3 research outputs found
<sup>1</sup>H Dynamic Nuclear Polarization Based on an Endogenous Radical
No full textWe 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
(Ï„<sub>B</sub>) 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 <i>T</i><sub>1n</sub> and Ï„<sub>B</sub> 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 Ï„<sub>B</sub> of TOTAPOL-based DNP in nonglassy samples was not accompanied
by a similarly important long <i>T</i><sub>1n</sub>, 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
Rigid Orthogonal Bis-TEMPO Biradicals with Improved Solubility for Dynamic Nuclear Polarization
No full textThe synthesis and characterization of oxidized bis-thioketal-trispiro
dinitroxide biradicals that orient the nitroxides in a rigid, approximately
orthogonal geometry are reported. The biradicals show better performance
as polarizing agents in dynamic nuclear polarization (DNP) NMR experiments
as compared to biradicals lacking the constrained geometry. In addition,
the biradicals display improved solubility in aqueous media due to
the presence of polar sulfoxides. The results suggest that the orientation
of the radicals is not dramatically affected by the oxidation state
of the sulfur atoms in the biradical, and we conclude that a biradical
polarizing agent containing a mixture of oxidation states can be used
for improved solubility without a loss in performance
Rigid Orthogonal Bis-TEMPO Biradicals with Improved Solubility for Dynamic Nuclear Polarization
No full textThe synthesis and characterization of oxidized bis-thioketal-trispiro
dinitroxide biradicals that orient the nitroxides in a rigid, approximately
orthogonal geometry are reported. The biradicals show better performance
as polarizing agents in dynamic nuclear polarization (DNP) NMR experiments
as compared to biradicals lacking the constrained geometry. In addition,
the biradicals display improved solubility in aqueous media due to
the presence of polar sulfoxides. The results suggest that the orientation
of the radicals is not dramatically affected by the oxidation state
of the sulfur atoms in the biradical, and we conclude that a biradical
polarizing agent containing a mixture of oxidation states can be used
for improved solubility without a loss in performance
