Theoretical Ab Initio Study of the Effects of Methylation on the Nature of Hydrogen Bonding in A:T Base Pair

Abstract

We report the results of a theoretical ab initio study of methylation in Watson-Crick A:T base pairs. Equilibrium geometries were obtained without symmetry restrictions by the gradient procedure at DFT level of theory with the standard 6–31G(d) basis set. Each local minima was verified by energy second derivative calculations. Single-point calculations for the DFT geometries have been performed at the MP2/6–31G(d,p), MP2/6–31++G(d,p), and MP2/6–311++G(2d,2p) levels of theory. The geometrical parameters, relative stabilities and counterpoise corrected interaction energies are reported. In addition, using a variation-perturbation energy decomposition scheme, we have found the important contributions to the total interaction energy.