Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy
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Author(s)
Gast, Peter
Soetbeer, Janne Marie
Walish, Joseph John
Zhao, Yanchuan
George, Christy
Yang, Chen
Swager, Timothy M
Griffin, Robert Guy
Mathies, Guinevere
Date Issued
September 2018
Journal
Physical Chemistry Chemical Physics
Publisher
Royal Society of Chemistry (RSC)
Citation
Soetbeer, Janne et al. “Conformation of Bis-Nitroxide Polarizing Agents by Multi-Frequency EPR Spectroscopy.” Physical Chemistry Chemical Physics 20, 39 (October 2018): 25506–25517 © 2018 Royal Society of Chemistry
Version
Final published version
Abstract
The chemical structure of polarizing agents critically determines the efficiency of dynamic nuclear polarization (DNP). For cross-effect DNP, biradicals are the polarizing agents of choice and the interaction and relative orientation of the two unpaired electrons should be optimal. Both parameters are affected by the molecular structure of the biradical in the frozen glassy matrix that is typically used for DNP/MAS NMR and likely differs from the structure observed with X-ray crystallography. We have determined the conformations of six bis-nitroxide polarizing agents, including the highly efficient AMUPol, in their DNP matrix with EPR spectroscopy at 9.7 GHz, 140 GHz, and 275 GHz. The multi-frequency approach in combination with an advanced fitting routine allows us to reliably extract the interaction and relative orientation of the nitroxide moieties. We compare the structures of six bis-nitroxides to their DNP performance at 500 MHz/330 GHz.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Francis Bitter Magnet Laboratory (Massachusetts Institute of Technology)
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Creative Commons Attribution 3.0 Unported license
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DOI of Published Version
https://doi.org/10.1039/c8cp05236k
