The structure of trimethyltin fluoride.

Tracking the evolution and differences between guest-induced phases of Ga-MIL-53 via ultra-wideline 69/71Ga solid-state NMR spectroscopy

Publisher Summary This article reviews the progress of solid-state nuclear magnetic resonance (NMR). It emphasizes on the methodological developments. The applications of the technical advances, particularly those that are significant to chemistry, biochemistry, biology, and materials science have been discussed. Higher magnetic fields, more intense decoupling power, higher spinning rates, more robust pulse sequences, and novel designs of RF coils remain the routes pursued in achieving better solid-state NMR spectra. These advances, mainly in hardware, along with developments of pulse sequences, have tremendous potential in virtually every aspect of solid-state NMR and nuclear magnetic resonance imaging. Each of these is covered in the chapter. It discusses the theoretical and computational progress in solid-state NMR, which includes calculations of the lineshapes and dynamic processes based on density matrix theory or computations of the interaction parameters based on quantum mechanics. The chapter is also devoted to progresses in the efficient decoupling of dipolar interactions in solid samples, which is another method for obtaining high-resolution NMR spectra. It summarizes recently proposed recoupling schemes and reviews various types of correlation spectroscopy. Developments in cross-polarization and spin diffusion/ exchange are reviewed and the main achievements in solid NMR imaging have also been summarized.

Vinyl and methyl-ester groups in the insoluble polymer drug patiromer identified and quantified by solid-state NMR

A comprehensive collection of solid-state 31P NMR spectra of aluminophosphate zeolites

Gas hydrate in core samples recovered from depths between 898 and 1107 m in the JAPEX/JNOC/GSC et al.Mallik 5L-38 gas hydrate production research well was characterized using powder X-ray diffraction (PXRD), Raman spectroscopy, and solid-state nuclear magnetic resonance (NMR) spectroscopy. The PXRD results show that the gas hydrate present is Structure I (sI), with typical lattice constants of 1.186 to 1.188 nm (at 100K). The 13CNMR spectra, obtained at 173K, show the characteristic sI hydrate pattern for methane distributed over the two sI hydrate cages.Variable line widths reflect the mineral content. The Raman spectra also reflect the presence of methane encaged in the two sI hydrate cages. The occupancy ratios for methane in the small and large cages, derived from the NMR and Raman spectra, were used to estimate hydration numbers according to the solid-solution theory of van der Waals and Platteeuw. Hydration numbers range from 6.1 to 6.3, in good agreement with those determined for pure gas hydrate.

Taking advantage of an order of magnitude in sensitivity enhancement obtained by sampling of quadrupolar-echo (QE) solid-state NMR spectra during a quadrupolar Carr−Purcell−Meiboom−Gill (QCPMG) pulse sequence, we demonstrate that the coordination environment of low-γ quadrupolar metal nuclei can be studied routinely for powders with these nuclei in natural abundance. The general applicability of the method is demonstrated by 39K, 25Mg, 67Zn, and 87Sr QCPMG solid-state NMR experiments for K2MoO4, KVO3, Mg(VO3)2, Zn(CH3COO)2·2H2O, Zn(Ala)2·H2O, Sr(NO3)2, and SrMoO4. For all samples the quadrupolar coupling parameters and the isotropic chemical shifts are extracted by numerical simulation and iterative fitting of the spin−echo sideband spectra observed in the experimental QCPMG NMR spectra. These parameters are discussed in light of the crystal structures for the compounds.

Characterization of the molecular structure and physicochemical solid-state properties of the solid forms of pharmaceutical compounds is a key requirement for successful commercialization as potential active ingredients in drug products. These properties can ultimately have a critical effect on the solubility and bioavailability of the final drug product. Here, the desmotropy of Albendazole forms I and II was investigated at the atomic level. Ultrafast magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectroscopy, together with powder X-ray diffraction, thermal analysis, and Fourier transform infrared spectroscopy, were performed on polycrystalline samples of the two solids in order to fully characterize and distinguish the two forms. High-resolution one-dimensional (1)H, (13)C, and (15)N together with two-dimensional (1)H/(1)H single quantum-single quantum, (1)H/(1)H single quantum-double quantum, and (1)H/(13)C chemical shift correlation solid-state NMR experiments under MAS conditions were extensively used to decipher the intramolecular and intermolecular hydrogen bonding interactions present in both solid forms. These experiments enabled the unequivocal identification of the tautomers of each desmotrope. Our results also revealed that both solid forms may be described as dimeric structures, with different intermolecular hydrogen bonds connecting the tautomers in each dimer.

Principle component analysis (PCA) was used to extract components from the solid-state nuclear magnetic resonance (NMR) spectra of bacterial cellulose (BC). Polymers such as cellulose have several domain structures, and their structure and dynamics are reflected in the variety of solid-state spectra derived from different parameters. The complexity of the obtained spectra makes the analysis of spectra from relaxation measurements difficult. Multivariate analysis, such as PCA, has been suggested as an option to improve NMR spectral analyses. In this study, we attempted to extract peak components from cross polarization (CP) experiment data from the variable contact time spectra of BC by using PCA. The extracted peaks were annotated according to previous reports, and the existence of crystalline Iα was clearly recognized. The important components of the BC structure (that is, crystalline Iα, amorphous form and mobility) were separated in the PCA-loading plot and CP curve. A multivariate analysis was used to extract components in solid-state nuclear magnetic resonance (NMR) spectra from bacterial cellulose (BC). Polymers such as cellulose have several domain structures, and their structure and dynamics are reflected in the variety of solid-state spectra derived from different parameters. Multivariate analysis, such as principle component analysis (PCA), is suggested as an option to improve analyses of complex NMR spectra from relaxation measurements. In this study we demonstrate the extraction of peak components using PCA from cross polarization experiment data with variable contact time spectra of BC.

Mesoporous titanium oxide synthesized using a dodecylamine template was treated with 0.2, 0.6, and 1.0 equiv of Li- or Na-naphthalene. The composite materials were characterized by nitrogen adsorption, powder X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, and solid-state 23Na and 7Li NMR spectroscopy. In all cases the wormhole mesoporosity was retained as evidenced by BET surface areas from 400 to 700 m(2)/g, Horvath-Kawazoe pore sizes in the 20 Angstroms range, and a lack of hysteresis in the nitrogen adsorption isotherms. Variable-temperature conductivity studies show that the Li-reduced materials are semiconductors, with conductivity values 3 orders of magnitude higher than those of the Na-reduced materials. Electrochemical measurements demonstrate reversible intercalation/deintercalation of Li+ ions into pristine mesoporous Ti oxides with good cycling capacity. Solid-state 23Na NMR reveals two distinct Na environments: one corresponding to sodium ions in the mesoporous channels and the other corresponding to sodium ions intercalated into the metal framework. 23Na NMR spectra also indicate that the relative population of the framework site increases with increased reduction levels. Solid-state 7Li NMR spectra display a single broad resonance, which increases in breadth with increased reduction levels, though individual resonances inferring the presence of channel and framework Li species are not resolved. Comparisons of the lithium chemical shifts with published values suggests an "anatase-like structure" with no long-range order in the least-reduced samples but a "lithium titanate-like structure" with no long-range order in the higher reduced materials.

A new layered aluminophosphate has been synthesized hydrothermally in the presence of 1,3-diaminopropane and its structure solved from X-ray powder diffraction data. The compound with the composition [C3H12N2]0.5[AlPO4(OH)(H2O)]·H2O crystallizes in the orthorhombic space group Pnma (No. 62) with a = 6.91848(11), b = 22.2989(4) and c = 9.6074(2) Å. The layers contain only 6-co-ordinated aluminium forming [–Al–(OH)–Al–] chains, and these are connected to one another via phosphorus tetrahedra. The structure of the layers is closely related to that of the layered aluminium methylphosphonate AlMepO-ζ. This compound represents the third example of layered aluminophosphates with an atomic ratio P∶Al = 1∶1. Its thermal decomposition has been monitored by X-ray diffraction and solid state NMR.

We report a combined solid-state (1H, 2H, 13C, 17O) NMR and plane-wave density functional theory (DFT) computational study of the O···H···O low-barrier hydrogen bonds (LBHBs) in two 1,3-diketone compounds: dibenzoylmethane (1) and curcumin (2). In the solid state, both 1 and 2 exist in the cis-keto-enol tautomeric form, each exhibiting an intramolecular LBHB with a short O···O distance (2.435 Å in 1 and 2.455 Å in 2). Whereas numerous experimental (structural and spectroscopic) and computational studies have been reported for the enol isomers of 1,3-diketones, a unified picture about the proton location within an LBHB is still lacking. This work reports for the first time the solid-state 17O NMR data for the O···H···O LBHBs in 1,3-diketones. The central conclusion of this work is that detailed information about the probability density distribution of the proton (nuclear zero-point motion) across an LBHB can be obtained from a combination of solid-state NMR and plane-wave DFT computations (both NMR parameter calculations and ab initio molecular dynamics simulations). We propose that the precise proton probability distribution across an LBHB should provide a common basis on which different and sometimes seemingly contradicting experimental results obtained from complementary techniques, such as X-ray diffraction, neutron diffraction, and solid-state NMR, can be reconciled.

Nuclear magnetic resonance spectroscopy is a very versatile technique for the investigation of biomolecular structures and dynamics. In this thesis, solution and solid state NMR methods have been applied to study a membrane protein and its interactions with a ligand and an antagonist, to characterize the thermodynamics of protein dimerization, and to observe changes in the hydrogen bond network of proteins and nucleic acids under the influence of high pressure. The first part describes the expression, purification, and characterization of the membrane protein CCR5 and its ligand RANTES. The second part is concerned with the effect of pressure on the hydrogen bond network in proteins and nucleic acids. The G protein-coupled receptor CCR5 is the major HIV-1 coreceptor and thus a very important target for the development of HIV-1 entry inhibitors. The large-scale expression and purification of CCR5, leading to 1 mg of pure protein per liter cell culture after purification, is described. The receptor's functionality is shown via recognition by a conformation-dependent antibody and by binding of the endogenous ligand RANTES. The possibility to obtain large amounts of functional CCR5 overcomes a major bottleneck for the structural characterization of this membrane protein. The receptor and its ligand were further characterized by NMR spectroscopy. First heteronuclear solution state NMR spectra of selectively labeled CCR5 were obtained. The interaction of the receptor with the chemokine RANTES was studied by solution NMR as well as in a lipid environment using solid state NMR experiments. In these experiments, binding of RANTES to CCR5 is observed. Many chemokines undergo dimerization in the low micro- to millimolar range, but the biological relevance of this phenomenon is under debate. The temperature and pressure dependence of the RANTES monomer/dimer equilibrium was characterized by NMR spectroscopy. This study reveals the enthalpy and entropy contributions to RANTES dimerization. In addition, a pressure-induced unfolded state was observed for the first time. A solely monomeric mutant of RANTES was designed and shown to inhibit HIV-1 infection in vitro. This is the basis for further studies of the complex between RANTES and CCR5 as well as CCR5-derived peptides. Hydrogen bonds are extremely important to stabilize the structures of proteins and nucleic acids. In this thesis, methods to measure the scalar couplings across hydrogen bonds in these biomolecules are described. They were applied to study pressure-dependent changes in the hydrogen bond scalar couplings in ubiquitin. The most pressure-labile regions of the protein were identified. These largely correspond to regions which are destabilized at elevated temperature. Pressure- and temperature-dependent hydrogen bond scalar couplings have also been measured in a small RNA hairpin. The data indicate that the average pressure-induced changes of hydrogen bond length are similar in nucleic acids and proteins.

Synthetic and commercial carboxymethyl cellulose (CMC) sodium salts were analyzed by CP-MAS 13C-NMR and plasma emission analysis. CMC was synthesized in the lab from cotton alkali cellulose and sodium chloroacetate. The progressive changes in the chemical composition and morphology (and reflected in the degree of substitution, DS) were followed by solid-state NMR. Observed differences in solid-state NMR spectra are discussed in terms of DS, chemical composition, dynamics, and polymorphism. The effect of molecular weight in CMC morphology and dynamics can be assessed by small differences observed in peak shapes and peak positions in the CP-MAS spectra.

A series of fumarate-based organocobalt(I) [CoCp(CO)(fumarate)] catalysts is synthesized and characterized by X-ray crystallography, multinuclear (13 C and 59 Co) solid-state NMR spectroscopy, and 59 Co NQR spectroscopy. Given the dearth of 59 Co solid-state NMR studies on CoI compounds, the present work constitutes the first systematic characterization of the 59 Co electric field gradient and chemical shift tensors for a series of cobalt complexes in this oxidation state. Using X-ray crystallography, the molecular geometry about the CoI centre is found to be nearly identical in all compounds studied herein. Owing to the 59 Co nucleus' large chemical shift range, solid-state NMR experiments are found to be able to detect small structural differences between the individual organocobalt(I) compounds. With the aid of density functional theory calculations on these complexes, it is shown that the 59 Co chemical shift anisotropy and the 59 Co quadrupolar coupling constant are both extremely sensitive gauges of the Fu-Co-Cp bond angle, providing a link between these 59 Co NMR observables and the catalysts' structures.

Solid-state nuclear magnetic resonance (NMR) spectroscopy is an atomic-level method used to determine the chemical structure, three-dimensional structure, and dynamics of solids and semi-solids. This Primer summarizes the basic principles of NMR as applied to the wide range of solid systems. The fundamental nuclear spin interactions and the effects of magnetic fields and radiofrequency pulses on nuclear spins are the same as in liquid-state NMR. However, because of the anisotropy of the interactions in the solid state, the majority of high-resolution solid-state NMR spectra is measured under magic-angle spinning (MAS), which has profound effects on the types of radiofrequency pulse sequences required to extract structural and dynamical information. We describe the most common MAS NMR experiments and data analysis approaches for investigating biological macromolecules, organic materials, and inorganic solids. Continuing development of sensitivity-enhancement approaches, including 1H-detected fast MAS experiments, dynamic nuclear polarization, and experiments tailored to ultrahigh magnetic fields, is described. We highlight recent applications of solid-state NMR to biological and materials chemistry. The Primer ends with a discussion of current limitations of NMR to study solids, and points to future avenues of development to further enhance the capabilities of this sophisticated spectroscopy for new applications.