Kinetics and mechanism for ligand substitution reactions of some square-planar platinum(II) complexes: Stability and reactivity correlations

A brief overview of mechanistic studies on the reactions of cis-[Pt(dap)(H2O)(2)](2+) (1) and cis-[Pt(pipen) (H2O)(2)](2+) (2) (where dap and pipen are 1,3-diaminopropane and 2-aminomethylpiperidine respectively) with 2-thiouracil (LH), a nitrogen and sulfur-donor bio molecule, is presented. All the substitution reactions have been monitored at 327(for 1) and 326 (for 2) nm respectively where the differences in abosorbances between the reactants and products are maximum. At pH 4.0, the kinetics shows two consecutive processes, i.e., they show a non linear dependence on the concentration of ligand: first process is [ligand] dependent but the second step is [ligand] independent. The activation parameters and the thermodynamic parameters were also calculated, which supports the spontaneous formation of an outer sphere association complex. The product of this reaction has been characterized with the help of Job's method, IR and ESI-MS spectroscopic analysis. The purpose of this work is to improve the understanding of the mechanism of action of Pt(II) complexes as potential anti-tumour drugs in the human body.