Ion exchange between divalent counterions in anionic micellar solution

Abstract

The ion exchange between divalent cations in anionic micellar systems were investigated by a fluorescence quenching technique using the anionic ruthenium complex RuL 4− 3 (L=4, 4′-dicarboxy-2, 2′-bipyridine) as an extramicellar probe and the N, N′-dimethyl-4, 4′-bipyridinium ion (MV 2+) as the quencher. Competitive ion exchange at the micellar surface between the divalent quencher counterion (MV 2+) and the divalent hexamethylethylenediammonium (HED 2+) counterion can be adequately described with a simple pseudophase ion-exchange formalism. The counterion exchange selectivity coefficients are K MV/HED=1.3 and 1.4 for HED-decyl sulfate [HED(DeS) 2] and HED-dodecylsulfate [HED(DS) 2] micelles, respectively. These results show that the MV 2+ cation only slightly more strongly bound to the micelle aggregates than the HED 2+ cation.