Binding of Platinum(II) to Some Biologicaly Important Thiols

Abstract

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, K₂, 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^°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.

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