Synthesis and surface activity of novel amino acid surfactants

Amino acid surfactants (AASs) based on environmentally friendly biomasses have the characteristics of renewable, easy biodegradation, antibacterial and low toxicity, and have been widely used in daily chemicals, pharmaceuticals, and other fields. This study concerned the use of octanal and amino acids as raw materials. In addition, seven types of amino acid-based surfactants, through Collins reagents, Wittig-Hornor reaction, and aza-Micheal addition reaction, and amino acid head groups were connected with the alkyl chain by the CN bond. The structures were confirmed by infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectroscopy (¹HNMR). Its surface activity and adsorption properties are evaluated. The physical properties of amino acid-based surfactants were tested by surface tension and dynamic contact angle. The results demonstrated that histidine-based amino acid surfactant (C8His) has the lowest critical micelle concentration (CMC) and surface tension at CMC (γCMC), 0.39 mmol L⁻¹ and 28.79 mN L⁻¹, respectively. Amino acid residues contribute to reducing the critical micelle concentration of surfactant. The interfacial adsorption of glycine-based amino acid surfactant (C8Gly) significantly improved with the increase in temperature, so the surface tension decreased significantly. In addition, sodium chloride could effectively enhance the interfacial adsorption, and the gas–liquid interfacial tension and contact angle of AASs decrease.