Degradation kinetics of a novel antimitogenic and antiviral palladium (II) coordination compound.

Abstract

The degradation kinetics of a new organometallic coordination compound, aquadichloro(2,6-diaminopyridine)palladium(II), were studied in acidic and acid halide media. In acidic solutions, the degradation was first order with respect to the complex concentration; e.g., at 77°, the apparent rate constants at pH 1.00, 1.22, and 1.50 were 0.00395, 0.00292, and 0.00225 min−1, respectively- Furthermore, a plot of log (apparent rate constant) versus pH gave a straight line with an approximate slope of 0.5, indicating pseudo-first-order catalysis with respect to complex concentration at a specified pH. Activation energies obtained from Arrhenius plots varied from 43 to 57 kcal/deg/mole for pH 1.00 and 1.50, respectively. The pH-independent activation energy was 15 kcal/ deg/mole. In acid halide solutions, utilizing the method of initial rates, the degradation was first order with respect to complex concentration. A plot of log (initial rate) versus log (chloride-ion concentration) gave a straight line with an apparent slope of 1.0. A plot of log (initial rate) versus pH resulted in a straight line with a slope of 0.5. Thus, pseudofirst-order catalysis with respect to complex concentration at a specified pH and pCl occurred. When the method of curve stripping was applied to the data, a plot of log (complex concentration undegraded) versus time resulted in a biexponential relationship; e.g., at pH 1.50,0.10 M chloride concentration, and 57°, the biexponential relationship between undegraded complex versus time giving the best fit to the data was: complex concentration=0.237e−00653t+2.213e−0.00276t. A general mechanistic explanation of the acid- and acid halide-catalyzed degradation of the complex is proposed.