Influence of organic ions on DNA damage induced by 1 eV to 60 keV electrons

Abstract

We report the results of a study on the influence of organic salts on the induction of single strand breaks (SSBs) and double strand breaks (DSBs) in DNA by electrons of 1 eV to 60 keV. Plasmid DNA films are prepared with two different concentrations of organic salts, by varying the amount of the TE buffer (Tris-HCl and EDTA) in the films with ratio of 1:1 and 6:1 Tris ions to DNA nucleotide. The films are bombarded with electrons of 1, 10, 100, and 60 000 eV under vacuum. The damage to the 3197 base-pair plasmid is analyzed ex vacuo by agarose gel electrophoresis.The highest yields are reached at 100 eV and the lowest ones at 60 keV. The ratios of SSB to DSB are surprisingly low at 10 eV (~4.3) at both salt concentrations, and comparable to the ratios measured with 100 eV electrons. At all characteristic electron energies, the yields of SSB and DSB are found to be higher for the DNA having the lowest salt concentration. However, the organic salts are more efficient at protecting DNA against the damage induced by 1 and 10 eV electrons. DNA damage and protection by organic ions are discussed in terms of mechanisms operative at each electron energy. It is suggested that these ions create additional electric fields within the groove of DNA, which modify the resonance parameter of 1 and 10 eV electrons, namely, by reducing the electron capture cross-section of basic DNA units and the lifetime of corresponding transient anions. An interstrand electron transfer mechanism is proposed to explain the low ratios for the yields of SSB to those of DSB produced by 10 eV electrons.

Absolute cross section for low-energy-electron damage to condensed macromolecules: A case study of DNA

“…This small increase suggests that although the CS for the sum of the ionization and fragmentation channels at 100 eV is reported to be larger by one or two orders of magnitude than that at 10 eV for most organic molecules [74][75][76], resonant and nonresonant mechanisms have relatively similar contributions to the generation of DNA SBs at both energies. Similar comparisons were also made in previous studies (i.e., the yields for the formation of single and double SBs by 10 and 100 eV electrons had comparable values) [73,77,78]. Therefore, our results confirm the previous suggestion that for a given CS value, the formation of transient anions and DEA are much more efficient processes than others to induce SBs in DNA.…”

Dissociative electron attachment to DNA-diamine thin films: Impact of the DNA close environment on the OH− and O− decay channels

“…More recently, Dumont et al 23 and Zheng and Sanche 24 observed a protective effect on DNA damage by organic salts, particularly in the chemical buffer used in most of the experiments involving DNA (Tris-HCl, EDTA). Single and double strand breaks (SSB and DSB) were considerably reduced in plasmid DNA under irradiation with 1 eV to 60 keV electrons.…”

Chemical Radiosensitivity of DNA Induced by Gold Nanoparticles

“…27 After lyophylization, the films were transferred directly to the UHV chamber of the LEE irradiator. The DNA films were then bombarded with an incident electron beam of 6 nA and electron energy of 10 ± 0.5 eV, during exposures of 5 to 60 s. The time-response of the yields was expressed in term of the fluence (i.e., the total number of electrons hitting the target).…”