Electronic Processes in Bilayer Lipid Membranes

Abstract

THE appearance of an e.m.f. on illumination of certain “black” or bilayer lipid membranes (BLM) containing chlorophylls and/or carotenoid pigments has been reported recently¹. Some of the earlier findings have been confirmed by Hesketh². The magnitude of the observed photo-e.m.f.'s was generally small, of the order of a few mV, which may be because the systems investigated have been in “symmetrical” conditions. The two aqueous solutions separated by the BLM were identical even though the exciting light approached the membrane from one direction only. This uneven illumination of the BLM and its supporting Plateau-Gibbs border by exciting light together with a slight mismatching of the contacting electrodes was apparently sufficient to give rise to the observed photoelectric effects. These light-induced effects have been explained in terms of charge carrier production and separation, as electrons and holes are generated in the BLM. It was predicted, if the above explanations were correct, that one side of the biface would become oxidizing and the other side reducing¹. We now report the results of further experiments with photoactive BLM under “asymmetrical” conditions. We have found that an open-circuit photo-e.m.f. greater than 100 mV can be generated across the BLM, and we also describe here other new findings on the photoactive BLM.