Insights into the dehydrogenation of 2-thiouracil induced by slow electrons: Comparison of 2-thiouracil and 1-methyl-2-thiouracil.

In the present contribution, we study dissociative electron attachment to 1-methyl-2-thiouracil that has been synthesized and purified prior to the measurements. We compare the results with those previously obtained from 2-thiouracil. The comparison of the yield of the dehydrogenated parent anion from both the compounds allows us to assign the site from which the H atom is expulsed and to predict the mechanism that is involved in the formation of the peaks within the ion yield curve. It appears that the dehydrogenation observed for 2-thiouracil arising from the vibrational Feshbach resonances (at 0.7 and 1.0 eV) and a π*/σ* transition (at 0.1 eV) involves the bond cleavage at the N1 site, while that at the N3 site operates via the π*/σ* transition and occurs in the energy range of 1.1-3.3 eV. Besides the loss of the H atom from 1-methyl-2-thiouracil, we observe a relatively strong signal due to the loss of an entire methyl group (not observed from methyl-substituted thymine and uracil) that is formed from the N1-CH3 bond cleavage and can mimic the N-glycosidic bond cleavage within the DNA macromolecule.