Prototropic tautomers of 5‐methylcytosine and enthalpy changes of their protonation, deprotonation, and deamination: Hybrid density functional B3LYP study

摘要: Molecular and thermodynamic properties such as geometric parameters, dipole moments, vibrational frequencies, the first ionization potentials, relative tautomerization energies, tautomeric equilibrium constants of all prototropic tautomers 5-methylcytosine have been studied at hybrid density functional level B3LYP/6-31+G(d,p). The methylation on C5 atom does not lead to significant deformation pyrimidine structures corresponding cytosine, which maintains similar stability order. species 2-oxo-4-amino [T(0)], 2-hydroxy-4-amino [T(1-2s) T(1-2t)], trans-2-oxo-4-imino [T(3-4t)] are predominated in gas phase. zwitterionic conformers tautomerism [T(1-4)] protonation [P(4), P(1-2s-4), P(1-2t-4), P(1-3-4)] investigated for time due their close relationship with deamination during genetic repair. Enthalpy changes (ΔrH) protonation, deprotonation, calculated these room temperature; it is noted that enthalpies [δ(ΔH)] rationalized well terms a second-order polynomial sum mean ΔrH values deprotonation processes. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem,