The antioxidant and antifungal activity of chitosan derivatives bearing Schiff bases and quaternary ammonium salts.

In order to improve the antioxidant and antifungal activity of chitosan, eight chitosan derivatives containing Schiff bases and quaternary ammonium salts were synthesized via an intermediate 6-O-chloroacetyl-2-N,N,N-trimethyl quaternary ammonium salt chitosan. Detailed structural characterization was carried out using FTIR and 1H NMR spectroscopy, and elemental analysis. The antifungal activity against F. oxysporum f. sp. cucumerium, B. cinerea, and F. oxysporum f. sp. niveum was evaluated using a mycelium growth rate test. The results indicated that the chitosan derivatives exhibited enhanced antifungal activity when compared to chitosan, especially at 1.0 mg/mL. 6-[4-(2,3-dihydroxyl-benzimide) pyridine] acetyl-2-N,N,N-trimethyl-chitosan chloride (2.3HBPATC), 6-[4-(2,3,4-trihydroxyl-benzimide) pyridine] acetyl-2-N,N,N-trimethyl-chitosan chloride (2.3.4HBPATC), 6-[4-(2-fluorine-benzimide) pyridine] acetyl-2-N,N,N-trimethyl-chitosan chloride (FBPATC), 6-[4-(2-chlorine-benzimide) pyridine] acetyl-2-N,N,N-trimethyl-chitosan chloride (CBPATC), 6-[4-(2-bromine-benzimide) pyridine] acetyl-2-N,N,N-trimethyl-chitosan chloride (BBPATC), and 6-[4-(2-hydroxyl-4-chlorine-benzimide) pyridine] acetyl-2-N,N,N-trimethyl-chitosan chloride (HCBPATC) showed inhibitory indices >90.0% at 1.0 mg/mL against F. oxysporum f. sp. cucumerium and B. cinerea. Furthermore, the chitosan derivatives showed stronger antioxidant activity than chitosan, especially 2.3HBPATC and 2.3.4HBPATC with inhibitory indices of 100.0% at 1.6 mg/mL against DPPH and superoxide radicals. Based on these data, it is reasonable to suggest that the introduction of phenolic hydroxyl and halogen groups enhances the antifungal and antioxidant activity of chitosan.