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Issue 39, 2018
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Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy

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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.

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

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Publication details

The article was received on 16 Aug 2018, accepted on 24 Sep 2018 and first published on 24 Sep 2018


Article type: Paper
DOI: 10.1039/C8CP05236K
Citation: Phys. Chem. Chem. Phys., 2018,20, 25506-25517
  • Open access: Creative Commons BY license
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    Conformation of bis-nitroxide polarizing agents by multi-frequency EPR spectroscopy

    J. Soetbeer, P. Gast, J. J. Walish, Y. Zhao, C. George, C. Yang, T. M. Swager, R. G. Griffin and G. Mathies, Phys. Chem. Chem. Phys., 2018, 20, 25506
    DOI: 10.1039/C8CP05236K

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