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Characterization of Frequency-Chirped Dynamic Nuclear Polarization in Rotating Solids

preprint
submitted on 20.01.2020 and posted on 24.01.2020 by Patrick Judge, Erika L. Sesti, Nicholas Alaniva, Edward P. Saliba, Lauren Price, Chukun Gao, Thomas Halbritter, Snorri Th. Sigurdsson, George B. Kyei, Alexander B. Barnes
Continuous wave (CW) dynamic nuclear polarization (DNP) is used with magic angle spinning (MAS) to enhance the typically poor sensitivity of nuclear magnetic resonance (NMR) by orders of magnitude. In a recent publication we show that further enhancement is obtained by using a frequency-agile gyrotron to chirp incident microwave frequency through the electron resonance frequency during DNP transfer. Here we characterize the effect of chirped MAS DNP by investigating the sweep time, sweep width, center-frequency, and electron Rabi frequency of the chirps. We show the advantages of chirped DNP with a trityl nitroxide biradical, and a lack of improvement with chirped DNP using AMUPol, a nitroxide biradical. Frequency-chirped DNP on a model system of urea in a cryoprotecting matrix yields an enhancement of 142, 21% greater than that obtained with CW DNP. We then go beyond this model system and apply chirped DNP to intact human cells. In human Jurkat cells, frequency-chirped DNP improves enhancement by 24% over CW DNP. The characterization of the chirped DNP effect reveals instrument limitations on sweep time and sweep width, promising even greater increases in sensitivity with further technology development. These improvements in gyrotron technology, frequency-agile methods, and in cell applications are expected to play a significant role in the advancement of MAS DNP.

Funding

NIH Director's New Innovator Award

NSF CAREER Award

Camille Dreyfus Teacher-Scholar Award

Deutsche Forschungsgemeinschaft Postdoctoral Fewlloship

University of Iceland Research Fund

History

Email Address of Submitting Author

judgept@wustl.edu

Institution

Washington University in St. Louis

Country

United States

ORCID For Submitting Author

0000-0002-1745-5920

Declaration of Conflict of Interest

The authors declare the following competing financial interest(s): A.B.B. is the author of a patent related to this work filed by the Washington University in Saint Louis (WO2015175507A1).

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