Hyperthermal Reactions in DNA Triggered by 1-20 eV Electrons: Absolute Cross Sections for Crosslinks, Strand Breaks, Clustered Damages and Base Modifications.

Absolute cross sections (ACSs) are needed to estimate cellular damage induced by high-energy radiation (HER). Low-energy electrons (LEEs), which are the most numerous secondary particles generated by HER, can trigger hyperthermal reactions in DNA. ACSs for such reactions are essential input parameters to calculate radiobiological effectiveness, particularly in targeted radiotherapy. Using a mathematical model, we generate ACSs from effective damage yields induced by LEE impact on 3197 base-pair plasmid DNA films. Direct or enzyme-revealed conformational damages, quantified by electrophoresis, provide the first complete set of ACSs for inducing crosslinks, double-strand breaks (DSBs), single-strand breaks, base-damage-related crosslinks, non-DSB clustered damages (NDCDs), and isolated base damages. These ACSs are generated across the 1-20 eV range, at one eV intervals. They exhibit a strong energy dependence with maximum values at 10 eV of 3.7 ± 0.8, 3.5 ± 0.6, 45.4 ± 4.1, 2.9 ± 1.1, 5.1 ± 1.4, and 54.0 ± 16.4 × 10 cm, respectively. ACSs for DSBs, NDCDs, and crosslinks clearly indicate that lesions threatening cell function and genetic stability can be generated by a single LEE. At 5 and 10 eV, total damage ACSs are 63% and 80% larger, respectively, than those previously determined for the same plasmids bound to arginine, a constituent of histones protecting DNA.