Book of Abstracts: Albany 2003
June 17-21 2003
The Nature of the Stability of Watson-Crick Nucleic Acids Base Pairs. Ab Initio Hartree-Fock and Post-Hartree-Fock Theory Studies
Despite considerable theoretical and experimental efforts the nature of stability of the H-bonded nucleic acid base pairs is essentially not understood yet. In this report the results of the calculations of Watson-Crick base pairs by the HF/6-31G** method and the second-order Moller-Plesset (MP2) perturbational method with the 6-31G*(0.25) and 6-31G* basis sets are presented. According to the HF/6-31G** results the Watson-Crick base pairs are perfectly planar. However optimization at the MP2 level leads to an intrinsically non-planar G-C base pair for the both basis sets with the propeller-twisted optimal geometry (angle between of the base planes is 7.5°) while the structure of A-T base pair remains planar. The hydrogen bond lengths (Å) after full geometry optimization at the MP2/6-31G*(0.25) and MP2/6-31G* levels of theory as well as dipole moments (D) of the canonical base pairs are given below.
1Institute of Molecular Biology and Genetics
The National Academy of Sciences of Ukraine
Kiev-143, 03143, Ukraine
31-038 Krakow, Poland
|For the quantitative elucidation of role of the different contributions determining the hydrogen bonding in the base pairs we carried out the decomposition of the HF interaction energy (EHF) by Morokuma-Kitaura method (electrostatic energy, EES, exchange repulsion energy, EXR, polarization energy, EPL, charge transfer energy, ECT, the higher order coupling term among various interaction components, EMIX). The EHF, EXR, ECT, EMIX, correlation interaction energy, ECOR and total interaction energy, EINT were corrected by the conventional counterpoise correction method. The EINT includes the deformation energy, EDEF. These data (kcal/mol) are given below.|
The analysis of the attraction energy shows that the electrostatic forces are the main factor of stabilization of the base pairs (64% and 70%, respectively). The polarization and charge transfer energies also make considerable contribution (23% and 25%, respectively) in the stabilization of the base pairs. Therefore this result confirms electrostatic nature of the hydrogen-bonding Watson-Crick base pairs. It is shown that the correlation interaction (mainly, at the expense of dispersion forces) makes commensurable contribution with the EPL and ECT contributions in the stabilization of the A-T base pair and notably lesser contribution in the stabilization of the G-C base pair.
V. I. Danilov