Solid‐state NMR spectra with sharp principal value features of the chemical shift tensor

Abstract

ABSTRACT:A straightforward, albeit still unexploited, approach to access sharp principal value features of the chemical shift tensor in slightly off-magic angle, slowly spinning powder solids is revisited. Its major advantages consist of (i) the direct visualization of axial or more general tensor/site symmetry, (ii) the absence of any rotor-synchronized or amplitude-matched radiofrequency pulse, and (iii) the use of routine single-pulse or cross-polarization acquisition modes upon modest spinning speeds on a standard cross-polarization/magic-angle spinning probe. The experiments and simulations show that the principal value features remain well resolved in an easily accessible range of chemical shift anisotropy/spinning frequency ratios and have fixed spectral positions at different spinning speeds. Several useful applications of this simple and robust approach can be envisaged in organic and inorganic solids.

Disentangling Crystallographic Inequivalence and Crystallographic Forms of l-Arginine by One- and Two-Dimensional Solid-State NMR Spectroscopy

“…All experiments with fully 13 C and 15 N-labeled l -arginine hydrochloride, purchased from Cambridge Isotope Laboratories (sample 1), fully 13 C, 15 N-labeled l -arginine hydrochloride monohydrate purchased from Cortecnet (sample 2), and natural abundance anhydrous l -arginine hydrochloride purchased from Sigma Aldrich (sample 3) were performed in a magnetic field of 9.4 T (400 MHz for 1 H) using spinning frequencies in the range between 20 and 30 kHz. The 13 C chemical shifts were referenced with respect to the carboxyl carbon of α-glycine (δ iso = 176.5 ppm) used as an external reference, while the 15 N chemical shifts were referenced to 15 NH 4 NO 3 (δ iso = −6.7 ppm). The recently introduced phase-alternated recoupling irradiation scheme (PARIS) and its phase-shifted counterpart PARIS-xy were used for 2D 15 N– 15 N and 13 C– 13 C correlation experiments, respectively.…”