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

Complexing in platinum(IV)-adenine-amino acid (alpha-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 H(2)PtCl(6) and amino acids produced the following coordination compounds: Pt(C(3)H(6)NO(2))(C(5)H(5)N(5))Cl(3) center dot 2H(2)O, or Pt(Ala-)(Ade)Cl(3) center dot 2H(2)O (I); Pt(C(5)H(5)N(5))(C(6)H(14)N(2)O(2))Cl(4) center dot 2H(2)O, or Pt(Ade)(Lys)Cl(4) center dot 2H(2)O (II); and Pt(C(5)H(5)N(5))(C(6)H(9)N(3)O(2))Cl(4) center dot 3H(2)O or Pt(Ade)(Hist)Cl(4) center dot 3H(2)O (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 alpha-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.