Preparation, characterization and antioxidant activity of phenolic acids grafted carboxymethyl chitosan

In this study, three phenolic acids including gallic acid (GA), caffeic acid (CA) and ferulic acid (FA) were grafted onto N,O-carboxymethyl chitosan (NOCC) by a free radical mediated grafting method. The grafted copolymers obtained were all water-soluble samples. UV-vis absorption peaks of the grafted copolymers shifted toward longer wavelengths. FT-IR spectroscopy of the grafted copolymers exhibited additional phenolic characteristics of the aromatic ring CC stretching within 1450-1650 cm(-1). NMR spectroscopy of the grafted copolymers showed new peaks at 6.2-7.6 ppm assigned to the phenyl protons of phenolic acids. These results all confirmed the successful grafting of three phenolic acids to NOCC. The conjugation probably occurred at amine of NOCC and carboxyl groups of phenolic acids. The grafted copolymers exhibited decreased crystallinity as compared to NOCC and chitosan. Moreover, antioxidant activity in vitro assays showed that the antioxidant property decreased in the order of GA-g-NOCC>CA-g-NOCC>FA-g-NOCC>NOCC>chitosan. Our results suggested the potential of phenolic acids grafted NOCC for the development of effective antioxidant agents.