Single-Strand Breaks in Double-Stranded DNA Irradiated in Anoxic Solution: Contribution of tert-Butanol Radicals

Yields of single-strand breaks induced by⁶⁰ Co ? or pulse irradiation in double-stranded calf thymus DNA have been measured in${\rm N}_{2}{\rm O}\text{-saturated}$ aqueous solution as a function of the concentration of tert-butanol. The yields were found to be dependent on dose rate. The experimental data were analyzed using a theoretical model based on non-homogeneous scavenging kinetics. It is concluded from this analysis that after⁶⁰ Co ? irradiation in the absence of oxygen, aside from breaks caused by hydroxyl radicals, additional breaks occur which are initiated by hydrogen atoms and secondary radicals of tert-butanol. The efficiency of hydrogen atoms in causing single-strand breaks in double-stranded calf thymus DNA was determined to be 2.3%, while the rate constant for the reaction of tert-butanol radicals with DNA and their efficiency in causing single-strand breaks was determined to be$4.1\times 10^{3}\ {\rm dm}^{3}\ {\rm mol}^{-1}\ {\rm s}^{-1}$ and 2%, respectively.