Oxidative 4-dechlorination of 2,4,6-trichlorophenol catalyzed by horseradish peroxidase

The well-known and easily available horseradish peroxidase (HRP) catalyzes the H2O2-dependent oxidative 4-dechlorination of the pollutant 2,4,6-trichl orophenol, which is recalcitrant to many organisms except those producing l igninases. UV-visible spectroscopy and gas chromatography-mass spectrometry identified the oxidized reaction product as 2,6-dichloro-1,4-benzoquinone. NMR and IR spectroscopic data further supported the above characterization . Experimental evidence for the elimination of HCl from the substrate was a cquired by detecting the decrease in pH of the reaction mixture, and by obs erving the presence of the beta-chlorocyclopentadicnone cation fragment in the mass spectrum of 2,6-dichloro-1,4-benzoquinone. Consequently, nucleophi lic attack by water on the 2,4,6-trichlorocyclohexadienone cation was propo sed to give the final product. Our results indicate an oxidative dechlorina tion pathway catalyzed by HRP for 2,3,6-trichlorophenol, similar to that by extracellular lignin peroxidases. The relative catalytic efficiency of HRP seems higher than that of lignin peroxidases. The HRP-H2O2 catalytic syste m could be utilized in the degradation of polychlorinated phenols for indus trial and biotechnological purposes.