Transfer of spin correlation between radical pairs in the initial steps of photosynthetic energy conversion

A simple theoretical description of the transfer of electron spin-correlation from one radical pair to another is presented. Solution of the coupled equations of motion of the two radical pairs, yields simple expressions for the spin-polarized electron paramagnetic resonance intensities of the secondary pair in terms of the magnetic and exchange interactions of the electron spins, and the rates of the forward and backward electron transfer reactions of the primary pair. This work is set in the context of the initial steps of bacterial photosynthesis in which the rate of formation of the secondary radical pair is reduced by Fe2+ removal or quinone substitution.