Mechanistic evaluation of hematin action as a horseradish peroxidase biomimetic on the 4-aminoantipyrine/phenol oxidation reaction

Abstract

Abstract: Hematin, a mimetic structure of heme peroxidases, was successfully applied for H2O2- mediated condensation reaction between phenol and 4-aminoantipyrine.The catalytic action was evaluated in comparison to horseradish peroxidase (HRP) by kinetic modelling and parametrization procedure. Expected side reactions were checked and discarded as model-relevant routes. The existence of the oxoperferryl-pi-cation radical and oxoperferryl species of hematin, as analogues of Compound I and II of HRP, can be postulated because simulated product formation fitted experimental data. However, in light of the optimized rate constants encountered, hematin was less active to peroxide activation and less specific to the coordination of phenol versus H2O2 than HRP. The model indicated that hematin bleaching from key intermediate oxoperferryl was induced rather than regenerated via Compound III formation. In contrast to the enzyme, the faster oxygen evolvement and the lack of precipitating polyphenol production observed with hematin after 4-aminoantipyrine depletion were interpreted as accumulation of oxidising HOO* radicals through the peroxide decomposition pathway. This study may be of interest for interpreting the catalytic performance of hematin. Moreover, the replacement of the enzyme by the less-expensive and non-polyphenol-forming hematin for this versatile colorimetric assay may provide convenient results, especially in flowinjection modes and analytical columns applications.