*3.1. Materials*

Chondroitin sulfate (CS) derived from shark cartilage (95% purity, Mw = 499.37, C107703) was purchased from Aladdin. CS is composed of chondroitin 6-sulfate and chondroitin 4-sulfate, and the proportion of chondroitin 6-sulfate and chondroitin 4-sulfate detected by high performance liquid chromatography is equal to or greater than 0.33:1. Na2SeO3, ascorbic acid (Vc), DPPH and ABTS were supplied by Shanghai Yuanye Biotechnology Co., Ltd. (Shanghai, China). The other chemicals and reagents were of analytical purity grade.
