Chlorination increases the persistence of semiquinone free radicals derived from polychlorinated biphenyl hydroquinones and quinones

Yang Song, Garry R. Buettner, Sean Parkin, Brett A. Wagner, Larry W. Robertson, Hans Joachim Lehmler

Research output: Contribution to journalArticlepeer-review

65 Scopus citations

Abstract

(Chemical Equation Presented) Polychlorinated biphenyls (PCBs) comprise a group of persistent organic pollutants that differ significantly in their physicochemical properties, their persistence, and their biological activities. They can be metabolized via hydroxylated and dihydroxylated metabolites to PCB quinone intermediates. We have recently demonstrated that both dihydroxy PCBs and PCB quinones can form semiquinone radicals (SQ•-) in vitro. These semiquinone radicals are reactive intermediates that have been implicated in the toxicity of lower chlorinated PCB congeners. Here we describe the synthesis of selected PCB metabolites with differing degrees of chlorination on the oxygenated phenyl ring, e.g., 4,4′-dichloro-biphenyl-2,5-diol, 3,6,4′-trichloro-biphenyl-2,5-diol, 3,4,6,-trichloro-biphenyl-2,5-diol, and their corresponding quinones. In addition, two chlorinated o-hydroquinones were prepared, 6-chloro-biphenyl-3,4-diol and 6,4′-dichlorobiphenyl-3,4- diol. These PCB (hydro-)quinones readily react with oxygen or via comproportionation to yield the corresponding semiquinone free radicals, as detected by electron paramagnetic resonance spectroscopy (EPR alias ESR). The greater the number of chlorines on the (hydro-)quinone (oxygenated) ring, the higher the steady-state level of the resulting semiquinone radical at near neutral pH.

Original languageEnglish
Pages (from-to)8296-8304
Number of pages9
JournalJournal of Organic Chemistry
Volume73
Issue number21
DOIs
StatePublished - Nov 7 2008

ASJC Scopus subject areas

  • Organic Chemistry

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