Specific solvation effects on the structures and properties of Watson- Crick and reverse Watson-Crick isocytosine-cytosine and guanine-cytosine base pairs: A theoretical ab initio study

Ab initio quantum chemical studies were performed for the standard and most favorable reverse Watson-Crick isocytosine-cytosine (iCC) and guanine- cytosine (GC) complexes in the gas phase and in a water solution. Full geometry optimizations at the Hartree-Fock (HF) level with the 6-31G(d) basis set without any constraints on the planarity of these complexes were carried out. The water solution was modeled by explicit inclusion of a different number of water molecules, which creates the first hydration shell around these base pairs. Single point calculations were also performed at the correlated MP2/6-31G(d) level. The interaction and solvation energies were corrected for the basis set superposition error. It was shown that both the base pairs considered, possessed similar molecular properties in the gas phase. The presence of the N9-H group in guanine causes changes in the structure of the first hydration shell around the RWC GC base pair compared to the RWC iCC pair.