Solid effect in magic angle spinning dynamic nuclear polarization
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Griffin_Solid effect.pdf
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Author(s)
Smith, Albert A.
Corzilius, Bjorn
Griffin, Robert Guy
Date Issued
August 2012
Journal
The Journal of Chemical Physics
Publisher
American Institute of Physics (AIP)
Citation
Corzilius, Bjorn, Albert A. Smith, and Robert G. Griffin. “Solid effect in magic angle spinning dynamic nuclear polarization.” The Journal of Chemical Physics 137, no. 5 (2012): 054201. © 2012 American Institute of Physics
Version
Final published version
Abstract
For over five decades, the solid effect (SE) has been heavily utilized as a mechanism for performing dynamic nuclear polarization (DNP). Nevertheless, it has not found widespread application in contemporary, high magnetic field DNP experiments because SE enhancements display an ω[−2 over 0] field dependence. In particular, for nominally forbidden zero and double quantum SE transitions to be partially allowed, it is necessary for mixing of adjacent nuclear spin states to occur, and this leads to the observed field dependence. However, recently we have improved our instrumentation and report here an enhancement of ɛ = 91 obtained with the organic radical trityl (OX063) in magic angle spinning experiments performed at 5 T and 80 K. This is a factor of 6-7 higher than previous values in the literature under similar conditions. Because the solid effect depends strongly on the microwave field strength, we attribute this large enhancement to larger microwave field strengths inside the sample volume, achieved with more efficient coupling of the gyrotron to the sample chamber. In addition, we develop a theoretical model to explain the dependence of the buildup rate of enhanced nuclear polarization and the steady-state enhancement on the microwave power. Buildup times and enhancements were measured as a function of [superscript 1]H concentration for both trityl and Gd-DOTA. Comparison of the results indicates that for trityl the initial polarization step is the slower, rate-determining step. However, for Gd-DOTA the spread of nuclear polarization via homonuclear [superscript 1]H spin diffusion is rate-limiting. Finally, we discuss the applicability of the solid effect at fields > 5 T and the requirements to address the unfavorable field dependence of the solid effect.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Francis Bitter Magnet Laboratory (Massachusetts Institute of Technology)
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DOI of Published Version
https://doi.org/10.1063/1.4738761
