Mechanism of Co-C photodissociation in adenosylcobalamin

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-D...

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Published in:Physical chemistry chemical physics : PCCP 2016-07, Vol.18 (28), p.19070-19082
Main Authors: Garabato, Brady D, Lodowski, Piotr, Jaworska, Maria, Kozlowski, Pawel M
Format: Article
Language:English
Subjects:
Bonding
Charge transfer
Cobalt - chemistry
Cobamides - chemistry
Elongation
Ligands
Metals - chemistry
Organometallic Compounds - chemistry
Pathways
Photodissociation
Photolysis
Quantum Theory
Time dependence
Vitamin B 12 - chemistry
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Summary: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.
ISSN:1463-9076
1463-9084
DOI:10.1039/c6cp02136k