Low Molecular Weight Chitosan-based Schiff Bases: Synthesis, Characterization and Antibacterial Activity

In the present study, Chitosan Schiff Bases (CSBs) were synthesized via condensation reaction of Low Molecular Weight Chitosan (LMWC) with aromatic aldehydes including either benzaldehyde, p-chlorobenzaldehyde, p-N,N-dimethylaminobenzaldehyde or p-methoxybenzaldehyde (anisaldehyde, naturally occurring aldehyde) to enhance the antibacterial activity of chitosan. The chemical structure of obtained Schiff bases were characterized using UV, FT-IR and 1H NMR spectroscopy. Moreover, the structural features were examined by Scanning Electron Microscopy (SEM). FT-IR spectra revealed that the characteristic bands of Schiff base owing to C-N stretching vibrations appeared at ~1645, 1634, 1632 and 1610 cm-1. The chemical substitutions were also confirmed in the four types of synthesized Schiff bases by 1H NMR spectroscopy, in which new signals were appeared at 7-12 ppm that are belonging to the aromatic moieties of the Schiff bases. The Degree of Substitution (DS) ranged from 20.5-22.9% depending on the type of reacted aromatic aldehydes. The contact angle measurements for the obtained chitosan Schiff bases-based films indicated that surface of these films are more hydrophobic than that of chitosan one. The antibacterial activity of CSBs were measured against two types of gram positive bacteria (Streptococcus pyogenes and Staphylococcus aureus) and two of gram negative bacteria (Escherichia coli and Shigella dysenteriae). The bacterial growth was assessed by measuring the Optical Density (OD) of culture media at 610 nm. These results exhibited that all prepared CSBs have higher inhibition efficiency against gram-positive bacteria than gram-negative ones. However, Schiff base of anisaldehyde exhibited the highest antibacterial activity.