Bromide/chloride counterion exchange at the surfaces of dioctadecyldimethylammonium vesicles

Abstract

The exchange between bromide and chloride counterions at the surfaces of dioctadecyldimethylammonium vesicles has been examined through fluorescence quenching experiments. The quenching of the fluorescence of vesicle-incorporated naphthalene derivatives by bromide counterions has been studied under different experimental conditions. The data are analyzed by following the pseudophase ion-exchange model and assuming that the observed quenching is a direct function of the local quencher concentration at the vesicle surfaces. The fluorescence quenching behavior is found to be accounted for by the ion-exchange formalism when experiments are performed on vesicles having the same ionic composition for the contacting solution at both the outer and inner aqueous pseudophases. From this type of experiment, a bromide/chloride counterion exchange constant equal to 4 ± 1 is obtained. Experiments performed by addition of a vesicle solution containing a single counterion (chloride) to an isotonic sol