The surface adsorption, aggregate structure and antibacterial activity of Gemini quaternary ammonium surfactants with carboxylic counterions

A group of Gemini quaternary ammonium surfactants with the formula C(n)H(2n+1)CONH(CH(2))(2)N(+)(CH(3))(2)(CH(2))(2)N(+)(CH(3))(2)(CH(2))(2) NHCOC(n)H(2n+1) · 2Y (n = 11, 13 and 15, Y = HCOO(−), CH(3)COO(−) and CH(3)CHOHCOO(−)) have been synthesized by a counterion conversion process and characterized by Fourier transform infrared spectroscopy and mass spectroscopy. Their adsorption and self-aggregation properties are investigated by surface tension, conductivity, dynamic light scattering and transmission electron microscopy (TEM) measurements. The results show that these surfactants reduce the surface tension of water to a minimum value of 26.51 mN m(−1) at a concentration of 5.72 × 10(−2) mmol l(−1). Furthermore, the increased alkyl chain length of the carboxylic counterions leads to the increased critical micelle concentration, the decreased degree of counterion binding (β) and the decreased self-assembly tendency, but the minimum area per surfactant molecule (A(min)) adsorbed at the air–aqueous solution are similar. TEM images reveal that these surfactants self-assemble spontaneously into aggregates with vesicle or bilayer structures. It is also found that they have superior antibacterial activity at a concentration of 0.1 g l(−1). The high surface activity and high antibacterial activity of the Gemini quaternary ammonium salt surfactants containing different carboxylic counterions bring more possibilities for the application in the field of biomedicine.