Radicals and Radical Pairs in Photosynthesis

Abstract

Light-induced radicals and radical pairs occur naturally in the primary photochemical reaction of photosynthesis. They have been at the focus of intense study ever since the first observation of an electron paramagnetic resonance (EPR) signal in plants and photosynthetic bacteria ( 1 , 2). The EPR and electron nuclear double resonance (ENDOR) techniques, along with a variety of optical methods, have been the main source of information about the identity and electronic structure of radicals that occur in photosynthetic systems during the various electron transfer (ET) reactions taking place as a result of light uptake. The chemical nature of most of the species that serve as electron donors and acceptors along the primary ET paths have been iden-