Synthesis and characterization of water-soluble chitosan derivatives: spectral, thermal and biological studies

Abstract

In this study, different water-soluble derivatives of chitosan were synthesized by treating chitosan with monochloroacetic acid to yield O-carboxymethyl chitosan (O-CMC) and this O-CMC treated with vanillin to form Schiff base. Metal complexes of this Schiff base were prepared with different salt of metal ions like Cu(II), Ni(II), Fe(II) and Zn(II). O-CMC and its Schiff base were characterized by FTIR, 1H-NMR and all other derivatives were characterized by using FTIR, UV-visible and fluorescence spectroscopic techniques. In FTIR study, the main characteristic peaks were observed at 1744 cm−1 (C = O str. in O-CMC), 1666 cm−1 (C = N str. peak in Schiff base) and 600–640 cm−1 (metal-ligand str.). In 1H-NMR different signals were obtained at δ 9.58 ppm due to the proton of imine group (–CH = N- in Schiff base) and signals in between δ 6.5 and 7.5 ppm due to aromatic protons. Antimicrobial activity of all these derivatives was also investigated against Bacillus subtilis (Gram-positive bacteria), Escherichia coli (Gram-negative bacteria) and Aspergillus niger (fungi). The result shows that Ni- and Zn-complexes of O-CMC Schiff base has almost similar activity as that of standard drug ampicillin. Thermal behavior of all these derivatives was also examined by using TG/DTG techniques.Research HighlightsWater-soluble derivatives of chitosan were synthesized (O-CMC, Schiff base and metal complexes).All derivatives were characterized by using different techniques (FTIR, 1H-NMR).Thermal, spectral and antimicrobial studies were also carried out.All derivatives are water-soluble and thermally stable and exhibited enhanced antimicrobial activity.