Photochemical regulation of ion transport through “quasi-channels” embedded in black lipid membrane

The black lipid membranes (BLM) of soybean lecithin doped with an amphiphilic azobenzene derivative, 4-octyl-4′-(5-carboxypentamethyleneoxy) azobenzene (8A5), was fabricated, and the K+ ion permeation through the “quasi-channels”, as represented by the steady d.c. current signal across the membrane, was photochemically regulated. A transient photocurrent overlapping with the steady d.c. current due to photoisomerization of 8A5 was observed in the BLM cell filled with a diluted KCl solution for the first time. Dependence of the steady photocurrent on the molar concentration ratio of 8 A5 to lecithin, [8 A5] / [lecithin], was also examined. It has been found that the normalized conductivity change, δG/G(trans), is roughly proportional to the square of [8A5]/[lecithin]. The result would suggest that one “quasichannel” consists of two 8A5 molecules.