title: Mechanism for the enhanced peroxidation of linoleic acid by a titanium dioxide/hypochlorite system.
abstract: 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.
authors.affiliation: School of Applied Science, Belfast Metropolitan College, Belfast, UK. pmcpherson@belfastmet.ac.uk
authors.forename: Peter A C
authors.initials: PA
authors.lastname: McPherson
authors.forename: Peter M
authors.initials: PM
authors.lastname: Boyle
authors.forename: Bryn T
authors.initials: BT
authors.lastname: Türemen
mesh_terms: D002384:Catalysis; D006997:Hypochlorous Acid / Q000737:chemistry*; D019787:Linoleic Acid / Q000737:chemistry*; D015227:Lipid Peroxidation; D053758:Nanoparticles / Q000737:chemistry*; D014025:Titanium / Q000737:chemistry*
chemical_list: C009495:titanium dioxide; D006997:Hypochlorous Acid; D019787:Linoleic Acid; D014025:Titanium