Binding of Platinum(II) to Some Biologicaly Important Thiols

The reactions between [Pt(terpy)Cl(+) and thiols, such as glutathione, L-cysteine, D-penicillamine and thioglycolic acid have been Studied by conventional UV-VIS spectrophotometry and H NMR spectroscopy. The second-ordero rate constants, K(2), are similar for these four thiols, varying between 1.06 x 10(-2) and 6.10 x 10(+3) M(-1) s(-1) at 25( degrees )C. The activation entropies have large negative values between -100 and -200 J mol(-1) which are compatible with an associative A mechanism. However, L-methionine, as thioether ligand, is unreactive under the same experimental conditions. The obtained results have been analyzed in relation to the antitumor activity and toxicity of platinum(II) complexes.