Beyond the Bragg Peak: Hyperthermal Heavy Ion Damage to DNA Components

We have observed the destruction of fundamental building blocks of DNA (nucleoside, base, and sugar) by hyperthermal ($0.25–1.75\mathrm{eV}/\mathrm{amu}$) heavy ion impact. Nucleoside damage pathways include base or sugar loss, and complete disintegration of either moiety. Sugar damage dominates, and in DNA will yield a complex strand break. Our results suggest that (a) heavy particle damage to biological media may extend to ion track ends beyond the Bragg peak, and (b) the nascent damage by hyperthermal secondary heavy particles, formed along the primary ion tracks, may be equally complex.

Figure 1

Cation and anion (insets) desorption mass spectra produced by 100 eV ${\mathrm{Ar}}^{+}$ impact on films of (a) thymine (T), (b) 2-deoxy-d-ribose (dR), and (c) thymidine (dT); each film is about 4 nominal monolayers ($4\mathrm{ML}\approx 200\mathrm{ng}/{\mathrm{cm}}^2$) on a Pt substrate.

Figure 2

Desorption energy thresholds for cation fragments produced by ${\mathrm{Ar}}^{+}$ impact on thymidine films (4 ML). The relative ion yields are normalized in intensity at 70 eV. The inset shows a close-up for ${\mathrm{H}}_3{\mathrm{O}}^{+}$ and ${\mathrm{CH}}_3{\mathrm{O}}^{+}$.