The effective selenylated polysaccharides (refer as TPS-Se) with an average molecular weight (M W ) of 3.109 × 104 Da was synthesized by the reduction of sodium selenite with ascorbic acid in the presence of Qingzhuan Dark Tea polysaccharides (TPS). The selenium (Se) content of TPS-Se was up to 37.05%. The differences between TPS and TPS-Se were compared in morphology, structure, antioxidant activity, and molecular weight using FT-IR, Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), SEM, AFM, and Integrated thermal gravimetric analysis. The results indicated that Se 4+ was reduced to Se 0 by ascorbic acid. Further, the Se 0 atoms aggregate into Se nuclei and bind to the C=O from TPS. Also, TPS-Se exhibited higher DPPH and ABTS radical-scavenging abilities than TPS. This difference may be attributed to the fact that Se has good antioxidant activity. The test results demonstrated that TPS-Se was prepared successfully by reducing sodium selenite with ascorbic acid, which exhibited a higher radical-scavenging ability. Finally, LD 50 value of 136.89 mg/kg, with a 95% confidence interval of 102.82~182.82 mg/kg, was determined by gavage administration for TPS-Se's.
Tea polysaccharides was one of the active ingredients of Qingzhuan dark tea, which had antioxidant, anti-tumor, and immuneenhancing effects. The complexation of metal ions of tea polysaccharides was one of the current research hotspots. It can combine the advantages of tea polysaccharides and their complexed trace metal elements, and had great potential development. In this study, the trace element-copper required by the human body was used for complexation with Qingzhuan dark tea polysaccharides, and the structure was characterized by various chemical methods. The copper complexes of Qingzhuan dark tea polysaccharides were characterized by UV spectroscopy, FT-IR, thermogravimetric analysis, X-ray diffraction (XRD), SEM, AFM and X-ray photoelectron spectroscopy (XPS). The tests results show that it was successfully complexed with tea polysaccharides. Meanwhile, the Qingzhuan dark tea polysaccharides copper complex compound (termed TPS-Cu) showed higher scavenging activity of hydroxyl radical and ABTS free radical than the tea polysaccharides (termed TPS). Therefore, TPS-Cu can be used as a potentially effective and stable copper supplement and preventive agent.
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