Chlorinated Ethene Reactivity with Vitamin B12 Is Governed by Cobalamin Chloroethylcarbanions as Crossroads of Competing Pathways
Open access
Datum
2018-04-06Typ
- Journal Article
Abstract
Chlorinated ethenes are toxic groundwater contaminants. Although they can be dechlorinated by microorganisms, reductive dehalogenases, and their corrinoid cofactor, biochemical reaction mechanisms remain unsolved. This study uncovers a mechanistic shift revealed by contrasting compound-specific carbon (ε13C) and chlorine (ε37Cl) isotope effects between perchloroethene, PCE (ε37Cl = −4.0‰) and cis-dichloroethene, cis-DCE (ε37Cl = −1.5‰), and a pH-dependent shift for trichloroethene, TCE (from ε37Cl = −5.2‰ at pH 12 to ε37Cl = −1.2‰ at pH 5). Different pathways are supported also by pH-dependent reaction rates, TCE product distribution, and hydrogen isotope effects. Mass balance deficits revealed reversible and irreversible cobalamin-substrate association, whereas high-resolution mass spectrometry narrowed down possible structures to chloroalkyl and chlorovinyl cobalamin complexes. Combined experimental evidence is inconsistent with initial electron transfer or alkyl or vinyl complexes as shared intermediates of both pathways. In contrast, it supports cobalamin chlorocarbanions as key intermediates from which Cl– elimination produces vinyl complexes (explaining rates and products of TCE at high pH), whereas protonation generates less reactive alkyl complexes (explaining rates and products of TCE at low pH). Multielement isotope effect analysis holds promise to identify these competing mechanisms also in real dehalogenases, microorganisms, and even contaminated aquifers. Mehr anzeigen
Persistenter Link
https://doi.org/10.3929/ethz-b-000258198Publikationsstatus
publishedExterne Links
Zeitschrift / Serie
ACS CatalysisBand
Seiten / Artikelnummer
Verlag
American Chemical SocietyThema
outer-sphere single-electron transfer; reductive dehalogenation; kinetic isotope effect; groundwater contamination; chlorinated ethenes; trichloroethene; mechanistic study; cobalaminOrganisationseinheit
03850 - McNeill, Kristopher / McNeill, Kristopher