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. 2011 Apr 21;115(15):4523-31.
doi: 10.1021/jp200947g. Epub 2011 Mar 31.

Soft X-ray and low energy electron-induced damage to DNA under N2 and O2 atmospheres

Elahe Alizadeh  1 , Pierre Cloutier, Darel Hunting, Léon Sanche
Affiliations

Soft X-ray and low energy electron-induced damage to DNA under N2 and O2 atmospheres

Elahe Alizadeh et al. J Phys Chem B. .

Abstract

DNA damage induced by low energy electrons (LEEs) and soft X-rays is measured under dry nitrogen and oxygen at atmospheric pressure and temperature. Five-monolayer plasmid DNA films deposited on tantalum and glass substrates are exposed to Al K(α) X-rays of 1.5 keV in the two different environments. From the damage yields for DNA, G values are extracted for X-rays and LEEs. The G values for LEEs are 3.5 and 3.4 higher than those for X-ray photons under N(2) and O(2) atmospheres, respectively. Because most of the measured damage is in the form of single strand breaks (SSB), this result indicates a much higher effectiveness for LEEs relative to X-rays in causing SSB in both environments. The results indicate that the oxygen fixation mechanism, which is highly effective in increasing radiobiological effectiveness, under aerobic conditions, is operative on the type of damage created at the early stage of DNA radiolysis by LEEs.

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Figures

Figure 1
Figure 1
Schematic view of the apparatus used to irradiate DNA samples with 1.5 keV Al Kα X-ray photons under nitrogen and oxygen gas at atmospheric pressure: (A) baratron, (B) adjustable leak valve, (C) concave aluminum cathode, (D) high voltage electric feedthrough, (E) glass-ceramic (Macor) support, (F) quartz tube, (G) aluminum foil target, (H) He-filled enclosed volume, (I) thin foil of Mylar, (J) aluminum plate as sample holder, (K) rotating disk, and (L) gas circulation valves.
Figure 2
Figure 2
Energy spectra of Al Kα X-ray induced secondary electron emission from a tantalum substrate in two different energy ranges.
Figure 3
Figure 3
Exposure-response curves for the loss of the supercoiled DNA deposited on glass and tantalum substrates and irradiated by 1.5 keV X-rays under (a) N2 and (b) O2 atmospheres. The points represent the means of three yield measurements and the error bars represent the standard deviation of the means.
Figure 4
Figure 4
Exposure-response curves for formation of circular (SSB) and linear DNA (DSB) in an O2 environment from LEE interaction with plasmid DNA deposited on tantalum substrates. The points represent the means of three measurements and the error bars represent standard deviation of the means.
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