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Internet Electronic Journal of Molecular Design - IEJMD, ISSN 1538-6414, CODEN IEJMAT
| ABSTRACT - Internet Electron. J. Mol. Des. November 2003, Volume 2, Number 11, 741-756 |
Theoretical Study of Alkali Metals Interactions with Thymine
Tautomers: Comparison and Analysis
M. Monajjemi, R. Ghiasi, H. Passdar, F. Mollaamin, S. Ketabi, F. Asaddian, B. Chahkandi, and M. Karimkhani
Internet Electron. J. Mol. Des. 2003, 2, 741-756
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Abstract:
The interaction of alkali metal with thymine is an interesting
target of studies in connection with bioinorganic chemistry and
biological chemistry of toxicity and carcinogenicity. We studied
interactions of one of the oxo groups of thymine and its
tautomers with alkali metals (Li, Na, K, Rb and Cs) by ab initio
calculations. The stability of these species has been studied in
gas and solution phases. Characterization of intermolecular
(C=O) and intramolecular (C-N) bonds has been studied with the
NBO method and, the interactions that cause the strongest
stabilization have been studied, as well. The stability of
metalated thymine and its tautomers has been studied
thermochemically. The present study reports the quantum
chemistry analysis of the metal-assisted tautomerization.
Ab initio and DFT methods at the HF and B3LYP levels of theory
were used. Interactions of alkali metals with oxo group of
thymine and its tautomers stabilize rare tautomers compared to
the major form. Investigation of interactions in solution phase
shows that with increasing dielectric constants of solvent, the
tautomers are stabilizing compared to the major form.
Thermochemical analysis shows that the stability of metalated
thymine is more for less electropositive metals. These results
show that basicity of metalated thymine has been increased.
NBO calculations show that in metalated thymine (1, metalated),
(5, metalated) the N2 and N4 lone pair is seen to be the lowest
occupancy and highest energy Lewis NBO and to be primarily
delocalized into antibonds the vicinal π* C3-O3 and π* C1-O1
NBO, respectively. In other species lowest occupancy and
highest energy Lewis NBO depend on alkali metal. Metalation of
one oxo group of thymine and its tautomers by alkali metals
cause to stabilize the rare tautomers. Metalation affects some
bonding and structural properties, such as bond distance and
atomic charges, are different compared to the nonmetalated form.
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