Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy

Janne Soetbeer, Peter Gast, Joseph J. Walish, Yanchuan Zhao, Christy George, Chen Yang, Timothy M. Swager, Robert G. Griffin, Guinevere Mathies

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)25506-25517
Number of pages12
JournalPhysical Chemistry Chemical Physics
Issue number39
StatePublished - 2018

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry


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