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Which Oxidation State Initiates Dehalogenation in the B12-Dependent Enzyme NpRdhA: Co-II, COI or Co-0?
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Number of Authors: 3
2015 (English)In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 12, 7350-7358 p.Article in journal (Refereed) Published
Abstract [en]

The quantum chemical cluster approach was used to elucidate the reaction mechanism of debromination catalyzed by the B12-dependent reductive dehalogenase NpRdliA. Various pathways, involving different oxidation states of the cobalt ion and different protonation states of the model, have been analyzed in order to find the most favorable one. We find that the reductive C Br cleavage takes place exclusively at the Co' state via a heterolytic pathway in the singlet state. Importantly, the C-H bond formation and the C Br bond cleavage proceeds via a concerted transition state, as opposed to the stepwise pathway suggested before. C Br cleavage at the Coll state has a very high barrier, and the reduction of Co' to Co is associated with a very negative potential; thus, reductive dehalogenation at Coll and Co can be safely ruled out. Examination of substrate with different halogen substitutions (F, Cl, Br, I) shows that the dehalogenation reactivity follows the order C I > C Br > C-C1 > C-F, and the barrier for defluorination is so high that NpRdhA cannot catalyze that reaction.

Place, publisher, year, edition, pages
2015. Vol. 5, no 12, 7350-7358 p.
Keyword [en]
density functional, reductive dehalogenation, reaction mechanism, enzyme catalysis, cobalamin
National Category
Organic Chemistry
URN: urn:nbn:se:su:diva-125659DOI: 10.1021/acscatal.5b01502ISI: 000366153300035OAI: diva2:895098
Available from: 2016-01-18 Created: 2016-01-15 Last updated: 2016-01-18Bibliographically approved

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Siegbahn, Per E. M.
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