The Effects of Amide Bonds and Aromatic Rings on the Surface Properties and Antimicrobial Activity of Cationic Surfactants

The cationic surfactants containing aromatic rings and amide bonds, N,N-dimethyl-N-dodecyl-2-pyrimidinylcarbamoylmethyl ammonium chloride ( a ), N,N-dimethyl-N-dodecyl-2-thiazolylcarbamoylmethyl ammonium chloride ( b ), and N,N-dimethyl-N-dodecyl-phenylcarbamoylmethyl ammonium chloride ( c ), were synthesized and characterized. The surface tension and conductivity values were employed to investigate the absorption and micellization behavior of the three cationic surfactants. The results showed that the synthesized surfactants have shown a low critical micelle concentration (CMC) and a high adsorption efficiency (pC₂₀) compared with the traditional cationic surfactant of N,N-dimethyl-N-dodecyl-N-benzyl ammonium chloride ( BAC-12 ). The aromatic rings of the a , b , and c molecular structures were analyzed using the ¹H NMR spectra for electrostatic repulsion effects between hydrophilic headgroups. The size distribution of the micelles was derived using dynamic light scattering (DLS) techniques. In addition, the foaming ability of a , b , c , and BAC-12 was investigated and the antimicrobial activity of a , b , c , and BAC-12 against Escherichia coli, Staphylococcus aureus, and Bacillus subtilis was examined. The effects of amide bonds and aromatic rings on the surface properties and antimicrobial activity of a , b , and c were analyzed and compared with BAC-12 of the same alkyl chain length. The synthesized surfactants exhibited a high surface ability and better antibacterial activity compared with BAC-12 .