KINETICS AND MECHANISM OF THE INTERACTION OF L-CYSTEINE WITH DIAQUAETHYLENEDIAMINEPLATINUM(II) PERCHLORATE IN AQUEOUS-SOLUTION

The kinetics of the interaction of L-cysteine with [Pt(en)(H2O)(2)](2) has been studied spectrophotometrically as a function of [Pt(en)(H2O )(2)(2+)], [L-cysteine], pH and temperature. The reaction has been mon itored at 230 nm, where the spectral difference is maximum although th e lambda(max) of the L-cysteine substituted product is at 213 nm. The activation parameters have been evaluated from temperature coefficient of the reaction rates. The low value of Delta H-not equal (61.1 kJ mo l(-1)) and large negative value of Delta S-not equal (-83 J K-1 mol(-1 )) indicate an associative mode of activation for the substitution pro cess. The additional advantage of using aquaamine complexes as an amin o acid binder is also discussed.