Aggregation numbers and fluorescence quenching kinetics of simple single-tailed amphiphilic vesicles of alkyltrimethylammonium bromides in water

Abstract

Simple single-tailed amphiphiles (STAs) can form vesicles in their single-component aqueous solutions, under the mediation of solid surfaces, particularly through a dehydration-rehydration (DHRH) process. However, knowledge about the characteristics of the STA vesicle-systems thus obtained is still lacking. In the current work, the vesicles formed by the simple STAs alkyl trimethylammonium bromides (CnTABs), including dodecyl, tetradecyl, and cetyl ones (DTAB, TTAB, and CTAB), via a DHRH process were chosen. The aggregation numbers of the STA vesicles (Nv) were first estimated, and their fluorescence quenching kinetics was then investigated by the time-resolved fluorescence quenching (TRFQ) technique, which were compared with those of conventional vesicle systems. In particular, the mole fractions of CnTAB existing in the form of micelles (fm) in the vesicle systems were estimated using the TRFQ data. The Nv values of DTAB, TTAB, and CTAB were obtained to be ca. 7.33×104, 8.33×104, and 10.6×104, respectively, similar to those of conventional vesicles. In addition, the values of fluorescence quenching kinetic parameters obtained for the STA vesicle-systems are also similar to those of conventional vesicles. For the STA vesicle systems, vesicles coexist with micelles, but the fm significantly decreases with an increase in chain length. DTAB molecules exist mainly in the form of micelles (with fm ~0.82), while TTAB and CTAB exist mainly in the form of vesicles (with fm ~10‒5). Overall, the properties of STA vesicles are similar to those of conventional vesicles. This work deepens our understanding on the features of simple STA-based vesicles. Key words: Single-tailed amphiphile; Alkyl trimethyl ammonium bromide; Vesicle; Aggregation number; Fluorescence quenching kinetics.