title: Polarized XANES Monitors Femtosecond Structural Evolution of Photoexcited Vitamin B12.
abstract: Ultrafast, polarization-selective time-resolved X-ray absorption near-edge structure (XANES) was used to characterize the photochemistry of vitamin B12, 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-NImbond on a 110 fs time scale is followed by corrin ring relaxation on a 260 fs time scale. These observations expose features of the potential energy surfaces controlling cobalamin reactivity and deactivation.
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Miller
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.|Biophysics, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Aniruddha
authors.initials: A
authors.lastname: Deb
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Roberto
authors.initials: R
authors.lastname: Alonso-Mori
authors.affiliation: Department of Chemistry, University of Louisville , 2320 South Brook Street, Louisville, Kentucky 40292, United States.
authors.forename: Brady D
authors.initials: BD
authors.lastname: Garabato
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: James M
authors.initials: JM
authors.lastname: Glownia
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Laura M
authors.initials: LM
authors.lastname: Kiefer
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Jake
authors.initials: J
authors.lastname: Koralek
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Marcin
authors.initials: M
authors.lastname: Sikorski
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Kenneth G
authors.initials: KG
authors.lastname: Spears
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Theodore E
authors.initials: TE
authors.lastname: Wiley
authors.affiliation: Linac Coherent Light Source, SLAC National Accelerator Laboratory , 2575 Sand Hill Road, Menlo Park, California 94025, United States.
authors.forename: Diling
authors.initials: D
authors.lastname: Zhu
authors.affiliation: Department of Chemistry, University of Louisville , 2320 South Brook Street, Louisville, Kentucky 40292, United States.|Department of Food Sciences, Medical University of Gdansk , Al. Gen J. Hallera 107, 80-416 Gdansk, Poland.
authors.forename: Pawel M
authors.initials: PM
authors.lastname: Kozlowski
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.|Biophysics, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Kevin J
authors.identifier: 0000-0003-1152-4734
authors.initials: KJ
authors.lastname: Kubarych
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.|Biophysics, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: James E
authors.identifier: 0000-0003-0314-1274
authors.initials: JE
authors.lastname: Penner-Hahn
authors.affiliation: Department of Chemistry, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.|Department of Physics, University of Michigan , 450 Church Street, Ann Arbor, Michigan 48109-1040, United States.|Biophysics, University of Michigan , 930 N University Avenue, Ann Arbor, Michigan 48109-1055, United States.
authors.forename: Roseanne J
authors.identifier: 0000-0001-6758-0132
authors.initials: RJ
authors.lastname: Sension
mesh_terms: D015394:Molecular Structure; D055668:Photochemical Processes; D013997:Time Factors; D014805:Vitamin B 12 / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D014805:Vitamin B 12