Abstract:

A series of novel cationic quaternary ammonium surfactants （C_nNDA, n=10, 12, 14 and 16） were designed and synthesized, whose structure had both naphthalimide and long hydrocarbon chain as hydrophobic moieties. Their structures were characterized by FT-IR, ¹H NMR, ¹³C NMR and ESI-MS, and all the synthesized compounds were target products. The surface activity, micellization behavior, foaming ability, foam stability and antibacterial properties were tested. The results showed that, C_nNDA showed excellent surface activity and foaming properties. When the carbon number of hydrocarbon chain was increased from 10 to16, the cmc decreased from 1.01 to 0.026 mmol/L; the foam volume of 10 mL aqueous solution of 0.10 g/L C₁₄NDA was 28 mL at 0 min and 26.5 mL at 5 min, and the half-life was 16 h. In addition, C_nNDA showed excellent antibacterial activities against E. coli and S. aureus, and the minimum bactericidal mass concentrations for C₁₆NDA were 3.0 and 1.2 μg/mL, respectively. The results of ¹H NMR of C₁₂NDA in DMSO-d₆ revealed that, the chemical shift of amide proton shifted to the low field by 0.13 with the concentration increased from 3.0 mmol/L to 9.0 mmol/L, indicative of the formation of hydrogen bond by the amido groups. From the fluorescence spectra of different concentrations of C₁₆NDA, it could be found that the fluorescence intensity was decreased and the emission peak was red-shifted by 2 nm when the concentration exceeded cmc, indicative of the π-π stacking between naphthalimide segments. The excellent properties of C_nNDA were mainly attributed to the hydrophobic interactions from naphthalimide segments and long alkyl chains, π-π stacking of the adjacent naphthalimide segments, hydrogen bonding of amides groups, and electrostatic interactions. Therefore, they might have potential applications in foam and bactericidal fields.

Key words: novel surfactant, naphthalimide, surface activity, foaming, antibacterial