Pt···H Nonclassical Interaction in Water-Dissolved Pt(II) Complexes: Coaction of Electronic Effects with...

The structure of the hydration shell of cisplatin, cis-[Pt(NH3)2Cl2], and its aquated derivatives cis-[Pt(NH3)2Cl(H2O)](+), cis-[Pt(NH3)2OH(H2O)](+), and cis-[Pt(NH3)2(H2O)2](2+) were studied by a number of density functional molecular dynamics (DFT-MD) simulations (from 30 to 250 ps) in which Pt(II) complexes were immersed in a periodic box with 72 explicit water molecules. Furthermore, Pt(II) complex-water binding energy curves and full DFT optimizations of clusters derived from the lowest potential energy DFT-MD frames offered a deeper insight into the structure of the first hydration shell and electronic changes connected with the formation of a nonclassical Pt···H-O-H (Pt···Hw) hydrogen bond (inverse hydration). The probability of a Pt···Hw interaction decreases with increasing charge of the platinum complex due to disadvantageous electrostatics. The main stabilization comes from the charge transfer being followed by polarization and dispersion. Ligands form a framework for the network of H-bond interactions between the solvent molecules, which play an important role in the promotion/suppression of the formation of the Pt···Hw interactions. In the +2 charged diaqua complex the Pt···Hw interaction is still attractive but cannot compete with classical H bonds between solvent molecules. Thus, the formation of a Pt···Hw interaction is the result of a suitable solvent H-bonding network and the probability of its incidence decreases with increasing flexibility of the solvent.