Schiff Base of O -Carboxymethyl Chitosan and Its Complexes with Transition Metal Ions: Syntheses, Structural, Antimicrobial and Thermal Studies

Schiff base of O-carboxymethyl chitosan (O-CMC) and its four transition metal complexes were synthesized to improve the antimicrobial properties. For this objective, first the incorporation of O-carboxymethyl chitosan (O-CMC) was carried out by modifying primary hydroxyl group and the modified compound was treated with 2,5-dimethoxy benzaldehyde to integrate Schiff base. The salts of transition metal ions as Zn (II), Ni (II), Fe (II) and Cu (II) were processed with Schiff base to form coordinated metal complexes. The structural changes in chitosan, after chemical modification, were investigated by various spectroscopic techniques such as FTIR, 1H NMR, XRD, SEM, UV–visible and fluorescence. At 1H NMR, distinct signals were accessed at δ 9.6626 ppm, which corresponds to an 1H-nuclei of the imine group (–CH=N– in Schiff base), whereas the value of δ in the range of 6.5–7.5 ppm corresponds to the aromatic protons. The magnetic moment and magnetism of the metal complexes were studied using a vibrating sample magnetometer (VSM). The thermal behavior of chitosan and its newly formed derivatives was also compared by TG/DTG techniques. All the samples were inspected against the Gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus, and Gram-negative bacteria such as Escherichia coli and Aspergillus niger (fungi) for the determination of their antimicrobial activity. The results were better than those reported in earlier reports, and Fe and Zn complexes of O-CMC Schiff base had almost the same activity as ampicillin (reference drug). Minimum inhibitory concentration (MIC) was also calculated by broth dilution method.