Preparation and antibacterial activity of C2-benzaldehyde-C6-aniline double Schiff base derivatives of chitosan

ABSTRACT C2-benzaldehyde-C6-aniline double Schiff base derivatives of chitosan were synthesized with positioning protection method for the first time. The structures and properties of the new synthesized products were characterized by Fourier transform infrared spectroscopy, 13C nuclear magnetic resonance, scanning electron microscope image, X-ray diffraction, and elemental analysis. The elemental analysis results indicated that the degrees of substitution of the products were from 39.6% to 48.2%. The synthesized compounds exhibited an excellent solubility in organic solvents. The antibacterial activities of all of the derivatives were tested in the experiment, and the results showed that the prepared chitosan derivatives had significantly improved antibacterial activity of chitosan and C2-benzaldehyde Schiff bases of chitosan toward Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 35218). Antibacterial activity of the Schiff bases against E. coli differs from the substituent at the same position of different anilines and increases as the sequence aniline > p-toluidine > o-toluidine, and the antibacterial activity of the Schiff bases against S. aureus increases as the sequence p-toluidine > aniline > o-toluidine. The IC50 of the C2-benzaldehyde-C6-aniline double Schiff base derivatives of chitosan against E. coli and S. aureus is 0.0035 and 0.0031 mg L−1, respectively, much lower than that of chitosan (0.0064 mg L−1) and C2-benzaldehyde Schiff bases of chitosan (0.0054 mg L−1). The cytotoxicity test showed that compared with chitosan and C2-benzaldehyde Schiff bases of chitosan, the prepared chitosan derivatives had lower cytotoxicity against SCG-7901. This paper provided a new method for the synthesis of Schiff bases of chitosan, which was enlightening. GRAPHICAL ABSTRACT