The free energy difference between the excited primary donor 1P∗ and the radical pair state P +H − in reaction centers of Rhodobacter sphaeroides

Abstract

The Gibbs free energy difference between the excited primary donor and the relaxed radical pair state P +H − in quinone-depleted reaction centers of Rhodobacter sphaeroides has been determined from various measurements of the delayed fluorescence to be 0.25 eV. Comparing this value with other energy data an entropy change of ΔS( 1 P∗ − P + H −) ⋍ 1.9 · 10 −4 eV/K is expected, giving only a small contribution at room temperature. Furthermore an upper limit, ΔG( 1 P∗ − P + B −) < 0.09 eV , is determined.