THE ELECTRON SCAVENGING ABILITY OF THE DNA BASES IN GLASSY MATRICES X-IRRADIATED AT 4 K

Dose-response curves for the four DNA nucleotides have been measured in a neutral 8 M LiCl glass and in an acidic 5 M NaH2PO4 glass at 4 K over a range of nucleotide concentrations. The initial yield of one-electron-reduced nucleotides per unit dose absorbed in the glass, the G values, are found to increase linearly as the concentration of the nucleotide is increased from 0 to similar to 5 mM. Above this, a saturation effect is observed. The G value per unit nucleotide concentration in the linear region corresponds to the scavenging ability of that nucleotide for radiation-released e(-) in the X irradiated glass. In the LiCl glass, the scavenging abilities are found to be, from the best to the worst, T similar to C similar to A > G. In the phosphate glass they are C similar to G > T > A. EPR spectra of the reduced DNA bases support the hypothesis that a rapid protonation reaction upon reduction of guanine and adenine strongly influence their relative e(-) scavenging abilities.