Surface Adsorption and Aggregation Properties of Novel L-Lysine-Based Gemini Surfactants

Four chiral l-lysine-based gemini surfactants with different spacers were synthesized, namely, disodium (18R,23R)-12,20,21,29-tetraoxo-13,19,22,28-tetraazatetracontane-18,23-dicarboxylate([C-12-2-C-12]Na-2), disodium (18R,25R)-12,20,23,31-tetraoxo-13,19,24,30-tetraazadotetracontane-18,25-dicarboxylate([C-12-4-C-12]Na-2), disodium(18R,27R)-12,20,25,33-tetraoxo-13,19,26,32-tetraazatetratetracontane-18,27-dicarboxylate([C-12-6-C-12]Na-2), disodium(2R,2'R)- 2,2'-(6-chloro-1,3,5-triazine-2,4-diyl)bis(azanediyl)bis(6-dodecanamidohexanoate) ([C-12-T-C-12]Na-2). The chemical structures of the prepared compounds were confirmed by H-1-NMR, ESI-MS and IR spectra. Further, the critical micelle concentration (CMC) of these surfactants in aqueous solutions was determined by surface tension and conductometry methods at 25 A degrees C. Moreover, the adsorption and micellization behaviors of these surfactants were estimated by pC(20), the minimum average area per surfactant molecule (A(min)), and standard free energy for micellization and adsorption ( and ). The results show that the four gemini surfactants have low CMC values and significantly low surface tension. Furthermore, the surfactants show strong adsorption at the air-water interface. The CMC and A(min) values of the surfactants were found to be in the order of [C-12-2-C-12]Na-2 < [C-12-4-C-12]Na-2 < [C-12-6-C-12]Na-2 < [C-12-T-C-12]Na-2, which were in agreement with the sequence of and . The circular dichroism of the surfactants indicated the formation of chiral aggregates above the CMC values.