Dynamic nuclear polarization (DNP) in solids

DNP Solid Shem

Schematic set-up for solid-state DNP and prototype installed by Bruker in 2009 at EPFL. Microwaves with a wave-length of 1.14 mm (ca. 5 W at 263.7 GHz) are generated by a gyrotron tube inserted into a 9.4 T magnet (A) and transmitted via the transmission line (B) to the MAS probe (D) in the NMR magnet (C). The sapphire rotors with an outer diameter of 3.2 mm are spun up to 16 kHz at temperatures near T = 100 K using three nitrogen gas flows for cooling, bearing and spinning (E) that are regulated by a heat exchanger (F) driven with gaseous and liquid nitrogen (G).

Pulse 1

Abstract

Currently, only gyrotrons can generate microwave fields that are sufficiently intense to saturate the EPR transitions, i.e., about 5 W in continuous mode. For NMR spectrometers operating at proton frequencies of 400, 600 or 800 MHz (4.9, 14 or 9.8 T), the microwave frequencies must be 263.7, 395.6, and 527.5 GHz, respectively. A sophisticated ‘corrugated’ low-loss transmission line guides the microwaves from the gyrotron to the sample that is spinning at rates on the order of 10 to 15 kHz in a specially designed MAS probe. A suitable set of heat exchangers generates three separately controlled jets of nitrogen to cool the sample, support the bearing, and drive the spinning of the rotor. Fig. 2 shows a schematic layout and actual implementation operating at 400 MHz in our laboratory at EPFL. A more sophisticated instrument operating at 800 MHz will be installed in our laboratory at ENS.

Related publications

  • Hall DA, Maus DC, Gerfen GJ, Inati SJ, Becerra LR, Dahlquist FW, Griffin RG (1997) Polarization-enhanced NMR spectroscopy of biomolecules in frozen solution. Science 276(5314):930–932
  • Solid-State Nitrogen-14 Nuclear Magnetic Resonance Enhanced by Dynamic Nuclear Polarization using a Gyrotron. V. Vitzthum, M. A. Caporini, and G. Bodenhausen, J. Magn. Reson. 205, 177-179 (2010).
  • Surface Enhanced NMR Spectroscopy by Dynamic Nuclear Polarization. A. Lesage, M. Lelli, D. Gajan, M. A. Caporini, V. Vitzthum, P. Miéville, J. Alauzun, A. Roussey, C. Thieuleux, A. Medhi, G. Bodenhausen, C. Copéret, and L. Emsley, J. Am. Chem. Soc. 132, 15459-15461 (2010) + supplement.
  • Lelli M, Gajan D, Lesage A, Caporini MA, Vitzthum V, Mieville P, Heroguel F, Rascon F, Roussey A, Thieuleux C, Boualleg M, Veyre L, Bodenhausen G, Coperet C, Emsley L (2011) Fast characterization of functionalized silica materials by silicon-29 surface-enhanced NMR spectroscopy using dynamic nuclear polarization. J Am Chem Soc 133(7):2104–2107
  • Vitzthum V, Mieville P, Carnevale D, Caporini MA, Gajan D, Coperet C, Lelli M, Zagdoun A, Rossini AJ, Lesage A, Emsley L, Bodenhausen G (2012) Dynamic nuclear polarization of quadrupolar nuclei using cross polarization from protons: surface-enhanced aluminium-27 NMR. Chem Commun 48(14):1988–1990
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