title: Formation of Halogenated Polyaromatic Compounds by Laccase Catalyzed Transformation of Halophenols.
abstract: Laccases are a type of extracellular enzyme produced by fungi, bacteria, and plants. Laccase can catalyze one-electron oxidation of a variety of phenolic compounds using molecular oxygen as the electron acceptor. In this study, transformation of halophenols (XPs) in laccase-catalyzed oxidation processes was explored. We first examined the intrinsic reaction kinetics and found that the transformation of XPs appeared first order to the concentrations of both XPs and laccase. A numerical model was developed to describe the role of humic acid (HA) in this process. It was demonstrated that HA could reverse the oxidation of XPs by acting as the inner filtrator of XP radical intermediates formed upon reactions between the substrates and laccase. The extent of such reversion was proportional to HA concentration. MS analysis in combination with quantum chemistry computation suggested that coupling products were generated. XPs coupled to each via C-C or C-O-C pathways, generating hydroxyl polyhalogenated biphenyl ethers (OH-PCDEs) and hydroxyl polyhalogenated biphenyls, respectively. Many of these polyhalogenated products are known to be hazardous to the ecosystem and human health, but they are not synthetic chemicals. This study shed light on their genesis in the environmental media.
authors.affiliation: †College of Resources and Environmental Science, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Junhe
authors.initials: J
authors.lastname: Lu
authors.affiliation: †College of Resources and Environmental Science, Nanjing Agricultural University, Nanjing 210095, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Shao
authors.affiliation: ‡School of Environment, Nanjing University, Nanjing 210093, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.affiliation: ‡School of Environment, Nanjing University, Nanjing 210093, China.
authors.forename: Zunyao
authors.initials: Z
authors.lastname: Wang
authors.affiliation: §Department of Crop and Soil Sciences, University of Georgia, Griffin, 30223, United States.
authors.forename: Qingguo
authors.initials: Q
authors.lastname: Huang
mesh_terms: D055162:Biocatalysis; D002851:Chromatography, High Pressure Liquid; D054879:Halogenation; D006812:Humic Substances / Q000032:analysis; D006841:Hydrocarbons, Aromatic / Q000378:metabolism*; D006846:Hydrocarbons, Halogenated / Q000378:metabolism*; D007700:Kinetics; D042845:Laccase / Q000378:metabolism*; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010636:Phenols / Q000378:metabolism*; D055454:Trametes / Q000201:enzymology
chemical_list: D006812:Humic Substances; D006841:Hydrocarbons, Aromatic; D006846:Hydrocarbons, Halogenated; D010636:Phenols; D042845:Laccase