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] 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-wPtNH3.2Cl2x. The calculations show that the cis-[Pt(NH3)2] coordination results in the breakage of thecytosine.N4–H–O6guanine.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)2] we can explain the predicted changes in geometry and binding energy of the GC complex.