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Title: Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B 12

Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B 12, cyanocobalamin (CNCbl), in solution. Cobalamins are important biological cofactors involved in methyl transfer, radical rearrangement, and light-activated gene regulation, while also holding promise as light-activated agents for spatiotemporal controlled delivery of therapeutics. We introduce polarized femtosecond XANES, combined with UV–visible spectroscopy, to reveal sequential structural evolution of CNCbl in the excited electronic state. Femtosecond polarized XANES provides the crucial structural dynamics link between computed potential energy surfaces and optical transient absorption spectroscopy. Polarization selectivity can be used to uniquely identify electronic contributions and structural changes, even in isotropic samples when well-defined electronic transitions are excited. Our XANES measurements reveal that the structural changes upon photoexcitation occur mainly in the axial direction, where elongation of the axial Co–CN bond and Co–N Im bond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. In conclusion, these observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [2] ;  [1] ;  [2] ;  [2] ;  [1] ;  [1] ;  [2] ;  [4] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  3. Univ. of Louisville, Louisville, KY (United States)
  4. Univ. of Louisville, Louisville, KY (United States); Medical Univ. of Gdansk, Gdansk (Poland)
Publication Date:
Grant/Contract Number:
CHE 1150660; CHE 1300239; CHE 1464584; AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 5; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1353170