Precipitation of enzyme-catalyzed phenol oxidative coupling products: Background ion and pH effects

The effects of solution pH and background ion types and concentrations on the precipitation of polymeric products generated in the catalytically facilitated oxidative coupling of phenol were investigated systematically. The coupling reactions mediated by horseradish peroxidase were carried out under a specific predetermined experimental condition. Acids, bases, and/or selected salts of ions having different valences were then added to the resulting product solutions to adjust pH and ionic conditions. Subsequent analyses of product distributions between dissolved and precipitated forms revealed that ionic conditions and pH significantly impact those distributions, and associated mechanisms are discussed. The findings reported will assist feasibility assessments and process optimization with respect to engineering applications of catalyzed oxidative coupling reactions for wastewater treatment and soil decontamination.