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Conversion of pentahalogenated phenols by microperoxidase-8/H2O2 to benzoquinone-type products

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Author: Osman, A.M. · Posthumus, M.A. · Veeger, C. · Bladeren, P.J. van · Laane, C. · Rietjens, I.M.C.M.
Type:article
Date:1998
Institution: Centraal Instituut voor Voedingsonderzoek TNO
Source:Chemical Research in Toxicology, 11, 11, 1319-1325
Identifier: 234849
doi: DOI:10.1021/tx980037l
Keywords: Nutrition · Benzoquinone derivative · Halophenol · Peroxidase · Catalyst · Chemical analysis · Chemical reaction · Chlorination · Dechlorination · Dehalogenation · Ascorbic Acid · Benzoquinones · Catalysis · Chromatography, High Pressure Liquid · Cytochrome P-450 Enzyme System · Gas Chromatography-Mass Spectrometry · Hydrogen Peroxide · Molecular Conformation · Peroxidases · Phenols · Protein Binding

Abstract

This study reports the microperoxidase-8 (MP8)/H2O2-catalyzed dehalogenation of pentafluorophenol and pentachlorophenol, compounds whose toxic effects and persistence in the environment are well documented. The primary products of this dehalogenation reaction appear to be the corresponding tetrahalo-p-benzoquinones. Under the conditions used, the fluorinated phenol and its intermediate products are more susceptible to degradation than the corresponding chlorinated analogue and its products. The main degradation products of tetrachloro-p-benzoquinone and tetrafluoro-p- benzoquinone were identified as trichlorohydroxyp-benzoquinone and trifluorohydroxy-p-benzoquinone, respectively. This secondary conversion of tetrafluoro-p-benzoquinone and tetrachloro-p-benzoquinone was not mediated by MP8, but was driven by H2O2. Evidence is presented for a mechanism where H2O2 molecules and not hydroxide anions are the reactive nucleophilic species attacking the tetrahalo-p-benzoquinones. In addition to the formation of the trihalohydroxy-p-benzoquinones, the formation of adducts of the tetrahalo-p-benzoquinone products with ethanol, present in the incubation medium, was observed. The adduct from the reaction of tetrachloro-p- benzoquinone with ethanol was isolated and identified as trichloroethoxyquinone. Thus, the present paper describes a system in which the formation of tetrahalo-p-benzoquinone-type products by an oxidative heme- based catalyst could be unequivocally demonstrated.