Negative ions in thymine and 5-bromouracil produced by low energy electrons

Bond Breaking and Temporary Anion States in Uracil and Halouracils: Implications for the DNA Bases

“…1 to note the existence of structures near 0.31 and 0.54 eV in the ET spectra of the halouracils. They match quite closely peaks in the DEA cross sections of chlorouracil reported at 0.24 and 0.57 eV [5] and at 0.28 eV in bromouracil [4]. As supported by our VOE calculations, these features cannot be associated with the lowest valence anion states, and thus we must seek another source.…”

“…Surprisingly, there is no sign of the major DEA feature at 1.01 eV, and we return to discuss this later. We note that uracil, thymine, cytosine, and chlorouracil all display peaks in DEA, at 1.01, 1.03, 1.11, and 0.99 eV, respectively [2][3][4][5]. Taken as a whole, the DNA bases and halouracils exhibit sharp features grouped in the ranges 0.24 -0.34, 0.54 -0.74, and 0.99-1.1 eV.…”

“…This work, in part, has served to motivate further gas phase studies of electron collisions with the DNA bases, the RNA base uracil, and the halouracils in an effort to understand the fundamental mechanisms involved. Most recently, Hanel et al [2] (uracil), Denifl et al [3] (uracil, thymine and cytosine), Abouaf et al [4] (thymine and 5-bromouracil), and Denifl et al [5] (5-chlorouracil) have examined the electron energy dependence of the production of various anion fragments and made estimates of the magnitudes of the dissociative electron attachment (DEA) cross sections. The radiological significance of the halouracils has been discussed in several of these references and will not be repeated here.…”

“…A few of the features have been attributed above to known resonances based on their relative energies. Abouaf et al [4] have ventured a mechanism for the sharpest peaks appearing in the bromouracil and thymine DEA data, suggesting that they are ''. .…”

Interaction of low-energy electrons with the pyrimidine bases and nucleosides of DNA

“…The yield curves for both of these anions show weak maxima near 0.3 eV. At higher energy, the ͑T-H͒ − yield closely resembles that observed in DA measurements on thymine itself, 7,11,12,16,17,21,[25][26][27]29 with a narrow peak near 1.0 eV and a broader maximum centered at about 1.7 eV, while the ͑2-deoxyribose-OH͒ − yield shows a single broad maximum centered near 1.2 eV. Since our calculations indicate only small shifts in the resonance positions between T and dT, the peak at 1.7 eV in ͑T-H͒ − yield from dT might be associated with the second * resonance, as has been suggested for the analogous peak in DA to T. 27 Likewise, the weak feature at 0.3 eV might be associated with trapping in the first * resonance.…”