18. ¹⁹F Magic Angle Spinning Dynamic Nuclear Polarization Enhanced NMR Spectroscopy
    Viger-Gravel, J.; Avalos, C. E.; Kubicki, D. J.; Gajan, D.; Lelli, M.; Ouari, O.; Lesage, A.; Emsley, L.
    Angew. Chem. Int. Ed. 2019, 58, 7249-7253

The introduction of high-frequency, high-power microwave sources, tailored biradicals, and low-temperature magic angle spinning (MAS) probes has led to a rapid development of hyperpolarization strategies for solids and frozen solutions, leading to large gains in NMR sensitivity. Here, we introduce a protocol for efficient hyperpolarization of ¹⁹F nuclei in MAS DNP enhanced NMR spectroscopy. We identified trifluoroethanol-d ₃ as a versatile glassy matrix and show that 12?mm AMUPol (with microcrystalline KBr) provides direct ¹⁹F DNP enhancements of over 100 at 9.4?T. We applied this protocol to obtain DNP-enhanced ¹⁹F and ¹⁹F–¹³C cross-polarization (CP) spectra for an active pharmaceutical ingredient and a fluorinated mesostructured hybrid material, using incipient wetness impregnation, with enhancements of approximately 25 and 10 in the bulk solid, respectively. This strategy is a general and straightforward method for obtaining enhanced ¹⁹F MAS spectra from fluorinated materials.

DOI : 10.1002/anie.201814416