Preparation And Properties Of Quaternized Chitosan-Terminal Carboxyl Xanthone Composite Antibacterial Materials By Electrostatic Self-Assembly

In recent years,owing to the enhancement of people's health awareness,antibacterial nano materials and composite antibacterial materials have been greatly developed.At present,many researchers have contributed to combining two kinds of antibacterial agent in order to obtain new antibacterial agent with complementary advantages.Xanthons are not soluble at neutral condition,and their antibacterial property is weak in neutral solution,which limits the application in the antibacterial and medical fields.While chitosan is only soluble in acid solution,thus its application is restricted by the poor solubility and antimicrobial activity at neutral condition.To overcome the disadvantages and make use of the advantages,a new kind of soluble composite antibaterial material was prepared by electrostatic self-assembly technology using quaternized chitosan(TMC)and 1,3-dihydroxy-6-oxyacetic acid-xanthone(CXan),so that the two substances exert synergistic antibacterial mechanism,and contribute to the overall antibacterial effect of the composite.The main works are as follows:1.At first,1,3,6-trihydroxyxanthone was prepared by the Fock acylation reaction,and then 1,3-dihydroxy-6-oxyaceticacid-xanthone(CXan)was prepared from Xan and bromoacetic acid through nucleophilic substitution.Xan and CXan were characterized by infrared spectra,nuclear magnetic spectra and mass spectra,and the solubility and antibacterial activity were invetigated before and after the modification by the hydrophilic group.The results suggested that the solubility was improved after inducing hydrophilic group,moreover,it exhibited better antibacterial activity against S.aureus and E.coli.2.Fistly,quaternized chitosan was prepared through two steps process by chitosan and alkyl groups.Composite antibacterial material(TMC-CXan)was prepared by electrostatic self-assembly of positively charged quaternized chitosan with negatively charged CXan in aqueous solution.The chemical structure,morphology,particle size and crystal type were characterized by fourier transform infrared spectroscopy,nuclear magnetic resonance spectroscopy,mass spectrometry,scanning electron microscopy,X-ray diffractometry and dynamic light scatterometer.In addition,the antibacterial property was studied by plate count agar method,and the antibacterial mechanism was revealed.TMC-CXan has good dispersibility,stability and antibacterial activity.Moreover,the antimicrobial effect of TMC-CXan was mproved greaty compared with TMC and CXan.The minimum inhibitory concentration(MIC)for E.coli was 100?g·m L^-1,and the minimum bactericidal concentration(MBC)was 200?g·m L^-1.While the minimum inhibitory concentration(MIC)against S.aureus was 25?g·m L^-1,and the minimum bactericidal concentration(MBC)was 100?g·m L^-1.The antibacterial mechanism showed that TMC accumulated on the surface of the bacterial cell membrane to hinder the circulation of substances inside and outside the cell.CXan could enter the cell and interact with the cytoplasm to affect the normal metabolic activities of the cells.They may play a synergistic antibacterial mechanism to achieve antibacterial function.