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77Se‐NMR is used to characterise several chalcogen bonded complexes of derivatives of the organoselenium drug ebselen, exploring a range of electron demand. NMR titration experiments support the intuitive understanding that chalcogen bond donors bearing more electron withdrawing substituents give rise stronger chalcogen bonds. The chemical shift of the selenium nucleus is also shown to move upfield as it participates in a chalcogen bond. Solid‐state NMR is used to explore chalcogen bonding in co‐crystals. Due to the lack of molecular reorientation on the NMR timescale in the solid state, the shape of the chemical shift tensor can be determined using this technique. A range of co‐crystals are shown to have extremely large chemical shift anisotropy, which suggests a strongly anisotropic electron density distribution around the selenium atom. A single crystal NMR experiment was conducted using one of the co‐crystals, affording the absolute orientation of the chemical shift tensor within the crystal. This showed that the selenium nucleus is strongly shielded in the direction of the chalcogen bond (due to the approach of the lone pair of the Lewis base), and strongly deshielded in the perpendicular direction. The orientation of the deshielded axis is consistent with the presence of a second σ‐hole which is not participating in a chalcogen bond, showing the profound effect of electron density anisotropy on the chemical shift. [ABSTRACT FROM AUTHOR]

Cerussite, PbCO 3 , like all members of the aragonite group, shows a tendency to form twins, due to high pseudo-symmetry within the crystal structure. We here demonstrate that the twin law of a cerussite contact twin may be established using only 207 Pb-NMR spectroscopy. This is achieved by a global fit of several sets of orientation-dependent spectra acquired from the twin specimen, allowing to determine the relative orientation of the twin domains. Also, the full 207 Pb chemical shift tensor in cerussite at room temperature is determined from these data, with the eigenvalues being δ 11 = (- 2315 ± 1) ppm, δ 22 = (- 2492 ± 3) ppm, and δ 33 = (- 3071 ± 3) ppm. [ABSTRACT FROM AUTHOR]

Spectator oxo ligands are ubiquitous in catalysis, in particular in olefin epoxidation and olefin metathesis. Here we use computationally derived 17O NMR parameters to probe the electronic structure of spectator oxo ligands in these two reactions. We show that 17O NMR parameters allow to distinguish between doubly-bonded and triply-bonded oxo ligands, giving detailed insights into the frontier molecular orbitals involved in the metaloxo bonds along the reaction pathway. On the one hand, our study shows that in olefin epoxidation catalysed by methyltrioxorhenium (MTO), the oxo ligand significantly changes its bonding mode upon formation of the oxygen-transferring Re-oxo-bisperoxo-species, changing its nature from a doubly bonded to a triply bonded oxo ligand. On the other hand, only minor changes in the binding mode are found along the olefin metathesis reaction pathway with Mo- and W-based oxo-alkylidene species, in which the oxo ligand behaves as a triply bonded ligand throughout the reaction. This finding contrasts earlier studies that proposed that the change of binding mode of the oxo ligand was key to metallacyclobutane formation.

77 Se-NMR is used to characterise several chalcogen bonded complexes of derivatives of the organoselenium drug ebselen, exploring a range of electron demand. NMR titration experiments support the intuitive understanding that chalcogen bond donors bearing more electron withdrawing substituents give rise stronger chalcogen bonds. The chemical shift of the selenium nucleus is also shown to move upfield as it participates in a chalcogen bond. Solid-state NMR is used to explore chalcogen bonding in co-crystals. Due to the lack of molecular reorientation on the NMR timescale in the solid state, the shape of the chemical shift tensor can be determined using this technique. A range of co-crystals are shown to have extremely large chemical shift anisotropy, which suggests a strongly anisotropic electron density distribution around the selenium atom. A single crystal NMR experiment was conducted using one of the co-crystals, affording the absolute orientation of the chemical shift tensor within the crystal. This showed that the selenium nucleus is strongly shielded in the direction of the chalcogen bond (due to the approach of the lone pair of the Lewis base), and strongly deshielded in the perpendicular direction. The orientation of the deshielded axis is consistent with the presence of a second σ-hole which is not participating in a chalcogen bond, showing the profound effect of electron density anisotropy on the chemical shift., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

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

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‐Mg3(HCOO)6 as an example, we demonstrated that 13C chemical shift tensor of organic linker can be utilized to probe the host–guest interaction in MOFs. Obtaining 13C chemical shift tensor components (δ11, δ22, and δ33, where δ11 ≥ δ22 ≥ δ33) 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 13C chemical shift tensors of each individual crystallographically non‐equivalent carbon in three microporous α‐Mg3(HCOO)6 samples with different guest species. The results indicate that the δ22 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 13C 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. [ABSTRACT FROM AUTHOR]

In the present work, the adsorption of the molecule cytosine on carbon nanotube [CNT] (6,6-6) was investigated for the first time using density functional theory (DFT) calculations in the gas phase. The non-bonded interaction effect of compounds cytosine and CNT(6,6-6) nanotube on the electronic properties, chemical shift tensors and natural charge was investigated. The electronic properties of the obtained complex change after cytosine adsorption. The natural charge analysis showed that the charge transfer occurs between cytosine and CNT(6,6-6) nanotube and it was induced the dipole moment to the CNT(6,6-6) nanotube. Moreover, the formation of an intermolecular hydrogen bond between cytosine and CNT(6,6-6) nanotube has been investigated. The electronic spectra of the isolated molecule cytosine and the complex CNT(6,6-6)/cytosine in the gas phase were calculated by time dependent density functional theory (TD-DFT). The various parameters such as equilibrium geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) of the cytosine and CNT(6,6-6) nanotube were calculated and discussed consequently. [ABSTRACT FROM AUTHOR]

Chemical shift tensors give valuable insights into the nature and the relative energy of frontier orbitals and their analysis allows for rationalizing the reactivities of molecules. In this article, we point out the principles that allow for the analysis of chemical shift. Through selected, illustrative examples we show how one can relate chemical shift to molecular electronic structure and thus to reactivity.

The design and implementation of a software package for the analysis of single-crystal NMR data is presented. The SCFit software can treat spectra arising from various interactions: (i) chemical shift tensor only; (ii) chemical shift tensor and quadrupolar coupling tensor; (iii) dipolar and indirect nuclear spin-spin coupling tensors; (iv) all four interactions. The software is demonstrated on recently reported 17O and 31P single-crystal NMR data for triphenylphosphine oxide and for two of its halogen-bonded cocrystals. The 17O single-crystal NMR data represent a case where all four above-mentioned interactions simultaneously affect the spectra. SCFit can fit the chemical shift and quadrupolar coupling in two ways: (i) through an unconstrained fitting process where all tensor parameters are freely optimized or (ii) through a constrained fitting process where the principal components of the tensors may be fixed to values known previously with high precision via the analysis of powder samples. The second strategy is explored in an effort to reduce the number of unknowns in the fitting process; an improvement in the precision of the resulting tensor orientations is noted in some cases. Image 1 • SCFit software for analyzing single-crystal NMR data is described. • Chemical shift, quadrupolar, and spin-spin coupling interactions are treated. • The utility of fixing tensor magnitudes to known values is explored. [ABSTRACT FROM AUTHOR]

In the present work, the non-bonding interaction of the new drug Alectinib and the CNT(6,6-6) nanotube has been studied at the B3LYP/6-31G* level of theory. Results have shown that the electronic properties, chemical shift tensors, and natural charges are sensitive to the adsorption on the CNT(6,6-6) nanotube. Furthermore, we studied the electronic spectra of the Alectinib and the complex CNT(6,6-6)/Alectinib by time dependent DFT (TD-DFT) method for investigation of the maximum wavelength value of the Alectinib before and after the non-bonded interaction with the CNT(6,6-6) nanotube. It was found that the adsorption of the compound Alectinib over the CNT(6,6-6) changed the value λmax as bathochromic shift. [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.

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.

Chemical shift tensors (CSTs) are an exquisite probe of local geometric and electronic structure. 15 N CST are very sensitive to hydrogen bonding, yet they have been reported for very few proteins to date. Here we present experimental results and statistical analysis of backbone amide 15 N CSTs for 100 residues of four proteins, two E. coli thioredoxin reassemblies (1-73-(U- 13 C, 15 N)/74-108-(U- 15 N) and 1-73-(U- 15 N)/74-108-(U- 13 C, 15 N)), dynein light chain 8 LC8, and CAP-Gly domain of the mammalian dynactin. The 15 N CSTs were measured by a symmetry-based CSA recoupling method, ROCSA. Our results show that the principal component δ 11 is very sensitive to the presence of hydrogen bonding interactions due to its unique orientation in the molecular frame. The downfield chemical shift change of backbone amide nitrogen nuclei with increasing hydrogen bond strength is manifested in the negative correlation of the principal components with hydrogen bond distance for both α-helical and β-sheet secondary structure elements. Our findings highlight the potential for the use of 15 N CSTs in protein structure refinement. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Physical adsorption of the CO and CO 2 on Furanocoumarins. • Investigation of the electronic properties after adsorption Co and CO 2 on Furanocoumarins. • Adsorption effect of the CO and CO 2 on the natural charges of the Furanocoumarins. • Comparison of the absorption spectra of the Furanocoumarins, before and after adsorption. Abstract For the first time in the present work, the adsorption properties of the Furanocoumarins derivatives at the non-bonded interaction with CO and CO 2 were investigated by density functional theory (DFT: B3LYP/6-311+G* and M06-2X/6-311+G* levels of theory) in the solvent water. The non-bonded interaction of the title compounds with CO and CO 2 on the electronic properties such as E HOMO , E LUMO , the energy gap between LUMO and HOMO, global hardness was determined. Furthermore, chemical shift tensors, natural charge of the Furanocoumarins derivatives and the related complexes were determined and discussed. We have also investigated the charge distribution for the related complexes by molecular electrostatic potential (MEP) calculations using the B3LYP/6-311+G* level of theory. The electronic spectra of the Furanocoumarins derivatives and the related complexes were calculated by time dependent DFT (TD-DFT) for investigation of the maximum wavelength value of the Furanocoumarins derivatives before and after the non-bonded interaction with the CO and CO 2. Furanocoumarins can be used as strong absorbers for air purification in contaminated territories and cities. [ABSTRACT FROM AUTHOR]

In the present work the adsorption properties of the molecule Resveratrol (RSV) ( trans -3,5,4′-Trihydroxystilbene) on CNT(8,0-10) nanotube was investigated by Density Functional Theory (DFT) in the gaseous phase for the first time. The non-bonded interaction effects of compounds RSV and CNT(8,0-10) nanotube on the electronic properties, chemical shift tensors and natural charge were determined and discussed. The electronic spectra of the RSV and the complex CNT(8,0-10)/RSV in the gaseous phase were calculated by Time Dependent Density Functional Theory (TD-DFT) for investigation of the maximum wavelength value of the RSV before and after the non-bonded interaction with the CNT(8,0-10) nanotube and molecular orbitals involved in the formation of absorption spectrum of the complex RSV at maximum wavelength. [ABSTRACT FROM AUTHOR]

In the present work, Density Functional Theory (DFT) was first time employed to investigate the interaction between new drug (6aR,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydrobenzo[c]chromen-1-ol (Syndros) and the CNT(6,6-6) Nanotube in the gaseous phase. The interaction effects of compounds Syndros and CNT (6,6-6) nanotube on the electronic properties, chemical shift tensors and natural charge was also determined and discussed. The electronic spectra of the Syndros and the complex CNT(6,6-6)/Syndros in the gas phase were calculated by Time Dependent Density Functional Theory (TD-DFT) for the formation of adsorption effect on maximum wavelength of the Syndros. Nucleus-Independent Chemical Shifts (NICS) calculations have also been carried out for the compound Syndors and the complex CNT(6,6-6)/Syndros and the aromaticity of the compound Syndors before and after interaction with the CNT(6,6-6) Nanotube was investigated. [ABSTRACT FROM AUTHOR]

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.

In this present work, first time interaction between new synthesized derivative of the 4-(( E )-((4-(( E )-phenyldiazenyl)phenyl)imino)methyl)benzoic acid (E-PABA) and the BN(6,6-7) Nanotube for medical applications were studied. The geometries of the compounds E-PABA, the BN(6,6-7) Nanotube and the Complex BN(6,6-7)/E-PABA were optimized by Density Functional Theory (DFT) in the gas phase. The adsorption effect of the compound E-PABA on the electronic properties, chemical shift tensors and natural charge of the BN(6,6-7) Nanotube was investigated and discussed. The electronic spectra of the E-PABA and the Complex BN(6,6-7)/E-PABA in the gas phase carried out by Time Dependent Density Functional Theory (TD-DFT) for the foundation adsorption effect on maximum wavelength of the E-PABA. [ABSTRACT FROM AUTHOR]

An improved implementation of single-crystal magic-angle-spinning (MAS) NMR is presented which gives access to chemical shift tensors both in orientation (relative to the crystal axis system) and principal axis values. For mounting arbitrary crystals inside ordinary MAS rotors, a mounting tool is described which allows to relate the crystal orientation determined by diffraction techniques to the rotor coordinate system. The crystal is finally mounted into a MAS rotor equipped with a special insert which allows a defined reorientation of the single-crystal by 90°. The approach is based on the idea that the dispersive spectra, which are obtained when applying read-pulses at specific rotor-phases, not only yield the size of the eigenvalues but also encode the orientation of the different chemical shift (rank-2) tensors. For this purpose two 2D-data sets with orthogonal crystal orientation are fitted simultaneously. The presented analysis for chemical shift tensors is supported by an analytical formula which allows fast calculation of phase and amplitude of individual spinning side-bands and by a protocol which solves the problem of finding the correct reference phase of the spectrum. Different rotor-synchronized pulse-sequences are introduced for the same reason. Experiments are performed on L -alanine and O-phosphorylethanolamine and the observed errors are analyzed in detail. The experimental data are opposed to DFT-computed chemical shift tensors which have been obtained by the extended embedded ion method. [ABSTRACT FROM AUTHOR]

We report synthesis and solid-state 17 O NMR characterization of four site-specifically 17 O-labeled 2-acylbenzoic acids (2-RC(O)C 6 H 4 COOH) where R=H and CH 3 ): 2-[3- 17 O]formylbenzoic acid, 2-[1,2- 17 O 2 ]formylbenzoic acid, 2-[3- 17 O]acetylbenzoic acid, and 2-[1,2,3- 17 O 3 ]acetylbenzoic acid. In the solid state, both 2-formyl- and 2-acetyl-benzoic acids exist as the cyclic phthalide form each containing a five-membered lactone ring and a cyclic hemiacetal/hemiketal group. Static and magic-angle-spinning 17 O NMR spectra were recorded at 14.1 and 21.1 T for these compounds, from which the 17 O chemical shift and nuclear quadrupolar coupling tensors were determined for each oxygen site. These results represent the first time that 17 O NMR tensors are fully characterized for lactone, cyclic hemiacetal, and cyclic hemiketal functional groups. We also report solid-state 17 O NMR data for the cyclic hemiketal group an anticoagulant drug, warfarin. Experimental 17 O NMR tensors in these compounds were compared with computational results obtained with a periodic DFT code BAND. [ABSTRACT FROM AUTHOR]