Applications of ESE spectroscopy in the study of electron spin polarization in bacterial photosynthesis

Abstract

In photosynthesis the photon energy of light is converted into chemical potential in the so-called Reaction Center (RC), a pigmented membrane protein that upon excitation gives rise to a charged radical pair. The radicals are spin correlated and in an external magnetic field the interactions (dipolar, exchange) between the two electron spins give rise to non-Boltzmann populations of their magnetic sublevels (spin polarization), which is probed by time-resolved EPR. An overview is given of polarization phenomena in RC of bacterial origin, and recent theoretical interpretations highlighted. It is demonstrated that in all likelihood the exchange interaction of the primary radical pair in the RC of purple bacteria is positive. The implications of this result for our understanding of the initial processes of solar energy conversion are discussed. © 1992 IUPAC