Nanoantioxidant Materials: Nanoengineering Inspired by Nature.

Oxidants are very active compounds that can cause damage to biological systems under specific environmental conditions. One effective way to counterbalance these adverse effects is the use of anti-oxidants. At low concentrations, an antioxidant is defined as a compound that can delay, control, or prevent an oxidative process. Antioxidants exist in plants, soil, and minerals; therefore, nature is a rich source of natural antioxidants, such as tocopherols and polyphenols. In nature, antioxidants perform in tandem with their bio-environment, which may tune their activity and protect them from degradation. In vitro use of antioxidants, i.e., out of their biomatrix, may encounter several drawbacks, such as auto-oxidation and polymerization. Artificial nanoantioxidants can be developed via surface modification of a nanoparticle with an antioxidant that can be either natural or synthetic, directly mimicking a natural antioxidant system. In this direction, state-of-the-art nanotechnology has been extensively incorporated to overcome inherent drawbacks encountered in vitro use of antioxidants, i.e., out of their biomatrix, and facilitate the production and use of antioxidants on a larger scale. Biomimetic nanoengineering has been adopted to optimize bio-medical antioxidant systems to improve stability, control release, enhance targeted administration, and overcome toxicity and biocompatibility issues. Focusing on biotechnological sciences, this review highlights the importance of nanoengineering in developing effective antioxidant structures and comparing the effectiveness of different nanoengineering methods. Additionally, this study gathers and clarifies the different antioxidant mechanisms reported in the literature and provides a clear picture of the existing evaluation methods, which can provide vital insights into bio-medical applications.

Antioxidant Hydrogen-Atom-Transfer to DPPH Radicals by Hybrids of {Hyaluronic-Acid Components}@SiO2.

Hydrogen-atom-transfer (HAT) is among the key mechanisms of antioxidant and antiradical activity in natural systems. Hyaluronic acid (HyA) is currently used extensively in health and cosmetics applications. Herein it is shown that {HyA@SiO2} hybrids based on hyaluronic acid (HyA) components grafted on SiO2 nanoparticles enable significant HAT activity versus DPPH radicals, while the homogeneous HyA counterparts are practically inactive. The {HyA@SiO2} hybrids consist of the two building blocks of HyA [d-glucuronic acid (GLA) and N-acetyl-d-glucosamine (GLAM)] covalently grafted on SiO2 nanoparticles. Based on the kinetic-thermodynamic Arrhenius study, we show that the {SiO2@GLA} hybrids operate spontaneously via hydrogen-atom-transfer (HAT) with a low activation energy barrier, i.e., by ΔΕα ∼ 20 kJ/mol vs the nongrafted counterparts. Moreover, a doubly grafted {GLA@SiO2@GLAM} nanohybrid, i.e. that contains both components of HyA, shows the most significant antioxidant activity. FTIR and Raman analysis reveal that local H-bonding between the SiO2 matrix, GLA, and GLAM in {GLA@SiO2@GLAM} decreases the activation barrier of the HAT mechanism. Thus, {GLA@SiO2@GLAM} nanohybrids exemplify a novel family of materials that are not the mere sum of their components. The present case is the first example of non-phenolic molecules being able to perform antiradical HAT, opening new perspectives not foreseen until today.