Chitosan (CS) is an abundant and renewable polysaccharide that is reported to exhibit a great variety of beneficial properties. However, the poor solubility of chitosan in water limits its applications. In this paper, we successfully synthesized single N-quaternized (QCS) and double N-diquaternized (DQCS) chitosan derivatives, and the resulting quaternized materials were water-soluble. The degree of quaternization (DQ) of QCS and DQCS was 0.8 and 1.3, respectively. These derivatives were characterized by FTIR, ¹H NMR, 13C NMR, TGA, and SEM. Moreover, the antioxidant activity of the chitosan was evaluated by free radical scavenging ability (against DPPH-radical, hydroxyl-radical, and superoxide-radical) and ferric reducing power. Our results suggested that the antioxidant abilities were in the order of DQCS > QCS > CS, which was consistent with the number of quaternized groups. These data demonstrate that the number of quaternized groups of chitosan derivatives contributes to their antioxidant activity. Therefore, DQCS, with a higher number of quaternized groups and higher positive charge density, is endowed with high antioxidant activity, and can be used as a candidate material in food and pharmaceutical industries.
Keywords: antioxidant ability; cationic chitosan derivatives; double quaternized chitosan; quaternized chitosan.