Dynamic nuclear polarization (DNP) is a methodology to increase the sensitivity of nuclear magnetic resonance (NMR) spectroscopy. It relies on the transfer of the electron spin polarization from a radical to coupled nuclear spins, driven by microwave excitation resonant with the electron spin transitions. In this work we explore the potential of pulsed multi-frequency microwave excitation in liquids. Here, the relevant DNP mechanism is the Overhauser effect. The experiments were performed with TEMPOL radicals in aqueous solution at room temperature using a Q-band frequency (1.2 T) electron paramagnetic resonance (EPR) spectrometer combined with a Minispec NMR spectrometer. A fast arbitrary waveform generator (AWG) enabled the generation of multi-frequency pulses used to either sequentially or simultaneously excite all three 14N-hyperfine lines of the nitroxide radical. The multi-frequency excitation resulted in a doubling of the observed DNP enhancements compared to single-frequency microwave excitation. Q-band free induction decay (FID) signals of TEMPOL were measured as a function of the excitation pulse length allowing the efficiency of the electron spin manipulation by the microwave pulses to be extracted. Based on this knowledge we could quantitatively model our pulsed DNP enhancements at 1.2 T by numerical solution of the Bloch equations, including electron spin relaxation and experimental parameters. Our results are in good agreement with theoretical predictions. Whereas for a narrow and homogeneous single EPR line continuous wave excitation leads to more efficient DNP enhancements compared to pulsed excitation for the same amount of averaged microwave power. The situation is different for radicals with several hyperfine lines or in the presence of inhomogeneous line broadening. In such cases pulsed single/multi-frequency excitation can lead to larger DNP enhancements.
Multi-Frequency Pulsed Overhauser DNP at 1.2 Tesla
From The DNP-NMR Blog:
Multi-Frequency Pulsed Overhauser DNP at 1.2 Tesla
Schöps, P., E. Spindler Philipp, and F. Prisner Thomas, Multi-Frequency Pulsed Overhauser DNP at 1.2 Tesla, in Z. Phys. Chem. 2017. p. 561.
https://www.degruyter.com/view/j/zpch.2017.231.issue-3/zpch-2016-0844/zpch-2016-0844.xml
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05-26-2018 01:57 AM
Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization #DNPNMR
From The DNP-NMR Blog:
Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization #DNPNMR
Scott, F.J., et al., Frequency-agile gyrotron for electron decoupling and pulsed dynamic nuclear polarization. J Magn Reson, 2018. 289: p. 45-54.
https://www.ncbi.nlm.nih.gov/pubmed/29471275
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04-27-2018 10:26 PM
Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature 13C ODNP at Moderately Low Fields and Natural Abundance #DNPNMR
From The DNP-NMR Blog:
Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature 13C ODNP at Moderately Low Fields and Natural Abundance #DNPNMR
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Dey, A., A. Banerjee, and N. Chandrakumar, Transferred Overhauser DNP: A Fast, Efficient Approach for Room Temperature 13C ODNP at Moderately Low Fields and Natural Abundance. The Journal of Physical Chemistry B, 2017. 121(29): p. 7156-7162.
https://www.ncbi.nlm.nih.gov/pubmed/28658577
A tailored multi-frequency EPR approach to accurately determine the magnetic resonance parameters of dynamic nuclear polarization agents: application to AMUPol #DNPNMR
From The DNP-NMR Blog:
A tailored multi-frequency EPR approach to accurately determine the magnetic resonance parameters of dynamic nuclear polarization agents: application to AMUPol #DNPNMR
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This is a very nice article illustrating the importance of understanding the EPR parameters of a polarizing agent used in DNP-NMR spectroscopy. Here the 9, 95 and 275 GHz EPR spectroscopy is used to characterize AMUPol and predict its performance in high-field DNP.
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06-05-2017 03:59 PM
Field-frequency locked X-band Overhauser effect spectrometer #DNPNMR
From The DNP-NMR Blog:
Field-frequency locked X-band Overhauser effect spectrometer #DNPNMR
This article is already a bit older. However, it nicely illustrates that DNP, specifically ODNP has been around for a while already, and gives some interesting specifics on the instrumentation that are still valid today.
Chandrakumar, N. and P.T. Narasimhan, Field-frequency locked X-band Overhauser effect spectrometer. Review of Scientific Instruments, 1981. 52(4): p. 533-538.
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04-11-2017 04:25 AM
Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence #DNPNMR
From The DNP-NMR Blog:
Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence #DNPNMR
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Nasibulov, E.A., et al., Theoretical treatment of pulsed Overhauser dynamic nuclear polarization: Consideration of a general periodic pulse sequence. JETP Letters, 2016. 103(9): p. 582-587.
http://dx.doi.org/10.1134/S0021364016090113
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02-22-2017 06:28 PM
Nonselective excitation of pulsed ELDOR using multi-frequency microwaves
Nonselective excitation of pulsed ELDOR using multi-frequency microwaves
Publication year: 2011
Source: Journal of Magnetic Resonance, Available online 17 September 2011</br>
Yuki*Asada, Risa*Mutoh, Masahiro*Ishiura, Hiroyuki*Mino</br>
The use of a polychromatic microwave pulse to expand the pumping bandwidth in pulsed electron-electron double resonance (PELDOR) was investigated. The pumping pulse was applied in resonance with the broad (~100 mT) electron paramagnetic resonance (EPR) signal of the manganese cluster of photosystem II in the S2state. The observation pulses were in...
Multi-Frequency Pulsed Overhauser DNP at 1.2 Tesla #DNPNMR #ODNP
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