Cross Sections for Low-Energy (10 – 50 eV) Electron Damage to DNA

Abstract

We report direct measurements of the formation of single-, double- and multiple strand breaks in pure plasmid DNA as a function of exposure to 10-50 eV electrons. The effective cross sections to produce these different types of DNA strand breaks were determined and were found to range from approximately 10(-17) to 3 x 10(-15) cm(2). The total effective cross section and the effective range for destruction of supercoiled DNA extend from 3.4 to 4.4 x 10(-15) cm(2) and 12 to 14 nm, respectively, over the range 10-50 eV. The variation of the effective cross sections with electron energy is discussed in terms of the electron's inelastic mean free path, penetration depth, and dissociation mechanisms, including resonant electron capture; the latter is found to dominate the effective cross sections for single- and double-strand breaks at 10 eV. The most striking observations are that (1) supercoiled DNA is approximately one order of magnitude more sensitive to the formation of double-strand breaks by low-energy electrons than is relaxed circular DNA, and (2) the dependence of the effective cross sections on the incident electron energy is unrelated to the corresponding ionization cross sections. This finding suggests that the traditional notion that radiobiological damage is related to the number of ionization events would not apply at very low energies.

Absolute cross section for loss of supercoiled topology induced by 10 eV electrons in highly uniform /DNA/1,3-diaminopropane films deposited on highly ordered pyrolitic graphite

“…The separation of the recovered DNA into the undamaged super-coiled (SC), nicked circular (C), and linear (L) structural forms was performed by agarose gel electrophoresis. 24,26 The DNA samples and the agarose gels were stained with SYBR Green I in concentrations of ×100 and ×10 000, respectively. The samples were passed on 1% agarose gel Tris-acetic acid-EDTA (TAE) buffer at 100 V for 7 min, then at 75 V for 68 min (5 V cm −1 ).…”

“…22 While measurement of LEE induced damage under such conditions is possible (e.g., Refs. [23][24][25][26] and has even allowed measurement of more transferable cross sections, 22 by varying film thicknesses, there exists a need for absolute cross sections for DNA damage induced by LEEs. Such values can be derived from experiments on uniform plasmid DNA films, which can be recovered from their substrate for post-irradiation analysis.…”

Total electron-scattering cross sections from pyrimidine as measured using a magnetically confined experimental system

“…These low-energy, possibly even subionizing, electrons play an important role in inducing damage such as strand breaks or molecular dissociations in biomolecular systems, as has been extensively demonstrated [e.g. [2][3][4]. Therefore, when studying radiation effects in biological media, it is essential that the particular electron interaction parameters (integral and differential cross sections, energy loss spectra, and partial scattering cross sections especially for dissociative interactions or radical generation) in the whole energy range are well known.…”

Interaction of low-energy electrons with the purine bases, nucleosides, and nucleotides of DNA

“…The observation that slow electrons cause damage to DNA, including single-and double-strand breaks, [1][2][3][4][5] has stimulated considerable interest in gas-and condensed-phase studies of low-energy electron interactions with the constituents of DNA and RNA. 6 Peaks in the damage rate as a function of electron energy indicate that resonant processes are involved.…”