Secondary Electron Attachment-Induced Radiation Damage to Genetic Materials

Abstract

Reactions of radiation-produced secondary electrons (SEs) with biomacromolecules (e.g., DNA) are considered one of the primary causes of radiation-induced cell death. In this Review, we summarize the latest developments in the modeling of SE attachmentinduced radiation damage. The initial attachment of electrons to genetic materials has traditionally been attributed to the temporary bound or resonance states. Recent studies have, however, indicated an alternative possibility with two steps. First, the dipole-bound states act as a doorway for electron capture. Subsequently, the electron gets transferred to the valence-bound state, in which the electron is localized on the nucleobase. The transfer from the dipole-bound to valencebound state happens through a mixing of electronic and nuclear degrees of freedom. In the presence of aqueous media, the water-bound states act as the doorway state, which is similar to that of the presolvated electron. Electron transfer from the initial doorway state to the nucleobase-bound state in the presence of bulk aqueous media happens on an ultrafast time scale, and it can account for the decrease in DNA strand breaks in aqueous environments. Analyses of the theoretically obtained results along with experimental data have also been discussed.

Electron-Binding Dynamics of the Dipole-Bound State: Correlation Effect on the Autodetachment Dynamics

“…Although the modification of the electrostatic potential that takes into account the induced-dipole by the intramolecular electric field could partially explain the qualitative trend of the experiment, the effect of the quantum-mechanical correlation interaction on the autodetachment dynamics has not yet been fully considered yet. It should be emphasized that the electron-binding nature of DBS is also closely associated with the nonadiabatic transition where the electron in the diffuse nonvalence-orbital is transferred into the valence orbital of the anion, which could lead to the eventual anionic fragmentation reactions. − As the DBS plays an important doorway role in such nonadiabatic transitions between the nonvalence- and valence-orbitals of the anion, − fundamentally understanding the relation between the nuclear motion and the electron movement (autodetachment and/or electron-transfer) of the DBS is essential for elucidating and/or controlling the whole anionic reaction dynamics.…”

DNA Protection against Damages Induced by Low-Energy Electrons: Absolute Cross Sections for Arginine–DNA Complexes

“…Other methods have addressed the direct and quasi-direct effects of HER and secondary electrons (SEs) on DNA or its constituents. ,,− Among these, thin film technology combined with monoenergetic electron beam techniques has allowed adoption of a “bottom up” approach in which one can study DNA damage from electron energies as low as 0.5 eV up to several keVs. − As the electron energy is increased, different phenomena gradually step in, and it becomes possible to experimentally distinguish their effects on DNA damage. For example, it has recently been possible to isolate completely from HER-induced chemistry in dry DNA the role of shape resonances [i.e., single-particle transient anions (TAs)] .…”

“…The interaction of 5 and 10 eV electrons with DNA principally results in the formation of core-excited TAs. , These TAs are formed by temporary LEE capture into the potential well of an electronically excited state of a base. ,− They can decay by dissociative electron attachment (DEA), thereby leading to BD, or the additional electron transfers to another base or the phosphate group where a lesion can be produced via DEA. When the initial base is left in a neutral dissociative excited state, a double lesion can be formed. , The possible combinations of BDs and transfer sites lead to the damages listed in Table .…”

“…When the initial base is left in a neutral dissociative excited state, a double lesion can be formed. , The possible combinations of BDs and transfer sites lead to the damages listed in Table . The magnitude of these damages relies essentially on the electron attachment probability to the bases, electron transfer rate to PO 4 – , and lifetime of TAs formed on the base and phosphate subunits. ,− In both complexes, these parameters should be affected by “scavenging” and the different counterion at the O – terminal of the phosphate . Proton transfer should also influence these parameters. − However, with such interconnected parameters, it is difficult to quantitate the change in their magnitude arising from the different bonds in Figure that produce the observed PFs.…”

Dissociative Electron Attachment to 5-Iodo-4-thio-2′-deoxyuridine: A Potential Radiosensitizer of Hypoxic Cells

“…It was shown that low-energy electrons may induce strand breaks and/or other damage in the biomolecular films of DNA and DNA origami triangles . Solution phase experiments also demonstrated that electrons, while still being quasi-free, may induce bond cleavage in DNA constituents. , In contrast, electrons entering the prehydrated or hydrated stage do not seem to be effective in DEA to DNA nucleobases in solution …”