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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.