Photolysis of Water by VUV Radiation and Reactions with DNA and Related Compounds in Aqueous Systems

Abstract

The induction of OH and H radicals in vuv-exposed aqueous solutions at wavelengths from 150 nm to 200 nm was investigated by a spin trapping method using DMPO. The generation of OH and H radicals as a result of the absorption of vuv-light by H20 was confirmed by measuring OH-DMPO and H-DMPO adducts with esr spectrometry. Free radicals produced in aqueous uridine solution by vuv radiation at 163 nm were studied by a method combining esr-spin trapping and gel permeation chromatography as a model experiment to elucidate the chemical pathways accounting for damage formation in vuv­ exposed DNA. Two base radicals were identified as precursors of the oxidative conversions of the base. Two sugar radicals were also identified as precursors to account for the strand break formation. The induction of single-strand breaks by vuv radiation (140-200 nm) in plasmid pBR 322 DNA was studied by agarose gel electrophoresis. A good parallelism in the action spectra between the induction of the single-strand breaks and the generation of OH radicals below 170 nm was found, suggesting that photo lysis of water was mainly responsible for the induction of the strand breaks.