Effect of the Phase Transition on the Photochemical Reactions in Lipid Bilayer Membranes

Abstract

The effect of phase transition on the photochemical reactions in liposome system containing amphiphilic dye is studied. The fluorescence intensity of the amphiphilic cyanine dye with two long alkyl chains, N, N'-distearylthiacarbocyanine bromide, which is incorporated into bilayer liposome, is considerably modified by the fluid-solid phase transition of the lipid bilayer, while the fluorescence of the cyanine dye with one long alkyl chain, N-stearyl-N'-methylthiacarbocyanine bromide, was not affected by the phase transition. These results were interpreted in terms of the suppression of the twisting motion of the chromophores around the bridging bond in the excited singlet state. Factors affecting the photoinduced coupling of redox reactions across bilayer membrane, i.e. reduction of Fe(CN)^3- ₆ in outside aqueous phase of liposome and oxidation of potassium ascorbate in inside solution, are also studied using chlorophyll a incorporating liposome. It is found that phase transition exerts the influence on the fluorescence intensity of chlorophyll a, and on the rate of bimolecular reaction of chlorophyll a with water-soluble species.