Effects of ionization, metal cationization and protonation on 2′-Deoxyguanosine:: Changes on sugar puckering and stability of the N-glycosidic bond

The influence of oxidation, protonation, and metal cationization with Cu+ and Cu2+ on the strength of the N-glycosidic bond in 2'-deoxyguanosine has been studied by means of quantum chemical calculations. In all cases, the N9-Cl' bond distance increases (0.03-0.06 angstrom) upon introducing positive charge in the guanine moiety, the observed variations being more important for the dicationic systems. Binding energies show that the effect of Xn+ in guanine hinders the homolytic dissociation, whereas it largely favors the heterolytic process. With respect to the deoxyribose ring, it has been found that metal binding, oxidation, and protonation do not significantly change the values of the phase angle of pseudorotation P. However, the glycosyl torsion angle X varies considerably (from 242.0 degrees to 189.8 degrees) as a consequence of a stabilizing guanine-sugar (H8-O4') interaction due to the increase of acidity of guanine C8-H8 upon cationization.