Synthesis and Physicochemical Characterization of Chiral Pyrrolidinium-Based Surfactants

Abstract

Chiral surfactants, (2S)-2-(hydroxymethyl)-1-methyl-1-alkyl pyrrolidinium bromides (L-CnPB, n = 12, 14, 16), were synthesized by the reaction of N-methyl-L-prolinol with long-chain alkyl bromides. The structures were characterized by IR spectra, 1H NMR, ESI-MS, and elemental analysis. Their surface activity, thermodynamic properties, and aggregation behavior were investigated by surface tension, electrical conductivity, and steady-state fluorescence. It was found that L-CnPB have lower critical micelle concentration (CMC) and surface tension at CMC (γcmc) in comparison with N,N,N-trimethyl-1-alkyl ammonium bromide (CnTAB) and N-alkyl-N-methyl pyrrolidinium bromide (CnMP). The CMC and the minimum average area per surfactant molecule (Amin) values of L-CnPB decreased with the increase in the alkyl chain length from 12 to 16. A series of thermodynamic parameters (, and ) of micellization obtained from electrical conductivity indicated that micellization is a spontaneous and entropy-driven process. Furthermore, the micelle aggregation number (Nagg) of L-CnPB obtained from steady-state fluorescence quenching was found to be 42, 48, and 53 for L-C12PB, L-C14PB, and L-C16PB, respectively.