Abstract
Complex-formation equilibria involving trans-diamine palladium(II) (PdII), 4,4′-bipyridine (bpy), and inosine were investigated at 25 °C and 0.1 M (NaNO3) ionic strength. The stability constants of all possible mono-nuclear and binuclear complexes were determined. The concentration distribution diagram for the binuclear complexes of PdII-bpy-inosine reveals the complexes that predominate in the physiological pH range and the quite feasible interaction of the binuclear complex PdII-bpy-PdII with inosine as a DNA constituent. On the basis of DFT calculations (B3LYP/LANL2DZp), the structures of the investigated equilibrium species show typical bond lengths for Pd–O and Pd–N bonds. The C–C bond in [Pd(4,4′-bpy)(NH3)2(OH2)]2+ is clearly shortened to 1.47 Å, leading to reduced aromaticity in bpy. Comparison with model compounds suggests that the uncoordinated aromatic ring can be understood as an electron donating group.
Acknowledgement
The authors kindly thank Prof. Tim Clark for hosting this work in the CCC and the Regionales Rechenzentrum Erlangen (RRZE) for a generous allotment of computer time.