ROLE OF ABIOTIC AND BIOTIC CATALYSTS IN THE TRANSFORMATION OF PHENOLIC-COMPOUNDS THROUGH OXIDATIVE COUPLING REACTIONS

Abiotic (various clays and clay minerals) and biotic (enzymes) agents were compared for their ability to oxidize phenolic compounds by measu ring O2 uptake and analyzing substrate disappearance by high-performan ce liquid chromatography (HPLC). Both abiotic and biotic agents behave d similarly in their capacity to oxidize different phenolic compounds. 2,6-Dimethoxyphenol was transformed in both abiotically and bioticall y catalyzed reactions, but O2 uptake was demonstrated only in enzyme c atalyzed reactions (as shown by chromatographic analysis). Birnessite catalyzed the transformation of 2,6-dimethoxyphenol, but O2 uptake was detected only in reactions containing low concentrations of birnessit e (3-800 mug ml-1) in water and not at all in buffer. These results su ggest that in enzymatically-catalyzed reactions O2 functions as an ele ctron acceptor, whereas in birnessite catalyzed reactions, manganese o xide functions as the electron acceptor. Furthermore, both laccase and tyrosinase continued oxidizing catechol after repeated additions of t he chemical, while birnessite, at the concentrations used in our exper iments, lost its oxidizing activity after the first addition of catech ol. Enzymes as homogeneous catalysts appeared to be more effective oxi dative agents as compared to the abiotic agents as heterogeneous catal ysts, but because of their abundance in nature, abiotic agents still s erve a significant role in the transformation of phenolic compounds.