Mixed-ligand platinum(IV) complexes with amino acids and adenine

Complexing in platinum(IV)-adenine-amino acid (α-alanine (Ala), lysine (Lys), or histidine (His)) systems was studied by pH titration. The stability constants of 1: 1: 1 complexes were determined. The stability of these mixed-ligand complexes changes in the following order: Lys < Ala < His. Reactions between aqueous solutions of H2PtCl6 and amino acids produced the following coordination compounds: Pt(C3H 6NO2)(C5H5N5)Cl 3 • 2H2O, or Pt(Ala-)(Ade)Cl3 • 2H2O (I); Pt(C5H5N5)(C 6H14N2O2)Cl4 • 2H2O, or Pt(Ade)(Lys)Cl4 • 2H2O (II); and Pt(C5H5N5)(C6H9N 3O2)Cl4 • 3H2O or Pt(Ade)(Hist)Cl4 • 3H2O (III). These complexes were characterized by 13C NMR, IR, and X-ray photoelectron spectroscopy. Alanine is complexed via both amino and carboxy groups; lysine, via α-amino group exclusively; and histidine, via the amino group and the N3 heterocyclic atom. Adenine in these complexes is monodentate due to the N7 heterocyclic atom. The adenine amino group is apparently H-bonded to a water oxygen atom. © 2008 Pleiades Publishing, Ltd.