Equilibrium studies on complex formation reactions of dichlorido[(R,R)-trans-1,2-diaminocyclohexane]platinum(II) complex with ligands of biological significance

Abstract

The hydrolysis and complex formation equilibria of [Pt(dach)(H2O)2]2+, where dach is (R,R)-trans-1,2-diaminocyclohexane, with some sulfur- and nitrogen-bonding ligands, such as l-methionine, glutathione, inosine, inosine-5′-monophosphate, and guanosine-5′-monophosphate, were studied in aqueous 0.10 M NaClO4 solution at 298 K by potentiometric titrations. The experimentally determined pK a values for the studied diaqua complex were 6.00 and 10.03, respectively. The acid dissociation constants of the ligands were also determined. The stoichiometry and stability constants of the formed complexes are reported, as well as the concentration distribution of the various complex species evaluated as a function of pH. In all studied systems, species with one coordinated molecule of ligand were detected. However, only in systems with l-methionine and inosine, complexes with two molecules of ligand directly coordinated to the Pt(II) ion were found. The results also show that glutathione formed the most stable complexes. These results could contribute to better understanding of the interactions between Pt(II) complexes and biologically significant molecules.