Free radical mediated grafting of chitosan with caffeic and ferulic acids: Structures and antioxidant activity

• Caffeic and ferulic acids were grafted onto chitosan by a free radical mediated method.
• Copolymers had good free radical scavenging and peroxidation inhibition effects.
• Copolymers significantly increased antioxidant enzymes activities and decreased malondialdehyde levels in d-galactose induced aging mice.

In this study, two water soluble chitosan derivatives were synthesized by grafting caffeic acid (CA) and ferulic acid (FA) onto chitosan via a free radical mediated method. The structural characterization, antioxidant activity in vitro and in vivo of chitosan derivatives were determined. Results showed that the UV–vis absorption peaks of chitosan derivatives shifted toward longer wavelengths. FT-IR spectroscopy exhibited the typical phenolic characteristics within 1450–1600 cm−1. 1H NMR spectroscopy showed new peaks of phenyl protons at 6.2–7.6 ppm. 13C NMR spectroscopy showed additional peaks between 110 and 150 ppm assigned to the CC of phenolic groups. These results all confirmed the successful grafting of CA and FA onto chitosan backbones. The chitosan derivatives had decreased thermal stability and crystallinity as compared to chitosan. In vitro assays showed that the antioxidant activity decreased in the order of CA-g-chitosan > FA-g-chitosan > chitosan. Moreover, administration of the chitosan derivatives could significantly increase antioxidant enzymes activities and decrease malondialdehyde levels in both serums and livers of d-galactose induced aging mice. Our results indicated the potential of CA-g-chitosan and FA-g-chitosan in the development of novel antioxidant agents.