Abstract
The kinetics of the interaction of DL-penicillamine with cis-[Pt(cis-dach)(OH2)2]2+ has been studied spectrophotometrically as a function of [cis-[Pt(cis-dach)(OH2)2]2+], [DL-penicillamine], and temperature at a particular pH (4.0), where the complex exists predominantly as the diaqua species and DL-penicillamine as a zwitterion. The substitution reaction proceeds via rapid outer sphere association, followed by two slow consecutive steps. The first is the conversion of title complex into an inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K E) for the outer sphere complex formation has been evaluated together with rate constant for two subsequent steps. The activation parameters for both steps have been evaluated using the Eyring equation: ( = 36 ± 4 kJ mol−1, = −175 ± 12 JK−1 mol−1 and = 44 ± 1 kJ mol−1, = −189 ± 3 JK−1 mol−1). The low enthalpy of activation and large negative value of entropy of activation are consistent with an associative mode of activation for both consecutive steps. The kinetic study has been substantiated by conductivity measurement, product isolation, IR and ESI-MS spectroscopic analysis.
Published Version
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