Department of Chemistry, Queen's University, Kingston, ON, Canada.
Department of Chemistry, University of Ottawa, Ottawa, ON, Canada.
Magn Reson Chem. 2021 Feb;59(2):162-171. doi: 10.1002/mrc.5097. Epub 2020 Sep 15.
We report solid-state 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 Rb quadrupole coupling constants (close to 20 MHz). We have also obtained static Rb NMR spectra for these two compounds and determined both Rb quadrupole coupling and chemical shift tensors. The experimental Rb 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 Rb NMR spectra for organic Rb solids at the natural abundance level. We anticipate that, with additional Rb isotope enrichment (up to 99%), the sensitivity of solid-state Rb NMR will be 400 times higher than K NMR, which makes the former an attractive surrogate probe for studying K ion binding in biological systems.
我们报告了两个铷离子载体配合物的固态 Rb NMR 谱，这些配合物是通过在 21.1 T 下进行快速魔角旋转（MAS）（高达 60 kHz）获得的。这些含有大环如苯并-15-冠-5 和 cryptand [2.2.2] 的铷离子载体配合物是典型的有机 Rb 盐，具有非常大的 Rb 四极耦合常数（接近 20 MHz）。我们还获得了这两种化合物的静态 Rb NMR 谱，并确定了 Rb 四极耦合和化学位移张量。实验 Rb NMR 张量参数与量子化学计算得到的参数进行了比较。我们的结果表明，快速 MAS（60 kHz 或更高）和高磁场（21.1 T 或更高）的组合足以在自然丰度水平下为有机 Rb 固体产生高质量的固态 Rb NMR 谱。我们预计，通过额外的 Rb 同位素富集（高达 99%），固态 Rb NMR 的灵敏度将比 K NMR 高 400 倍，这使得前者成为研究生物系统中 K 离子结合的有吸引力的替代探针。
