Study Of Interactions Between Cationic Gemini Surfactants And DNA Or Phospholipid

Gemini surfactants are a new family of surfactants with special structures. These amphiphiles are made up of two hydrophilic and two hydrophobic groups in the molecule. The two hydrophobic tails connected by a spacer group at, or very close to the head groups. This new class of surfactants has shown excellent properties such as a strong ability to lower surface tension, better wetting ability, stronger biological activity, enhanced dispersion, much lower C20values and much lower critical micelle concentrations (CMC) when compared with conventional surfactants of one hydrophobic chain and one hydrophilic group.In this paper a series of bis-quaternary ammonium compounds were prepared from tertiary amine, epichlorohydrin, and alkyl halide. The Molecular formulas are [CnH2n+1N+(CH3)2CH2CH(OH)CH2(CH3)N+CnH2n+1]2C1-(abbrevited as n-3(OH)-n),[CnH2n+1N+(CH3)2(CH2)m(CH3)N+CnH2n+1]2Br-(abbrevited as n-m-n), while n=8,12,16; m=2,3,4.When compared with the traditional single tail surfactant, we found that Gemini surfactant have shown excellent surface properties. The length of hydrophobic carbon tails shown great influences on CMC of each Gemini surfactants.Using E.coli as Biological model, the antimicrobial activities of these quaternary ammonium salts were studied by using the TAM air Isothermal Microcalorimeter. Due to the electrostatic force between negative charged phospholipids which embedded in microbial cell membrane and cationic surfactants, the integrity of cell membrane were destroyed. As a result, prepared cationic Gemini surfactants showed excellent antimicrobial properties on E.coli. We found that the half inhibition concentration IC50of8-3(OH)-8,12-3(OH)-12, and16-3(OH)-16were1.389x10-5mol/L,1.389x10-5mol/Land1.389x10-5mol/L, respectively.The complexation of DNA and the cationic Gemini surfactant in aqueous solutions were investigated by Fluorescence emission spectroscopy using EB probe and UV-vis transmittance. The results showed that negative charges of DNA were neutralized by cationic surfactants effectively. The complexations were due to the electrostatic and hydrophobic interactions between DNA and cationic Gemini surfactant.The monolayer films of these surfactants, as well as the mixed monolayer behavior of cationic Gemini surfactant and DNA or phosphatidylcholine at air/water interface were investigated. The surface pressure (p)-area per molecular (A) isotherms were measured. With different structures, the p-A isotherms of mixed monolayer shown different compressibility and film-formation probability.