Quaternary ammonium salts of chitosan containing aromatic ring: Synthesis, characterization, antimicrobial, antioxidant and cytotoxicity

Quaternary ammonium salts of chitosan have been widely used in the development of anti-microbial biomaterials for their important role in inhibiting the growth of microorganisms. However, it is important to modify its structure to obtain more efficient and biologically active derivatives. Herein, a series of chitosan derivatives with antibacterial, antifungal, antioxidant, and non-cytotoxic properties was synthesized. These four quaternary ammonium salts of chitosan were prepared by incorporating 2-thiophenecarboxaldehyde, 2-furancarboxaldehyde, 2-pyridinecarboxaldehyde and benzaldehyde to form schiff bases, followed by a reductive amination to obtain the chitosan N -derivatives, and quaternized by iodomethane. The inhibition rate of thiophenecarboxaldehyde chitosan trimethyl ammonium iodide (TpTMC) to B. cinerea could reach 93.78% and the inhibition ability of pyridinecarboxaldehyde chitosan trimethyl ammonium iodide (PyTMC) to F. graminearum could reach 98.08% at the concentration of 1.0 mg/mL. Furthermore, furancarboxaldehyde chitosan trimethyl ammonium iodide (FrTMC) exhibited a strong ability to scavenge hydroxyl radicals and DPPH radicals, especially the DPPH radicals scavenging ability was comparable to that of L-ascorbic acid at the concentration of 1.6 mg/mL. The B3LYP/6-311++G (d, p) basis set was employed to determine electronic properties, including HOMO-LUMO energies, and to analyze the chemical reactivity of the compounds. L929 cells were used to evaluate the cytotoxicity of compounds at different concentrations (1−1000 μg/mL). The results demonstrated the diverse applications of aromatic ring-modified quaternary ammonium salts of chitosan, along with their significant antioxidant and antifungal effects against plant fungi. Therefore, these compounds have potential applications in the preparation of agricultural, biological, and medical materials.