Kinetics and Mechanism of the Interaction of DL-methionine with Di--Hydroxobis(1,10-Phenanthroline)Dipalladium(II) Ion in Aqueous Solution

The kinetics of interaction between DL-methionine with the di--hydroxobis(1,10-phenanthroline)dipalladium(II) ion complex has been studied spectrophotometrically, in pseudo-first-order conditions in aqueous solution as a function of [complex], [ligand], pH and temperature at constant ionic strength. At pH 6.5 the interaction of DL-methionine with the complex shows two distinct consecutive steps, i.e., it shows linear dependence on the concentration of DL-methionine. Both the steps are [ligand] dependent. The second order rate constants for the two steps are in the order of k1 approximate to 10-5dm3mol-1s-1 and k2 approximate to 10[image omitted]dm3mol-1s-1. The activation parameters are calculated from Eyring equation are found, H double dagger 1= 73.16 +/- 2.5KJ mol-1, S double dagger 1= -93.03 +/- 4.45 JK-1mol-1, H double dagger 2= 66.50 +/- 3.35 KJ mol-1, S double dagger 2= - 63.21 +/- 4.2 JK-1mole-1. On the basis of the kinetic data and thermodynamical activation parameters an associative mechanism is proposed for the interaction process.