cis-[Pt(NH3)2]2+ coordination to the N7 and O6 sites of a guanine–cytosine pair: disruption of the Watson–Crick H-bonding pattern

The coordination of cis-[Pt(NH3)2]2+ to the N7 and O6 sites of guanine of the guanine–cytosine (GC) nucleic base pair is studied at the SCF, DFT and MP2 levels of theory, and by an ab initio BSSE-free optimization algorithm, concerning the possible mechanisms of the antitumor activity of cis-[Pt(NH3)2Cl2]. The calculations show that the cis-[Pt(NH3)2]2+ coordination results in the breakage of the (cytosine)N4–H–O6(guanine) H-bond and a substantial non-planarity of the GC moiety. From an analysis of the electrostatic potential at the O6, N1–H and N2–H sites of cis-[Pt(NH3)2G]2+ we can explain the predicted changes in geometry and binding energy of the GC complex.