Completing the Picture: Determination of 13C Hyperfine Coupling Constants of Flavin Semiquinone Radicals by Photochemically Induced Dynamic Nuclear Polarization Spectroscopy

Nils Pompe; Boris Illarionov; Markus Fischer; Adelbert Bacher; Stefan Weber

doi:10.1021/acs.jpclett.2c00919

Completing the Picture: Determination of ¹³C Hyperfine Coupling Constants of Flavin Semiquinone Radicals by Photochemically Induced Dynamic Nuclear Polarization Spectroscopy

J Phys Chem Lett. 2022 Jun 5:5160-5167. doi: 10.1021/acs.jpclett.2c00919. Online ahead of print.

Authors

Nils Pompe¹, Boris Illarionov², Markus Fischer², Adelbert Bacher³, Stefan Weber¹

Affiliations

¹ Institute of Physical Chemistry, University of Freiburg, 79104 Freiburg im Breisgau, Germany.
² Hamburg School of Food Science, University of Hamburg, 20146 Hamburg, Germany.
³ Department of Chemistry, Technical University of Munich, 85748 Garching, Germany.

PMID: 35658481
DOI: 10.1021/acs.jpclett.2c00919

Abstract

We investigate the electronic structure of flavin semiquinone radicals in terms of their ¹³C hyperfine coupling constants. Photochemically induced dynamic nuclear polarization (photo-CIDNP) spectroscopy was used to study both the neutral and anionic radical species of flavin mononucleotide (FMN) in bulk aqueous solution. Apart from universally ¹³C-labeled FMN, partially labeled isotopologues are used to increase sensitivity for nuclei exhibiting very small hyperfine couplings and to cope with spectral overlap. In addition, experimental findings are supported by quantum chemical calculations, and implications for the spin density distribution in free flavin radicals are discussed.