Early Events in Radiobiology: Isolated and Cluster DNA Damage Induced by Initial Cations and Nonionizing Secondary Electrons

Abstract

Radiobiological damage is principally triggered by an initial cation and a secondary electron (SE). We address the fundamental questions: What lesions are first produced in DNA by this cation or nonionizing SE? What are their relative contributions to isolated and potentially lethal cluster lesions? Five monolayer films of dry plasmid DNA deposited on graphite or tantalum substrates are bombarded by 0.1−100 eV electrons in a vacuum. From measurements of the current transmitted through the films, 3.5 and 4.5 cations per incident 60 and 100 eV electrons, respectively, are estimated to be produced and stabilized within DNA. Damage analysis at 6, 10, 20, 30, 60, and 100 eV indicates that essentially all lesions, but preferentially cluster damages, are produced by non-ionizing or weakly ionizing electrons of energies below 12 eV. Most of these lesions are induced within femtosecond times, via transient anions and electron transfer within DNA, with little contributions from the numerous cations.

Electron Attachment to 5-Fluorouracil: The Role of Hydrogen Fluoride in Dissociation Chemistry

“…Electrons with kinetic energies of up to 15 eV are known to play a role in DNA damage upon attachment. The ability of these free electrons to induce strand breaks and other types of damage in plasmid DNA was reported by Sanche and co-workers [ 9 , 10 , 11 , 12 , 13 ]. Low-energy electrons (LEEs) can induce selective fragmentation in molecules through the dissociative electron attachment mechanism, which begins with the initial formation of a transient negative ion (TNI) state and further decomposition of the TNI into a negatively charged fragment and neutral counterpart(s).…”

A Missing Puzzle in Dissociative Electron Attachment to Biomolecules: The Detection of Radicals

“…Undoubtedly, the complexity of the radiation-induced processes in the cellular environment, and the secondary electrons' contribution to the damage of living matter, including the process of DEA [21][22][23], remains the subject of vigorous debate among physicists and chemists. Beyond the physical and chemical changes induced by ionizing radiation, ionizing radiation has also two general types of adverse biological effects: deterministic and stochastic [24,25].…”

Shape Resonances in DNA: Nucleobase Release, Reduction, and Dideoxynucleoside Products Induced by 1.3 to 2.3 eV Electrons

“…Interestingly, the maximum yield of single- and double-strand breaks, as well as those of DNA repair enzyme-sensitive damage, are obtained at incident energies coinciding with the most probable energy (∼10 eV) for plasmids irradiated with LEEs in vacuum . Numerous theoretical and experimental studies have established the ability of LEEs to induce single- and double-strand breaks, principally via the decay of transient negative ions (TNIs) into either autoionization or dissociative electron attachment (DEA) channels. − …”