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Single crystals of the compound [ { S c ( H 2 O) 5 (μ - O H) } 2 ]Cl 4 ⋅ 2H 2 O were studied by 45Sc-NMR, with the effect of the quadrupolar coupling interaction on the spectra of the spin-7/2 nucleus analysed in the hierarchical framework of perturbation theory. Orientation-dependent spectra acquired at B 0 = 17.6 T showed strong second-order effects due to the comparatively large coupling constant of χ = |14.613 ± 0.006| MHz, with an associated asymmetry parameter of η Q = 0.540 9 ± 0.000 4. By analysing the splittings of the ±3/2 satellites, which in good approximation are subjected to first-order effects only, the full quadrupolar coupling tensor could be determined. The second-order effects caused by this tensor were calculated according to theoretical predictions for all orientations, and subtracted from both the centres of gravity of the satellites, and the central transitions. This allowed extraction of the full chemical shift tensor, with the eigenvalues being δ 11 = (5.6 ± 0.9) ppm, δ 22 = (12.4 ± 0.9) ppm, and δ 33 = (38.5 ± 0.9) ppm. In spectra acquired at a lower magnetic field of B 0 = 9.4 T, third-order effects could be detected, and similarly quantified using analytical expressions. [Display omitted] • Single-crystal NMR of 45Sc (I = 7/2) in [{Sc(H 2 O) 5 (μ-OH)} 2 ]Cl 4 . 2H 2 O. • Spectra analysed in the hierarchical framework of perturbation theory. • Compact new notation for quadrupolar effects of second and third order. • Full tensor of quadrupolar interaction and chemical shift determined. [ABSTRACT FROM AUTHOR]

Abstract: Chemical shift tensors for the carboxyl and methyl carbons of l-alanine crystals were determined using a magnetically oriented microcrystal array (MOMA) prepared from a microcrystalline powder sample of l-alanine. A MOMA is a single-crystal-like composite in which microcrystals are aligned three-dimensionally in a matrix resin. The single-crystal rotation method was applied to the MOMA to determine the principal values and axes of the chemical shift tensors. The result showed good agreement with the literature data for the single crystal of l-alanine. This demonstrates that the present technique is a powerful tool for determining the chemical shift tensor of a crystal from a microcrystal powder sample. [Copyright &y& Elsevier]

The results of a 35/37Cl solid-state nuclear magnetic resonance (SSNMR) study of the 1-butyl-3-methylimidazolium chloride complex of meso-octamethylcalix[4]pyrrole ( 1) are reported. Line shapes obtained from magic-angle-spinning and stationary powder samples collected at 9.4 and 21.1 T are analyzed to provide the 35/37Cl quadrupolar tensor and chemical shift (CS) tensor and their relative orientation. The relatively high symmetry of the chloride ion coordination environment is manifested in the small value of the quadrupole coupling constant, CQ(35Cl) = 1.0 MHz. The isotropic chemical shift of 120 ppm (with respect to NaCl(s)) is at the upper edge of the typical range seen for organic hydrochlorides. Consideration of chemical shift anisotropy (span, Ω = 50 ppm) and non-coincidence of the quadrupolar and CS tensors were essential to properly simulate the experimental spectra. The utility of gauge-including projector-augmented wave density functional theory (GIPAW-DFT) calculations of chlorine quadrupolar and CS tensors in organic chlorides was explored by validation against available benchmark experimental data for solid amino acid hydrochlorides. The calculations are shown to systematically overestimate the value of the 35Cl quadrupole coupling constant. Additional calculations on various hydrated and solvated models of 1 are consistent with a structure in which solvent and water of hydration are absent. [ABSTRACT FROM AUTHOR]

Abstract: 5-Fluoro-dl-tryptophan (5F-Trp) is a very sensitive probe used to investigate orientation and dynamics of biomacromolecules at the in situ level. In order to establish a 19F NMR strategy, the crystal structure and 19F chemical shielding tensor of 5F-Trp are reported. A novel approach was developed to use F–F homonuclear dipole–dipole coupling information to analyze single-crystal NMR data without determining crystal orientations. The measured values for the principal components of the shielding tensor are σ 11 =0.9, σ 22 =−63.3, and σ 33 =−82.9ppm relative to TFA in D2O. The principal axes of the shielding tensors coincide with the indole ring symmetry, which makes it a straightforward and powerful tool to monitor protein alignment in oriented environments. Hartree–Fock (HF) and density functional theory (DFT) calculations of the chemical shielding tensors are also reported. [Copyright &y& Elsevier]

Abstract: Bayesian statistics and information theory are used to analyze the reliability of extracting chemical shift parameters from spinning sideband patterns of spin 1/2 systems. Efficient code has been written to calculate the two-dimensional posterior probability as a function of the chemical shift anisotropy, δ, and the asymmetry parameter, η, given the sideband intensities and the signal-to-noise ratio. This method has the advantage of assuming only that the noise in the sideband intensities is distributed as a Gaussian. It assumes nothing about the distribution of the values of parameters δ and η, which are shown in some cases to be highly non-Gaussian. The utility of Bayesian analysis is demonstrated on 1D slow-spinning MAS spectra and on sideband patterns extracted from 2D PASS spectra. Previous investigations have shown that there is an optimal range of spinning frequencies for determining δ. In this study, information theory is used to determine the signal-to-noise ratio dependence of the entropy in δ, η, and total entropy in spinning sideband spectra. The entropy is a measure of the information content of a probability distribution. When the entropy is zero, there is perfect information on a system, while if it is infinite, there is no information on the system. It is found that for all values of η and for signal-to-noise ratios in the range 50–1000, an entropy minimum in ν δ /ν r occurs for values 1.5⩽ ν δ /ν r ⩽3. In the same range of signal-to-noise ratios, the entropy in η is a monotonically decreasing function of ν δ /ν r . The global information content of a spinning sideband pattern (i.e., the total entropy) is dependent on the signal-to-noise ratio and has an optimal value at ν δ /ν r ≈2 at a signal-to-noise ratio of 50 and increasing to ≈2.5 for signal-to-noise ratios of 1000. Finally, the increase of information in a sideband pattern as a function of the number of sidebands used in the analysis is examined. Most of the information about δ and η is contained in the five central sidebands; i.e., sidebands −2 to 2. [Copyright &y& Elsevier]

The individual components of the backbone 15N CSA tensor, σ11, σ22, σ33, and the orientation of σ11 relative to the NH bond described by the angle β have been determined for uniformly labeled 15N, 13C ubiquitin from partial alignment in phospholipid bicelles, Pf1 phage, and poly(ethylene glycol) by measuring the residue-specific residual dipolar couplings and chemical shift deviations. No strong correlation between any of the CSA tensor components is observed with any single structural feature. However, the experimentally determined tensor components agree with the previously determined average CSA principal components [Cornilescu and Bax (2000) J. Am. Chem. Soc. 122, 10143–10154]. Significant deviations from the averages coincide with residues in β-strand or extended regions, while α-helical residue tensor components cluster close to the average values. [ABSTRACT FROM AUTHOR]

Abstract: A new interpretation of 13C chemical shift tensors of amino acid carboxyl groups is presented. It is based on NMR results for 50 crystalline complexes of β-alanine, betaine, glycine and sarcosine with different inorganic and organic acids (XH), X-ray and vibrational data on the same systems and GIAO calculations for model complexes: (CH3COO–HX)−. Sensitivity of the chemical shift tensors on the amino acid electronic structure, crystal lattice, kind and strength of the hydrogen bonds is characterised in this way. Four categories of the complexes and hydrogen bonds are considered: (i) MO – the molecular complexes with the bonding proton not transferred to the amino acid carboxylate group, COO−⋯H–X; (ii) IP – the hydrogen bonded ion pairs with the bonding proton localised at the amino acid oxygen atom, COO–H⋯X−; (iii) BHB – the homoconjugated amino acid complexes with the bonding proton in the central region of short hydrogen bond, (COO–H–OOC)−; (iv) low-barrier hydrogen bonds with disordered proton position. Properties of the last category bonds are discussed by means of Mulliken theory of CT complexes. [Copyright &y& Elsevier]

Cobalt-59 and nitrogen-15 NMR spectra of the nitritopentamminecobalt(III) chloride, [(NH3)5Co-ONO]Cl2, and nitropentamminecobalt(III) chloride, [(NH3)5Co-NO2]Cl2, isomers in the solid state have been obtained at several applied magnetic field strengths. The 59Co NMR line shapes indicate that both the cobalt nuclear quadrupolar coupling constant (CQ) and the span of the chemical shift tensor (Ω) decrease when the complex isomerizes from [(NH3)5Co-ONO]2+ to [(NH3)5Co-NO2]2+; CQ decreases from 23 to 10.3 MHz and Ω changes from 1650 to 260 ppm. The 15N NMR line shapes also show a significant change in the nitrogen magnetic shielding tensor upon isomerization, with Ω decreasing from 710 to 547 ppm; also, an indirect spin-spin coupling, 1J(59Co,15N) = 63 Hz, is observed in the 15N NMR spectra of the nitro isomer. The NMR parameters are rationalized based on differences in the molecular structure of the two isomers. NMR spectra have also been recorded as the isomerization progresses with time and demonstrate the practicality of the technique for the study of solid-state isomerizations. [ABSTRACT FROM AUTHOR]

Two different crystalline polymorphs of valinomycin, the triclinic and monoclinic forms, have been studied by high resolution, solid state 13C CP-MAS NMR spectroscopy. Although the two polymorphs of the crystal are remarkably similar, there are distinct differences in the isotropic chemical shifts between the two spectra. For the triclinic form, the carbon chemical shift tensor components for the alpha carbons adjacent to oxygen in the lactic acid and hydroxyisovaleric acid residues and the ester carbonyls of the valine residue were obtained using the FIREMAT experiment. From the measured components, it was found that the behavior of the isotropic chemical shift, δiso, for valine residue ester carbonyl carbons is predominately influenced by the intermediate component, δ22. Additionally it was found that the smallest shift component, δ33, for the L-lactic acid (L-Lac) and D-α-hydroxyisovaleric acid (D-Hyi) Cα -O carbon was significantly displaced depending upon the nature of individual amino acid residues, and it is the δ33 component that governs the behavior of δiso in these alpha carbons. [ABSTRACT FROM AUTHOR]

The 29Si-NMR chemical shift tensors of 21 simple singlet silylenes, R2Si:, are studied at the GIAO/MP2/6-311+G(2df,p)//B3LYP/6-311G(d,p) level of theory. The NMR chemical shielding tensor for all silylenes is predicted to be highly anisotropic, with a very large paramagnetic eigenvalue δ11 in the plane of the central R2Si unit and perpendicular to its C2 axis. Very large substituent effects on δ29Si are found, i.e., while for H2Si: δ29Si=772 is predicted, the divalent silicon in F2Si is strongly shielded (δ29Si=−9.3). On the other hand for (H3Si)2Si: δ29Si=1223 is computed. This exceptional substituent effects are a direct consequence of large changes of the dominant eigenvalue δ11. The theoretical analysis reveals, that δ11 in silylenes is determined by the energy difference between its lowest excited singlet state, S1, and the S0 ground state. Therefore, a direct relation between the experimentally easy accessible λmax of silylenes and the isotropic 29Si-NMR chemical shift exists. This correlation can be used to facilitate the NMR characterization of highly substituted silylenes. [Copyright &y& Elsevier]

Solid-state 17O NMR spectra were obtained at 4.70, 11.75 and 19.60 T for potassium hydrogen [17O4]dibenzoate (PHB) under both magic-angle spinning and stationary conditions. Spectral analyses yielded both the magnitude and orientation of the 17O chemical shift (CS) tensor and the electric field gradient (EFG) tensor for each of the two chemically distinct oxygen sites in PHB. For the oxygen site that is not involved in hydrogen bonding, the experimental 17O NMR tensors are: δiso=287±2 ppm, δ11=470±5 ppm, δ22=380±5 ppm, δ33=10±5 ppm, CQ=8.30±0.02 MHz, ηQ=0.23±0.05, α=0±5°, β=90±5°, and γ=30±5°. For the oxygen site in the short O⋯H⋯O hydrogen bond, the experimental 17O NMR tensors are: δiso=213±2 ppm, δ11=370±5 ppm, δ22=190±5 ppm, δ33=80±5 ppm, CQ=5.90±0.02 MHz, ηQ=0.55±0.05, α=5±5°, β=90±5°, and γ=90±5°. Extensive quantum mechanical calculations at both restricted Hartree–Fock and density functional theory levels were performed to investigate the effects of an effectively symmetrical O⋯H⋯O hydrogen bond on 17O CS and EFG tensors. [Copyright &y& Elsevier]

Cobalt-59 NMR experiments have been carried out on single-crystal and polycrystalline (powder) samples of (±)-tris(ethylenediamine)cobalt(III) chloride trihydrate, (±)-[Co(en)3]Cl3·3H2O, and of its dehydrate. In addition, the X-ray crystal structure of the dehydrated sample has been determined. X-ray diffraction measurements confirm a long-held assumption that dehydration has only minor effects on the structure of the [Co(en)3]3+ cation. Nevertheless, these small differences have a detectable effect on the 59Co nuclear magnetic resonance properties of these compounds; in particular, the nuclear quadrupole coupling constant, CQ. Straightforward identification of the c-axis for large single crystals of (±)-[Co(en)3]Cl3·3H2O and of its dehydrate allowed us to obtain single-crystal 59Co NMR data by orienting the crystals in an MAS rotor. Data collected on single crystals and polycrystalline samples indicate that CQ=−3.05±0.05 and −2.80±0.05 MHz for the hydrated and dehydrated samples, respectively; the signs have been assigned on the basis of a point charge model. The chemical shift tensor principal components were also determined: for the hydrated sample, δ⊥=7281±2 ppm, δ||=7004±4 ppm and δiso=7189 ppm; for the dehydrated sample, δ⊥=7288±2 ppm, δ||=7008±4 ppm and δiso=7195 ppm. The electric field gradient and chemical shift tensors are axially symmetric, as required by crystal symmetry. [Copyright &y& Elsevier]

Silver methanesulfonate, AgSO3CH3, is a photo-stable, commercially available compound which is a superior 109Ag standard for setting up CP/MAS experiments. The 109Ag CP/MAS spectrum at moderate sample spinning speeds easily yields a single, relatively narrow peak with a single transient. The 109Ag chemical shift of solid AgSO3CH3 is 87.2 ppm with respect to a 9 M aqueous solution of AgNO3. The static spectrum yields chemical shift tensor components δ11=191 ppm, δ22=63 ppm and δ33=8 ppm. Therefore the span, Ω, is 183 ppm and the skew, κ, is −0.39. These values are in accord with the known crystal structure. [Copyright &y& Elsevier]

The Cα chemical shift tensors of proteins contain information on the backbone conformation. We have determined the magnitude and orientation of the Cα chemical shift tensors of two peptides with α-helical torsion angles: the Ala residue in G*AL (φ=-65.7°, ψ=-40°), and the Val residue in GG*V (φ=-81.5°, ψ=-50.7°). The magnitude of the tensors was determined from quasi-static powder patterns recoupled under magic-angle spinning, while the orientation of the tensors was extracted from Cα–Hα and Cα–N dipolar modulated powder patterns. The helical Ala Cα chemical shift tensor has a span of 36 ppm and an asymmetry parameter of 0.89. Its σ11 axis is 116° ± 5° from the Cα–Hα bond while the σ22 axis is 40° ± 5° from the Cα–N bond. The Val tensor has an anisotropic span of 25 ppm and an asymmetry parameter of 0.33, both much smaller than the values for β-sheet Val found recently (Yao and Hong, 2002). The Val σ33 axis is tilted by 115° ± 5° from the Cα–Hα bond and 98° ± 5° from the Cα–N bond. These represent the first completely experimentally determined Cα chemical shift tensors of helical peptides. Using an icosahedral representation, we compared the experimental chemical shift tensors with quantum chemical calculations and found overall good agreement. These solid-state chemical shift tensors confirm the observation from cross-correlated relaxation experiments that the projection of the Cα chemical shift tensor onto the Cα–Hα bond is much smaller in α-helices than in β-sheets. [ABSTRACT FROM AUTHOR]

The electronic surroundings of phosphorus and lithium atoms in the ionic conductor lithium dihydrogen phosphate (LDP) have been studied by single-crystal nuclear magnetic resonance (NMR) spectroscopy at room temperature. From orientation-dependent NMR spectra of a large homegrown LDP single crystal, the full 31P chemical shift (CS) and 7Li quadrupole coupling (QC) tensor was determined, using a global fit over three rotation patterns. The resulting CS tensor is characterized by its three eigenvalues: δ 11 P A S = (67.0 ± 0.6) ppm, δ 22 P A S = (13.9 ± 1.5) ppm, and δ 33 P A S = (− 78.7 ± 0.9) ppm. All eigenvalues have also been verified by magic-angle spinning NMR on a polycrystalline sample, using Herzfeld–Berger analysis of the rotational side band pattern. The resulting 7Li QC tensor is characterized by its quadrupolar coupling constant χ = Q 33 P A S = (− 71 ± 1) kHz and the two eigenvalues Q 11 P A S = (22.3 ± 0.9) kHz, and Q 22 P A S = (48.4 ± 0.8) kHz. The initially unknown orientation of the mounted crystal, expressed by the orientation of the rotation axis in the orthorhombic crystal frame, was included in the global data fit as well, thus obtaining it from NMR data only. [ABSTRACT FROM AUTHOR]

Both the chemical shift and quadrupole coupling tensors for 14 N and 27 Al in the wurtzite structure of aluminum nitride have been determined to high precision by single-crystal NMR spectroscopy. A homoepitaxially grown AlN single crystal with known morphology was used, which allowed for optical alignment of the crystal on the goniometer axis. From the analysis of the rotation patterns of 14 N ( I = 1 ) and 27 Al ( I = 5 / 2 ), the quadrupolar coupling constants were determined to χ (14 N) = (8.19 ± 0.02) kHz, and χ (27 Al) = (1.914 ± 0.001) MHz. The chemical shift parameters obtained from the data fit were δ i s o = − (292.6 ± 0.6) ppm and δ Δ = − (1.9 ± 1.1) ppm for 14 N, and (after correcting for the second-order quadrupolar shift) δ i s o = (113.6 ± 0.3) ppm and δ Δ = (12.7 ± 0.6) ppm for 27 Al. DFT calculations of the NMR parameters for non-optimized crystal geometries of AlN generally did not match the experimental values, whereas optimized geometries came close for 27 Al with χ ¯ calc = (1.791 ± 0.003) MHz, but not for 14 N with χ ¯ calc = − (19.5 ± 3.3) kHz. [ABSTRACT FROM AUTHOR]

We report solid-state 87 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 87 Rb quadrupole coupling constants (close to 20 MHz). We have also obtained static 87 Rb NMR spectra for these two compounds and determined both 87 Rb quadrupole coupling and chemical shift tensors. The experimental 87 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 87 Rb NMR spectra for organic Rb solids at the natural abundance level. We anticipate that, with additional 87 Rb isotope enrichment (up to 99%), the sensitivity of solid-state 87 Rb NMR will be 400 times higher than 39 K NMR, which makes the former an attractive surrogate probe for studying K + ion binding in biological systems., (© 2020 John Wiley & Sons, Ltd.)

Metal-organic frameworks (MOFs) are a class of important porous materials with many current and potential applications. Their applications almost always involve the interaction between host framework and guest species. Therefore, understanding of host-guest interaction in MOF systems is fundamentally important. Solid-state NMR spectroscopy is an excellent technique for investigating host-guest interaction as it provides information complementary to that obtained from X-ray diffraction. In this work, using MOF α-Mg 3 (HCOO) 6 as an example, we demonstrated that 13 C chemical shift tensor of organic linker can be utilized to probe the host-guest interaction in MOFs. Obtaining 13 C chemical shift tensor components (δ 11 , δ 22 , and δ 33 , where δ 11 ≥ δ 22 ≥ δ 33 ) in this MOF is particularly challenging as there are six coordinatively equivalent but crystallographically non-equivalent carbons in the unit cell with very similar local coordination environment. Two-dimensional magic-angle-turning experiments were employed to measure the 13 C chemical shift tensors of each individual crystallographically non-equivalent carbon in three microporous α-Mg 3 (HCOO) 6 samples with different guest species. The results indicate that the δ 22 component (with its direction approximately being co-planar with the formate anion and perpendicular to the C-H bond) is more sensitive to the adsorbate molecules inside the MOF channel due to the weak C-H···O hydrogen bonding or the ring current effect of benzene. The 13 C isotropic chemical shift, on the other hand, seems much less sensitive to the subtle changes in the local environment around formate linker induced by adsorption. The approach described in this study may be used in future studies on host-guest interaction within MOFs., (© 2019 John Wiley & Sons, Ltd.)

The full 207 Pb chemical shift (CS) tensor of lead in the mineral anglesite, PbSO 4 , was determined from orientation-dependent nuclear magnetic resonance (NMR) spectra of a large natural single crystal, using a global fit over two rotation patterns. The resulting tensor is characterised by the reduced anisotropy Δ δ = (− 327 ± 4) ppm, asymmetry η C S = 0.529 ± 0.002 , and δ i s o = (− 3615 ± 3) ppm, with the isotropic chemical shift δ i s o also verified by magic-angle spinning NMR on a polycrystalline sample. The initially unknown orientation of the mounted single crystal was included in the global data fit as well, thus obtaining it from NMR data only. By use of internal crystal symmetries, the amount of data acquisition and processing for determination of the CS tensor and crystal orientation was reduced. Furthermore, a linear correlation between the 207 Pb isotropic chemical shift and the shortest Pb–O distance in the co-ordination sphere of Pb 2 + solely surrounded by oxygen has been established for a large database of lead-bearing natural minerals. [ABSTRACT FROM AUTHOR]

NMR studies measuring chemical shift tensors are increasingly being employed to assign structure in difficult-to-crystallize solids. For small organic molecules, such studies usually focus on 13 C sites, but proteins and peptides are more commonly described using 15 N amide sites. An important and often neglected consideration when measuring shift tensors is the evaluation of their accuracy against benchmark standards, where available. Here we measure 15 N tensors in the dipeptide glycylglycine at natural abundance using the slow-spinning FIREMAT method with SPINAL-64 decoupling. The accuracy of these 15 N tensors is evaluated by comparing to benchmark single crystal NMR 15 N measurements and found to be statistically indistinguishable. These FIREMAT experimental results are further used to evaluate the accuracy of theoretical predictions of tensors from four different density functional theory (DFT) methods that include lattice effects. The best theoretical approach provides a root mean square (rms) difference of ±3.9 ppm and is obtained from a fragment-based method and the PBE0 density functional., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)