Synthesis, characterization, and the antifungal activity of chitosan derivatives containing urea groups.

As an abundant and renewable polysaccharide, chitosan has been drawing broad attention due to its natural properties. For the further utilization of chitosan, chemical modification can be applied in improving its water solubility and the bioactivities. In this study, four chitosan derivatives were synthesized by the reaction of chloracetyl chitosan derivative with quaternary ammonium salt (CTCS) and urea groups bearing 4-amino-pyridine, including BCTCS, 2CBCTCS, 3CBCTCS, and 4CBCTCS. The structure characteristics of synthesized products were established based on FT-IR spectroscopy, 1H NMR, and elemental analysis. Their antifungal activities against Fusarium oxysporum f. sp. niveum, Phomopsis asparagus, Fusarium oxysporum f. sp. cucumebrium Owen, and Botrytis cinerea were estimated by hyphal measurement in vitro. Generally, the inhibition ratio of most products was higher than 80% at 1.0mg/mL. Their inhibitory activity decreased roughly in the order: 4CBCTCS>3CBCTCS>2CBCTCS>BCTCS>CTCS>chitosan, resulted from the different degrees of substitution of the effectively active groups-urea groups. Meanwhile, the effects on beneficial soil microbes, including Bacillus cereus, Bacillus subtilis, and Sinorhizobium saheli LMG7837, of these synthesized chitosan derivatives were evaluated by disk diffusion method. The results showed that these substances do not inhibit the growth of beneficial bacteria and some of them could be employed as green antifungal biomaterials.