Study On The Preparation Of Water-Soluble Chitosan Derivatives And Its Antibacterial Property

Three kinds of water-soluble chitosan derivatives of N-carboxymethyl chitosan (N-CMC),N-carboxyethyl chitosan (N-CEC) and low molecular weight chitosan were prepared using chitosan as materials. N-CMC and N-CEC mailly obtained from introducing water-soluble groups carboxymethyl and carboxyethyl into the amino groups of chitosan. Water-soluble low molecular weight chitosan was achieved from acidic hydrolysis method and its silver complex was alse prepared. The structure of samples were characterize by FT-IR,XRD,1H-NMR,13C-NMR and antibacterial property of samples to the Escherichia coli,Staphylococcus aureus and Bacillus subtilis were studied with plate count and nephelometry method. (1) N-carboxymethyl chitosans were synthesized using chitosan and chloroacetic acid instead of high price glyoxylic acid in aqueous solution. The optimal reaction conditions were as follows:90℃, reaction time,4h; mass ratio of chloroacetic acid to chitosan,5:1. The degree of substitution (DS) of product exceeded 1.39. The samples were characterized by FT-IR,XRD,1H-NMR,13C-NMR and the water solubility and isoelectric point of N-CMC with different degrees of substitution were determined. FT-IR and NMR data has confirmed that the substitution reaction occurred on the amino groups.The results of antibacterial property showed that the concentration of sample and degrees of substituted have certain effects on antibacterial ratio. With increasing of concentration of product, antibacterial ratio increased accordingly, when the concentration is 5mg/mL, the antibacterial ratio of N-carboxymethyl chitosan to Staphylococcus aureus reached 100% in 24h, and the antibacterial ratio of N-carboxymethyl chitosan to Escherichia coli and Bacillus subtilis reached 100% in 24h at the concentration in 6 mg/mL. Howerer, antibacterial ratio decreased with the DS increasement. Antibacterial results showed that the antibacterial ratio of Staphylococcus aureus is high, second is the Bacillus subtilis, that of Escherichia coli is relatively low.(2) The carboxyethyl chitosan (CEC) was synthesized using chitosan and acrylic acid as materails by Michael reaction. The factors such as mass ratio, pH value, time and temperature were investigated and the structure of the CEC was characterized by FT-IR,1H-NMR. The results showed that the mass ratio is 1:4, the best pH value is 6, the time is 5h and the optimum temperature is 90℃, the substitution degree of CEC is 0.75, the reaction proceeded in a short time compared with literature. The carboxyethylation mainly occurred on-NH2.(3) The water-soluble low molecular weight chitosan and its silver complexes were prepared using acid degradation of chitosan. The results showed that the particles of low molecular weight chitosan was about the 100-200um. The antibacterail rate of the low molecular weight chitosan to Escherichia coli, Staphylococcus aureus and Bacillus subtilis reached 87.1%,98.5% and 86.6% respectively at the concentration of 5mg/mL. The antibacterial rate of low molecular weight chitosan-Ag+ complex to Escherichia coli and Bacillus subtilis reached 100% in 6h and 12h respectively at the concentration of 4.8 mg/mL. At the concentration of 5.6 mg/mL and 12h, the antibacterial rate on Staphylococcus aureus asle can reach 100%. Results showed antibacterial rate of low molecular weight chitosan-Ag+ complex is higher than that of low molecular weight chitosan.