24 T High-Resolution and -Sensitivity Solid-State NMR Measurements of Low-Gamma Half-Integer Quadrupolar Nuclei 35Cl and 37Cl

Abstract

Solid-state NMR observations of low-gamma half-integer quadrupolar nuclei, 35 Cl and 37 Cl, were demonstrated using a 24 T hybrid magnet ( 1 H resonance frequency of 1.02 GHz) comprised of the high-temperature (HTS) and low-temperature (LTS) superconductors, and compared with results using a 14.1 T standard NMR magnet. While at 24 T the linewidth is 1.7 times narrower than that at 14.1 T, the gain in the sensitivity is 7.0 times because of enhanced polarization, reduced linewidth, and the use of larger rotor. A simple theoretical model was used to rationalize the sensitivity enhancements. The ratio of 35 Cl and 37 Cl quadrupolar couplings agrees well with the ratio of quadrupolar moments, and no isotopedependent chemical shift has been observed. In addition, the 3QMAS spectrum of 35 Cl is shown to demonstrate the high sensitivity rendered by the 24 T spectrometer.

NMR of Macromolecular Assemblies and Machines at 1 GHz and Beyond: New Transformative Opportunities for Molecular Structural Biology

“…However, there are many additional NMR active nuclei with critical roles in biology for which work has been limited to date due to sensitivity- and resolution-related challenges, such as 35/37 Cl and 23 Na. The group at NIMS in Japan has demonstrated measurements at 24 T on the spin 3/2 nuclei 35 Cl and 37 Cl (44, 45), as well as 17 O (1, 23). One of the fields with greatest potential for growth with the advent of magnetic fields over 1GHz is 17 O NMR (39, 46), a critical element in biology which could serve as an exquisite probe for a variety of mechanistic and structural questions, including enzyme catalysis, pharmaceuticals analysis, protein structure and hydration (47, 48), as well as materials/MOF applications mentioned above.…”

Field‐stepped ultra‐wideline NMR at up to 36 T: On the inequivalence between field and frequency stepping

“…High magnetic fields can effectively reduce the broadening effects of the second-order quadrupolar interaction. This line narrowing, along with the enhanced polarization and higher resonance frequency, leads to dramatic enhancements in both spectral resolution and signal sensitivity [2][3][4]. These gains are especially important for many quadrupolar nuclei that exhibit poor sensitivity due to their low gyromagnetic ratios, low natural abundances, and large nuclear quadrupole moments [5][6][7].…”

Solid‐state nuclear magnetic resonance and nuclear quadrupole resonance as complementary tools to study quadrupolar nuclei in solids

“…Contrarily, in NQR experiments, one may be forced to search over extremely wide spectral windows (tens of MHz or more) to find the resonances in the absence of a priori information on the magnitude of the quadrupolar interaction in a given sample. Additionally, with technological developments, such as high magnetic fields and so‐called ultra‐fast magic angle spinning rates, SSNMR can be used routinely to obtain information on the chemical shift tensor, quadrupolar coupling tensor, the dipolar coupling tensor, and J ‐coupling . However, NQR is not obsolete, as it can be used to study quadrupolar nuclei with large quadrupole moments, offering comparatively sharp resonances without the need for a stable external magnetic field.…”