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Dynamic nuclear polarization enhanced NMR at 187 GHz/284 MHz using an extended interaction klystron amplifier
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Kemp, Thomas F., Dannatt, Hugh R., Barrow, Nathan S., Watts, Anthony, Brown, Steven P., Newton, Mark E. and Dupree, Ray (2016) Dynamic nuclear polarization enhanced NMR at 187 GHz/284 MHz using an extended interaction klystron amplifier. Journal of Magnetic Resonance, 265 . pp. 77-82. doi:10.1016/j.jmr.2016.01.021 ISSN 1090-7807.
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Official URL: http://dx.doi.org/10.1016/j.jmr.2016.01.021
Abstract
A Dynamic Nuclear Polarisation (DNP) enhanced solid-state Magic Angle Spinning (MAS) NMR spectrometer which uses a 187 GHz (corresponding to 1H NMR frequency of 284 MHz) Extended Interaction Klystron (EIK) amplifier as the microwave source is briefly described. Its performance is demonstrated for a biomolecule (bacteriorhodopsin), a pharmaceutical, and surface functionalised silica. The EIK is very compact and easily incorporated into an existing spectrometer. The bandwidth of the amplifier is sufficient that it obviates the need for a sweepable magnetic field, once set, for all commonly used radicals.
The variable power (CW or pulsed) output from the EIK is transmitted to the DNP-NMR probe using a quasi-optic system with a high power isolator and a corrugated waveguide which feeds the microwaves into the DNP-NMR probe. Curved mirrors inside the probe project the microwaves down the axis of the MAS rotor, giving a very efficient system such that maximum DNP enhancement is achieved with less than 3 W output from the microwave source. The DNP-NMR probe operates with a sample temperature down to 90 K whilst spinning at 8 kHz. Significant enhancements, in excess of 100 for bacteriorhodopsin in purple membrane (bR in PM), are shown along with spectra which are enhanced by ≈25 with respect to room temperature, for both the pharmaceutical furosemide and surface functionalised silica. These enhancements allow hitherto prohibitively time consuming experiments to be undertaken. The power at which the DNP enhancement in bR in PM saturates does not change significantly between 90 K and 170 K even though the enhancement drops by a factor of ≈11. As the DNP build up time decreases by a factor 3 over this temperature range, the reduction in T1n is presumably a significant contribution to the drop in enhancement.
Item Type: | Journal Article | ||||||||||
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Subjects: | Q Science > QC Physics | ||||||||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||||
Library of Congress Subject Headings (LCSH): | Klystrons, Nuclear magnetic resonance | ||||||||||
Journal or Publication Title: | Journal of Magnetic Resonance | ||||||||||
Publisher: | Academic Press | ||||||||||
ISSN: | 1090-7807 | ||||||||||
Official Date: | April 2016 | ||||||||||
Dates: |
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Volume: | 265 | ||||||||||
Number of Pages: | 6 | ||||||||||
Page Range: | pp. 77-82 | ||||||||||
DOI: | 10.1016/j.jmr.2016.01.021 | ||||||||||
Status: | Peer Reviewed | ||||||||||
Publication Status: | Published | ||||||||||
Access rights to Published version: | Restricted or Subscription Access | ||||||||||
Date of first compliant deposit: | 9 February 2016 | ||||||||||
Date of first compliant Open Access: | 9 February 2016 | ||||||||||
RIOXX Funder/Project Grant: |
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