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A cocrystal of 2,3,5,6-tetramethylpyrazine and 1,3,4,5-tetrabromo-2,6-difluorobenzene has been prepared and its crystal structure has been determined via single-crystal X-ray diffraction. Infinite chains of roughly coplanar donor and acceptor molecules are held together by two crystallographically distinct and highly linear Br···N halogen bonds. Four further crystallographically distinct Br···Br halogen bonds are also observed. Each of the two Br atoms in the 3 and 5 positions on the benzene ring acts simultaneously as a halogen bond donor and acceptor to two additional bromines on two neighbouring 1,3,4,5-tetrabromo-2,6-difluorobenzene molecules. These halogen bonds are also classified as type II halogen-halogen contacts. As a result of these contacts, a staggered herringbone arrangement of the infinite chains results. These structural features are shown to be consistent with computed molecular electrostatic potential and Hirshfeld surfaces. The insights gained through this analysis imply that additional systematic variations in the substitution motifs of aromatic halogen bond donors may lead to new structures and properties. As part of this work, a single-crystal X-ray structure of 1,3,4,5-tetrabromo-2,6-difluorobenzene of moderate quality is also reported. The single-crystal X-ray diffraction structure of a 1:1 cocrystal of 2,3,5,6-tetramethylpyrazine and 1,3,4,5-tetrabromo-2,6-difluorobenzene is reported. Bromine-nitrogen halogen bonds link the two types of molecules together, forming infinite chains. Bromine-bromine halogen bonds (type II contacts) between aromatic molecules stabilize a herringbone-like packing arrangement. [ABSTRACT FROM AUTHOR]

Users of the microbond test assume that a microbond resin droplet’s properties are equivalent to a macroscale specimen. However, there is currently no standardised methodology for determining the cure state of droplet specimens used in the microbond test. In this paper, we present a technique for microbond test users to better understand the properties of thermoset droplet specimens. Utilising a conventional benchtop spectrometer, a novel sample preparation technique involving curing epoxy droplets on thin-steel filaments allowed for high-throughput determination of the microbond droplet cure state. The parity between steel filament and glass fibre microbond samples was confirmed by infrared microspectroscopy. It is shown that cure schedules used in manufacturing composite parts produced microbond droplets with degrees of cure lower than that of bulk matrix specimens subjected to an identical thermal history. Testable microbond droplets could only be prepared for commercial resin systems when introducing a room temperature pre-curing time of at least 2 h. It is concluded that microbond testing should be supported by some droplet cure state characterisation methods to ensure that interfacial effects are not artefacts of droplet sample preparation. [ABSTRACT FROM AUTHOR]

Background: In patients with end-stage heart failure, durable Left Ventricular Assist Devices (LVADs) can be used as a bridge to transplant or destination therapy. LVADs have been shown to improve survival for patients with heart failure (HF). HF is associated with electrolyte abnormalities and the development of sustained arrhythmias. However, data on the influence of arrhythmias and electrolyte imbalances on inpatient outcomes in LVAD patients are lacking. Furthermore, previous works assessing inpatient outcomes focused mainly on the role of chronic comorbidities in those outcomes. Methods: In this cross-sectional study, we used discharge data from the National Inpatient Sample from 2019 to 2020 to assess the influence of acute arrhythmias on inpatient mortality in patients with LVADs. We also investigated the relationship between acute medical conditions and mortality. Results: There were 9418 (not survey-adjusted) hospitalizations with LVAD, among which 2539 (27%) died during the hospitalization. Univariate analysis of arrhythmias showed that ventricular arrhythmias (VAs)—ventricular fibrillation/flutter and ventricular tachycardia—as well as complete heart block were associated with significantly higher odds of mortality. Follow-up multivariable logistic analysis showed that these arrhythmias retain their increased association with death. Hyperkalemia and acidosis had increased adjusted odds of death (1.54 (95% confidence interval: 1.28–1.85) (p < 0.001) and 2.44 (CI: 2.14–2.77) (p < 0.001), respectively). Conclusions: VAs, complete heart block, hyperkalemia, and acidosis were associated with increased odds of all-cause mortality. Females had higher odds of inpatient mortality. These findings suggest that electrolyte management, maintenance of optimal acid–base balance, and interventions to treat sustained ventricular arrhythmias may be suitable therapeutic targets to reduce mortality in hospitalized patients with LVADs. [ABSTRACT FROM AUTHOR]

Lithium salts continue to find pharmaceutical applications, particularly as psychiatric medications. As with any active pharmaceutical ingredient, structural polymorphism is an important concern for lithium-based medications that can influence solubility and other physicochemical properties. Here we report a 13C, 1H, and 7Li magic-angle spinning solid-state nuclear magnetic resonance (MAS SSNMR) study of two 1:1 polymorphic ionic cocrystals of lithium 4-methoxybenzoate and L-proline (L4MPRO(α) and L4MPRO(β)). One-dimensional 13C cross-polarization MAS and two-dimensional heteronuclear correlation NMR spectra hint at differential mobilities of the proline and benzoate moieties for the two polymorphs. Five key resonances differ in 13C chemical shift by more than 1 ppm between the two polymorphs, clearly distinguishing between them. Gauge-including projector-augmented-wave density functional theory calculations of 13C and 1H magnetic shielding constants correlate strongly with the experimental chemical shifts for both polymorphs. R2 and root-mean-square deviation metrics are shown to be insufficient in the case of 13C, but sufficient in the case of 1H, for differentiating between the polymorphs. 7Li satellite-transition MAS NMR of both polymorphs are identical, as are the computed lithium magnetic shielding constants, demonstrating the insensitivity of 7Li NMR to polymorphism in these samples. This work highlights the utility of solid-state NMR spectroscopy for examining ionic salt cocrystals and also highlights some caveats in this regard. [ABSTRACT FROM AUTHOR]

This recommendation proposes a definition for the term "pnictogen bond"; the term pnictogen bond designates a subset of the attractive interactions between an electrophilic region on a pnictogen atom in a molecular entity and a nucleophilic region in another, or the same, molecular entity. [ABSTRACT FROM AUTHOR]

Ameloblastic carcinoma is a locally aggressive odontogenic tumor that most commonly affects young and middle-aged adults. Metastatic disease may develop insidiously and manifest months or years after the initial diagnosis. Herein, we describe the clinical, imaging, and pathologic findings of a 31-year-old male who presented to the emergency department with headache and vision loss of 3 months duration and was subsequently found to have ameloblastic carcinoma with hepatic metastases. Initial computed tomography (CT) and magnetic resonance imaging revealed a multilocular cystic mass with avidly-enhancing nodular soft-tissue components associated with the right temporal fossa. Histologic examination of a tissue sample showed findings consistent with ameloblastic carcinoma. An initial staging CT scan showed several small hepatic cystic lesions. Follow-up surveillance imaging showed interval growth. A subsequent biopsy of a hepatic lesion showed findings compatible with metastatic ameloblastic carcinoma. The patient was started on systemic chemotherapy with evidence of disease progression at 1-year follow-up. [ABSTRACT FROM AUTHOR]

Double-rotation (DOR) solid-state NMR spectroscopy is a high-resolution technique developed in the late 1980s. Although multiple-quantum magic-angle spinning (MQMAS) became the most widely used high-resolution method for half-integer spin quadrupoles after 1995, development and application of DOR NMR to a variety of chemical and materials science problems has endured. This Trend article recapitulates the development of DOR NMR, discusses various applications, and describes possible future directions. The main technical limitations specific to DOR NMR are simply related to the size of the double rotor system. The relatively large outer rotor (and thus coil) used for most applications over the past 35 years translates into relatively low rotor spinning frequencies, a low filling factor, and weak radiofrequency powers available for excitation and for proton decoupling. Ongoing developments in NMR instrumentation, including ever-shrinking MAS rotors and spherical NMR rotors, could solve many of these problems and may augur a renaissance for DOR NMR. [Display omitted] • Advances in double-rotation solid-state NMR spectroscopy are reviewed. • DOR NMR provides high-resolution spectra of quadrupolar nuclei in one dimension. • Limitations include a poor filling factor, low spinning rates, and low rf powers. • New developments in magic angle spinning technology could reinvigorate DOR NMR. [ABSTRACT FROM AUTHOR]

A pair of novel polymorphic ionic cocrystals of 3,4‐dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single‐crystal XRD. Strong and directional non‐covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid‐state NMR to reveal large and anisotropic J(125Te,79/81Br) coupling tensors, providing unequivocal evidence for non‐Fermi contact contributions across ChBs. Along with large 79/81Br quadrupolar couplings for the Br− anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs. [ABSTRACT FROM AUTHOR]

A pair of novel polymorphic ionic cocrystals of 3,4‐dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single‐crystal XRD. Strong and directional non‐covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid‐state NMR to reveal large and anisotropic J(125Te,79/81Br) coupling tensors, providing unequivocal evidence for non‐Fermi contact contributions across ChBs. Along with large 79/81Br quadrupolar couplings for the Br− anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs. [ABSTRACT FROM AUTHOR]

Diffuse large B‐cell lymphoma often presents with extranodal manifestations involving the musculoskeletal system. Shoulder pain is particularly worrisome for malignancy. Individuals presenting with refractory upper extremity complaints should undergo a prompt and thorough evaluation for cancer, as a delay in diagnosis can result in an unfavorable outcome. [ABSTRACT FROM AUTHOR]

This recommendation proposes a definition for the term "chalcogen bond"; it is recommended the term is used to designate the specific subset of inter- and intramolecular interactions formed by chalcogen atoms wherein the Group 16 element is the electrophilic site. [ABSTRACT FROM AUTHOR]

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]

A revised absolute magnetic shielding scale for oxygen is established based on a recently reported highly precise experimental measurement of the [SUP17]O spin-rotation constant in carbon monoxide. The isotropic oxygen magnetic shielding constant for [SUP12]C[SUP17]O at the equilibrium geometry, σ[SUBe], is found to be -56.8 ± 0.6 ppm. The experimental rovibrationally averaged value of the shielding constant at 300 K, 〈&sigma 〉[SUB300K], is -62.7 ±0.6 ppm, in excellent agreement with the ab initio value reported by Vaara et al. [J. Chem. Phys. 109, 8388 (1998)]. Based on the revised scale and on experimentally known oxygen chemical shifts, 〈σ〉[SUB300K] (H[SUB2]O(l)) is 287.5 ± 0.6 ppm and 〈σ〉 [SUB300K] (H[SUB2]0(g)) is 323.6 ± 0.6ppm. [ABSTRACT FROM AUTHOR]

Selected highlights of the recent literature on solid-state NMR of some of the lesser studied nuclei are provided. The roles of ultrahigh magnetic fields, radiofrequency pulse sequences, dynamic nuclear polarization, isotopic enrichment, and nuclear quadrupole resonance in opening up the periodic table to in-depth study are discussed. [ABSTRACT FROM AUTHOR]

The phospholipid-water partition coefficient is a commonly measured parameter that correlates with drug efficacy, small-molecule toxicity, and accumulation of molecules in biological systems in the environment. Despite the utility of this parameter, methods for measuring phospholipid- water partition coefficients are limited. This is due to the difficulty of making quantitative measurements in vesicle membranes or supported phospholipid bilayers, both of which are small-volume phases that challenge the sensitivity of many analytical techniques. In this work, we employ in situ confocal Raman microscopy to probe the partitioning of a model membrane-active compound, 2-(4-isobutylphenyl) propionic acid or ibuprofen, into both hybrid- and supportedphospholipid bilayers deposited on the pore walls of individual chromatographic particles. The large surface-area-to-volume ratio of chromatographic silica allows interrogation of a significant lipid bilayer area within a very small volume. The local phospholipid concentration within a confocal probe volume inside the particle can be as high as 0.5 M, which overcomes the sensitivity limitations of making measurements in the limited membrane areas of single vesicles or planar supported bilayers. Quantitative determination of ibuprofen partitioning is achieved by using the phospholipid acyl-chains of the within-particle bilayer as an internal standard. This approach is tested for measurements of pH-dependent partitioning of ibuprofen into both hybrid-lipid and supported-lipid bilayers within silica particles, and the results are compared with octanol-water partitioning and with partitioning into individual optically trapped phospholipid vesicle membranes. Additionally, the impact of ibuprofen partitioning on bilayer structure is evaluated for both within-particle model membranes and compared with the structural impacts of partitioning into vesicle lipid bilayers. [ABSTRACT FROM AUTHOR]

Permeabilization of the outer mitochondrial membrane is an integral step in apoptosis. The resulting release of pro-apoptotic signaling proteins leads to cell destruction through activation of the cysteine-aspartic protease (caspase) cascade. However, the mechanism of outer mitochondrial membrane (OMM) permeabilization remains unclear. It was recently shown that cytochrome c can induce pore formation in cardiolipin-containing phospholipid membranes, leading to large dextran and protein permeability. In this work, the interaction of cytochrome c with cardiolipin-containing phospholipid vesicles, serving as models of the OMM, is investigated to probe cytochrome c-induced permeability. Lipid vesicles having either a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or mixed-DPPC/cardiolipin membrane and containing a membrane-impermeable Raman tracer 3-nitrobenzenesulfonate (3-NBS) were optically trapped, translated into a solution containing cytochrome c, and monitored for 3-NBS leakage. Cytochrome-correlated leakage was observed only in cardiolipin-containing vesicles. Structural changes observed in the Raman spectra during permeabilization indicated acyl chain disordering along with decreased intensity of the cardiolipin cis-double-bond stretching modes. When the vesicle-associated cytochrome c Raman spectrum is compared with a spectrum in buffer, heme-resonance bands are absent, indicating loss of Met-80 coordination. To verify selective interactions of cytochrome c with cardiolipin, these experiments were repeated where the DPPC acyl chains were deuterated (D62-DPPC), allowing spectral resolution of the DPPC acyl chain response from that of cardiolipin. Interestingly, D62-DPPC acyl chains were unaffected by cytochrome c accumulation, while cardiolipin showed major changes in acyl chain structure. These results suggest that cytochrome-induced permeabilization proceeds through selective interaction of cytochrome c with cardiolipin, resulting in protein unfolding, where the unfolded form interacts with cardiolipin acyl chains within the bilayer to induce permeability. [ABSTRACT FROM AUTHOR]

Porous silica is used as a support in a variety of separation processes, including chromatographic separation and solid-phase extraction. The resolution and efficiency of these applications is significantly impacted by the kinetics of partitioning and molecular transport into the interior of the porous particles. Molecular transport in porous silica has been explored previously by measuring chromatographic elution profiles, but such measurements are limited to relatively low retention conditions, where within-particle molecular transport must be inferred from elution profiles of solutes emerging from a packed column. In this work, a measurement of within-particle molecular transport is carried out using confocal Raman microscopy to probe the time-dependent accumulation of pyrene from an aqueous mobile phase into the center of individual C18-chromatographic particles. The measured time constants for pyrene accumulation were much slower than diffusion-limited transport of solute in solution to the particle surface. Furthermore, the accumulation into the center of the particle did not show a time-lag characteristic of slow-transport into the particle interior. The exponential rise of pyrene concentration is, however, consistent with first-order Langmuir adsorption kinetics at low surface coverages. The linear dependence of the time-constant on particle radius indicates an adsorption barrier near the outer boundary of the particle, where the accumulation rate depends on flux across the boundary (proportional to the particle area) to satisfy the within-particle capacity at equilibrium (proportional to the particle volume). The pyrene accumulation kinetics into the porous particle, expressed as a heterogeneous rate constant, were nearly 50-times faster than the pyrene adsorption rate at a planar C18-functionalized silica surface, which demonstrates the impact of multiple surface encounters within the porous structure leading to much greater capture efficiency compared to a planar surface. Monte Carlo simulations of within-particle pyrene diffusion, with the adsorption efficiency estimated from the planar-surface adsorption rate, predict a diffusion-to-capture distance within the porous particle that is within 40% of that observed in the radial dependence of the pyrene within-particle accumulation results. [ABSTRACT FROM AUTHOR]

Abstract: Solid‐state nuclear magnetic resonance (SSNMR) spectroscopy has largely overtaken nuclear quadrupole resonance (NQR) spectroscopy for the study of quadrupolar nuclei. In addition to information on the electric field gradient, SSNMR spectra may offer additional information concerning other NMR interactions such as magnetic shielding. With continued technological advances contributing to developments such as higher magnetic fields, SSNMR boasts several practical advantages over NQR. However, NQR is still a relevant technique, as it may often be the most practical approach in cases of extremely large quadrupolar coupling constants. Here, we discuss the advantages and disadvantages of SSNMR and NQR spectroscopies, with the quadrupolar halogens serving as examples. The purpose of this article is to serve as a guide on using SSNMR and NQR as complementary tools, covering some of their practicalities, limitations, and experimental challenges. [ABSTRACT FROM AUTHOR]

Multidimensional least squares analysis is a well-established technique for resolving component vibrational spectra from mixed samples or systems. Component resolution of temperature-dependent vibrational spectra is challenging, however, due to the lack of a suitable model for the variation in sample composition with temperature. In this work, analysis of temperature-dependent Raman spectra of lipid membranes is accomplished by using ''concentration'' vectors independently derived from enthalpy changes determined by differential scanning calorimetry. Specifically, the lipid-bilayer phase transitions of DMPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) are investigated through Raman spectra acquired from individual, optically trapped vesicles in suspension as a function of temperature. Heat capacity profiles of the same vesicle suspension are measured using differential scanning calorimetry and numerically integrated to generate enthalpy change curves of each phase transition, which are in turn used to construct composition vectors. Multidimensional least squares analysis optimized for a fit to these composition vectors allows resolution of the component spectra corresponding to gel, ripple, and liquid-crystalline phases of the DMPC. The quality of fit of the calorimetry-derived results is confirmed by unstructured residual differences between the data and the model, and a composition variation predicted by the resolved spectra that matches the calorimetry results. This approach to analysis of temperature-dependent spectral data could be readily applied in other areas of materials characterization, where one is seeking to learn about structural changes that occur through temperature-dependent phase transitions. [ABSTRACT FROM AUTHOR]

CO2 injected into depleted oil or gas reservoirs for long-term storage has the potential to mobilize organic compounds and distribute them between sediments and reservoir brines. Understanding this process is important when considering health and environmental risks, but little quantitative data currently exists on the partitioning of organics between supercritical CO2 and water. In this work, a high-pressure, in situ measurement capability was developed to assess the distribution of organics between CO2 and water at conditions relevant to deep underground storage of CO2. The apparatus consists of a titanium reactor with quartz windows, near-infrared and UV spectroscopic detectors, and switching valves that facilitate quantitative injection of organic reagents into the pressurized reactor. To demonstrate the utility of the system, partitioning coefficients were determined for benzene in water/supercritical CO2 over the range 35-65 °C and approximately 25-150 bar. Density changes in the CO2 phase with increasing pressure were shown to have dramatic impacts on benzene's partitioning behavior. Our partitioning coefficients were approximately 5-15 times lower than values previously determined by ex situ techniques that are prone to sampling losses. The in situ methodology reported here could be applied to quantify the distribution behavior of a wide range of organic compounds that may be present in geologic CO2 storage scenarios. [ABSTRACT FROM AUTHOR]

Weak hydrogen bonds are important structure-directing elements in supramolecular chemistry and biochemistry. We consider here weak CH⋯O hydrogen bonds in a series of cocrystals of theophylline and caffeine and assess to what extent the CH⋯O distance and angle govern the observed 13C and 1H isotropic chemical shifts. Gauge-including projector-augmented wave density functional theory (GIPAW DFT) calculations consistently predict a decrease in the 13C and 1H magnetic shielding constants upon hydrogen bond formation on the order of 2–5 ppm (13C) and 1–2 ppm (1H). These trends are reproduced using the machine-learning approach implemented in ShiftML. Experimental 13C and 1H chemical shifts obtained for powdered samples using one-dimensional NMR spectroscopy as well as heteronuclear correlation (HETCOR) spectroscopy correlate well with the GIPAW DFT results. However, the experimental 13C NMR response only correlates moderately well with the hydrogen bond length and angle, while the experimental 1H chemical shifts only show very weak correlations to these local structural elements. DFT computations on isolated imidazole-formaldehyde models show that the 13C and 1H chemical shifts generally decrease with the C⋯O distance but show no clear dependence on the CH⋯O angle. These results demonstrate that the 13C and 1H response to weak CH⋯O hydrogen bonding is influenced significantly by additional weak contacts within cocrystal heterodimeric units. [Display omitted] • Weak CH⋯O hydrogen bonds involving the methine group of imidazole ring fragments are investigated. • Experimental 13C and 1H chemical shifts for solid cocrystals of caffeine and theophylline are assessed. • GIPAW-DFT, ShiftML machine learning, and cluster model calculations show the impact of hydrogen bond geometry on chemical shift response. • The most robust correlation is noted between the 13C isotropic chemical shift and the hydrogen bond length. [ABSTRACT FROM AUTHOR]

This article describes some highlights of the research which has been carried out in my laboratory at the University of Ottawa over the period covering 2005 to 2014. My research is in the general areas of solid-state NMR, applications of quantum chemistry, and biomolecular NMR. The format will follow that of my 2014 Canadian Society for Chemistry Keith Laidler Award presentation given in Vancouver in June 2014 at the 97th Canadian Chemistry Conference and Exhibition. Following a brief introduction, I will present some of our most interesting and exciting recent advances according to the following six themes: 1. Fundamental solid-state NMR. 2. Materials characterization and NMR crystallography. 3. Pharmaceuticals and polymorphism. 4. Non-covalent interactions: Halogen bonds. 5. Biomolecular NMR. 6. Software development. [ABSTRACT FROM AUTHOR]

The vaterite polymorph of CaCO 3 has puzzled crystallographers for decades in part due to difficulties in obtaining single crystals. The multiple proposed structures for the vaterite polymorph of CaCO 3 are assessed using a combined 43 Ca solid-state nuclear magnetic resonance (SSNMR) spectroscopic and computational approach. A combination of improved experimental and computational methods, along with a calibrated chemical shift scale and 43 Ca nuclear quadrupole moment, allow for improved insights relative to our earlier work (Bryce et al., J. Am. Chem. Soc. 2008, 130, 9282). Here, we synthesize a 43 Ca isotopically-enriched sample of vaterite and perform high-resolution quadrupolar SSNMR experiments including magic-angle spinning (MAS), double-rotation (DOR), and multiple-quantum (MQ) MAS experiments at magnetic field strengths of 9.4 and 21.1 T. We identify one crystallographically unique Ca 2+ site in vaterite with a slight distribution in both chemical shifts and quadrupolar parameters. Both the experimental 43 Ca electric field gradient tensor and the isotropic chemical shift for vaterite are compared to those calculated with the gauge-including projector-augmented-wave (GIPAW) DFT method in an attempt to identify the model that best represents the crystal structure of vaterite. Simulations of 43 Ca DOR and MAS NMR spectra based on the NMR parameters computed for a total of 18 structural models for vaterite allow us to distinguish between these models. Among these 18, the P 3 2 21 and C 2 structures provide simulated spectra and diffractograms in best agreement with all experimental data. [ABSTRACT FROM AUTHOR]

Phenomena such as anticooperativity and competition among non‐covalent bond donors and acceptors are key considerations when exploring the polymorphic and stoichiomorphic landscapes of binary and higher‐order cocrystalline architectures. We describe the preparation of four cocrystals of 1,3,5‐trifluoro‐2,4,6‐triiodobenzene with N‐heterocyclic compounds, namely acridine, 3‐aminopyridine, 4‐methylaminopyridine, and 1,2‐di(4‐pyridyl)ethane. The cocrystals, which are characterized by single‐crystal and powder X‐ray diffraction experiments, all show moderately strong and directional iodine⋅⋅⋅nitrogen halogen bonds with reduced distance parameters ranging from 0.79 to 0.92 and carbon‐iodine⋅⋅⋅nitrogen bond angles ranging from 165.4(3) to 175.31(7)°. The cocrystal comprising 1,3,5‐trifluoro‐2,4,6‐triiodobenzene and acridine provides a relatively rare example where all three halogen bond donor sites form halogen bonds with three acceptor molecules, overcoming an anticooperative effect. This effect manifests itself through the lengthening of non‐halogen‐bonded C−I bonds, weakening their potential to form halogen bonds. The effect is only observed once two halogen bonds have been formed to 1,3,5‐trifluoro‐2,4,6‐triiodobenzene; one such bond does not appear to be adequate. Among the four cocrystals studied, competition between the pyridyl nitrogen atoms and the amine nitrogen atoms suggests that the former are the preferred halogen bond acceptors. Analysis by Hirshfeld fingerprint plots and 13C and 19F magic‐angle spinning solid‐state nuclear magnetic resonance (NMR) spectroscopy provides additional insights into the prevalence of various short contacts in the crystal structures and into the spectral response to halogen‐bond‐induced cocrystallization. [ABSTRACT FROM AUTHOR]

Highlights: [•] J coupling multiplets for quadrupolar spin pairs are given. [•] The impact of chemical equivalence on the measurement of J coupling between quadrupoles is discussed. [•] The impact of various interactions is analyzed by simulating DOR and J-resolved spectra. [•] The second-order quadrupolar-dipolar cross-term does not adversely affect J-resolved experiments. [ABSTRACT FROM AUTHOR]

Chemically informative J couplings between pairs of quadrupolar nuclei in dimetallic and dimetalloid coordination motifs are measured using J-resolved solid-state NMR experiments. It is shown that the application of a double-quantum filter is necessary to observe the J splittings and that, under these conditions, only a simple doublet is expected. Interestingly, the splitting is amplified if the spins are magnetically equivalent, making it possible to measure highly precise J couplings and unambiguously probe the symmetry of the molecule. This is demonstrated experimentally by chemically breaking the symmetry about a pair of boron spins by reaction with an N-heterocyclic carbene to form a β-borylation reagent. The results show that the J coupling is a sensitive probe of bonding in diboron compounds and that the J values quantify the weakening of the B-B bond which occurs when forming an sp2-sp3 diboron compound, which is relevant to their reactivity. Due to the prevalence of quadrupolar nuclei among transition metals, this work also provides a new approach to probe metal-metal bonding; results for Mn2(CO)10 are provided as an example. [ABSTRACT FROM AUTHOR]

Three novel chalcogen‐bonded cocrystals featuring 3,4‐dicyano‐1,2,5‐selenodiazole (C4N4Se) or 3,4‐dicyano‐1,2,5‐tellurodiazole (C4N4Te) as chalcogen‐bond donors and hydroquinone (C6H6O2), tetraphenylphosphonium chloride (C24H20P+·Cl−) or tetraethylphosphonium chloride (C8H20P+·Cl−) as chalcogen‐bond acceptors have been prepared and characterized by single‐crystal X‐ray diffraction (XRD), powder X‐ray diffraction and 77Se/125Te magic‐angle spinning solid‐state NMR spectroscopy. The single‐crystal XRD results show that the chalcogenodiazole molecules interact with the electron donors through two σ‐holes on each of the chalcogen atoms, which results in highly directional and moderately strong chalcogen bonds. Powder XRD confirms that the crystalline phases are preserved upon moderate grinding of the samples for solid‐state NMR experiments. Measurement of 77Se and 125Te chemical shift tensors via magic‐angle spinning solid‐state NMR spectroscopy confirms the number of magnetically unique chalcogen sites in each asymmetric unit and reveals the impact of chalcogen‐bond formation on the local electronic structure. These NMR data are further assessed in the context of analogous data for a wider range of crystalline chalcogen‐bonded systems. [ABSTRACT FROM AUTHOR]

Abstract: Residual dipolar couplings between spin-1/2 and quadrupolar nuclei are often observed and exploited in the magic-angle spinning (MAS) NMR spectra of spin-1/2 nuclei. These orientation-dependent splittings contain information on the dipolar interaction, which can be translated into structural information. The same type of splittings may also be observed for pairs of quadrupolar nuclei, although information is often difficult to extract from the quadrupolar-broadened lineshapes. Here, the complete theory for describing the dipolar coupling between two quadrupolar nuclei in the frequency domain by Hamiltonian diagonalization is given. The theory is developed under MAS and double-rotation (DOR) conditions, and is valid for any spin quantum numbers, quadrupolar coupling constants, asymmetry parameters, and tensor orientations at both nuclei. All terms in the dipolar Hamiltonian become partially secular and contribute to the NMR spectrum. The theory is validated using experimental 11B and 35/37Cl NMR experiments carried out on powdered B-chlorocatecholborane, where both MAS and DOR are used to help separate effects of the quadrupolar interaction from those of the dipolar interaction. It is shown that the lineshapes are sensitive to the quadrupolar coupling constant of both nuclei and to the J coupling (including its sign). From these experiments, the dipolar coupling constant for a heteronuclear spin pair of quadrupolar nuclei may be obtained as well as the sign of the quadrupolar coupling constant of the perturbing nucleus; these are two parameters that are difficult to obtain experimentally otherwise. [Copyright &y& Elsevier]

Abstract: Double-rotation (DOR) is the only technique generally capable of yielding high-resolution NMR spectra of half-integer quadrupolar nuclei in one dimension for solids without the need for sophisticated coherence pathway selection. Unfortunately, due to the low outer rotor spinning frequencies currently available, the spectra often contain a large number of spinning sidebands which may overlap with the resonances of interest. We implement a simple, robust, and easy to use family of pulse sequences, which in practice are fully analogous to the ‘total suppression of sidebands’ (TOSS) sequences, to suppress all sidebands arising from the spinning of the outer rotor in DOR experiments. By removing the rotor phase dependence of the evolution of the sidebands, the sidebands destructively interfere with one another during the course of signal averaging to yield ‘solution-like’ spectra of half-integer quadrupolar nuclei in solids. Advantages and shortcomings of the method compared to other DOR sideband suppression methods are explored with the aid of simulations. [Copyright &y& Elsevier]

The group 2 metal halides and corresponding metal halide hydrates serve as useful model systems for understanding the relationship between the electric field gradient (EFG) and chemical shift (CS) tensors at the halogen nuclei and the local molecular and electronic structure. Here, we present a 35/37Cl and 43Ca solid-state nuclear magnetic resonance (SSNMR) study of CaCl2. The 35Cl nuclear quadrupole coupling constant, 8.82(8) MHz, and the isotropic chlorine CS, 105(8) ppm (with respect to dilute NaCl(aq)), are different from the values reported previously for this compound, as well as those reported for CaCl2·2H2O. Chlorine-35 SSNMR spectra are also presented for CaCl2·6H2O, and when taken in concert, the SSNMR observations for CaCl2, CaCl2·2H2O, and CaCl2·6H2O clearly demonstrate the sensitivity of the chlorine EFG and CS tensors to the local symmetry and to changes in the hydration state. For example, the value of δiso decreases with increasing hydration. Gauge-including projector-augmented wave (GIPAW) density functional theory (DFT) calculations are used to substantiate the experimental SSNMR findings, to rule out the presence of other hydrates in our samples, to refine the hydrogen positions in CaCl2·2H2O, and to explore the isostructural relationship between CaCl2 and CaBr2. Finally, the 43Ca CS tensor span is measured to be 31(5) ppm for anhydrous CaCl2, which represents only the fifth CS tensor span measurement for calcium. [ABSTRACT FROM AUTHOR]

Zeroth-order regular approximation (ZORA) density functional theory (DFT) calculations of one-bond X-19F indirect nuclear spin-spin coupling ( J) tensors were performed on a series of fluorine-containing compounds covering several valence shell electron pair repulsion (VSEPR) theory geometries for which J, by symmetry, is not required to be axially symmetric. The calculations show that the antisymmetric components of J are only of the same order of magnitude as the principal components of the symmetric J-coupling tensor for a few geometries, and that in cases of approximate axial symmetry along the bond, J remains nearly axially symmetric with its unique component along the bond. In general, different species having the same nominal geometry tend to have similar tensor orientations, magnitudes of anisotropy of J relative to the isotropic coupling constant, as well as the same dominant contributions from the different coupling mechanisms. Structures are also systematically modified to determine how the tensor components depend on geometrical parameters. The isotropic coupling constants are subsequently interpreted using a natural localized molecular orbital (NLMO) approach. Our results could prove to be useful for future experimental characterizations of J tensors in systems having symmetry properties that do not force J to be axially symmetric or coincident with the dipolar coupling tensor. [ABSTRACT FROM AUTHOR]

Calcium is an important component of materials, metalloproteins, minerals, glasses, and small inorganic and organic complexes. However, NMR spectroscopy of the quadrupolar 43Ca nuclide remains difficult primarily due to its low natural abundance and low resonance frequency. In this Perspective, experimental challenges and recent successes in the field are highlighted, with a focus on solid-state 43Ca NMR spectroscopy. Solution 43Ca NMR studies of calcium-binding biomolecules are also presented. The structural insights afforded from quadrupolar and chemical shift parameters are examined. For example: isotropic chemical shifts have been shown to correlate with the mean Ca–O distance and also with calcium coordination number; quadrupolar coupling constants and chemical shift tensor spans have been shown to be useful probes of polymorphism; and, distance measurements involving 43Ca have been recently demonstrated. Lastly, challenges and opportunities for the future are considered. [ABSTRACT FROM AUTHOR]

XH/π interactions make important contributions to biomolecular structure and function. These weakly polar interactions, involving π-system acceptor groups, are usually identified from the three-dimensional structures of proteins. Here, nuclear magnetic resonance spectroscopy has been used to directly detect methyl/π (Me/π) interactions in proteins at atomic resolution. Density functional theory calculations predict the existence of weak scalar (J) couplings between nuclei involved in Me/π interactions. Using an optimized isotope-labelling strategy, these J couplings have been detected in proteins using nuclear magnetic resonance spectroscopy. The resulting spectra provide direct experimental evidence of Me/π interactions in proteins and allow a simple and unambiguous assignment of donor and acceptor groups. The use of nuclear magnetic resonance spectroscopy is an elegant way to identify and experimentally characterize Me/π interactions in proteins without the need for arbitrary geometric descriptions or pre-existing three-dimensional structures. [ABSTRACT FROM AUTHOR]

Abstract: Using 31P solid-state NMR spectroscopy, anisotropy in the indirect 199Hg-31P spin–spin coupling tensor (ΔJ) for powdered [HgPCy3(OAc)2]2 (1) has been measured as 4700±300Hz. Zeroth-order regular approximation (ZORA) density functional theory (DFT) calculations, including scalar and spin-orbit relativistic effects, performed on 1 and a series of other related compounds show that ΔJ(199Hg, 31P) arises entirely from the ZORA Fermi-contact–spin-dipolar cross term. The calculations validate assumptions made in the spectral analysis of 1 and in previous determinations of ΔJ in powder samples, namely that J is axially symmetric and shares its principal axis system with the direct dipolar coupling tensor (D). Agreement between experiment and theory for various 199Hg, 31P spin–spin coupling anisotropies is reasonable; however, experimental values of 1 J(199Hg, 31P)iso are significantly underestimated by the calculations. The most important improvements in the agreement were obtained as a result of including more of the crystal lattice in the model used for the calculations, e.g., a change of 43% was noted for 1 J(199Hg, 31P)iso in [HgPPh3(NO3)2]2 depending on whether the two or three nearest nitrate ions are included in the model. Finally, we have written a computer program to simulate the effects of non-axial symmetry in J and of non-coincidence of the J and D on powder NMR spectra. Simulations clearly show that both of these effects have a pronounced impact on the 31P NMR spectrum of 199Hg–31P spin pairs, suggesting that the effects should be observable experimentally if a suitable compound can be identified. [Copyright &y& Elsevier]

NMR parameters such as indirect nuclear spin–spin coupling (J), nuclear magnetic shielding (σ), direct dipolar coupling (D), and electric field gradient (V) are properly described by second-rank tensors. Each may be decomposed into isotropic, symmetric, and antisymmetric components; the number of these three components which may be nonzero is a distinguishing attribute of each interaction tensor. The rank-1 antisymmetric portion of J (Janti) holds the distinction of remaining the only nonzero part of these fundamental NMR interaction tensors which has never been observed experimentally. Accordingly, effects from Janti are usually ignored, but it is important to consider when this is valid. An experimental strategy for observing Janti in powdered samples of tightly coupled homonuclear spin pairs, based on ideas originally presented by Andrew and Farnell (Mol. Phys. 1968, 15, 157), is described. The theory of Andrew and Farnell is extended to powder samples, and methods for analyzing NMR spectra from powdered samples are presented. It is found that, in certain rare cases, Janti has the potential to affect the NMR line shapes from AB spin systems, but that even in these systems, the most intense features of the spectra are not affected and may be analyzed independently of Janti. Furthermore, Janti will only have an observable effect on the NMR spectra when its magnitude is comparable with that of Jiso and with the difference in chemical shifts (in Hz) between the two sites. Finally, the first experimental attempts to measure Janti are reported, and experimental proof that no elements of Janti(119Sn,119Sn) in hexa(p-tolyl)ditin are larger than 2900 Hz is given. The benefits of modern double-quantum filtering NMR pulse sequences in isolating effects from Janti are also illustrated. [ABSTRACT FROM AUTHOR]

The accurate calculation of the isotropic (Jiso) and anisotropic (ΔJ) parts of indirect nuclear spin–spin coupling tensors is a stringent test for quantum chemistry, particularly for couplings involving heavy isotopes where relativistic effects and relativity – electron correlation cross terms are expected to play an important role. Experimental measurements on diatomic molecules in the gas phase offer ideal data for testing the success of computational approaches, since the data are essentially free from intermolecular effects, and precise coupling anisotropies may be reliably extracted in favourable cases. On the basis of available experimental molecular-beam coupling-tensor parameters for diatomic alkali metal halides, we tabulate known values of Jiso and, taking rotational–vibrational corrections to the direct dipolar coupling constant into account, precise values of ΔJ are determined for the ground rovibrational state. First-principles calculations of the coupling tensors were performed using a recently developed program based on hybrid density functional theory using the two-component relativistic zeroth-order regular approximation (ZORA). Experimental trends in Jiso and ΔJ are reproduced with correlation coefficients of 0.993 and 0.977, respectively. Periodic trends in the coupling constants and their dependence on the product of the atomic numbers of the coupled nuclei are discussed. Finally, the hybrid functional method is also successfully tested against experimental data for a series of polyatomic xenon fluorides and group-17 fluorides. [ABSTRACT FROM AUTHOR]

Natural-abundance 43Ca solid-state NMR spectroscopy at 21.1 T and gauge-including projector-augmented-wave (GIPAW) DFT calculations are developed as tools to provide insight into calcium binding environments, with special emphasis on the calcium chemical shift (CS) tensor. The first complete analysis of a 43Ca solid-state NMR spectrum, including the relative orientation of the CS and electric field gradient (EFG) tensors, is reported for calcite. GIPAW calculations of the 43Ca CS and EFG tensors for a series of small molecules are shown to reproduce experimental trends; for example, the trend in available solid-state chemical shifts is reproduced with a correlation coefficient of 0.983. The results strongly suggest the utility of the calcium CS tensor as a novel probe of calcium binding environments in a range of calcium-containing materials. For example, for three polymorphs of CaCO3 the CS tensor span ranges from 8 to 70 ppm and the symmetry around calcium is manifested differently in the CS tensor as compared with the EFG tensor. The advantages of characterizing the CS tensor are particularly evident in very high magnetic fields where the effect of calcium CS anisotropy is augmented in hertz while the effect of second-order quadrupolar broadening is often obscured for 43Ca because of its small quadrupole moment. Finally, as an application of the combined experimental-theoretical approach, the solid-state structure of the vaterite polymorph of calcium carbonate is probed and we conclude that the hexagonal P63/mmc space group provides a better representation of the structure than does the orthorhombic Pbnm space group, thereby demonstrating the utility of 43Ca solid-state NMR as a complementary tool to X-ray crystallographic methods. [ABSTRACT FROM AUTHOR]

Abstract: A coherent laser radar (or Doppler lidar) operating at a wavelength of 1.55μm has been mounted on the nacelle of a 2.3MW wind turbine in order to measure the wind speed in front of the blades at ranges up to 200m. The lidar measures the component of wind speed along its beam direction but, since it rotates with the nacelle to point into the wind, this component normally differs negligibly from the actual wind speed. As an example to demonstrate the lidar''s capabilities, we present samples of wind data gathered over an 18h period in March 2003, illustrating the development of gusts that appears to be associated with the onset of solar ground heating. Wind speeds over the full period lay in the range 4–10ms−1, and the gusts were evident as a near-discontinuity in wind speed typically of order 1–2ms−1, but reaching values larger than 3ms−1. The typical timescale between gusts was of order 1min. Improvements to this experiment are proposed that will provide more detailed information on spatial and temporal structure of such gusts. [Copyright &y& Elsevier]

Reaction of RuCl2(PPh3)3 with LiNN′ (NN′ = 2-[(2,6-diisopropylphenyl)imino]pyrrolide) affords a single product, with the empirical formula RuCl[(2,6-iPr2C6H3)N=CHC4H3N](PPh3)2. We identify this species as a σ-pyrrolato complex, [Ru(NN′)(PPh3)2]2(μ-Cl)2 (3b), rather than mononuclear RuCl(NN′)(PPh3)2 (3a), on the basis of detailed 1D and 2D NMR characterization in solution and in the solid state. Retention of the chelating, σ-bound iminopyrrolato unit within 3b, despite the presence of labile (dative) chloride and PPh3 donors, indicates that the chelate effect is sufficient to inhibit σ → π isomerization of 3b to a piano-stool, π-pyrrolato structure. 2D COSY, SECSY, and J-resolved solid-state 31p NMR experiments confirm that the PPh3 ligands on each metal center are magnetically and crystallographically inequivalent, and 31p CP/MAS NMR experiments reveal the largest 99Ru-31P spin-spin coupling constant (¹J(99Ru,31P) = 244 ± 20 Hz) yet measured. Finally, 31P dipolar-chemical shift spectroscopy is applied to determine benchmark phosphorus chemical shift tensors for phosphine ligands in hexacoordinate ruthenium complexes. [ABSTRACT FROM AUTHOR]

The results of a detailed systematic chlorine solid-state NMR study of several hydrochloride salts of amino acids implicated in chloride ion transport channel selectivity are reported. 35Cl and 37Cl NMR spectra have been obtained for stationary and/or magic-angle spinning powdered samples of the following compounds on 500 and/or 900 MHz spectrometers: DL-arginine HCI monohydrate, L-lysine HCI, L-serine HCI, L-glutamic acid HCI, L-proline HCI, L-isoleucine HCI, L-valine HCI, L-phenylalanine HCI, and glycine HCI. Spectral analyses provide information on the anisotropic properties and relative orientations of the chlorine electric field gradient and chemical shift (CS) tensors, which are intimately related to the local molecular and electronic structure. Data obtained at 900 MHz provide unique examples of the effects of CS anisotropy on the NMR spectrum of a quadrupolar nucleus. The range of chlorine quadrupolar coupling constants (CQ) measured, -6.42 to 2.03 MHz, demonstrates the sensitivity of this parameter to the chloride ion environment and suggests the applicability of chlorine solid-state NMR as a novel experimental tool for defining chloride binding environments in larger ion channel systems. Salts of hydrophobic amino acids are observed to tend to exhibit larger values of CQ than salts of hydrophilic amino acids. A simple model for rationalizing the observed trend in CQ is proposed. For salts for which neutron diffraction structures are available, we identify a quantum chemical method which reproduces experimental values of CQ with a root-mean-square deviation of 0.1 MHz and a correlation coefficient of 0.9998. On the basis of this, chlorine NMR tensors are predicted for the Cl- binding site in CIC channels. [ABSTRACT FROM AUTHOR]

Incomplete motional averaging of chemical shift anisotropy upon weak alignment of nucleic acids and proteins in a magnetic field results in small changes in chemical shift. Knowledge of nucleus-specific chemical shift (CS) tensor magnitudes and orientations is necessary to take full advantage of these measurements in biomolecular structure determination. We report the determination by liquid crystal NMR of the CS tensors for all ribose carbons in A-form helical RNA, using a series of novel 3D NMR pulse sequences for accurate and resolved measurement of the ribose 13C chemical shifts. The orientation of the riboses relative to the rhombic alignment tensor of the molecule studied, a stem-loop sequence corresponding to helix-35 of 238 rRNA, is known from an extensive set of residual dipolar couplings (RDC), previously used to refine its structure. Singular-value-decomposition fits of the chemical shift changes to this structure, or alternatively to a database of helical RNA X-ray structures, provide the CS tensor for each type of carbon. Quantum chemical calculations complement the experimental results and confirm that the most shielded tensor component lies approximately along the local carbon-oxygen bond axis in all cases and that shielding anisotropy for C3' and C4' is much larger than for C1' and C2', with C5' being intermediate. [ABSTRACT FROM AUTHOR]

Solid-state [sup 17]O NMR spectroscopy is employed to characterize powdered samples of known monoclinic and orthorhombic modifications of [sup 17]O-enriched triphenylphosphine oxide, Ph[sub 3]PO. Precise data on the orientationdependent [sup 17]O electric field gradient (EFG) and chemical shift (CS) tensors are obtained for both polymorphs. While the [sup 17]O nuclear quadrupolar coupling constants (C[sub Q]) are essentially identical for the two polymorphs (C[sub Q] = -4.59 ± 0.01 MHz (orthorhombic); C[sub Q] = -4.57 ± 0.01 MHz (monoclinic)), the spans (Ω) of the CS tensors are distinctly different (Ω = 135 ± 3 ppm (orthorhombic); Ω = 155 ± 5 ppm (monoclinic)). The oxygen CS tensor is discussed in terms of Ramsey's theory and the electronic structure of the phosphorus-oxygen bond. The NMR results favor the hemipolar σ-bonded R[sub 3]P[sup +]-O[sup -] end of the resonance structure continuum over the multiple bond representation. Indirect nuclear spin-spin (J) coupling between [sup 31]P and [sup 17]O is observed directly in [sup 17]O magicangle-spinning (MAS) NMR spectra as well as in [sup 31]P MAS NMR spectra. Ab initio and density-functional theory calculations of the [sup 17]O EFG, CS, and ¹J([sup 31]P,[sup 17]O) tensors have been performed with a variety of basis sets to complement the experimental data. This work describes an interesting spin system for which the CS, quadrupolar, J, and direct dipolar interactions all contribute significantly to the observed [sup 17]O NMR spectra and demonstrates the wealth of information which is available from NMR studies of solid materials. [ABSTRACT FROM AUTHOR]

Examines the structure of silver cyanide by solid-state multinuclear magnetic resonance spectroscopy. Linearity of polymeric chains; Domination of two-site model by indirect nuclear spin-spin coupling between [sup 109/107]Ag and [sup 12]C nuclei; Application of the zeroth-order regular approximation density functional theory calculation.

Examines the nuclear spin-spin coupling tensors for polyatomic xenon fluorides and group 17 fluorides. Reduction of coupling constants for halogen-noble gas spin pairs; Use of zeroth-order regular approximation density-functional theory method in interpreting spin-spin coupling of polyatomic systems; Mechanisms of chlorine-fluorine isotropic coupling constants.

Examines the advantages on the calculations of an indirect nuclear pin-spin coupling tensors. Usability of nuclear magnetic resonance spectroscopy; Characterization of an inorganic semiconducting materials; Complexity of the polyatomic molecules.

Presents a computational quantum chemistry experiment that illustrates the connection between nuclear magnetic resonance parameters and state-of-the-art ab initio calculations. Chemical shifts and nuclear magnetic shielding; Connection of nuclear magnetic shielding tensors to nuclear spin-rotation tensors; Quadropolar coupling constants.

Compares results obtained by experiment and first principle calculations on indirect nuclear spin to spin coupling tensors in diatomic molecules. Equivalence of hyperfine parameter in isotropic spin to spin coupling constant; Calculation of complete tensor determination reliability; Observation of isolated molecules in the experimental data.

Among the interactions which govern NMR spectra, spin-spin coupling interactions provide the most direct form of structural information which is of interest to chemists. Dipolar coupling may be used to measure internuclear distances directly and J coupling may be used to identify bonding interactions and provide insights into the nature of the bonds. It is well known that the presence of a quadrupolar interaction reintroduces the dipolar interaction in spinning samples; however, similarly to the J coupling, this information is often lost if the observed nucleus is quadrupolar due to quadrupolar spectral broadening. Here we show for multiple spin pairs that double-rotation (DOR) NMR fully removes the effects of the quadrupolar interaction on the NMR spectrum leaving only the effects of dipolar and J couplings. We also demonstrate that the J coupling multiplets do not disappear for quadrupolar A2 spin pairs as they do for spin-1/2 nuclei. With DOR NMR, it is then straightforward to measure homonuclear J coupling constants between magnetically equivalent quadrupolar nuclei. A deeper understanding of the origins of the magnitudes and dominant mechanisms of J coupling for quadrupolar spin pairs in a series of related compounds is obtained by decomposing computed J coupling constants into their major molecular orbital contributions. [ABSTRACT FROM AUTHOR]

This Virtual Special Issue brings together new and original research articles covering a range of industrial applications of solid-state NMR. The issue comprises six original research articles as well as a report entitled Solid State NMR Service Across the World. Industrial applications of solid-state NMR are not necessarily always as widely publicized as are academic applications or applications of solution NMR in industry. [Extracted from the article]