Interpretation Of Nuclear Magnetic Resonance Research Articles

High-Resolution Zero-Field NMR J-Spectroscopy of Aromatic Compounds

We report the acquisition and interpretation of nuclear magnetic resonance (NMR) J-spectra at zero magnetic field for a series of benzene derivatives, demonstrating the analytical capabilities of zero-field NMR. The zeroth-order spectral patterns do not overlap, which allows for straightforward determination of the spin interactions of substituent functional groups. Higher-order effects cause additional line splittings, revealing additional molecular information. We demonstrate resonance linewidths as narrow as 11 mHz, permitting resolution of minute frequency differences and precise determination of long-range J-couplings. The measurement of J-couplings with the high precision offered by zero-field NMR may allow further refinements in the determination of molecular structure and conformation.

Origin of the Conformational Modulation of the 13C NMR Chemical Shift of Methoxy Groups in Aromatic Natural Compounds

The interpretation of nuclear magnetic resonance (NMR) parameters is essential to understanding experimental observations at the molecular and supramolecular levels and to designing new and more efficient molecular probes. In many aromatic natural compounds, unusual (13)C NMR chemical shifts have been reported for out-of-plane methoxy groups bonded to the aromatic ring (~62 ppm as compared to the typical value of ~56 ppm for an aromatic methoxy group). Here, we analyzed this phenomenon for a series of aromatic natural compounds using Density Functional Theory (DFT) calculations. First, we checked the methodology used to optimize the structure and calculate the NMR chemical shifts in aromatic compounds. The conformational effects of the methoxy group on the (13)C NMR chemical shift then were interpreted by the Natural Bond Orbital (NBO) and Natural Chemical Shift (NCS) approaches, and by excitation analysis of the chemical shifts, breaking down the total nuclear shielding tensor into the contributions from the different occupied orbitals and their magnetic interactions with virtual orbitals. We discovered that the atypical (13)C NMR chemical shifts observed are not directly related to a different conjugation of the lone pair of electrons of the methoxy oxygen with the aromatic ring, as has been suggested. Our analysis indicates that rotation of the methoxy group induces changes in the virtual molecular orbital space, which, in turn, correlate with the predominant part of the contribution of the paramagnetic deshielding connected with the magnetic interactions of the BD(CMet-H)→BD*(CMet-OMet) orbitals, resulting in the experimentally observed deshielding of the (13)C NMR resonance of the out-of-plane methoxy group.

Anisotropy of hyperfine interactions as a tool for interpretation of NMR spectra in magnetic materials

Approach for interpretation of nuclear magnetic resonance (NMR) spectra in magnetic materials is presented, consisting in employing the anisotropy of hyperfine interaction. The anisotropic parts of hyperfine magnetic fields on 57Fe nuclei are calculated ab initio for a model example of lithium ferrite and utilized to assign the experimental NMR spectral lines to iron sites in the crystal structure.

Dynamic adaptive binning: an improved quantification technique for NMR spectroscopic data

The interpretation of nuclear magnetic resonance (NMR) experimental results for metabolomics studies requires intensive signal processing and multivariate data analysis techniques. A key step in this process is the quantification of spectral features, which is commonly accomplished by dividing an NMR spectrum into several hundred integral regions or bins. Binning attempts to minimize effects from variations in peak positions caused by sample pH, ionic strength, and composition, while reducing the dimensionality for multivariate statistical analyses. Herein we develop an improved novel spectral quantification technique, dynamic adaptive binning. With this technique, bin boundaries are determined by optimizing an objective function using a dynamic programming strategy. The objective function measures the quality of a bin configuration based on the number of peaks per bin. This technique shows a significant improvement over both traditional uniform binning and other adaptive binning techniques. This improvement is quantified via synthetic validation sets by analyzing an algorithm’s ability to create bins that do not contain more than a single peak and that maximize the distance from peak to bin boundary. The validation sets are developed by characterizing the salient distributions in experimental NMR spectroscopic data. Further, dynamic adaptive binning is applied to a 1H NMR-based experiment to monitor rat urinary metabolites to empirically demonstrate improved spectral quantification.

Water in the Polar and Nonpolar Cavities of the Protein Interleukin-1β

Water in the protein interior serves important structural and functional roles and is also increasingly recognized as a relevant factor in drug binding. The nonpolar cavity in the protein interleukin-1β has been reported to be filled by water on the basis of some experiments and simulations and to be empty on the basis of others. Here we study the thermodynamics of filling the central nonpolar cavity and the four polar cavities of interleukin-1β by molecular dynamics simulation. We use different water models (TIP3P and SPC/E) and protein force fields (amber94 and amber03) to calculate the semigrand partition functions term by term that quantify the hydration equilibria. We consistently find that water in the central nonpolar cavity is thermodynamically unstable, independent of force field and water model. The apparent reason is the relatively small size of the cavity, with a volume less than ∼80 Å(3). Our results are consistent with the most recent X-ray crystallographic and simulation studies but disagree with an earlier interpretation of nuclear magnetic resonance (NMR) experiments probing protein-water interactions. We show that, at least semiquantitatively, the measured nuclear Overhauser effects indicating the proximity of water to the methyl groups lining the nonpolar cavity can, in all likelihood, be attributed to interactions with buried and surface water molecules near the cavity. The same methods applied to determine the occupancy of the polar cavities show that they are filled by the same number of water molecules observed in crystallography, thereby validating the theoretical and simulation methods used to study the water occupancy in the nonpolar protein cavity.

Hyperfine Interactions in Half-Doped and 2/3-Doped Charge-Ordering Manganites

The present work is devoted to the theoretical interpretation of nuclear magnetic resonance (NMR) spectra on nonmagnetic lanthanum ion in charge-ordered La0.5Ca0.5MnO3 and La0.33Ca0.67MnO3 compounds. It is shown that the anisotropic hyperfine interaction, which arises due to the polarization of lanthanum’s external p-shells, plays a crucial role in spectrum forming. Our model allows to explain experimental spectra. The work is partially supported by CRDF REC-005.

Time-domain frequency-selective processing in nuclear magnetic resonance: a spatial-spectral holographic perspective

The fundamental nuclear magnetic resonance (NMR) imaging equation can be derived from a spatial-spectral holographic wavefront reconstruction formulation similar to that in quantum optics. A spatial-spectral holographic interpretation arises naturally in NMR from the inhomogeneous linewidth broadening due to either an imposed set of linear orthogonal gradient fields or from the intrinsic chemical anisotropy of the spin system. We can thus think of NMR k-space as a spatial-spectral holographic grating. The spatial holographic component arises from dielectric effects at high field strength (>4 T) when the excitation wavelength is less than or commensurate with the size of the imaging sample. The holographic properties of storage, time-reversal, recognition, and triple correlations are experimentally demonstrated in an inhomogeneously broadened NMR sample. This holographic NMR interpretation has additional implications on selective radio-frequency pulse design, microscopy imaging, and the use of conjugate imaging for field inhomogeneity corrections using the time-reversed component of the readout, to be the subject of a subsequent paper.

Ab initio calculation of 1H, 17O, 27Al and 29Si NMR parameters, vibrational frequencies and bonding energetics in hydrous silica and Na-aluminosilicate glasses

Ab initio, molecular orbital (MO) calculations were performed on model systems of SiO 2, NaAlSi 3O 8 (albite), H 2O-SiO 2 and H 2O-NaAlSi 3O 8 glasses. Model nuclear magnetic resonance (NMR) isotropic chemical shifts (δ iso) for 1H, 17O, 27Al and 29Si are consistent with experimental data for the SiO 2, NaAlSi 3O 8, H 2O-SiO 2 systems where structural interpretations of the NMR peak assignments are accepted. For H 2O-NaSi 3AlO 8 glass, controversy has surrounded the interpretation of NMR and infrared (IR) spectra. Calculated δ iso 1H, δ iso 17O, δ iso 27Al and δ iso 29Si are consistent with the interpretation of Kohn et al. (1992) that Si-(OH)-Al linkages are responsible for the observed peaks in hydrous Na-aluminosilicate glasses. In addition, a theoretical vibrational frequency associated with the Kohn et al. (1992) model agrees well with the observed shoulder near 900 cm −1 in the IR and Raman spectra of hydrous albite glasses. MO calculations suggest that breaking this Si-(OH)-Al linkage requires ∼+56 to +82 kJ/mol which is comparable to the activation energies for viscous flow in hydrous aluminosilicate melts.

NMR Relaxation of Clay/Brine Mixtures

Summary Effective interpretation of nuclear magnetic resonance (NMR) logs in shaly sands requires an understanding of the NMR contribution of clays. Of particular importance is the role of clays in the rapidly relaxing part of the NMR signal. In this study we measured the transverse relaxation time spectrum (T2) of brine mixed with four clays (illite, smectite, kaolinite and glauconite) as a function of compaction. The Larmor frequency was 2 MHz and the echo spacing 0.16 ms. Mild compaction was achieved by centrifuging the clay slurry at three successive pressures ranging from 1 to 125 psi. Highly compacted samples were produced in a uniaxial press at six sequential pressures ranging from 500 to 16,000 psi. Each clay/brine slurry and its associated compacted sample showed a single peak in the T2 distribution spectrum. A second peak, which could be interpreted as the "clay-bound water," was never observed. The T2 peak position shifted to faster relaxation times as compaction increased, in proportion to the pore volume-to-surface ratio, Vp /As. The single peak and Vp /As proportionality are consistent with fast diffusion between the pore water and the monolayer of water on the clay surface. Surface relaxivity varied among the four clay minerals; glauconite, the clay with the highest magnetic susceptibility and iron content had the largest surface relaxivity. These results have important implications for the interpretation of NMR logs in shaly sands. Because of the effects of compaction and to a lesser extent the iron content on a clay's T2 peak position, it is not possible to independently determine clay type from some characteristic relaxation time. These data also imply that it is not feasible to estimate the cation exchange capacity from a single time cutoff of the T2 distribution without additional information such as laboratory measurements or other log data.

Correlation of porosity types derived from NMR data and thin section image analysis in a carbonate reservoir

Nuclear Magnetic Resonance (NMR) longitudinal relaxation ( T 1,) experiments on water saturated plugs can be used to derive pore size frequency distributions in naturally porous media. These distributions can be cross validated with related distributions derived from petrographic image analysis (PIA). The decomposition of both NMR and PIA polymodal distributions yields pore types. Each pore type represents a subdistribution of pores possessing a characteristic size and shape. NMR pore types and PIA pore types are linearly related with respect to size. The constant of proportionality of this relationship can be used to estimate a value for the enhancement of relaxation caused by the nuclei interacting with the pore wall, called surface relaxivity (ϱ). The nature of the NMR pore type spectra indicate that a low T 1 component is associated with all the NMR pore types. The calculation of an estimated value of ϱ can be either from the linear relationship or from individual NMR/PIA pore type relationships. The various calculated values are very similar, and thus, a mean value for a given sample suite can be calculated. The estimation of ϱ is critical in the interpretation of NMR T 1 data, and external calibration is essential. This study demonstrates that calibration to PIA is one method, and that it is advantageous because PIA is the best method of deriving mean pore size from thin section. Moreover, PIA is advantageous because geometry effects are directly evident from thin section and SAWVEC B (an unmixing algorithm that decomposes polymodal data), as well as the ability of inferring mineralogy. In addition, PIA is advantageous because of its direct correlation to petrophysical properties. Therefore, NMR and PIA derived pore sizes can be used to cross validate each other. Thus, the relationship that commonly exists between pore size and throat size ensures that NMR and PIA derived pore sizes will have relevance in the understanding of petrophysical properties associated with fluid flow in natural porous media.

Application of the integrated NMR-TDEM method in groundwater exploration in Israel

The Nuclear Magnetic Resonance (NMR) method is the only physical tool currently available which is able to detect directly the presence of fresh water in the subsurface. The Time Domain Electromagnetic (TDEM) method, in turn, has been proven highly efficient in detecting saline groundwater. The combined application of these two methods is the most promising way to delineate accurately groundwater-bearing aquifers and to evaluate the quality of the water. This idea was tested during the feasibility study carried out under different hydrogeological conditions throughout Israel during August–September 1992. The Russian Hydroscope and Geonics P ROTEM-IV instruments were used for the NMR and TDEM measurements, respectively. A total of 36 NMR and 12 TDEM stations was established, mostly in close proximity to existing observation wells. Among these only 19 NMR measurements showed reasonable signal-to-noise characteristics, while the rest were obviously distorted by ambient noise. The number of distorted measurements could have been even greater had they been carried out at all points planned. However, a significant number of the NMR stations were cancelled due to their proximity (less than 1–1.5 km) to electric power lines. As a result almost the entire Mediterranean coast of Israel, which was originally chosen as the main test site for this survey, turned out to be unsuitable owing to the low ambient noise protection of the Hydroscope. Another serious limitation of NMR measurements is the maximum penetration depth. The deepest information obtained during the feasibility study was from a depth of 74 m. Nevertheless, within the framework of its applicability, the NMR measurements proved to be sufficiently accurate and to have a high resolving capability. A comparison with the borehole data shows that, in most cases, NMR is able not only to detect the presence of water, but also to delineate different subaquifers. At the same time, however, the transmissivity and aquifer texture are much less reliably detected. The combined application of the NMR and TDEM methods may essentially improve the reliability of the interpretation. In all cases where the NMR anomaly fits the drop in TDEM resistivity, water of a different salinity is found at approximately the same depth. A reasonable correlation between the interpreted resistivities and water salinities is obtained for these horizons. However, if only one method indicates the presence of water, this, in many cases, was not confirmed by the borehole data. The TDEM anomalies were obviously caused by low-resistivity lithologies, while some of the false NMR signals could be explained by a low signal-to-noise ratio. As regards the freshwater/seawater interface, this was, in all cases, accurately detected by the TDEM measurements alone. It is interesting to note that at the same depth, NMR measurements indicated a drastically increasing anomaly followed by the absence of water at greater depths. The latter can most likely be explained by the very low resistivity of the sea water, which is not taken into account by the existing NMR interpretation.

Inhibition of sendai virus fusion with phospholipid vesicles and human erythrocyte membranes by hydrophobic peptides

Hydrophobic di- and tripeptides which are capable of inhibiting enveloped virus infection of cells are also capable of inhibiting at least three different types of membrane fusion events. Large unilamellar vesicles (LUV) of N-methyl dioleoylphosphatidylethanolamine ( N-methyl DOPE), containing encapsulated 1-aminonaphthalene-3,6,8-trisulfonic acid (ANTS) and/or p-xylene bis(pyridinium bromide) (DPX), were formed by extrusion. Vesicle fusion (contents mixing) and leakage were then monitored with the ANTS/DPX fluorescence assay. Sendai virus fusion with lipid vesicles and Sendai virus fusion with human erythrocyte membranes were measured by following the relief of fluorescence quenching of virus labeled with octadecylrhodamine B chloride (R 18), a lipid mixing assay for fusion. This study found that the effectiveness of the peptides carbobenzoxy- l-Phe- l-Phe (Z- l-Phe- l-Phe), Z- l-Phe, Z-D-Phe, and Z-GIy- l-Phe- l-Phe in inhibiting N-methyl DOPE LUV fusion or fusion of virus with N-methyl DOPE LUV also paralleled their reported ability to block viral infectivity. Furthermore, Z- d-Phe- l-PheGly and Z-GIy- l-Phe inhibited Sendai virus fusion with human erythrocyte membranes with the same relative potency with which they inhibited vesicle-vesicle and virus-vesicle fusion. The evidence suggests a mechanism by which these peptides exert their inhibition of plaque formation by enveloped viruses. This class of inhibitors apparently acts by inhibiting fusion of the viral envelope with the target cell membrane, thereby preventing viral infection. The physical pathway by which these peptides inhibit membrane fusion was investigated. 31 P nuclear magnetic resonance (NMR) of proposed intermediates in the pathway for membrane fusion in LUV revealed that the potent fusion inhibitor Z- d-Phe- l-PheGly selectively altered the structure (or dynamics) of the hypothesized fusion intermediates and that the poor inhibitor Z-GIy- l-Phe did not. One possible interpretation of these 31P NMR results was that the inhibitory peptide stabilized a membrane structure with a large radius of curvature, when the fusion pathway demanded a membrane defect with a small radius of curvature. This hypothesis was tested by determining the influence of an inhibitory and a noninhibitory peptide on the formation of membraneous structures with small radii of curvature, through ultrasonic irradiation of phospholipid dispersions. The inhibitory peptide prevented the formation of membrane structures with small radii of curvature, while the noninhibitory peptide did not prevent the formation of such structures. These data taken collectively suggest that the peptides that inhibit the fusion of enveloped viruses could act, at least in part, by interfering with the formation of intermediates in membrane fusion (possibly punctate membrane defects induced by the virus) that force lipids into structures with small radii of curvature.

9] Distance geometry

Publisher Summary This chapter discusses a descriptive introduction to the mathematics and a user's guide to the distance geometry computer programs. The chapter also discusses other approaches to the problem of determining molecular structures in noncrystalline environments. Distance geometry is concerned with building structures from internal distances. This chapter will explain the method and its application to the interpretation of nuclear magnetic resonance (NMR) data. The approach is quite general and can be used to search conformation space subject to a wide variety of constraints beyond those obtainable from NMR. The same mathematics has also been used as a tool for statistical analysis of data that is known as “multidimensional scaling.” While it is difficult to determine systematic errors, the rather close correspondence of X-ray and NMR structures of rigid proteins, such as BPTI and tendamistat suggests that the systematic errors for proteins are not much worse than the random errors. The same may not be true for nucleic acid structures. These molecules have lower hydrogen densities than proteins do, leading to fewer NOEs. They are frequently more elongated, and the long distances in such systems may be significantly distorted.

An Alternative Interpretation of Nuclear Magnetic Resonance Observations in the Gel State of Lipid Bilayers

In the established interpretation of nuclear magnetic resonance (NMR) spectra of phospholipid bilayers in the gel state, the molecules are assumed to perform rotational diffusion about their long axis. Here we present an alternative model of the molecular mobility in this phase, which considers the positions of the lipid molecules in the two-dimensional bilayer lattice as fixed within the NMR timescale. Instead we assume an intramolecular two-site hopping of the hydrocarbon chains about their long axis. It is shown that deuterium NMR spectra of chain-labeled compounds are very sensitive to the precise angle of this flip-flop motion near 90 degrees , so that the diversity of these gel-phase spectra is easily explained by slight variations of this angle. In addition, it is argued that the axial symmetry of (13)C spectra of carbonyl-labeled phospholipids might also result from this intramolecular mobility.

Nuclear magnetic resonance interpretation with graphics

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTNuclear magnetic resonance interpretation with graphicsR. D. Draper and B. R. Penfold Cite this: J. Chem. Educ. 1984, 61, 9, 789Publication Date (Print):September 1, 1984Publication History Received3 August 2009Published online1 September 1984Published inissue 1 September 1984https://doi.org/10.1021/ed061p789RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Prototropic charge migration in water. Part 2.—Interpretation of nuclear magnetic resonance and conductivity data in terms of model mechanisms

Download options Please wait... Article information DOI https://doi.org/10.1039/F29837901047 Article type Paper Download Citation J. Chem. Soc., Faraday Trans. 2, 1983,79, 1047-1073 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Prototropic charge migration in water. Part 2.—Interpretation of nuclear magnetic resonance and conductivity data in terms of model mechanisms B. Halle and G. Karlström, J. Chem. Soc., Faraday Trans. 2, 1983, 79, 1047 DOI: 10.1039/F29837901047 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author Bertil Halle Gunnar Karlström

A self-consistent interpretation of nuclear magnetic resonance and quasi-elastic neutron scattering data from the smectic A and nematic phases of ethyl 4-(4′ acetoxybenzylidine) aminocinnamate

Nuclear magnetic resonance measurements of translational diffusion in the smectic A, nematic and isotropic phases of ethyl 4-(4′ acetoxybenzylidine) aminocinnamate (EABAC) are presented. These and high resolution, incoherent quasi-elastic neutron scattering results are interpreted in terms of anisotropic translational diffusion with a weak (11 kJ mole-1) periodic potential barrier to diffusion perpendicular to the smectic layers. A detailed analysis of the localized diffusive molecular motions in the smectic A and nematic mesophases has confirmed previous indications that there is an appreciable amplitude of motion (∼ 1 Å) parallel to the long molecular axes. This probably results from a coupling with the uniaxial rotational diffusion which the molecules undergo in both mesophases.

Influence of Polymer Association on the Interpretation of Nuclear Magnetic Resonance Measured Tacticity of Poly(vinyl chloride) in Solution

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInfluence of Polymer Association on the Interpretation of Nuclear Magnetic Resonance Measured Tacticity of Poly(vinyl chloride) in SolutionCharles E. WilkesCite this: Macromolecules 1971, 4, 4, 443–444Publication Date (Print):July 1, 1971Publication History Published online1 May 2002Published inissue 1 July 1971https://doi.org/10.1021/ma60022a015RIGHTS & PERMISSIONSArticle Views76Altmetric-Citations11LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (277 KB) Get e-Alerts Get e-Alerts

A new interpretation of nuclear magnetic resonance in dilute ferromagnetic alloys

The effect of dipolar and quadrupole interactions on the nuclear magnetic resonance line shape from a ferromagnet is calculated by taking an average over the domain wall weighted by the enhancement factor which varies through the wall. The results obtained disagree with the earlier work of Portis and Kanamori who used intuitive arguments to obtain the positions of the dipolar satellites. Detailed line shapes are calculated for face-centred cubic and body-centred cubic lattices which contain impurity atoms producing dipolar magnetic fields and electric quadrupole fields on their neighbours and also for hexagonal lattices where homogeneous electric field gradients are present. These are compared with experiment and used to reinterpret the available data and to show that the observed satellite lines generally come from different shells of neighbours and not from dipolar splitting as suggested by Portis and Kanamori.