Kinetics Of Trolox Nano-Antixoidants And Autoxidantion Of Danshensu

For decades, considerable effort has been devoted to make more potent antioxidants than the natural antioxidantα-tocopherol (α-TOH, Trolox). Several methods have been proven to improve the antioxidant activity, most of which taken the way of modifing the structure of the phenolic hydroxyl moiety or the chromanol ring. As our report previously, a combination of nano-material engineering with antioxidants was established. The Trolox-functionalized gold nanoparticles (Au@Trolox) showed eight times greater reactivity toward peroxyl radicals. This strategy represents a novel and versatile way to make better antioxidants.We have a continuing research in the Trolox-functionalized gold nanoparticles. In the synthesis of functionalized gold nanoparticles, polyethylene glycol (PEG) was used in substitution for the thiol ligand. The product Au@PEG-Trolox represents markedly water-solubility, the transmission electron microscopy (TEM) image shows that the size of the nanopricles is 4.5nm. The radical scavenging ability and kinetic properties of Au@PEG-Trolox have been compared to those of Trolox according the DPPH-scavenging efficiency (antioxidant activity). The apparent activation energy (Ea) of Au@PEG-Trolox is 10.9 kJ·mol-1, while much lower than the 23.20 kJ·mol-1 of Trolox. The mechanism for this phenomenon is attributed to the preconcentration of the reactants and the aromatic stacking of the phenol rings in adjacent Trolox. Cell culture experiments were taken to determine the toxicology of Au@PEG-Trolox.As the developing research in polyphenol antioxidant, some of them exhibit autoxidantion and prooxidantion by metal cation significantly, such as Tea polyphenol. Danshensu has the similar polyphenol structure with Tea polyphenol, and the autoxidantion of Danshensu was concerned here. A hydrogen peroxide (H2O2) sensor and electron spin resonance (ESR) were used to continuously monitor and analyze the autoxidation and prooxidation of Danshensu in aqueous solutions of various pH. We found that Danshensu exhibited obvious autoxidative activity in alkalescence buffer solutions (pH=8.5) and the presence of Cu2+ evidently accelerated the generation of H2O2. The primary product of the autoxidation was a superoxide anion radical (O2·-) and then it could be converted into H2O2. Consequently, the autoxidation and prooxidation of Danshensu cannot be completely ignored when used in clinical practice especially under alkaline body fluid conditions. This nano-antioxidant shows well biocompatibility and little cytotoxicity thus paving the way for nano-antioxidant used in biomedicine.