2 research outputs found
Dynamic Nuclear Polarization of Oxygen-17
Oxygen-17-detected DNP NMR of a water/glycerol glass
enabled an
80-fold enhancement of signal intensity at 82 K, using the biradical
TOTAPOL. The >6000-fold savings in acquisition time enable <sup>17</sup>O–<sup>1</sup>H distance measurements and heteronuclear
correlation
experiments. These experiments are the initial demonstration of the
feasibility of DNP NMR on quadrupolar <sup>17</sup>O
Peptide and Protein Dynamics and Low-Temperature/DNP Magic Angle Spinning NMR
In DNP MAS NMR experiments
at ∼80–110 K, the structurally
important −<sup>13</sup>CH<sub>3</sub> and −<sup>15</sup>NH<sub>3</sub><sup>+</sup> signals in MAS spectra of biological samples
disappear due to the interference of the molecular motions with the <sup>1</sup>H decoupling. Here we investigate the effect of these dynamic
processes on the NMR line shapes and signal intensities in several
typical systems: (1) microcrystalline APG, (2) membrane protein bR,
(3) amyloid fibrils PI3-SH3, (4) monomeric alanine-CD<sub>3</sub>,
and (5) the protonated and deuterated dipeptide N-Ac-VL over 78–300
K. In APG, the three-site hopping of the Ala-C<sub>β</sub> peak
disappears completely at 112 K, concomitant with the attenuation of
CP signals from other <sup>13</sup>C’s and <sup>15</sup>N’s.
Similarly, the <sup>15</sup>N signal from Ala-NH<sub>3</sub><sup>+</sup> disappears at ∼173 K, concurrent with the attenuation in
CP experiments of other <sup>15</sup>N’s as well as <sup>13</sup>C’s. In bR and PI3-SH3, the methyl groups are attenuated at
∼95 K, while all other <sup>13</sup>C’s remain unaffected.
However, both systems exhibit substantial losses of intensity at ∼243
K. Finally, with spectra of Ala and N-Ac-VL, we show that it is possible
to extract site specific dynamic data from the temperature dependence
of the intensity losses. Furthermore, <sup>2</sup>H labeling can assist
with recovering the spectral intensity. Thus, our study provides insight
into the dynamic behavior of biological systems over a wide range
of temperatures, and serves as a guide to optimizing the sensitivity
and resolution of structural data in low temperature DNP MAS NMR spectra