A solid-state 14N magic-angle spinning NMR study of some amino acids

Broadband excitation in solid-state NMR using interleaved DANTE pulse trains with N pulses per rotor period

“…[9]. The 14 N nuclei in c-glycine have a quadrupolar coupling constant of C Q = 1.18 MHz, and an electric field gradient (efg) asymmetry parameter of g Q = 0.5 [13,22,35]. However, in other samples, 14 N nuclei can be subject to larger quadrupole interactions [14,23,24,36].…”

“…In that case, MAS powder spectra feature numerous spinning sidebands. Such wide spectra are encountered when: (i) the nuclei are close either to unpaired electrons in paramagnetic samples [2][3][4][5][6][7][8][9][10][11][12] or to conduction electrons in electrical conductors, (ii) the nuclei are subject to large quadrupole interactions (I > 1/2) [13][14][15][16][17][18][19][20][21][22][23][24][25], or (iii) their chemical shift anisotropy (CSA) is large, particularly when the static magnetic field is high [26,27].…”

Direct detection of nitrogen-14 in solid-state NMR spectroscopy

“…In applying this method to study various amino acids, the authors chose not to apply 1 H decoupling since they noted that the removal of the low-pass filters on the 14 N channel lowered the apparent quality factor of the probe, effectively increasing its bandwidth and reducing the attenuation of higher order spinning sidebands [112]. Thus, sideband manifolds with widths well in excess of 1 MHz were obtained from these samples, allowing C Q s of up to 1.2 MHz to be measured (Fig.…”

“…Reproduced from reference [92] by permission of The Royal Society of Chemistry. Reproduced with permission from reference [112]. Copyright 2004 Elsevier.…”

Natural abundance 14N and 15N solid-state NMR of pharmaceuticals and their polymorphs

“…Furthermore, it has been recently demonstrated that 35 Cl SSNMR can provide important structural information about the chlorine sites in different polymorphic forms in APIs, including the nature of the hydrogen bonding environments and impurity phases, in reduced experimental times compared to conventional pXRD and 13 C SSNMR experiments. 24,32,[39][40][41] For further reading on the use of SSNMR to characterize pharmaceutical compounds, we refer readers to recent reviews by Vogt and Monti et al [42][43][44] Given the ubiquity of nitrogen in functional groups such as amines, amides and numerous heterocycles, and the importance of intermolecular hydrogen-bonding interactions of nitrogen in solid APIs, the naturally occurring NMR-active nitrogen nuclei, 14 [55][56][57][58][59][60][61][62] and pharmaceuticals. 27,63-69 14 N nuclear quadrupole resonance (NQR) spectroscopy has also recently been applied, with some success, to a variety of APIs for purposes of quantification and polymorph differentiation.…”