Stabilization of very rare tautomers of 1-methylcytosine by an excess electron
We characterized valence anionic states of 1-methylcytosine using various electronic structure methods. We found that the most stable valence anion is related to neither the canonical amino-oxo nor a rare imino-oxo tautomer, in which a proton is transferred from the N4 to N3 atom. Instead, it is related to an imino-oxo tautomer, in which the C5 atom is protonated. This anion is characterized by an electron vertical detachment energy (VDE) of 2.12 eV and it is more stable than the anion based on the canonical tautomer by 1.0 kcal/mol. The latter is characterized by a VDE of 0.31 eV. Another unusual low-lying imino-oxo tautomer with a VDE of 3.60 eV has the C6 atom protonated and is 3.6 kcal/mol less stable than the anion of the canonical tautomer. All these anionic states are adiabatically unbound with respect to the canonical amino-oxo neutral, with the instability of 5.8 kcal/mol for the most stable valence anion. The mechanism of formation of anionic tautomers with carbon atoms protonated may involve intermolecular proton transfer or dissociative electron attachment to the canonical neutral tautomer followed by a barrier-free attachment of a H atom to the C5 or C6 atom. The six-member ring structure is unstable upon an excess electron detachment. It collapses without a barrier to a linear or a bicyclo structure. Within the PCM hydration model, the anions become adiabatically bound with respect to the corresponding neutrals, and the tautomer with C6 protonated becomes the most stable, being followed by the tautomer with C5 protonated.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 876900
- Report Number(s):
- PNNL-SA-44296; JPCAFH; KP1102020; TRN: US0601545
- Journal Information:
- Journal of Physical Chemistry A, 109(50):11495-11503, Vol. 109, Issue 50; ISSN 1089-5639
- Country of Publication:
- United States
- Language:
- English
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