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

摘要

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-tetraazatetraco-ntane-18,23-dicarboxylate([C_(12)-2-C_(12)]Na2),disodium(18R, 25R)-12,20,23,31-tetraoxo-13,19,24,30-tetraazadotetracontane-18,25-dicarboxylate([C_(12)-4-C_(12)]Na2), disodium(18R,27R)-12,20,25,33-tetraoxo-13,19,26,32-tetraazatetratetraconta-ne-18,27-dicarboxylate([C_(12)-6-C_(12)]Na2), disodium(2R,2'R)- 2, 2'-(6-chloro-1,3,5-triazine-2,4-diyl)bis(azanediyl)bis(6-do-decanamidohexanoate) ([C_(12)-T-C_(12)]Na2). The chemical structures of the prepared compounds were confirmed by ~1H-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 °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 (ΔG°_(mic) and ΔG°_(ads)). 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)]Na2 < [C_(12)-4-C_(12)]Na2 < [C_(12)-6-C_(12)]Na2 < [C_(12)-T-C_(12)] Na2, which were in agreement with the sequence of ΔG°_(mic) and ΔG°_(ads). The circular dichroism of the surfactants indicated the formation of chiral aggregates above the CMC values.