Photochemical electron transfer across surfactant bilayers mediated by 2,1,3-benzothiadiazole-4,7-dicarbonitrile

Abstract

2,1,3-Benzothiadiazole-4,7-dicarbonitrile (BTDN) has been photochemically reduced by 4-morpholine-ethanesulphonic acid (MES) in the presence of vesicles of dioctadecyldimethylammonium bromide (DODAB) or egg yolk phosphatidylcholine containing DODAB. Using asymmetrical vesciles, electron transfer can occur from MES entrapped within the inner water pools to suitable anthraquinonesulphonates (1; 1,5; 2,6 but not 2) in the bulk water mediated by BTDN. Evidence is presented that these reactions involve the genuine transport of the electron across the bilayer and not leakage of either donor or acceptor across the bilayer. Kinetic and flash photolysis studies show that the rate-determining step of the reaction is electron transport across the vesicle, that this occurs by diffusion of BTDN^˙– and that the rate of this diffusion reaction is in turn controlled by the charge-compensating diffusion of OH^– in the opposite direction across the bilayer.