Abstract:
The decomposition of hydrogen peroxide catalysed by quatcrpyridineiron(ni) complex ions has been studied within the pH range 6.5-8. The reaction obeys total third-order kinetics with a partial order of two with respect to the substrate. At pH Rs 7.6, where the reaction velocity exhibits a maximum asymptotic value, the apparent activation energy is 29.3±2.9 kJ mol-1. Addition of poly (L-glutamate) (PLG) in solution determines a change in the overall kinetics. In this case, the process follows a total second-order equation and has an apparent activation energy of 53.1 ±6.3 kJ moly . At a fixed concentration of complex, saturation phenomena are observed in all cases on increasing the concentration of substrate. As expected, the Lineweaver-Burk plot of the polymer- free complex-catalysed reaction is nonlinear, whereas it is linear when the complex + PLG system is us5.d', At 25°C, the rate constant for the irreversible decomposition of the Michealis “ complex ”, which represents the rate-determining step, is k3 = 4.9 ±0.2 and 2.7 ± 0.2 s-1 for [Fe(tctpy) X2]nF and 1 c(. etpy)X2]"++PLG catalytic systems, respectively. Implications of the role played by the poly- pep ice matrix as environmental controller of the catalysis under study are briefly discussed.
