3 years ago

Mechanism of Cobalamin-Mediated Reductive Dehalogenation of Chloroethylenes

Mechanism of Cobalamin-Mediated Reductive Dehalogenation of Chloroethylenes
Shujing Ji, Kasper P. Kepp, Li Ji, Piotr Paneth, Chenchen Wang
Reductive dehalogenation involving cobalamin has been proved to be a promising strategy for decontamination of the polluted environment. However, cob(I)alamin can act both as a strong reductant and a powerful nucleophile, and thus, several competing dehalogenation pathways may be involved. This work uses experimentally calibrated density functional theory on a realistic cobalamin model to resolve controversies of cobalamin-mediated reduction of chloroethylenes by exploring mechanisms of electron transfer, nucleophilic substitution, and nucleophilic addition. The computational results provide molecular-level insight into the competing pathways for chloroethylenes reacting with cob(I)alamin: the computed ratios of inner-sphere to outer-sphere pathways for perchloroethylene and trichloroethylene are 17:1 and 3.5:1, respectively, in accord with the corresponding experimental ratios of >10:1 and >2.3:1, while the computed outer-sphere pathway for other less-chlorinated ethylenes is hampered by high barriers (>25 kcal/mol). Thus, a new mechanistic picture has been obtained in which the highly chlorinated ethylenes primarily react via an inner-sphere nucleophilic-substitution pathway, whereas the less-chlorinated ethylenes mainly react through an inner-sphere nucleophilic-addition pathway. Especially, the quantitative comparison of standard reduction potentials between the formed chlorinated-cobalamin and cob(II)alamin/cob(I)alamin couple can be used to distinguish whether the inner-sphere pathway can proceed or not, and linear free-energy relationships have been developed to predict the reductive dehalogenation reactivity within a given mechanism. Finally, we propose new dual-isotope analyses for distinguishing the various environmental dehalogenation mechanisms.

Publisher URL: http://dx.doi.org/10.1021/acscatal.7b00540

DOI: 10.1021/acscatal.7b00540

You might also like
Discover & Discuss Important Research

Keeping up-to-date with research can feel impossible, with papers being published faster than you'll ever be able to read them. That's where Researcher comes in: we're simplifying discovery and making important discussions happen. With over 19,000 sources, including peer-reviewed journals, preprints, blogs, universities, podcasts and Live events across 10 research areas, you'll never miss what's important to you. It's like social media, but better. Oh, and we should mention - it's free.

  • Download from Google Play
  • Download from App Store
  • Download from AppInChina

Researcher displays publicly available abstracts and doesn’t host any full article content. If the content is open access, we will direct clicks from the abstracts to the publisher website and display the PDF copy on our platform. Clicks to view the full text will be directed to the publisher website, where only users with subscriptions or access through their institution are able to view the full article.