Preparation And Antibacterial Activities Of Novel Derivatives Of Chitosan

For many years, chitosan has attracted much attention because of its fascinating structural features and potential applications. However, chitosan is limited in various application domains for the poor solubility. Novel derivatives of chitosan were synthesized by the acylated reaction and Schiff base reaction. The effect of reaction factors on the yield had been investigated and the suitable conditions were achieved. The structures of derivatives have been characterized by the FTIR spectroscopy and elemental analysis. The antimicrobial activities of chitosan and derivatives were investigated against Escherichia coil, Staphylococcus aureus and Aspergillus niger.The main contents and conclusions are described as follows:1. Preparation and Characterization of N-acyl Chitosans Preparation of sorbyl chitosan. Sorbyl chloride was synthesized by the reaction of sorbic acid with thionyl chloride. Then chitosan reacted with sorbyl chloride to form the sorbyl chitosan working under high-intensity ultrasound. The product was filtered and extracted in a Soxhlet apparatus with acetone, vacuum drying. The optimal conditions were temperature 50℃, the ratio of chitosan to sorbic acid, 1:4 and reaction time, 4h. The maximum degree of substitution was 0.81 under optimum conditions. The structure of sorbyl chitosan has been characterized by the FTIR spectroscopy and elemental analysis. The results confirmed that amino groups on chitosan reacted with sorbyl chloride to form the sorbyl chitosan.Preparation of p-aminobenzoyl chitosan. P-aminobenzoyl chloride was synthesized by the reaction of p-aminobenzoyl acid with thionyl chloride. Then chitosan reacted with p-aminobenzoyl chloride to form the p-aminobenzoyl chitosan working under high-intensity ultrasound. The product was filtered and extracted in a Soxhlet apparatus with acetone, vacuum drying. The optimal conditions were temperature 50℃, the ratio of chitosan to p-aminobenzoyl acid, 1:3 and reaction time, 3h. The maximum degree of substitution was 0.79 under optimum conditions. The structure of p-aminobenzoyl chitosan has been characterized by the FTIR spectroscopy and elemental analysis. The results confirmed that amino groups on chitosan reacted with p-aminobenzoyl chloride to form the p-aminobenzoyl chitosan.2. Preparation and Characterization of Schiff base of Chitosans Preparation of Schiff base from chitosan and citral. Chitosan was dispersed in methanol in the three-necked flask. Then citral dissolved in anhydrous ethanol was added drop-wise to the solution under high-intensity ultrasound at certain temperature for some time. When the reaction ended, the product was filtered and the unreacted citral was extracted in a Soxhlet apparatus with anhydrous ethanol, and then dried. The optimal conditions were temperature 40-50℃, the ratio of chitosan to citral, 1:6 and reaction time, 10h. The maximum yield achieved was 86.41% and the degree of substitution was 0.82 under optimum conditions. The structure of Schiff base has been characterized by the FTIR spectroscopy and elemental analysis. The results confirmed that amino groups on chitosan reacted with citral to form the Schiff base.Preparation of Schiff base from chitosan and cinnamaldehyde. Chitosan was dispersed in methanol in the three-necked flask. Then cinnamaldehyde dissolved in anhydrous ethanol was added drop-wise to the solution under high-intensity ultrasound at certain temperature for some time. When the reaction ended, the product was filtered and the unreacted cinnamaldehyde was extracted in a Soxhlet apparatus with anhydrous ethanol, and then dried. The optimal conditions were temperature 40℃, the ratio of chitosan to cinnamaldehyde, 1:6 and reaction time, 8h. The maximum yield achieved was 89.38% and the degree of substitution was 0.84 under optimum conditions. The structure of Schiff base has been characterized by the FTIR spectroscopy and elemental analysis. The results confirmed that amino groups on chitosan reacted with cinnamaldehyde to form the Schiff base.3. Antibacterial activities of novel derivatives of chitosan The antibacterial activities of chitosan and derivatives were investigated by assessing the inhibitory rates of Escherichia coil, Staphylococcus aureus and Aspergillus niger. The growth curves were also described.The results indicated that the derivatives had the effect of bacteriostasis and the antibacterial activity increased with increasing the concentration. It was also found that the antibacterial activities of the derivatives were stronger than that of chitosan. The minimum inhibitory concentration (MIC) of Schiff base of chitosan with cinnamaldehyde to E. coil was 0.08%; MIC of sorbyl chitosan to S. aureus was 0.08%; MICs of Schiff base of chitosan with citral and Schiff base of chitosan with cinnamaldehyde to A. niger were both 0.5%. The results indicated that the derivatives of chitosan had better antimicrobial activities than chitosan. The novel chitosan derivatives improve the antimicrobial activity of chitosan and expand the antimicrobial spectrum compared with that of chitosan.