Antifungal activity of double Schiff bases of chitosan derivatives bearing active halogeno-benzenes.

In this study, a series of chitosan derivatives bearing active halogenated aromatic imines were successfully synthesized via Schiff bases with the high degrees of substitution. Detailed structural characterization was carried out using Fourier transform infrared (FTIR) spectroscopy, solid-state C nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis. Besides, the antifungal activity against three common plant pathogenic fungi, including Botrytis cinerea, Fusarium oxysporum f. sp. cucumerinum, and Fusarium oxysporum f. sp. niveum, was investigated using in vitro hyphal measurements. The results showed that double Schiff bases of chitosan derivatives exhibited enhanced antifungal activity compared with chitosan, especially at 1.0 mg/mL. The double Schiff bases of chitosan bearing halogeno-benzenes showed >95% inhibitory indices at 1.0 mg/mL against Botrytis cinereal since halogens had the stronger electron-withdrawing property. The higher degree of substitution was another positive effect to improve the antifungal activity. This study provides a practical strategy to synthesize new double Schiff bases of chitosan derivatives bearing halogeno-benzenes, which could be developed into stronger antifungal agents.