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Chlorine isotope effects from isotope ratio mass spectrometry suggest intramolecular C-Cl bond competition in Trichloroethene (TCE) reductive dehalogenation.
Molecules 19, 6450-6473 (2014)
Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE) dehalogenation was investigated. Selective biotransformation reactions (i) of tetrachloroethene (PCE) to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii) of TCE to cis-1,2-dichloroethene (cis-DCE) in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were -19.0‰ ± 0.9‰ (PCE) and -12.2‰ ± 1.0‰ (TCE) (95% confidence intervals). Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (-5.0‰ ± 0.1‰) and TCE (-3.6‰ ± 0.2‰). In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by -16.3‰ ± 1.4‰ (standard error)) than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of -2.4‰ ± 0.3‰ and the product chloride an isotope effect of -6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals). A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect). These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition). This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I) or single electron transfer as reductive dehalogenation mechanisms.
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Publication type
Article: Journal article
Document type
Scientific Article
Keywords
Reductive Dehalogenation ; Chlorinated Ethenes ; Trichloroethene ; Biodegradation ; Organohalide Respiration ; Dechlorination Mechanism ; Regioselectivity ; Vitamin B-12 ; Reductive Dehalogenase; Vinyl-chloride; Dce Isomers; Dechlorination; Tetrachloroethene; Transformation; Fractionation; Complexes; Cobalamin; Carbon; Iron
ISSN (print) / ISBN
1420-3049
e-ISSN
1420-3049
Journal
Molecules
Quellenangaben
Volume: 19,
Issue: 5,
Pages: 6450-6473
Publisher
MDPI
Publishing Place
Basel
Non-patent literature
Publications
Reviewing status
Peer reviewed
Institute(s)
Institute of Groundwater Ecology (IGOE)