Antioxidant Activity of Metal Nanoparticles Coated with Tocopherol-Like Residues-The Importance of Studies in Homo- and Heterogeneous Systems.

Adrian Konopko,Jaroslaw Kusio,Grzegorz Litwinienko

doi:10.3390/antiox9010005

Abstract

Functionalized nanoparticles (NPs) attract great attention in pharmacy, diagnostics, and biomedical areas due to benefits like localization and unique interactions of NPs with biocomponents of living cells. In the present paper, we prepared and characterized two kinds of gold nanoparticles (AuNPs) coated with α-tocopherol-like residues: 1A were soluble in non-polar solvents and their antioxidant activity was tested during the peroxidation of a model hydrocarbon in a homogeneous system, whereas nanoparticles 1B were soluble in polar solvents and were applied as antioxidants in micellar and liposomal systems. The effectiveness of 1A is comparable to 2,2,5,7,8-pentamethylchroman-6-ol (PMHC, an analogue of α-tocopherol). Taking the results of the kinetic measurements, we calculated an average number of 2150 chromanol residues per one NP, suggesting a thick organic coating around the metal core. In heterogeneous systems, the peroxidation of methyl linoleate dispersed in Triton X-100 micelles or DMPC liposomes resulted in the observation that 1B (545 chromanol residues per one NP) was active enough to effectively inhibit peroxidation in a micellar system, but in a liposomal system, 1B behaved as a retardant (no clear induction period). The importance of microenvironment in heterogeneous systems on the overall antioxidant activity of nanoparticles is discussed.

Highlights

Unique physical and chemical properties of metal and metal oxide nanoparticles (NPs) make them desirable products that find industrial applications as catalysts, co-catalysts, and as intermediates used for the manufacturing of advanced materials
Using multi-step synthesis, two kinds of gold nanoparticles coated with chromanol residues were prepared and characterized
Nanoparticles 1A (23% Au, average diameter of metal core 4.41 ± 0.65 nm) were coated with co-adsorbed tetraoctylammonium bromide (TOAB) to make them soluble in non-polar solvents, whereas nanoparticles 1B (64% Au, average diameter of metal core 3.15 ± 0.40 nm), coated with pure chromanol residues attached to the metal core, were soluble in methanol and ethanol but unstable in water or in non-polar non-H-bonding solvents

Summary

Introduction

Unique physical and chemical properties of metal and metal oxide nanoparticles (NPs) make them desirable products that find industrial applications as catalysts, co-catalysts, and as intermediates used for the manufacturing of advanced materials. As the majority of nanoparticles are redox active species, special attention is paid to their interaction with organic materials and there is an increasing interest in studies of their (cyto)toxicity [2,3]. One of the most accepted mechanisms of NPs cytotoxicity is their possibility to generate reactive oxygen species which can induce oxidative stress [4,5,6,7,8]. There are several mechanisms underlying the pro-oxidative activity of nanoparticles. A presence of pro-oxidative groups or metal ions make the NPs able to react with molecular oxygen and to generate reactive oxygen species. Other classes of mechanisms include interactions with particular parts of the cells where the core of NP-containing

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