Field-stepwise-swept solid-state 127I NMR of 1,4-diiodobenzene

Field-stepwise-swept solid-state 127I NMR experiments of 1,4-diiodobenzene, C6H4I2, applied to a Zeeman-perturbed NQR region, have been presented. A series of QCPMG measurements is performed at T = 90 K with resonant frequencies of 271 MHz in the range of magnetic fields from 2.5 T to zero with the interval of 12 mT. The spectral simulation, in which a numerical calculation involves the diagonalization of the combined Zeeman-quadrupolar Hamiltonian, provides quadrupole coupling constant (CQ) = 1863(5) MHz and the asymmetry parameter (ηQ) = 0.04(2). The 127I NQR spectrum is observed at T = 90 K, which is consistent in the above experimental results.

A sulfur-33 nuclear quadrupole resonance study of 33 S2 -labeled L-cystine

The sulfur electric-field-gradient tensor for a disulfide bond in ³³ S₂ -labeled L-cystine has been investigated by ³³ S nuclear quadrupole resonance (NQR). ³³ S₂ -labeled L-cystine is synthesized by introduction of disulfide ions prepared from elemental ³³ S-sulfur into an amino acid derivative, the side chain of which is iodinated. In its NQR spectrum, sharp single peaks are observed at between 24.63 and 24.90 MHz in the temperature range from 80 to 298 K. The two-dimensional nutation echo ³³ S NQR experiment is carried out at 160 K, and the quadrupole coupling constant, C_Q , and the asymmetric parameter, η_Q , are obtained to be 46.9(9) MHz and 0.6(1), respectively. The calculated ³³ S electric-field-gradient tensor components with respect to the molecular frame is briefly discussed.

Recent progress in solid-state nuclear magnetic resonance of half-integer spin low-γ quadrupolar nuclei applied to inorganic materials

An overview is presented of recent progress in the solid-state nuclear magnetic resonance (NMR) observation of low-γ nuclei, with a focus on applications to inorganic materials. The technological and methodological advances in the last 20 years, which have underpinned the increased accessibility of low-γ nuclei for study by solid-state NMR techniques, are summarised, including improvements in hardware, pulse sequences and associated computational methods (e.g., first principles calculations and spectral simulation). Some of the key initial observations from inorganic materials of these nuclei are highlighted along with some recent (most within the last 10 years) illustrations of their application to such materials. A summary of other recent reviews of the study of low-γ nuclei by solid-state NMR is provided so that a comprehensive understanding of what has been achieved to date is available.

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

Field-stepped NMR spectroscopy at up to 36 T using the series-connected hybrid (SCH) magnet at the U.S. National High Magnetic Field Laboratory is demonstrated for acquiring ultra-wideline powder spectra of nuclei with very large quadrupolar interactions. Historically, NMR evolved from the continuous-wave (cw) field-swept method in the early days to the pulsed Fourier-transform method in the modern era. Spectra acquired using field sweeping are generally considered to be equivalent to those acquired using the pulsed method. Here, it is shown that field-stepped wideline spectra of half-integer spin quadrupolar nuclei acquired using WURST/CPMG methods can be significantly different from those acquired with the frequency-stepped method commonly used with superconducting magnets. The inequivalence arises from magnetic field-dependent NMR interactions such as the anisotropic chemical shift and second-order quadrupolar interactions; the latter is often the main interaction leading to ultra-wideline powder patterns of half-integer spin quadrupolar nuclei. This inequivalence needs be taken into account to accurately and correctly determine the quadrupolar coupling and chemical shift parameters. A simulation protocol is developed for spectral fitting to facilitate analysis of field-stepped ultra-wideline NMR spectra acquired using powered magnets. A MATLAB program which implements this protocol is available on request.

Field-stepwise-swept QCPMG solid-state 115In NMR of indium oxide

Experimental and theoretical investigations of indium-115 electric-field-gradient (EFG) tensors of indium(III) oxide, In₂O₃, have been presented. Field-stepwise-swept QCPMG solid-state ¹¹⁵In NMR experiments are carried out at T ​= ​120 ​K, observed at 52.695 ​MHz, and in the range of external magnetic fields between 4.0 and 6.5 ​T. The spectral simulations yield the quadrupolar coupling constant, C_Q value, of 183(2) MHz and the asymmetry parameter, η_Q, of 0.05(5), for In(1), and that of 126(2) MHz and η_Q of 0.86(5) for In(2). Quantum chemical calculations are carried out to provide ¹¹⁵In EFG tensor orientations with respect to the molecular structure. A relationship between operative frequencies and variable ranges of external magnetic fields is briefly discussed for field-swept solid-state ¹¹⁵In NMR.

33S nuclear quadrupole resonance study of dibenzyl disulfide toward understanding of cross-linked structures in rubber

Experimental and theoretical investigations of a sulfur-33 electric-field-gradient (EFG) tensor of disulfide bonds in ³³S-labled dibenzyl disulfide have been presented. Temperature dependence of quadrupolar frequencies, ν_Q, is observed in the temperature range between 80 and 280 K, in which single peaks appear in all the ³³S nuclear quadrupole resonance (NQR) spectra. Analysis of nutation echo ³³S NQR spectra at 200 K yields the quadrupolar coupling constant, C_Q value, of 46.8(6) MHz and the asymmetry parameter, η_Q, of 0.48(7). The orientation of the ³³S EFG tensor of the disulfide is obtained by quantum chemical calculations: the largest EFG tensor component, V_ZZ, is approximately perpendicular to the molecular plane (C-S-S), and the smallest component, V_XX, is approximately 41° off the C-S bond. Extensive quantum chemical calculations are systematically performed to investigate dependences of ³³S EFG tensors on changes of torsion angles in disulfide and trisulfide bonds, indicating that analysis of ν_Q and C_Q values potentially makes it possible to assign the secondary structures of cross-linking in a rubber.