The influence of intermolecular halogen bonds on the tautomerism of nucleobases. I. Guanine
In this paper, we report a computational study of the influence of halogen bonds (XB) on the tautomerism of 9-methylguanine, a model of guanosine and GTP. Molecular Electrostatic Potentials (MEP), interaction energies, Atoms in Molecules (AIM) and Natural Bond Orbitals (NBO) were used to characterize the complexes between three tautomers of 9-methylguanine (one oxo and two hydroxy) and five dihalogens molecules (Br2, BrCl, BrF, Cl2 and ClF). The results concerning the halogen bonds were compared with the effect of hydrogen bonds using hydrogen fluoride as a hydrogen bond donor. The binding energies of the complexes have been analyzed using a Free-Wilson model to obtain the individual interactions. An important conclusion of this study is that halogen bonds are able to strongly modify the order of stability of the three most stable tautomers that, in turn, could induce mutations according to the ‘rare tautomer hypothesis’.