KINETICS OF CHLOROPHYLL PHOTOSENSITIZED ELECTRON TRANSFER REACTIONS IN PHOspHOLIPID BILAYER VESICLES

Abstract The effects of electrostatic surface charge and valinomycin addition in the presence of K* on the kinetics and the inside-outside asymmetry properties of light-induced electron transfer reactions between chlorophyll triplet state and benzoquinone, ferricyanide and methyl viologen in large unilamellar vesicles have been investigated using laser flash photolysis. Modifying the surface charge of the bilayers by incorporating charged surfactants or decreasing the ionic strength of the suspending medium caused large changes in the dynamics of the electron transfer reactions, which could be interpreted in terms of electrostatic interactions between reactants, products and membrane components, and the existence of a spontaneous transmembrane electrical potential corresponding to an excess of negative charge at the outer surface of the vesicle bilayer. The presence of valinomycin had more specific effects on these reactions, which were consistent with an electrostatic influence of the presence of the positively-charged K⁺-valinomycin complex within the bilayer on the dynamics of only those triplet quenching and radical formation and decay processes which occur in this region of the vesicle structure.