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 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 · 2H 2 O, or Pt(Ala − )(Ade)Cl 3 · 2H 2 O ( I ); Pt(C 5 H 5 N 5 )(C 6 H 14 N 2 O 2 )Cl 4 · 2H 2 O, or Pt(Ade)(Lys)Cl 4 · 2H 2 O ( II ); and Pt(C 5 H 5 N 5 )(C 6 H 9 N 3 O 2 )Cl 4 · 3H 2 O or Pt(Ade)(Hist)Cl 4 · 3H 2 O ( III ). These complexes were characterized by 13 C 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.