Ultrafast X-ray Absorption Spectroscopy Reveals Excited-State Dynamics of B12 Coenzymes Controlled by the Axial Base
Taewon Chung1, Taylor P McClain2, Roberto Alonso-Mori3
1Department of Chemistry, University of Michigan, 930 N University Avenue, Ann Arbor, Michigan 481091055, United States.
None:
Polarized time-resolved X-ray absorption spectroscopy at the Co K-edge is used to probe the excited-state dynamics and photolysis of base-off methylcobalamin and the excited-state structure of base-off adenosylcobalamin. For both molecules, the final excited-state minimum shows evidence for an expansion of the cavity around the Co ion by ca. 0.04 to 0.05 Å. The 5-coordinate base-off cob(II)alamin that is formed following photodissociation has a structure similar to that of the 5-coordinate base-on cob(II)alamin, with a ring expansion of 0.03 to 0.04 Å and a contraction of the lower axial bond length relative to that in the 6-coordinate ground state. These data provide insights into the role of the lower axial ligand in modulating the reactivity of B12 coenzymes.
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