SELECTIVITY COEFFICIENTS FOR IODIDE BROMIDE AND IODIDE CHLORIDE COUNTERION EXCHANGES AT THE SURFACES OF DIOCTADECYLDIMETHYLAMMONIUM VESICLES

Selectivity coefficients for the I-/C1- and I-/Br- ion exchanges at the surfaces of dioctadecyldimeth-ylammonium (large) vesicles were obtained from fluorescence-quenching experiments. The fluorescence of 1-pyrenenonanoic acid incorporated into dioctadecyldimethylammonium chloride and dioctadecyldi-methylammonium bromide vesicles is quenched by iodide addition to the intervesicular media. Below the phase transition temperature of the bilayers, temporal changes in probe fluorescence intensity after iodide addition can be interpreted in terms of fast ion exchange at the outer surface, followed by a slow iodide permeation until a final state is achieved in which ion exchange takes place at both surfaces. From data obtained immediately after the iodide addition to DODAB vesicles, it is learned that K(I-/Br-) at the outer surface is 8.0 ± 1.5. From quenching data after total counterion equilibration, values of K(I-/ Br) = 6.6 ± 1 and K(I-/C1-) = 31 ± 5 are obtained. © 1990, American Chemical Society. All rights reserved.