Antioxidant and Antiradical SiO₂ Nanoparticles Covalently Functionalized with Gallic Acid

Abstract

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 SiO(2) nanoparticles (NPs). A proof-of-concept is provided herein, using four types of well-characterized SiO(2) NPs of specific surface area (SSA) 96-352 m(2)/g. All such hybrid SiO(2)-GA NPs had the same surface density of GA molecules (~1 GA per nm(2)). The radical-scavenging capacity (RSC) of the SiO(2)-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 SiO(2)-GA NPs showed mixed-phase kinetics: An initial fast-phase (t(1/2) <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.

Direct chemical grafted curcumin on halloysite nanotubes as dual-responsive prodrug for pharmacological applications

“…In the case of HNT-Cur, the n value is about 2 for both ROO • and oDPPH • radicals suggesting a more complex mechanism. A stoichiometry decrease of the radical trapping was previously observed for phenols linked to nanoparticles [62,68] in agreement with the self-decay of the radical of the antioxidant (A • in Eq. (6)), which is not involved in the trapping of a second radical because of the formation of A-A dimers [67].…”

A synergic nanoantioxidant based on covalently modified halloysite–trolox nanotubes with intra-lumen loaded quercetin

“…For instance, a covalent link between gallic acid (a food-grade antioxidant) and SiO 2 nanoparticles (SiO 2 NPs) was proposed for reducing its leaching and volatility, and this material showed radical trapping activity toward the 1,1-diphenyl-2-picrylhydrazyl (DPPH ) radical. 6 Some of us recently demonstrated that carbon-coated cobalt nanomagnets decorated by a-tocopherol units are able to effectively counteract the autoxidation of organic substrates, and can be efficiently controlled by an external magnet. 7 Nanomaterials can also serve as carriers for controlled release of antioxidants.…”

“…Despite the large variety of currently known antioxidants, 2 several challenges still exist in specific applications such as in food technology, 21 pharmaceutical and cosmetics technology, or for biomedical applications, namely: (a) the potential toxicity of several antioxidants; 22 (b) antioxidant leaching or migration to unwanted compartments, 23 which is a major challenge in food preservation 24 and food packaging; 6 With the aim of further improving the usefulness and versatility of HNT-based antioxidants, we have devised the synthesis of novel HNT nanomaterials, in which different phenolic antioxidants are, for the first time, both loaded in the inner lumen and grafted on the outer surface. Indeed, the combining of different antioxidant functions on the same nanostructured material would sum up the advantages outlined in points (a)-(d) and offer distinctive additional advantages, i.e.…”

“…Trolox, a mimic of a-tocopherol bearing a carboxylic group (see Scheme 1), was chosen as the surface exposed antioxidant because of its known high reactivity with radicals. 6 The natural polyphenol quercetin was instead loaded in the inner lumen, because of its renown importance as a radical trapping agent 34 and as a bioactive compound to counteract oxidative stress in many pathologies. 35 The synergism between the two functionalities and the performance of this novel material have been investigated using both the reaction with DPPH radicals (see Scheme 2) and inhibited autoxidation studies of two model organic substrates in solvents of different polarities.…”

One Can Slow Down the Aging through Antioxidants

“…The research team of Yiannis Deligiannakis, a visiting professor at the Institute of Process Engineering at the Swiss Federal Institute of Technology in Zurich (ETHZ), has developed a nanoantioxidant with enhanced stability (Deligiannakis et al, 2012). This discovery is published in the journal ACS Applied Materials and Interfaces.…”