Synthesis and antimicrobial activity of some novel terephthaloyl thiourea cross-linked carboxymethyl chitosan hydrogels

Four novel hydrogels composed of carboxymethyl chitosan (CM-chitosan) cross-linked with various contents of terephthaloyl thiourea moieties (TTUCM-chitosan-1, TTUCM-chitosan-2, TTUCM-chitosan-3, TTUCM-chitosan-4) have been successfully synthesized. The hydrogels were characterized by elemental analyses, FTIR, C-13 NMR, SEM, XRD, solubility and swell ability in various solvents. The antimicrobial activities of these hydrogels against three crop-threatening pathogenic fungi (Aspergillus fumigatus, Geotrichum candidum and Candida albicans) and against three bacterial species (Bacillis subtilis, Staphylococcus aureus and Escherichia coli) were investigated. The hydrogels showed higher antibacterial activity than the parent CM-chitosan as judged by their higher inhibition zone diameter and lower minimum inhibition concentration. They are more active against Gram-positive bacteria than against Gram-negative bacteria. The results also indicated that the hydrogels have effective antifungal activity as compared with CM-chitosan. The antimicrobial activity of the hydrogels increased with increasing their cross-linking density.