Ab initio and DFT methods have been used to study the seven tautomeric forms of 5-methylcytosine molecule. The related tautomer in gas phase have been studied at HF/6-31G, HF/6-31G* and B3LYP/6-31G* levels of theory. The structures,enthalpies,entropies,Gibbs free energies,relative tautomerization energies of tautomers and tautomeric equilibrium constants were compared and analyzed along with full geometry optimization. The calculations showed that the Oxo-amino(6), Oxo-imino(7) and Hydroxy-amino(4) tautomers are the most stable in the gas phase. The results are in a good agreement with the available experimental data. The entropy effect on the Gibbs free energy of the 5-methylcytosine bases is very small and it has a little significance on the tautomeric equilibria of pyrimidine bases.Therefore the enthalpic term is dominant in the determination of the equilibrium constants. 13C-NMR studies have been carried out for these tautomers and the results are discussed.We have also evaluated the hybridation coefficient for bonds and hetero atom LPS in the aromatic ring for the stable tautomers. Natural Bond Orbital Theory (NBO) calculation showed that the stable tautomers must be considered aromatic.
Zare, K., Monajjemi, M., Zahedi, E., & Aghaie, H. (2007). Ab initio and DFT studies on tautomerism of 5-methyl cytosine in gaseous phase. Journal of Physical & Theoretical Chemistry, 4(2), 17-28.
MLA
K. Zare; M. Monajjemi; E. Zahedi; H. Aghaie. "Ab initio and DFT studies on tautomerism of 5-methyl cytosine in gaseous phase". Journal of Physical & Theoretical Chemistry, 4, 2, 2007, 17-28.
HARVARD
Zare, K., Monajjemi, M., Zahedi, E., Aghaie, H. (2007). 'Ab initio and DFT studies on tautomerism of 5-methyl cytosine in gaseous phase', Journal of Physical & Theoretical Chemistry, 4(2), pp. 17-28.
VANCOUVER
Zare, K., Monajjemi, M., Zahedi, E., Aghaie, H. Ab initio and DFT studies on tautomerism of 5-methyl cytosine in gaseous phase. Journal of Physical & Theoretical Chemistry, 2007; 4(2): 17-28.
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