Dynamic nuclear polarization at 700MHz/460GHz
Author(s)
Herzfeld, Judith; Barnes, Alexander; Markhasin, Evgeny; Daviso, Eugenio; Michaelis, Vladimir K.; Nanni, Emilio Alessandro; Jawla, Sudheer K.; Mena, Elijah L.; Thakkar, Ajay V; Temkin, Richard J; Griffin, Robert Guy; DeRocher, Ronald; Woskov, Paul P.; ... Show more Show less
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We describe the design and implementation of the instrumentation required to perform DNP-NMR at higher field strengths than previously demonstrated, and report the first magic-angle spinning (MAS) DNP-NMR experiments performed at ¹H/e⁻ frequencies of 700 MHz/460 GHz. The extension of DNP-NMR to 16.4 T has required the development of probe technology, cryogenics, gyrotrons, and microwave transmission lines. The probe contains a 460 GHz microwave channel, with corrugated waveguide, tapers, and miter-bends that couple microwave power to the sample. Experimental efficiency is increased by a cryogenic exchange system for 3.2 mm rotors within the 89 mm bore. Sample temperatures ⩽85 K, resulting in improved DNP enhancements, are achieved by a novel heat exchanger design, stainless steel and brass vacuum jacketed transfer lines, and a bronze probe dewar. In addition, the heat exchanger is preceded with a nitrogen drying and generation system in series with a pre-cooling refrigerator. This reduces liquid nitrogen usage from >700 l per day to <200 l per day and allows for continuous (>7 days) cryogenic spinning without detrimental frost or ice formation. Initial enhancements, ε = −40, and a strong microwave power dependence suggests the possibility for considerable improvement. Finally, two-dimensional spectra of a model system demonstrate that the higher field provides excellent resolution, even in a glassy, cryoprotecting matrix.
Date issued
2012-08Department
Massachusetts Institute of Technology. Plasma Science and Fusion Center; Francis Bitter Magnet Laboratory (Massachusetts Institute of Technology)Journal
Journal of Magnetic Resonance
Publisher
Elsevier
Citation
Barnes, Alexander B.; Markhasin, Evgeny; Daviso, Eugenio; Michaelis, Vladimir K.; Nanni, Emilio A.; Jawla, Sudheer K. and Mena, Elijah L. et al. “Dynamic Nuclear Polarization at 700MHz/460GHz.” Journal of Magnetic Resonance 224 (November 2012): 1–7 © 2012 Elsevier Inc
Version: Author's final manuscript
ISSN
1090-7807
1096-0856