PEROXIDASE-CATALYZED COOXIDATION OF HALOGEN-SUBSTITUTED PHENOLS AND 4-AMINOANTIPYRINE

Horseradish peroxidase-catalyzed co-oxidation of 8 phenols (phenol, p-cresol, pyrocatechol, 2,4-dichlorophenol, p-chloro-, p-bromo- and p-iodophenols) with 4-aminoantipyrine (AAP) has been studied in 0.1 M phosphate buffer, pH 7.0, at 25-degrees-C. The initial rates of product (antipyrilquinoneimines) formation depended on the phenol and enzyme concentrations and pH, but did not depend on the AAP concentration above 0.5 mM. Under optimum conditions, the kinetic constants, k(cat) and K(M), were determined for eight pairs of substrates. A scheme for the phenol co-oxidation with AAP is proposed and compared with the kinetic regularities of a process. The correlation of catalytic constants with sigma-constants of Hammett for halogen-substituted phenols is discussed and the anomalous reactivity of halophenols in peroxidatic oxidation shown. The complex dependence of rates for the co-oxidation of AAP with the halophenols on initial hydrogen peroxide concentration in the presence and absence of peroxidase-specific antibodies is also discussed.