Preparation, characterization, and antioxidant properties of gallic acid-grafted-chitosans

Gallic acid-grafted-chitosans (GA-g-chitosans) with four different grafting ratios were prepared by a free radical-induced grafting reaction in order to improve antioxidant and water-solubility. To verify the synthesis of GA-g-chitosans, 1H NMR and thin layer chromatography were employed, and the results revealed that GA was grafted onto the chitosan. The antioxidant properties of the GA-g-chitosans were evaluated using several in vitro models. GA-g-chitosan (I), which has the highest GA content, showed 92.26% scavenging activity against 2,2-diphenyl-1-picrylhydrazyl and 93.15% hydrogen peroxide scavenging activity at 50 μg/mL. GA-g-chitosan (I) was also showed higher reducing power compared to others. All GA-g-chitosans showed improved antioxidant capacities compared to plain chitosan treated in the same conditions without gallic acid grafting. Furthermore, the GA-g-chitosans also exhibited good cytocompatibility and effectively inhibited the formation of intracellular reactive oxygen species (ROS) in time- and dose-dependent manner in RAW264.7 macrophages.