Methyl groups matter: Photo-CIDNP characterizations of the semiquinone radicals of FMN and demethylated FMN analogs

Nils Pompe; Jing Chen; Boris Illarionov; Sabrina Panter; Markus Fischer; Adelbert Bacher; Stefan Weber

doi:10.1063/1.5130557

Methyl groups matter: Photo-CIDNP characterizations of the semiquinone radicals of FMN and demethylated FMN analogs

J Chem Phys. 2019 Dec 21;151(23):235103. doi: 10.1063/1.5130557.

Authors

Nils Pompe¹, Jing Chen¹, Boris Illarionov², Sabrina Panter¹, Markus Fischer², Adelbert Bacher³, Stefan Weber¹

Affiliations

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

PMID: 31864274
DOI: 10.1063/1.5130557

Abstract

In this contribution, the relative hyperfine couplings are determined for the ¹H nuclei of the flavin mononucleotide (FMN) radical in an aqueous environment. In addition, three structural analogs with different methylation patterns are characterized and the influence of the substituents at the isoalloxazine moiety on the electronic structure of the radicals is explored. By exploiting nuclear hyperpolarization generated via the photo-CIDNP (chemically induced dynamic nuclear polarization) effect, it is possible to study the short-lived radical species generated by in situ light excitation. Experimental data are extracted by least-squares fitting and supported by quantum chemical calculations and published values from electron paramagnetic resonance and electron-nuclear double resonance. Furthermore, mechanistic details of the photoreaction of the investigated flavin analogs with l-tryptophan are derived from the photo-CIDNP spectra recorded at different pH values. Thereby, the neutral and anionic radicals of FMN and three structural analogs are, for the first time, characterized in terms of their electronic structure in an aqueous environment.