Equilibrium, kinetic and HPLC study of the reactions between platinum(II) complexes and DNA constituents in the presence and absence of glutathione

The complex formation equilibria of Pt(SMC)(H(2)O)(2)](+) and Pt(terpy)H(2)O](2+), where SMC =S-methyl-L-cysteine and terpy = 2,2':6',2"-terpyridine, with some biologically relevant ligands such as inosine (INO), inosine-5'-monophosphate (5'-IMP), guanosine-5'-monophosphate (5'-GMP) and glutathione (GSH) were studied. The stoichiometry and stability constants of the complexes formed are reported, and the concentration distribution of the various complex species have been evaluated as a function of pH. Also the kinetics and mechanism of the complex formation reactions were studied as a function of nucleophile concentration and temperature. For the complex Pt(SMC)(H(2)O)(2)](+), two consecutive reaction steps, which both depend on the nucleophile concentration, were observed under all conditions. The negative entropies of activation support an associative complex formation mechanism. Reaction of guanosine-5'-monophosphate (5'-GMP) with Pt(II) complexes was carried out in the presence and absence of glutathione (GSH) at neutral pH. The rate constants clearly showed a kinetic preference toward GSH at neutral pH. The reactions were also monitored by HPLC. However, only a small amount of coordinated 5'-GMP was detected in the HPLC trace. The products were isolated and characterized by MALDI-TOF mass spectrometry.