Influence of Electron Scavengers on the Radical Formation in Thymidine-5′-monophosphate and DNA in Frozen Aqueous Solution and Glasses

Abstract

Structural and quantitative effects of different electron scavenger concentrations on the free radical formation in the nucleotide thymidine-5′-monophosphate (TMP) and in deoxyribonucleic acid (DNA) after X-irradiation in frozen aqueous solution and glasses (BeF₂/H₂O for TMP and LiCl/H₂O for DNA) at 77 K are investigated. At the highest concentration used (100 mmol dm⁻³) about 80% (TMP) and 70% (DNA) of the radicals are scavenged compared with the control in both matrices. In TMP, allyl radicals form the major population of radicals left unscavenged at 77 K. These are shown to transform into a quintet pattern upon annealing (⩾ 220 K). Analysis of various substrates for quintet formation shows that a sugar-group and a C₄-carbonyl group are necessary structural prerequisites. For DNA three components can be extracted from spectra obtained with different scavenger concentration in frozen solutions. There are two components in LiCl glasses, which are comparable with two of the three in frozen aqueous solution. Their potential origin is discussed in comparison with nucleotide spectra.