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(C₃H₆NO₂)(C₅H₅N₅)Cl₃ · 2H₂O, or Pt(Ala^?)(Ade)Cl₃ · 2H₂O (I); Pt(C₅H₅N₅)(C₆H₁₄N₂O₂)Cl₄ · 2H₂O, or Pt(Ade)(Lys)Cl₄ · 2H₂O (II); and Pt(C₅H₅N₅)(C₆H₉N₃O₂)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.