title: Solid state nuclear magnetic resonance with magic-angle spinning and dynamic nuclear polarization below 25 K.
abstract: 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, 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 (13)C 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 (13)C MAS NMR spectra of frozen solutions of uniformly (13)C-labeled l-alanine and melittin, a 26-residue helical peptide that we have synthesized with four uniformly (13)C-labeled amino acids.
authors.affiliation: Laboratory of Chemical Physics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0520, United States. thurberk@niddk.nih.gov
authors.forename: Kent R
authors.initials: KR
authors.lastname: Thurber
authors.forename: Alexey
authors.initials: A
authors.lastname: Potapov
authors.forename: Wai-Ming
authors.initials: WM
authors.lastname: Yau
authors.forename: Robert
authors.initials: R
authors.lastname: Tycko
mesh_terms: D000409:Alanine / Q000737:chemistry; D001514:Bee Venoms / Q000737:chemistry; D001966:Bromine; D007554:Isotopes; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008555:Melitten / Q000737:chemistry; D008872:Microwaves; D013696:Temperature
chemical_list: D001514:Bee Venoms; D007554:Isotopes; D008555:Melitten; D000409:Alanine; D001966:Bromine