaction centre, such as: why is there a dimer; what is the role of the intermediate chlorophyll and why does the reaction only proceed along one branch of the pseudo-symmetric pigment complex?

© 1986 Optical Society of America