Frequency-chirped dynamic nuclear polarization with magic angle spinning using a frequency-agile gyrotron

Chukun Gao; Nicholas Alaniva; Edward P Saliba; Erika L Sesti; Patrick T Judge; Faith J Scott; Thomas Halbritter; Snorri Th Sigurdsson; Alexander B Barnes

doi:10.1016/j.jmr.2019.106586

Frequency-chirped dynamic nuclear polarization with magic angle spinning using a frequency-agile gyrotron

J Magn Reson. 2019 Nov:308:106586. doi: 10.1016/j.jmr.2019.106586. Epub 2019 Aug 29.

Authors

Chukun Gao¹, Nicholas Alaniva¹, Edward P Saliba¹, Erika L Sesti², Patrick T Judge³, Faith J Scott², Thomas Halbritter⁴, Snorri Th Sigurdsson⁴, Alexander B Barnes⁵

Affiliations

¹ Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Physical Chemistry, ETH-Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland.
² Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
³ Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Biochemistry, Biophysics & Structural Biology, Washington University in St. Louis, St. Louis, MO 63110, USA.
⁴ University of Iceland, Department of Chemistry, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland.
⁵ Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Physical Chemistry, ETH-Zurich, Vladimir-Prelog-Weg 2, 8093 Zurich, Switzerland. Electronic address: abarnes@ethz.ch.

PMID: 31525550
DOI: 10.1016/j.jmr.2019.106586

Abstract

We demonstrate that frequency-chirped dynamic nuclear polarization (DNP) with magic angle spinning (MAS) improves the enhancement of nuclear magnetic resonance (NMR) signal beyond that of continuous-wave (CW) DNP. Using a custom, frequency-agile gyrotron we implemented frequency-chirped DNP using the TEMTriPol-1 biradical, with MAS NMR at 7 T. Frequency-chirped microwaves yielded a DNP enhancement of 137, an increase of 19% compared to 115 recorded with CW. The chirps were 120 MHz-wide and centered over the trityl resonance, with 7 W microwave power incident on the sample (estimated 0.4 MHz electron spin Rabi frequency). We describe in detail the design and fabrication of the frequency-agile gyrotron used for frequency-chirped MAS DNP. Improvements to the interaction cavity and internal mode converter yielded efficient microwave generation and mode conversion, achieving >10 W output power over a 335 MHz bandwidth with >110 W peak power. Frequency-chirped DNP with MAS is expected to have a significant impact on the future of magnetic resonance.

Keywords: Dynamic nuclear polarization; Frequency-agile gyrotron; Frequency-chirped DNP; Frequency-chirped microwaves; Magic angle spinning; Nuclear magnetic resonance.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Electromagnetic Fields
Equipment Design
Magnetic Resonance Spectroscopy / instrumentation*
Magnetic Resonance Spectroscopy / methods
Microwaves

Grants and funding

DP2 GM119131/GM/NIGMS NIH HHS/United States