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Enzymatic synthesis of bromo- and chlorocarbazoles and elucidation of their structures by molecular modeling.
MedLine Citation:
PMID:  23757025     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
3-Chlorocarbazole, 3,6-dichlorocarbazole, dibromocarbazole, and 1,3,6,8-tetrabromocarbazole are emerging environmental contaminants which have been detected recently in water, sediment, and soil samples. However, their sources and occurrence have not been explained. Here, we report an enzymatic synthesis of bromo- and chlorocarbazoles by chloroperoxidase from Caldariomyces fumago in water. Density functional theory (DFT) method was used to predict the most stable products. Carbazole and chloroperoxidase were assayed in vitro in the presence of hydrogen peroxide, bromide, and chloride ions in different substrate ratio treatments against constant and varying enzyme concentrations. Halogenated carbazoles formed were identified by high-resolution gas chromatography coupled to mass spectrometry. In all treatments, bromination and chlorination took place, but the composition and concentration of compounds formed varied from one treatment to another. Mono-, di-, tri-, and tetra-substituted bromo- and chlorocarbazoles which include the reported environmental contaminants were synthesized. 3-Substituted and 3,6-substituted congeners were relatively higher in concentration. Enzyme concentration did not favor preferential formation of any of the compounds synthesized. However, their synthesis was influenced by halide concentration. Congeners with bromine and chlorine at position of C-3, C-3,6, C-1,3,6, and C-1,3,6,8 were calculated as the stable intermediate sigma complexes by DFT method. Regioselectivity in halogenation is discussed and hypothesis of the likely stable products in the environment explained. This study provides evidence that bromo- and chlorocarbazoles reported previously can be formed enzymatically in the environment, demonstrating the need to consider aromatic pollutants transformation and their potential toxicity enhancements in the management of water pollution and contaminated sites.
Authors:
John Mumbo; Dieter Lenoir; Bernhard Henkelmann; Karl-Werner Schramm
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-6-12
Journal Detail:
Title:  Environmental science and pollution research international     Volume:  -     ISSN:  1614-7499     ISO Abbreviation:  Environ Sci Pollut Res Int     Publication Date:  2013 Jun 
Date Detail:
Created Date:  2013-6-12     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9441769     Medline TA:  Environ Sci Pollut Res Int     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Helmholtz Zentrum München-German Research Center for Environmental Health (GmbH), Molecular EXposomics (MEX), Ingolstädter Landstraße 1, 85764, Neuherberg, Germany, john.mumbo@tum.de.
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