Abstract
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.
Original language | English |
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Article number | 106702 |
Journal | Journal of Magnetic Resonance |
Volume | 313 |
DOIs | |
Publication status | Published - Apr 2020 |
Bibliographical note
Funding Information:The research reported in this publication was supported by an NIH Director’s New Innovator Award [grant number DP2GM119131 ], an NSF CAREER Award [grant number DBI-1553577 ], a Camille Dreyfus Teacher-Scholar Award, a Deutsche Forschungsgemeinschaft (DFG) Postdoctoral Fellowship [ 414196920 ], and the University of Iceland Research Fund. We also thank Faith Scott, Sarah Overall, Asif Equbal, and Songi Han for helpful discussions.
Publisher Copyright:
© 2020
Other keywords
- Dynamic nuclear polarization (DNP)
- Frequency-chirped DNP
- Gyrotron
- Magic angle spinning NMR
- Pulsed DNP