PHOTOELECTRON TRANSFER BETWEEN A CHARGED DERIVATIVE OF CHLOROPHYLL AND FERRICYANIDE AT THE LIPID BILAYER-WATER INTERFACE

Abstract— Flash illumination of a lipid bilayer containing a positively charge pigment: chlorophyll b cholyl hydrazone and separating two salt solutions, one of which contained ferricyanide, resulted in a photovoltage of ∼20mV, acceptor side negative. The positive charge on the pigment resulted in several novel effects. (1) The photo-emf is twice that of chlorophyll a and five times that of chlorophyll b at a given concentration. A higher surface concentration of the charged derivative is the likely cause of this effect. (2) The pheophytin of chlorophyll b cholyl hydrazone produces about one-half the photo emf of the magnesium derivative whereas pheophytin a or b produced only one-tenth the signal. This may be a reflection of the changed redox potential of the cation chlorophyll b cholyl hydrazone. (3) A voltage drop of 100 mV across the membrane, the acceptor side negatively biased, causes a 3–4-fold increase in the charge recombination rate. Biasing the acceptor side 100 mV positive has no effect. Chlorophyll a or b do not show this field effect. This asymmetric effect is explained as a movement of the more polar chlorophyll dication towards the water interface, leading to more rapid reaction with donor. Thus the kinetics of the charge reversal are a sensitive and specific probe of the polar interfacial region of the lipid bilayer-water interface.