Nuclear Magnetic Resonance Properties Research Articles

Computational studies of effects of tubular lengths on the NMR properties of pristine and carbon decorated boron phosphide nanotubes

Density functional theory (DFT) calculations were performed to investigate the effects of tubular lengths on the nuclear magnetic resonance (NMR) properties of boron phosphide (BP) nanotubes. To this aim, the properties of pristine and carbon decorated (C-decorated) models of representative zigzag and armchair BP nanotubes were investigated. The results indicated that the atoms at the edges of nanotubes do not detect any significant changes. The NMR properties of boron atoms only detect slight changes but those of phosphorous atoms are more notable.

New insights into the synthesis and characterization of 2‐methoxy‐3‐alkylpyrazines and their deuterated isotopologues

AbstractA previously described synthetic route for preparation of 2‐methoxy‐3‐alkylprazines (MPs) based on condensation of glyoxal with an α‐amino acid amide, followed by methylation with iodomethane yields 3‐alkyl‐1‐methyl‐1H‐pyrazin‐2‐ones (N‐methyl derivatives), rather than the designated 2‐methoxy‐3‐alkylpyrazines (O‐methyl derivatives). Despite similar nuclear magnetic resonance and mass spectral properties, gas chromatographic (GC) retention indices differ significantly, indicating chemical difference. With the example of 3‐sec‐butyl‐1‐methyl‐1H‐pyrazin‐2‐one and its 3‐sec‐butyl‐1‐[2H3]methyl‐1H‐pyrazin‐2‐one isotopologue, the position of the methyl group introduced could be assigned unambiguously, using heteronuclear multiple bond correlation (HMBC) NMR experiments. For future characterization, the spectroscopic (NMR, EI+MS) as well as GC retention index data on two stationary phases of the most aroma relevant MPs and their deuterated isotopologues are summarized. Copyright © 2011 John Wiley & Sons, Ltd.

DFT calculations of NMR properties for GaP nanotubes

Density functional theory calculations were performed to investigate representative models of (6,0) zigzag and (4,4) armchair gallium phosphide nanotubes (GaPNTs). Nuclear magnetic resonance properties including isotropic and anisotropic chemical shielding parameters (CSI and CSA) were calculated for 69Ga and 31P atoms of the optimized structures. The calculated CS parameters indicated that the P atoms detect slight changes of electronic environment in the GaPNT structures, but the changes for the Ga atoms are more significant. Moreover, armchair GaPNTs could be considered a more reactive material than the zigzag model for interactions with other atoms or molecules.

95Mo nuclear magnetic resonance parameters of molybdenum hexacarbonyl from density functional theory: appraisal of computational and geometrical parameters

Solid-state (95)Mo nuclear magnetic resonance (NMR) properties of molybdenum hexacarbonyl have been computed using density functional theory (DFT) based methods. Both quadrupolar coupling and chemical shift parameters were evaluated and compared with parameters of high precision determined using single-crystal (95)Mo NMR experiments. Within a molecular approach, the effects of major computational parameters, i.e. basis set, exchange-correlation functional, treatment of relativity, have been evaluated. Except for the isotropic parameter of both chemical shift and chemical shielding, computed NMR parameters are more sensitive to geometrical variations than computational details. Relativistic effects do not play a crucial part in the calculations of such parameters for the 4d transition metal, in particular isotropic chemical shift. Periodic DFT calculations were tackled to measure the influence of neighbouring molecules on the crystal structure. These effects have to be taken into account to compute accurate solid-state (95)Mo NMR parameters even for such an inorganic molecular compound.

Nuclear-Magnetic-Resonance Petrophysics in Thin Sand/Shale Laminations

Summary We discuss the use of nuclear-magnetic-resonance (NMR) logging in the petrophysical evaluation of thin sand/shale laminations. NMR helps detect thin beds, determine fluid type, establish the hydrocarbon type and volume if hydrocarbon is present, and, finally, determine the permeability of the sand layers (as opposed to that of the sand/shale system). Experiments were conducted on samples of 100% sand, 100% clay, and sand/clay layers with an NMR-logging tool at surface to verify the characteristic T2 bimodal relaxation distribution often observed in NMR logs that are acquired in thin beds. From the bimodal distribution, it is often possible to determine a cutoff to separate the productive sand layers from the shale layers and, with it, the porosity fraction of each component. Subsequently, the sand fraction, or net/gross ratio, can be estimated assuming that the 100%-sand porosity is known. Because gas, oil, and water have different NMR properties, fluid-typing techniques such as 2D NMR offer useful insights into the fluid type and properties in thin-layer sands. Because the laminations thickness is often less than the antenna aperture, the estimated permeability of the sand/ shale system will undercall the true permeability of the sand layers only. In this case, their permeability can be estimated quickly from Darcy's fluid-flow model. We show examples of thin sand/shale laminations that are oil-bearing and gas-bearing. In each case, the NMR detection was verified against borehole-imaging logs, and the fluid type in the sands was determined from multidimensional NMR analysis. The derived hydrocarbon volume was then compared with the results estimated from a triaxial induction tool. Permeability of the sand layers was also computed and compared to that of nearby thick sands. Core data in one well was used to validate NMR detection, porosity, permeability, and net sand thickness.

NMR of Biopolymer-Apatite Composites: Developing a Model of the Molecular Structure of the Mineral-Matrix Interface in Calcium Phosphate Biomaterials

Nanoparticulate hydroxyapatites (HAps) reproducing some of the subnanometre length scale intermolecular interactions characteristic of hard tissue have been prepared for nuclear magnetic resonance (NMR) structural elucidation. HAps were precipitated at physiological pH and temperature from dilute aqueous solutions, in the presence of acidic polysaccharides (chondroitin sulfate, dermatan sulfate, hyaluronic acid, dextran sulfate, polygalacturonic acid), and of hydrophilic poly aminoacids (poly-l-glutamate, poly-l-asparagine, poly-l-lysine). The HAp resembles that of bone with respect to its 31P NMR properties, broad reflections in X-ray powder diffraction, and the coexistence of an ordered crystalline core, surrounded by a less ordered surface containing water and hydrogen phosphate. 13C{31P} rotational echo double resonance (REDOR) NMR, which probes carbon−phosphorus proximities below ca. 1 nm, shows that all the HAps are molecular composites in which each biopolymer forms intimate intermolecular associat...

Hyperfine interaction in graphene: The relevance for spintronics

AbstractWe study the nuclear magnetic resonance (NMR) properties of graphene. The interaction between nuclear spins and the orbital motion of Dirac electrons is strongly modified by the linear electronic dispersion with respect to its canonical form. The NMR shift and spin‐lattice relaxation time are calculated as function of temperature, chemical potential, and magnetic field for clean and impure graphene, and three distinct regimes are identified: Fermi‐, Dirac‐gas, and extreme quantum limit (EQL) behaviors. A critical spectrometer assessment shows that NMR is within reach for fully 13C enriched graphene of reasonable size.

ChemInform Abstract: NMR Spectroscopy as a Probe of Surfaces of Supported Metal Catalysts

The nuclear magnetic resonance (NMR) properties of bulk metals are usually dominated by a magnetic coupling between the nuclear spin and the spin of the conduction electrons. The coupling is proportional to the density of one-electron-states at the Fermi energy and results in NMR shifts that are large in comparison with the usual chemical shift range and also in a characteristic temperature dependence of the nuclear spin lattice relaxation rate. In systems that lack the translational invariance of the extended solid, these properties depend on the local electronic environment of the resonating nucleus (the local density of states). Examples of such systems are bulk random alloys and small metal particles, such as those in supported metal catalysts. In certain cases an adsorbate on a metal also acquires such metallic NMR properties; this often happens with carbon monoxide and probably also with hydrogen, the only adsorbates considered in this review. These metallic NMR characteristics are of interest in catalysis for several reasons. In investigations of the metal (typically 195 Pt), the local density of states on the surface is different from that in the bulk so that NMR spectroscopy can be used to determine the metal dispersion. The 1 H NMR shift of adsorbed hydrogen induced by the metal surface can be used to distinguish hydrogen on the metal from that on the support, e.g., in investigations of hydrogen spillover. The spin lattice relaxation rate of adsorbed 13 CO shows that the chemisorption bond has metallic character. On a theoretical level, the local density of electron states at the Fermi energy on metal surface sites plays a role in frontier orbital theories of chemisorption. This quantity can be measured by NMR of the metal for catalysts that have undergone various surface treatments, not necessarily under vacuum conditions, and the results can be qualitatively interpreted in a much simplified version of such a theoretical framework. This review provides a brief presentation of the relevant theory of metals and a thorough discussion of the metallic characteristics observed in the NMR spectroscopy of hydrogen, carbon monoxide, and platinum.

The Analysis of Hyperfine Shifts of Mono-Ligand High-Spin Cobalt(II) Pyrazolylborate Complexes

In this paper, we present the detailed study on the correlation of the nuclear magnetic resonance (NMR) parameters with the results of density functional theory calculations performed for paramagnetic high-spin cobalt(II) complexes with trispyrazolylborate ligands. This work focuses on estimation of dipolar and contact shifts in mono-ligand high-spin cobalt(II) pyrazolylborate systems along with discussion on 1H NMR properties of the mentioned tetra-, penta- and hexacoordinate complexes. The calculation results show frontier molecular orbitals that may be responsible for contact shift. The calculated contact shift values are compared with the dipolar shift and hyperfine ones.

Proton Magnetic Resonance Imaging of Specimens in Simulated Microgravity

In situ proton stray-field (STRAFI) nuclear magnetic resonance (NMR) imaging of diamagnetic samples in simulated microgravity is described. The magnetic field gradient at the edge of the superconductive coil in the magnet of a NMR spectrometer is exploited to levitate diamagnetic samples and, at the same time, obtain their corresponding one-dimensional NMR images. Proton T2 (spin-spin relaxation time)/ diffusion-weighted profiles of samples under simulated microgravity conditions are acquired with a solid-echo radiofrequency pulse sequence. Since water is a diamagnetic main constituent substance of living systems, the methodology described could be useful to monitor non-destructively changes in the NMR properties of water protons induced by simulated microgravity and magnetic forces. Furthermore, this approach may be used to observe other NMR-sensitive nuclei of interest, e.g., fluor-19, phosphorous-31, carbon-13, etc.

Pairwise additivity in the nuclear magnetic resonance interactions of atomic xenon

Nuclear magnetic resonance (NMR) of atomic (129/131)Xe is used as a versatile probe of the structure and dynamics of various host materials, due to the sensitivity of the Xe NMR parameters to intermolecular interactions. The principles governing this sensitivity can be investigated using the prototypic system of interacting Xe atoms. In the pairwise additive approximation (PAA), the binary NMR chemical shift, nuclear quadrupole coupling (NQC), and spin-rotation (SR) curves for the xenon dimer are utilized for fast and efficient evaluation of the corresponding NMR tensors in small xenon clusters Xe(n) (n = 2-12). If accurate, the preparametrized PAA enables the analysis of the NMR properties of xenon clusters, condensed xenon phases, and xenon gas without having to resort to electronic structure calculations of instantaneous configurations for n > 2. The binary parameters for Xe(2) at different internuclear distances were obtained at the nonrelativistic Hartree-Fock level of theory. Quantum-chemical (QC) calculations at the corresponding level were used to obtain the NMR parameters of the Xe(n) (n = 2-12) clusters at the equilibrium geometries. Comparison of PAA and QC data indicates that the direct use of the binary property curves of Xe(2) can be expected to be well-suited for the analysis of Xe NMR in the gaseous phase dominated by binary collisions. For use in condensed phases where many-body effects should be considered, effective binary property functions were fitted using the principal components of QC tensors from Xe(n) clusters. Particularly, the chemical shift in Xe(n) is strikingly well-described by the effective PAA. The coordination number Z of the Xe site is found to be the most important factor determining the chemical shift, with the largest shifts being found for high-symmetry sites with the largest Z. This is rationalized in terms of the density of virtual electronic states available for response to magnetic perturbations.

Extensive theoretical studies of a new energetic material: Tetrazino‐tetrazine‐tetraoxide (TTTO)

[1,2,3,4]Tetrazino-[5,6-e]-[1,2,3,4]tetrazine-[1,3,5,7]tetraoxide (TTTO, C2N8O4) was suggested to be a possible candidate of high energy density materials (HEDM). The most stable conformation of TTTO is a planar structure with C2h symmetry. Using various high-level ab initio methods including Gaussian-n, Complete Basis Set, Full Coupled Cluster, and W1U models of chemistry together with density functional theory based models, the enthalpies of formation of TTTO at 0 K and standard state were calculated precisely. Moreover, the rovibrational and nuclear magnetic resonance properties were predicted as well. The solid state TTTO was studied using the crystal packing models with the Dreiding force-filed and the plane-wave periodic local-density approximation density functional theory. Three stable polymorphous cells of TTTO have been found with either P212121 or P21/C symmetry. The high heat of formation (>200 kcal/mol), the high density (>2.0 g/cm3), the planar nonpolar electronic structure, and the perfect oxygen balance lead TTTO be a very promising HEDM with exceptional performance. This work provides the first theoretical support for further experimental synthesis and testing.

Nonaqueous Magnetic Nanoparticle Suspensions with Controlled Particle Size and Nuclear Magnetic Resonance Properties

We report the preparation of monodisperse maghemite (gamma-Fe2O3) nanoparticle suspensions in heptane, by thermal decomposition of iron(III) acetylacetonate in the presence of oleic acid and oleylamine surfactants. By varying the surfactant/Fe precursor mole ratio during synthesis, control was exerted both over the nanocrystal core size, in the range from 3 to 6 nm, and over the magnetic properties of the resulting nanoparticle dispersions. We report field-cycling 1H NMR relaxation analysis of the superparamagnetic relaxation rate enhancement of nonaqueous suspensions for the first time. This approach permits measurement of the relaxivity and provides information on the saturation magnetization and magnetic anisotropy energy of the suspended particles. The saturation magnetization was found to be in the expected range for maghemite particles of this size. The anisotropy energy was found to increase significantly with decreasing particle size, which we attribute to increased shape anisotropy. This study can be used as a guide for the synthesis of maghemite nanoparticles with selected magnetic properties for a given application.

Reservoir Crude Oil Viscosity Estimation From Wireline NMR Measurements - Rajasthan, India

Summary In 2004, the Mangala, Aishwariya, and Bhagyam fields were discovered in Rajasthan, India. In these high-permeability paraffinic reservoirs, viscosity is one of the main factors controlling performance. Pressure, volume, and temperature (PVT) data show areal and vertical variations in crude properties. Meter-by-meter geo-chemical core analyses corroborate vertical variations in oil composition. Continuous wireline measurements of nuclear magnetic resonance (NMR) properties and station NMR properties from wells drilled with both water-based muds (WBM) and synthetic oil-based muds (OBM) were also used to calculate a viscosity profile. This paper correlates results from all techniques and shows how NMR measurements can provide oil viscosity profiles in com-positionally complex pools. Black-oil PVT samples typically test several meters of reservoir, while Rajasthan geochemical data are available at meter scale. NMR logs provide continuous data, and calibrated to PVT and geochemistry, they can provide the most detailed picture of in-situ viscosity variations. Results were used to construct a detailed spatial description of the reservoir's in-situ oil viscosity. The NMR data helped to define a zone of biodegraded oil up to ∼25 m thick above the oil-water contact (OWC) and showed thin accumulations of higher-viscosity oil on top of minor shale layers within oil columns. The major conclusion is that detailed in-situ oil viscosity profiles can be developed from conventional wireline T2 measurements.

Stray-field nuclear magnetic resonance imaging in microgravity conditions

Magnetic levitation has been proposed as an alternative approach to simulate on Earth microgravity conditions encountered in space, allowing the investigation of weightlessness on materials and biological systems. In general, very strong magnetic fields, 15T or higher, are required to achieve levitation for a majority of diamagnetic substances. Here, we show that it is possible to achieve levitation of these substances in a commercial superconductive magnet operating with a nuclear magnetic resonance (NMR) spectrometer at 9.4T at ambient conditions. Furthermore, stray-field proton NMR imaging is performed in situ at the location where a sample is levitating, showing that it is feasible to obtain the corresponding one-dimensional profile. Considering that water is a diamagnetic substance and the main constituent of living systems, the outlined approach could be useful to investigate alterations in water proton NMR properties induced by low gravity and magnetic forces upon levitating, e.g., seeds, cells, etc. In addition to protons, it would also be possible to observe other nuclei (e.g., F19, P31, etc.) that may be of interest in metabolic and therapeutic investigations.

Transverse and longitudinal nuclear magnetic resonance in superfluid 3He in anisotropic aerogel

It is found that the properties of nuclear magnetic resonance of both superfluid phases of 3He in an anisotropic aerogel can be described in terms of the bulk superfluid order parameters with the orbital order parameter vector fixed by anisotropy of the aerogel sample. It is also shown that, by proper squeezing, it is possible to attain a sample with isotropic NMR properties.

Theoretical predictions of nuclear magnetic resonance parameters in a novel organo-xenon species: Chemical shifts and nuclear quadrupole couplings in HXeCCH

We calibrate the methodology for the calculation of nuclear magnetic resonance (NMR) properties in novel organo-xenon compounds. The available state-of-the-art quantum-chemical approaches are combined and applied to the HXeCCH molecule as the model system. The studied properties are (129)Xe, (1)H, and (13)C chemical shifts and shielding anisotropies, as well as (131)Xe and (2)H nuclear quadrupole coupling constants. The aim is to obtain, as accurately as currently possible, converged results with respect to the basis set, electron correlation, and relativistic effects, including the coupling of relativity and correlation. This is done, on one hand, by nonrelativistic correlated ab initio calculations up to the CCSD(T) level and, on the other hand, for chemical shifts and shielding anisotropies by the leading-order relativistic Breit-Pauli perturbation theory (BPPT) with correlated ab initio and density-functional theory (DFT) reference states. BPPT at the uncorrelated Hartree-Fock level as well as the corresponding fully relativistic Dirac-Hartree-Fock method are found to be inapplicable due to a dramatic overestimation of relativistic effects, implying the influence of triplet instability in this multiply bonded system. In contrast, the fully relativistic second-order Moller-Plesset perturbation theory method can be applied for the quadrupole coupling, which is a ground-state electric property. The performance of DFT with various exchange-correlation functionals is found to be inadequate for the nonrelativistic shifts and shielding anisotropies as compared to the CCSD(T) results. The relativistic BPPT corrections to these quantities can, however, be reasonably predicted by DFT, due to the improved triplet excitation spectrum as compared to the Hartree-Fock method, as well as error cancellation within the five main BPPT contributions. We establish three computationally feasible models with characteristic error margins for future calculations of larger organo-xenon compounds to guide forthcoming experimental NMR efforts. The predicted (129)Xe chemical shift in HXeCCH is in a novel range for this nucleus, between weakly bonded or solvated atomic xenon and xenon in the hitherto characterized molecules.

Reservoir Crude-Oil-Viscosity Estimation From Wireline-NMR Measurements - Rajasthan, India

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 101689, "Reservoir Crude- Oil-Viscosity Estimation From Wireline- NMR Measurements-Rajasthan, India," by R.J. Zittel, SPE, D. Beliveau, SPE, T. O'Sullivan, SPE, and R. Mohanty, Cairn Energy India Ltd., and J. Miles, Oil Optimizers Ltd., prepared for the 2006 SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 24- 27 September. In 2004, the Mangala, Aishwariya, and Bhagyam fields were discovered in Rajasthan, India. Oil viscosity is a main factor controlling performance from these high-permeability paraffinic reservoirs. Pressure/volume/temperature (PVT) data indicate areal and vertical variations in crude-oil properties. Meter-by-meter geochemical core data corroborate vertical variations in oil composition. Continuous wireline measurements of nuclear-magnetic-resonance (NMR) log properties and station NMR properties from wells drilled with water-based mud or synthetic-oil-based mud also were used to calculate a viscosity profile. This study correlated results from all techniques and showed how NMR measurements can provide oil-viscosity profiles in compositionally complex pools. Introduction Oil viscosity was estimated for the Mangala and Aishwariya fields by use of a variety of wireline data and methods. The objective was to investigate and use correlations between wireline and laboratory NMR measurements and in-situ PVT properties (especially oil viscosity) measured on oil samples collected from the fields. Further, correlations were made with geochemical analyses taken from field cores. The result was estimation of in-situ oil viscosity as a function of depth in the wells where appropriate data were available, along with fieldwide correlations of viscosity as a function of height above the oil/water contact (OWC). One desirable property of these viscosity estimates would be that they have the same depth resolution as the wireline-log data from which they were derived. The available data were from routine suites of wireline logs, NMR logs, station NMR measurements, PVT properties measured on reservoir-oil samples, and detailed geochemistry data. Estimating In-Situ Oil Viscosity The empirical relationship represented by µoil=4(T+273.16)/T2 between crude-oil viscosity, µoil (in centipoise), and the logarithmic mean of the measured T2 relaxation-time distribution of the oil, was derived from data for a variety of crude oils and has been demonstrated in industry literature. In this algorithm, T2 is the logarithmic mean of the NMR-T2 distribution of the bulk oil and T is the temperature in degrees Celsius. Laboratory measurements of the T2 distribution of bulk oil from drillstem tests were studied. Data acquired in Mangala, Bhagyam, and Aishwariya fields led to the speculation that crude-oil viscosity might be estimated from the continuous wireline NMR-T2 distribution data by use of an adaptation of the Kleinberg-Vinegar algorithm. A distinct peak in the distributions that occurs near 150 milliseconds apparently is caused by the oil in the reservoir having little or no influence from the water fraction. It was recognized that this peak was unlikely to represent the bulk-oil response, completely uncontaminated by diffusion and other effects, so it would be necessary to calibrate the results of the Kleinberg-Vinegar computation to the in-situ viscosities from PVT analyses on samples of the field crude oils.

Diffusion-ordered nuclear magnetic resonance spectroscopy for analysis of DNA secondary structural elements

Structure determination of secondary DNA structural elements, such as G-quadruplexes, gains an increasing importance as fundamental physiological roles are being associated with the formation of such structures in vivo. A truncated native DNA sequence generally requires further optimization to obtain a candidate with desired nuclear magnetic resonance (NMR) properties for structural analysis in solution. The optimum sequence is expected to form one dominant, stable molecular entity in solution with well-resolved NMR peaks. However, DNA sequences are prone to form structures composed of one, two, three, or four strands depending on sequence and solution conditions. The thorough characterization of the molecularity (stoichiometry and molecular weight) and appropriate solution conditions for sequences with different modifications traditionally applies analytical techniques that generally do not represent the solution conditions for NMR structure determination. Here we present the application of diffusion-ordered NMR spectroscopy as a useful analytical tool for the optimization and analysis of DNA secondary structural elements, specifically, the DNA G-quadruplex structures, including those formed in the human telomeric sequence and in the promoter regions of bcl-2 and c-myc genes.

Methodological aspects in the calculation of parity-violating effects in nuclear magnetic resonance parameters

We examine the quantum chemical calculation of parity-violating (PV) electroweak contributions to the spectral parameters of nuclear magnetic resonance (NMR) from a methodological point of view. Nuclear magnetic shielding and indirect spin-spin coupling constants are considered and evaluated for three chiral molecules, H2O2, H2S2, and H2Se2. The effects of the choice of a one-particle basis set and the treatment of electron correlation, as well as the effects of special relativity, are studied. All of them are found to be relevant. The basis-set dependence is very pronounced, especially at the electron correlated ab initio levels of theory. Coupled-cluster and density-functional theory (DFT) results for PV contributions differ significantly from the Hartree-Fock data. DFT overestimates the PV effects, particularly with nonhybrid exchange-correlation functionals. Beginning from third-row elements, special relativity is of importance for the PV NMR properties, shown here by comparing perturbational one-component and various four-component calculations. In contrast to what is found for nuclear magnetic shielding, the choice of the model for nuclear charge distribution--point charge or extended (Gaussian)--has a significant impact on the PV contribution to the spin-spin coupling constants.