The Study On Chemical Modification And Antibacterial Performance Of Chitosan And Its Derivatives

Chitosan is a kind of polymer poly cationic compounds and it has found so far the only natural basic polysaccharide.Its annual output is only inferior to cellulose and in second place.Because of its special physicochemical properties and biological characteristics,chitosan has many good properties such as reduction of blood glucose level,regulation of lipid metabolism and inhibition of bacteria activity.Moreover,it is called as the sixth life key element with broad application prospects.However,due to inter-and intra-molecular hydrogen bonds,chitosan is insoluble in water and soluble in weak acid only,which limits its application.Through the study of the chemical modification of chitosan and its derivatives,a series of chitosan derivatives was prepared.This effectively improved not only the solubility in water of these derivatives,but also antibacterial effect and biocompatibility.First,chitosan reacted with etherifying agent(2,3-eposypropyltrimethyl ammonium chloride)under certain conditions to produce quaternary ammonium salt of chitosan.The water-solubility of quaternary ammonium-modified chitosan was greatly increased,and its minimal inhibitory concentration against Staphylococcus aureus was 0.5 mg/mL.Meanwhile,the influences of dispersant volumes,adding methods of etherifying agent on the experiment were examined.When the mass ratio of isopropyl alcohol/water ratio and chitosan/etherifying agent were 2.5:1 and 1:3,respectively,and the etherifying agent was added by one-time,the yield of the quaternary ammonium-modified chitosan reached the maximun.But the addition of quaternary ammonium salt leaded to an increase in the cytotoxicity.When the concentration was lower than 0.01 mg/mL,quaternary ammonium-modified chitosan showed an acceptable level of cytotoxicity.To further improve the cytotoxicity of quaternary ammonium salt-modified chitosan,we used water-soluble carboxymethyl chitosan to prepare amino acid-modified carboxymethyl chitosan.Then the impact of nature of amino acids,mass ratio and concentration on the antimicrobial properties was investigated for the modified carboxymethyl chitosan.Experimental results showed that the leucine-modified carboxymethyl chitosan had no obvious antibacterial effect,and even promoted the growth of the bacteria.With the charge ratio of carboxymethyl chitosan and arginine increasing,the antibacterial rate of arginine-modified carboxymethyl chitosan against E.coli increased first,and reached a plateau at 99.8%.When the mass ratio was above 20:1,the antibacterial rate decreased and the antibacterial rate of it against E.coli was 87.5%.In short,when the charge ratio ofcarboxymethyl chitosan and arginine is 5:1,the antimicrobial properties of arginine-modified carboxymethyl chitosan will decline as the solution concentration decreases,and The minimum inhibitory concentration of it to E.coli is 2.5 mg/mL.Moreover,the biocompatibility of arginine-modified carboxymethyl chitosan was better than that of the carboxymethyl chitosan.for a concentration of 10 mg/mL,the relative growth rate of the arginine-modified carboxymethyl chitosan was 79.9% and that of the latter was 42.8%.Although arginine-modified carboxymethyl chitosan had relatively good biocompatibility,its antibacterial performance could not meet the needs of the application.Conversely,the quaternary ammonium salt of chitosan had better antibacterial performance,but its cytotoxicity was high.Therefore,chitosan can be double modified.The effect of mass ratio of chitosan quaternary ammonium salt and arginine on the antibacterial properties of arginine-modified chitosan quaternary ammonium salt have been explored.Obtained results indicated that compared with the modification of chitosan quaternary ammonium salt,the minimum inhibitory concentration of double modified chitosan against staphylococcus aureus was reduced by nearly 10 times.At the concentration of 0.05 mg/mL,the antibacterial rate of the double modified chitosan against staphylococcus aureus reached 99%.