Improved Antioxidant and Antifungal Activity of Chitosan Derivatives Bearing Urea Groups.

Eight novel chitosan derivatives bearing urea groups are designed and synthesized. Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance spectrometer, and elemental analysis are performed to confirm the structural characteristics of chitosan derivatives. The antioxidant activities, including superoxide radicals' scavenging activity, 1,1‐diphenyl‐2‐picrylhydrazyl radicals' scavenging activity, and hydroxyl radical' scavenging activity, of the derivatives are explored within different concentrations in the reaction system. In vitro fungicidal activity of these compounds is further tested against Fusarium oxysporum f. sp. niveum, Phomopsis asparagus, F. oxysporum f. sp. cucumebrium Owen, and Botrytis cinerea, respectively, particularly compounds exhibit significant control effect at 1.0 mg mL−1. The experimental results indicate that the products bearing urea groups show enhanced antifungal property and antioxidant activity compared with pristine chitosan. Meanwhile, their bioactivities follow some regularity on the whole, that is, they are related to the electron‐withdrawing property of the different substituted groups of urea. Derivatives with stronger electron‐withdrawing property will have higher biological activities. L929 cells are used to carry out cytotoxicity test of chitosan and chitosan derivatives by Cell Counting Kit‐8 assay. The results indicate that some of the samples show low cytotoxicity. This research will be helpful to broaden the application of chitosan in materials. [ABSTRACT FROM AUTHOR]