Protection by organic ions against DNA damage induced by low energy electrons

Abstract

It is well known that electrons below 15 eV induce strand breaks in DNA essentially via the formation of transient anions which decay by dissociative electron attachment (DEA) or into dissociative electronics states. The present article reports the results of a study on the influence of organic ions on this mechanism. tris and EDTA are incorporated at various concentrations within DNA films of different thicknesses. The amino group of tris molecules and the carboxylic acid function of ethylenediamine tetra-acetic acid (EDTA) molecules together can be taken as simple model for the amino acids components of proteins, such as histones, which are intimately associated with the DNA of eukaryotic cells. The yield of single strand breaks induced by 10 eV electrons is found to decrease dramatically as a function of the number of organic ions/nucleotide. As few as 2 organic ions/nucleotide are sufficient to decrease the yield of single strand breaks by 70%. This effect is partly explained by an increase in multiple inelastic electrons scattering with film thickness but changes in the resonance parameters can also contribute to DNA protection. This can occur if the electron captures cross section and the lifetime of the transient anions (i.e., core-excited resonances) formed at 10 eV are reduced by the presence of organic ions within the grooves of DNA. Moreover, it is proposed that the tris molecules may participate in the repair of DNA anions [such as G(-H) − ]induced by DEA on DNA bases.

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

“…The formation of an oxide layer on the metal surface creates a stable and chemically inert surface, ensuring no direct DNA-metal interaction, thus causing minimal DNA substrate induced damage in the presence of organic ions. 45,46 Lyophilization on other metal substrates can produce considerably more damage; for example, a gold surface induces up to 25% SSB to 5 ML unirradiated buffered DNA films in the vacuum. 31 In our experiments where DNA was lyophilized on tantalum and glass and immediately recovered without exposure to radiation, the induced damage was less than 1%.…”

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

“…TE buffer (Tris-EDTA: 10 mM/1 mM) was extracted from the plasmid with a home-made microcolumn of Sephadex G-50 resin on a bed of glass beads. Sephadex G-50 is highly efficient for the removal of the small molecules and thus purified DNA solution was considered containing a minimal amount of Tris-EDTA (Dumont et al, 2010). The DNA concentration was measured spectrophotometrically by measuring its absorbance at 260 nm, assuming a molar absorption coefficient of 5.3×10 7 L.mol −1 .cm −1 at pH 7.0 for DNA (Manchester, 1996).…”

Low energy electron stimulated desorption from DNA films dosed with oxygen

“…Thus, a series of experiments were recently undertaken to add to vacuum DNA other components found in the cell nucleus, so as to systematically investigate modifications of the mechanisms of action of LEEs by molecular constituents of the nucleus. Recently, it has been shown that organic ions 9 and proteins 10 protect DNA against LEE-induced damage and that the presence of water around DNA modifies the TNI manifold and corresponding decay channels. 11,12 O 2 is another molecule present with DNA in the cell nucleus and is known as an efficient radiosensitizer.…”