Interactions between a surface-active cationic 3H-indole molecular probe and micellar environments

Abstract

We report herein the interactions of a cationic surface-active molecular probe having long aliphatic chains, i.e., [2-(p-hexylamino)phenyl-3,3-dimethyl-5-ethoxycarbonyl-3H-indole]methyldioctadecylammonium iodide (1), with SDS (sodium dodecyl sulfate) and CTAB (cetyltrimethylammonium bromide) micelles investigated by spectral and photophysical characterizations. According to the absorption and fluorescence spectral characteristics and the fluorescence quantum yield, the interaction of 1 with SDS exhibits different patterns that depend on the SDS concentration: (1) formation of ion-pairs at very low concentration of SDS; (2) complex coacervation below the critical micellar concentration (c.m.c.) of SDS; (3) solubilization of the coacervate phase into micelles above the c.m.c. The fluorescence quantum yield measurement as well as the pH effect studies reveal that the hexyl group and a part of the anilino moiety of 1 penetrate the micellar interface, while the indolic moiety of 1 resides in the bulk phase. Lifetime measurements support the existence of three interaction patterns between 1 and SDS, and further indicate that 1recognizes one location in the SDS micelle and two in the CTAB micelle.