INFLUENCE OF ELECTRON SCAVENGERS ON THE RADICAL FORMATION IN THYMIDINE-5'-MONOPHOSPHATE AND DNA IN FROZEN AQUEOUS-SOLUTION AND GLASSES

Structural and quantitative effects of different electron scavenger co ncentrations on the free radical formation in the nucleotide thymidine -5'-monophosphate (TMP) and in deoxyribonucleic acid (DNA) after X-irr adiation in frozen aqueous solution and glasses (BeF2/H2O for TMP and LiCl/H2O for DNA) at 77 K are investigated. At the highest concentrati on used (100 mmol dm(-3)) about 80% (TMP) and 70% (DNA) of the radical s are scavenged compared with the control in both matrices. In TMP, al lyl radicals form the major population of radicals left unscavenged at 77 K. These are shown to transform into a quintet pattern upon anneal ing (greater than or equal to 220 K). Analysis of Various substrates f or quintet formation shows that a sugar-group and a C-4-carbonyl group are necessary structural prerequisites. For DNA three components can be extracted from spectra obtained with different scavenger concentrat ion in frozen solutions. There are two components in LiCl glasses, whi ch are comparable with two of the three in frozen aqueous solution. Th eir potential origin is discussed in comparison with nucleotide spectr a.