Viger-Gravel, Jasmine, Claudia E. Avalos, Dominik J. Kubicki, David Gajan, Moreno Lelli, Olivier Ouari, Anne Lesage, and Lyndon Emsley. “19F Magic Angle Spinning Dynamic Nuclear Polarization Enhanced NMR Spectroscopy.” Angewandte Chemie International Edition 58, no. 22 (May 27, 2019): 7249–53.
The introduction of high frequency, high power microwave sources, tailored biradicals, and low-temperature magic- 30 angle spinning 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. We identify trifluoroethanol-d3 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 apply this protocol to 10 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 40 impregnation with enhancements of ~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.