linoleic-acid and titanium-dioxide

Nanosized titanium dioxide (TiO₂) is a common component of sunscreen preparations and cosmetics as it reflects UV and visible light in accordance to Rayleigh's law. However, in aqueous environments, TiO₂ is an efficient photocatalyst, producing superoxide O₂⁻· and hydroxyl (HO·) radicals, which are highly damaging to biomolecules. We investigated the role of TiO₂ in promoting the peroxidation of linoleic acid (LA) alone and in the presence of hypochlorous acid (HOCl). TiO₂ significantly enhanced peroxidation of LA, which was further enhanced in the presence of HOCl. This latter finding involved the formation of singlet molecular oxygen in a Russell-type mechanism appearing to involve preformed lipid hydroperoxides (LOOH). In addition to lipid peroxidation, HOCl also mediated formation of 18:1 monochlorohydrins, which in the presence of TiO₂ appeared to decompose to kinetic products which supplemented peroxidation of linoleic acid. We present a theoretical mechanism which fits the available experimental data and may partially explain the dichotomy associated with HOCls role in lipid modification.

Topics: Catalysis; Hypochlorous Acid; Linoleic Acid; Lipid Peroxidation; Nanoparticles; Titanium

A safe UV filter may be obtained by inhibiting the photo-generation of free radicals through modification of the surface of TiO(2) nanoparticles with carbon.

Topics: Carbon; Linoleic Acid; Metal Nanoparticles; Oxidation-Reduction; Reactive Oxygen Species; Sunscreening Agents; Surface Properties; Titanium; Ultraviolet Rays

TiO(2) nanoparticles hazard is associated to their photocatalytic activity causing release of DNA damaging ROS (Reactive Oxygen Species), lipid peroxidation and skin damage. Various coatings have been proposed to minimize photocatalysis, while keeping the potential to block UV radiations. Uncoated and variously coated commercial nano-titania have been classified on the basis of UVB-induced lipoperoxidation of linoleic acid. A selection of the most and the least protective specimens was then examined by ESR (Electron Spin Resonance) to evidence the presence of surface paramagnetic centres and the release of ROS in aqueous suspensions (spin trapping). Paramagnetic centres and ROS were correlated with the extent of lipid peroxidation. When tested on porcine skin (mimicking the human one), titania acted as on linoleic acid. The combined use of lipid peroxidation of simple fatty acids with ESR analysis is here proposed as a possible screening tool for the evaluation of the potential toxicity of nano-titania in sunscreen preparations.

Topics: Animals; Coated Materials, Biocompatible; DNA Damage; Electron Spin Resonance Spectroscopy; Linoleic Acid; Lipid Peroxidation; Nanoparticles; Oxidative Stress; Reactive Oxygen Species; Skin; Spin Trapping; Swine; Titanium