Environmental control of reactions. Influence of poly(L-glutamate) on the kinetics of decomposition of hydrogen peroxide catalysed by quaterpyridineiron (III) complex ions
- 1 January 1978
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 74, 288-296
- https://doi.org/10.1039/f19787400288
Abstract
The decomposition of hydrogen peroxide catalysed by quaterpyridineiron(III) 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 ≈ 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 mol–1. 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 used. 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(tetpy) X2]n+ and [Fe(tetpy) X2]n++ PLG catalytic systems, respectively. Implications of the role played by the poly-peptide matrix as environmental controller of the catalysis under study are briefly discussed.Keywords
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