Nanoscopic aspects of radiobiological damage: Fragmentation induced by secondary low‐energy electrons

Abstract

Low-energy electrons (LEEs) are produced in large quantities in any type of material irradiated by high-energy particles. In biological media, these electrons can fragment molecules and lead to the formation of highly reactive radicals and ions. The results of recent experiments performed on biomolecular films bombarded with LEEs under ultra-high vacuum conditions are reviewed in the present article. The major type of experiments, which measure fragments produced in such films as a function of incident electron energy (0.1-45 eV), are briefly described. Examples of the results obtained from DNA films are summarized along with those obtained from the fragmentation of elementary components of the DNA molecule (i.e., thin solid films of H(2)O, DNA bases, sugar analogs, and oligonucleotides) and proteins. By comparing the results of these different experiments, it is possible to determine fundamental mechanisms that are involved in the dissociation of biomolecules and the production of single- and double-strand breaks in DNA, and to show that base damage is dependent on the nature of the bases and on their sequence context. Below 15 eV, electron resonances (i.e., the formation of transient anions) play a dominant role in the fragmentation of all biomolecules investigated. These transient anions fragment molecules by decaying into dissociative electronically excited states or by dissociating into a stable anion and a neutral radical. These fragments usually initiate other reactions with nearby molecules, causing further chemical damage. The damage caused by transient anions is dependent on the molecular environment.

Stable Valence Anions of Nucleic Acid Bases and DNA Strand Breaks Induced by Low Energy Electrons

“…The last decade has witnessed immense advances in our understanding of the effects of ionizing radiation on biological systems [1,2]. DNA as a genetic information carrier is the most important species, among cellular components, prone to damage by high energy photons.…”

Soft X-ray and Low Energy Electron-Induced Damage to DNA under N2 and O2 Atmospheres

“…13,14 Thus, in recent years much research interest has been focused on the fragmentation and modification of DNA by low energy electrons (LEEs). 15,16,17 In experiments, molecular solid films of DNA held under ultra high vacuum (UHV) were bombarded with LEEs. Below about 15 eV, LEEs were found to induce strand breaks in DNA essentially via the formation of transient anions located on specific DNA components.…”

“…15 However, it is now well established that the processes induced by electron impact on the bio-molecules are highly dependent on their environment. 16,18,19 To gain further knowledge of LEE-DNA interactions in biological systems, it is therefore important to perform LEE-DNA experiments under conditions closer to those in the cell.…”

Induction of strand breaks in DNA films by low energy electrons and soft X-ray under nitrous oxide atmosphere

“…Numerous studies on phenomena involving low energy electrons (LEEs) have shown that these particles play a central role in determining the effects of ionizing radiation. Thus, in recent years much research interest has been focused on the fragmentation and modification of DNA by LEEs (Sanche, 2002(Sanche, , 2005. The initial experiments on LEE-DNA were performed on DNA molecules under dry high vacuum conditions (Sanche, 2009;Boudaïffa et al, 2000;Cai et al, 2005).…”

“…The initial experiments on LEE-DNA were performed on DNA molecules under dry high vacuum conditions (Sanche, 2009;Boudaïffa et al, 2000;Cai et al, 2005). However, the damaging effects of LEEs on the DNA molecule are known to be dependent on its environment (Sanche, 2002;Lehnert, 2008;Ptasińska and Sanche, 2007;Barilla and Lokajíček, 2000). Thus, to better understand the damaging effects of LEE on DNA, attempts have been made to perform LEE-irradiation experiments under conditions more closely approximating those found in the cell.…”