The Effect Of The Structure Of O-acylation Chitosan Quaternary Ammonium Salts And Media On Their Antibacterial Activity

Two acylated chitosan quaternary ammonium salt derivatives were synthesizedon the base of O-methyl-free N,N,N-trimethyl chitosan （TMC）. Then the antibacterialactivity against Escherichia coli （E.coli） and Staphylococcus aureu （S.aureus）through investigating minimum inhibitory concentration （MIC） and inhibition ratewas evaluated. And the effect of the structure of chitosan-based materials and externalmedia （pH, metal ions and surfactants） on antibacterial activity was also studied,which provided a theoretical possibility for these new chitosan-based materials as anexcellent antibacterial agent.TMC was separately reacted with hexanoyl chloride and succinic anhydride inthe methanesulfonic acid, then we got two acylated chitosan quaternary ammoniumsalt derivatives, O-hexanoyl quaternary ammonium chitosan （TMHC） and O-succinylquaternary ammonium chitosan （TMSAC）. FTIR,1H NMR, EA, XRD and TGmethods were used to characterize the structure of the products. The results showedthat the products were synthesized successfully.The experimental results indicted that the antibacterial activity of TMHC andTMSAC was stronger than that of TMC, and increased as the substitution degree ofacylation increased. The antibacterial activity of TMHC was stronger than TMSAC atthe similar degree of substitution.Different surfactants could affect the antibacterial activity. Cationic surfactantcetyl trimethyl ammonium bromide （CTAB） could increase the antibacterial activityof TMHC and TMSAC, while anionic surfactant sodium dodecyl sulfate （SDS）decreasing. The low concentration of nonionic surfactant Tween-80（10mM） had no effect on TMHC and TMHC, the antibacterial activity of TMHC became stronger asthe concentration of the surfactant increasing （10mM to50mM）, but the antibacterialactivity of TMSAC was weaker at the same condition. Betaine type amphotericsurfactant (C₁₂BE) increased the antibacterial activity of TMHC, but decreased theantibacterial activity of TMSAC.Mg²⁺, Ca²⁺and Ba²⁺（25mM） could reduce the antibacterial activity of TMHCslightly, in the order of Ba²⁺> Ca²⁺> Mg²⁺. When the concentration of Mg²⁺reachedto100mM, the antibacterial activity decreased clearly. As for TMSAC, the metal ionsat25mM could reduce its antibacterial activity obviously, in the order of Ba²⁺> Ca²⁺> Mg²⁺. The different results between TMHC and TMSAC may be induced todifferent side chains. Compared with acyl chain, the carboxyl group could chelatewith metal ions more easily.In addition, TMC, TMHC and TMSAC showed stronger antibacterial activity inthe acidic medium, the stronger pH of the medium, the stronger the antibacterialactivity. The products showed stronger antibacterial activity against E. coli thanS. aureus in the test condition.