Main content area

Antioxidant and Antiradical SiO2 Nanoparticles Covalently Functionalized with Gallic Acid

Deligiannakis, Yiannis, Sotiriou, Georgios A., Pratsinis, Sotiris E.
ACS applied materials 2012 v.4 no.12 pp. 6609-6617
2,2-diphenyl-1-picrylhydrazyl, antioxidants, electron paramagnetic resonance spectroscopy, free radicals, gallic acid, medicine, nanoparticles, nutrients, polymers, silica, surface area, ultraviolet-visible spectroscopy, washing
Gallic acid (GA) and its derivatives are natural polyphenolic substances widely used as antioxidants in nutrients, medicine and polymers. Here, nanoantioxidant materials are engineered by covalently grafting GA on SiO₂ nanoparticles (NPs). A proof-of-concept is provided herein, using four types of well-characterized SiO₂ NPs of specific surface area (SSA) 96–352 m²/g. All such hybrid SiO₂-GA NPs had the same surface density of GA molecules (∼1 GA per nm²). The radical-scavenging capacity (RSC) of the SiO₂-GA NPs was quantified in comparison with pure GA based on the 2,2-diphenyl-1-picrylhydrazyl (DPPH•) radical method, using electron paramagnetic resonance (EPR) and UV–vis spectroscopy. The scavenging of DPPH radicals by these nanoantioxidant SiO₂-GA NPs showed mixed-phase kinetics: An initial fast-phase (t₁/₂ <1 min) corresponding to a H-Atom Transfer (HAT) mechanism, followed by a slow-phase attributed to secondary radical–radical reactions. The slow-reactions resulted in radical-induced NP agglomeration, that was more prominent for high-SSA NPs. After their interaction with DPPH radicals, the nanoantioxidant particles can be reused by simple washing with no impairment of their RSC.