Study On Synthsis, Antibacterial Activities Of Chitosan Derivatives

In addition to celluose, chitosan is the most renewable polysaccharide polymer on the earth, and is the only food fiber with positive charge in the nature. Furthermore, chitosan is particularly attractive for biological applications due to its nontoxicity, biodegradability, physiological and antibacterial properties. However, chitosan has not been fully utilized because of its limited solubility in neutral and alkaline aqueous media because of its rigid structure. In this thesis, three different chitosan derivatives have been synthesized, characterized, and their anbacterial activities against Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis)、Gram-positive bacteria (Escherichia coli and Salmonella cholerae-suis,) have further been investigated. The results are as follows:1. Soluble quaternary ammonium chitosan,(N,N,N-trimethyl chitosan, TMC) was synthesized and characterized by FT-IR and1H NMR. Its molecular weight was9400determined by gel permeation chromatography (GPC). The MICs of TMC against E. coli, S. cholerae-suis, S. aureus and B. subtilis was0.040,0.160,0.160and0.020mg/mL, and the MBCs was0.160,0.320,0.160and0.080mg/mL respectively. The result demonstrated that TMC exhibited stronger antibacterial effect than unmodified chitosan. Kill-time analysis of MIC,2×MIC and4×MIC showed that TMC performed lethal ability to the tested bacteria when the concentrations were up to their MBCs, and could kill all bacteria in6h (approximately105cfu/mL). Furthermore, transmission electron microscope (TEM) clearly showed serious damage on cell membrane of E. coli and S. aureus after being treated with4×TMC.2. Based on the reduciliby and stability properies of chitosan, the preparation of silver chitosan was carried on under alkali condition with high temperature reaction synstem. The product was characterized by FT-IR and UV-visible specrrophotometer. The MICs of TMC against E. coli, S. cholerae-suis, S. aureus and B. subtilis was0.064、0.064、0.064and0.032mg/mL, and the MBCs was0.128、0.256、0.256and0.128mg/mL, respectively. The values of MICs and MBCs were much lower than those of unmodified chitosan and tea polyphenols. Kill-time analysis of MIC,2×MIC and4x MIC showed that silver chitosan performed lethal ability to the tested bacteria when the concentration was up to their MBC. However, its lethal ability was weaker than that of TMC. Finally, all bacteria could be totally killed in24h (approximately105cfu/mL).3. Fe3O4magnetic particles were synthesized by co-precipitation method, and then its surface was coated by several surfactants. CMP was obtained after linking with chitosan through amide linkage. The product was characterized by FT-IR and particle-size distribution. The optimum reaction time was40,30,40and40min when the optimum concentrations of CMP against E. coli, S. cholerae-suis, S. aureus and B. subtilis was0.300,0.300,0.400and0.400mg/mL, respectively. The capture capacity of Gram-negative bacteria (>73%) was a little bit higher than those of Gram-negative bacteria (60%-70%).