Mechanism of Co–C photodissociation in adenosylcobalamin (original) (raw)
* Corresponding authors
a Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40202, USA
E-mail: pawel@louisville.edu
Fax: +502 852-8149
Tel: +502 852-6609
b Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
c Department of Food Sciences, Medical University of Gdansk, Al. Gen. J. Hallera 107, 80-416 Gdansk, Poland
Abstract
A mechanism of Co–C bond photodissociation in the base-on form of adenosylcobalamin (AdoCbl) was investigated by time-dependent density functional theory (TD-DFT). The key mechanistic step involves singlet radical pair (RP) generation from the first electronically excited state (S1). To connect TD-DFT calculations with ultra-fast excited state dynamics, the potential energy surface (PES) of the S1 state was constructed using Co–C and Co–NIm axial coordinates. The S1 PES can be characterized by two minima separated by a seam resulting from the crossing of two surfaces, of metal-to-ligand charge transfer (MLCT) character near the minimum, and a shallow ligand field (LF) surface at elongated axial bond distances. Only one possible pathway for photolysis (path A) was identified based on energetic grounds. This pathway is characterized by the first elongation of the Co–C bond, followed by photolysis from an LF state where the axial base is partially detached. A new perspective on the photolysis of AdoCbl is then gained by connecting TD-DFT results with available experimental observations.
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Article information
DOI
https://doi.org/10.1039/C6CP02136K
Article type
Paper
Submitted
31 Mar 2016
Accepted
14 Jun 2016
First published
15 Jun 2016
Download Citation
Phys. Chem. Chem. Phys., 2016,18, 19070-19082
Permissions
Mechanism of Co–C photodissociation in adenosylcobalamin
B. D. Garabato, P. Lodowski, M. Jaworska and P. M. Kozlowski,Phys. Chem. Chem. Phys., 2016, 18, 19070DOI: 10.1039/C6CP02136K
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