Perspectives of fast magic-angle spinning $^{87}$Rb NMR of organic solids at high magnetic fields

See also:Erratum: "Perspectives of fast magic-angle spinning 87 Rb NMR of organic solids at high magnetic fields".Wu G., Terskikh V., Wong A., in : Magn. Reson. Chem. 2021 Sep;59(9-10):1101. doi: 10.1002/mrc.5198.International audienceWe report solid-state $^{87}$Rb NMR spectra from two Rb-ionophore complexes obtained with fast magic-angle spinning (MAS) (up to 60 kHz) at 21.1 T. These Rb-ionophore complexes containing macrocycles such as benzo-15-crown-5 and cryptand [2.2.2] are typical of organic Rb salts that exhibit very large $^{87}$Rb quadrupole coupling constants (close to 20 MHz). We have also obtained static $^{87}$Rb NMR spectra for these two compounds and determined both $^{87}$Rb quadrupole coupling and chemical shift tensors. The experimental 87Rb NMR tensor parameters are compared with those obtained by quantum chemical computations. Our results demonstrate that the combination of fast MAS (60 kHz or higher) and a high magnetic field (21.1 T or higher) is sufficient to produce high-quality solid-state $^{87}$Rb NMR spectra for organic Rb solids at the natural abundance level. We anticipate that, with additional $^{87}$Rb isotope enrichment (up to 99%), the sensitivity of solid-state $^{87}$Rb NMR will be 400 times higher than $^{39}$K NMR, which makes the former an attractive surrogate probe for studying K$^+$ ion binding in biological systems