Ab initio study of the crystallographic solvation pattern of the cytosine-guanine base pair in DNA

The influence of hydration on the Watson-Crick cytosine-guanine base pair w as investigated, testing the ability of the self-consistent field for molec ular interaction (SCF-MI) ab initio method to reproduce the hydration patte rn present in a real system (the base pair in the DNA framework). The posit ions of hydration sites around the base pair predicted by a knowledge-based approach employing crystallographic data were compared to the ab initio op timized structures. The SCF-MI method was applied to perform basis set supe rposition error (BSSE)-free geometry optimization. The hydration shell take n into account-comprising five water molecules, three on guanine and two on cytosine-"saturates" the base pair, engaging all of the available hydrogen bond donors/accepters. The interaction between water and the base pair was also analyzed from the energetic viewpoint, highlighting the role of water in the pair stabilization.