Solid state nuclear magnetic resonance with magic-angle spinning and dynamic nuclear polarization below 25 K
 

Solid state nuclear magnetic resonance with magic-angle spinning and dynamic nuclear polarization below 25 K


Available online 20 November 2012
Publication year: 2012
Source:Journal of Magnetic Resonance</br>
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We describe an apparatus for solid state nuclear magnetic resonance (NMR) with dynamic nuclear polarization (DNP) and magic-angle spinning (MAS) at 20-25 K and 9.4 Tesla. The MAS NMR probe uses helium to cool the sample space and nitrogen gas for MAS drive and bearings, as described earlier (Thurber et al., J. Magn. Reson. 2008) [1], but also includes a corrugated waveguide for transmission of microwaves from below the probe to the sample. With a 30 mW circularly polarized microwave source at 264 GHz, MAS at 6.8 kHz, and 21 K sample temperature, greater than 25-fold enhancements of cross-polarized 13C NMR signals are observed in spectra of frozen glycerol/water solutions containing the triradical dopant DOTOPA-TEMPO when microwaves are applied. As demonstrations, we present DNP-enhanced one-dimensional and two-dimensional 13C MAS NMR spectra of frozen solutions of uniformly 13C-labeled L-alanine and melittin, a 26-residue helical peptide that we have synthesized with four uniformly 13C-labeled amino acids.
Graphical abstract

http://origin-ars.els-cdn.com/conten...003461-fx1.jpg Highlights

? Probe for solid state NMR with dynamic nuclear polarization (DNP) and magic-angle spinning (MAS) at 20 K and 9.4 Tesla. ? Signal enhancement greater than 25 fold (microwaves on versus microwaves off) using 30 mW of microwaves. ? 2D 13C-13C spectra for 160 nanomoles of the 26 residue peptide melittin in frozen solution, taken in ~2½ hr.</br>
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Source: Journal of Magnetic Resonance