Synthesis Of Nano-Antioxidants And Study Of Its Antioxidant Ability

Oxygen is reduced by single electron to certain active substances named reactive oxygen species.Normally,the production and clearance of oxygen free radicals keep dynamically balanced.Once the oxygen free radicals were over produced or anti-oxidation system failure,the oxygen free radicals' metabolism will be imbalanced,or called oxidative stress,which could cause cell damage and lead to many chronic diseases,such as heart disease and cancer.To deal with these damage people have being studied antioxidant for a long time.Traditional strategy for design potent new antioxidant is to optimize the functional structure of existing antioxidants.Nano-sized matter possesses new and special physical chemical and biological properties,leading to important applications in many areas ranging from chemistry,material science,medical science and biology.Because of the special property of nano-sized matter,especially its outstanding catalysis,we developed a novel method to improve antioxidant activity based on the self-assembly of antioxidant group on the gold nanoparticles.Unlike traditional strategy,our new method avoided unpexpected pro-oxidizability or toxicity led by change of antioxidant group's structure.For realization this method,we prepared a novel antioxidant functionalized gold nanoparticles(ANPs)--Au@Trolox,a 4.5 nm gold nanoparticle covered with a Trolox(a Vitamin E analogue)-derivate monolayer. The results of DPPH^* radical scavenging assay indicated that encapping Trolox group on the ANPs significantly enhanced the DPPH^* scavenging efficiency (antioxidant activity)of Trolox alone.The stopped-flow ESR experiments revealed that the rate constant of the reaction of Au@Trolox with DPPH^* was about 8 times greater than that of Trolox,which proves the effectiveness of our novel design method.Two mechanisms had been given for explaining our observations:preconcentrating the reactants and the aromatic stacking of the adjacent chromanol group.In recent years,NMR was widely used on analysis of nano-particles.To study reaction mechanism of nano-antioxidant and DPPH^*,we planed to analyses their products mainly by NMR,FT-IR and UV-Vis.As Au@Trolox has large core diameter and short ligands,which were don't fit NMR analyses, we designed another nano-antioxidant Au@C₁₁H₂₂Trolox with 1.5 nm core diameter.Products of Au@C₁₁H₂₂Trolox,Trolox and Trolox propyl ester-a similar compound with the antioxidative ligands on gold nanoparticlse-reacted with DPPH^* in DMSO were analyzed.The mechanisms of either Au@C₁₁H₂₂Trolox or Trolox react with DPPH^* were compared and found to be partially different.In addition Au@C₁₁H₂₂Trolox showed significantly increase of DPPH^* scavenging efficiency than that of Trolox.This is might due to inadequate protection of nuclear caused by small diameter and long ligands, where DPPH^* had chance to reach gold core which could quenching free radicals.