| Xanthones was a kind of oxyheterocyclic compounds extracted from medical plants.Since it was found,its derivatives were attracted considerable attention in the field of medicine,pharmacy and chemistry due to the high pharmacological activities,such as anti-bacterial,antitumor,anti-oxidation,anti-HIV.However,most of them were insoluble in neutral and acidic medium,which caused the decrease of antibaceterial activity,and thus limited their application in the antibacterial material field and medical field.In order to overcome these problems,the structure of xanthone have usually been changed by chemical modification.In this paper the 1,3-dihydroxy-xanthone（Xan）was synthesized firstly,and then it was modified by hydrophilic substitutes and covalent grafted to improve the solubility and antibacterial activity,the specific methods were as follows:1.1,3-Dihydroxy-xanthone was synthesized by salicylic acid and phloroglucinol as raw materials.The pure product was successfully separated by column chromatography.And then the solubility and antibacterial activity were further studied.The results showed that the xanthone can dissolved in alkaline aqueous solution,but insoluble in acidic and aqueous solution.Moreover,the inhibition effect against E.coli was obvious and the mininum inhibitory concentration was about 500μg·mL-1,while no obvious inhibitory effect had been observed toward S.aureus.In order to improve the solubility and antibacterial activity in aqueous solution,hydrophilic modification was processedfirstly.andweusebromoaceticacidreactedwith1,3-dihydroxy-xanthone（Xan）to obtain 1-hydroxy-3-carboxymethyl-xanthone（CXan）.The final product exhibited better solubility in water and improved antibacterial activity against E.coli and S.aureus.The mininum inhibitory concentration toward S.aureus was about 500μg·mL-1.2.Quaternized chitosan（TMC）was synthesized by two step method.Then monochloroacetic was used as carboxylation reagent to react with TMC,and finally O-carboxymethyl-quaternized chitosan（CTMC）was obtained.The degree of quaternization was 40%,and the degree of carboxylation was 60%.The antibacterial test showed that the growth of S.aureus and E.coli could be inhibited obviously when the concentration of CTMC or TMC is 1000μg·mL-1,but could not kill all of the bacteria.3.1,3-dihydroxy-xanthone was further modified by grafting with O-carboxymethyl-quaternized chitosan.Xan was successfully covalently bound with CTMC through trying a series of of catalyst and reaction medium.Finally the grafting rate of the product was 40%.Thermogravimetric analysis showed that the hydrogen-bond interaction between molecules was of great importance for the thermostability of chitosan derivatives,moreover,with the introducing of carboxyl to chitosan backbone,the thermostability of chitosan derivatives was dramatically increased,and the residual weight was 50%at 850℃.Solubility test showed that the grafted product could completely dissolved in water and kept stable for long time.But CTMC-Xan had decomposed as CTMC and Xan when the solution medium was changed to strong basic or strong acid.In addition,the antibacterial assay suggested that the minimal bactericidal concentration against E.coli was 125μg·mL-11 and the minimal bactericidal concentration against S.aureus was 250μg·mL-1,which because that there was a synergistic antibacterial effect between CTMC and Xan,... |
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