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Issue 12, 2017
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Efficient cross-effect dynamic nuclear polarization without depolarization in high-resolution MAS NMR

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Abstract

Dynamic nuclear polarization (DNP) has the potential to enhance the sensitivity of magic-angle spinning (MAS) NMR by many orders of magnitude and therefore to revolutionize atomic resolution structural analysis. Currently, the most widely used approach to DNP for studies of chemical, material, and biological systems involves the cross-effect (CE) mechanism, which relies on biradicals as polarizing agents. However, at high magnetic fields (≥5 T), the best biradicals used for CE MAS-DNP are still far from optimal, primarily because of the nuclear depolarization effects they induce. In the presence of bisnitroxide biradicals, magic-angle rotation results in a reverse CE that can deplete the initial proton Boltzmann polarization by more than a factor of 2. In this paper we show that these depolarization losses can be avoided by using a polarizing agent composed of a narrow-line trityl radical tethered to a broad-line TEMPO. Consequently, we show that a biocompatible trityl-nitroxide biradical, TEMTriPol-1, provides the highest MAS NMR sensitivity at ≥10 T, and its relative efficiency increases with the magnetic field strength. We use numerical simulations to explain the absence of depolarization for TEMTriPol-1 and its high efficiency, paving the way for the next generation of polarizing agents for DNP. We demonstrate the superior sensitivity enhancement using TEMTriPol-1 by recording the first solid-state 2D 13C–13C correlation spectrum at natural isotopic abundance at a magnetic field of 18.8 T.

Graphical abstract: Efficient cross-effect dynamic nuclear polarization without depolarization in high-resolution MAS NMR

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Publication details

The article was received on 16 May 2017, accepted on 01 Oct 2017 and first published on 02 Oct 2017


Article type: Edge Article
DOI: 10.1039/C7SC02199B
Citation: Chem. Sci., 2017,8, 8150-8163
  • Open access: Creative Commons BY-NC license
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    Efficient cross-effect dynamic nuclear polarization without depolarization in high-resolution MAS NMR

    F. Mentink-Vigier, G. Mathies, Y. Liu, A. Barra, M. A. Caporini, D. Lee, S. Hediger, R. G. Griffin and G. De Paëpe, Chem. Sci., 2017, 8, 8150
    DOI: 10.1039/C7SC02199B

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