At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiationElectronic supplementary information (ESI) available. See DOI: 10.1039/c7cp05125e

• Main Authors: Tomanová, Kate ina, Precek, Martin, Mú ka, Viliam, Vyšín, Lud k, Juha, Libor, uba, Václav
• Format: Journal Article
• Published: 08.11.2017
• DOI: 10.1039/c7cp05125e
• ISSN: 1463-9076

Formation yields of &z.rad;OH radicals were precisely determined in aqueous solutions of coumarin-3-carboxylic acid and ferrous sulfate ( i.e. , Fricke dosimeter) exposed to 253.7 nm radiation delivered from a continuous source. Quantum yield of &z.rad;OH radicals was determined as ∼0.08, i.e. , roughly one out of twelve photons, efficiently absorbed in UV-illuminated solutions, produced one &z.rad;OH radical. Energetically, a water molecule should undergo a correlated action of at least two 4.9 eV photons delivering enough energy for direct H-OH dissociation (5.0-5.4 eV). We suggest a mechanism based on an interaction of two water molecules, both in long-living triplet states. An intermolecular transfer of excitation energy provided a sufficient amount of energy for the dissociation of one water molecule into &z.rad;OH and H&z.rad; radicals. In an aqueous solution of phospholipids, quantum yields of hydroperoxides formed under these irradiation conditions decreased with total effectively absorbed energy ( i.e. a dose), similar to the radiation chemical yields obtained during an exposure to ionizing radiation, such as gamma rays from radionuclide sources. Under 253.7 nm irradiation, one &z.rad;OH radical causes a peroxidation of 34 phospholipid molecules. This implicates chain mechanism of the reaction. We provide evidence on the formation of &z.rad;OH radicals via 253.7 nm photolysis of aqueous solutions, determine their quantum yields, and apply the knowledge to photo-induced formation of phospholipid hydroperoxides.