嘧啶及其异构体的密度泛函理论研究

Density functional theory study on tautomers of cytosine,uracil and thymine

Molecular structures for tautomers of cytosine,uracil and thymine were calculated by the B3LYP/6-311Gmethod,both in the gas and aqueous phases,with full geometries optimization.The Onsager solvate theory model was employed for aqueous solution calculations.The structures,total energy,standard enthalpy,standard entropy and standard Gibbs free energy were obtained.The calculation results show that the oxo-amino or dioxo tautomers are the most stable isomer both in the gas and aqueous phasee.The results are in good agreement with available experimental data.The entropy effect on the Gibbs free energy of cytosine,uracil and thymine base is very small and there is little significance for the tautomeric equilibria of these base.The enthalpic term is dominant in the determination of tautomeric equilibria.The Gibbs free energy of solvation is well correlated with the dipole moments of cytosine,uracil and thymine tautomers.