The interaction of photo-excited chlorophyll a with duroquinone, α -tocopherylquinone and vitamin K 1

Abstract

The reversible electron transfer between photoexcited chlorophyll a and duroquinone has been studied in neutral, acid and alkaline ethanolic solutions. Rates for the reaction of chlorophyll a singlet and triplet states with duroquinone have been determined, and the kinetics for the decay of the radicals so formed have been investigated. In neutral and alkaline solution, evidence has been found for the recombination of the chlorophyll radical cation with the semiquinone radical anion of duroquinone at a rate close to that for a diffusion controlled reaction. In acidic solutions, the chlorophyll radical cation decays by two processes: 60% reacts by second-order process within milliseconds, and the residual 40% decays by the first-order process having a lifetime of approximately 1 s. The decay rate of these oxidized chlorophyll a species is greatly increased by durohydroquinone. Analogous reactions have been found for triplet chlorophyll a with $\alpha $-tocopherylquinone and with vitamin K$_{1}$.