A mechanistic study of peroxidase -catalyzed phenol coupling in water /soil /sediment systems.

This dissertation describes a systematic investigation of peroxidase-mediated phenol coupling reactions in the presence of soil/sediment materials. The goal of the work was to develop a mechanistic understanding of the influences of geological materials on enzymatic coupling reactions, and to formulate models and methods for predicting such influences. Extensive experiments of enzymatic coupling reactions were performed under strategically selected conditions in systems containing natural or model soil/sediment materials having distinctly different properties and chemical characteristics. It was revealed in the study that geosorbents influence peroxidase-mediated phenol coupling through one or both of two principal mechanisms; i.e., (i) mitigation of enzyme inactivation, and (ii) participation in cross-coupling reactions. Such influences were found to correlate with the chemical characteristics of the sorbent materials, and can be simulated well by the modeling approach formulated in the study. The dissolved organic and inorganic components of soil/water systems were found to have significant influences on phenol coupling reactions, particularly on the properties of the resultant products. Dissolved organic matter may react with phenolic substrates via cross-coupling reactions, thus being incorporated in the products and affecting their physicochemical and toxicological properties. Solution pH and inorganic ionic constituents were found to regulate the precipitation behavior of the polyphenol products resulting from phenol-coupling reactions, probably through general electrostatic effects and/or protonation/deprotonation phenomena. Co-precipitation of phenol and phenanthrene was observed in peroxidase-mediated reaction systems containing both chemicals. This co-precipitation appears to occur via both physical sorption of phenanthrene on the phenol coupling products and chemical binding of phenanthrene to the products of coupling reactions. Such a finding verifies the possibility of simultaneous treatment of phenolic contaminants and other more recalcitrant organic xenobiotics using enzymatic coupling reactions. The investigation described in this dissertation provides a mechanistic framework for understanding and predicting reaction behaviors and efficiencies of peroxidase-mediated phenol coupling processes in systems containing varied soil/sediment materials. The results have particular implications for potential engineering applications of enzymatic coupling reactions in soil/subsurface remediation practice.PhDApplied SciencesEnvironmental engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123406/2/3079463.pd