Synthesis of Hydroxypropyltrimethyl Ammonium Chitosan Derivatives Bearing Thioctate and the Potential for Antioxidant Application

Hydroxypropyltrimethyl ammonium chloride chitosan (HACC) is one of the most important water-soluble chitosan derivatives; its derivatives have gained growing attention due to their potential biomedical applications. Here, hydroxypropyltrimethyl ammonium chitosan derivatives bearing thioctate (HACTs), with different degrees of substitution of thioctate, were prepared using HACC and α-lipoic acid as the reaction precursors, using an ion exchange method. The structural characteristics of the synthesized derivatives were confirmed by FTIR, (1)H NMR, and (13)C NMR spectroscopy. In addition, their antioxidant behaviors were also investigated in vitro by the assays of reducing power, and scavenging activities against hydroxyl radicals and DPPH radicals. The antioxidant assay indicated that HACTs displayed strong antioxidant activity compared with HACC, especially in terms of reducing power. Besides, the antioxidant activities of the prepared products were further enhanced with the increase in the test concentration and the degrees of substitution of thioctate. At the maximum test concentration of 1.60 mg/mL, the absorbance value at 700 nm of HACTs, under the test conditions, was 4.346 ± 0.296, while the absorbance value of HACC was 0.041 ± 0.007. The aforementioned results support the use of HACTs as antioxidant biomaterials in food and the biomedical field.