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Issue 43, 2017
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At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiation

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Abstract

Formation yields of ˙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 ˙OH radicals was determined as ∼0.08, i.e., roughly one out of twelve photons, efficiently absorbed in UV-illuminated solutions, produced one ˙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 ˙OH and H˙ 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 ˙OH radical causes a peroxidation of 34 phospholipid molecules. This implicates chain mechanism of the reaction.

Graphical abstract: At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiation

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Publication details

The article was received on 28 Jul 2017, accepted on 09 Oct 2017 and first published on 10 Oct 2017


Article type: Paper
DOI: 10.1039/C7CP05125E
Citation: Phys. Chem. Chem. Phys., 2017,19, 29402-29408
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    At the crossroad of photochemistry and radiation chemistry: formation of hydroxyl radicals in diluted aqueous solutions exposed to ultraviolet radiation

    K. Tomanová, M. Precek, V. Múčka, L. Vyšín, L. Juha and V. Čuba, Phys. Chem. Chem. Phys., 2017, 19, 29402
    DOI: 10.1039/C7CP05125E

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