1H dynamic nuclear polarization based on an endogenous radical

Thorsten Maly, Dongtao Cui, Robert G. Griffin, Anne Frances Miller

Research output: Contribution to journalArticlepeer-review

52 Scopus citations

Abstract

We demonstrate a 15-fold enhancement of solid-state NMR signals via dynamic nuclear polarization (DNP) based on a stable, naturally occurring radical in a protein: the flavin mononucleotide (FMN) semiquinone of flavodoxin. The line width of flavodoxin's EPR signal suggests that the dominant DNP mechanism is the solid effect, consistent with the field-dependent DNP enhancement profile. The magnitude of the enhancement as well as the bulk-polarization build-up time constant (τB) with which it develops are dependent on the isotopic composition of the protein. Deuteration of the protein to 85% increased the nuclear longitudinal relaxation time T1n and τB by factors of five and seven, respectively. Slowed dissipation of polarization can explain the 2-fold higher maximal enhancement than that obtained in proteated protein, based on the endogenous semiquinone. In contrast, the long τB of TOTAPOL-based DNP in nonglassy samples was not accompanied by a similarly important long T1n, and in this case the enhancement was greatly reduced. The low concentrations of radicals occurring naturally in biological systems limit the magnitude of DNP enhancement that is attainable by this means. However, our enhancement factors of up to 15 can nonetheless make an important difference to the feasibility of applying solid-state NMR to biochemical systems. We speculate that DNP based on endogenous radicals may facilitate MAS NMR characterization of biochemical complexes and even organelles, and could also serve as a source of additional structural and physiological information.

Original languageEnglish
Pages (from-to)7055-7065
Number of pages11
JournalJournal of Physical Chemistry B
Volume116
Issue number24
DOIs
StatePublished - Jun 21 2012

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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