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Sample records for n-15 nmr relaxation

  1. N-15 NMR Spectroscopy as a Method for Comparing the Rates of Imidization of Several Diamines

    NASA Technical Reports Server (NTRS)

    Johnson, J. Christopher; Kuczmarski, Maria A.

    2006-01-01

    The relative rates of the conversion of amide-acid to imide was measured for a series or aromatic diamines that have been identified as potential replacements for 4,4'-methylene dianiline (MDA) in high-temperature polyimides and polymer composites. These rates were compared with the N-15 NMR resonances of the unreacted amines. The initial rates of imidization track with the difference in chemical shift between the amine nitrogens in MDA and those in the subject diamines. This comparison demonstrated that N-15 NMR spectroscopy is appropriate for the rapid screening of candidate diamines to determine their reactivity relative to MDA, and can serve to provide guidance to the process of creating the time-temperature profiles used in processing these materials into polymer matrix composites.

  2. Relaxation time estimation in surface NMR

    DOEpatents

    Grunewald, Elliot D.; Walsh, David O.

    2017-03-21

    NMR relaxation time estimation methods and corresponding apparatus generate two or more alternating current transmit pulses with arbitrary amplitudes, time delays, and relative phases; apply a surface NMR acquisition scheme in which initial preparatory pulses, the properties of which may be fixed across a set of multiple acquisition sequence, are transmitted at the start of each acquisition sequence and are followed by one or more depth sensitive pulses, the pulse moments of which are varied across the set of multiple acquisition sequences; and apply processing techniques in which recorded NMR response data are used to estimate NMR properties and the relaxation times T.sub.1 and T.sub.2* as a function of position as well as one-dimensional and two-dimension distributions of T.sub.1 versus T.sub.2* as a function of subsurface position.

  3. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1988-01-01

    This report covers the progress made on the title project during the current reporting period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups in coals that determine the reactivity of coals. Other methods are being developed which will also determine how these functional groups are linked together. A third area of investigation concerns how molecular mobility in coals impacts NMR relaxation times, which is important for interpretation of such data in terms of the mobile phase in coals model. Along the same lines we are also using these studies to establish protocols for obtaining the best quantitative response from coals in solid state C-13 NMR spectra. This quarter we have focused on variable temperature spin lattice relaxation measurements for several of the Argonne coals. 5 figs.

  4. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1988-01-01

    This report covers the progress made on the title project during the current reporting period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups in coals that determine the reactivity of coals. Other methods are being developed which will also determine how these functional groups are linked together. A third area of investigation concerns how molecular mobility in coals impacts NMR relaxation times, which is important for interpretation of such data in terms of the mobile phase in coals model. Along the same lines we are also using these studies to establish protocols for obtaining the best quantitative response from coals in solid state C-13 NMR spectra. This quarter we have focussed on spin lattice relaxation measurements for several of the Argonne coals. 2 figs., 1 tab.

  5. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1989-01-01

    This report covers the progress made on the title project during the past reporting period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups in coals that determine the reactivity of coals. Other methods are being developed which will also determine how these functional groups are linked together. A third area of investigation concerns how molecular mobility in coals impacts NMR relaxation times, which is important for interpretation of such data in terms of the mobile phase in coals model. Along the same lines the authors are also using these studies to establish protocols for obtaining the best quantitative response from coals in solid state C-13 NMR spectra. The effects of very high MAS rates (>10 kHz) on cross polarization dynamics are also being investigated for similar reasons. The authors have been reinvestigating the prospects of using zero field NMR types of techniques for two dimensional NMR structural analysis of complex organic solids such as coals. Currently MAS spin rates are not sufficiently high to permit zero field in high field NMR for protons in typical organic solids, however they are compatible with {sup 13}C-{sup 13}C dipolar couplings. In collaboration with Dr. Robert Tycko of AT T Bell Laboratories, inventor of the zero field in high field NMR method, the authors have performed the first zero field in high field {sup 13}C NMR experiments. These results are described. 9 refs., 2 figs.

  6. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1992-05-27

    This report covers the progress made on the title project for the project period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins are particularly promising. Methods combining proton-proton spin diffusion with {sup 13}C CPMAS readout are being developed to determine the connectivity of functional groups in coals in a high sensitivity relay type of experiment. Additional work is aimed a delineating the role of methyl group rotation in the proton NMR relaxation behavior of coals.

  7. Fat Emulsification Measured Using NMR Transverse Relaxation

    NASA Astrophysics Data System (ADS)

    Marciani, L.; Ramanathan, C.; Tyler, D. J.; Young, P.; Manoj, P.; Wickham, M.; Fillery-Travis, A.; Spiller, R. C.; Gowland, P. A.

    2001-11-01

    This paper presents a novel method of measuring the droplet size in oil-in-water emulsions. It is based on changes in the NMR transverse relaxation rate due to the effect of microscopic magnetic susceptibility differences between fat droplets and the surrounding water. The longitudinal and transverse relaxation rates of a series of emulsions with constant oil volume fraction and five different mean droplet sizes, in the range 0.4-20.9 μm, were measured in vitro at 37°C using EPI. While the longitudinal relaxation rate 1/T1 did not change significantly, 1/T2 was observed to increase with mean droplet size. The measured changes in 1/T2 were found to be in good agreement with results predicted from proton random walk simulations, and were also consistent with analytical solutions based on an outer sphere relaxation model. Measurements of 1/T2 on emulsions with a higher oil volume fraction, and on emulsions of a fixed size where the water phase was doped with gadolinium to modulate the susceptibility difference between the phases, also showed the predicted behavior. As part of this study the susceptibility difference between olive oil and water was measured to be 1.55 ppm.

  8. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1990-01-01

    This report covers the progress made on the title project and summarizes the accomplishments for the project period. Four major areas of inquiry have been pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups in coals that determine the reactivity of coals. Other methods are being developed which will also determine how these functional groups are linked together. A third area of investigation concerns how molecular mobility in coals impacts NMR relaxation times, which is important for interpretation of such data in terms of the mobile phase in coals model. Along the same lines the authors are also using these studies to establish protocols for obtaining the best quantitative response from coals in solid state C-13 NMR spectra. The effects of very high MAS rates (>10 kHz) on cross polarization dynamics are also being investigated for similar reasons. The authors have concentrated on a theoretical treatment of pairs of tightly coupled spin {1/2} nuclei under magic angle spinning conditions. The average Hamiltonian theory developed here is required for a quantitative understanding of two dimensional NMR experiments of such spin pairs in solids. These experiments in turn provide a means of determining connectivities between resonances in solid state NMR spectra. Development of these techniques will allow us to establish connectivities between functional components in coals. The complete description of these spin dynamics has turned out to be complex, and is necessary to provide a foundation upon which such experiments may be quantitatively interpreted in complex mixtures such as coals. 25 refs., 4 figs., 3 tabs.

  9. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1989-01-01

    This report covers the progress made on the title project and summarizes the accomplishments for the project period. Four major areas of inquiry have been pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups in coals that determine the reactivity of coals. Other methods are being developed which will also determine how these functional groups are linked together. A third area of investigation concern how molecular mobility in coals impacts NMR relaxation times, which is important for interpretation of such data in terms of the mobile phase in coals model. Along the same lines we are also using these studies to establish protocols for obtaining the best quantitative response from coals in solid state C-13 NMR spectra. The effects of very high MAS rates (>10 kHz) on cross polarization dynamics are also being investigated for similar reasons. During the last quarter the authors have concentrated on improvements in cross polarization (CP) sequences with a goal of making the CP process insensitive to experimental conditions such as the magic angle spinning (MAS) rate. In order to be able to use fields the order of 7.0 T or higher, CP efficiency must be maintained at MAS rates of over 10 kHz. The standard sequences have severe limitations at these rates which lead to intensity distortions in {sup 13}C CPMAS spectra. Thus in order to be able to take advantage of the increases in sensitivity and resolution that accompany high field operation, improvements in the NMR methods are required. The new sequences the authors are developing will be especially important for quantitative analysis of coal structure by {sup 13}C solid state NMR at high field strengths. 13 refs., 7 figs., 2 tabs.

  10. Two dimensional NMR and NMR relaxation studies of coal structure

    SciTech Connect

    Zilm, K.W.

    1989-01-01

    This report covers the progress made on the title project and summarizes the accomplishments for the project period. Four major areas of inquiry have been pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups in coals that determine the reactivity of coals. Other methods are being developed which will also determine how these functional groups are linked together. A third area of investigation concerns how molecular mobility in coals impacts NMR relaxation times, which is important for interpretation of such data in terms of the mobile phase in coal models. Along the same lines the author are also using these studies to establish protocols for obtaining the best quantitative response from coals in solid state C-13 NMR spectra. The effects of very high MAS rates (>10 kHz) on cross polarization dynamics are also being investigated for similar reasons. During the last quarter the authors has concentrated on improvements in cross polarization (CP) sequences with a goal of making the CP process insensitive to experimental conditions such as the Hartmann-Hahn mismatch. It has been found that the usual theories of CP are incorrect, and that the CP process is very heterogeneous in nature. This has significant implications on methods typically used in quantifying {sup 13}C CPMAS spectra of coals. 19 refs., 11 figs.

  11. Jointly deriving NMR surface relaxivity and pore size distributions by NMR relaxation experiments on partially desaturated rocks

    NASA Astrophysics Data System (ADS)

    Mohnke, O.; Hughes, B.

    2014-06-01

    Nuclear magnetic resonance (NMR) relaxometry is a geophysical method widely used in borehole and laboratory applications to nondestructively infer transport and storage properties of rocks and soils as it is directly sensitive to the water/oil content and pore sizes. However, for inferring pore sizes, NMR relaxometry data need to be calibrated with respect to a surface interaction parameter, surface relaxivity, which depends on the type and mineral constituents of the investigated rock. This study introduces an inexpensive and quick alternative to the classical calibration methods, e.g., mercury injection, pulsed field gradient (PFG) NMR, or grain size analysis, which allows for jointly estimating NMR surface relaxivity and pore size distributions using NMR relaxometry data from partially desaturated rocks. Hereby, NMR relaxation experiments are performed on the fully saturated sample and on a sample partially drained at a known differential pressure. Based on these data, the (capillary) pore radius distribution and surface relaxivity are derived by joint optimization of the Brownstein-Tarr and the Young-Laplace equation assuming parallel capillaries. Moreover, the resulting pore size distributions can be used to predict water retention curves. This inverse modeling approach—tested and validated using NMR relaxometry data measured on synthetic porous borosilicate samples with known petrophysical properties (i.e., permeability, porosity, inner surfaces, pore size distributions)—yields consistent and reproducible estimates of surface relaxivity and pore radii distributions. Also, subsequently calculated water retention curves generally correlate well with measured water retention curves.

  12. Relaxation dispersion NMR spectroscopy for the study of protein allostery.

    PubMed

    Farber, Patrick J; Mittermaier, Anthony

    2015-06-01

    Allosteric transmission of information between distant sites in biological macromolecules often involves collective transitions between active and inactive conformations. Nuclear magnetic resonance (NMR) spectroscopy can yield detailed information on these dynamics. In particular, relaxation dispersion techniques provide structural, dynamic, and mechanistic information on conformational transitions occurring on the millisecond to microsecond timescales. In this review, we provide an overview of the theory and analysis of Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion NMR experiments and briefly describe their application to the study of allosteric dynamics in the homeodomain from the PBX transcription factor (PBX-HD). CPMG NMR data show that local folding (helix/coil) transitions in one part of PBX-HD help to communicate information between two distant binding sites. Furthermore, the combination of CPMG and other spin relaxation data show that this region can also undergo local misfolding, reminiscent of conformational ensemble models of allostery.

  13. NMR relaxation dispersion of vulcanized natural rubber.

    PubMed

    Kariyo, Sobiroh; Stapf, Siegfried

    2004-01-01

    The dependence of the 1H spin-lattice relaxation time on the magnetic field strength has been determined for linear and cross-linked polyisoprene for Larmor frequencies between 5 kHz and 20 MHz. Universal power-law relations are found for all temperatures and cross-link densities under investigation and are compared to published results of rotating-frame experiments on similar natural rubber samples. The shape of the individual dispersion functions can be superposed into a master curve using appropriate shift factors. While addition of filler particles even at large weight fractions has only a minor effect on the relaxation times, uniaxial deformation and swelling are demonstrated to alter the molecular dynamics significantly.

  14. relax: the analysis of biomolecular kinetics and thermodynamics using NMR relaxation dispersion data

    PubMed Central

    Morin, Sébastien; Linnet, Troels E.; Lescanne, Mathilde; Schanda, Paul; Thompson, Gary S.; Tollinger, Martin; Teilum, Kaare; Gagné, Stéphane; Marion, Dominique; Griesinger, Christian; Blackledge, Martin; d’Auvergne, Edward J.

    2014-01-01

    Nuclear magnetic resonance (NMR) is a powerful tool for observing the motion of biomolecules at the atomic level. One technique, the analysis of relaxation dispersion phenomenon, is highly suited for studying the kinetics and thermodynamics of biological processes. Built on top of the relax computational environment for NMR dynamics is a new dispersion analysis designed to be comprehensive, accurate and easy-to-use. The software supports more models, both numeric and analytic, than current solutions. An automated protocol, available for scripting and driving the graphical user interface (GUI), is designed to simplify the analysis of dispersion data for NMR spectroscopists. Decreases in optimization time are granted by parallelization for running on computer clusters and by skipping an initial grid search by using parameters from one solution as the starting point for another —using analytic model results for the numeric models, taking advantage of model nesting, and using averaged non-clustered results for the clustered analysis. Availability and implementation: The software relax is written in Python with C modules and is released under the GPLv3+ license. Source code and precompiled binaries for all major operating systems are available from http://www.nmr-relax.com. Contact: edward@nmr-relax.com PMID:24764461

  15. relax: the analysis of biomolecular kinetics and thermodynamics using NMR relaxation dispersion data.

    PubMed

    Morin, Sébastien; Linnet, Troels E; Lescanne, Mathilde; Schanda, Paul; Thompson, Gary S; Tollinger, Martin; Teilum, Kaare; Gagné, Stéphane; Marion, Dominique; Griesinger, Christian; Blackledge, Martin; d'Auvergne, Edward J

    2014-08-01

    Nuclear magnetic resonance (NMR) is a powerful tool for observing the motion of biomolecules at the atomic level. One technique, the analysis of relaxation dispersion phenomenon, is highly suited for studying the kinetics and thermodynamics of biological processes. Built on top of the relax computational environment for NMR dynamics is a new dispersion analysis designed to be comprehensive, accurate and easy-to-use. The software supports more models, both numeric and analytic, than current solutions. An automated protocol, available for scripting and driving the graphical user interface (GUI), is designed to simplify the analysis of dispersion data for NMR spectroscopists. Decreases in optimization time are granted by parallelization for running on computer clusters and by skipping an initial grid search by using parameters from one solution as the starting point for another -using analytic model results for the numeric models, taking advantage of model nesting, and using averaged non-clustered results for the clustered analysis. The software relax is written in Python with C modules and is released under the GPLv3+ license. Source code and precompiled binaries for all major operating systems are available from http://www.nmr-relax.com. edward@nmr-relax.com. © The Author 2014. Published by Oxford University Press.

  16. Distribution of NMR relaxations in a random Heisenberg chain.

    PubMed

    Shiroka, T; Casola, F; Glazkov, V; Zheludev, A; Prša, K; Ott, H-R; Mesot, J

    2011-04-01

    NMR measurements of the (29)Si spin-lattice relaxation time T(1) were used to probe the spin-1/2 random Heisenberg chain compound BaCu(2)(Si(1-x)Ge(x))(2)O(7). Remarkable differences between the pure (x=0) and the fully random (x=0.5) cases are observed, indicating that randomness generates a distribution of local magnetic relaxations. This distribution, which is reflected in a stretched exponential NMR relaxation, exhibits a progressive broadening with decreasing temperature, caused by a growing inequivalence of magnetic sites. Compelling independent evidence for the influence of randomness is also obtained from magnetization data and Monte Carlo calculations. These results suggest the formation of random-singlet states in this class of materials, as previously predicted by theory.

  17. Extracting protein dynamics information from overlapped NMR signals using relaxation dispersion difference NMR spectroscopy.

    PubMed

    Konuma, Tsuyoshi; Harada, Erisa; Sugase, Kenji

    2015-12-01

    Protein dynamics plays important roles in many biological events, such as ligand binding and enzyme reactions. NMR is mostly used for investigating such protein dynamics in a site-specific manner. Recently, NMR has been actively applied to large proteins and intrinsically disordered proteins, which are attractive research targets. However, signal overlap, which is often observed for such proteins, hampers accurate analysis of NMR data. In this study, we have developed a new methodology called relaxation dispersion difference that can extract conformational exchange parameters from overlapped NMR signals measured using relaxation dispersion spectroscopy. In relaxation dispersion measurements, the signal intensities of fluctuating residues vary according to the Carr-Purcell-Meiboon-Gill pulsing interval, whereas those of non-fluctuating residues are constant. Therefore, subtraction of each relaxation dispersion spectrum from that with the highest signal intensities, measured at the shortest pulsing interval, leaves only the signals of the fluctuating residues. This is the principle of the relaxation dispersion difference method. This new method enabled us to extract exchange parameters from overlapped signals of heme oxygenase-1, which is a relatively large protein. The results indicate that the structural flexibility of a kink in the heme-binding site is important for efficient heme binding. Relaxation dispersion difference requires neither selectively labeled samples nor modification of pulse programs; thus it will have wide applications in protein dynamics analysis.

  18. Microscale simulations of NMR relaxation in porous media

    NASA Astrophysics Data System (ADS)

    Mohnke, Oliver; Klitzsch, Norbert

    2010-05-01

    In petrophysical applications of nuclear magnetic resonance (NMR), the measured relaxation signals originate from the fluid filled pore space. Hence, in rocks or sediments the water content directly corresponds to the initial amplitude of the recorded NMR relaxation signals. The relaxation rate (longitudinal/transversal decay time T1, T2) is sensitive to pore sizes and physiochemical properties of rock-fluid interfaces (surface relaxivity), as well as the concentration of paramagnetic ions in the fluid phases (bulk relaxivity). In the subproject A2 of the TR32 we aim at improving the basic understanding of these processes at the pore scale and thereby advancing the interpretation of NMR data by reducing the application of restrictive approximated interpretation schemes, e.g. for deriving pore size distributions, connectivity or permeability. In this respect we numerically simulate NMR relaxation data at the micro sale to study the impact of physical and hydrological parameters such as internal field gradients or pore connectivities on NMR signals. Joint numerical simulations of the NMR relaxation behavior (Bloch equations) in the presence of internal gradients (Ampere's law) and fluid flow (Navier-Stokes) on a pore scale dimension have been implemented in a finite element (FE) model using Comsol Multiphysics. Processes governing the time and spatial behavior of the nuclear magnetization density in a porous medium are diffusion and surface interactions at the rock-fluid interface. Based on Fick's law of diffusive motion Brownstein and Tarr (1979) introduced differential equations that describe the relaxation behavior of the Spin magnetization in single isolated pores and derived analytical solutions for simple geometries, i.e. spherical, cylindrical and planar. However, by numerically solving these equations in a general way using a FE algorithm this approach can be applied to study and simulate coupled complex pore systems, e.g. derived from computer tomography (CT

  19. Microscale simulations of NMR relaxation in porous media

    NASA Astrophysics Data System (ADS)

    Mohnke, O.; Klitzsch, N.; Clauser, C.

    2009-12-01

    In petrophysical applications of nuclear magnetic resonance (NMR), the measured relaxation signals originate from the fluid filled pore space. Hence, in rocks or sediments the water content directly corresponds to the initial amplitude of the recorded NMR relaxation signals. The relaxation rate (longitudinal/transversal decay time T1, T2) is sensitive to pore sizes and physiochemical properties of rock-fluid interfaces (surface relaxivity), as well as the concentration of paramagnetic ions in the fluid phases (bulk relaxivity). We aim at improving the basic understanding of these processes at the pore scale and thereby advancing the interpretation of NMR data by reducing the application of restrictive approximated interpretation schemes, e.g. for deriving pore size distributions, connectivity or permeability. In this respect we numerically simulate NMR relaxation data at the micro sale to study the impact of physical and hydrological parameters such as internal field gradients or pore connectivities on NMR signals. Joint numerical simulations of the NMR relaxation behavior (Bloch equations) in the presence of internal gradients (Ampere’s law) and fluid flow (Navier-Stokes) on a pore scale dimension have been implemented in a finite element (FE) model using Comsol Multiphysics. Processes governing the time and spatial behavior of the nuclear magnetization density in a porous medium are diffusion and surface interactions at the rock-fluid interface. Based on Fick's law of diffusive motion Brownstein and Tarr (1979) introduced differential equations that describe the relaxation behavior of the Spin magnetization in single isolated pores and derived analytical solutions for simple geometries, i.e. spherical, cylindrical and planar. However, by numerically solving these equations in a general way using a FE algorithm this approach can be applied to study and simulate coupled complex pore systems, e.g. derived from computer tomography (CT). In this respect substantial

  20. NMR spin relaxation rates in the Heisenberg bilayer

    NASA Astrophysics Data System (ADS)

    Mendes, Tiago; Curro, Nicholas; Scalettar, Richard; Paiva, Thereza; Dos Santos, Raimundo R.

    One of the striking features of heavy fermions is the fact that in the vicinity of a quantum phase transition these systems exhibit the breakdown of Fermi-liquid behavior and superconductivity. Nuclear magnetic resonance (NMR) expirements play an important role in the study of these phenomena. Measurements of NMR spin relaxation rates and Knight shift, for instance, can be used to probe the electronic spin susceptibility of these systems. Here we studied the NMR response of the Heisenberg bilayer model. In this model, it is well known that the increase of the interplane coupling between the planes, Jperp, supresses the antiferromagnetic order at a quantum critical point (QCP). We use stochastic series expansion (SSE) and the maximum-entropy analytic continuation method to calculate the NMR spin lattice relaxation rate 1 /T1 and the spin echo decay 1 /T2 G as function of Jperp. The spin echo decay, T2 G increases for small Jperp, due to the increase of the order parameter, and then vanishes abruptly in the QCP. The effects of Jperp dilution disorder in the QCP and the relaxation rates are also discussed. This research was supported by the NNSA Grant Number DE-NA 0002908, and Ciência sem fronteiras program/CNPQ.

  1. 129 Xe NMR Relaxation-Based Macromolecular Sensing

    SciTech Connect

    Gomes, Muller D.; Dao, Phuong; Jeong, Keunhong; Slack, Clancy C.; Vassiliou, Christophoros C.; Finbloom, Joel A.; Francis, Matthew B.; Wemmer, David E.; Pines, Alexander

    2016-07-29

    A 129Xe NMR relaxation-based sensing approach is reported on that exploits changes in the bulk xenon relaxation rate induced by slowed tumbling of a cryptophane-based sensor upon target binding. The amplification afforded by detection of the bulk dissolved xenon allows sensitive detection of targets. The sensor comprises a xenon-binding cryptophane cage, a target interaction element, and a metal chelating agent. Xenon associated with the target-bound cryptophane cage is rapidly relaxed and then detected after exchange with the bulk. Here we show that large macromolecular targets increase the rotational correlation time of xenon, increasing its relaxation rate. Upon binding of a biotin-containing sensor to avidin at 1.5 μM concentration, the free xenon T2 is reduced by a factor of 4.

  2. Effective rotational correlation times of proteins from NMR relaxation interference

    NASA Astrophysics Data System (ADS)

    Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt

    2006-01-01

    Knowledge of the effective rotational correlation times, τc, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of τc enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine τc for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.

  3. Solid-state NMR relaxation studies of Australian spider silks.

    PubMed

    Kishore, A I; Herberstein, M E; Craig, C L; Separovic, F

    Solid-state NMR techniques were used to study two different types of spider silk from two Australian orb-web spider species, Nephila edulis and Argiope keyserlingi. A comparison of (13)C-T(1) and (1)H-T(1rho) solid-state NMR relaxation data of the Ala Calpha, Ala Cbeta, Gly Calpha, and carbonyl resonances revealed subtle differences between dragline and cocoon silk. (13)C-T(1rho) and (1)H-T(1) relaxation experiments showed significant differences between silks of the two species with possible structural variations. Comparison of our data to previous (13)C-T(1) relaxation studies of silk from Nephila clavipes (A. Simmons et al., Macromolecules, 1994, Vol. 27, pp. 5235-5237) also supports the finding that differences in molecular mobility of dragline silk exist between species. Interspecies differences in silk structure may be due to different functional properties. Relaxation studies performed on wet (supercontracted) and dry silks showed that the degree of hydration affects relaxation properties, and hence changes in molecular mobility are correlated with functional properties of silk. Copyright 2002 Wiley Periodicals, Inc.

  4. NMR relaxation rate and the libron energy of solid hydrogen

    NASA Technical Reports Server (NTRS)

    Sugawara, K.; Woollam, J. A.

    1978-01-01

    By taking the rotational relaxation of orthohydrogen (o-H2) in solid hydrogen into account, the authors have theoretically investigated the longitudinal NMR spin lattice relaxation rate of o-H2. The rate is characterized by an anomalous maximum, as a function of temperature, at temperatures close to the mean libron energy of o-H2. Application of the theory for o-H2 concentrations between 42% and 75% reveals a nearly concentration-independent mean libron energy equivalent to about 1 K. This qualitatively and quantitatively contradicts the conclusions of other theories, but agrees with recent experiments.

  5. NMR relaxation rate and the libron energy of solid hydrogen

    NASA Technical Reports Server (NTRS)

    Sugawara, K.; Woollam, J. A.

    1978-01-01

    By taking the rotational relaxation of orthohydrogen (o-H2) in solid hydrogen into account, the authors have theoretically investigated the longitudinal NMR spin lattice relaxation rate of o-H2. The rate is characterized by an anomalous maximum, as a function of temperature, at temperatures close to the mean libron energy of o-H2. Application of the theory for o-H2 concentrations between 42% and 75% reveals a nearly concentration-independent mean libron energy equivalent to about 1 K. This qualitatively and quantitatively contradicts the conclusions of other theories, but agrees with recent experiments.

  6. Analysis of 2D NMR relaxation data using Chisholm approximations.

    PubMed

    Huber, S; Haase, A; Gleich, B

    2017-08-01

    To analyze 2D NMR relaxation data based on a discrete delta-like relaxation map we extended the Padé-Laplace method to two dimensions. We approximate the forward Laplace image of the time domain signal by a Chisholm approximation, i.e. a rational polynomial in two dimensions. The poles and residues of this approximation correspond to the relaxation rates and weighting factors of the underlying relaxation map. In this work we explain the principle ideas of our algorithm and demonstrate its applicability. Therefore we compare the inversion results of the Chisholm approximation and Tikhonov regularization method as a function of SNR when the investigated signal is based on a given discrete relaxation map. Our algorithm proved to be reliable for SNRs larger than 50 and is able to compete with the Tikhonov regularization method. Furthermore we show that our method is also able to detect the simulated relaxation compartments of narrow Gaussian distributions with widths less or equal than 0.05s(-1). Finally we investigate the resolution limit with experimental data. For a SNR of 750 the Chisholm approximation method was able to resolve two relaxation compartments in 8 of 10 cases when both compartments differ by a factor of 1.7. Copyright © 2017 Elsevier Inc. All rights reserved.

  7. Analysis of 2D NMR relaxation data using Chisholm approximations

    NASA Astrophysics Data System (ADS)

    Huber, S.; Haase, A.; Gleich, B.

    2017-08-01

    To analyze 2D NMR relaxation data based on a discrete delta-like relaxation map we extended the Padé-Laplace method to two dimensions. We approximate the forward Laplace image of the time domain signal by a Chisholm approximation, i.e. a rational polynomial in two dimensions. The poles and residues of this approximation correspond to the relaxation rates and weighting factors of the underlying relaxation map. In this work we explain the principle ideas of our algorithm and demonstrate its applicability. Therefore we compare the inversion results of the Chisholm approximation and Tikhonov regularization method as a function of SNR when the investigated signal is based on a given discrete relaxation map. Our algorithm proved to be reliable for SNRs larger than 50 and is able to compete with the Tikhonov regularization method. Furthermore we show that our method is also able to detect the simulated relaxation compartments of narrow Gaussian distributions with widths less or equal than 0.05 s-1. Finally we investigate the resolution limit with experimental data. For a SNR of 750 the Chisholm approximation method was able to resolve two relaxation compartments in 8 of 10 cases when both compartments differ by a factor of 1.7.

  8. Automated NMR relaxation dispersion data analysis using NESSY.

    PubMed

    Bieri, Michael; Gooley, Paul R

    2011-10-27

    Proteins are dynamic molecules with motions ranging from picoseconds to longer than seconds. Many protein functions, however, appear to occur on the micro to millisecond timescale and therefore there has been intense research of the importance of these motions in catalysis and molecular interactions. Nuclear Magnetic Resonance (NMR) relaxation dispersion experiments are used to measure motion of discrete nuclei within the micro to millisecond timescale. Information about conformational/chemical exchange, populations of exchanging states and chemical shift differences are extracted from these experiments. To ensure these parameters are correctly extracted, accurate and careful analysis of these experiments is necessary. The software introduced in this article is designed for the automatic analysis of relaxation dispersion data and the extraction of the parameters mentioned above. It is written in Python for multi platform use and highest performance. Experimental data can be fitted to different models using the Levenberg-Marquardt minimization algorithm and different statistical tests can be used to select the best model. To demonstrate the functionality of this program, synthetic data as well as NMR data were analyzed. Analysis of these data including the generation of plots and color coded structures can be performed with minimal user intervention and using standard procedures that are included in the program. NESSY is easy to use open source software to analyze NMR relaxation data. The robustness and standard procedures are demonstrated in this article.

  9. Spotting the Gel Point of Photopolymers by Examining NMR Relaxation

    NASA Astrophysics Data System (ADS)

    Lee, Jack; Hofmeister, Gretchen; Baylor, Martha-Elizabeth

    Spotting when a polymer goes from liquid to solid during polymerization is necessary when working with certain optically cured polymers used to fabricate optofluidic devices that contain both optical and microfluidic features. Through the use of nuclear magnetic resonance (NMR) it may be possible to determine when the transition from liquid to solid, called the gel point, occurs. In examining the proton longitudinal relaxation time for one species of monomers in our polymer mix, our data shows as the polymer cures the relaxation time increases. By examining this data we were able to extract a time to gel point that was within the margin of error of the theoretical gel point of our materials. Outlined here is evidence of why we think longitudinal relaxation is applicable to studying polymerization, and how we are using it to attempt to extract the gel point.

  10. Nuclear Spin-Lattice Relaxation Times from Continuous Wave NMR Spectroscopy.

    ERIC Educational Resources Information Center

    Wooten, Jan B.; And Others

    1979-01-01

    The experiment described, suitable for undergraduate physical chemistry laboratories, illustrates the general principles of relaxation and introduces the nmr concepts of saturation and spin-inversion. (BB)

  11. Characterizing RNA Excited States using NMR Relaxation Dispersion

    PubMed Central

    Xue, Yi; Kellogg, Dawn; Kimsey, Isaac J; Sathyamoorthy, Bharathwaj; Stein, Zachary W; McBrairty, Mitchell; Al-Hashimi, Hashim M.

    2016-01-01

    Changes in RNA secondary structure play fundamental roles in the cellular functions of a growing number of non-coding RNAs. This chapter describes NMR-based approaches for characterizing microsecond-to-millisecond changes in RNA secondary structure that are directed toward short-lived and low-populated species often referred to as “excited states”. Compared to larger-scale changes in RNA secondary structure, transitions towards excited states do not require assistance from chaperones, are often orders of magnitude faster, and are localized to a small number of nearby base pairs in and around non-canonical motifs. Here we describe a procedure for characterizing RNA excited states using off-resonance R1ρ NMR relaxation dispersion utilizing low-to-high spin-lock fields (25–3000 Hz). R1ρ NMR relaxation dispersion experiments are used to measure carbon and nitrogen chemical shifts in base and sugar moieties of the excited state. The chemical shift data is then interpreted with the aid of secondary structure prediction to infer potential excited states that feature alternative secondary structures. Candidate structures are then tested by using mutations, single-atom substitutions, or by changing physiochemical conditions, such as pH and temperature, to either stabilize or destabilize the candidate excited state. The resulting chemical shifts of the mutants or under different physiochemical conditions are then compared to those of the ground and excited state. Application is illustrated with a focus on the transactivation response element (TAR) from the human immune deficiency virus type 1 (HIV-1), which exists in dynamic equilibrium with at least two distinct excited states. PMID:26068737

  12. Diffusion MRI/NMR magnetization equations with relaxation times

    NASA Astrophysics Data System (ADS)

    de, Dilip; Daniel, Simon

    2012-10-01

    Bloch-Torrey diffusion magnetization equation ignores relaxation effects of magnetization. Relaxation times are important in any diffusion magnetization studies of perfusion in tissues(Brain and heart specially). Bloch-Torrey equation cannot therefore describe diffusion magnetization in a real-life situation where relaxation effects play a key role, characteristics of tissues under examination. This paper describes derivations of two equations for each of the y and z component diffusion NMR/MRI magnetization (separately) in a rotating frame of reference, where rf B1 field is applied along x direction and bias magnetic field(Bo) is along z direction. The two equations are expected to further advance the science & technology of Diffusion MRI(DMRI) and diffusion functional MRI(DFMRI). These two techniques are becoming increasingly important in the study and treatment of neurological disorders, especially for the management of patients with acute stroke. It is rapidly becoming a standard for white matter disorders, as diffusion tensor imaging (DTI) can reveal abnormalities in white matter fibre structure and provide models of brain connectivity.

  13. NMR Relaxation and Diffusion Study of Ultrasound Recycling of Polyurethanes

    NASA Astrophysics Data System (ADS)

    von Meerwall, E.; Ghose, S.; Isayev, A. I.

    2004-04-01

    We have examined the effect of intense ultrasound on unfilled polyurethane foam and rubber using proton NMR transverse relaxation and pulsed-gradient diffusion studies, sol extraction, GPC characterization, and glass transition measurements. Results correlate well with ultrasound amplitude. The proton T2 relaxation at 70.5 deg. C exhibits three discrete components, due to heavily entangled sol and crosslinked network; unentangled polymeric sol plus dangling network chain ends; and oligomer remnants. Devulcanizing produces heavy sol, increases segmental mobility of all species, and generates more dangling chain ends. In foams, but not in rubber, additional light sol is generated at the expense of network. All mobilities are significantly lower than in the other rubbers we have studied, an effect unrelated to the glass transition, nearly constant at -60 deg. C. Diffusion measurements, possible only in foams, show a bimodal spectrum whose fast component slows markedly with ultrasound amplitude, attesting to the production of fragments heavier than the original oligomers, as confirmed by GPC analysis. This work is the first to study ultrasound devulcanization in industrial rubbery foams.

  14. Parameterization of NMR relaxation curves in terms of logarithmic moments of the relaxation time distribution

    NASA Astrophysics Data System (ADS)

    Petrov, Oleg V.; Stapf, Siegfried

    2017-06-01

    This work addresses the problem of a compact and easily comparable representation of multi-exponential relaxation data. It is often convenient to describe such data in a few parameters, all being of physical significance and easy to interpret, and in such a way that enables a model-free comparison between different groups of samples. Logarithmic moments (LMs) of the relaxation time constitute a set of parameters which are related to the characteristic relaxation time on the log-scale, the width and the asymmetry of an underlying distribution of exponentials. On the other hand, the calculation of LMs does not require knowing the actual distribution function and is reduced to a numerical integration of original data. The performance of this method has been tested on both synthetic and experimental NMR relaxation data which differ in a signal-to-noise ratio, the sampling range and the sampling rate. The calculation of two lower-order LMs, the log-mean time and the log-variance, has proved robust against deficiencies of the experiment such as scattered data point and incomplete sampling. One may consider using them as such to monitor formation of a heterogeneous structure, e.g., in phase separation, vitrification, polymerization, hydration, aging, contrast agent propagation processes. It may also assist in interpreting frequency and temperature dependences of relaxation, revealing a crossover from slow to fast exchange between populations. The third LM was found to be a less reliable quantity due to its susceptibility to the noise and must be used with caution.

  15. N-15 NMR study of the immobilization of 2,4- and 2,6-dinitrotoluene in aerobic compost.

    PubMed

    Thorn, Kevin A; Pennington, Judith C; Kennedy, Kay R; Cox, Larry G; Hayes, Charolett A; Porter, Beth E

    2008-04-01

    Large-scale aerobic windrow composting has been used to bioremediate washout lagoon soils contaminated with the explosives TNT (2,4,6-trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) at several sites within the United States. We previously used 15N NMR to investigate the reduction and binding of T15NT in aerobic bench-scale reactors simulating the conditions of windrow composting. These studies have been extended to 2,4-dinitrotoluene (2,4DNT) and 2,6-dinitrotoluene (2,6DNT), which, as impurities in TNT, are usually presentwherever soils have been contaminated with TNT. Liquid-state 15N NMR analyses of laboratory reactions between 4-methyl-3-nitroaniline-15N, the major monoamine reduction product of 2,4DNT, and the Elliot soil humic acid, both in the presence and absence of horseradish peroxidase, indicated that the amine underwent covalent binding with quinone and other carbonyl groups in the soil humic acid to form both heterocyclic and non-heterocyclic condensation products. Liquid-state 15N NMR analyses of the methanol extracts of 20 day aerobic bench-scale composts of 2,4-di-15N-nitrotoluene and 2,6-di-15N-nitrotoluene revealed the presence of nitrite and monoamine, but not diamine, reduction products, indicating the occurrence of both dioxygenase enzyme and reductive degradation pathways. Solid-state CP/MAS 15N NMR analyses of the whole composts, however, suggested that reduction to monoamines followed by covalent binding of the amines to organic matter was the predominant pathway.

  16. N-15 NMR study of the immobilization of 2,4- and 2,6-dinitrotoluene in aerobic compost

    USGS Publications Warehouse

    Thorn, K.A.; Pennington, J.C.; Kennedy, K.R.; Cox, L.G.; Hayes, C.A.; Porter, B.E.

    2008-01-01

    Large-scale aerobic windrow composting has been used to bioremediate washout lagoon soils contaminated with the explosives TNT (2,4,6- trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) at several sites within the United States. We previously used 15N NMR to investigate the reduction and binding of T15NT in aerobic bench -scale reactors simulating the conditions of windrow composting. These studies have been extended to 2,4-dinitrotoluene (2,4DNT) and 2,6-dinitrotoluene (2,6DNT), which, as impurities in TNT, are usually present wherever soils have been contaminated with TNT. Liquid-state 15N NMR analyses of laboratory reactions between 4-methyl-3-nitroaniline-15N, the major monoamine reduction product of 2,4DNT, and the Elliot soil humic acid, both in the presence and absence of horseradish peroxidase, indicated that the amine underwent covalent binding with quinone and other carbonyl groups in the soil humic acid to form both heterocyclic and non-heterocyclic condensation products. Liquid-state 15N NMR analyses of the methanol extracts of 20 day aerobic bench-scale composts of 2,4-di-15N-nitrotoluene and 2,6-di-15N-nitrotoluene revealed the presence of nitrite and monoamine, but not diamine, reduction products, indicating the occurrence of both dioxygenase enzyme and reductive degradation pathways. Solid-state CP/MAS 15N NMR analyses of the whole composts, however, suggested that reduction to monoamines followed by covalent binding of the amines to organic matter was the predominant pathway. ?? 2008 American Chemical Society.

  17. A Simple Approach to Analyzing Protein Side-Chain Dynamics from 13C NMR Relaxation Data

    NASA Astrophysics Data System (ADS)

    Daragan, Vladimir A.; Mayo, Kevin H.

    1998-02-01

    A simple approach to deriving motional dynamics information of protein and peptide side chains by using13C NMR relaxation data is presented. By using linear approximation of internal rotational correlation functions, simple equations for relating side-chain conformation, bond rotational amplitudes, and rotational correlation coefficients with different NMR relaxation parameters have been obtained. Auto- and cross-correlation spectral densities are considered, and it is shown that proton-coupled13C NMR relaxation measurements allow detailed motional information to be obtained.

  18. Molecular dynamics simulations of NMR relaxation and diffusion of bulk hydrocarbons and water

    NASA Astrophysics Data System (ADS)

    Singer, Philip M.; Asthagiri, Dilip; Chapman, Walter G.; Hirasaki, George J.

    2017-04-01

    Molecular dynamics (MD) simulations are used to investigate 1H nuclear magnetic resonance (NMR) relaxation and diffusion of bulk n-C5H12 to n-C17H36 hydrocarbons and bulk water. The MD simulations of the 1H NMR relaxation times T1,2 in the fast motion regime where T1 =T2 agree with measured (de-oxygenated) T2 data at ambient conditions, without any adjustable parameters in the interpretation of the simulation data. Likewise, the translational diffusion DT coefficients calculated using simulation configurations agree with measured diffusion data at ambient conditions. The agreement between the predicted and experimentally measured NMR relaxation times and diffusion coefficient also validate the forcefields used in the simulation. The molecular simulations naturally separate intramolecular from intermolecular dipole-dipole interactions helping bring new insight into the two NMR relaxation mechanisms as a function of molecular chain-length (i.e. carbon number). Comparison of the MD simulation results of the two relaxation mechanisms with traditional hard-sphere models used in interpreting NMR data reveals important limitations in the latter. With increasing chain length, there is substantial deviation in the molecular size inferred on the basis of the radius of gyration from simulation and the fitted hard-sphere radii required to rationalize the relaxation times. This deviation is characteristic of the local nature of the NMR measurement, one that is well-captured by molecular simulations.

  19. On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water.

    PubMed

    Carof, Antoine; Salanne, Mathieu; Charpentier, Thibault; Rotenberg, Benjamin

    2015-11-21

    Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as (7)Li(+), (23)Na(+), (25)Mg(2+), (35)Cl(-), (39)K(+), or (133)Cs(+). Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.

  20. On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water

    NASA Astrophysics Data System (ADS)

    Carof, Antoine; Salanne, Mathieu; Charpentier, Thibault; Rotenberg, Benjamin

    2015-11-01

    Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as 7Li+, 23Na+, 25Mg2+, 35Cl-, 39K+, or 133Cs+. Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.

  1. NMR surface relaxivity of calcite with adsorbed Mn{sup 2+}

    SciTech Connect

    Kenyon, W.E.; Kolleeny, J.A.

    1995-03-15

    Calcite particles were exposed to Mn{sup 2+} in aqueous solution to allow adsorption. The calcite particles were then packed, and the NMR longitudinal relaxation time T{sub 1} of water saturating the interparticle pores was measured. NMR surface relaxivity was then computed as 1/(T{sub 1}{times}S{sub p}/V{sub p}), where S{sub p}/V{sub p} is the ratio of surface area to pore volume. Adsorbed manganese increases the NMR surface relaxivity to approximately 2.4 {times} 10{sup {minus}3} cm/s, roughly 50 times the surface relaxivity of very pure calcite. Flowing water with 4 {mu}M Mn{sup 2+} through a porous limestone plug decreased its T{sub 1} by a factor of 6. Iron as adsorbate produced relatively small increases in surface relaxivity. These results suggest that manganese dominates the surface relaxivity, of limestone rocks in situ, which is important in the interpretation of NMR borehole logs. Observations suggest that some adsorbed manganese eventually becomes buried by freshly precipitated calcite. In particular, the surface relaxivity increased with initial adsorption, but gradually decreased at long reaction times, even as the aqueous manganese concentration continued to decrease. NMR evidently senses only the manganese in the outermost atomic layer, and thus might prove useful in more detailed studies of adsorption.

  2. The eigenmode perspective of NMR spin relaxation in proteins

    NASA Astrophysics Data System (ADS)

    Shapiro, Yury E.; Meirovitch, Eva

    2013-12-01

    We developed in recent years the two-body (protein and probe) coupled-rotator slowly relaxing local structure (SRLS) approach for elucidating protein dynamics from NMR spin relaxation. So far we used as descriptors the set of physical parameters that enter the SRLS model. They include the global (protein-related) diffusion tensor, D1, the local (probe-related) diffusion tensor, D2, and the local coupling/ordering potential, u. As common in analyzes based on mesoscopic dynamic models, these parameters have been determined with data-fitting techniques. In this study, we describe structural dynamics in terms of the eigenmodes comprising the SRLS time correlation functions (TCFs) generated by using the best-fit parameters as input to the Smoluchowski equation. An eigenmode is a weighted exponential with decay constant given by an eigenvalue of the Smoluchowski operator, and weighting factor determined by the corresponding eigenvector. Obviously, both quantities depend on the SRLS parameters as determined by the SRLS model. Unlike the set of best-fit parameters, the eigenmodes represent patterns of motion of the probe-protein system. The following new information is obtained for the typical probe, the 15N-1H bond. Two eigenmodes, associated with the protein and the probe, dominate when the time scale separation is large (i.e., D2 ≫ D1), the tensorial properties are simple, and the local potential is either very strong or very weak. When the potential exceeds these limits while the remaining conditions are preserved, new eigenmodes arise. The multi-exponentiality of the TCFs is associated in this case with the restricted nature of the local motion. When the time scale separation is no longer large, the rotational degrees of freedom of the protein and the probe become statistically dependent (coupled dynamically). The multi-exponentiality of the TCFs is associated in this case with the restricted nature of both the local and the global motion. The effects of local

  3. Using Paramagnetism to Slow Down Nuclear Relaxation in Protein NMR.

    PubMed

    Orton, Henry W; Kuprov, Ilya; Loh, Choy-Theng; Otting, Gottfried

    2016-12-01

    Paramagnetic metal ions accelerate nuclear spin relaxation; this effect is widely used for distance measurement and called paramagnetic relaxation enhancement (PRE). Theoretical predictions established that, under special circumstances, it is also possible to achieve a reduction in nuclear relaxation rates (negative PRE). This situation would occur if the mechanism of nuclear relaxation in the diamagnetic state is counterbalanced by a paramagnetic relaxation mechanism caused by the metal ion. Here we report the first experimental evidence for such a cross-correlation effect. Using a uniformly (15)N-labeled mutant of calbindin D9k loaded with either Tm(3+) or Tb(3+), reduced R1 and R2 relaxation rates of backbone (15)N spins were observed compared with the diamagnetic reference (the same protein loaded with Y(3+)). The effect arises from the compensation of the chemical shift anisotropy tensor by the anisotropic dipolar shielding generated by the unpaired electron spin.

  4. Curie-type paramagnetic NMR relaxation in the aqueous solution of Ni(II).

    PubMed

    Mareš, Jiří; Hanni, Matti; Lantto, Perttu; Lounila, Juhani; Vaara, Juha

    2014-04-21

    Ni(2+)(aq) has been used for many decades as a model system for paramagnetic nuclear magnetic resonance (pNMR) relaxation studies. More recently, its magnetic properties and also nuclear magnetic relaxation rates have been studied computationally. We have calculated electron paramagnetic resonance and NMR parameters using quantum-mechanical (QM) computation of molecular dynamics snapshots, obtained using a polarizable empirical force field. Statistical averages of hyperfine coupling, g- and zero-field splitting tensors, as well as the pNMR shielding terms, are compared to the available experimental and computational data. In accordance with our previous work, the isotropic hyperfine coupling as well as nuclear shielding values agree well with experimental measurements for the (17)O nuclei of water molecules in the first solvation shell of the nickel ion, whereas larger deviations are found for (1)H centers. We report, for the first time, the Curie-type contribution to the pNMR relaxation rate using QM calculations together with Redfield relaxation theory. The Curie relaxation mechanism is analogous to chemical shift anisotropy relaxation, well-known in diamagnetic NMR. Due to the predominance of other types of paramagnetic relaxation mechanisms for this system, it is possible to extract the Curie term only computationally. The Curie mechanism alone would result in around 16 and 20 s(-1) of relaxation rates (R1 and R2 respectively) for the (1)H nuclei of water molecules bonded to the Ni(2+) center, in a magnetic field of 11.7 T. The corresponding (17)O relaxation rates are around 33 and 38 s(-1). We also report the Curie contribution to the relaxation rate for molecules beyond the first solvation shell in a 1 M solution of Ni(2+) in water.

  5. Effect of magnetic pore surface coating on the NMR relaxation and diffusion signal in quartz sand.

    PubMed

    Duschl, Markus; Pohlmeier, Andreas; Brox, Timothy I; Galvosas, Petrik; Vereecken, Harry

    2016-12-01

    Magnetic impurities are ubiquitous in natural porous media such as sand and soil. They generate internal magnetic field gradients because of increased magnetic susceptibility differences between solid and liquid phase in the pore space and because of the presence of magnetic centers. These internal gradients accelerate NMR relaxation rates and thus might limit the possibility of pore space characterization using NMR. In this study, we investigate the effects of coating the surface of natural sands by the antiferromagnetic iron oxyhydroxide goethite on NMR relaxation and diffusion properties. We found a non-quadratic dependence of the relaxation time distributions on the echo time indicating that the relaxation experiments were not performed in the fast diffusion limit, while the weak dependence on the external magnetic field strength is explained by the preponderance of the surface relaxation over the effect of diffusion in internal gradients. The surface to volume ratio of the pore space, determined by NMR diffusimetry ((S/V)NMR ) remains approximately constant, whereas the same quantity, determined from gas adsorption ((S/V)BET ) increases proportional to the coating density. This is because gas adsorption measures surface roughness on sub-nanometer scale, whereas NMR diffusimetry averages over structures smaller than few microns. This has consequences for the calculation of the surface relaxivities. The usage of the (S/V)NMR leads to constant values, whereas the usage of (S/V)BET leads to apparently decreasing relaxivities with increasing coating, which is unrealistic. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  6. Effect of Paramagnetic Ions on NMR Relaxation of Fluids at Solid Surfaces

    NASA Astrophysics Data System (ADS)

    Foley, I.; Farooqui, S. A.; Kleinberg, R. L.

    Proton NMR longitudinal and transverse relaxation times of water-saturated powder packs have been measured. The powders were a series of synthetic calcium silicates with known concentrations of iron or manganese paramagnetic ions. The rate of water proton relaxation has been found to be linearly proportional to the concentration of paramagnetic ion. The constant of proportionality is used to determine the electron relaxation time of ions at the fluid-solid interface. A substantial relaxivity is found in the absence of paramagnetic ions. Thus the oxide surface itself is an unexpectedly good relaxer of fluid-borne nuclear spins. The results answer some long-standing questions connected with the NMR properties of fluid-saturated sedimentary rocks.

  7. New approach for understanding experimental NMR relaxivity properties of magnetic nanoparticles: focus on cobalt ferrite.

    PubMed

    Rollet, Anne-Laure; Neveu, Sophie; Porion, Patrice; Dupuis, Vincent; Cherrak, Nadine; Levitz, Pierre

    2016-12-07

    Relaxivities r1 and r2 of cobalt ferrite magnetic nanoparticles (MNPs) have been investigated in the aim of improving the models of NMR relaxation induced by magnetic nanoparticles. On one hand a large set of relaxivity data has been collected for cobalt ferrite MNP dispersions. On the other hand the relaxivity has been calculated for dispersions of cobalt ferrite MNPs with size ranging from 5 to 13 nm, without using any fitting procedure. The model is based on the magnetic dipolar interaction between the magnetic moments of the MNPs and the (1)H nuclei. It takes into account both the longitudinal and transversal contributions of the magnetic moments of MNPs leading to three contributions in the relaxation equations. The comparison of the experimental and theoretical data shows a good agreement of the NMR profiles as well as the temperature dependence.

  8. Paramagnetic nanoparticles as potential MRI contrast agents: characterization, NMR relaxation, simulations and theory.

    PubMed

    Vuong, Quoc Lam; Van Doorslaer, Sabine; Bridot, Jean-Luc; Argante, Corradina; Alejandro, Gabriela; Hermann, Raphaël; Disch, Sabrina; Mattea, Carlos; Stapf, Siegfried; Gossuin, Yves

    2012-12-01

    Paramagnetic nanoparticles, mainly rare earth oxides and hydroxides, have been produced these last few years for use as MRI contrast agents. They could become an interesting alternative to iron oxide particles. However, their relaxation properties are not well understood. Magnetometry, (1)H and (2)H NMR relaxation results at different magnetic fields and electron paramagnetic resonance are used to investigate the relaxation induced by paramagnetic particles. When combined with computer simulations of transverse relaxation, they allow an accurate description of the relaxation induced by paramagnetic particles. For gadolinium hydroxide particles, both T(1) and T(2) relaxation are due to a chemical exchange of protons between the particle surface and bulk water, called inner sphere relaxation. The inner sphere is also responsible for T(1) relaxation of dysprosium, holmium, terbium and erbium containing particles. However, for these latter compounds, T(2) relaxation is caused by water diffusion in the field inhomogeneities created by the magnetic particle, the outer-sphere relaxation mechanism. The different relaxation behaviors are caused by different electron relaxation times (estimated by electron paramagnetic resonance). These findings may allow tailoring paramagnetic particles: ultrasmall gadolinium oxide and hydroxide particles for T(1) contrast agents, with shapes ensuring the highest surface-to-volume ratio. All the other compounds present interesting T(2) relaxation performance at high fields. These results are in agreement with computer simulations and theoretical predictions of the outer-sphere and static dephasing regime theories. The T(2) efficiency would be optimum for spherical particles of 40-50 nm radius.

  9. Distinguishing magnetic vs. quadrupolar relaxation in b-NMR using 8Li and 9Li

    NASA Astrophysics Data System (ADS)

    Chatzichristos, A.; McFadden, R. M. L.; Karner, V. L.; Cortie, D. L.; Fang, A.; Levy, C. D. P.; Macfarlane, W. A.; Morris, G. D.; Pearson, M. R.; Salman, Z.; Kiefl, R. F.

    2016-09-01

    Beta-detected NMR is a powerful technique in condensed matter physics. It uses the parity violation of beta decay to detect the NMR signal from a beam of highly polarized radionuclides implanted in a sample material. Spin-lattice relaxation (SLR) is studied by monitoring the rate with which the asymmetry between the beta counts in two opposing detectors is lost. Unlike classical NMR, b-NMR can study thin films and near-surface effects. The most common b-NMR isotope at TRIUMF is 8Li, which has a quadrupole moment, thus it is sensitive to both magnetic fields and electric field gradients. A challenge with 8Li b-NMR is identifying the predominant mechanism of SLR in a given sample. It is possible to distinguish between SLR mechanisms by varying the probe isotope. For two isotopes with different nuclear moments, the ratio of SLR rates should be different in the limits of either pure magnetic or quadrupolar relaxation. This method has been used in classical NMR and we report its first application to b-NMR. We measured the SLR rates for 8Li and 8Li in Pt foil and SrTiO3. Pt is a test case for pure magnetic relaxation. SrTiO3 is a non-magnetic insulator, but the source of its relaxation is not well understood. Here we show that its relaxation is mainly quadrupolar. We thank TRIUMF's CMMS for their technical support. This work was supported by: NSERC Discovery Grants to R.F.K. and W.A.M.; and IsoSiM fellowships to A.C. and R.M.L.M.

  10. On the microscopic fluctuations driving the NMR relaxation of quadrupolar ions in water

    SciTech Connect

    Carof, Antoine; Salanne, Mathieu; Rotenberg, Benjamin; Charpentier, Thibault

    2015-11-21

    Nuclear Magnetic Resonance (NMR) relaxation is sensitive to the local structure and dynamics around the probed nuclei. The Electric Field Gradient (EFG) is the key microscopic quantity to understand the NMR relaxation of quadrupolar ions, such as {sup 7}Li{sup +}, {sup 23}Na{sup +}, {sup 25}Mg{sup 2+}, {sup 35}Cl{sup −}, {sup 39}K{sup +}, or {sup 133}Cs{sup +}. Using molecular dynamics simulations, we investigate the statistical and dynamical properties of the EFG experienced by alkaline, alkaline Earth, and chloride ions at infinite dilution in water. Specifically, we analyze the effect of the ionic charge and size on the distribution of the EFG tensor and on the multi-step decay of its auto-correlation function. The main contribution to the NMR relaxation time arises from the slowest mode, with a characteristic time on the picosecond time scale. The first solvation shell of the ion plays a dominant role in the fluctuations of the EFG, all the more that the ion radius is small and its charge is large. We propose an analysis based on a simplified charge distribution around the ion, which demonstrates that the auto-correlation of the EFG, hence the NMR relaxation time, reflects primarily the collective translational motion of water molecules in the first solvation shell of the cations. Our findings provide a microscopic route to the quantitative interpretation of NMR relaxation measurements and open the way to the design of improved analytical theories for NMR relaxation for small ionic solutes, which should focus on water density fluctuations around the ion.

  11. Improved Characterization of Healthy and Malignant Tissue by NMR Line-Shape Relaxation Correlations

    PubMed Central

    Peemoeller, H.; Shenoy, R.K.; Pintar, M.M.; Kydon, D.W.; Inch, W.R.

    1982-01-01

    We performed a relaxation-line-shape correlation NMR experiment on muscle, liver, kidney, and spleen tissues of healthy mice and of mouse tumor tissue. In each tissue studied, five spin groups were resolved and characterized by their relaxation parameters. We report a previously uncharacterized semi-solid spin group and discuss briefly the value of this method for the identification of malignant tissues. PMID:7104438

  12. Challenging lanthanide relaxation theory: erbium and thulium complexes that show NMR relaxation rates faster than dysprosium and terbium analogues.

    PubMed

    Funk, Alexander M; Harvey, Peter; Finney, Katie-Louise N A; Fox, Mark A; Kenwright, Alan M; Rogers, Nicola J; Senanayake, P Kanthi; Parker, David

    2015-07-07

    Measurements of the proton NMR paramagnetic relaxation rates for several series of isostructural lanthanide(III) complexes have been performed in aqueous solution over the field range 1.0 to 16.5 Tesla. The field dependence has been modeled using Bloch-Redfield-Wangsness theory, allowing values for the electronic relaxation time, Tle and the magnetic susceptibility, μeff, to be estimated. Anomalous relaxation rate profiles were obtained, notably for erbium and thulium complexes of low symmetry 8-coordinate aza-phosphinate complexes. Such behaviour challenges accepted theory and can be interpreted in terms of changes in Tle values that are a function of the transient ligand field induced by solvent collision and vary considerably between Ln(3+) ions, along with magnetic susceptibilities that deviate significantly from free-ion values.

  13. Ultra-low-field NMR relaxation and diffusion measurements using an optical magnetometer.

    PubMed

    Ganssle, Paul J; Shin, Hyun D; Seltzer, Scott J; Bajaj, Vikram S; Ledbetter, Micah P; Budker, Dmitry; Knappe, Svenja; Kitching, John; Pines, Alexander

    2014-09-08

    Nuclear magnetic resonance (NMR) relaxometry and diffusometry are important tools for the characterization of heterogeneous materials and porous media, with applications including medical imaging, food characterization and oil-well logging. These methods can be extremely effective in applications where high-resolution NMR is either unnecessary, impractical, or both, as is the case in the emerging field of portable chemical characterization. Here, we present a proof-of-concept experiment demonstrating the use of high-sensitivity optical magnetometers as detectors for ultra-low-field NMR relaxation and diffusion measurements.

  14. Anomalous NMR Relaxation in Cartilage Matrix Components and Native Cartilage: Fractional-Order Models

    PubMed Central

    Magin, Richard L.; Li, Weiguo; Velasco, M. Pilar; Trujillo, Juan; Reiter, David A.; Morgenstern, Ashley; Spencer, Richard G.

    2011-01-01

    We present a fractional-order extension of the Bloch equations to describe anomalous NMR relaxation phenomena (T1 and T2). The model has solutions in the form of Mittag-Leffler and stretched exponential functions that generalize conventional exponential relaxation. Such functions have been shown by others to be useful for describing dielectric and viscoelastic relaxation in complex, heterogeneous materials. Here, we apply these fractional-order T1 and T2 relaxation models to experiments performed at 9.4 and 11.7 Tesla on type I collagen gels, chondroitin sulfate mixtures, and to bovine nasal cartilage (BNC), a largely isotropic and homogeneous form of cartilage. The results show that the fractional-order analysis captures important features of NMR relaxation that are typically described by multi-exponential decay models. We find that the T2 relaxation of BNC can be described in a unique way by a single fractional-order parameter (α), in contrast to the lack of uniqueness of multi-exponential fits in the realistic setting of a finite signal-to-noise ratio. No anomalous behavior of T1 was observed in BNC. In the single-component gels, for T2 measurements, increasing the concentration of the largest components of cartilage matrix, collagen and chondroitin sulfate, results in a decrease in α, reflecting a more restricted aqueous environment. The quality of the curve fits obtained using Mittag-Leffler and stretched exponential functions are in some cases superior to those obtained using mono- and bi-exponential models. In both gels and BNC, α appears to account for microstructural complexity in the setting of an altered distribution of relaxation times. This work suggests the utility of fractional-order models to describe T2 NMR relaxation processes in biological tissues. PMID:21498095

  15. Anomalous NMR relaxation in cartilage matrix components and native cartilage: fractional-order models.

    PubMed

    Magin, Richard L; Li, Weiguo; Pilar Velasco, M; Trujillo, Juan; Reiter, David A; Morgenstern, Ashley; Spencer, Richard G

    2011-06-01

    We present a fractional-order extension of the Bloch equations to describe anomalous NMR relaxation phenomena (T(1) and T(2)). The model has solutions in the form of Mittag-Leffler and stretched exponential functions that generalize conventional exponential relaxation. Such functions have been shown by others to be useful for describing dielectric and viscoelastic relaxation in complex, heterogeneous materials. Here, we apply these fractional-order T(1) and T(2) relaxation models to experiments performed at 9.4 and 11.7 Tesla on type I collagen gels, chondroitin sulfate mixtures, and to bovine nasal cartilage (BNC), a largely isotropic and homogeneous form of cartilage. The results show that the fractional-order analysis captures important features of NMR relaxation that are typically described by multi-exponential decay models. We find that the T(2) relaxation of BNC can be described in a unique way by a single fractional-order parameter (α), in contrast to the lack of uniqueness of multi-exponential fits in the realistic setting of a finite signal-to-noise ratio. No anomalous behavior of T(1) was observed in BNC. In the single-component gels, for T(2) measurements, increasing the concentration of the largest components of cartilage matrix, collagen and chondroitin sulfate, results in a decrease in α, reflecting a more restricted aqueous environment. The quality of the curve fits obtained using Mittag-Leffler and stretched exponential functions are in some cases superior to those obtained using mono- and bi-exponential models. In both gels and BNC, α appears to account for micro-structural complexity in the setting of an altered distribution of relaxation times. This work suggests the utility of fractional-order models to describe T(2) NMR relaxation processes in biological tissues.

  16. Anomalous NMR relaxation in cartilage matrix components and native cartilage: Fractional-order models

    NASA Astrophysics Data System (ADS)

    Magin, Richard L.; Li, Weiguo; Pilar Velasco, M.; Trujillo, Juan; Reiter, David A.; Morgenstern, Ashley; Spencer, Richard G.

    2011-06-01

    We present a fractional-order extension of the Bloch equations to describe anomalous NMR relaxation phenomena ( T1 and T2). The model has solutions in the form of Mittag-Leffler and stretched exponential functions that generalize conventional exponential relaxation. Such functions have been shown by others to be useful for describing dielectric and viscoelastic relaxation in complex, heterogeneous materials. Here, we apply these fractional-order T1 and T2 relaxation models to experiments performed at 9.4 and 11.7 Tesla on type I collagen gels, chondroitin sulfate mixtures, and to bovine nasal cartilage (BNC), a largely isotropic and homogeneous form of cartilage. The results show that the fractional-order analysis captures important features of NMR relaxation that are typically described by multi-exponential decay models. We find that the T2 relaxation of BNC can be described in a unique way by a single fractional-order parameter ( α), in contrast to the lack of uniqueness of multi-exponential fits in the realistic setting of a finite signal-to-noise ratio. No anomalous behavior of T1 was observed in BNC. In the single-component gels, for T2 measurements, increasing the concentration of the largest components of cartilage matrix, collagen and chondroitin sulfate, results in a decrease in α, reflecting a more restricted aqueous environment. The quality of the curve fits obtained using Mittag-Leffler and stretched exponential functions are in some cases superior to those obtained using mono- and bi-exponential models. In both gels and BNC, α appears to account for micro-structural complexity in the setting of an altered distribution of relaxation times. This work suggests the utility of fractional-order models to describe T2 NMR relaxation processes in biological tissues.

  17. Molecular motion of micellar solutes: a /sup 13/C NMR relaxation study

    SciTech Connect

    Stark, R.E.; Kasakevich, M.L.; Granger, J.W.

    1982-02-04

    A series of simple NMR relaxation experiments have been performed on nitrobenzene and aniline dissolved in the ionic detergents sodium dodecyl sulfate (SDS) and hexadecyltrimethylammonium bromide (CTAB). Using /sup 13/C relaxation rates at various molecular sites, and comparing data obtained in organic media with those for micellar solutions, the viscosity at the solubilization site was estimated and a detailed picture of motional restrictions imposed by the micellar enviroment was derived. Viscosities of 8 to 17 cp indicate a rather fluid environment for solubilized nitrobenzene; both additives exhibit altered motional preferences in CTAB solutions only. As an aid in interpretation of the NMR data, quasi-elastic light scattering and other physical techniques have been used to evaluate the influence of organic solutes on micellar size and shape. The NMR methods are examined critically in terms of their general usefulness for studies of solubilization in detergent mice

  18. Determination of Spin-Lattice Relaxation of Time Using (Super 13)C NMR: An Undergraduate Physical Chemistry Laboratory Experiment

    ERIC Educational Resources Information Center

    Gasyna, Zbigniew L.; Jurkiewicz, Antoni

    2004-01-01

    An experiment designed for the physical chemistry laboratory where (super 13)C NMR is applied to determine the spin-lattice relaxation time for carbon atoms in n-hexanol is proposed. It is concluded that students learn the principles and concepts of NMR spectroscopy as well as dynamic NMR experiments.

  19. Joint numerical microscale simulations of multi-phase flow and NMR relaxation behaviour in porous media

    NASA Astrophysics Data System (ADS)

    Mohnke, O.; Ahrenholz, B.

    2011-12-01

    Nuclear Magnetic Resonance (NMR) is a useful tool for analyzing gas (methane) and fluids (water, oil) in rock formations in order to derive transport and storage properties such as pore-size distributions or relative permeability. Even though there is considerable NMR data available about hydraulic properties of rock formations, this information is only empirical. Thus, the aim of this paper is to present joint NMR and multi-phase flow simulations in micro-scale pore systems derived from micro-CT images to quantify relationships between NMR parameters and transport and storage properties of partially saturated rocks. Hereby, the NMR differential equations were implemented using an advection/diffusion lattice-Boltzmann method (LBM) where the flow field is computed by a coupled LBM CFD solver. The results of numerical imbibition and drainage experiments quantitatively agree with laboratory experiments with regard to frequently found peak shifts and bimodal NMR decay time distributions related to residual water in films and corners as well as to fluids/gases trapped in large pores. This numerical framework enables one to quantitatively describe NMR surface and bulk relaxation processes, diffusive coupling along with the multi-phase flow properties of partially saturated porous systems. Furthermore, it is a viable alternative to the more time-consuming and less controllable laboratory experiments. Such virtual experimental setups can considerably help to benchmark and validate statistical network models to better understand hydraulic properties of partially saturated rocks by using experimentally obtained NMR data.

  20. 1H and 19F NMR relaxation studies of fleroxacin with Micrococcus luteus.

    PubMed

    Waibel, Benjamin; Holzgrabe, Ulrike

    2007-04-11

    In order to investigate and characterize interaction processes between the fluoroquinolone fleroxacin and bacterial cells we used non-selective (all resonances are excited), selective (observed resonance is excited) spin-lattice relaxation rates and spin-spin relaxation measurements. The signals of three hydrogens at different moieties of the fleroxacin molecule were considered to get an insight in the complexation behavior. The enhancement of selective relaxation rates was observed with increasing fleroxacin concentrations and keeping the bacterial mass constant. The obtained relaxation rates of the affected hydrogens were analyzed via a Lineweaver-Burk-plot to determine the KD values. Furthermore, 19F NMR spectra were recorded and spin-spin relaxation rates (R2) were determined by a Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence. Because of the dependency of the line width of NMR peaks on transversal relaxation time T2, we compared the line width at half-height at different fleroxacin concentrations in order to investigate the involvement of fluorine atoms in different positions in the complexation. All findings point to core quinolone moiety to be involved in the interaction with bacterial cells.

  1. Nanoscale coordination polymers exhibiting luminescence properties and NMR relaxivity

    NASA Astrophysics Data System (ADS)

    Chelebaeva, Elena; Larionova, Joulia; Guari, Yannick; Ferreira, Rute A. S.; Carlos, Luis D.; Trifonov, Alexander A.; Kalaivani, Thangavel; Lascialfari, Alessandro; Guérin, Christian; Molvinger, Karine; Datas, Lucien; Maynadier, Marie; Gary-Bobo, Magali; Garcia, Marcel

    2011-03-01

    This article presents the first example of ultra-small (3-4 nm) magneto-luminescent cyano-bridged coordination polymer nanoparticles Ln0.333+Gdx3+/[Mo(CN)8]3- (Ln = Eu (x = 0.34), Tb (x = 0.35)) enwrapped by a natural biocompatible polymer chitosan. The aqueous colloidal solutions of these nanoparticles present a luminescence characteristic of the corresponding lanthanides (5D0 --> 7F0-4 (Eu3+) or the 5D4 --> 7F6-2 (Tb3+)) under UV excitation and a green luminescence of the chitosan shell under excitation in the visible region. Magnetic Resonance Imaging (MRI) efficiency, i.e. the nuclear relaxivity, measurements performed for Ln0.333+Gdx3+/[Mo(CN)8]3- nanoparticles show r1p and r2p relaxivities slightly higher than or comparable to the ones of the commercial paramagnetic compounds Gd-DTPA® or Omniscan® indicating that our samples may potentially be considered as a positive contrast agent for MRI. The in vitro studies performed on these nanoparticles show that they maybe internalized into human cancer and normal cells and well detected by fluorescence at the single cell level. They present high stability even at low pH and lack of cytotoxicity both in human cancer and normal cells.This article presents the first example of ultra-small (3-4 nm) magneto-luminescent cyano-bridged coordination polymer nanoparticles Ln0.333+Gdx3+/[Mo(CN)8]3- (Ln = Eu (x = 0.34), Tb (x = 0.35)) enwrapped by a natural biocompatible polymer chitosan. The aqueous colloidal solutions of these nanoparticles present a luminescence characteristic of the corresponding lanthanides (5D0 --> 7F0-4 (Eu3+) or the 5D4 --> 7F6-2 (Tb3+)) under UV excitation and a green luminescence of the chitosan shell under excitation in the visible region. Magnetic Resonance Imaging (MRI) efficiency, i.e. the nuclear relaxivity, measurements performed for Ln0.333+Gdx3+/[Mo(CN)8]3- nanoparticles show r1p and r2p relaxivities slightly higher than or comparable to the ones of the commercial paramagnetic compounds Gd

  2. Accounting for Relaxation During Pulse Effects in Surface NMR for Long Pulses and Fast Relaxation Times

    NASA Astrophysics Data System (ADS)

    Grombacher, D.; Behroozmand, A. A.; Auken, E.

    2016-12-01

    Surface nuclear magnetic resonance provides the ability to non-invasively quantify and map subsurface water content. To ensure reliable water content estimates are produced the transmit portion of the experiment (called excitation) must be modeled accurately. This requires that relaxation during pulse (RDP) effects be accounted for as they may lead to biased water content estimates if neglected. The standard approach to account for these effects involves estimating the initial amplitude of the signal by extrapolating the measured decay to the midpoint of the pulse, while neglecting these effects in the excitation modeling. The reasoning behind such an approach is that initial amplitudes estimated by extrapolation to the midpoint of the pulse (in combination with excitation modeling that neglects RDP) can reliably reproduce the correct water content. This technique works well in the regime where the time constants describing the decay of the observed signal (called relaxation times) are greater than the pulse duration. However, recent hardware advancements now allow the routine measurement of much faster relaxation times where this approach may lead to poor water content estimates. Furthermore, a growing desire to use alternative transmit schemes demands a flexible protocol to account for RDP effects in the presence of fast relaxation times for arbitrary transmit schemes. To accomplish this goal a data driven approach involving direct modeling of RDP processes is presented. Relaxation times estimated from the observed decay are directly incorporated into the excitation modeling (while the initial amplitude is estimated at the end of the pulse) in order to produce more robust water content estimates. Synthetic and laboratory data is presented to demonstrate that such an approach is expected to broaden the range of relaxation times where water contents can be reliably estimated and better extends functionality to alternative transmit schemes.

  3. Measurement of interfacial area from NMR time dependent diffusion and relaxation measurements.

    PubMed

    Fleury, M

    2017-09-07

    The interfacial area between two immiscible phases in porous media is an important parameter for describing and predicting 2 phase flow. Although present in several models, experimental investigations are sparse due to the lack of appropriate measurement techniques. We propose two NMR techniques for the measurement of oil-water interfacial area: (i) a time dependent NMR diffusion technique applicable in static conditions, similar to those used for the measurement of the solid specific surface of a porous media, and (ii) a fast relaxation technique applicable in dynamic conditions while flowing, based on an interfacial relaxation mechanism induced by the inclusion of paramagnetic salts in the water phase. For dodecane relaxing on doped water, we found an oil interfacial relaxivity of 1.8μm/s, large enough to permit the measurement of specific interfacial surface as small as 1000cm(2)/cm(3). We demonstrate both NMR techniques in drainage followed by imbibition, in a model porous media with a narrow pore size distribution. While flowing, we observe that the interfacial area is larger in imbibition than in drainage, implying a different organization of the oil phase. In a carbonate sample with a wide pore size distribution, we evidence the gradual invasion of the smallest pores as the oil-water pressure difference is increased. Copyright © 2017. Published by Elsevier Inc.

  4. NMR permeability estimators in 'chalk' carbonate rocks obtained under different relaxation times and MICP size scalings

    NASA Astrophysics Data System (ADS)

    Rios, Edmilson Helton; Figueiredo, Irineu; Moss, Adam Keith; Pritchard, Timothy Neil; Glassborow, Brent Anthony; Guedes Domingues, Ana Beatriz; Bagueira de Vasconcellos Azeredo, Rodrigo

    2016-07-01

    The effect of the selection of different nuclear magnetic resonance (NMR) relaxation times for permeability estimation is investigated for a set of fully brine-saturated rocks acquired from Cretaceous carbonate reservoirs in the North Sea and Middle East. Estimators that are obtained from the relaxation times based on the Pythagorean means are compared with estimators that are obtained from the relaxation times based on the concept of a cumulative saturation cut-off. Select portions of the longitudinal (T1) and transverse (T2) relaxation-time distributions are systematically evaluated by applying various cut-offs, analogous to the Winland-Pittman approach for mercury injection capillary pressure (MICP) curves. Finally, different approaches to matching the NMR and MICP distributions using different mean-based scaling factors are validated based on the performance of the related size-scaled estimators. The good results that were obtained demonstrate possible alternatives to the commonly adopted logarithmic mean estimator and reinforce the importance of NMR-MICP integration to improving carbonate permeability estimates.

  5. Two dimensional NMR and NMR relaxation studies of coal structure. Progress report, September 13, 1991--December 31, 1991

    SciTech Connect

    Zilm, K.W.

    1992-05-27

    This report covers the progress made on the title project for the project period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins are particularly promising. Methods combining proton-proton spin diffusion with {sup 13}C CPMAS readout are being developed to determine the connectivity of functional groups in coals in a high sensitivity relay type of experiment. Additional work is aimed a delineating the role of methyl group rotation in the proton NMR relaxation behavior of coals.

  6. Two dimensional NMR and NMR relaxation studies of coal structure. Progress report, January 1, 1992--March 31, 1992

    SciTech Connect

    Zilm, K.W.

    1992-07-01

    This report covers the progress made on the title project for the project period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins are particularly promising. Methods combining proton-proton spin diffusion with {sup 13}C CPMAS readout are being developed to determine the connectivity of functional groups in coals in a high sensitivity relay type of experiment. Additional work is aimed at delineating the role of methyl group rotation in the proton NMR relaxation behavior of coals.

  7. Two dimensional NMR and NMR relaxation studies of coal structure. Progress report, April 1, 1992--June 30, 1992

    SciTech Connect

    Zilm, K.W.

    1992-09-01

    This report covers the progress made on the title project for the project period. Four major areas of inquiry are being pursued. Advanced solid state NMR methods are being developed to assay the distribution of the various important functional groups that determine the reactivity of coals. Special attention is being paid to methods that are compatible with the very high magic angle sample spinning rates needed for operation at the high magnetic field strengths available today. Polarization inversion methods utilizing the difference in heat capacities of small groups of spins are particularly promising. Methods combining proton-proton spin diffusion with {sup 13}C CPMAS readout are being developed to determine the connectivity of functional groups in coals in a high sensitivity relay type of experiment. Additional work is aimed at delineating the role of methyl group rotation in the proton NMR relaxation behavior of coals.

  8. Motions and entropies in proteins as seen in NMR relaxation experiments and molecular dynamics simulations.

    PubMed

    Allnér, Olof; Foloppe, Nicolas; Nilsson, Lennart

    2015-01-22

    Molecular dynamics simulations of E. coli glutaredoxin1 in water have been performed to relate the dynamical parameters and entropy obtained in NMR relaxation experiments, with results extracted from simulated trajectory data. NMR relaxation is the most widely used experimental method to obtain data on dynamics of proteins, but it is limited to relatively short timescales and to motions of backbone amides or in some cases (13)C-H vectors. By relating the experimental data to the all-atom picture obtained in molecular dynamics simulations, valuable insights on the interpretation of the experiment can be gained. We have estimated the internal dynamics and their timescales by calculating the generalized order parameters (O) for different time windows. We then calculate the quasiharmonic entropy (S) and compare it to the entropy calculated from the NMR-derived generalized order parameter of the amide vectors. Special emphasis is put on characterizing dynamics that are not expressed through the motions of the amide group. The NMR and MD methods suffer from complementary limitations, with NMR being restricted to local vectors and dynamics on a timescale determined by the rotational diffusion of the solute, while in simulations, it may be difficult to obtain sufficient sampling to ensure convergence of the results. We also evaluate the amount of sampling obtained with molecular dynamics simulations and how it is affected by the length of individual simulations, by clustering of the sampled conformations. We find that two structural turns act as hinges, allowing the α helix between them to undergo large, long timescale motions that cannot be detected in the time window of the NMR dipolar relaxation experiments. We also show that the entropy obtained from the amide vector does not account for correlated motions of adjacent residues. Finally, we show that the sampling in a total of 100 ns molecular dynamics simulation can be increased by around 50%, by dividing the

  9. Heteronuclear Cross-Relaxation Effects in the NMR Spectroscopy of Hyperpolarized Targets

    PubMed Central

    Donovan, Kevin J.; Lupulescu, Adonis; Frydman, Lucio

    2016-01-01

    Dissolution DNP enables high-sensitivity solution phase NMR experiments on long-lived nuclear spin species such as 15N and 13C. This report explores certain features arising in solution-state 1H NMR, upon polarizing low-γ nuclear species. Following solid state hyperpolarization of both 13C and 1H, solution-phase 1H NMR experiments on dissolved samples revealed transient effects whereby peaks arising from protons bonded to the naturally-occurring 13C nuclei, appeared larger than the typically dominant 12C-bonded 1H resonances. This enhancement of the satellite-peaks was examined in detail, with respect to a variety of mechanisms that could potentially originate it. Both two- and three-spin phenomena active in the solid state could lead to this kind of effect; still, experimental observations revealed that the enhancement originates from 13C→1H polarization transfer processes active in the liquid state. Kinetic equations based on modified heteronuclear cross-relaxation models were examined, and found to describe well the distinct patterns of growth and decay shown by the 13C-bound 1H NMR satellite resonances. The dynamics of these novel cross-relaxation phenomena were determined, and their potential usefulness as tools for investigating hyperpolarized ensembles and for obtaining enhanced-sensitivity 1H NMR traces, is explored. PMID:24403222

  10. Surface NMR measurement of proton relaxation times in medium to coarse-grained sand aquifer.

    PubMed

    Shushakov, O A

    1996-01-01

    A surface NMR investigation of groundwater in the geomagnetic field is under study. To detect the surface NMR a wire loop with a diameter of about 100 m, being an antenna for both an exciting field source and the NMR signal receiver, is laid out on the ground. A sinusoidal current pulse with a rectangular envelope is passed through the loop to excite the NMR signal. The carrier frequency of the oscillating current in this pulse is equal to the Larmor frequency of protons in the Earth's magnetic field. The current amplitude is changed up to 200 amps and the pulse duration is fixed and is equal to 40 ms. The exciting pulse is followed by an induction emf signal caused by the Larmor nuclear precession in geomagnetic field. The relaxation times T1, T2, and T2* were measured by the surface NMR for both groundwater in medium to coarse-grained sand at borehole and for bulk water under the ice surface of frozen lake. To determine T1, a longitudinal interference in experiments with repeated pulses was measured. A sequence with equal period between equal excitation pulses was used. The relaxation times T1, T2, measured for bulk water under the ice of the Ob reservoir were 1.0 s and 0.7 s, respectively. To estimate an influence of dissolved oxygen T1 of the same water at the same temperature was measured by lab NMR with and without pumping of oxygen. The relaxation time T1 measured for water in the medium to coarse-grained sand is 0.65 s. The relaxation time T2 estimated by spin echo sequence is found to be equal to 0.15 s. The relaxation time T2* is found to be about 80 ms. This result contradicts published earlier phenomenological correlation between relaxation time T2* and grain size of water-bearing rock. This could be as a result of unsound approach based on grain size or influence of paramagnetic impurities.

  11. Nonexponential relaxation functions above Tg analysed by multidimensional NMR and novel spin-echo decay techniques

    NASA Astrophysics Data System (ADS)

    Leisen, J.; Schmidt-Rohr, K.; Spiess, H. W.

    1993-12-01

    New multidimensional NMR relaxation experiments are described. These experiments allow the measurement of slowly decaying relaxation functions for selected subensembles. They are applied for chain deuterated polystyrene at temperatures slightly above the caloric glass transition. The usual nonexponential loss of correlation is observed for the overall sample. However, a subensemble of slow components can be selected. An analysis of the relaxation functions in terms of the Kohlrausch-Williams-Watts function shows that the relaxation function of the selected components corresponds to a narrower distribution of correlation times than that of the entire sample. This gives clear evidence of a spatially heterogeneous distribution of correlation times and not an intrinsically nonexponential loss of correlation in a homogeneous system. For the hydrocarbon chain of polystyrene the observed nonexponential loss of correlation due to motions of the 100 Hz range (α-process) is linked to the nonexponential T1 relaxation observed close to Tg which is dominated by rapid motions with spectral density in the range of 100 MHz (β-process). Hence in spatial regions where the α-relaxation is slow, also slow T1 relaxation is observed.

  12. The generalized Phillips-Twomey method for NMR relaxation time inversion.

    PubMed

    Gao, Yang; Xiao, Lizhi; Zhang, Yi; Xie, Qingming

    2016-10-01

    The inversion of NMR relaxation time involves the Fredholm integral equation of the first kind. Due to its ill-posedness, numerical solutions to this type of equations are often found much less accurate and bear little resemblance to the true solution. There has been a strong interest in finding a well-posed method for this ill-posed problem since 1950s. In this paper, we prove the existence, the uniqueness, the stability and the convergence of the generalized Phillips-Twomey regularization method for solving this type of equations. Numerical simulations and core analyses arising from NMR transverse relaxation time inversion are conducted to show the effectiveness of the generalized Phillips-Twomey method. Both the simulation results and the core analyses agree well with the model and the realities.

  13. NMR relaxation investigation of the native corn starch structure with plasticizers

    NASA Astrophysics Data System (ADS)

    Cioica, N.; Fechete, R.; Cota, C.; Nagy, E. M.; David, L.; Cozar, O.

    2013-07-01

    The influences of starch, glycerol and water ratios on the structure, morphology and dynamics of starch polymer chains were investigated by NMR relaxation method. The 1H NMR CPMG echo decays and saturation recovery build-up curves were recorded and analyzed using the UPIN algorithm in order to get the spin-spin T2 and spin-lattice T1 relaxation times distributions. Significant differences between the CPMG curves were observed for native starch and the formulas in which water is added, whether these have or not glycerol in composition. For the formula which contains both plasticizers (water and glycerol), the CPMG curves decay slowly, indicating the presence of more mobile components.

  14. The generalized Phillips-Twomey method for NMR relaxation time inversion

    NASA Astrophysics Data System (ADS)

    Gao, Yang; Xiao, Lizhi; Zhang, Yi; Xie, Qingming

    2016-10-01

    The inversion of NMR relaxation time involves the Fredholm integral equation of the first kind. Due to its ill-posedness, numerical solutions to this type of equations are often found much less accurate and bear little resemblance to the true solution. There has been a strong interest in finding a well-posed method for this ill-posed problem since 1950s. In this paper, we prove the existence, the uniqueness, the stability and the convergence of the generalized Phillips-Twomey regularization method for solving this type of equations. Numerical simulations and core analyses arising from NMR transverse relaxation time inversion are conducted to show the effectiveness of the generalized Phillips-Twomey method. Both the simulation results and the core analyses agree well with the model and the realities.

  15. Measurement of Ligand–Target Residence Times by 1H Relaxation Dispersion NMR Spectroscopy

    PubMed Central

    2016-01-01

    A ligand-observed 1H NMR relaxation experiment is introduced for measuring the binding kinetics of low-molecular-weight compounds to their biomolecular targets. We show that this approach, which does not require any isotope labeling, is applicable to ligand–target systems involving proteins and nucleic acids of variable molecular size. The experiment is particularly useful for the systematic investigation of low affinity molecules with residence times in the micro- to millisecond time regime. PMID:27933946

  16. Measurement of Ligand-Target Residence Times by (1)H Relaxation Dispersion NMR Spectroscopy.

    PubMed

    Moschen, Thomas; Grutsch, Sarina; Juen, Michael A; Wunderlich, Christoph H; Kreutz, Christoph; Tollinger, Martin

    2016-12-08

    A ligand-observed (1)H NMR relaxation experiment is introduced for measuring the binding kinetics of low-molecular-weight compounds to their biomolecular targets. We show that this approach, which does not require any isotope labeling, is applicable to ligand-target systems involving proteins and nucleic acids of variable molecular size. The experiment is particularly useful for the systematic investigation of low affinity molecules with residence times in the micro- to millisecond time regime.

  17. NMR measurement of oil shale magnetic relaxation at high magnetic field

    USGS Publications Warehouse

    Seymour, Joseph D.; Washburn, Kathryn E.; Kirkland, Catherine M.; Vogt, Sarah J.; Birdwell, Justin E.; Codd, Sarah L.

    2013-01-01

    Nuclear magnetic resonance (NMR) at low field is used extensively to provide porosity and pore-size distributions in reservoir rocks. For unconventional resources, due to low porosity and permeability of the samples, much of the signal exists at very short T2 relaxation times. In addition, the organic content of many shales will also produce signal at short relaxation times. Despite recent improvements in low-field technology, limitations still exist that make it difficult to account for all hydrogen-rich constituents in very tight rocks, such as shales. The short pulses and dead times along with stronger gradients available when using high-field NMR equipment provides a more complete measurement of hydrogen-bearing phases due to the ability to probe shorter T2 relaxation times (-5 sec) than can be examined using low-field equipment. Access to these shorter T2 times allows for confirmation of partially resolved peaks observed in low-field NMR data that have been attributed to solid organic phases in oil shales. High-field (300 MHz or 7 T) NMR measurements of spin-spin T2 and spin-lattice T1 magnetic relaxation of raw and artificially matured oil shales have potential to provide data complementary to low field (2 MHz or 0.05T) measurements. Measurements of high-field T2 and T1-T2 correlations are presented. These data can be interpreted in terms of organic matter phases and mineral-bound water known to be present in the shale samples, as confirmed by Fourier transform infrared spectroscopy, and show distributions of hydrogen-bearing phases present in the shales that are similar to those observed in low field measurements.

  18. Carbon-13 chemical shift anisotropy in DNA bases from field dependence of solution NMR relaxation rates.

    PubMed

    Ying, Jinfa; Grishaev, Alexander; Bax, Ad

    2006-03-01

    Knowledge of (13)C chemical shift anisotropy (CSA) in nucleotide bases is important for the interpretation of solution-state NMR relaxation data in terms of local dynamic properties of DNA and RNA. Accurate knowledge of the CSA becomes particularly important at high magnetic fields, prerequisite for adequate spectral resolution in larger oligonucleotides. Measurement of (13)C relaxation rates of protonated carbons in the bases of the so-called Dickerson dodecamer, d(CGCGAATTCGCG)(2), at 500 and 800 MHz (1)H frequency, together with the previously characterized structure and diffusion tensor yields CSA values for C5 in C, C6 in C and T, C8 in A and G, and C2 in A that are closest to values previously reported on the basis of solid-state FIREMAT NMR measurements, and mostly larger than values obtained by in vacuo DFT calculations. Owing to the noncollinearity of dipolar and CSA interactions, interpretation of the NMR relaxation rates is particularly sensitive to anisotropy of rotational diffusion, and use of isotropic diffusion models can result in considerable errors.

  19. Collective water dynamics in the first solvation shell drive the NMR relaxation of aqueous quadrupolar cations

    NASA Astrophysics Data System (ADS)

    Carof, Antoine; Salanne, Mathieu; Charpentier, Thibault; Rotenberg, Benjamin

    2016-09-01

    Using molecular simulations, we analyze the microscopic processes driving the Nuclear Magnetic Resonance (NMR) relaxation of quadrupolar cations in water. The fluctuations of the Electric Field Gradient (EFG) experienced by alkaline and magnesium cations, which determine the NMR relaxation time, are mainly due to the dynamics of water molecules in their solvation shell. The dynamics of the ion plays a less important role, with the exception of the short-time dynamics in the lighter Li+ case, for which rattling in the solvent cage results in oscillations of the EFG autocorrelation function (ACF). Several microscopic mechanisms that may a priori contribute to the decay of the EFG-ACF occur in fact over too long time scales: entrance/exit of individual water molecules into/from the solvation shell, rotation of a molecule around the ion, or reorientation of the molecule. In contrast, the fluctuations of the ion-water distance are clearly correlated to that of the EFG. Nevertheless, it is not sufficient to consider a single molecule due to the cancellations arising from the symmetry of the solvation shell. The decay of the EFG-ACF, hence NMR relaxation, is in fact governed by the collective symmetry-breaking fluctuations of water in the first solvation shell.

  20. Intermolecular relaxation in glycerol as revealed by field cycling 1H NMR relaxometry dilution experiments.

    PubMed

    Meier, R; Kruk, D; Gmeiner, J; Rössler, E A

    2012-01-21

    (1)H spin-lattice relaxation rates R(1) = 1/T(1) have been measured for partly deuterated glycerol-h(5) diluted in fully deuterated glycerol-h(0) for progressively lower concentrations of glycerol-h(5). By means of the field cycling (FC) technique relaxation dispersion data, R(1)(ω), have been collected for several temperatures in the frequency range of 10 kHz-20 MHz. In order to disclose the spectral shape of the intra- and intermolecular relaxation, extrapolation of the relaxation data to the zero concentration limit has been performed. The paper confirms that the low frequency excess contribution to the total relaxation rate R(1)(ω) previously reported for several liquids is of intermolecular origin and reflects translational motion, whereas the high-frequency part is attributed to molecular rotation. Thus, intra- and intermolecular relaxation contributions are spectrally separated. The intermolecular relaxation itself contains also a contribution from rotational motion, which is due to non-central positions of the interacting nuclei in the molecule. This eccentricity effect is quantitatively reproduced by treating the intermolecular spectral density as a sum of translational-like (described by the free diffusion model) and rotational-like contributions (described by a Cole-Davidson function). Applying frequency-temperature superposition master curves as well as individual relaxation dispersion data, R(1)(ω), are analyzed. It is demonstrated that, in spite of the rotational influence, the translational diffusion coefficients, D(T), can be extracted from the (1)H relaxation dispersion which gives (1)H NMR relaxometry the potential to become a routine technique determining the diffusion coefficient in liquids. © 2012 American Institute of Physics

  1. Effects of fiber type and diet on nuclear magnetic resonance (NMR) relaxation times of skeletal muscle

    SciTech Connect

    Mardini, I.A.; McCarter, R.J.; Fullerton, G.D.

    1986-03-01

    NMR studies of muscle have typically used muscles of mixed fiber composition and have not taken into account the metabolic state of the host. Samples of psoas (type IIB fibers) and soleus (type I fibers) muscles were obtained from 3 groups of rabbits: group C, fed regular chow; group DK fed a potassium deficient diet; and group HC fed a high cholesterol diet. The T/sub 1/ and T/sub 2/ relaxation times of psoas and soleus muscles were not significantly different for group C. Following dietary manipulation, (groups KD and HC), however, the relaxation times of the psoas and soleus muscles were significantly different. There was also a significant difference in water content of psoas muscles in groups KD and HC vs. group C but the observed differences in NMR results could be only partially accounted for by the shift in water content. The authors results suggest that (1) changes in ion or cholesterol concentration are capable of inducing changes in water bonding and structuring in muscle tissues; (2) diet must be added to the growing list of environmental factors that can cause NMR contrast changes; (3) selective use of muscles rich in one fiber type or another for NMR measurements could provide either control or diagnostic information, related to changes in body composition.

  2. Ultrafast NMR T1 relaxation measurements: probing molecular properties in real time.

    PubMed

    Smith, Pieter E S; Donovan, Kevin J; Szekely, Or; Baias, Maria; Frydman, Lucio

    2013-09-16

    The longitudinal relaxation properties of NMR active nuclei carry useful information about the site-specific chemical environments and about the mobility of molecular fragments. Molecular mobility is in turn a key parameter reporting both on stable properties, such as size, as well as on dynamic ones, such as transient interactions and irreversible aggregation. In order to fully investigate the latter, a fast sampling of the relaxation parameters of transiently formed molecular species may be needed. Nevertheless, the acquisition of longitudinal relaxation data is typically slow, being limited by the requirement that the time for which the nucleus relaxes be varied incrementally until a complete build-up curve is generated. Recently, a number of single-shot-inversion-recovery methods have been developed capable of alleviating this need; still, these may be challenged by either spectral resolution restrictions or when coping with very fast relaxing nuclei. Here, we present a new experiment to measure the T1s of multiple nuclear spins that experience fast longitudinal relaxation, while retaining full high-resolution chemical shift information. Good agreement is observed between T1s measured with conventional means and T1s measured using the new technique. The method is applied to the real-time investigation of the reaction between D-xylose and sodium borate, which is in turn elucidated with the aid of ancillary ultrafast and conventional 2D TOCSY measurements. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Effect of fluctuations on the NMR relaxation beyond the Abrikosov vortex state

    DOE PAGES

    Glatz, A.; Galda, A.; Varlamov, A. A.

    2015-08-25

    Here, the effect of fluctuations on the nuclear magnetic resonance (NMR) relaxation rate W = T–11 is studied in a complete phase diagram of a two-dimensional superconductor above the upper critical field line Hc2(T). In the region of relatively high temperatures and low magnetic fields, the relaxation rate W is determined by two competing effects. The first one is its decrease in the result of suppression of the quasiparticle density of states (DOS) due to formation of fluctuation Cooper pairs (FCPs). The second one is a specific, purely quantum relaxation process of the Maki-Thompson (MT) type, which for low fieldmore » leads to an increase of the relaxation rate. The latter describes particular fluctuation processes involving self-pairing of a single electron on self-intersecting trajectories of a size up to phase-breaking length ℓΦ which becomes possible due to an electron spin-flip scattering event at a nucleus. As a result, different scenarios with either growth or decrease of the NMR relaxation rate are possible upon approaching the normal-metal–type-II superconductor transition. The character of fluctuations changes along the line Hc2(T) from the thermal long-wavelength type in weak magnetic fields to the clusters of rotating FCPs in fields comparable to Hc2(0). We find that below the well-defined temperature T*0 ≈ 0.6Tc0, the MT process becomes ineffective even in the absence of intrinsic pair breaking. The small scale of the FCP rotations ξxy in such high fields impedes formation of long (≲ℓΦ) self-intersecting trajectories, causing the corresponding relaxation mechanism to lose its efficiency. This reduces the effect of superconducting fluctuations in the domain of high fields and low temperatures to just the suppression of quasiparticle DOS, analogous to the Abrikosov vortex phase below the Hc2(T) line.« less

  4. Sensitivity of proton NMR relaxation times in a HTPB based polyurethane elastomer to thermo-oxidative aging.

    SciTech Connect

    Assink, Roger Alan; Mowery, Daniel Michael; Celina, Mathias Christopher

    2004-09-01

    Solid-state {sup 1}H NMR relaxometry studies were conducted on a hydroxy-terminated polybutadiene (HTPB) based polyurethane elastomer thermo-oxidatively aged at 80 C. The {sup 1}H T{sub 1}, T{sub 2}, and T{sub 1{rho}} relaxation times of samples thermally aged for various periods of time were determined as a function of NMR measurement temperature. The response of each measurement was calculated from a best-fit linear function of the relaxation time vs. aging time. It was found that the T{sub 2,H} and T{sub 1{rho},H} relaxation times exhibited the largest response to thermal degradation, whereas T{sub 1,H} showed minimal change. All of the NMR relaxation measurements on solid samples showed significantly less sensitivity to thermal aging than the T{sub 2,H} relaxation times of solvent-swollen samples.

  5. Theory of nonrigid rotational motion applied to NMR relaxation in RNA.

    PubMed

    Emani, Prashant S; Olsen, Gregory L; Varani, Gabriele; Drobny, Gary P

    2011-11-10

    Solution NMR spectroscopy can elucidate many features of the structure and dynamics of macromolecules, yet relaxation measurements, the most common source of experimental information on dynamics, can sample only certain ranges of dynamic rates. A complete characterization of motion of a macromolecule thus requires the introduction of complementary experimental approaches. Solid-state NMR spectroscopy successfully probes the time scale of nanoseconds to microseconds, a dynamic window where solution NMR results have been deficient, and probes conditions where the averaging effects of rotational diffusion of the molecule are absent. Combining the results of the two distinct techniques within a single framework provides greater insight into dynamics, but this task requires the common interpretation of results recorded under very different experimental conditions. Herein, we provide a unified description of dynamics that is robust to the presence of large-scale conformational exchange, where the diffusion tensor of the molecule varies on a time scale comparable to rotational diffusion in solution. We apply this methodology to the HIV-1 TAR RNA molecule, where conformational rearrangements are both substantial and functionally important. The formalism described herein is of greater generality than earlier combined solid-state/solution NMR interpretations, if detailed molecular structures are available, and can offer a more complete description of RNA dynamics than either solution or solid-state NMR spectroscopy alone.

  6. Temperature dependence of proton NMR relaxation times at earth's magnetic field

    NASA Astrophysics Data System (ADS)

    Niedbalski, Peter; Kiswandhi, Andhika; Parish, Christopher; Ferguson, Sarah; Cervantes, Eduardo; Oomen, Anisha; Krishnan, Anagha; Goyal, Aayush; Lumata, Lloyd

    The theoretical description of relaxation processes for protons, well established and experimentally verified at conventional nuclear magnetic resonance (NMR) fields, has remained untested at low fields despite significant advances in low field NMR technology. In this study, proton spin-lattice relaxation (T1) times in pure water and water doped with varying concentrations of the paramagnetic agent copper chloride have been measured from 6 to 92oC at earth's magnetic field (1700 Hz). Results show a linear increase of T1 with temperature for each of the samples studied. Increasing the concentration of the copper chloride greatly reduced T1 and reduced dependence on temperature. The consistency of the results with theory is an important confirmation of past results, while the ability of an ultra-low field NMR system to do contrast-enhanced magnetic resonance imaging (MRI) is promising for future applicability to low-cost medical imaging and chemical identification. This work is supported by US Dept of Defense Award No. W81XWH-14-1-0048 and the Robert A. Welch Foundation Grant No. AT-1877.

  7. Ligand-detected relaxation dispersion NMR spectroscopy: dynamics of preQ1-RNA binding.

    PubMed

    Moschen, Thomas; Wunderlich, Christoph Hermann; Spitzer, Romana; Levic, Jasmin; Micura, Ronald; Tollinger, Martin; Kreutz, Christoph

    2015-01-07

    An NMR-based approach to characterizing the binding kinetics of ligand molecules to biomolecules, like RNA or proteins, by ligand-detected Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments is described. A (15)N-modified preQ1 ligand is used to acquire relaxation dispersion experiments in the presence of low amounts of the Fsu class I preQ1 aptamer RNA, and increasing ligand concentrations to probe the RNA small molecule interaction. Our experimental data strongly support the conformational selection mechanism postulated. The approach gives direct access to two parameters of a ligand-receptor interaction: the off rate and the population of the small molecule-receptor complex. A detailed description of the kinetics underlying the ligand binding process is of crucial importance to fully understanding a riboswitch's function and to evaluate potential new antibiotics candidates targeting the noncoding RNA species. Ligand-detected NMR relaxation dispersion experiments represent a valuable diagnostic tool for the characterization of binding mechanisms. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Interaction of ferulic acid derivatives with human erythrocytes monitored by pulse field gradient NMR diffusion and NMR relaxation studies.

    PubMed

    Anselmi, Cecilia; Bernardi, Francesca; Centini, Marisanna; Gaggelli, Elena; Gaggelli, Nicola; Valensin, Daniela; Valensin, Gianni

    2005-04-01

    Ferulic acid (Fer), a natural anti-oxidant and chemo-protector, is able to suppress experimental carcinogenesis in the forestomach, lungs, skin, tongue and colon. Several Fer derivatives have been suggested as promising candidates for cancer prevention, being the biological activity related also to the capacity of partitioning between aqueous and lipid phases. In the present work, pulsed field gradient (PFG) NMR diffusion measurement and NMR relaxation rates have been adopted for investigating the interaction of three Fer derivatives (Fer-C11, Fer-C12 and Fer-C13) with human erythrocytes. Binding to the erythrocyte membrane has been shown for all derivatives, which displayed a similar interaction mode such that the aromatic moiety and the terminal part of the alkyl chain were the most affected. Quantitative analysis of the diffusion coefficients was used to show that Fer-C12 and Fer-C13 display higher affinity for the cell membrane when compared with Fer-C11. These findings agree with the higher anti-oxidant activity of the two derivatives.

  9. Effects of vorticity and impurity on NMR relaxation rate in chiral p-wave superconductors

    NASA Astrophysics Data System (ADS)

    Tanaka, Kenta K.; Ichioka, Masanori; Onari, Seiichiro

    2016-11-01

    In order to study site-selective NMR in chiral p-wave superconductors, we calculate local nuclear relaxation rate T1-1 in the vortex lattice state by Eilenberger theory with and without non-magnetic impurity scattering in the Born limit and unitary limit. The local T1-1 in the NMR resonance line shape is different between two chiral states p±, depending on whether the chirality is parallel or anti-parallel to the vorticity. In the p--wave, anomalous suppression of local T1-1 occurs around the vortex core due to the negative coherence term coming from odd-frequency s-wave Cooper pair induced around the vortex. We especially examine the site dependence of the anomalous suppression of local T1-1, including the applied magnetic field dependence and the impurity effects.

  10. Microscopic insights into the NMR relaxation based protein conformational entropy meter

    PubMed Central

    Kasinath, Vignesh; Sharp, Kim A.; Wand, A. Joshua

    2013-01-01

    Conformational entropy is a potentially important thermodynamic parameter contributing to protein function. Quantitative measures of conformational entropy are necessary for an understanding of its role but have been difficult to obtain. An empirical method that utilizes changes in conformational dynamics as a proxy for changes in conformational entropy has recently been introduced. Here we probe the microscopic origins of the link between conformational dynamics and conformational entropy using molecular dynamics simulations. Simulation of seven pro! teins gave an excellent correlation with measures of side-chain motion derived from NMR relaxation. The simulations show that the motion of methyl-bearing side-chains are sufficiently coupled to that of other side chains to serve as excellent reporters of the overall side-chain conformational entropy. These results tend to validate the use of experimentally accessible measures of methyl motion - the NMR-derived generalized order parameters - as a proxy from which to derive changes in protein conformational entropy. PMID:24007504

  11. Microscopic insights into the NMR relaxation-based protein conformational entropy meter.

    PubMed

    Kasinath, Vignesh; Sharp, Kim A; Wand, A Joshua

    2013-10-09

    Conformational entropy is a potentially important thermodynamic parameter contributing to protein function. Quantitative measures of conformational entropy are necessary for an understanding of its role but have been difficult to obtain. An empirical method that utilizes changes in conformational dynamics as a proxy for changes in conformational entropy has recently been introduced. Here we probe the microscopic origins of the link between conformational dynamics and conformational entropy using molecular dynamics simulations. Simulation of seven proteins gave an excellent correlation with measures of side-chain motion derived from NMR relaxation. The simulations show that the motion of methyl-bearing side chains are sufficiently coupled to that of other side chains to serve as excellent reporters of the overall side-chain conformational entropy. These results tend to validate the use of experimentally accessible measures of methyl motion--the NMR-derived generalized order parameters--as a proxy from which to derive changes in protein conformational entropy.

  12. Requirements on paramagnetic relaxation enhancement data for membrane protein structure determination by NMR.

    PubMed

    Gottstein, Daniel; Reckel, Sina; Dötsch, Volker; Güntert, Peter

    2012-06-06

    Nuclear magnetic resonance (NMR) structure calculations of the α-helical integral membrane proteins DsbB, GlpG, and halorhodopsin show that distance restraints from paramagnetic relaxation enhancement (PRE) can provide sufficient structural information to determine their structure with an accuracy of about 1.5 Å in the absence of other long-range conformational restraints. Our systematic study with simulated NMR data shows that about one spin label per transmembrane helix is necessary for obtaining enough PRE distance restraints to exclude wrong topologies, such as pseudo mirror images, if only limited other NMR restraints are available. Consequently, an experimentally realistic amount of PRE data enables α-helical membrane protein structure determinations that would not be feasible with the very limited amount of conventional NOESY data normally available for these systems. These findings are in line with our recent first de novo NMR structure determination of a heptahelical integral membrane protein, proteorhodopsin, that relied extensively on PRE data.

  13. Structural fidelity and NMR relaxation analysis in a prototype RNA hairpin

    PubMed Central

    Giambaşu, George M.; York, Darrin M.; Case, David A.

    2015-01-01

    RNA hairpins are widespread and very stable motifs that contribute decisively to RNA folding and biological function. The GTP1G2C3A4C5U6U7C8G9G10U11G12C13C14 construct (with a central UUCG tetraloop) has been extensively studied by solution NMR, and offers and excellent opportunity to evaluate the structure and dynamical description afforded by molecular dynamics (MD) simulations. Here, we compare average structural parameters and NMR relaxation rates estimated from a series of multiple independent explicit solvent MD simulations using the two most recent RNA AMBER force fields (ff99 and ff10). Predicted overall tumbling times are ∼20% faster than those inferred from analysis of NMR data and follow the same trend when temperature and ionic strength is varied. The Watson–Crick stem and the “canonical” UUCG loop structure are maintained in most simulations including the characteristic syn conformation along the glycosidic bond of G9, although some key hydrogen bonds in the loop are partially disrupted. Our analysis pinpoints G9–G10 backbone conformations as a locus of discrepancies between experiment and simulation. In general the results for the more recent force-field parameters (ff10) are closer to experiment than those for the older ones (ff99). This work provides a comprehensive and detailed comparison of state of the art MD simulations against a wide variety of solution NMR measurements. PMID:25805858

  14. Plastic ice in confined geometry: the evidence from neutron diffraction and NMR relaxation

    NASA Astrophysics Data System (ADS)

    Webber, J. Beau W.; Dore, John C.; Strange, John H.; Anderson, Ross; Tohidi, Bahman

    2007-10-01

    Neutron diffraction and nuclear magnetic resonance (NMR) relaxation studies have been made of water/ice in mesoporous SBA-15 silica with ordered structures of cylindrical mesopores with a pore diameter ~8.6 nm, over the temperature range 180-300 K. Both measurements show similar depressed freezing and melting points due to the Gibb-Thomson effect. The neutron diffraction measurements for fully filled pores show, in addition to cubic and hexagonal crystalline ice, the presence of a disordered water/ice component extending a further 50-80 K, down to around or below 200 K. NMR relaxation measurements over the same temperature range show a free induction decay that is partly Gaussian and characteristic of brittle ice but that also exhibits a longer exponential relaxation component. An argument has been made (Liu et al 2006 J. Phys:. Condens. Matter 18 10009-28 Webber et al 2007 Magn. Reson. Imag. 25 533-6) to suggest that this is an observation of ice in a plastic or rotationally mobile state, and that there is a fully reversible inter-conversion between brittle and plastic states of ice as the temperature is lowered or raised. More recent detailed NMR measurements are also discussed that allow the extraction of activation enthalpies and an estimate to be made of the equilibrium thickness, as a function of temperature, if the the assumption is made that the plastic component is in the form of a layer at the silica interface. The two different techniques suggest a maximum layer thickness of about 1.0-1.5 nm.

  15. Plastic ice in confined geometry: the evidence from neutron diffraction and NMR relaxation.

    PubMed

    Webber, J Beau W; Dore, John C; Strange, John H; Anderson, Ross; Tohidi, Bahman

    2007-10-17

    Neutron diffraction and nuclear magnetic resonance (NMR) relaxation studies have been made of water/ice in mesoporous SBA-15 silica with ordered structures of cylindrical mesopores with a pore diameter ∼8.6 nm, over the temperature range 180-300 K. Both measurements show similar depressed freezing and melting points due to the Gibb-Thomson effect. The neutron diffraction measurements for fully filled pores show, in addition to cubic and hexagonal crystalline ice, the presence of a disordered water/ice component extending a further 50-80 K, down to around or below 200 K. NMR relaxation measurements over the same temperature range show a free induction decay that is partly Gaussian and characteristic of brittle ice but that also exhibits a longer exponential relaxation component. An argument has been made (Liu et al 2006 J. Phys:. Condens. Matter 18 10009-28; Webber et al 2007 Magn. Reson. Imag. 25 533-6) to suggest that this is an observation of ice in a plastic or rotationally mobile state, and that there is a fully reversible inter-conversion between brittle and plastic states of ice as the temperature is lowered or raised. More recent detailed NMR measurements are also discussed that allow the extraction of activation enthalpies and an estimate to be made of the equilibrium thickness, as a function of temperature, if the the assumption is made that the plastic component is in the form of a layer at the silica interface. The two different techniques suggest a maximum layer thickness of about 1.0-1.5 nm.

  16. On the reliability of NMR relaxation data analyses: a Markov Chain Monte Carlo approach.

    PubMed

    Abergel, Daniel; Volpato, Andrea; Coutant, Eloi P; Polimeno, Antonino

    2014-09-01

    The analysis of NMR relaxation data is revisited along the lines of a Bayesian approach. Using a Markov Chain Monte Carlo strategy of data fitting, we investigate conditions under which relaxation data can be effectively interpreted in terms of internal dynamics. The limitations to the extraction of kinetic parameters that characterize internal dynamics are analyzed, and we show that extracting characteristic time scales shorter than a few tens of ps is very unlikely. However, using MCMC methods, reliable estimates of the marginal probability distributions and estimators (average, standard deviations, etc.) can still be obtained for subsets of the model parameters. Thus, unlike more conventional strategies of data analysis, the method avoids a model selection process. In addition, it indicates what information may be extracted from the data, but also what cannot.

  17. A subzero 1H NMR relaxation investigation of water dynamics in tomato pericarp.

    PubMed

    Foucat, Loïc; Lahaye, Marc

    2014-09-01

    (1)H NMR relaxation times (T1 and T2) were measured at low field (0.47 T) in pericarp tissues of three tomato genotypes (Ferum, LA0147 and Levovil) at subzero temperature (-20 °C) and two ripening stages (mature green and red). The unfrozen water dynamics was characterised by two T1 and three T2 components. The relaxation time values and their associated relative populations allowed differentiating the ripening stage of only LA0147 and Levovil lines. But the three genotypes were unequivocally discriminated at the red ripe stage. The unfrozen water distribution was discussed in terms of specific interactions, especially with sugars, in relation with their osmoprotectant effects.

  18. Probing the Carbonyl Functionality of a Petroleum Resin and Asphaltene through Oximation and Schiff Base Formation in Conjunction with N-15 NMR.

    PubMed

    Thorn, Kevin A; Cox, Larry G

    2015-01-01

    Despite recent advances in spectroscopic techniques, there is uncertainty regarding the nature of the carbonyl groups in the asphaltene and resin fractions of crude oil, information necessary for an understanding of the physical properties and environmental fate of these materials. Carbonyl and hydroxyl group functionalities are not observed in natural abundance 13C nuclear magnetic resonance (NMR) spectra of asphaltenes and resins and therefore require spin labeling techniques for detection. In this study, the carbonyl functionalities of the resin and asphaltene fractions from a light aliphatic crude oil that is the source of groundwater contamination at the long term USGS study site near Bemidji, Minnesota, have been examined through reaction with 15N-labeled hydroxylamine and aniline in conjunction with analysis by solid and liquid state 15N NMR. Ketone groups were revealed through 15N NMR detection of their oxime and Schiff base derivatives, and esters through their hydroxamic acid derivatives. Anilinohydroquinone adducts provided evidence for quinones. Some possible configurations of the ketone groups in the resin and asphaltene fractions can be inferred from a consideration of the likely reactions that lead to heterocyclic condensation products with aniline and to the Beckmann reaction products from the initially formed oximes. These include aromatic ketones and ketones adjacent to quaternary carbon centers, β-hydroxyketones, β-diketones, and β-ketoesters. In a solid state cross polarization/magic angle spinning (CP/MAS) 15N NMR spectrum recorded on the underivatized asphaltene as a control, carbazole and pyrrole-like nitrogens were the major naturally abundant nitrogens detected.

  19. Probing the Carbonyl Functionality of a Petroleum Resin and Asphaltene through Oximation and Schiff Base Formation in Conjunction with N-15 NMR

    PubMed Central

    Thorn, Kevin A.; Cox, Larry G.

    2015-01-01

    Despite recent advances in spectroscopic techniques, there is uncertainty regarding the nature of the carbonyl groups in the asphaltene and resin fractions of crude oil, information necessary for an understanding of the physical properties and environmental fate of these materials. Carbonyl and hydroxyl group functionalities are not observed in natural abundance 13C nuclear magnetic resonance (NMR) spectra of asphaltenes and resins and therefore require spin labeling techniques for detection. In this study, the carbonyl functionalities of the resin and asphaltene fractions from a light aliphatic crude oil that is the source of groundwater contamination at the long term USGS study site near Bemidji, Minnesota, have been examined through reaction with 15N-labeled hydroxylamine and aniline in conjunction with analysis by solid and liquid state 15N NMR. Ketone groups were revealed through 15N NMR detection of their oxime and Schiff base derivatives, and esters through their hydroxamic acid derivatives. Anilinohydroquinone adducts provided evidence for quinones. Some possible configurations of the ketone groups in the resin and asphaltene fractions can be inferred from a consideration of the likely reactions that lead to heterocyclic condensation products with aniline and to the Beckmann reaction products from the initially formed oximes. These include aromatic ketones and ketones adjacent to quaternary carbon centers, β-hydroxyketones, β-diketones, and β-ketoesters. In a solid state cross polarization/magic angle spinning (CP/MAS) 15N NMR spectrum recorded on the underivatized asphaltene as a control, carbazole and pyrrole-like nitrogens were the major naturally abundant nitrogens detected. PMID:26556054

  20. Probing the carbonyl functionality of a petroleum resin and asphaltene through oximation and schiff base formation in conjunction with N-15 NMR

    USGS Publications Warehouse

    Thorn, Kevin A.; Cox, Larry G.

    2015-01-01

    Despite recent advances in spectroscopic techniques, there is uncertainty regarding the nature of the carbonyl groups in the asphaltene and resin fractions of crude oil, information necessary for an understanding of the physical properties and environmental fate of these materials. Carbonyl and hydroxyl group functionalities are not observed in natural abundance 13C nuclear magnetic resonance (NMR) spectra of asphaltenes and resins and therefore require spin labeling techniques for detection. In this study, the carbonyl functionalities of the resin and asphaltene fractions from a light aliphatic crude oil that is the source of groundwater contamination at the long term USGS study site near Bemidji, Minnesota, have been examined through reaction with 15N-labeled hydroxylamine and aniline in conjunction with analysis by solid and liquid state 15N NMR. Ketone groups were revealed through 15N NMR detection of their oxime and Schiff base derivatives, and esters through their hydroxamic acid derivatives. Anilinohydroquinone adducts provided evidence for quinones. Some possible configurations of the ketone groups in the resin and asphaltene fractions can be inferred from a consideration of the likely reactions that lead to heterocyclic condensation products with aniline and to the Beckmann reaction products from the initially formed oximes. These include aromatic ketones and ketones adjacent to quaternary carbon centers, β-hydroxyketones, β-diketones, and β-ketoesters. In a solid state cross polarization/magic angle spinning (CP/MAS) 15N NMR spectrum recorded on the underivatized asphaltene as a control, carbazole and pyrrole-like nitrogens were the major naturally abundant nitrogens detected.

  1. High resolution NMR study of T{sub 1} magnetic relaxation dispersion. IV. Proton relaxation in amino acids and Met-enkephalin pentapeptide

    SciTech Connect

    Pravdivtsev, Andrey N.; Yurkovskaya, Alexandra V.; Ivanov, Konstantin L.; Vieth, Hans-Martin

    2014-10-21

    Nuclear Magnetic Relaxation Dispersion (NMRD) of protons was studied in the pentapeptide Met-enkephalin and the amino acids, which constitute it. Experiments were run by using high-resolution Nuclear Magnetic Resonance (NMR) in combination with fast field-cycling, thus enabling measuring NMRD curves for all individual protons. As in earlier works, Papers I–III, pronounced effects of intramolecular scalar spin-spin interactions, J-couplings, on spin relaxation were found. Notably, at low fields J-couplings tend to equalize the apparent relaxation rates within networks of coupled protons. In Met-enkephalin, in contrast to the free amino acids, there is a sharp increase in the proton T{sub 1}-relaxation times at high fields due to the changes in the regime of molecular motion. The experimental data are in good agreement with theory. From modelling the relaxation experiments we were able to determine motional correlation times of different residues in Met-enkephalin with atomic resolution. This allows us to draw conclusions about preferential conformation of the pentapeptide in solution, which is also in agreement with data from two-dimensional NMR experiments (rotating frame Overhauser effect spectroscopy). Altogether, our study demonstrates that high-resolution NMR studies of magnetic field-dependent relaxation allow one to probe molecular mobility in biomolecules with atomic resolution.

  2. The effects of bone on proton NMR relaxation times of surrounding liquids

    NASA Technical Reports Server (NTRS)

    Davis, C. A.; Genant, H. K.; Dunham, J. S.

    1986-01-01

    Preliminary attempts by our group at UCSF to assess fat content of vertebral marrow in the lumbar spine using relaxation time information demonstrated that the presence of trabecular bone affects relaxation times. The objective of this work was a thorough study of the effects of bone on NMR relaxation characteristics of surrounding liquids. Trabecular bone from autopsy specimens was ground up and sifted into a series of powders with graded densities ranging from 0.3 gm/cc to 0.8 gm/cc. Each powder was placed first in n-saline and then in cottonseed oil. With spectroscopy, spin-lattice relaxation times (T1) and effective spin-spin relaxation times (T2*) were measured for each liquid in each bone powder. As bone density and surface to volume ratio increased, T1 decreased faster for saline than for oil. T2* decreased significantly for both water and oil as the surface to volume ratio increased. It was concluded that effects of water on T1 could be explained by a surface interaction at the bone/liquid interface, which restricted rotational and translational motion of nearby molecules. The T1s of oil were not affected since oil molecules are nonpolar, do not participate in significant intermolecular hydrogen bonding, and therefore would not be expected to interact strongly with the bone surface. Effects on T2* could be explained by local magnetic field inhomogeneities created by discontinuous magnetic susceptibility near the bone surface. These preliminary results suggest that water in contact with trabecular bone in vivo will exhibit shortened relaxation times.

  3. NMR relaxation in the topological Kondo insulator SmB6

    NASA Astrophysics Data System (ADS)

    Schlottmann, P.

    2014-10-01

    SmB6 has been predicted to be a strong topological Kondo insulator, and experimentally it has been confirmed that at low temperatures the electrical conductivity only takes place at the surfaces of the crystal. We study the temperature and magnetic field dependence of the NMR Knight shift and relaxation rate arising from the topological conduction states. For the clean surface the Landau quantization of the surface states gives rise to highly degenerate discrete levels for which the Knight shift is proportional to the magnetic field B and inversely proportional to the temperature T. The relaxation rate 1/T1 is not Korringa-like. For the more realistic case of a surface with a low concentration of defects (dirty limit) the scattering of the electrons leads to a broadening of the Landau levels and hence to a finite density of states. The mildly dirty surface case leads to a T-independent Knight shift proportional to B and a Korringa-like 1/T1 at low T. The wave functions of the surface states are expected to fall off exponentially with distance from the surface giving rise to a superposition of relaxation times, i.e., a stretched exponential. It is questionable that the experimental 11B Knight shift and relaxation rate arise from the surface states of the TKI. An alternative explanation is that the bulk susceptibility and the 11B NMR properties are the consequence of the in-gap bulk states originating from magnetic exciton bound states proposed by Riseborough [Phys. Rev. B 68, 235213 (2003), 10.1103/PhysRevB.68.235213].

  4. NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning.

    PubMed

    Shmyreva, Anna A; Safdari, Majid; Furó, István; Dvinskikh, Sergey V

    2016-06-14

    Orders of magnitude decrease of (207)Pb and (199)Hg NMR longitudinal relaxation times T1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead(ii) halides, the most dramatic decrease of T1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200-15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

  5. NMR longitudinal relaxation enhancement in metal halides by heteronuclear polarization exchange during magic-angle spinning

    NASA Astrophysics Data System (ADS)

    Shmyreva, Anna A.; Safdari, Majid; Furó, István; Dvinskikh, Sergey V.

    2016-06-01

    Orders of magnitude decrease of 207Pb and 199Hg NMR longitudinal relaxation times T1 upon magic-angle-spinning (MAS) are observed and systematically investigated in solid lead and mercury halides MeX2 (Me = Pb, Hg and X = Cl, Br, I). In lead(ii) halides, the most dramatic decrease of T1 relative to that in a static sample is in PbI2, while it is smaller but still significant in PbBr2, and not detectable in PbCl2. The effect is magnetic-field dependent but independent of the spinning speed in the range 200-15 000 Hz. The observed relaxation enhancement is explained by laboratory-frame heteronuclear polarization exchange due to crossing between energy levels of spin-1/2 metal nuclei and adjacent quadrupolar-spin halogen nuclei. The enhancement effect is also present in lead-containing organometal halide perovskites. Our results demonstrate that in affected samples, it is the relaxation data recorded under non-spinning conditions that characterize the local properties at the metal sites. A practical advantage of fast relaxation at slow MAS is that spectral shapes with orientational chemical shift anisotropy information well retained can be acquired within a shorter experimental time.

  6. Limits of metastability in amorphous ices: 2H-NMR relaxation.

    PubMed

    Löw, Florian; Amann-Winkel, Katrin; Geil, Burkhard; Loerting, Thomas; Wittich, Carolin; Fujara, Franz

    2013-01-14

    The high-frequency reorientation dynamics of O-(2)H bonds is investigated in various amorphous ices including eHDA (expanded high density amorphous ice), LDA-II (low density amorphous ice II) and HGW (hyperquenched glassy water) using (2)H-NMR spin-lattice relaxation as a local probe. Both low density forms, HGW and LDA-II, show similar spin-lattice relaxation but differ in the thermal stability with respect to the transition into crystalline cubic ice I(c). HGW already transforms slightly above 135 K whereas LDA-II crystallizes at 150 K. eHDA is distinguishable from other high density amorphous ices in its thermal stability and spin-lattice relaxation. Its relaxation times are much larger compared to those of VHDA (very high density amorphous ice) and uHDA (unrelaxed high density amorphous ice). eHDA does not show annealing effects, transforms sharply into LDA-II above 123 K and provides higher thermal stability as compared to other high density forms.

  7. N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society

    SciTech Connect

    Thorn, Kevin A.; Cox, Larry G.

    2009-02-28

    The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS ¹⁵N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by ¹⁵N NMR. Liquid state ¹⁵N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (¹H–¹⁵N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.

  8. N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society

    USGS Publications Warehouse

    Thorn, K.A.; Cox, L.G.

    2009-01-01

    The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS 15N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by 15N NMR. Liquid state 15N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (1H-15N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.

  9. Effect of fluctuations on the NMR relaxation beyond the Abrikosov vortex state

    SciTech Connect

    Glatz, A.; Galda, A.; Varlamov, A. A.

    2015-08-25

    Here, the effect of fluctuations on the nuclear magnetic resonance (NMR) relaxation rate W = T–11 is studied in a complete phase diagram of a two-dimensional superconductor above the upper critical field line Hc2(T). In the region of relatively high temperatures and low magnetic fields, the relaxation rate W is determined by two competing effects. The first one is its decrease in the result of suppression of the quasiparticle density of states (DOS) due to formation of fluctuation Cooper pairs (FCPs). The second one is a specific, purely quantum relaxation process of the Maki-Thompson (MT) type, which for low field leads to an increase of the relaxation rate. The latter describes particular fluctuation processes involving self-pairing of a single electron on self-intersecting trajectories of a size up to phase-breaking length ℓΦ which becomes possible due to an electron spin-flip scattering event at a nucleus. As a result, different scenarios with either growth or decrease of the NMR relaxation rate are possible upon approaching the normal-metal–type-II superconductor transition. The character of fluctuations changes along the line Hc2(T) from the thermal long-wavelength type in weak magnetic fields to the clusters of rotating FCPs in fields comparable to Hc2(0). We find that below the well-defined temperature T*0 ≈ 0.6Tc0, the MT process becomes ineffective even in the absence of intrinsic pair breaking. The small scale of the FCP rotations ξxy in such high fields impedes formation of long (≲ℓΦ) self-intersecting trajectories, causing the corresponding relaxation mechanism to lose its efficiency. This reduces the effect of superconducting fluctuations in the domain of high fields and low temperatures to just the suppression of quasiparticle DOS, analogous to the Abrikosov vortex phase below the Hc2(T) line.

  10. NMR Relaxation Spectra in Ultrasound-Devulcanized Poly(dimethyl siloxane) Rubber.

    NASA Astrophysics Data System (ADS)

    Parr, J. C.; von Meerwall, E. D.; Shim, S. E.; Isayev, A.

    2001-04-01

    We had previously reported proton NMR transverse relaxation and pulsed-gradient spin-echo self-diffusion measurements at 70 deg. C in PDMS rubber before and after crosslinking, and after subsequent devulcanization by intense ultrasound. Relaxation spectra extracted from the transverse magnetization decays display three distinct components, which are further refined by a direct fit. The components are attributed to entangled and crosslinked network; light sol and dangling network fragments, and oligomers including 4 percent of an unreactive species. Ultrasound produces extractable sol strongly dependent on feed rate and transducer amplitude. Our results vary monotonically with the amount of sol: all three mobilities (T2) and the amounts of the two most mobile fractions increase with sol content, but the diffusion rates decrease, likely due to the production of higher-M sol. Similar reanalysis of data from our earlier NMR studies of ultrasound devulcanization of styrene-butadiene and natural rubber shows strong similarities. The main difference is the greater extent in PDMS of loosely attached network fragments.

  11. Relaxation NMR as a tool to study the dispersion and formulation behavior of nanostructured carbon materials.

    PubMed

    Fairhurst, David; Cosgrove, Terence; Prescott, Stuart W

    2016-06-01

    Solvent relaxation NMR has been used to estimate the surface areas and wettability of various types of nanostructured carbon materials in a range of solvents including water, ethanol, and tetrahydrofuran. We illustrate the application of the technique through several short case studies using samples including nanocarbon blacks, graphene oxide, nanographites, and porous graphenes. The technique is shown to give a good measure of surface area, correlating well with conventional surface area estimates obtained by nitrogen adsorption, transmission electron microscopy, or light scattering for the non-porous samples. NMR relaxation has advantages in terms of speed of analysis and being able to use concentrated, wet, and opaque samples. For samples that are porous, two distinct surface areas can be estimated assuming the two environments ('inner' and 'outer') have the same surface chemistry, and that there is a slow exchange of solvent molecules between them. Furthermore, we show that differences in wettability and dispersability between samples dispersed in water, ethanol, and cyclopentanone can be observed, along with changes to the surface chemistry of the interface. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

  12. Active site dynamics in NADH oxidase from Thermus thermophilus studied by NMR spin relaxation.

    PubMed

    Miletti, Teresa; Farber, Patrick J; Mittermaier, Anthony

    2011-09-01

    We have characterized the backbone dynamics of NADH oxidase from Thermus thermophilus (NOX) using a recently-developed suite of NMR experiments designed to isolate exchange broadening, together with (15)N R (1), R (1ρ ), and {(1)H}-(15)N steady-state NOE relaxation measurements performed at 11.7 and 18.8 T. NOX is a 54 kDa homodimeric enzyme that belongs to a family of structurally homologous flavin reductases and nitroreductases with many potential biotechnology applications. Prior studies have suggested that flexibility is involved in the catalytic mechanism of the enzyme. The active site residue W47 was previously identified as being particularly important, as its level of solvent exposure correlates with enzyme activity, and it was observed to undergo "gating" motions in computer simulations. The NMR data are consistent with these findings. Signals from W47 are dynamically broadened beyond detection and several other residues in the active site have significant R ( ex ) contributions to transverse relaxation rates. In addition, the backbone of S193, whose side chain hydroxyl proton hydrogen bonds directly with the FMN cofactor, exhibits extensive mobility on the ns-ps timescale. We hypothesize that these motions may facilitate structural rearrangements of the active site that allow NOX to accept both FMN and FAD as cofactors.

  13. A proton NMR relaxation study of water dynamics in bovine serum albumin nanoparticles.

    PubMed

    Belotti, Monica; Martinelli, Andrea; Gianferri, Raffaella; Brosio, Elvino

    2010-01-14

    Water dynamics and compartmentation in glutaraldehyde cross-linked bovine serum albumin nanoparticles have been investigated by an integrated nuclear magnetic resonance (NMR) protocol based on water relaxation times and self-diffusion coefficients measurements. Multi-exponentially of water relaxation curves has been accounted for according to a diffusive and chemical exchange model (see B. P. Hills, S. F. Takacs and P. S. Belton, Mol. Phys., 1989, 67(4), 903, and Mol. Phys., 1989, 67(4), 913; E. Brosio, M. Belotti and R. Gianferri, in Food Science and Technology: New Research, ed. L. V. Greco and M. N. Bruno, Nova Science Publishers, Hauppauge (NY), 2008) that made it possible to single out water molecules in the molecular spaces in the interior of albumin nanoparticles, in the meso-cavities formed by packed nanoparticles and in the meniscus on top of the nanoparticles suspension. A quantitative rationalization of T(2) values of water different components allowed morphological information to be acquired as for the size of water filled compartments, while self-diffusion coefficient measurements of water excess or fluxed packed nanoparticles suspensions are describers of transport properties of soft biomaterials. The paper reports an NMR approach that can be seen as a general and relevant method to characterize excess-water-swollen soft biomaterials.

  14. Molecular dynamics simulation of spin-lattice NMR relaxation in poly-L-lysine dendrimers: manifestation of the semiflexibility effect.

    PubMed

    Markelov, Denis A; Falkovich, Stanislav G; Neelov, Igor M; Ilyash, Maxim Yu; Matveev, Vladimir V; Lähderanta, Erkki; Ingman, Petri; Darinskii, Anatolii A

    2015-02-07

    NMR relaxation experiments are widely used to investigate the local orientation mobility in dendrimers. In particular, the NMR method allows one to measure the spin-lattice relaxation rate, 1/T1, which is connected with the orientational autocorrelation function (ACF) of NMR active groups. We calculate the temperature (Θ) and frequency (ω) dependences of the spin-lattice NMR relaxation rates for segments and NMR active CH2 groups in poly-L-lysine (PLL) dendrimers in water, on the basis of full-atomic molecular dynamics simulations. It is shown that the position of the maximum of 1/T1(ω) depends on the location of the segments inside the dendrimer. This dependence of the maximum is explained by the restricted flexibility of the dendrimer. Such behavior has been predicted recently by the analytical theory based on the semiflexible viscoelastic model. The simulated temperature dependences of 1/T1 for terminal and inner groups in PLL dendrimers of n = 2 and n = 4 generations dissolved in water are in good agreement with the NMR experimental data, which have been obtained for these systems previously by us. It is shown that in the case of PLL dendrimers, the traditional procedure of the interpretation of NMR experimental data - when smaller values of 1/T1 correspond to higher orientation mobility - is applicable to the whole accessible frequency interval only for the terminal groups. For the inner groups, this procedure is valid only at low frequencies.

  15. Translational diffusion of macromolecular assemblies measured using transverse relaxation-optimized PFG-NMR

    PubMed Central

    Horst, Reto; Horwich, Arthur L.

    2012-01-01

    In structural biology, pulsed field gradient (PFG) NMR for characterization of size and hydrodynamic parameters of macromolecular solutes has the advantage over other techniques that the measurements can be recorded with identical solution conditions as used for NMR structure determination or for crystallization trials. This paper describes two transverse relaxation-optimized (TRO) 15N-filtered PFG stimulated-echo (STE) experiments for studies of macromolecular translational diffusion in solution, 1H-TRO-STE and 15N-TRO-STE, which include CRINEPT and TROSY elements. Measurements with mixed micelles of the Escherichia coli outer membrane protein X (OmpX) and the detergent Fos-10 were used for a systematic comparison of 1H-TRO-STE and 15N-TRO-STE with conventional 15N-filtered STE experimental schemes. The results provide an extended platform for evaluating the NMR experiments available for diffusion measurements in structural biology projects with molecular particles of different size ranges. An initial application of the 15N-TRO-STE experiment with very long diffusion delays showed that the tedradecamer structure of the 800 kDa Thermus thermophilus chaperonin GroEL is preserved in aqueous solution over the temperature range 25–60°C. PMID:21919531

  16. Translational diffusion of macromolecular assemblies measured using transverse-relaxation-optimized pulsed field gradient NMR.

    PubMed

    Horst, Reto; Horwich, Arthur L; Wüthrich, Kurt

    2011-10-19

    In structural biology, pulsed field gradient (PFG) NMR spectroscopy for the characterization of size and hydrodynamic parameters of macromolecular solutes has the advantage over other techniques that the measurements can be recorded with identical solution conditions as used for NMR structure determination or for crystallization trials. This paper describes two transverse-relaxation-optimized (TRO) (15)N-filtered PFG stimulated-echo (STE) experiments for studies of macromolecular translational diffusion in solution, (1)H-TRO-STE and (15)N-TRO-STE, which include CRINEPT and TROSY elements. Measurements with mixed micelles of the Escherichia coli outer membrane protein X (OmpX) and the detergent Fos-10 were used for a systematic comparison of (1)H-TRO-STE and (15)N-TRO-STE with conventional (15)N-filtered STE experimental schemes. The results provide an extended platform for evaluating the NMR experiments available for diffusion measurements in structural biology projects involving molecular particles with different size ranges. An initial application of the (15)N-TRO-STE experiment with very long diffusion delays showed that the tedradecamer structure of the 800 kDa Thermus thermophilus chaperonin GroEL is preserved in aqueous solution over the temperature range 25-60 °C.

  17. Solution deuterium NMR quadrupolar relaxation study of heme mobility in myoglobin

    SciTech Connect

    Johnson, R.D.; La Mar, G.N.; Smith, K.M.; Parish, D.W.; Langry, K.C. )

    1989-01-18

    NMR spectroscopy has been used to monitor the quadrupolar relaxation and motional dynamics of {sup 2}H selectively incorporated into skeletal and side chain positions of the heme in sperm whale myoglobin. The hyperfine shifts of the heme resonances in paramagnetic states of myoglobin allow resolution of the signals of interest, and paramagnetic contributions to the observed line widths are shown to be insignificant. The {sup 2}H line widths for the skeletal positions of deuterohemin-reconstituted myoglobin yield a correlation time identical with that of overall protein tumbling (9 ns at 30{degree}C) and hence reflect an immobile heme group. The {sup 2}H NMR line widths of heme methyl groups exhibit motional narrowing indicative of very rapid internal rotation. Hence the methyl rotation is effectively decoupled from the overall protein tumbling, and the residual quadrupolar line width can be used directly to determine the protein tumbling rate. The {sup 2}H NMR lines from heme vinyl groups were found narrower than those from the heme skeleton. However, the range of quadrupolar coupling constants for sp{sup 2} hybridized C-{sup 2}H bonds does not permit an unequivocal interpretation in terms of mobility. 48 refs., 4 figs.

  18. Solvent dynamical behavior in an organogel phase as studied by NMR relaxation and diffusion experiments.

    PubMed

    Yemloul, Mehdi; Steiner, Emilie; Robert, Anthony; Bouguet-Bonnet, Sabine; Allix, Florent; Jamart-Grégoire, Brigitte; Canet, Daniel

    2011-03-24

    An organogelation process depends on the gelator-solvent pair. This study deals with the solvent dynamics once the gelation process is completed. The first approach used is relaxometry, i.e., the measurement of toluene proton longitudinal relaxation time T(1) as a function of the proton NMR resonance frequency (here in the 5 kHz to 400 MHz range). Pure toluene exhibits an unexpected T(1) variation, which has been identified as paramagnetic relaxation resulting from an interaction of toluene with dissolved oxygen. In the gel phase, this contribution is retrieved with, in addition, a strong decay at low frequencies assigned to toluene molecules within the gel fibers. Comparison of dispersion curves of pure toluene and toluene in the gel phase leads to an estimate of the proportion of toluene embedded within the organogel (found around 40%). The second approach is based on carbon-13 T(1) and nuclear Overhauser effect measurements, the combination of these two parameters providing direct information about the reorientation of C-H bonds. It appears clearly that reorientation of toluene is the same in pure liquid and in the gel phase. The only noticeable changes in carbon-13 longitudinal relaxation times are due to the so-called chemical shift anisotropy (csa) mechanism and reflect slight modifications of the toluene electronic distribution in the gel phase. NMR diffusion measurements by the pulse gradient spin-echo (PGSE) method allow us to determine the diffusion coefficient of toluene inside the organogel. It is roughly two-thirds of the one in pure toluene, thus indicating that self-diffusion is the only dynamical parameter to be slightly affected when the solvent is inside the gel structure. The whole set of experimental observations leads to the conclusion that, once the gel is formed, the solvent becomes essentially passive, although an important fraction is located within the gel structure.

  19. Quadrupolar NMR Relaxation from ab Initio Molecular Dynamics: Improved Sampling and Cluster Models versus Periodic Calculations.

    PubMed

    Philips, Adam; Marchenko, Alex; Truflandier, Lionel A; Autschbach, Jochen

    2017-09-12

    Quadrupolar NMR relaxation rates are computed for (17)O and (2)H nuclei of liquid water, and of (23)Na(+), and (35)Cl(-) in aqueous solution via Kohn-Sham (KS) density functional theory ab initio molecular dynamics (aiMD) and subsequent KS electric field gradient (EFG) calculations along the trajectories. The calculated relaxation rates are within about a factor of 2 of experimental results and improved over previous aiMD simulations. The relaxation rates are assessed with regard to the lengths of the simulations as well as configurational sampling. The latter is found to be the more limiting factor in obtaining good statistical sampling and is improved by averaging over many equivalent nuclei of a system or over several independent trajectories. Further, full periodic plane-wave basis calculations of the EFGs are compared with molecular-cluster atomic-orbital basis calculations. The two methods deliver comparable results with nonhybrid functionals. With the molecular-cluster approach, a larger variety of electronic structure methods is available. For chloride, the EFG computations benefit from using a hybrid KS functional.

  20. Structural Analysis of Protein-RNA Complexes in Solution Using NMR Paramagnetic Relaxation Enhancements.

    PubMed

    Hennig, Janosch; Warner, Lisa R; Simon, Bernd; Geerlof, Arie; Mackereth, Cameron D; Sattler, Michael

    2015-01-01

    Biological activity in the cell is predominantly mediated by large multiprotein and protein-nucleic acid complexes that act together to ensure functional fidelity. Nuclear magnetic resonance (NMR) spectroscopy is the only method that can provide information for high-resolution three-dimensional structures and the conformational dynamics of these complexes in solution. Mapping of binding interfaces and molecular interactions along with the characterization of conformational dynamics is possible for very large protein complexes. In contrast, de novo structure determination by NMR becomes very time consuming and difficult for protein complexes larger than 30 kDa as data are noisy and sparse. Fortunately, high-resolution structures are often available for individual domains or subunits of a protein complex and thus sparse data can be used to define their arrangement and dynamics within the assembled complex. In these cases, NMR can therefore be efficiently combined with complementary solution techniques, such as small-angle X-ray or neutron scattering, to provide a comprehensive description of the structure and dynamics of protein complexes in solution. Particularly useful are NMR-derived paramagnetic relaxation enhancements (PREs), which provide long-range distance restraints (ca. 20Å) for structural analysis of large complexes and also report on conformational dynamics in solution. Here, we describe the use of PREs from sample production to structure calculation, focusing on protein-RNA complexes. On the basis of recent examples from our own research, we demonstrate the utility, present protocols, and discuss potential pitfalls when using PREs for studying the structure and dynamic features of protein-RNA complexes.

  1. Structural fidelity and NMR relaxation analysis in a prototype RNA hairpin.

    PubMed

    Giambaşu, George M; York, Darrin M; Case, David A

    2015-05-01

    RNA hairpins are widespread and very stable motifs that contribute decisively to RNA folding and biological function. The GTP1G2C3A4C5U6U7C8G9G10U11G12C13C14 construct (with a central UUCG tetraloop) has been extensively studied by solution NMR, and offers and excellent opportunity to evaluate the structure and dynamical description afforded by molecular dynamics (MD) simulations. Here, we compare average structural parameters and NMR relaxation rates estimated from a series of multiple independent explicit solvent MD simulations using the two most recent RNA AMBER force fields (ff99 and ff10). Predicted overall tumbling times are ∼20% faster than those inferred from analysis of NMR data and follow the same trend when temperature and ionic strength is varied. The Watson-Crick stem and the "canonical" UUCG loop structure are maintained in most simulations including the characteristic syn conformation along the glycosidic bond of G9, although some key hydrogen bonds in the loop are partially disrupted. Our analysis pinpoints G9-G10 backbone conformations as a locus of discrepancies between experiment and simulation. In general the results for the more recent force-field parameters (ff10) are closer to experiment than those for the older ones (ff99). This work provides a comprehensive and detailed comparison of state of the art MD simulations against a wide variety of solution NMR measurements. © 2015 Giambaşu et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.

  2. Estimating Pore Properties from NMR Relaxation Time Measurements in Heterogeneous Media

    NASA Astrophysics Data System (ADS)

    Grunewald, E.; Knight, R.

    2008-12-01

    The link between pore geometry and the nuclear magnetic resonance (NMR) relaxation time T2 is well- established for simple systems but is poorly understood for complex media with heterogeneous pores. Conventional interpretation of NMR relaxation data employs a model of isolated pores in which each hydrogen proton samples only one pore type, and the T2-distribution is directly scaled to estimate a pore-size distribution. During an actual NMR measurement, however, each proton diffuses through a finite volume of the pore network, and so may sample multiple pore types encountered within this diffusion cell. For cases in which heterogeneous pores are strongly coupled by diffusion, the meaning of the T2- distribution is not well understood and further research is required to determine how such measurements should be interpreted. In this study we directly investigate the implications of pore coupling in two groups of laboratory NMR experiments. We conduct two suites of experiments, in which samples are synthesized to exhibit a range of pore coupling strengths using two independent approaches: (a) varying the scale of the diffusion cell and (b) varying the scale over which heterogeneous pores are encountered. In the first set of experiments, we vary the scale of the diffusion cell in silica gels which have a bimodal pore-size distribution comprised of intragrannular micropores and much larger intergrannular pores. The untreated gel exhibits strong pore coupling with a single broad peak observed in the T2-distribution. By treating the gel with varied amounts of paramagnetic iron surface coatings, we decrease the surface relaxation time, T2S, and effectively decrease both the size of the diffusion cell and the degree of pore coupling. As more iron is coated to the grain surfaces, we observe a separation of the broad T2-distribution into two peaks that more accurately represent the true bimodal pore-size distribution. In the second set of experiments, we vary the scale over

  3. Estimating the surface relaxivity as a function of pore size from NMR T2 distributions and micro-tomographic images

    NASA Astrophysics Data System (ADS)

    Benavides, Francisco; Leiderman, Ricardo; Souza, Andre; Carneiro, Giovanna; Bagueira, Rodrigo

    2017-09-01

    In the present work, we formulate and solve an inverse problem to recover the surface relaxivity as a function of pore size. The input data for our technique are the T2 distribution measurement and the micro-tomographic image of the rock sample under investigation. We simulate the NMR relaxation signal for a given surface relaxivity function using the random walk method and rank different surface relaxivity functions according to the correlation of the resulting simulated T2 distributions with the measured T2 distribution. The optimization is performed using genetic algorithms and determines the surface relaxivity function whose corresponding simulated T2 distribution best matches the measured T2 distribution. In the proposed methodology, pore size is associated with a number of collisions in the random walk simulations. We illustrate the application of the proposed method by performing inversions from synthetic and laboratory input data and compare the obtained results with those obtained using the uniform relaxivity assumption.

  4. Temperature-Dependent Oxygen Effect on NMR D-[Formula: see text] Relaxation-Diffusion Correlation of n-Alkanes.

    PubMed

    Shikhov, Igor; Arns, Christoph H

    2016-01-01

    Nuclear magnetic resonance (NMR) diffusion-relaxation correlation experiments (D-[Formula: see text]) are widely used for the petrophysical characterisation of rocks saturated with petroleum fluids both in situ and for laboratory analyses. The encoding for both diffusion and relaxation offers increased fluid typing contrast by discriminating fluids based on their self-diffusion coefficients, while relaxation times provide information about the interaction of solid and fluid phases and associated confinement geometry (if NMR responses of pure fluids at particular temperature and pressure are known). Petrophysical interpretation of D-[Formula: see text] correlation maps is typically assisted by the "standard alkane line"-a relaxation-diffusion correlation valid for pure normal alkanes and their mixtures in the absence of restrictions to diffusing molecules and effects of internal gradients. This correlation assumes fluids are free from paramagnetic impurities. In situations where fluid samples cannot be maintained at air-free state the diffusion-relaxation response of fluids shift towards shorter relaxation times due to oxygen paramagnetic relaxation enhancement. Interpretation of such a response using the "standard alkane line" would be erroneous and is further complicated by the temperature-dependence of oxygen solubility for each component of the alkane mixture. We propose a diffusion-relaxation correlation suitable for interpretation of low-field NMR D-[Formula: see text] responses of normal alkanes and their mixtures saturating rocks over a broad temperature range, in equilibrium with atmospheric air. We review and where necessary revise existing viscosity-relaxation correlations. Findings are applied to diffusion-relaxation dependencies taking into account the temperature dependence of oxygen solubility and solvent vapour pressure. The effect is demonstrated on a partially saturated carbonate rock.

  5. General order parameter based correlation analysis of protein backbone motions between experimental NMR relaxation measurements and molecular dynamics simulations.

    PubMed

    Liu, Qing; Shi, Chaowei; Yu, Lu; Zhang, Longhua; Xiong, Ying; Tian, Changlin

    2015-02-13

    Internal backbone dynamic motions are essential for different protein functions and occur on a wide range of time scales, from femtoseconds to seconds. Molecular dynamic (MD) simulations and nuclear magnetic resonance (NMR) spin relaxation measurements are valuable tools to gain access to fast (nanosecond) internal motions. However, there exist few reports on correlation analysis between MD and NMR relaxation data. Here, backbone relaxation measurements of (15)N-labeled SH3 (Src homology 3) domain proteins in aqueous buffer were used to generate general order parameters (S(2)) using a model-free approach. Simultaneously, 80 ns MD simulations of SH3 domain proteins in a defined hydrated box at neutral pH were conducted and the general order parameters (S(2)) were derived from the MD trajectory. Correlation analysis using the Gromos force field indicated that S(2) values from NMR relaxation measurements and MD simulations were significantly different. MD simulations were performed on models with different charge states for three histidine residues, and with different water models, which were SPC (simple point charge) water model and SPC/E (extended simple point charge) water model. S(2) parameters from MD simulations with charges for all three histidines and with the SPC/E water model correlated well with S(2) calculated from the experimental NMR relaxation measurements, in a site-specific manner.

  6. NMR spin relaxation in proteins: The patterns of motion that dissipate power to the bath

    NASA Astrophysics Data System (ADS)

    Shapiro, Yury E.; Meirovitch, Eva

    2014-04-01

    We developed in recent years the two-body coupled-rotator slowly relaxing local structure (SRLS) approach for the analysis of NMR relaxation in proteins. The two bodies/rotators are the protein (diffusion tensor D1) and the spin-bearing probe, e.g., the 15N-1H bond (diffusion tensor, D2), coupled by a local potential (u). A Smoluchowski equation is solved to yield the generic time correlation functions (TCFs), which are sums of weighted exponentials (eigenmodes). By Fourier transformation one obtains the generic spectral density functions (SDFs) which underlie the experimental relaxation parameters. The typical paradigm is to characterize structural dynamics in terms of the best-fit values of D1, D2, and u. Additional approaches we pursued employ the SRLS TCFs, SDFs, or eigenmodes as descriptors. In this study we develop yet another perspective. We consider the SDF as function of the angular velocity associated with the fluctuating fields underlying NMR relaxation. A parameter called j-fraction, which represents the relative contribution of eigenmode, i, to a given value of the SDF function at a specific frequency, ω, is defined. j-fraction profiles of the dominant eigenmodes are derived for 0 ≤ ω ≤ 1012 rad/s. They reveal which patterns of motion actuate power dissipation at given ω-values, what are their rates, and what is their relative contribution. Simulations are carried out to determine the effect of timescale separation, D1/D2, axial potential strength, and local diffusion axiality. For D1/D2 ≤ 0.01 and strong local potential of 15 kBT, power is dissipated by global diffusion, renormalized (by the strong potential) local diffusion, and probe diffusion on the surface of a cone (to be called cone diffusion). For D1/D2 = 0.1, power is dissipated by mixed eigenmodes largely of a global-diffusion-type or cone-diffusion-type, and a nearly bare renormalized-local-diffusion eigenmode. For D1/D2 > 0.1, most eigenmodes are of a mixed type. The analysis is

  7. Changes in Porcine Muscle Water Characteristics during Growth—An in Vitro Low-Field NMR Relaxation Study

    NASA Astrophysics Data System (ADS)

    Bertram, Hanne Christine; Rasmussen, Marianne; Busk, Hans; Oksbjerg, Niels; Karlsson, Anders Hans; Andersen, Henrik Jørgen

    2002-08-01

    This study investigates the effects of developmental stage and muscle type on the mobility and distribution of water within skeletal muscles, using low-field 1H-NMR transverse relaxation measurements in vitro on four different porcine muscles ( M. longissimus dorsi, M. semitendinosus, M. biceps femoris, M. vastus intermedius) from a total of 48 pigs slaughtered at various weight classes between 25 kg and 150 kg. Principal component analysis (PCA) revealed effects of both slaughter weight and muscle type on the transverse relaxation decay. Independent of developmental stage and muscle type, distributed exponential analysis of the NMR T 2 relaxation data imparted the existence of three distinct water populations, T 2b, T 21, and T 22, with relaxation times of approximately 1-10, 45-120, and 200-500 ms, respectively. The most profound change during muscle growth was a shift toward faster relaxation in the intermediate time constant, T 21. It decreased by approx. 24% in all four muscle types during the period from 25 to 150 kg live weight. Determination of dry matter, fat, and protein content in the muscles showed that the changes in relaxation time of the intermediate time constant, T 21, during growth should be ascribed mainly to a change in protein content, as the protein content explained 77% of the variation in the T 21 time constant. Partial least squares (PLS) regression revealed validated correlations in the region of 0.58 to 0.77 between NMR transverse relaxation data and muscle development for all the four muscle types, which indicates that NMR relaxation measurements may be used in the prediction of muscle developmental stage.

  8. Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.

    PubMed

    Field, Timothy R

    2014-11-01

    Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties.

  9. NMR relaxation and water self-diffusion studies in whey protein solutions and gels.

    PubMed

    Colsenet, Roxane; Mariette, François; Cambert, Mireille

    2005-08-24

    The changes in water proton transverse relaxation behavior induced by aggregation of whey proteins are explained in terms of the simple molecular processes of diffusion and chemical exchange. The water self-diffusion coefficient was measured in whey protein solutions and gels by the pulsed field gradient NMR method. As expected, water self-diffusion was reduced with increased protein concentrations. Whatever the concentration, the water molecules were free to diffuse over distances varying from 15 to 47 mum. Water diffusion was constant over these distances, demonstrating that no restrictions were found to explain the water hindrance. The modification in protein structure by gelation induced a decrease in water diffusion. The effects of protein concentration on water diffusion are discussed and modeled. Two approaches were compared, the obstruction effect induced by a spherical particle and the cell model, which considered two water compartments with specific self-diffusion coefficients.

  10. Relationships between 1H NMR Relaxation Data and Some Technological Parameters of Meat: A Chemometric Approach

    NASA Astrophysics Data System (ADS)

    Brown, Robert J. S.; Capozzi, Francesco; Cavani, Claudio; Cremonini, Mauro A.; Petracci, Massimiliano; Placucci, Giuseppe

    2000-11-01

    In this paper chemometrics (ANOVA and PCR) is used to measure unbiased correlations between NMR spin-echo decays of pork M. Longissimus dorsi obtained through Carr-Purcell-Meiboom-Gill (CPMG) experiments at low frequency (20 MHz) and the values of 14 technological parameters commonly used to assess pork meat quality. On the basis of the ANOVA results, it is also found that the CPMG decays of meat cannot be best interpreted with a "discrete" model (i.e., by expanding the decays in a series of a discrete number of exponential components, each with a different transverse relaxation time), but rather with a "continuous" model, by which a continuous distribution of T2's is allowed. The latter model also agrees with literature histological results.

  11. Relationships between (1)H NMR relaxation data and some technological parameters of meat: a chemometric approach.

    PubMed

    Brown, R J; Capozzi, F; Cavani, C; Cremonini, M A; Petracci, M; Placucci, G

    2000-11-01

    In this paper chemometrics (ANOVA and PCR) is used to measure unbiased correlations between NMR spin-echo decays of pork M. Longissimus dorsi obtained through Carr-Purcell-Meiboom-Gill (CPMG) experiments at low frequency (20 MHz) and the values of 14 technological parameters commonly used to assess pork meat quality. On the basis of the ANOVA results, it is also found that the CPMG decays of meat cannot be best interpreted with a "discrete" model (i.e., by expanding the decays in a series of a discrete number of exponential components, each with a different transverse relaxation time), but rather with a "continuous" model, by which a continuous distribution of T(2)'s is allowed. The latter model also agrees with literature histological results. Copyright 2000 Academic Press.

  12. Substrate Modulated Dynamics of the ADP/ATP Transporter Revealed by NMR Relaxation Dispersion

    PubMed Central

    Brüschweiler, Sven; Yang, Qin; Run, Changqing; Chou, James J.

    2015-01-01

    The ADP/ATP carrier (AAC) transports ADP and ATP across the inner mitochondrial membrane. Unlike most transporters that have 2-fold direct or inverted quasi-symmetry, AAC has the apparent 3-fold rotational symmetry. Further, its transport rate is fast for transporters that carry large solutes. Here, we perform comprehensive NMR relaxation dispersion measurements for the yeast AAC carrier 3, which provide residue-specific information on the protein conformational exchange. Our data indicate that AAC is predominantly in the cytosol-facing open state and converts to a lowly populated state in an asymmetric manner despite its three-fold structural symmetry. Binding of the substrate ADP significantly increases the rate of conformational exchange, whereas the inhibitor CATR slows the exchange. These results suggest that while the transporter catalyzes the translocation of substrate, the substrate also facilitates interconversion between alternating states that may be relevant to the transport function. PMID:26167881

  13. General order parameter based correlation analysis of protein backbone motions between experimental NMR relaxation measurements and molecular dynamics simulations

    SciTech Connect

    Liu, Qing; Shi, Chaowei; Yu, Lu; Zhang, Longhua; Xiong, Ying; Tian, Changlin

    2015-02-13

    Internal backbone dynamic motions are essential for different protein functions and occur on a wide range of time scales, from femtoseconds to seconds. Molecular dynamic (MD) simulations and nuclear magnetic resonance (NMR) spin relaxation measurements are valuable tools to gain access to fast (nanosecond) internal motions. However, there exist few reports on correlation analysis between MD and NMR relaxation data. Here, backbone relaxation measurements of {sup 15}N-labeled SH3 (Src homology 3) domain proteins in aqueous buffer were used to generate general order parameters (S{sup 2}) using a model-free approach. Simultaneously, 80 ns MD simulations of SH3 domain proteins in a defined hydrated box at neutral pH were conducted and the general order parameters (S{sup 2}) were derived from the MD trajectory. Correlation analysis using the Gromos force field indicated that S{sup 2} values from NMR relaxation measurements and MD simulations were significantly different. MD simulations were performed on models with different charge states for three histidine residues, and with different water models, which were SPC (simple point charge) water model and SPC/E (extended simple point charge) water model. S{sup 2} parameters from MD simulations with charges for all three histidines and with the SPC/E water model correlated well with S{sup 2} calculated from the experimental NMR relaxation measurements, in a site-specific manner. - Highlights: • Correlation analysis between NMR relaxation measurements and MD simulations. • General order parameter (S{sup 2}) as common reference between the two methods. • Different protein dynamics with different Histidine charge states in neutral pH. • Different protein dynamics with different water models.

  14. relaxGUI: a new software for fast and simple NMR relaxation data analysis and calculation of ps-ns and μs motion of proteins.

    PubMed

    Bieri, Michael; d'Auvergne, Edward J; Gooley, Paul R

    2011-06-01

    Investigation of protein dynamics on the ps-ns and μs-ms timeframes provides detailed insight into the mechanisms of enzymes and the binding properties of proteins. Nuclear magnetic resonance (NMR) is an excellent tool for studying protein dynamics at atomic resolution. Analysis of relaxation data using model-free analysis can be a tedious and time consuming process, which requires good knowledge of scripting procedures. The software relaxGUI was developed for fast and simple model-free analysis and is fully integrated into the software package relax. It is written in Python and uses wxPython to build the graphical user interface (GUI) for maximum performance and multi-platform use. This software allows the analysis of NMR relaxation data with ease and the generation of publication quality graphs as well as color coded images of molecular structures. The interface is designed for simple data analysis and management. The software was tested and validated against the command line version of relax.

  15. Ultrasound Treatment of Butyl Gum and Rubber, Studied by NMR Relaxation

    NASA Astrophysics Data System (ADS)

    von Meerwall, E. D.; Feng, Wenlai; Isayev, A. I.

    2004-10-01

    We have examined the effects of intense ultrasound on butyl gum and unfilled vulcanizates using proton transverse NMR relaxation, sol extraction, GPC analysis, and glass transition measurements. At 100 deg.C the spin echo decays exhibit three components, due to entangled molecules and network, unentangled sol plus dangling chain ends, and oligomer remnants; two components suffice to describe most vulcanizates. Compared to other rubbers we have studied, all component spin relaxation times are shorter and less sensitive to ultrasound, and the fraction of the short-T2 component is significantly higher. In the gums sonication produces chain scission but no significant crosslinking. In sol extracted from sonicated rubber, the T2 component amplitudes correlate well with the trimodal molecular-weight distribution. In spite of the low glass transition temperatures (near -60 deg.C) even the longest T2 up to 120 deg.C was too short to permit pulsed-gradient diffusion measurements. The low extractable sol fraction at standard ultrasound settings confirms the conclusion that in butyl rubber sonication is less effective for network destruction than in other rubbers.

  16. Diffusion dependence of proton NMR relaxation rates in the presence of ferritin

    NASA Astrophysics Data System (ADS)

    Boss, Michael; Hammel, P. Chris

    2009-03-01

    Ferritin is the predominant iron-storage protein in living organisms. It may serve as an indicator of neurodegenerative diseases such as Alzheimer's. Measuring brain ferritin concentration non-invasively via MRI could enable better diagnoses and treatments of such diseases. Quantitative MRI determination of the ferritin concentration requires an understanding of the NMR relaxation mechanisms of hydrogen protons in the presence of ferritin. In aqueous solutions, ferritin enhances the transverse relaxation rate (R2) of the protons. This is thought to occur due to a diffusive mechanism, where protons diffusing near ferritin pass through a region of elevated magnetic field, and a chemical exchange mechanism, where protons bind to the protein for a period of time, experiencing an even higher magnetic field. These two mechanisms exhibit different dependencies on the self-diffusion coefficient of the protons. By adding glycerol to aqueous solutions, we control the self-diffusion of protons. We measure the R2 of protons in ferritin-containing binary mixtures of water and glycerol using CPMG sequences, and compare the experimental results to theoretical predictions of diffusion dependence in order to distinguish the relative importance of the mechanisms.

  17. NMR Relaxation Studies on the Hydrate Layer of Intrinsically Unstructured Proteins

    PubMed Central

    Bokor, Mónika; Csizmók, Veronika; Kovács, Dénes; Bánki, Péter; Friedrich, Peter; Tompa, Peter; Tompa, Kálmán

    2005-01-01

    Intrinsically unstructured/disordered proteins (IUPs) exist in a disordered and largely solvent-exposed, still functional, structural state under physiological conditions. As their function is often directly linked with structural disorder, understanding their structure-function relationship in detail is a great challenge to structural biology. In particular, their hydration and residual structure, both closely linked with their mechanism of action, require close attention. Here we demonstrate that the hydration of IUPs can be adequately approached by a technique so far unexplored with respect to IUPs, solid-state NMR relaxation measurements. This technique provides quantitative information on various features of hydrate water bound to these proteins. By freezing nonhydrate (bulk) water out, we have been able to measure free induction decays pertaining to protons of bound water from which the amount of hydrate water, its activation energy, and correlation times could be calculated. Thus, for three IUPs, the first inhibitory domain of calpastatin, microtubule-associated protein 2c, and plant dehydrin early responsive to dehydration 10, we demonstrate that they bind a significantly larger amount of water than globular proteins, whereas their suboptimal hydration and relaxation parameters are correlated with their differing modes of function. The theoretical treatment and experimental approach presented in this article may have general utility in characterizing proteins that belong to this novel structural class. PMID:15613629

  18. Determination of the nature of fluctuations using 8Li and 9Liβ -NMR and spin-lattice relaxation

    NASA Astrophysics Data System (ADS)

    Chatzichristos, A.; McFadden, R. M. L.; Karner, V. L.; Cortie, D. L.; Levy, C. D. P.; MacFarlane, W. A.; Morris, G. D.; Pearson, M. R.; Salman, Z.; Kiefl, R. F.

    2017-07-01

    We report a comparison of the 1 /T1 spin-lattice relaxation rates for 9Li and 8Li in Pt and SrTiO3, in order to differentiate between magnetic and electric quadrupolar relaxation mechanisms. In Pt, the ratio of the 1 /T1 spin relaxation rates RPt was found to be 6.82(29), which is close to but less than the theoretical limit of ˜7.68 for pure magnetic relaxation. In SrTiO3 this ratio was found to be 2.7(3), which is close to but larger than the theoretical limit of ˜2.14 expected for pure electric quadrupolar relaxation. These results bring insight into the nature of the fluctuations in the local environment of implanted 8Li observed by β -NMR.

  19. Sensitivity and resolution of two-dimensional NMR diffusion-relaxation measurements

    NASA Astrophysics Data System (ADS)

    Kausik, Ravinath; Hürlimann, Martin D.

    2016-09-01

    The performance of 2D NMR diffusion-relaxation measurements for fluid typing applications is analyzed. In particular, we delineate the region in the diffusion - relaxation plane that can be determined with a given gradient strength and homogeneity, and compare the performance of the single and double echo encoding with the stimulated echo diffusion encoding. We show that the diffusion editing based approach is able to determine the diffusion coefficient only if the relaxation time T2 exceeds a cutoff value T2,cutoff , that scales like T2,cutoff ∝g - 2 / 3D - 1 / 3 . For stimulated echo encoding, the optimal diffusion encoding times (Td and δ), that provide the best diffusion sensitivity, rely only on the T1 /T2 ratios and not on the diffusion coefficients of the fluids or the applied gradient strengths. Irrespective of T1 , for high enough gradients (i.e. when γ2g2 DT23 >102), the Hahn echo based encoding is superior to encoding based on the stimulated echo. For weaker gradients, the stimulated echo is superior only if the T1 /T2 ratio is much larger than 1. For single component systems, the diffusion sensitivity is not adversely impacted by the uniformity of the gradients and the diffusion distributions can be well measured. The presence of non-uniform gradients can affect the determination of the diffusion distributions when you have two fluids of comparable T2 . In such situations the effective single component diffusion coefficient is always closer to the geometric mean diffusion coefficient of the two fluids.

  20. Extracting Diffusion Constants from Echo-Time-Dependent PFG NMR Data Using Relaxation-Time Information

    NASA Astrophysics Data System (ADS)

    Vandusschoten, D.; Dejager, P. A.; Vanas, H.

    Heterogeneous (bio)systems are often characterized by several water-containing compartments that differ in relaxation time values and diffusion constants. Because of the relatively small differences among these diffusion constants, nonoptimal measuring conditions easily lead to the conclusion that a single diffusion constant suffices to describe the water mobility in a heterogeneous (bio)system. This paper demonstrates that the combination of a T2 measurement and diffusion measurements at various echo times (TE), based on the PFG MSE sequence, enables the accurate determination of diffusion constants which are less than a factor of 2 apart. This new method gives errors of the diffusion constant below 10% when two fractions are present, while the standard approach of a biexponential fit to the diffusion data in identical circumstances gives larger (>25%) errors. On application of this approach to water in apple parenchyma tissue, the diffusion constant of water in the vacuole of the cells ( D = 1.7 × 10 -9 m 2/s) can be distinguished from that of the cytoplasm ( D = 1.0 × 10 -9 m 2/s). Also, for mung bean seedlings, the cell size determined by PFG MSE measurements increased from 65 to 100 μm when the echo time increased from 150 to 900 ms, demonstrating that the interpretation of PFG SE data used to investigate cell sizes is strongly dependent on the T2 values of the fractions within the sample. Because relaxation times are used to discriminate the diffusion constants, we propose to name this approach diffusion analysis by relaxation- time- separated (DARTS) PFG NMR.

  1. Wide-ranging molecular mobilities of water in active pharmaceutical ingredient (API) hydrates as determined by NMR relaxation times.

    PubMed

    Yoshioka, Sumie; Aso, Yukio; Osako, Tsutomu; Kawanishi, Toru

    2008-10-01

    In order to examine the possibility of determining the molecular mobility of hydration water in active pharmaceutical ingredient (API) hydrates by NMR relaxation measurement, spin-spin relaxation and spin-lattice relaxation were measured for the 11 API hydrates listed in the Japanese Pharmacopeia using pulsed (1)H-NMR. For hydration water that has relatively high mobility and shows Lorentzian decay, molecular mobility as determined by spin-spin relaxation time (T(2)) was correlated with ease of evaporation under both nonisothermal and isothermal conditions, as determined by DSC and water vapor sorption isotherm analysis, respectively. Thus, T(2) may be considered a useful parameter which indicates the molecular mobility of hydration water. In contrast, for hydration water that has low mobility and shows Gaussian decay, T(2) was found not to correlate with ease of evaporation under nonisothermal conditions, which suggests that in this case, the molecular mobility of hydration water was too low to be determined by T(2). A wide range of water mobilities was found among API hydrates, from low mobility that could not be evaluated by NMR relaxation time, such as that of the water molecules in pipemidic acid hydrate, to high mobility that could be evaluated by this method, such as that of the water molecules in ceftazidime hydrate. (c) 2008 Wiley-Liss, Inc. and the American Pharmacists Association

  2. Study of cross - relaxation and molecular dynamics in the solid 3-(trifluoromethyl) benzoic acid by solid state NMR off - resonance.

    PubMed

    Woźniak-Braszak, Aneta

    2017-02-01

    Molecular dynamics of the solid 3-(trifluoromethyl) benzoic acid containing proton (1)H and fluorine (19)F nuclei was explored by the solid-state NMR off - resonance technique. Contrary to the previous experiments the proton nuclei system I relaxed in the off - resonance effective field B→e while fluorine nuclei system S was saturated for short time in comparison to the relaxation time T1I. New cross - relaxation solid - state NMR off - resonance experiments were conducted on a homebuilt pulse spectrometer operating at the on-resonance frequency of 30.2MHz, at the off - resonance frequency varied between 30.2 and 30.6MHz for protons and at the frequency of 28.411MHz for fluorines, respectively. Based on the experimental data the dispersions of the proton off - resonance spin - lattice relaxation rate ρρ(I), the fluorine off - resonance spin - lattice relaxation rate ρρ(S) and the cross - relaxation rate σρ in the rotating frame were determined. Copyright © 2016 Elsevier Inc. All rights reserved.

  3. A minor conformation of a lanthanide tag on adenylate kinase characterized by paramagnetic relaxation dispersion NMR spectroscopy.

    PubMed

    Hass, Mathias A S; Liu, Wei-Min; Agafonov, Roman V; Otten, Renee; Phung, Lien A; Schilder, Jesika T; Kern, Dorothee; Ubbink, Marcellus

    2015-02-01

    NMR relaxation dispersion techniques provide a powerful method to study protein dynamics by characterizing lowly populated conformations that are in dynamic exchange with the major state. Paramagnetic NMR is a versatile tool for investigating the structures and dynamics of proteins. These two techniques were combined here to measure accurate and precise pseudocontact shifts of a lowly populated conformation. This method delivers valuable long-range structural restraints for higher energy conformations of macromolecules in solution. Another advantage of combining pseudocontact shifts with relaxation dispersion is the increase in the amplitude of dispersion profiles. Lowly populated states are often involved in functional processes, such as enzyme catalysis, signaling, and protein/protein interactions. The presented results also unveil a critical problem with the lanthanide tag used to generate paramagnetic relaxation dispersion effects in proteins, namely that the motions of the tag can interfere severely with the observation of protein dynamics. The two-point attached CLaNP-5 lanthanide tag was linked to adenylate kinase. From the paramagnetic relaxation dispersion only motion of the tag is observed. The data can be described accurately by a two-state model in which the protein-attached tag undergoes a 23° tilting motion on a timescale of milliseconds. The work demonstrates the large potential of paramagnetic relaxation dispersion and the challenge to improve current tags to minimize relaxation dispersion from tag movements.

  4. Analysis of Molecular Interaction of Drugs Within β-Cyclodextrin Cavity by Solution State Nuclear Magnetic Resonance (NMR) Relaxation.

    PubMed

    Kumar, Deepak; Krishnan, Yogeshwaran; Paranjothy, Manikandan; Pal, Samanwita

    2017-03-09

    The prime focus of the present study is to employ NMR relaxation measurement to address the intermolecular interactions as well as motional dynamics of drugs viz., paracetamol and aspirin encapsulated within β-cyclodextrin (β-CD) cavity. In this report we have attempted to demonstrate the applicability of nonselective (R1(ns) ), selective (R1(se)) and bi-selective (R1(bs)) spin-lattice relaxation rates to infer dynamical parameters e.g., molecular rotational correlation times (τc) and cross-relaxation rates (σij) of the encapsulated drugs. Molecular rotational correlation times of the free drugs were calculated using selective relaxation rate in the fast molecular motion time regime ( ωH(2)τc(2)<1 and R1(ns)/R1(se)≈ 1.500), whereas that of the 1:1 complexed drugs were found from the ratio of R1(ns)/R1(se) in the intermediate motion time regime ( ωH(2)τc(2)≈ 1 and R1(ns)/R1(se) ≈ 1.054) and compared with each other to confirm the formation of inclusion complexes. Furthermore the cross-relaxation rates have been used to evaluate the intermolecular proton distances. Also, density functional theory (DFT) calculations were performed to determine the minimum energy geometry of the inclusion complexes and the results compared with experiments. The report thus presents the possibility of utilizing NMR relaxation data, a more cost effective experiments to calculate internuclear distances in case of drug-supramolecule complexes that are generally addressed by extremely time consuming 2D Nuclear Overhauser Enhancement (NOE) based methods. Plausible mode of insertion of drug molecules into the β-CD cavity has also been described based on experimental NMR relaxation data analysis.

  5. Increasing the sensitivity of NMR diffusion measurements by paramagnetic longitudinal relaxation enhancement, with application to ribosome–nascent chain complexes

    PubMed Central

    Cassaignau, Anaïs M. E.; Cabrita, Lisa D.

    2016-01-01

    The translational diffusion of macromolecules can be examined non-invasively by stimulated echo (STE) NMR experiments to accurately determine their molecular sizes. These measurements can be important probes of intermolecular interactions and protein folding and unfolding, and are crucial in monitoring the integrity of large macromolecular assemblies such as ribosome–nascent chain complexes (RNCs). However, NMR studies of these complexes can be severely constrained by their slow tumbling, low solubility (with maximum concentrations of up to 10 μM), and short lifetimes resulting in weak signal, and therefore continuing improvements in experimental sensitivity are essential. Here we explore the use of the paramagnetic longitudinal relaxation enhancement (PLRE) agent NiDO2A on the sensitivity of 15N XSTE and SORDID heteronuclear STE experiments, which can be used to monitor the integrity of these unstable complexes. We exploit the dependence of the PLRE effect on the gyromagnetic ratio and electronic relaxation time to accelerate recovery of 1H magnetization without adversely affecting storage on Nz during diffusion delays or introducing significant transverse relaxation line broadening. By applying the longitudinal relaxation-optimized SORDID pulse sequence together with NiDO2A to 70S Escherichia coli ribosomes and RNCs, NMR diffusion sensitivity enhancements of up to 4.5-fold relative to XSTE are achieved, alongside ~1.9-fold improvements in two-dimensional NMR sensitivity, without compromising the sample integrity. We anticipate these results will significantly advance the use of NMR to probe dynamic regions of ribosomes and other large, unstable macromolecular assemblies. PMID:26253948

  6. Non-polymeric asymmetric binary glass-formers. II. Secondary relaxation studied by dielectric, 2H NMR, and 31P NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Pötzschner, B.; Mohamed, F.; Bächer, C.; Wagner, E.; Lichtinger, A.; Bock, D.; Kreger, K.; Schmidt, H.-W.; Rössler, E. A.

    2017-04-01

    We investigate the secondary (β-) relaxations of an asymmetric binary glass former consisting of a spirobichroman derivative (SBC; Tg = 356 K) as the high-Tg component and the low-Tg component tripropyl phosphate (TPP; Tg = 134 K). The main relaxations are studied in Paper I [B. Pötzschner et al., J. Chem. Phys. 146, 164503 (2017)]. A high Tg contrast of ΔTg = 222 K is put into effect in a non-polymeric system. Component-selective studies are carried out by combining results from dielectric spectroscopy (DS) for mass concentrations cTPP ≥ 60% and those from different methods of 2H and 31P NMR spectroscopy. In the case of NMR, the full concentration range (10% ≤ cTPP ≤ 100%) is covered. The neat components exhibit a β-relaxation (β1 (SBC) and β2 (TPP)). The latter is rediscovered by DS in the mixtures for all concentrations with unchanged time constants. NMR spectroscopy identifies the β-relaxations as being alike to those in neat glasses. A spatially highly restricted motion with angular displacement below ±10° encompassing all molecules is involved. In the low temperature range, where TPP shows the typical 31P NMR echo spectra of the β2-process, very similar spectral features are observed for the (deuterated) SBC component by 2H NMR, in addition to its "own" β1-process observed at high temperatures. Apparently, the small TPP molecules enslave the large SBC molecules to perform a common hindered reorientation. The temperature dependence of the spin-lattice relaxation time of both components is the same and reveals an angular displacement of the SBC molecules somewhat smaller than that of TPP, though the time constants τβ2 are the same. Furthermore, T1(T) of TPP in the temperature region of the β2-process is absolutely the same as in the mixture TPP/polystyrene investigated previously. It appears that the manifestations of the β-process introduced by one component are essentially independent of the second component. Finally, at cTPP ≤ 20% one

  7. Hyperpolarized 13C NMR lifetimes in the liquid-state: relating structures and T1 relaxation times

    NASA Astrophysics Data System (ADS)

    Parish, Christopher; Niedbalski, Peter; Hashami, Zohreh; Fidelino, Leila; Kovacs, Zoltan; Lumata, Lloyd

    Among the various attempts to solve the insensitivity problem in nuclear magnetic resonance (NMR), the physics-based technique dissolution dynamic nuclear polarization (DNP) is probably the most successful method of hyperpolarization or amplifying NMR signals. Using this technique, liquid-state NMR signal enhancements of several thousand-fold are expected for low-gamma nuclei such as carbon-13. The lifetimes of these hyperpolarized 13C NMR signals are directly related to their 13C spin-lattice relaxation times T1. Depending upon the 13C isotopic location, the lifetimes of hyperpolarized 13C compounds can range from a few seconds to minutes. In this study, we have investigated the hyperpolarized 13C NMR lifetimes of several 13C compounds with various chemical structures from glucose, acetate, citric acid, naphthalene to tetramethylallene and their deuterated analogs at 9.4 T and 25 deg C. Our results show that the 13C T1s of these compounds can range from a few seconds to more than 60 s at this field. Correlations between the chemical structures and T1 relaxation times will be discussed and corresponding implications of these results on 13C DNP experiments will be revealed. US Dept of Defense Award No. W81XWH-14-1-0048 and Robert A. Welch Foundation Grant No. AT-1877.

  8. Unraveling the complexity of protein backbone dynamics with combined (13)C and (15)N solid-state NMR relaxation measurements.

    PubMed

    Lamley, Jonathan M; Lougher, Matthew J; Sass, Hans Juergen; Rogowski, Marco; Grzesiek, Stephan; Lewandowski, Józef R

    2015-09-14

    Typically, protein dynamics involve a complex hierarchy of motions occurring on different time scales between conformations separated by a range of different energy barriers. NMR relaxation can in principle provide a site-specific picture of both the time scales and amplitudes of these motions, but independent relaxation rates sensitive to fluctuations in different time scale ranges are required to obtain a faithful representation of the underlying dynamic complexity. This is especially pertinent for relaxation measurements in the solid state, which report on dynamics in a broader window of time scales by more than 3 orders of magnitudes compared to solution NMR relaxation. To aid in unraveling the intricacies of biomolecular dynamics we introduce (13)C spin-lattice relaxation in the rotating frame (R1ρ) as a probe of backbone nanosecond-microsecond motions in proteins in the solid state. We present measurements of (13)C'R1ρ rates in fully protonated crystalline protein GB1 at 600 and 850 MHz (1)H Larmor frequencies and compare them to (13)C'R1, (15)N R1 and R1ρ measured under the same conditions. The addition of carbon relaxation data to the model free analysis of nitrogen relaxation data leads to greatly improved characterization of time scales of protein backbone motions, minimizing the occurrence of fitting artifacts that may be present when (15)N data is used alone. We also discuss how internal motions characterized by different time scales contribute to (15)N and (13)C relaxation rates in the solid state and solution state, leading to fundamental differences between them, as well as phenomena such as underestimation of picosecond-range motions in the solid state and nanosecond-range motions in solution.

  9. Ultrasound Devulcanization of Natural Rubber, Studied by NMR Relaxation and Diffusion

    NASA Astrophysics Data System (ADS)

    von Meerwall, E.

    2005-03-01

    In support of recycling of industrial rubbers, we have studied the effect of intense ultrasound on unfilled natural rubber networks using proton and carbon transverse NMR relaxation and diffusion, sol extraction, and bulk characterization. At 70.5^o C the proton echo decay exhibits three components, due to entangled sol and crosslinked network; unentangled polymeric sol plus dangling chain ends; and oligomer remnants. Contrary to the 13C results which indicate backbone mobilities decreasing with sonication (hence with increasing sol fraction), all 1H component T2 values, hence intermolecular mobilities, increase by similar modest factors; the network component amplitude decreases strongly. Diffusion of unentangled sol is sharply bimodal, arising from intermediate fractions and unreactive oligomers. Both diffusion rates decrease slightly with sonication in spite of plasticization by sol, because degradation adds sol primarily of intermediate molecular weights. We compare these results with our earlier work in SBR. Although ultrasound devulcanization does not recover many properties of the virgin melt, recyclability is not compromised.

  10. Ultrasound Treatment of Polyisoprene Rubber, Studied by NMR Relaxation and Diffusion.

    NASA Astrophysics Data System (ADS)

    von Meerwall, E.; Sun, X. M.; Joshi, T.; Isayev, A. I.

    2006-10-01

    In support of rubber recycling, we have studied the effect of intense ultrasound on unfilled cis-polyisoprene (PI) melts and networks using proton NMR T2 relaxation and pulsed-gradient diffusion. At 70.5 deg.C the echo decays show two components, due to entangled sol and crosslinked network; and unentangled sol, dangling ends, and oligomers. Component T2 values, hence intermolecular mobilities, increase with sonication, with modest changes in relative amplitudes. The high melt molecular weight(M) without a low-M tail precluded diffusion measurements. We then examined PI melts degraded by ultrasound with and without subsequent vulcanization. Here the T2 decays are consistent with three components. Sonication shifts and broadens the M-distribution but produces no network. Curing generates at least 94% network, lowers all mobilities, and decreases the proportions of unentangled sol and of oligomers. The diffusion spectrum is bimodal, arising from intermediate fractions and oligomeric species. Both diffusion rates and all T2 values increase slightly with ultrasound amplitude. We compare these results with our earlier work in natural rubber.

  11. Surface-NMR measurements of the longitudinal relaxation time T1 in a homogeneous sandy aquifer in Skive, Denmark

    NASA Astrophysics Data System (ADS)

    Walbrecker, J.; Behroozmand, A.

    2011-12-01

    Efficient groundwater management requires reliable means of characterizing shallow groundwater aquifers. One key parameter in this respect is hydraulic conductivity. Surface nuclear magnetic resonance (NMR) is a geophysical exploration technique that can potentially provide this type of information in a noninvasive, cost-effective way. The technique is based on measuring the precession of nuclear spins of protons in groundwater molecules. It involves large loop antennas deployed on Earth's surface to generate electromagnetic pulses tuned to specifically excite and detect groundwater proton spins. Naturally, the excited state of spins is transitory - once excited, spins relax back to their equilibrium state. This relaxation process is strongly influenced by the spin environment, which, in the case of groundwater, is defined by the aquifer. By employing empirical relations, changes in relaxation behavior can be used to identify changes in aquifer hydraulic conductivity, making the NMR relaxation signal a very important piece of information. Particularly, efforts are made to record the longitudinal relaxation parameter T1, because it is known from laboratory studies that it often reliably correlates with hydraulic conductivity, even in the presence of magnetic species. In surface NMR, T1 data are collected by recording the NMR signal amplitude following two sequential excitation pulses as a function of the delay time τ between the two pulses. In conventional acquisition, the two pulses have a mutual phase shift of π. Based on theoretical arguments it was recently shown that T1 times acquired according to this conventional surface-NMR scheme are systematically biased. It was proposed that the bias can be minimized by cycling the phase of the two pulses between π and zero in subsequent double-pulse experiments, and subtracting the resulting signal amplitudes (phase-cycled pseudosaturation recovery scheme, pcPSR). We present the first surface-NMR T1 data set recorded

  12. The Effect of Magnetic Field Inhomogeneity on the Transverse Relaxation of Quadrupolar Nuclei Measured by Multiple Quantum Filtered NMR

    NASA Astrophysics Data System (ADS)

    Eliav, U.; Kushnir, T.; Knubovets, T.; Itzchak, Y.; Navon, G.

    1997-09-01

    The effects of magnetic fieldsB0andB1inhomogeneities on techniques which are commonly used for the measurements of triple-quantum-filtered (TQF) NMR spectroscopy of23Na in biological tissues are analyzed. The results of measurements by pulse sequences with and without refocusing ofB0inhomogeneities are compared. It is shown that without refocusing the errors in the measurement of the transverse relaxation times by TQF NMR spectroscopy may be as large as 100%, and thus, refocusing of magnetic field inhomogeneity is mandatory. Theoretical calculations demonstrate that without refocusingB0inhomogeneities the spectral width and phase depend on the interpulse time intervals, thus, leading to errors in the measured relaxation times. It is shown that pulse sequences that were used for the refocusing of the magnetic field (B0) inhomogeneity also reduce the sensitivity of the experimental results to radiofrequency (B1) magnetic field inhomogeneity.

  13. Probing the transient dark state of substrate binding to GroEL by relaxation-based solution NMR.

    PubMed

    Libich, David S; Fawzi, Nicolas L; Ying, Jinfa; Clore, G Marius

    2013-07-09

    The mechanism whereby the prototypical chaperonin GroEL performs work on substrate proteins has not yet been fully elucidated, hindered by lack of detailed structural and dynamic information on the bound substrate. Previous investigations have produced conflicting reports on the state of GroEL-bound polypeptides, largely due to the transient and dynamic nature of these complexes. Here, we present a unique approach, based on combined analysis of four complementary relaxation-based NMR experiments, to probe directly the "dark" NMR-invisible state of the model, intrinsically disordered, polypeptide amyloid β (Aβ40) bound to GroEL. The four NMR experiments, lifetime line-broadening, dark-state exchange saturation transfer, relaxation dispersion, and small exchange-induced chemical shifts, are dependent in different ways on the overall exchange rates and populations of the free and bound states of the substrate, as well as on residue-specific dynamics and structure within the bound state as reported by transverse magnetization relaxation rates and backbone chemical shifts, respectively. Global fitting of all the NMR data shows that the complex is transient with a lifetime of <1 ms, that binding involves two predominantly hydrophobic segments corresponding to predicted GroEL consensus binding sequences, and that the structure of the bound polypeptide remains intrinsically and dynamically disordered with minimal changes in secondary structure propensity relative to the free state. Our results establish a unique method to observe NMR-invisible dynamic states of GroEL-bound substrates and to describe at atomic resolution the events between substrate binding and encapsulation that are crucial for understanding the normal and stress-related metabolic function of chaperonins.

  14. Magnetic field dependence of the distribution of NMR relaxation times in the living human brain.

    PubMed

    Oros-Peusquens, A M; Laurila, M; Shah, N J

    2008-03-01

    the bulk white and grey matter T1 values was well reproduced by both Bottomley's [1] and Fischer's [2] formulae, with parameters taken from the literature. The separation between the centroids was, however, either overestimated or underestimated by the two formulae. The width of the T1 distributions was found to increase with increasing field. The study of the field dependence of the NMR relaxation times is expected to allow for better differentiation between regions which are structurally different, provide a better insight into the microscopic structure of the brain and the molecular substrate of its function.

  15. Probing RNA dynamics via longitudinal exchange and CPMG relaxation dispersion NMR spectroscopy using a sensitive 13C-methyl label.

    PubMed

    Kloiber, Karin; Spitzer, Romana; Tollinger, Martin; Konrat, Robert; Kreutz, Christoph

    2011-05-01

    The refolding kinetics of bistable RNA sequences were studied in unperturbed equilibrium via (13)C exchange NMR spectroscopy. For this purpose a straightforward labeling technique was elaborated using a 2'-(13)C-methoxy uridine modification, which was prepared by a two-step synthesis and introduced into RNA using standard protocols. Using (13)C longitudinal exchange NMR spectroscopy the refolding kinetics of a 20 nt bistable RNA were characterized at temperatures between 298 and 310K, yielding the enthalpy and entropy differences between the conformers at equilibrium and the activation energy of the refolding process. The kinetics of a more stable 32 nt bistable RNA could be analyzed by the same approach at elevated temperatures, i.e. at 314 and 316 K. Finally, the dynamics of a multi-stable RNA able to fold into two hairpin- and a pseudo-knotted conformation was studied by (13)C relaxation dispersion NMR spectroscopy.

  16. Sodium-23 NMR analysis of human whole blood, erythrocytes, and plasma. Chemical shift, spin relaxation, and intracellular sodium concentration studies

    NASA Astrophysics Data System (ADS)

    Pettegrew, Jay W.; Woessner, Donald E.; Minshew, Nancy J.; Glonek, Thomas

    Sodium-23 NMR analysis was performed on freshly obtained human whole blood, erythrocytes, and plasma. The intracellular and extracellular sodium signals were separated by adding dysprosium: tripolyphosphate to the plasma bathing the erythrocytes. Quantitation of the intracellular sodium content was easily accomplished by sodium NMR and was shown to agree well with the values obtained by flame photometry. T1 and T2 relaxation studies demonstrated that the sodium in human plasma and within human erythrocytes is substantially different in its physical characteristics than sodium in aqueous solution, and that some fraction of the plasma and erythrocyte sodium is relatively immobilized. Sodium NMR would appear therefore to be a useful method for studying sodium biology in inherited and acquired human diseases.

  17. Dipolar cross-relaxation modulates signal amplitudes in the 1H NMR spectrum of hyperpolarized [ 13C]formate

    NASA Astrophysics Data System (ADS)

    Merritt, Matthew E.; Harrison, Crystal; Mander, William; Malloy, Craig R.; Dean Sherry, A.

    2007-12-01

    The asymmetry in the doublet of a spin coupled to hyperpolarized 13C has been used previously to measure the initial polarization of 13C. We tested the hypothesis that a single observation of the 1H NMR spectrum of hyperpolarized 13C formate monitors 13C polarization. Depending on the microwave frequency during the polarization process, in-phase or out-of-phase doublets were observed in the 1H NMR spectrum. Even in this simple two-spin system, 13C polarization was not reflected in the relative area of the JCH doublet components due to strong heteronuclear cross-relaxation. The Solomon equations were used to model the proton signal as a function of time after polarization and to estimate 13C polarization from the 1H NMR spectra.

  18. NMR quantification of diffusional exchange in cell suspensions with relaxation rate differences between intra and extracellular compartments

    PubMed Central

    Eriksson, Stefanie; Elbing, Karin; Söderman, Olle; Lindkvist-Petersson, Karin; Topgaard, Daniel

    2017-01-01

    Water transport across cell membranes can be measured non-invasively with diffusion NMR. We present a method to quantify the intracellular lifetime of water in cell suspensions with short transverse relaxation times, T2, and also circumvent the confounding effect of different T2 values in the intra- and extracellular compartments. Filter exchange spectroscopy (FEXSY) is specifically sensitive to exchange between compartments with different apparent diffusivities. Our investigation shows that FEXSY could yield significantly biased results if differences in T2 are not accounted for. To mitigate this problem, we propose combining FEXSY with diffusion-relaxation correlation experiment, which can quantify differences in T2 values in compartments with different diffusivities. Our analysis uses a joint constrained fitting of the two datasets and considers the effects of diffusion, relaxation and exchange in both experiments. The method is demonstrated on yeast cells with and without human aquaporins. PMID:28493928

  19. A suite of Mathematica notebooks for the analysis of protein main chain 15N NMR relaxation data.

    PubMed

    Spyracopoulos, Leo

    2006-12-01

    A suite of Mathematica notebooks has been designed to ease the analysis of protein main chain 15N NMR relaxation data collected at a single magnetic field strength. Individual notebooks were developed to perform the following tasks: nonlinear fitting of 15N-T1 and -T2 relaxation decays to a two parameter exponential decay, calculation of the principal components of the inertia tensor from protein structural coordinates, nonlinear optimization of the principal components and orientation of the axially symmetric rotational diffusion tensor, model-free analysis of 15N-T1, -T2, and {1H}-15N NOE data, and reduced spectral density analysis of the relaxation data. The principle features of the notebooks include use of a minimal number of input files, integrated notebook data management, ease of use, cross-platform compatibility, automatic visualization of results and generation of high-quality graphics, and output of analyses in text format.

  20. Revisiting spin-lattice relaxation time measurements for dilute spins in high-resolution solid-state NMR spectroscopy.

    PubMed

    Fu, Riqiang; Li, Jun; Cui, Jingyu; Peng, Xinhua

    2016-07-01

    Numerous nuclear magnetic resonance (NMR) measurements of spin-lattice relaxation times (T1S) for dilute spins such as (13)C have led to investigations of the motional dynamics of individual functional groups in solid materials. In this work, we revisit the Solomon equations and analyze how the heteronuclear cross relaxation between the dilute S (e.g. (13)C) and abundant I (e.g. (1)H) spins affects the measured T1S values in solid-state NMR in the absence of (1)H saturation during the recovery time. It is found theoretically that at the beginning of the S spin magnetization recovery, the existence of non-equilibrium I magnetization introduces the heteronuclear cross relaxation effect onto the recovery of the S spin magnetization and confirmed experimentally that such a heteronuclear cross relaxation effect results in the recovery overshoot phenomena for the dilute spins when T1S is on the same order of T1H, leading to inaccurate measurements of the T1S values. Even when T1S is ten times larger than T1H, the heteronuclear cross relaxation effect on the measured T1S values is still noticeable. Furthermore, this cross relaxation effect on recovery trajectory of the S spins can be manipulated and even suppressed by preparing the initial I and S magnetization, so as to obtain the accurate T1S values. A sample of natural abundance l-isoleucine powder has been used to demonstrate the T1S measurements and their corresponding measured T1C values under various experimental conditions.

  1. 87Rb spin-lattice relaxation times in ferroelectric-paraelectric-incommensurate phases of Rb2CoBr4 using static NMR and MAS NMR

    NASA Astrophysics Data System (ADS)

    Lim, Ae Ran

    2017-04-01

    To better elucidate the structural properties of Rb2CoBr4 in paraelectric, incommensurate, and ferroelectric phases, we studied the 87Rb nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation times in laboratory frame T1 and in rotating frame T1ρ. The resonance frequency and the chemical shift do not change abruptly near the phase transition temperature of Ti = 333 K and TC = 192 K, whereas T1 and T1ρ display discontinuous changes near Ti and TC. The abrupt changes in the relaxation times near these temperatures seem to be a result of the structural phase transitions. The results are distinctly different from those reported for Rb2CoCl4.

  2. Acceleration of natural-abundance solid-state MAS NMR measurements on bone by paramagnetic relaxation from gadolinium-DTPA

    NASA Astrophysics Data System (ADS)

    Mroue, Kamal H.; Zhang, Rongchun; Zhu, Peizhi; McNerny, Erin; Kohn, David H.; Morris, Michael D.; Ramamoorthy, Ayyalusamy

    2014-07-01

    Reducing the data collection time without affecting the signal intensity and spectral resolution is one of the major challenges for the widespread application of multidimensional nuclear magnetic resonance (NMR) spectroscopy, especially in experiments conducted on complex heterogeneous biological systems such as bone. In most of these experiments, the NMR data collection time is ultimately governed by the proton spin-lattice relaxation times (T1). For over two decades, gadolinium(III)-DTPA (Gd-DTPA, DTPA = Diethylene triamine pentaacetic acid) has been one of the most widely used contrast-enhancement agents in magnetic resonance imaging (MRI). In this study, we demonstrate that Gd-DTPA can also be effectively used to enhance the longitudinal relaxation rates of protons in solid-state NMR experiments conducted on bone without significant line-broadening and chemical-shift-perturbation side effects. Using bovine cortical bone samples incubated in different concentrations of Gd-DTPA complex, the 1H T1 values were calculated from data collected by 1H spin-inversion recovery method detected in natural-abundance 13C cross-polarization magic angle spinning (CPMAS) NMR experiments. Our results reveal that the 1H T1 values can be successfully reduced by a factor of 3.5 using as low as 10 mM Gd-DTPA without reducing the spectral resolution and thus enabling faster data acquisition of the 13C CPMAS spectra. These results obtained from 13C-detected CPMAS experiments were further confirmed using 1H-detected ultrafast MAS experiments on Gd-DTPA doped bone samples. This approach considerably improves the signal-to-noise ratio per unit time of NMR experiments applied to bone samples by reducing the experimental time required to acquire the same number of scans.

  3. Origin of abrupt rise in deuteron NMR longitudinal relaxation times of protein methyl groups below 90 K.

    PubMed

    Vugmeyster, Liliya; Ostrovsky, Dmitry; Lipton, Andrew S

    2013-05-23

    In order to examine the origin of the abrupt change in the temperature dependence of (2)H NMR longitudinal relaxation times observed previously for methyl groups of L69 in the hydrophobic core of villin headpiece protein at around 90 K (Vugmeyster et al. J. Am. Chem. Soc. 2010, 132, 4038-4039), we extended the measurements to several other methyl groups in the hydrophobic core. We show that, for all methyl groups, relaxation times experience a dramatic jump several orders of magnitude around this temperature. Theoretical modeling supports the conclusion that the origin of the apparent transition in the relaxation times is due to the existence of the distribution of conformers distinguished by their activation energy for methyl three-site hops. It is also crucial to take into account the differential contribution of individual conformers into overall signal intensity. When a particular conformer approaches the regime at which its three-site hop rate constant is on the order of the quadrupolar coupling interaction constant, the intensity of the signal due to this conformer experiences a sharp drop, thus changing the balance of the contributions of different conformers into the overall signal. As a result, the observed apparent transition in the relaxation rates can be explained without the assumption of an underlying transition in the rate constants. This work in combination with earlier results also shows that the model based on the distribution of conformers explains the relaxation behavior in the entire temperature range between 300 and 70 K.

  4. Origin of Abrupt Rise in Deuteron NMR Longitudinal Relaxation Times of Protein Methyl Groups Below 90 K

    SciTech Connect

    Vugmeyster, Liliya; Ostrovsky, Dmitry; Lipton, Andrew S.

    2013-05-23

    In order to examine the origin of the abrupt change in the temperature dependence of NMR longitudinal relaxation times observed earlier for methyl groups of L69 in the hydrophobic core of villin headpiece protein at around 90 K (Vugmeyster et al. J. Am. Chem. Soc. 2010, 132, 4038), we extended the measurements to several other methyl groups in the hydrophobic core. We show that for all methyl groups, relaxation times experience a dramatic jump several orders of magnitude around this temperature. Theoretical modeling supports the conclusion that the origin of the apparent transition in the relaxation times is due to the existence of the distribution of conformers distinguished by their activation energy for methyl three-site hops. It is also crucial to take into account the differential contribution of individual conformers into overall signal intensity. When a particular conformer approaches the regime at which its three-site hops rate constant is on the order of the quadrupolar coupling interaction constant, the intensity of the signal due to this conformer experiences a sharp drop, thus changing the balance of the contributions of different conformers into the overall signal. As a result, the observed apparent transition in the relaxation rates can be explained without the assumption of an underlying transition in the rate constants. This work in combination with earlier results also shows that the model based on the distribution of conformers explains the relaxation behavior in the entire temperature range between 300-70 K.

  5. Rapid and simple determination of T1 relaxation times in time-domain NMR by Continuous Wave Free Precession sequence

    NASA Astrophysics Data System (ADS)

    Moraes, Tiago Bueno; Monaretto, Tatiana; Colnago, Luiz Alberto

    2016-09-01

    Longitudinal (T1) and transverse (T2) relaxation times have been widely used in time-domain NMR (TD-NMR) to determine several physicochemical properties of petroleum, polymers, and food products. The measurement of T2 through the CPMG pulse sequence has been used in most of these applications because it denotes a rapid, robust method. On the other hand, T1 has been occasionally used in TD-NMR due to the long measurement time required to collect multiple points along the T1 relaxation curve. Recently, several rapid methods to measure T1 have been proposed. Those methods based upon single shot, known as Continuous Wave Free Precession (CWFP) pulse sequences, have been employed in the simultaneous measurement of T1 and T2 in a rapid fashion. However, these sequences can be used exclusively in instrument featuring short dead time because the magnitude of the signal at thermal equilibrium is required. In this paper, we demonstrate that a special CWFP sequence with a low flip angle can be a simple and rapid method to measure T1 regardless of instruments dead time. Experimental results confirmed that the method called CWFP-T1 may be used to measure both single T1 value and T1 distribution in heterogeneous samples. Therefore, CWFP-T1 sequence can be a feasible alternative to CPMG in the determination of physicochemical properties, particularly in processes where fast protocols are requested such as industrial applications.

  6. Ligand-Detected Relaxation Dispersion NMR Spectroscopy: Dynamics of preQ1–RNA Binding**

    PubMed Central

    Moschen, Thomas; Wunderlich, Christoph Hermann; Spitzer, Romana; Levic, Jasmin; Micura, Ronald; Tollinger, Martin; Kreutz, Christoph

    2015-01-01

    An NMR-based approach to characterizing the binding kinetics of ligand molecules to biomolecules, like RNA or proteins, by ligand-detected Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments is described. A 15N-modified preQ1 ligand is used to acquire relaxation dispersion experiments in the presence of low amounts of the Fsu class I preQ1 aptamer RNA, and increasing ligand concentrations to probe the RNA small molecule interaction. Our experimental data strongly support the conformational selection mechanism postulated. The approach gives direct access to two parameters of a ligand–receptor interaction: the off rate and the population of the small molecule–receptor complex. A detailed description of the kinetics underlying the ligand binding process is of crucial importance to fully understanding a riboswitch’s function and to evaluate potential new antibiotics candidates targeting the noncoding RNA species. Ligand-detected NMR relaxation dispersion experiments represent a valuable diagnostic tool for the characterization of binding mechanisms. PMID:25403518

  7. A novel analysis for the NMR magic sandwich echo in polymers: application to the α-relaxation in polybutadiene

    NASA Astrophysics Data System (ADS)

    Pieruccini, Marco; Sturniolo, Simone; Corti, Maurizio; Rigamonti, Attilio

    2015-11-01

    On the basis of a method to describe the relaxation dynamics in an ensemble of spin pairs, an analytical expression is derived for the magic sandwich echo refocusing efficiency of 1H-NMR signals from systems where dipolar interaction dominates. At the sake of illustration the method is applied to the analysis of the α-relaxation in poly(butadiene). The Vogel-Fulcher-Tammann behaviour of the central relaxation rates, derived by fitting the refocusing efficiency as a function of the temperature, follows very well independent measurements performed with stimulated echo 2H-NMR experiments. Comparison with literature data worked out by broad band dielectric spectroscopy also shows very good agreement. In the framework of an Havriliak-Negami representation of the distribution of correlation times, information about width and asymmetry of the frequency profile is also provided by the analysis. This novel method is believed to represent a suitable path to extract basic information on the motional distribution in a variety of similar systems.

  8. NMR relaxation of neritic carbonates: An integrated petrophysical and petrographical approach

    NASA Astrophysics Data System (ADS)

    Vincent, Benoit; Fleury, Marc; Santerre, Yannick; Brigaud, Benjamin

    2011-05-01

    A set of carbonate outcrop samples, covering a wide range of the sedimentary textures and depositional environments existing on carbonate systems, was studied through an integrated petrographical and petrophysical approach. With the aim of improving the understanding of the NMR (Nuclear Magnetic Resonance) signal of carbonates, this work is: 1) providing an atlas for various carbonate reservoir rock-types, 2) providing a workflow for integrating geological and petrophysical data and, 3) documenting common shortfalls in NMR/MICP analyses in carbonates. The petrographical investigation includes thin section and SEM (Secondary Electron Microscope) observations, whereas petrophysical investigation includes porosity (Φ), permeability (K), NMR, MICP (Mercury Injection Capillary Pressure), and specific surface area (BET) measurements. On the basis of NMR and MICP data, 4 groups of samples were identified: (1) microporous samples, (2) micro-mesoporous samples, (3) wide multimodal samples, and (4) atypical samples. The microporous samples allow us to define a maximum NMR threshold for microporosity at a T 2 of 200 ms. NMR and MICP response of the investigated carbonates are often comparable in terms of modal distribution (microporous, micro-mesoporous and wide multimodal samples). In particular, micritization, a well known but underestimated early diagenetic process, tends to homogenize the NMR signal of primarily different sedimentary facies. A grainstone with heavily micritized grains can display well sorted unimodal NMR and MICP signatures very similar, even identical, to a mudstone-wackestone. Their signatures are comparable to that of a simple sphere packing model. On the contrary, several samples (labeled atypical samples) show a discrepancy between NMR and MICP response. This discrepancy is explained by the fact that MICP can be affected by the physical connectivity of the pore network, in case of disseminated and isolated molds in a micrite matrix for instance

  9. Molecular dynamics of regioregular poly(3-hexylthiophene) investigated by NMR relaxation and an interpretation of temperature dependent optical absorption.

    PubMed

    Yazawa, Koji; Inoue, Yoshio; Shimizu, Tadashi; Tansho, Masataka; Asakawa, Naoki

    2010-01-28

    The molecular structure and dynamics of regioregulated poly(3-hexylthiophene) (P3HT) were investigated using high-resolution solid-state (13)C nuclear magnetic resonance (NMR) and optical absorption spectroscopies. A crystal (C)-plastic crystal (PC) transition induced by the molecular motion of the aliphatic side group was observed for P3HT in the temperature dependence analysis of (13)C NMR spectra and spin-lattice relaxation time (T(1C)). The aliphatic side group motion in the crystalline state weakened intermolecular pi-pi interaction, resulting in the blue shift of the characteristic absorption of the interchain exciton. Above the transition temperature, the thiophene twisting motion induces not only further collapsing of the intermolecular interaction but also localizing of the intrachain exciton, leading to the blue shift of the absorption of both the inter- and intrachain exciton.

  10. Analysis of 31P MAS NMR spectra and transversal relaxation of bacteriophage M13 and tobacco mosaic virus.

    PubMed Central

    Magusin, P C; Hemminga, M A

    1994-01-01

    Phosphorus magic angle spinning nuclear magnetic resonance (NMR) spectra and transversal relaxation of M13 and TMV are analyzed by use of a model, which includes both local backbone motions of the encapsulated nucleic acid molecules and overall rotational diffusion of the rod-shaped virions about their length axis. Backbone motions influence the sideband intensities by causing a fast restricted reorientation of the phosphodiesters. To evaluate their influence on the observed sideband patterns, we extend the model that we used previously to analyze nonspinning 31P NMR lineshapes (Magusin, P.C.M.M., and M. A. Hemminga. 1993a. Biophys. J. 64:1861-1868) to magic angle spinning NMR experiments. Backbone motions also influence the conformation of the phosphodiesters, causing conformational averaging of the isotropic chemical shift, which offers a possible explanation for the various linewidths of the centerband and the sidebands observed for M13 gels under various conditions. The change of the experimental lineshape of M13 as a function of temperature and hydration is interpreted in terms of fast restricted fluctuation of the dihedral angles between the POC and the OCH planes on both sides of the 31P nucleus in the nucleic acid backbone. Backbone motions also seem to be the main cause of transversal relaxation measured at spinning rates of 4 kHz or higher. At spinning rates less than 2 kHz, transversal relaxation is significantly faster. This effect is assigned to slow, overall rotation of the rod-shaped M13 phage about its length axis. Equations are derived to simulate the observed dependence of T2e on the spinning rate. PMID:8038391

  11. A nonlinear BOLD model accounting for refractory effect by applying the longitudinal relaxation in NMR to the linear BOLD model.

    PubMed

    Jung, Kwan-Jin

    2009-09-01

    A mathematical model to regress the nonlinear blood oxygen level-dependent (BOLD) fMRI signal has been developed by incorporating the refractory effect into the linear BOLD model of the biphasic gamma variate function. The refractory effect was modeled as a relaxation of two separate BOLD capacities corresponding to the biphasic components of the BOLD signal in analogy with longitudinal relaxation of magnetization in NMR. When tested with the published fMRI data of finger tapping, the nonlinear BOLD model with the refractory effect reproduced the nonlinear BOLD effects such as reduced poststimulus undershoot and saddle pattern in a prolonged stimulation as well as the reduced BOLD signal for repetitive stimulation.

  12. The dark energy of proteins comes to light: Conformational entropy and its role in protein function revealed by NMR relaxation

    PubMed Central

    Wand, A. Joshua

    2012-01-01

    Historically it has been virtually impossible to experimentally determine the contribution of residual protein entropy to fundamental protein activities such as the binding of ligands. Recent progress has illuminated the possibility of employing NMR relaxation methods to quantitatively determine the role of changes in conformational entropy in molecular recognition by proteins. The method rests on using fast internal protein dynamics as a proxy. Initial results reveal a large and variable role for conformational entropy in the binding of ligands by proteins. Such a role for conformational entropy in molecular recognition has significant implications for enzymology, signal transduction, allosteric regulation and the development of protein-directed pharmaceuticals. PMID:23246280

  13. NMR Water Self–Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions

    PubMed Central

    Bai, Ruiliang; Basser, Peter J.; Briber, Robert M.; Horkay, Ferenc

    2013-01-01

    Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca2+ and Na+. Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na+ on the mobility of water molecules was practically undetectable. By contrast, addition of Ca2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced. PMID:24409001

  14. NMR Water Self-Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions.

    PubMed

    Bai, Ruiliang; Basser, Peter J; Briber, Robert M; Horkay, Ferenc

    2014-03-15

    Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca(2+) and Na(+). Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na(+) on the mobility of water molecules was practically undetectable. By contrast, addition of Ca(2+) strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced.

  15. Site-resolved 2H relaxation experiments in solid materials by global line-shape analysis of MAS NMR spectra

    NASA Astrophysics Data System (ADS)

    Lindh, E. L.; Stilbs, P.; Furó, I.

    2016-07-01

    We investigate a way one can achieve good spectral resolution in 2H MAS NMR experiments. The goal is to be able to distinguish between and study sites in various deuterated materials with small chemical shift dispersion. We show that the 2H MAS NMR spectra recorded during a spin-relaxation experiment are amenable to spectral decomposition because of the different evolution of spectral components during the relaxation delay. We verify that the results are robust by global least-square fitting of the spectral series both under the assumption of specific line shapes and without such assumptions (COmponent-REsolved spectroscopy, CORE). In addition, we investigate the reliability of the developed protocol by analyzing spectra simulated with different combinations of spectral parameters. The performance is demonstrated in a model material of deuterated poly(methacrylic acid) that contains two 2H spin populations with similar chemical shifts but different quadrupole splittings. In 2H-exchanged cellulose containing two 2H spin populations with very similar chemical shifts and quadrupole splittings, the method provides new site-selective information about the molecular dynamics.

  16. Use of cross-correlated NMR relaxation for the study of motional anisotropy of liquid crystals

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Rangeet; Kumar, Anil

    2003-04-01

    A method to measure the rotational diffusion coefficients of a liquid crystal based on the measurements of auto and cross-correlated relaxation is presented here. We report the measurements of cross-correlations between the relaxation processes originating from the chemical shift anisotropy (CSA) of 13C and its dipolar coupling with the attached proton, for various carbons in a liquid crystal. The spectral densities are expressed as a function of motional parameters, using extended Lipari-Szabo model-free approach. These motional parameters were extracted from the measured self-relaxation, cross-relaxation and the cross-correlation rates. The potential of this method is demonstrated by the determination of the rotational diffusion coefficients of N-4-methoxybenzylidene-4-butylaniline (MBBA) at 297 K undergoing magic angle sample spinning.

  17. Spectral density mapping at multiple magnetic fields suitable for (13)C NMR relaxation studies.

    PubMed

    Kadeřávek, Pavel; Zapletal, Vojtěch; Fiala, Radovan; Srb, Pavel; Padrta, Petr; Přecechtělová, Jana Pavlíková; Šoltésová, Mária; Kowalewski, Jozef; Widmalm, Göran; Chmelík, Josef; Sklenář, Vladimír; Žídek, Lukáš

    2016-05-01

    Standard spectral density mapping protocols, well suited for the analysis of (15)N relaxation rates, introduce significant systematic errors when applied to (13)C relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and (13)C frequencies can be obtained from data acquired at three magnetic fields for uniformly (13)C-labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions. Copyright © 2016 Elsevier Inc. All rights reserved.

  18. Spectral density mapping at multiple magnetic fields suitable for 13C NMR relaxation studies

    NASA Astrophysics Data System (ADS)

    Kadeřávek, Pavel; Zapletal, Vojtěch; Fiala, Radovan; Srb, Pavel; Padrta, Petr; Přecechtělová, Jana Pavlíková; Šoltésová, Mária; Kowalewski, Jozef; Widmalm, Göran; Chmelík, Josef; Sklenář, Vladimír; Žídek, Lukáš

    2016-05-01

    Standard spectral density mapping protocols, well suited for the analysis of 15N relaxation rates, introduce significant systematic errors when applied to 13C relaxation data, especially if the dynamics is dominated by motions with short correlation times (small molecules, dynamic residues of macromolecules). A possibility to improve the accuracy by employing cross-correlated relaxation rates and on measurements taken at several magnetic fields has been examined. A suite of protocols for analyzing such data has been developed and their performance tested. Applicability of the proposed protocols is documented in two case studies, spectral density mapping of a uniformly labeled RNA hairpin and of a selectively labeled disaccharide exhibiting highly anisotropic tumbling. Combination of auto- and cross-correlated relaxation data acquired at three magnetic fields was applied in the former case in order to separate effects of fast motions and conformational or chemical exchange. An approach using auto-correlated relaxation rates acquired at five magnetic fields, applicable to anisotropically moving molecules, was used in the latter case. The results were compared with a more advanced analysis of data obtained by interpolation of auto-correlated relaxation rates measured at seven magnetic fields, and with the spectral density mapping of cross-correlated relaxation rates. The results showed that sufficiently accurate values of auto- and cross-correlated spectral density functions at zero and 13C frequencies can be obtained from data acquired at three magnetic fields for uniformly 13C -labeled molecules with a moderate anisotropy of the rotational diffusion tensor. Analysis of auto-correlated relaxation rates at five magnetic fields represents an alternative for molecules undergoing highly anisotropic motions.

  19. Miscibility of nifedipine and hydrophilic polymers as measured by (1)H-NMR spin-lattice relaxation.

    PubMed

    Aso, Yukio; Yoshioka, Sumie; Miyazaki, Tamaki; Kawanishi, Tohru; Tanaka, Kazuyuki; Kitamura, Satoshi; Takakura, Asako; Hayashi, Takashi; Muranushi, Noriyuki

    2007-08-01

    The miscibility of a drug with excipients in solid dispersions is considered to be one of the most important factors for preparation of stable amorphous solid dispersions. The purpose of the present study was to elucidate the feasibility of (1)H-NMR spin-lattice relaxation measurements to assess the miscibility of a drug with excipients. Solid dispersions of nifedipine with the hydrophilic polymers poly(vinylpyrrolidone) (PVP), hydroxypropylmethylcellulose (HPMC) and alpha,beta-poly(N-5-hydroxypentyl)-L-aspartamide (PHPA) with various weight ratios were prepared by spray drying, and the spin-lattice relaxation decay of the solid dispersions in a laboratory frame (T(1) decay) and in a rotating frame (T(1rho) decay) were measured. T(1rho) decay of nifedipine-PVP solid dispersions (3 : 7, 5 : 5 and 7 : 3) was describable with a mono-exponential equation, whereas T(1rho) decay of nifedipine-PHPA solid dispersions (3 : 7, 4 : 6 and 5 : 5) was describable with a bi-exponential equation. Because a mono-exponential T(1rho) decay indicates that the domain sizes of nifedipine and polymer in solid dispersion are less than several nm, it is speculated that nifedipine is miscible with PVP but not miscible with PHPA. All the nifedipine-PVP solid dispersions studied showed a single glass transition temperature (T(g)), whereas two glass transitions were observed for the nifedipine-PHPA solid dispersion (3 : 7), thus supporting the above speculation. For nifedipine-HPMC solid dispersions (3 : 7 and 5 : 5), the miscibility of nifedipine and HPMC could not be determined by DSC measurements due to the lack of obviously evident T(g). In contrast, (1)H-NMR spin-lattice relaxation measurements showed that nifedipine and HPMC are miscible, since T(1rho) decay of the solid dispersions (3 : 7, 5 : 5 and 7 : 3) was describable with a mono-exponential equation. These results indicate that (1)H-NMR spin-lattice relaxation measurements are useful for assessing the miscibility of a drug and an

  20. Probing RNA dynamics via longitudinal exchange and CPMG relaxation dispersion NMR spectroscopy using a sensitive 13C-methyl label

    PubMed Central

    Kloiber, Karin; Spitzer, Romana; Tollinger, Martin; Konrat, Robert; Kreutz, Christoph

    2011-01-01

    The refolding kinetics of bistable RNA sequences were studied in unperturbed equilibrium via 13C exchange NMR spectroscopy. For this purpose a straightforward labeling technique was elaborated using a 2′-13C-methoxy uridine modification, which was prepared by a two-step synthesis and introduced into RNA using standard protocols. Using 13C longitudinal exchange NMR spectroscopy the refolding kinetics of a 20 nt bistable RNA were characterized at temperatures between 298 and 310 K, yielding the enthalpy and entropy differences between the conformers at equilibrium and the activation energy of the refolding process. The kinetics of a more stable 32 nt bistable RNA could be analyzed by the same approach at elevated temperatures, i.e. at 314 and 316 K. Finally, the dynamics of a multi-stable RNA able to fold into two hairpin- and a pseudo-knotted conformation was studied by 13C relaxation dispersion NMR spectroscopy. PMID:21252295

  1. Collisional cross-section of water molecules in vapour studied by means of 1H relaxation in NMR

    PubMed Central

    Mammoli, Daniele; Canet, Estel; Buratto, Roberto; Miéville, Pascal; Helm, Lothar; Bodenhausen, Geoffrey

    2016-01-01

    In gas phase, collisions that affect the rotational angular momentum lead to the return of the magnetization to its equilibrium (relaxation) in Nuclear Magnetic Resonance (NMR). To the best of our knowledge, the longitudinal relaxation rates R1 = 1/T1 of protons in H2O and HDO have never been measured in gas phase. We report R1 in gas phase in a field of 18.8 T, i.e., at a proton Larmor frequency ν0 = 800 MHz, at temperatures between 353 and 373 K and pressures between 9 and 101 kPa. By assuming that spin rotation is the dominant relaxation mechanism, we estimated the effective cross-section σJ for the transfer of angular momentum due to H2O-H2O and HDO-D2O collisions. Our results allow one to test theoretical predictions of the intermolecular potential of water in gas phase. PMID:28008913

  2. Intrinsic unfoldase/foldase activity of the chaperonin GroEL directly demonstrated using multinuclear relaxation-based NMR

    PubMed Central

    Libich, David S.; Tugarinov, Vitali; Clore, G. Marius

    2015-01-01

    The prototypical chaperonin GroEL assists protein folding through an ATP-dependent encapsulation mechanism. The details of how GroEL folds proteins remain elusive, particularly because encapsulation is not an absolute requirement for successful re/folding. Here we make use of a metastable model protein substrate, comprising a triple mutant of Fyn SH3, to directly demonstrate, by simultaneous analysis of three complementary NMR-based relaxation experiments (lifetime line broadening, dark state exchange saturation transfer, and Carr–Purcell–Meinboom–Gill relaxation dispersion), that apo GroEL accelerates the overall interconversion rate between the native state and a well-defined folding intermediate by about 20-fold, under conditions where the “invisible” GroEL-bound states have occupancies below 1%. This is largely achieved through a 500-fold acceleration in the folded-to-intermediate transition of the protein substrate. Catalysis is modulated by a kinetic deuterium isotope effect that reduces the overall interconversion rate between the GroEL-bound species by about 3-fold, indicative of a significant hydrophobic contribution. The location of the GroEL binding site on the folding intermediate, mapped from 15N, 1HN, and 13Cmethyl relaxation dispersion experiments, is composed of a prominent, surface-exposed hydrophobic patch. PMID:26124125

  3. Collisional cross-section of water molecules in vapour studied by means of 1H relaxation in NMR

    NASA Astrophysics Data System (ADS)

    Mammoli, Daniele; Canet, Estel; Buratto, Roberto; Miéville, Pascal; Helm, Lothar; Bodenhausen, Geoffrey

    2016-12-01

    In gas phase, collisions that affect the rotational angular momentum lead to the return of the magnetization to its equilibrium (relaxation) in Nuclear Magnetic Resonance (NMR). To the best of our knowledge, the longitudinal relaxation rates R1 = 1/T1 of protons in H2O and HDO have never been measured in gas phase. We report R1 in gas phase in a field of 18.8 T, i.e., at a proton Larmor frequency ν0 = 800 MHz, at temperatures between 353 and 373 K and pressures between 9 and 101 kPa. By assuming that spin rotation is the dominant relaxation mechanism, we estimated the effective cross-section σJ for the transfer of angular momentum due to H2O-H2O and HDO-D2O collisions. Our results allow one to test theoretical predictions of the intermolecular potential of water in gas phase.

  4. Applications of DNP-NMR for the measurement of heteronuclear T1 relaxation times

    NASA Astrophysics Data System (ADS)

    Day, Iain J.; Mitchell, John C.; Snowden, Martin J.; Davis, Adrian L.

    2007-08-01

    Measurement of heteronuclear spin-lattice relaxation times is hampered by both low natural abundance and low detection sensitivity. Combined with typically long relaxation times, this results in extended acquisition times which often renders the experiment impractical. Recently a variant of dynamic nuclear polarisation has been demonstrated in which enhanced nuclear spin polarisation, generated in the cryo-solid state, is transferred to the liquid state for detection. Combining this approach with small flip angle pulse trains, similar to the FLASH- T1 imaging sequence, allows the rapid determination of spin-lattice relaxation times. In this paper we explore this method and its application to the measurement of T1 for both carbon-13 and nitrogen-15 at natural abundance. The effects of RF inhomogeneity and the influence of proton decoupling in the context of this experiment are also investigated.

  5. Applications of DNP-NMR for the measurement of heteronuclear T1 relaxation times.

    PubMed

    Day, Iain J; Mitchell, John C; Snowden, Martin J; Davis, Adrian L

    2007-08-01

    Measurement of heteronuclear spin-lattice relaxation times is hampered by both low natural abundance and low detection sensitivity. Combined with typically long relaxation times, this results in extended acquisition times which often renders the experiment impractical. Recently a variant of dynamic nuclear polarisation has been demonstrated in which enhanced nuclear spin polarisation, generated in the cryo-solid state, is transferred to the liquid state for detection. Combining this approach with small flip angle pulse trains, similar to the FLASH-T(1) imaging sequence, allows the rapid determination of spin-lattice relaxation times. In this paper we explore this method and its application to the measurement of T(1) for both carbon-13 and nitrogen-15 at natural abundance. The effects of RF inhomogeneity and the influence of proton decoupling in the context of this experiment are also investigated.

  6. Mineralogical controls on NMR rock surface relaxivity: A case study of the Fontainebleau Sandstone

    NASA Astrophysics Data System (ADS)

    Livo, Kurt

    Pore size distribution is derived from nuclear magnetic resonance, but is scaled by surface relaxivity. While nuclear magnetic resonance studies generally focus on the difficulty of determining pore size distribution in unconventional shale reservoirs, there is a lack of discussion concerning pure quartz sandstones. Long surface relaxivity causes complications analyzing nuclear magnetic resonance data for pore size distribution determination. Currently, I am unaware of research that addresses the complicated pore size distribution determination in long relaxing, pure sandstone formations, which is essential to accurate downhole petrophysical modeling. The Fontainebleau sandstone is well known for its homogenous mineralogical makeup and wide range of porosity and permeability. The Hibernia sandstone exhibits a similar mineralogy and is characterized by a similar and porosity-permeability range to the Fontainebleau sandstones, but with a significantly higher portion of clay minerals (1-6%). I present systematic petrophysical properties such as porosity, pore size distribution from nuclear magnetic resonance transverse relaxation times, permeability, and volumetric magnetic susceptibility to aide in characterization of the Fontainebleau sandstone. Analysis of collected nuclear magnetic resonance data is then compared to other petrophysical studies from literature such as helium porosity and permeability, magnetic susceptibility, and electrical conductivity. I find that the lack of impurities on the grain surfaces of pure quartz samples imparts a lower surface relaxivity as compared to clay containing sandstones and makes nuclear magnetic resonance analysis more complex. Thus, inverted nuclear magnetic resonance data from cleaner outcrop samples incorrectly models pore size distribution without accounting for wider surface relaxivity variation and is improperly used when characterizing the Fontainebleau sandstone. This is further supported by evidence from less

  7. NMR relaxation of protein and water protons in diamagnetic hemoglobin solutions.

    PubMed

    Eisenstadt, M

    1985-07-02

    We have measured T1 and T2 of protein and water protons in hemoglobin solutions using broad-line pulse techniques; selective excitation and detection methods enabled the intrinsic protein and water relaxation rates, as well as the spin-transfer rate between them, to be obtained at 5, 10, and 20 MHz. Water and protein T1 data were also obtained at 100 and 200 MHz for hemoglobin in H2O/D2O mixtures by using commercial Fourier-transform instruments. The T1 data conform to a simple model of two well-mixed spin systems with single intrinsic relaxation times and an average spin-transfer rate, with each phase recovering from a radio-frequency excitation with a biexponential time dependence. At low frequencies, protein T1 and T2 agree reasonably with a model of dipolar relaxation of an array of fixed protons tumbling in solution, explicitly calculating methyl and methylene relaxation and using a continuum approximation for the others. Differing values in H2O and D2O are mainly ascribed to solvent viscosity. For water-proton relaxation, T1, T2, and spin transfer were measured for H2O and HDO, which enabled a separation of inter-and intramolecular contributions to relaxation. Despite such detail, few firm conclusions could be reached about hydration water. But it seems clear that few long-lived hydration sites are needed to explain T1 and T2, and the spin-transfer value mandates fewer than five sites with a lifetime longer than 10(-8) s.

  8. (1)H NMR Relaxation Study of a Magnetic Ionic Liquid as a Potential Contrast Agent.

    PubMed

    Daniel, Carla I; Vaca Chávez, Fabián; Portugal, Carla A M; Crespo, João G; Sebastião, Pedro J

    2015-09-03

    A proton nuclear magnetic relaxation dispersion (1)H NMRD study of the molecular dynamics in mixtures of magnetic ionic liquid [P66614][FeCl4] with [P66614][Cl] ionic liquid and mixtures of [P66614][FeCl4] with dimethyl sulfoxide (DMSO) is presented. The proton spin-lattice relaxation rate, R1, was measured in the frequency range of 8 kHz-300 MHz. The viscosity of the binary mixtures was measured as a function of an applied magnetic field, B, in the range of 0-2 T. In the case of DMSO/[P66614][FeCl4] the viscosity was found to be independent from the magnetic field, while in the case of the [P66614][Cl]/[P66614][FeCl4] system viscosity decreased with the increase of the magnetic field strength. The spin-lattice relaxation results were analyzed for all systems taking into account the relaxation mechanisms associated with the molecular motions with correlation times in a range between 10(-11) and 10(-7)s, usually observed by NMRD, and the paramagnetic relaxation contributions associated with the presence of the magnetic ions in the systems. In the case of the DMSO/[P66614][FeCl4] system the R1 dispersion shows the relaxation enhancement due to the presence of the magnetic ions, similar to that reported for contrast agents. For the [P66614][Cl]/[P66614][FeCl4] system, the R1 dispersion presents a much larger paramagnetic relaxation contribution, in comparison with that observed for the DMSO/[P66614][FeCl4] mixtures but different from that reported for other magnetic ionic liquid system. In the [P66614][Cl]/[P66614][FeCl4] system the relaxation enhancement associated with the paramagnetic ions is clearly not proportional to the concentration of magnetic ions, in contrast with what is observed for the DMSO/[P66614][FeCl4] system.

  9. Thermal diffusivity and nuclear spin relaxation: a continuous wave free precession NMR study.

    PubMed

    Venâncio, Tiago; Engelsberg, Mario; Azeredo, Rodrigo B V; Colnago, Luiz A

    2006-07-01

    Continuous wave free precession (CWFP) nuclear magnetic resonance is capable of yielding quantitative and easily obtainable information concerning the kinetics of processes that change the relaxation rates of the nuclear spins through the action of some external agent. In the present application, heat flow from a natural rubber sample to a liquid nitrogen thermal bath caused a large temperature gradient leading to a non-equilibrium temperature distribution. The ensuing local changes in the relaxation rates could be monitored by the decay of the CWFP signals and, from the decays, it was possible to ascertain the prevalence of a diffusive process and to obtain an average value for the thermal diffusivity.

  10. A Unique and Simple Approach to Improve Sensitivity in 15N-NMR Relaxation Measurements for NH3+ Groups: Application to a Protein-DNA Complex

    PubMed Central

    Nguyen, Dan; Lokesh, Ganesh L.R.; Volk, David E.; Iwahara, Junji

    2017-01-01

    NMR spectroscopy is a powerful tool for research on protein dynamics. In the past decade, there has been significant progress in the development of NMR methods for studying charged side chains. In particular, NMR methods for lysine side-chain NH3+ groups have been proven to be powerful for investigating the dynamics of hydrogen bonds or ion pairs that play important roles in biological processes. However, relatively low sensitivity has been a major practical issue in NMR experiments on NH3+ groups. In this paper, we present a unique and simple approach to improve sensitivity in 15N relaxation measurements for NH3+ groups. In this approach, the efficiency of coherence transfers for the desired components are maximized, whereas undesired anti-phase or multi-spin order components are purged through pulse schemes and rapid relaxation. For lysine side-chain NH3+ groups of a protein-DNA complex, we compared the data obtained with the previous and new pulse sequences under the same conditions and confirmed that the 15N relaxation parameters were consistent for these datasets. While retaining accuracy in measuring 15N relaxation, our new pulse sequences for NH3+ groups allowed an 82% increase in detection sensitivity of 15N longitudinal and transverse relaxation measurements. PMID:28809801

  11. A Unique and Simple Approach to Improve Sensitivity in (15)N-NMR Relaxation Measurements for NH₃⁺ Groups: Application to a Protein-DNA Complex.

    PubMed

    Nguyen, Dan; Lokesh, Ganesh L R; Volk, David E; Iwahara, Junji

    2017-08-15

    NMR spectroscopy is a powerful tool for research on protein dynamics. In the past decade, there has been significant progress in the development of NMR methods for studying charged side chains. In particular, NMR methods for lysine side-chain NH₃⁺ groups have been proven to be powerful for investigating the dynamics of hydrogen bonds or ion pairs that play important roles in biological processes. However, relatively low sensitivity has been a major practical issue in NMR experiments on NH₃⁺ groups. In this paper, we present a unique and simple approach to improve sensitivity in (15)N relaxation measurements for NH₃⁺ groups. In this approach, the efficiency of coherence transfers for the desired components are maximized, whereas undesired anti-phase or multi-spin order components are purged through pulse schemes and rapid relaxation. For lysine side-chain NH₃⁺ groups of a protein-DNA complex, we compared the data obtained with the previous and new pulse sequences under the same conditions and confirmed that the (15)N relaxation parameters were consistent for these datasets. While retaining accuracy in measuring (15)N relaxation, our new pulse sequences for NH₃⁺ groups allowed an 82% increase in detection sensitivity of (15)N longitudinal and transverse relaxation measurements.

  12. Very short NMR relaxation times of anions in ionic liquids: new pulse sequence to eliminate the acoustic ringing.

    PubMed

    Klimavicius, Vytautas; Gdaniec, Zofia; Balevicius, Vytautas

    2014-11-11

    NMR relaxation processes of anions were studied in two neat imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride. The spin-lattice and spin-spin relaxations of 81Br and 35Cl nuclei were found to be extremely fast due to very strong quadrupolar interactions. The determined relaxation rates are comparable with those observed in the solids or in some critical organic solute/water/salt systems. In order to eliminate the acoustic ringing of the probe-head during relaxation times measurements the novel pulse sequence has been devised. It is based on the conventional inversion recovery pulse sequence, however, instead of the last 90° pulse the subsequence of three 90° pulses applied along axes to fulfill the phase cycling condition is used. Using this pulse sequence it was possible to measure T1 for both studied nuclei. The viscosity measurements have been carried out and the rotational correlation times were calculated. The effective 35Cl quadrupolar coupling constant was found to be almost one order lower than that for 81Br, i.e. 1.8 MHz and 16.0 MHz, respectively. Taking into account the facts that the ratio of (Q(35Cl)/Q(81Br))2≈0.1 and EFG tensors on the anions are quite similar, analogous structural organizations are expected for both RTILs. The observed T1/T2 (1.27-1.44) ratios were found to be not sufficiently high to confirm the presence of long-living (on the time scale of ≥10(-8) s) mesoscopic structures or heterogeneities in the studied neat ionic liquids.

  13. NMR relaxation and exchange in metal-organic frameworks for surface area screening

    SciTech Connect

    Chen, JJ; Mason, JA; Bloch, ED; Gygi, D; Long, JR; Reimer, JA

    2015-03-15

    We describe a robust screening technique that correlates the surface area of metal organic frameworks to the proton T-2 relaxation behavior of imbibed solvent at low field (13 MHz). In frameworks with small pore sizes (<1 nm) or strong solvent-framework interactions, diffusional exchange between the pore-confined and inter-particle solvent populations remains slow compared to the T-2 of the pore-confined solvent, allowing for a direct porosity analysis of the T-2 spectrum obtained from Laplace inversions. Increases in framework pore-size (>1 nm) lead to corresponding increases in the rate of solvent exchange, as confirmed by T-2 relaxation exchange (REXSY) experiments; increases in the pore size also increases the T-2 of the pore-confined solvent. The combination of these two effects results in comparable rates of relaxation and exchange, which precludes the direct analysis of Laplace inversions. Thus, two- and three-site kinetics models were applied to extract porosity from relaxation decays, thereby improving the utility of the porosity screening tool. (C) 2014 Elsevier Inc. All rights reserved.

  14. Proton and tritium NMR relaxation studies of peptide inhibitor binding to bacterial collagenase: Conformation and dynamics

    SciTech Connect

    Dive, V.; Lai, A.; Valensin, G.; Saba, G.; Yiotakis, A.; Toma, F. )

    1991-02-15

    The interaction of succinyl-Pro-Ala, a competitive inhibitor of Achromobacter iophagus collagenase, with the enzyme was studied by longitudinal proton and tritium relaxation. Specific deuterium and tritium labeling of the succinyl part at vicinal positions allowed the measurement of the cross-relaxation rates of individual proton or tritium spin pairs in the inhibitor-enzyme complex as well as in the free inhibitor. Overall correlation times, internuclear distances, and qualitative information on the internal mobility in Suc1 (as provided by the generalized order parameter S2) could be deduced by the comparison of proton and tritium cross-relaxation of spin pairs at complementary positions in the -CH2- CH2- moiety as analyzed in terms of the model-free approach by Lipari and Szabo. The conformational and motional parameters of the inhibitor in the free and enzyme-bound state were directly compared by this method. The measurement of proton cross-relaxation in the Ala residue provided additional information on the inhibitor binding. The determination of the order parameter in different parts of the inhibitor molecule in the bound state indicates that the succinyl and alanyl residues are primarily involved in the interaction with the enzyme activity site. The succinyl moiety, characterized in solution by the conformational equilibrium among the three staggered rotamers--i.e., trans: 50%; g+: 20%; g-: 30%--adopted in the bound state the unique trans conformation.

  15. Hydration water dynamics in biopolymers from NMR relaxation in the rotating frame

    NASA Astrophysics Data System (ADS)

    Blicharska, Barbara; Peemoeller, Hartwig; Witek, Magdalena

    2010-12-01

    Assuming dipole-dipole interaction as the dominant relaxation mechanism of protons of water molecules adsorbed onto macromolecule (biopolymer) surfaces we have been able to model the dependences of relaxation rates on temperature and frequency. For adsorbed water molecules the correlation times are of the order of 10 -5 s, for which the dispersion region of spin-lattice relaxation rates in the rotating frame R1ρ = 1/ T1ρ appears over a range of easily accessible B1 values. Measurements of T1ρ at constant temperature and different B1 values then give the "dispersion profiles" for biopolymers. Fitting a theoretical relaxation model to these profiles allows for the estimation of correlation times. This way of obtaining the correlation time is easier and faster than approaches involving measurements of the temperature dependence of R1 = 1/ T1. The T1ρ dispersion approach, as a tool for molecular dynamics study, has been demonstrated for several hydrated biopolymer systems including crystalline cellulose, starch of different origins (potato, corn, oat, wheat), paper (modern, old) and lyophilized proteins (albumin, lysozyme).

  16. The role of diffusion in NMR proton relaxation enhancement by ferritin

    NASA Astrophysics Data System (ADS)

    Boss, Michael A.

    By using binary solutions of water and glycerol, we controlled diffusion so as to better understand its role in the relaxation rate enhancement of protons in the vicinity of ferritin at 7 tesla. The slower diffusion rates and higher external magnetic field used in these experiments are more consistent with the conditions expected in MRI experiments. New data was obtained on the diffusion coefficients of water and glycerol in binary solutions with relatively dilute amounts of glycerol. The effects of chemical exchange in such systems was also quantified. Two main relaxation mechanisms have been proposed for protons in the vicinity of ferritin: an outer-sphere mechanism (OS) in which spins diffuse past ferritin and experience a changing Larmor frequency by moving through the ferritin's magnetic field, and a proton exchange dephasing mechanism (PE), where protons temporarily reside on the surface of the ferritin core and sample a single, enhanced, Larmor frequency. At high-field, the OS mechanism becomes increasingly important because of a quadratic dependence on field strength, versus linear for the competing mechanism involving proton exchange. It was found that the relaxation enhancement of protons of both water and glycerol in the presence of ferritin was inversely proportional to their diffusion coefficients, in agreement with the OS model of relaxation enhancement. The strength of the relaxation enhancement on inverse diffusion coefficient was weaker for slow-diffusing glycerol than for water: glycerol molecules spent more time in a weaker magnetic field, indicating that glycerol did not approach the ferritin core as closely as water, potentially answering questions about molecular intake into the ferritin structure. The results of these experiments have important implications for the quantification of brain iron in vivo.

  17. The dark energy of proteins comes to light: conformational entropy and its role in protein function revealed by NMR relaxation.

    PubMed

    Wand, A Joshua

    2013-02-01

    Historically it has been virtually impossible to experimentally determine the contribution of residual protein entropy to fundamental protein activities such as the binding of ligands. Recent progress has illuminated the possibility of employing NMR relaxation methods to quantitatively determine the role of changes in conformational entropy in molecular recognition by proteins. The method rests on using fast internal protein dynamics as a proxy. Initial results reveal a large and variable role for conformational entropy in the binding of ligands by proteins. Such a role for conformational entropy in molecular recognition has significant implications for enzymology, signal transduction, allosteric regulation and the development of protein-directed pharmaceuticals. Copyright © 2012 Elsevier Ltd. All rights reserved.

  18. Temperature dependence of 1H NMR relaxation time, T2, for intact and neoplastic plant tissues

    NASA Astrophysics Data System (ADS)

    Lewa, Czesław J.; Lewa, Maria

    Temperature dependences of the spin-spin proton relaxation time, T2, have been shown for normal and tumorous tissues collected from kalus culture Nicotiana tabacum and from the plant Kalanchoe daigremontiana. For neoplastic plant tissues, time T2 was increased compared to that for intact plants, a finding similar to that for animal and human tissues. The temperature dependences obtained were compared to analogous relations observed with animal tissues.

  19. Excited States of Nucleic Acids Probed by Proton Relaxation Dispersion NMR Spectroscopy

    PubMed Central

    Juen, Michael Andreas; Wunderlich, Christoph Hermann; Nußbaumer, Felix; Tollinger, Martin; Kontaxis, Georg; Konrat, Robert

    2016-01-01

    Abstract In this work an improved stable isotope labeling protocol for nucleic acids is introduced. The novel building blocks eliminate/minimize homonuclear 13C and 1H scalar couplings thus allowing proton relaxation dispersion (RD) experiments to report accurately on the chemical exchange of nucleic acids. Using site‐specific 2H and 13C labeling, spin topologies are introduced into DNA and RNA that make 1H relaxation dispersion experiments applicable in a straightforward manner. The novel RNA/DNA building blocks were successfully incorporated into two nucleic acids. The A‐site RNA was previously shown to undergo a two site exchange process in the micro‐ to millisecond time regime. Using proton relaxation dispersion experiments the exchange parameters determined earlier could be recapitulated, thus validating the proposed approach. We further investigated the dynamics of the cTAR DNA, a DNA transcript that is involved in the viral replication cycle of HIV‐1. Again, an exchange process could be characterized and quantified. This shows the general applicablility of the novel labeling scheme for 1H RD experiments of nucleic acids. PMID:27533469

  20. Excited States of Nucleic Acids Probed by Proton Relaxation Dispersion NMR Spectroscopy.

    PubMed

    Juen, Michael Andreas; Wunderlich, Christoph Hermann; Nußbaumer, Felix; Tollinger, Martin; Kontaxis, Georg; Konrat, Robert; Hansen, D Flemming; Kreutz, Christoph

    2016-09-19

    In this work an improved stable isotope labeling protocol for nucleic acids is introduced. The novel building blocks eliminate/minimize homonuclear (13) C and (1) H scalar couplings thus allowing proton relaxation dispersion (RD) experiments to report accurately on the chemical exchange of nucleic acids. Using site-specific (2) H and (13) C labeling, spin topologies are introduced into DNA and RNA that make (1) H relaxation dispersion experiments applicable in a straightforward manner. The novel RNA/DNA building blocks were successfully incorporated into two nucleic acids. The A-site RNA was previously shown to undergo a two site exchange process in the micro- to millisecond time regime. Using proton relaxation dispersion experiments the exchange parameters determined earlier could be recapitulated, thus validating the proposed approach. We further investigated the dynamics of the cTAR DNA, a DNA transcript that is involved in the viral replication cycle of HIV-1. Again, an exchange process could be characterized and quantified. This shows the general applicablility of the novel labeling scheme for (1) H RD experiments of nucleic acids. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Complexation of κ-carrageenan with gelatin in the aqueous phase analysed by (1)H NMR kinetics and relaxation.

    PubMed

    Voron'ko, Nicolay G; Derkach, Svetlana R; Vovk, Mikhail A; Tolstoy, Peter M

    2017-08-01

    The (1)H NMR spectroscopy is used to study the kinetics of gelation in the aqueous mixtures of κ-carrageenan with gelatin. The time dependence of NMR signals intensities shows that the kinetics of gel formation consists of classical 'fast' (rate constant k≈6h(-1)) and 'slow' (k≈1h(-1)) periods, corresponding to a coil→helix transition and subsequent aggregation of helices. Upon increase of the κ-carrageenan/gelatin (w/w) ratio Z the rate of the fast process slows down by a factor of 1.6-2.4. Further analysis was done by studying the dependence of spin-spin relaxation times of protons of gelatin on Z in the aqueous phase. A qualitative scheme describing hydrogel formation in the complex solution is given. It is hypothesized that at higher concentration of PECs the hydrogel structure network is stabilized by three types of nodes: triple helices of gelatin and intra-/inter-molecular double helices of κ-carrageenan. Copyright © 2017 Elsevier Ltd. All rights reserved.

  2. Molecular interactions in the ionic liquid emim acetate and water binary mixtures probed via NMR spin relaxation and exchange spectroscopy.

    PubMed

    Allen, Jesse J; Bowser, Sage R; Damodaran, Krishnan

    2014-05-07

    Interactions of ionic liquids (ILs) with water are of great interest for many potential IL applications. 1-Ethyl-3-methylimidazolium (emim) acetate, in particular, has shown interesting interactions with water including hydrogen bonding and even chemical exchange. Previous studies have shown the unusual behavior of emim acetate when in the presence of 0.43 mole fraction of water, and a combination of NMR techniques is used herein to investigate the emim acetate-water system and the unusual behavior at 0.43 mole fraction of water. NMR relaxometry techniques are used to describe the effects of water on the molecular motion and interactions of emim acetate with water. A discontinuity is seen in nuclear relaxation behavior at the concentration of 0.43 mole fraction of water, and this is attributed to the formation of a hydrogen bonded network. EXSY measurements are used to determine the exchange rates between the H2 emim proton and water, which show a complex dependence on the concentration of the mixture. The findings support and expand our previous results, which suggested the presence of an extended hydrogen bonding network in the emim acetate-water system at concentrations close to 0.50 mole fraction of H2O.

  3. Synthesis, complexation and NMR relaxation properties of Gd3+ complexes of Mes(DO3A)3.

    PubMed

    Miéville, Pascal; Jaccard, Hugues; Reviriego, Felipe; Tripier, Raphaël; Helm, Lothar

    2011-04-28

    Medium sized molecules endowed with multiple Gd(3+) complexes are efficient high magnetic field MRI contrast agents. The novel ligand Mes(DO3A)(3), presenting three DO3A (1,4,7,10-tetraazacyclododecane-N,N',N''-triacetatic acid) units grafted on the methyl positions of a central mesitylene (1,3,5-trimethylbenzene), has been synthesized. Designed as an MRI contrast agent, this ligand is complexed with Gd(3+) and its efficiency is characterized by variable field (1)H-NMR and variable temperature (17)O-NMR. The evaluation of the relaxation and paramagnetic chemical shift data allowed the identification of an undesired binuclear complex which is obtained by using the classical procedure for complexation as described in the literature. An intramolecular capping mechanism appears to be responsible for the failure to introduce a third Gd(3+) ion into the ligand. A new alternative method, based on pre-complexation with Mg(2+) followed by transmetallation is described here and leads to the expected trinuclear Gd(3+) complex [Mes{Gd(DO3A)(H(2)O)(2)}(3)]. The rate constants for the water exchange (k(ex)(298) = 32 × 10(6) s(-1)) for the bi- and trinuclear complex appeared to be the same, which is surprising in relation to the difference in the charge of the complex and to the difference in the number of coordinated water molecules, one and two per Gd(3+) for the binuclear and trinuclear complex, respectively.

  4. "Ensemble" iterative relaxation matrix approach: a new NMR refinement protocol applied to the solution structure of crambin.

    PubMed

    Bonvin, A M; Rullmann, J A; Lamerichs, R M; Boelens, R; Kaptein, R

    1993-04-01

    The structure in solution of crambin, a small protein of 46 residues, has been determined from 2D NMR data using an iterative relaxation matrix approach (IRMA) together with distance geometry, distance bound driven dynamics, molecular dynamics, and energy minimization. A new protocol based on an "ensemble" approach is proposed and compared to the more standard initial rate analysis approach and a "single structure" relaxation matrix approach. The effects of fast local motions are included and R-factor calculations are performed on NOE build-ups to describe the quality of agreement between theory and experiment. A new method for stereospecific assignment of prochiral groups, based on a comparison of theoretical and experimental NOE intensities, has been applied. The solution structure of crambin could be determined with a precision (rmsd from the average structure) of 0.7 A on backbone atoms and 1.1 A on all heavy atoms and is largely similar to the crystal structure with a small difference observed in the position of the side chain of Tyr-29 which is determined in solution by both J-coupling and NOE data. Regions of higher structural variability (suggesting higher mobility) are found in the solution structure, in particular for the loop between the two helices (Gly-20 to Pro-22).

  5. Characterization of Protein-Protein Interfaces in Large Complexes by Solid-State NMR Solvent Paramagnetic Relaxation Enhancements.

    PubMed

    Öster, Carl; Kosol, Simone; Hartlmüller, Christoph; Lamley, Jonathan M; Iuga, Dinu; Oss, Andres; Org, Mai-Liis; Vanatalu, Kalju; Samoson, Ago; Madl, Tobias; Lewandowski, Józef R

    2017-09-06

    Solid-state NMR is becoming a viable alternative for obtaining information about structures and dynamics of large biomolecular complexes, including ones that are not accessible to other high-resolution biophysical techniques. In this context, methods for probing protein-protein interfaces at atomic resolution are highly desirable. Solvent paramagnetic relaxation enhancements (sPREs) proved to be a powerful method for probing protein-protein interfaces in large complexes in solution but have not been employed toward this goal in the solid state. We demonstrate that (1)H and (15)N relaxation-based sPREs provide a powerful tool for characterizing intermolecular interactions in large assemblies in the solid state. We present approaches for measuring sPREs in practically the entire range of magic angle spinning frequencies used for biomolecular studies and discuss their benefits and limitations. We validate the approach on crystalline GB1, with our experimental results in good agreement with theoretical predictions. Finally, we use sPREs to characterize protein-protein interfaces in the GB1 complex with immunoglobulin G (IgG). Our results suggest the potential existence of an additional binding site and provide new insights into GB1:IgG complex structure that amend and revise the current model available from studies with IgG fragments. We demonstrate sPREs as a practical, widely applicable, robust, and very sensitive technique for determining intermolecular interaction interfaces in large biomolecular complexes in the solid state.

  6. Characterization of Protein–Protein Interfaces in Large Complexes by Solid-State NMR Solvent Paramagnetic Relaxation Enhancements

    PubMed Central

    2017-01-01

    Solid-state NMR is becoming a viable alternative for obtaining information about structures and dynamics of large biomolecular complexes, including ones that are not accessible to other high-resolution biophysical techniques. In this context, methods for probing protein–protein interfaces at atomic resolution are highly desirable. Solvent paramagnetic relaxation enhancements (sPREs) proved to be a powerful method for probing protein–protein interfaces in large complexes in solution but have not been employed toward this goal in the solid state. We demonstrate that 1H and 15N relaxation-based sPREs provide a powerful tool for characterizing intermolecular interactions in large assemblies in the solid state. We present approaches for measuring sPREs in practically the entire range of magic angle spinning frequencies used for biomolecular studies and discuss their benefits and limitations. We validate the approach on crystalline GB1, with our experimental results in good agreement with theoretical predictions. Finally, we use sPREs to characterize protein–protein interfaces in the GB1 complex with immunoglobulin G (IgG). Our results suggest the potential existence of an additional binding site and provide new insights into GB1:IgG complex structure that amend and revise the current model available from studies with IgG fragments. We demonstrate sPREs as a practical, widely applicable, robust, and very sensitive technique for determining intermolecular interaction interfaces in large biomolecular complexes in the solid state. PMID:28780861

  7. Protein Dynamics from NMR: The Slowly Relaxing Local Structure Analysis Compared with Model-Free Analysis

    PubMed Central

    Meirovitch, Eva; Shapiro, Yury E.; Polimeno, Antonino; Freed, Jack H.

    2009-01-01

    15N-1H spin relaxation is a powerful method for deriving information on protein dynamics. The traditional method of data analysis is model-free (MF), where the global and local N-H motions are independent and the local geometry is simplified. The common MF analysis consists of fitting single-field data. The results are typically field-dependent, and multi-field data cannot be fit with standard fitting schemes. Cases where known functional dynamics has not been detected by MF were identified by us and others. Recently we applied to spin relaxation in proteins the Slowly Relaxing Local Structure (SRLS) approach which accounts rigorously for mode-mixing and general features of local geometry. SRLS was shown to yield MF in appropriate asymptotic limits. We found that the experimental spectral density corresponds quite well to the SRLS spectral density. The MF formulae are often used outside of their validity ranges, allowing small data sets to be force-fitted with good statistics but inaccurate best-fit parameters. This paper focuses on the mechanism of force-fitting and its implications. It is shown that MF force-fits the experimental data because mode-mixing, the rhombic symmetry of the local ordering and general features of local geometry are not accounted for. Combined multi-field multi-temperature data analyzed by MF may lead to the detection of incorrect phenomena, while conformational entropy derived from MF order parameters may be highly inaccurate. On the other hand, fitting to more appropriate models can yield consistent physically insightful information. This requires that the complexity of the theoretical spectral densities matches the integrity of the experimental data. As shown herein, the SRLS densities comply with this requirement. PMID:16821820

  8. 1H NMR relaxation of water: a probe for surfactant adsorption on kaolin.

    PubMed

    Totland, Christian; Lewis, Rhiannon T; Nerdal, Willy

    2011-11-01

    In this study, (1)H NMR is used to investigate properties of sodium dodecyl sulfate (SDS), tetradecyl trimethyl ammonium bromide (TTAB), and dodecyl trimethyl ammonium bromide (DTAB) adsorbed on kaolin by NMR T(1) and T(2) measurements of the water proton resonance. The results show that adsorbed surfactants form a barrier between sample water and the paramagnetic species present on the clay surface, thus significantly increasing the proton T(1) values of water. This effect is attributed to the amount of adsorbed surfactants and the arrangement of the surfactant aggregates. The total surface area covered by the cationic (DTAB and TTAB) and anionic (SDS) surfactants could be estimated from the water T(1) data and found to correspond to the fractions of negatively and positively charged surface area, respectively. For selected samples, the amount of paramagnetic species on the clay surface was reduced by treatment with hydrofluoric (HF) acid. For these samples, T(1) and T(2) measurements were taken in the temperature range 278-338 K, revealing detailed information on molecular mobility and nuclear exchange for the sample water that is related to surfactant behavior both on the surface and in the aqueous phase.

  9. 1H-19F spin-lattice relaxation spectroscopy: proton tunnelling in the hydrogen bond studied by field-cycling NMR.

    PubMed

    Noble, D L; Aibout, A; Horsewill, A J

    2009-12-01

    Proton tunnelling in the hydrogen bonds of two fluorine substituted benzoic acid dimers has been investigated using field-cycling NMR relaxometry. The close proximity of the (19)F nuclei to the hydrogen bond protons introduces heteronuclear (19)F-(1)H dipolar interactions into the spin-lattice relaxation processes. This renders the (1)H magnetisation-recovery biexponential and introduces multiple spectral density components into the relaxation matrix characterised by frequencies that are sums and differences of the (19)F and (1)H Larmor frequencies. Using field-cycling NMR pulse sequences that measure the spin-lattice relaxation and cross-relaxation rates we demonstrate how some of these multiple spectral density components can be separately resolved. This leads to an accurate determination of the correlation times that characterise the proton tunnelling motion. A broad spectrum of relaxation behaviour is illustrated and explored in the chosen samples and the investigation is used to explore the theory and practise of field-cycling NMR relaxometry in cases where heteronuclear interactions are significant.

  10. A study of spin-lattice relaxation rates of glucose, fructose, sucrose and cherries using high-T c SQUID-based NMR in ultralow magnetic fields

    NASA Astrophysics Data System (ADS)

    Liao, Shu-Hsien; Wu, Pei-Che

    2017-08-01

    We study the concentration dependence of spin-lattice relaxation rates, T 1 -1, of glucose, fructose, sucrose and cherries by using high-T c SQUID-based NMR at magnetic fields of ˜97 μT. The detected NMR signal, Sy (T Bp), is fitted to [1 - exp(-T Bp/T 1)] to derive T 1 -1, where Sy (T Bp) is the strength of the NMR signal, T Bp is the duration of pre-polarization and T 1 -1 is the spin-lattice relaxation rate. It was found that T 1 -1 increases as the sugar concentrations increase. The increased T 1 -1 is due to the presence of more molecules in the surroundings, which increases the spin-lattice interaction and in turn enhances T 1 -1. The T 1 -1 versus degrees Brix curve provides a basis for determining unknown Brix values for cherries as well as other fruits.

  11. Observation of the vortex lattice melting by NMR spin-lattice relaxation in the mixed state

    SciTech Connect

    Bulaevskii, L.N.; Hammel, P.C.; Vinokur, V.M.

    1994-01-01

    For anisotropic layered superconductors the effect of moving vortices on the nuclear spin magnetization is calculated. Current is supposed to flow along layers, and applied magnetic field is tilted with respect to c-axis. In the solid phase the motion of the vortex lattice produces an alternating magnetic field perpendicular to the applied field which causes the decay of the spin-echo amplitude. This decay rate will display an array of peaks as a function of frequency. In the liquid phase this alternating field contribute to the longitudinal relaxation rate W{sub 1} which has a single peak.

  12. Cross-Correlated Relaxation of Dipolar Coupling and Chemical-Shift Anisotropy in Magic-Angle Spinning R1ρ NMR Measurements: Application to Protein Backbone Dynamics Measurements

    PubMed Central

    Kurauskas, Vilius; Weber, Emmanuelle; Hessel, Audrey; Ayala, Isabel; Marion, Dominique; Schanda, Paul

    2016-01-01

    Transverse relaxation rate measurements in MAS solid-state NMR provide information about molecular motions occurring on nanoseconds-to-milliseconds (ns-ms) time scales. The measurement of heteronuclear (13C, 15N) relaxation rate constants in the presence of a spin-lock radio-frequency field (R1ρ relaxation) provides access to such motions, and an increasing number of studies involving R1ρ relaxation in proteins has been reported. However, two factors that influence the observed relaxation rate constants have so far been neglected, namely (i) the role of CSA/dipolar cross-correlated relaxation (CCR), and (ii) the impact of fast proton spin flips (i.e. proton spin diffusion and relaxation). We show that CSA/D CCR in R1ρ experiments is measurable, and that this cross-correlated relaxation rate constant depends on ns-ms motions, and can thus itself provide insight into dynamics. We find that proton spin-diffusion attenuates this cross-correlated relaxation, due to its decoupling effect on the doublet components. For measurements of dynamics, the use of R1ρ rate constants has practical advantages over the use of CCR rates, and the present manuscript reveals factors that have so far been disregarded and which are important for accurate measurements and interpretation. PMID:27500976

  13. Structure and dynamics of water in tendon from NMR relaxation measurements.

    PubMed Central

    Peto, S; Gillis, P; Henri, V P

    1990-01-01

    Nuclear magnetic relaxation times were measured in collagen tissue when varying the orientation of the fiber with respect to the static field. T1 was found to be only slightly dependent on theta, the fiber-to-field angle, but T2 was very sensitive to the orientation, with a maximum value at the magic angle. The transverse decay curves were multiexponential. Their deconvolution displayed four components; the ones that decayed most slowly were almost independent of theta, but the two fastest ones showed a strong angular dependence that was interpreted with a cross-relaxation model. Quadrupolar dips were visible in the 1/T1 dispersion curves. These dips were independent of theta, so that the magnetization transfer could also be assumed to be independent of the fiber orientation. Finally, each component was assigned to a fraction of protons localized in the macromolecular structure and characterized by particular dynamics. The model of Woessner was applied to the water molecules tightly bound into the macromolecules, which resulted in a dynamical description of this water fraction. This description is compatible with the two-sites model of Ramachandran based on x-ray diffraction and with the extensive studies of Berendsen. However, the important indications obtained from the deconvolution lead to a less static representation of the tissue. PMID:2297563

  14. Intracellular sodium and lithium NMR relaxation times in the perfused frog heart.

    PubMed

    Burstein, D; Fossel, E T

    1987-03-01

    We have used a combination of a shift reagent and mathematical filtering or presaturation of the extracellular sodium resonance for the quantitative investigation of the intracellular sodium and lithium relaxation times in the perfused frog heart. While the T1 of the intracellular sodium was found to consist of a single-exponential time constant (approximately 23 ms), the T2 was better fit as a double-exponential decay with time constants of approximately 2 and 17 ms. However, the relative amplitudes of the two time constants in the T2 decay were found to be inconsistent with those which would be expected from a homogeneous pool of nuclei undergoing quadrupolar interactions. The relaxation times were not changed by a fivefold increase in the intracellular sodium level (due to perfusion with a ouabain-containing buffer). The T1 and T2 of the intracellular lithium (after perfusion with lithium-containing buffer) were both well fit by single exponentials (700- and 31-ms time constants, respectively).

  15. Temperature dependence of the NMR spin-lattice relaxation rate for spin-1/2 chains

    NASA Astrophysics Data System (ADS)

    Coira, E.; Barmettler, P.; Giamarchi, T.; Kollath, C.

    2016-10-01

    We use recent developments in the framework of a time-dependent matrix product state method to compute the nuclear magnetic resonance relaxation rate 1 /T1 for spin-1/2 chains under magnetic field and for different Hamiltonians (XXX, XXZ, isotropically dimerized). We compute numerically the temperature dependence of the 1 /T1 . We consider both gapped and gapless phases, and also the proximity of quantum critical points. At temperatures much lower than the typical exchange energy scale, our results are in excellent agreement with analytical results, such as the ones derived from the Tomonaga-Luttinger liquid (TLL) theory and bosonization, which are valid in this regime. We also cover the regime for which the temperature T is comparable to the exchange coupling. In this case analytical theories are not appropriate, but this regime is relevant for various new compounds with exchange couplings in the range of tens of Kelvin. For the gapped phases, either the fully polarized phase for spin chains or the low-magnetic-field phase for the dimerized systems, we find an exponential decrease in Δ /(kBT ) of the relaxation time and can compute the gap Δ . Close to the quantum critical point our results are in good agreement with the scaling behavior based on the existence of free excitations.

  16. Whence so much N-15

    NASA Astrophysics Data System (ADS)

    Kerridge, J. F.

    1982-02-01

    Models for mechanisms which cause the widely varying N-15/N-14 stable isotope ratios observed in meteoritic and lunar samples are discussed. Interstellar ionization has been observed to be insufficient to account for the fractionations seen in the samples, which vary by as much as 5% from what is judged to be remnants of protosolar nebular material. An upper limit of less than -21% is suggested for the protosolar ratio, which implies a production of N-15 in surface regions of the sun, although gamma ray flux measurements of the sun indicate that the levels of nuclear activity are too low to form satisfactory quantities of N-15. The addition of N-15 by alien matter is not supportable due to the paucity of N-15 in the interstellar medium. Spacecraft measurements have also cast doubt on an influx due to solar wind ejection, and it is noted that the Galileo mission to Jupiter may resolve the estimates of the protosolar N-15/N-14 ratio because no net fractionation would have occurred during accretion by Jupiter, thereby leaving all Jovian nitrogen bound up in NH3.

  17. Second order rate constants for intramolecular conversions: Application to gas-phase NMR relaxation times

    NASA Astrophysics Data System (ADS)

    Bauer, S. H.; Lazaar, K. I.

    1983-09-01

    The usually quoted expression for the second order rate constant, for a unimolecular reaction at the low pressure limit, is valid only for strictly irreversible processes. Its application to isomerization reactions (which are to some extent reversible) is demonstrably in error; corrected expressions have been published. Attention is directed to intramolecular conversions over low barriers, for which the inappropriateness of the unidirectional expression becomes obvious. For such isomerizations we propose a model which incorporates only operationally observable states, so that an essential conceptual ambiguity is avoided. Use of this model is illustrated for the syn⇄anti conversions of methyl nitrite, derived from a gas phase NMR coalescence curve (Mc:Tc). The present data suggest that during isomerization the alkyl nitrites may not be completely ergodic on a time scale of 10-9 s. A regional phase-space model is proposed which has the appropriate formalism to account for this behavior.

  18. NMR relaxation of the orientation of single segments in semiflexible dendrimers

    SciTech Connect

    Markelov, Denis A. Gotlib, Yuli Ya.; Dolgushev, Maxim; Blumen, Alexander

    2014-06-28

    We study the orientational properties of labeled segments in semiflexible dendrimers making use of the viscoelastic approach of Dolgushev and Blumen [J. Chem. Phys. 131, 044905 (2009)]. We focus on the segmental orientational autocorrelation functions (ACFs), which are fundamental for the frequency-dependent spin-lattice relaxation times T{sub 1}(ω). We show that semiflexibility leads to an increase of the contribution of large-scale motions to the ACF. This fact influences the position of the maxima of the [1/T{sub 1}]-functions. Thus, going from outer to inner segments, the maxima shift to lower frequencies. Remarkably, this feature is not obtained in the classical bead-spring model of flexible dendrimers, although many experiments on dendrimers manifest such a behavior.

  19. Local folding and misfolding in the PBX homeodomain from a three-state analysis of CPMG relaxation dispersion NMR data.

    PubMed

    Farber, Patrick J; Slager, Jelle; Mittermaier, Anthony K

    2012-08-30

    NMR Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion experiments represent a powerful approach for characterizing protein internal motions and for gaining insight into fundamental biological processes such as protein folding, catalysis, and allostery. In most cases, CPMG data are analyzed assuming that the protein exchanges between two different conformational states. Systems exchanging among more than two states are far more challenging to characterize by CPMG NMR. For example, in the case of three-state exchange in the fast time scale regime, it is difficult to uniquely connect the parameters extracted from CPMG analyses with the physical parameters of most interest, intercoversion rates, populations, and chemical shift differences for exchanging states. We have developed a grid search selection procedure that allows these physical parameters to be uniquely determined from CPMG data, based on additional information, which in this study comprises ligand-induced chemical shift perturbations. We applied this approach to the PBX homeodomain (PBX-HD), a three-helix protein with a C-terminal extension that folds into a fourth helix upon binding to DNA. We recently showed that the C-terminal extension transiently folds, even in the absence DNA, in a process that is likely tied to the cooperative binding of PBX-HD to DNA and other homeodomains. Using the grid search selection procedure, we found that PBX-HD undergoes exchange between three different conformational states, a major form in which the C-terminal extension is unfolded, the previously identified state in which the C-terminal extension forms a fourth helix, and an additional state in which the C-terminal extension is misfolded.

  20. Measurement of protein unfolding/refolding kinetics and structural characterization of hidden intermediates by NMR relaxation dispersion

    PubMed Central

    Meinhold, Derrick W.; Wright, Peter E.

    2011-01-01

    Detailed understanding of protein function and malfunction hinges on the ability to characterize transiently populated states and the transitions between them. Here, we use 15N, , and 13CO NMR R2 relaxation dispersion to investigate spontaneous unfolding and refolding events of native apomyoglobin. Above pH 5.0, dispersion is dominated by processes involving fluctuations of the F-helix region, which is invisible in NMR spectra. Measurements of R2 dispersion for residues contacted by the F-helix region in the native (N) structure reveal a transient state formed by local unfolding of helix F and undocking from the protein core. A similar state was detected at pH 4.75–4.95 and determined to be an on-pathway intermediate (I1) in a linear three-state unfolding scheme (N⇆I1⇆MG) leading to a transiently populated molten globule (MG) state. The slowest steps in unfolding and refolding are N → I1 (36 s-1) and MG → I1 (26 s-1), respectively. Differences in chemical shift between N and I1 are very small, except in regions adjacent to helix F, showing that their core structures are similar. Chemical shift changes between the N and MG states, obtained from R2 dispersion, reveal that the transient MG state is structurally similar to the equilibrium MG observed previously at high temperature and low pH. Analysis of MG state chemical shifts shows the location of residual helical structure in the transient intermediate and identifies regions that unfold or rearrange into nonnative structure during the N → MG transition. The experiments also identify regions of energetic frustration that “crack” during unfolding and impede the refolding process. PMID:21562212

  1. Adaptive truncation of matrix decompositions and efficient estimation of NMR relaxation distributions

    NASA Astrophysics Data System (ADS)

    Teal, Paul D.; Eccles, Craig

    2015-04-01

    The two most successful methods of estimating the distribution of nuclear magnetic resonance relaxation times from two dimensional data are data compression followed by application of the Butler-Reeds-Dawson algorithm, and a primal-dual interior point method using preconditioned conjugate gradient. Both of these methods have previously been presented using a truncated singular value decomposition of matrices representing the exponential kernel. In this paper it is shown that other matrix factorizations are applicable to each of these algorithms, and that these illustrate the different fundamental principles behind the operation of the algorithms. These are the rank-revealing QR (RRQR) factorization and the LDL factorization with diagonal pivoting, also known as the Bunch-Kaufman-Parlett factorization. It is shown that both algorithms can be improved by adaptation of the truncation as the optimization process progresses, improving the accuracy as the optimal value is approached. A variation on the interior method viz, the use of barrier function instead of the primal-dual approach, is found to offer considerable improvement in terms of speed and reliability. A third type of algorithm, related to the algorithm known as Fast iterative shrinkage-thresholding algorithm, is applied to the problem. This method can be efficiently formulated without the use of a matrix decomposition.

  2. 13C NMR Relaxation Study of Segmental Motion of Poly(l-histidine) in Aqueous Solution

    NASA Astrophysics Data System (ADS)

    Uchino, Shinichi; Hiraoki, Toshifumi; Tsutsumi, Akihiro

    2004-05-01

    To study the segmental motion of poly (l-histidine) (PLH) in aqueous solution, the 13C spin-lattice relaxation time (T1) was measured at six resonance frequencies (ωC/2π) ranging from 15 to 100 MHz at temperatures from 10 to 80°C. For backbone Cα, plots of log(T1/ωC) against log(ωC) gave the well-superposed master curve, showing that the time-temperature reduction rule is realized. The shift factor obeyed the Arrhenius-type temperature dependence with the activation energy of 25.0 kJmol-1. Using this activation energy for the temperature dependence of the correlation time, the master curve was well reproduced by the Dejean-Lauprêtre-Monnerie (DLM) model. One of the parameters relating to the segmental motion was τ0/τ1=15, where τ0 and τ1 are the correlation times for the isolated single and correlated pair conformational transitions, respectively. It was found that the spectral density function J(ωC) has the exponent to the correlation time τ1 as ωCJ(ωC)˜(ωCτ1)0.71 in the region of ωCτ1≪ 1.

  3. Analysis of internal motions of interleukin-13 variant associated with severe bronchial asthma using {sup 15}N NMR relaxation measurements

    SciTech Connect

    Yoshida, Yuichiro; Ohkuri, Takatoshi; Takeda, Chika; Kuroki, Ryota; Izuhara, Kenji; Imoto, Taiji; Ueda, Tadashi . E-mail: ueda@phar.kyushu-u.ac.jp

    2007-06-22

    The single nucleotide polymorphism interleukin-13 (IL-13) R110Q is associated with severe bronchial asthma because its lower affinity leads to the augmentation of local IL-13 concentration, resulting in an increase in the signal transduction via IL-13R. Since the mutation site does not directly bind to IL-13R{alpha}2, we carried out NMR relaxation analyses of the wild-type IL-13 and IL-13-R110Q in order to examine whether the R110Q mutation affects the internal motions in IL-13 molecules. The results showed that the internal motion in the micro- to millisecond time scale on helix D, which is suggested to be important for the interaction between IL-13 and IL-13R{alpha}2, is increased in IL-13-R110Q compared with that in the wild-type IL-13. It therefore appears that the difference in the internal motions on helix D between the wild-type IL-13 and IL-13-R110Q may be involved in their affinity differences with IL-13R{alpha}2.

  4. Interactions and exchange of CO2 and H2O in coals: an investigation by low-field NMR relaxation

    PubMed Central

    Sun, Xiaoxiao; Yao, Yanbin; Liu, Dameng; Elsworth, Derek; Pan, Zhejun

    2016-01-01

    The mechanisms by which CO2 and water interact in coal remain unclear and these are key questions for understanding ECBM processes and defining the long-term behaviour of injected CO2. In our experiments, we injected helium/CO2 to displace water in eight water-saturated samples. We used low-field NMR relaxation to investigate CO2 and water interactions in these coals across a variety of time-scales. The injection of helium did not change the T2 spectra of the coals. In contrast, the T2 spectra peaks of micro-capillary water gradually decreased and those of macro-capillary and bulk water increased with time after the injection of CO2. We assume that the CO2 diffuses through and/or dissolves into the capillary water to access the coal matrix interior, which promotes desorption of water molecules from the surfaces of coal micropores and mesopores. The replaced water mass is mainly related to the Langmuir adsorption volume of CO2 and increases as the CO2 adsorption capacity increases. Other factors, such as mineral composition, temperature and pressure, also influence the effective exchange between water and CO2. Finally, we built a quantified model to evaluate the efficiency of water replacement by CO2 injection with respect to temperature and pressure. PMID:26817784

  5. Analysis of amorphous solid dispersions using 2D solid-state NMR and (1)H T(1) relaxation measurements.

    PubMed

    Pham, Tran N; Watson, Simon A; Edwards, Andrew J; Chavda, Manisha; Clawson, Jacalyn S; Strohmeier, Mark; Vogt, Frederick G

    2010-10-04

    Solid-state NMR (SSNMR) can provide detailed structural information about amorphous solid dispersions of pharmaceutical small molecules. In this study, the ability of SSNMR experiments based on dipolar correlation, spin diffusion, and relaxation measurements to characterize the structure of solid dispersions is explored. Observation of spin diffusion effects using the 2D (1)H-(13)C cross-polarization heteronuclear correlation (CP-HETCOR) experiment is shown to be a useful probe of association between the amorphous drug and polymer that is capable of directly proving glass solution formation. Dispersions of acetaminophen and indomethacin in different polymers are examined using this approach, as well as (1)H double-quantum correlation experiments to probe additional structural features. (1)H-(19)F CP-HETCOR serves a similar role for fluorinated drug molecules such as diflunisal in dispersions, providing a rapid means to prove the formation of a glass solution. Phase separation is detected using (13)C, (19)F, and (23)Na-detected (1)H T(1) experiments in crystalline and amorphous solid dispersions that contain small domains. (1)H T(1) measurements of amorphous nanosuspensions of trehalose and dextran illustrate the ability of SSNMR to detect domain size effects in dispersions that are not glass solutions via spin diffusion effects. Two previously unreported amorphous solid dispersions involving up to three components and containing voriconazole and telithromycin are analyzed using these experiments to demonstrate the general applicability of the approach.

  6. Fast-time scale dynamics of outer membrane protein A by extended model-free analysis of NMR relaxation data.

    PubMed

    Liang, Binyong; Arora, Ashish; Tamm, Lukas K

    2010-02-01

    In order to better understand the dynamics of an integral membrane protein, backbone amide (15)N NMR dynamics measurements of the beta-barrel membrane protein OmpA have been performed at three magnetic fields. A total of nine relaxation data sets were globally analyzed using an extended model-free formalism. The diffusion tensor was found to be prolate axially symmetric with an axial ratio of 5.75, indicating a possible rotation of the protein within the micelle. The generalized order parameters gradually decreased from the mid-plane towards the two ends of the barrel, counteracting the dynamic gradient of the lipids in a matching bilayer, and were dramatically reduced in the extracellular loops. Large-scale internal motions on the ns time scale indicate that entire loops most likely undergo concerted ("sea anemone"-like) motions emanating from their anchoring points on the barrel. The case of OmpA in DPC micelles also illustrates inherent limitations of analyzing the data with even the most sophisticated current models of the model-free formalism. It is likely that conformational exchange processes on the ms-mus also play a role in describing the motions of some residues, but their analysis did not produce unique results that could be independently verified. Copyright 2009 Elsevier B.V. All rights reserved.

  7. 1H NMR z-spectra of acetate methyl in stretched hydrogels: Quantum-mechanical description and Markov chain Monte Carlo relaxation-parameter estimation

    NASA Astrophysics Data System (ADS)

    Shishmarev, Dmitry; Chapman, Bogdan E.; Naumann, Christoph; Mamone, Salvatore; Kuchel, Philip W.

    2015-01-01

    The 1H NMR signal of the methyl group of sodium acetate is shown to be a triplet in the anisotropic environment of stretched gelatin gel. The multiplet structure of the signal is due to the intra-methyl residual dipolar couplings. The relaxation properties of the spin system were probed by recording steady-state irradiation envelopes ('z-spectra'). A quantum-mechanical model based on irreducible spherical tensors formed by the three magnetically equivalent spins of the methyl group was used to simulate and fit experimental z-spectra. The multiple parameter values of the relaxation model were estimated by using a Bayesian-based Markov chain Monte Carlo algorithm.

  8. Backbone dynamics of a biologically active human FGF-1 monomer, complexed to a hexasaccharide heparin-analogue, by 15N NMR relaxation methods.

    PubMed

    Canales-Mayordomo, Angeles; Fayos, Rosa; Angulo, Jesús; Ojeda, Rafael; Martín-Pastor, Manuel; Nieto, Pedro M; Martín-Lomas, Manuel; Lozano, Rosa; Giménez-Gallego, Guillermo; Jiménez-Barbero, Jesús

    2006-08-01

    The binding site and backbone dynamics of a bioactive complex formed by the acidic fibroblast growth factor (FGF-1) and a specifically designed heparin hexasaccharide has been investigated by HSQC and relaxation NMR methods. The comparison of the relaxation data for the free and bound states has allowed showing that the complex is monomeric, and still induces mutagenesis, and that the protein backbone presents reduced motion in different timescale in its bound state, except in certain points that are involved in the interaction with the fibroblast growth factor receptor (FGFR).

  9. Water mobility and microstructure evolution in the germinating Medicago truncatula seed studied by NMR relaxometry. A revisited interpretation of multicomponent relaxation.

    PubMed

    Lahaye, Marc; Falourd, Xavier; Limami, Anis M; Foucat, Loïc

    2015-02-18

    The water status of Medicago truncatula Gaertn. seed was followed by low-field NMR relaxometry during germination with and without oryzalin or fusicoccin used as growth modulators. T1 and T2 relaxation times and proportions P1 and P2 were determined on fresh, frozen, and freeze-thawed samples to characterize changes in water dynamics and compartmentation and in the nonfreezing water fraction. The results demonstrate that low-field NMR relaxometry allowed differentiating germination phases and events occurring during them as well as perturbations related to the presence of growth modulators. The results provide clear evidence that the classical multicomponent relaxation interpretation cannot directly relate T2 components and morphological compartments in biological tissue.

  10. Estimating side-chain order in methyl-protonated, perdeuterated proteins via multiple-quantum relaxation violated coherence transfer NMR spectroscopy.

    PubMed

    Sun, Hechao; Godoy-Ruiz, Raquel; Tugarinov, Vitali

    2012-03-01

    Relaxation violated coherence transfer NMR spectroscopy (Tugarinov et al. in J Am Chem Soc 129:1743-1750, 2007) is an established experimental tool for quantitative estimation of the amplitudes of side-chain motions in methyl-protonated, highly deuterated proteins. Relaxation violated coherence transfer experiments monitor the buildup of methyl proton multiple-quantum coherences that can be created in magnetically equivalent spin-systems as long as their transverse magnetization components relax with substantially different rates. The rate of this build-up is a reporter of the methyl-bearing side-chain mobility. Although the build-up of multiple-quantum (1)H coherences is monitored in these experiments, the decay of the methyl signal during relaxation delays occurs when methyl proton magnetization is in a single-quantum state. We describe a relaxation violated coherence transfer approach where the relaxation of multiple-quantum (1)H-(13)C methyl coherences during the relaxation delay period is quantified. The NMR experiment and the associated fitting procedure that models the time-dependence of the signal build-up, are applicable to the characterization of side-chain order in [(13)CH(3)]-methyl-labeled, highly deuterated protein systems up to ~100 kDa in molecular weight. The feasibility of extracting reliable measures of side-chain order is experimentally verified on methyl-protonated, perdeuterated samples of an 8.5-kDa ubiquitin at 10°C and an 82-kDa Malate Synthase G at 37°C.

  11. The mechanism of paramagnetic NMR relaxation produced by Mn(II): role of orthorhombic and fourth-order zero field splitting terms.

    PubMed

    Sharp, Robert

    2008-10-14

    Mn(II) is a spin-5/2 paramagnetic ion that mediates a characteristically large NMR paramagnetic relaxation enhancement (NMR-PRE) of nuclear spins in solution. In the range of high magnetic field strengths (above about 0.3 T), where the electronic Zeeman interaction provides the largest term of the electron spin Hamiltonian, NMR relaxation mechanism is well understood. In the lower field range, the physical picture is more complex because of the presence in the spin Hamiltonian of zero field splitting (ZFS) terms that are comparable to or greater than the Zeeman term. This work describes a systematic study of the relaxation mechanism in the low field range, particularly aspects involving the dependence of NMR-PRE on the orthorhombic (E) and fourth-order (a(q)(4), q=0,2,4) ZFS tensor components. It is shown that the fourfold (a(4)(4)) and twofold (a(2)(4)) fourth-order components exert large orientation-dependent influences on the NMR-PRE. Thus, fourth-order terms with magnitudes equal to only a few percent of the quadratic ZFS terms (D,E) produce large changes in the shape of the magnetic field profile of the PRE. Effects arising from the orthorhombic quadratic ZFS term (E) are much smaller than those of the fourth-order terms and can in most cases be neglected. However, effects due to a(4)(4) and a(2)(4) need to be included in simulations of low field data.

  12. Effect of gel firmness at cutting time, pH, and temperature on rennet coagulation and syneresis: an in situ 1H NMR relaxation study.

    PubMed

    Hansen, Christian Lyndgaard; Rinnan, Asmund; Engelsen, Søren Balling; Janhøj, Thomas; Micklander, Elisabeth; Andersen, Ulf; van den Berg, Frans

    2010-01-13

    The objective of this study was to monitor rennet-induced milk gel formation and mechanically induced gel syneresis in situ by low-field NMR. pH, temperature, and gel firmness at cutting time were varied in a factorial design. The new curve-fitting method Doubleslicing revealed that during coagulation two proton populations with distinct transverse relaxation times (T2,1=181, T2,2=465 ms) were present in fractions (f1=98.9%, f2=1.1%). Mechanical cutting of the gel in the NMR tube induced macrosyneresis, which led to the appearance of an additional proton population (T2,3=1500-2200 ms) identified as whey. On the basis of NMR quantification of whey water the syneresis rate was calculated and found to be significantly dependent on pH and temperature.

  13. Spin liquid state in the 3D frustrated antiferromagnet PbCuTe2O6: NMR and muon spin relaxation studies

    DOE PAGES

    Khuntia, P.; Bert, F.; Mendels, P.; ...

    2016-03-11

    In this study, PbCuTe2O6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneousmore » magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.« less

  14. ¹³C solid-state NMR analysis of the most common pharmaceutical excipients used in solid drug formulations Part II: CP kinetics and relaxation analysis.

    PubMed

    Pisklak, Dariusz Maciej; Zielińska-Pisklak, Monika; Szeleszczuk, Łukasz; Wawer, Iwona

    2016-04-15

    Excipients used in the solid drug formulations differ in their NMR relaxation and (13)C cross-polarization (CP) kinetics parameters. Therefore, experimental parameters like contact time of cross-polarization and repetition time have a major impact on the registered solid state NMR spectra and in consequence on the results of the NMR analysis. In this work the CP kinetics and relaxation of the most common pharmaceutical excipients: anhydrous α-lactose, α-lactose monohydrate, mannitol, sucrose, sorbitol, sodium starch glycolate type A and B, starch of different origin, microcrystalline cellulose, hypromellose, ethylcellulose, methylcellulose, hydroxyethylcellulose, sodium alginate, magnesium stearate, sodium laurilsulfate and Kollidon(®) were analyzed. The studied excipients differ significantly in their optimum repetition time (from 5 s to 1200 s) and T(1ρ)(I) parameters (from 2 ms to 73 ms). The practical use of those differences in the excipients composition analysis was demonstrated on the example of commercially available tablets containing indapamide as an API. The information presented in this article will help to choose the correct acquisition parameters and also will save the time and effort needed for their optimization in the NMR analysis of the solid drug formulations.

  15. Spin Liquid State in the 3D Frustrated Antiferromagnet PbCuTe_{2}O_{6}: NMR and Muon Spin Relaxation Studies.

    PubMed

    Khuntia, P; Bert, F; Mendels, P; Koteswararao, B; Mahajan, A V; Baenitz, M; Chou, F C; Baines, C; Amato, A; Furukawa, Y

    2016-03-11

    PbCuTe_{2}O_{6} is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu^{2+} ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T_{1} NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.

  16. Evidence for the role of fluxoids in enhancing NMR spin-lattice relaxation and implications for intrinsic pinning of the flux lattice in organic superconductors

    NASA Astrophysics Data System (ADS)

    de Soto, S. M.; Slichter, C. P.; Wang, H. H.; Geiser, U.; Williams, J. M.

    1993-05-01

    The authors report 1H NMR spin-lattice relaxation rates, T-11, in the quasi-2D organic superconductor κ-(ET)2Cu[N(CN)2]Br (Tc=11.6 K), for an aligned single crystal. The relaxation in the normal-state obeys the Korringa law (T1T=const). In the superconducting state, for weak fields (H0=0.59 T), T-11 is greatly enhanced and displays strong orientation dependence for field directions nearly parallel to the superconducting layers. This behavior indicates that motion of the fluxoid system is the cause of the extra relaxation, and is evidence for a ``lock-in'' transition of the flux lattice.

  17. Superconducting state of κ-(ET)2CUBr studied by 13C NMR: Evidence for vortex-core-induced nuclear relaxation and unconventional pairing

    NASA Astrophysics Data System (ADS)

    Mayaffre, H.; Wzietek, P.; Jérome, D.; Lenoir, C.; Batail, P.

    1995-11-01

    We present the first 13C NMR measurements carried out in the superconducting state of a two-dimensional organic superconducting single crystal. Spin lattice relaxation rate and Knight shift are reported for magnetic fields parallel and perpendicular to the conducting layers. For perpendicular fields, the relaxation is dominated by the electronic excitations in the vortex cores. From the field dependence of (T1)-1 we obtain the upper critical field. In parallel orientation, the absence of field dependence reveals the existence of a lock-in state, where only relaxation by superconducting excitations is expected. The (T1)-1 then exhibits a T3 law suggesting an unconventional pairing with a very anisotropic gap.

  18. Flexible and rigid structures in HIV-1 p17 matrix protein monitored by relaxation and amide proton exchange with NMR.

    PubMed

    Ohori, Yuka; Okazaki, Honoka; Watanabe, Satoru; Tochio, Naoya; Arai, Munehito; Kigawa, Takanori; Nishimura, Chiaki

    2014-03-01

    The HIV-1 p17 matrix protein is a multifunctional protein that interacts with other molecules including proteins and membranes. The dynamic structure between its folded and partially unfolded states can be critical for the recognition of interacting molecules. One of the most important roles of the p17 matrix protein is its localization to the plasma membrane with the Gag polyprotein. The myristyl group attached to the N-terminus on the p17 matrix protein functions as an anchor for binding to the plasma membrane. Biochemical studies revealed that two regions are important for its function: D14-L31 and V84-V88. Here, the dynamic structures of the p17 matrix protein were studied using NMR for relaxation and amide proton exchange experiments at the physiological pH of 7.0. The results revealed that the α12-loop, which includes the 14-31 region, was relatively flexible, and that helix 4, including the 84-88 region, was the most protected helix in this protein. However, the residues in the α34-loop near helix 4 had a low order parameter and high exchange rate of amide protons, indicating high flexibility. This region is probably flexible because this loop functions as a hinge for optimizing the interactions between helices 3 and 4. The C-terminal long region of K113-Y132 adopted a disordered structure. Furthermore, the C-terminal helix 5 appeared to be slightly destabilized due to the flexible C-terminal tail based on the order parameters. Thus, the dynamic structure of the p17 matrix protein may be related to its multiple functions.

  19. Effects of T2-relaxation in MAS NMR spectra of the satellite transitions for quadrupolar nuclei: a 27Al MAS and single-crystal NMR study of alum KAl(SO4)2.12H2O.

    PubMed

    Andersen, Morten Daugaard; Jakobsen, Hans J; Skibsted, Jørgen

    2005-04-01

    Asymmetries in the manifold of spinning sidebands (ssbs) from the satellite transitions have been observed in variable-temperature 27Al MAS NMR spectra of alum (KAl(SO4)2.12H2O), recorded in the temperature range from -76 to 92 degrees C. The asymmetries decrease with increasing temperature and reflect the fact that the ssbs exhibit systematically different linewidths for different spectral regions of the manifold. From spin-echo 27Al NMR experiments on a single-crystal of alum, it is demonstrated that these variations in linewidth originate from differences in transverse (T2) relaxation times for the two inner (m=1/2<-->m=3/2 and m=-1/2<-->m=-3/2) and correspondingly for the two outer (m=3/2<-->m=5/2 and m=-3/2<-->m=-5/2) satellite transitions. T2 relaxation times in the range 0.5-3.5 ms are observed for the individual satellite transitions at -50 degrees C and 7.05 T, whereas the corresponding T1 relaxation times, determined from similar saturation-recovery 27Al NMR experiments, are almost constant (T1=0.07-0.10 s) for the individual satellite transitions. The variation in T2 values for the individual 27Al satellite transitions for alum is justified by a simple theoretical approach which considers the cross-correlation of the local fluctuating fields from the quadrupolar coupling and the heteronuclear (27Al-1H) dipolar interaction on the T2 relaxation times for the individual transitions. This approach and the observed differences in T2 values indicate that a single random motional process modulates both the quadrupolar and heteronuclear dipolar interactions for 27Al in alum at low temperatures.

  20. Effects of T2-relaxation in MAS NMR spectra of the satellite transitions for quadrupolar nuclei: a 27Al MAS and single-crystal NMR study of alum KAl(SO 4) 2 · 12H 2O

    NASA Astrophysics Data System (ADS)

    Andersen, Morten Daugaard; Jakobsen, Hans J.; Skibsted, Jørgen

    2005-04-01

    Asymmetries in the manifold of spinning sidebands (ssbs) from the satellite transitions have been observed in variable-temperature 27Al MAS NMR spectra of alum (KAl(SO 4) 2 · 12H 2O), recorded in the temperature range from -76 to 92 °C. The asymmetries decrease with increasing temperature and reflect the fact that the ssbs exhibit systematically different linewidths for different spectral regions of the manifold. From spin-echo 27Al NMR experiments on a single-crystal of alum, it is demonstrated that these variations in linewidth originate from differences in transverse ( T2) relaxation times for the two inner ( m = 1/2 ↔ m = 3/2 and m = -1/2 ↔ m = -3/2) and correspondingly for the two outer ( m = 3/2 ↔ m = 5/2 and m = -3/2 ↔ m = -5/2) satellite transitions. T2 relaxation times in the range 0.5-3.5 ms are observed for the individual satellite transitions at -50 °C and 7.05 T, whereas the corresponding T1 relaxation times, determined from similar saturation-recovery 27Al NMR experiments, are almost constant ( T1 = 0.07-0.10 s) for the individual satellite transitions. The variation in T2 values for the individual 27Al satellite transitions for alum is justified by a simple theoretical approach which considers the cross-correlation of the local fluctuating fields from the quadrupolar coupling and the heteronuclear ( 27Al- 1H) dipolar interaction on the T2 relaxation times for the individual transitions. This approach and the observed differences in T2 values indicate that a single random motional process modulates both the quadrupolar and heteronuclear dipolar interactions for 27Al in alum at low temperatures.

  1. Uranyl Carbonate Complexes in Aqueous Solution and Their Ligand NMR Chemical Shifts and (17)O Quadrupolar Relaxation Studied by ab Initio Molecular Dynamics.

    PubMed

    Marchenko, Alex; Truflandier, Lionel A; Autschbach, Jochen

    2017-07-03

    Dynamic structural effects, NMR ligand chemical shifts, and (17)O NMR quadrupolar relaxation rates are investigated in the series of complexes UO2(2+), UO2(CO3)3(4-), and (UO2)3(CO3)6(6-). Car-Parrinello molecular dynamics (CPMD) is used to simulate the dynamics of the complexes in water. NMR properties are computed on clusters extracted from the CPMD trajectories. In the UO2(2+) complex, coordination at the uranium center by water molecules causes a decrease of around 300 ppm for the uranyl (17)O chemical shift. The final value of this chemical shift is within 40 ppm of the experimental range. The UO2(CO3)3(4-) and (UO2)3(CO3)6(6-) complexes show a solvent dependence of the terminal carbonate (17)O and (13)C chemical shifts that is less pronounced than that for the uranyl oxygen atom. Corrections to the chemical shift from hybrid functionals and spin-orbit coupling improve the accuracy of chemical shifts if the sensitivity of the uranyl chemical shift to the uranyl bond length (estimated at 140 ppm per 0.1 Å from trajectory data) is taken into consideration. The experimentally reported trend in the two unique (13)C chemical shifts is correctly reproduced for (UO2)3(CO3)6(6-). NMR relaxation rate data support large (17)O peak widths, but remain below those noted in the experimental literature. Comparison of relaxation data for solvent-including versus solvent-free models suggest that carbonate ligand motion overshadows explicit solvent effects.

  2. Proton NMR T1, T2, and T1 rho relaxation studies of native and reconstituted sarcoplasmic reticulum and phospholipid vesicles.

    PubMed Central

    Deese, A J; Dratz, E A; Hymel, L; Fleischer, S

    1982-01-01

    The phospholipids protons of native and reconstituted sarcoplasmic reticulum (SR) membrane vesicles yield well-resolved nuclear magnetic resonance (NMR) spectra. Resonance area measurements, guided by the line shape theory of Bloom and co-workers, imply that we are observing a large fraction of the lipid intensity and that the protein does not appear to reduce the percent of the signal that is well resolved. We have measured the spin-lattice (T1) and spin-spin (T2) relaxation rates of the choline, methylene, and terminal methyl protons at 360 MHz and the spin-lattice relaxation rate in the rotating frame (T1 rho) at 100 MHz. Both the T1 and T2 relaxation rates are single exponential processes for all of the resonances if the residual water proton signal is thoroughly eliminated by selective saturation. The T1 and T2 relaxation rates increase as the protein concentration increases, and T2 rate decrease with increasing temperature. This implies that the protein is reducing both high frequency (e.g., trans-gauche methylene isomerizations) and low frequency (e.g., large amplitude, chain wagging) lipid motions, from the center of the bilayer to the surface. It is possible that spin diffusion contributes to the effect of protein on lipid T1's although some of the protein-induced T1 change is due to motional effects. The T2 relaxation times are observed to be near 1 ms for the membranes with highest protein concentration and approximately 10 ms for the lipids devoid of protein. This result, combined with the observation that the T2 rates are monophasic, suggests that at least two lipid environments exist in the presence of protein, and that the lipids are exchanging between these environments at a rate greater than 1/T2 or 10(3) s-1. The choline resonance yields single exponential T1 rho relaxation in the presence and absence of protein, whereas the other resonances measured exhibit biexponential relaxation. Protein significantly increases the single T1 rho relaxation

  3. A slowly relaxing rigid biradical for efficient dynamic nuclear polarization surface-enhanced NMR spectroscopy: expeditious characterization of functional group manipulation in hybrid materials.

    PubMed

    Zagdoun, Alexandre; Casano, Gilles; Ouari, Olivier; Lapadula, Giuseppe; Rossini, Aaron J; Lelli, Moreno; Baffert, Mathieu; Gajan, David; Veyre, Laurent; Maas, Werner E; Rosay, Melanie; Weber, Ralph T; Thieuleux, Chloé; Coperet, Christophe; Lesage, Anne; Tordo, Paul; Emsley, Lyndon

    2012-02-01

    A new nitroxide-based biradical having a long electron spin-lattice relaxation time (T(1e)) has been developed as an exogenous polarization source for DNP solid-state NMR experiments. The performance of this new biradical is demonstrated on hybrid silica-based mesostructured materials impregnated with 1,1,2,2-tetrachloroethane radical containing solutions, as well as in frozen bulk solutions, yielding DNP enhancement factors (ε) of over 100 at a magnetic field of 9.4 T and sample temperatures of ~100 K. The effects of radical concentration on the DNP enhancement factors and on the overall sensitivity enhancements (Σ(†)) are reported. The relatively high DNP efficiency of the biradical is attributed to an increased T(1e), which enables more effective saturation of the electron resonance. This new biradical is shown to outperform the polarizing agents used so far in DNP surface-enhanced NMR spectroscopy of materials, yielding a 113-fold increase in overall sensitivity for silicon-29 CPMAS spectra as compared to conventional NMR experiments at room temperature. This results in a reduction in experimental times by a factor >12,700, making the acquisition of (13)C and (15)N one- and two-dimensional NMR spectra at natural isotopic abundance rapid (hours). It has been used here to monitor a series of chemical reactions carried out on the surface functionalities of a hybrid organic-silica material. © 2011 American Chemical Society

  4. Is the manifestation of the local dynamics in the spin-lattice NMR relaxation in dendrimers sensitive to excluded volume interactions?

    PubMed

    Shavykin, Oleg V; Neelov, Igor M; Darinskii, Anatolii A

    2016-09-21

    The effect of excluded volume (EV) interactions on the manifestation of the local dynamics in the spin-lattice NMR relaxation in dendrimers has been studied by using Brownian dynamics simulations. The study was motivated by the theory developed by Markelov et al., [J. Chem. Phys., 2014, 140, 244904] for a Gaussian dendrimer model without EV interactions. The theory connects the experimentally observed dependence of the spin-lattice relaxation rate 1/T(1)H on the location of NMR active groups with the restricted flexibility (semiflexibility) of dendrimers. Semiflexibility was introduced through the correlations between the orientations of different segments. However, these correlations exist even in flexible dendrimer models with EV interactions. We have simulated coarse-grained flexible and semiflexible dendrimer models with and without EV interactions. Every dendrimer segment consisted of two rigid bonds. Semiflexibility was introduced through a potential which restricts the fluctuations of angles between neighboring bonds but does not change orientational correlations in the EV model as compared to the flexible case. The frequency dependence of the reduced 1/T(1)H(ωH) for segments and bonds belonging to different dendrimer shells was calculated. It was shown that the main effect of EV interactions consists of a much stronger contribution of the overall dendrimer rotation to the dynamics of dendrimer segments as compared to phantom models. After the exclusion of this contribution the manifestation of internal dynamics in spin-lattice NMR relaxation appears to be practically insensitive to EV interactions. For the flexible models, the position ωmax of the peak of the modified 1/T(1)H(ωH) does not depend on the shell number. For semiflexible models, the maximum of 1/T(1)H(ωH) for internal segments or bonds shifts to lower frequencies as compared to outer ones. The dependence of ωmax on the number of dendrimer shells appears to be universal for segments and

  5. Molecular motions of [Beta]-carotene and a carotenoporphyrin dyad in solution. A carbon-13 NMR spin-lattice relaxation time study

    SciTech Connect

    Li, S.; Swindle, S.L.; Smith, S.K.; Nieman, R.A.; Moore, A.L.; Moore, T.A.; Gust, D. )

    1995-03-09

    Analysis of [sup 13]C NMR spin-lattice relaxation times (T[sub 1]) yields information concerning both overall tumbling of molecules in solution and internal rotations about single bonds. Relaxation time and nuclear Overhauser effect data have been obtained for [Beta]-carotene and two related molecules, squalane and squalene, for zinc meso-tetraphenylporphyrin, and for a dyad consisting of a porphyrin covalently linked to a carotenoid polyene through a trimethylene bridge. Squalane and squalene, which lack conjugated double bonds, behave essentially as limp string, with internal rotations at least as rapid as overall isotropic tumbling motions. In contrast, [Beta]-carotene reorients as a rigid rod, with internal motions which are too slow to affect relaxation times. Modeling it as an anisotropic rotor yields a rotational diffusion coefficient for motion about the major axis which is 14 times larger than that for rotation about axes perpendicular to that axis. The porphyrin reorients more nearly isotropically and features internal librational motions about the single bonds to the phenyl groups. The relaxation time data for the carotenoporphyrin are consistent with internal motions similar to those of a medieval military flail. 31 refs., 3 figs., 5 tabs.

  6. NMR Method for Characterizing Microsecond-to-Millisecond Chemical Exchanges Utilizing Differential Multiple-Quantum Relaxation in High Molecular Weight Proteins.

    PubMed

    Toyama, Yuki; Osawa, Masanori; Yokogawa, Mariko; Shimada, Ichio

    2016-02-24

    Chemical exchange processes of proteins on the order of microseconds (μs) to milliseconds (ms) play critical roles in biological functions. Developments in methyl-transverse relaxation optimized spectroscopy (methyl-TROSY), which observes the slowly relaxing multiple quantum (MQ) coherences, have enabled the studies of biologically important large proteins. However, the analyses of μs to ms chemical exchange processes based on the methyl-TROSY principle are still challenging, because the interpretation of the chemical exchange contributions to the MQ relaxation profiles is complicated, as significant chemical shift differences occur in both (1)H and (13)C nuclei. Here, we report a new methyl-based NMR method for characterizing chemical exchanges, utilizing differential MQ relaxation rates and a heteronuclear double resonance pulse technique. The method enables quantitative evaluations of the chemical exchange processes, in which significant chemical shift differences exist in both the (1)H and (13)C nuclei. The versatility of the method is demonstrated with the application to KirBac1.1, with an apparent molecular mass of 200 kDa.

  7. Feasibility of high-resolution one-dimensional relaxation imaging at low magnetic field using a single-sided NMR scanner applied to articular cartilage

    NASA Astrophysics Data System (ADS)

    Rössler, Erik; Mattea, Carlos; Stapf, Siegfried

    2015-02-01

    Low field Nuclear Magnetic Resonance increases the contrast of the longitudinal relaxation rate in many biological tissues; one prominent example is hyaline articular cartilage. In order to take advantage of this increased contrast and to profile the depth-dependent variations, high resolution parameter measurements are carried out which can be of critical importance in an early diagnosis of cartilage diseases such as osteoarthritis. However, the maximum achievable spatial resolution of parameter profiles is limited by factors such as sensor geometry, sample curvature, and diffusion limitation. In this work, we report on high-resolution single-sided NMR scanner measurements with a commercial device, and quantify these limitations. The highest achievable spatial resolution on the used profiler, and the lateral dimension of the sensitive volume were determined. Since articular cartilage samples are usually bent, we also focus on averaging effects inside the horizontally aligned sensitive volume and their impact on the relaxation profiles. Taking these critical parameters into consideration, depth-dependent relaxation time profiles with the maximum achievable vertical resolution of 20 μm are discussed, and are correlated with diffusion coefficient profiles in hyaline articular cartilage in order to reconstruct T2 maps from the diffusion-weighted CPMG decays of apparent relaxation rates.

  8. Sub-millisecond (125)Te NMR spin-lattice relaxation times and large Knight shifts in complex tellurides: Validation of a quadratic relation across the spectrum.

    PubMed

    Levin, E M; Cui, J-F; Schmidt-Rohr, K

    2016-09-01

    (125)Te NMR spectra and spin-lattice relaxation times, T1, have been measured for several GeTe-based materials with Te excess. The spectra show inhomogeneous broadening by several thousand ppm and a systematic variation in T1 relaxation time with resonance frequency. The quadratic dependence of the spin-lattice relaxation rate, 1/T1, on the Knight shift in the Korringa relation is found to be valid over a wide range of Knight shifts. This result confirms that T1 relaxation in GeTe-based materials is mostly dominated by hyperfine interaction between nuclei and free charge carriers. In GeTe with 2.5% excess of Te, about 15% of the material exhibits a Knight shift of ≥4500ppm and a T1 of only 0.3ms, indicating a high hole concentration that could correspond to close to 50% vacancies on the Ge sublattice in this component. Our findings provide a basis for determining the charge carrier concentration and its distribution in complex thermoelectric and phase-change tellurides, which should lead to a better understanding of electronic and thermal transport properties as well as chemical bonding in these materials.

  9. Sub-millisecond 125Te NMR spin-lattice relaxation times and large Knight shifts in complex tellurides: Validation of a quadratic relation across the spectrum

    DOE PAGES

    Levin, E. M.; Iowa State Univ., Ames, IA; Cui, J. -F.; ...

    2016-07-16

    125Te NMR spectra and spin-lattice relaxation times, T1, have been measured for several GeTe-based materials with Te excess. In this paper, the spectra show inhomogeneous broadening by several thousand ppm and a systematic variation in T1 relaxation time with resonance frequency. The quadratic dependence of the spin-lattice relaxation rate, 1/T1, on the Knight shift in the Korringa relation is found to be valid over a wide range of Knight shifts. This result confirms that T1 relaxation in GeTe-based materials is mostly dominated by hyperfine interaction between nuclei and free charge carriers. In GeTe with 2.5% excess of Te, about 15%more » of the material exhibits a Knight shift of ≥4500 ppm and a T1 of only 0.3 ms, indicating a high hole concentration that could correspond to close to 50% vacancies on the Ge sublattice in this component. Lastly, our findings provide a basis for determining the charge carrier concentration and its distribution in complex thermoelectric and phase-change tellurides, which should lead to a better understanding of electronic and thermal transport properties as well as chemical bonding in these materials.« less

  10. Water confinement in faujasite cages: a deuteron NMR investigation in a wide temperature range. 2. Spectra and relaxation at high temperature.

    PubMed

    Szymocha, A M; Lalowicz, Z T; Birczyński, A; Krzystyniak, M; Stoch, G; Góra-Marek, K

    2014-07-24

    Deuteron NMR spectra and spin-lattice relaxation were measured for D2O confined in NaX, NaY, and DY faujasites with various loadings at temperatures ranging from 200 to 310 K with the aim to study molecular mobility of confined water. Hysteresis of spin-lattice relaxation was observed for both DY and NaY(2.4) samples at 500% loading (280 water molecules per unit cell) in a heating-cooling cycle between 264.5 and 277.7 K. The hysteresis is most likely reflecting formation and decomposition of water clusters at different temperature. Spin-lattice relaxation rates obtained from the experiment are consistent with a picture of the fast magnetization exchange between two dynamically different deuteron populations. The observed relaxation behavior as a function of temperature and loading is most likely an effect of interplay between translational and rotational diffusion. Translational diffusion of water molecules is found to be related to the strength of the electrostatic interaction of water oxygen atoms to faujasite sodium cations, whereas water molecule reorientations seem to depend on the strength of hydrogen bonding to faujasite oxygen atoms and the strength of hydrogen bonds between water molecules, at outer and inner positions in water clusters, respectively.

  11. The effects of exchange and interfacial reaction in two-phase systems on N.M.R. lineshapes and relaxation processes

    NASA Astrophysics Data System (ADS)

    Belton, P. S.; Hills, B. P.

    The effects of molecular exchange between two immiscible fluid phases are of considerable importance when interpreting N.M.R. lineshapes and relaxation times in systems such as emulsions or coacervates, but have not been fully explored theoretically. In general the nuclei in each phase must be considered as belonging to distinct chemical species which are interchanged by chemical reaction localized at the interface between the two fluids. By solving the Bloch-Torrey equations with new generalized boundary conditions describing this localized interfacial reaction we show how the N.M.R. spectral lineshape and relaxation times depend on the morphology of the system as well as on the rates of diffusion and interfacial reaction. Our results differ fundamentally from the traditional phenomenological description of exchange based on the Bloch-McConnell or Zimmerman-Brittin equations which take no explicit account of these factors. In order to illustrate these differences exact analytical solutions are derived for the simplest geometry where the two phases are lamellar. More complicated geometries can be treated by numerical methods.

  12. An NMR thermometer for cryogenic magic-angle spinning NMR: the spin-lattice relaxation of (127)I in cesium iodide.

    PubMed

    Sarkar, Riddhiman; Concistrè, Maria; Johannessen, Ole G; Beckett, Peter; Denning, Mark; Carravetta, Marina; Al-Mosawi, Maitham; Beduz, Carlo; Yang, Yifeng; Levitt, Malcolm H

    2011-10-01

    The accurate temperature measurement of solid samples under magic-angle spinning (MAS) is difficult in the cryogenic regime. It has been demonstrated by Thurber et al. (J. Magn. Reson., 196 (2009) 84-87) [10] that the temperature dependent spin-lattice relaxation time constant of (79)Br in KBr powder can be useful for measuring sample temperature under MAS over a wide temperature range (20-296 K). However the value of T(1) exceeds 3 min at temperatures below 20K, which is inconveniently long. In this communication, we show that the spin-lattice relaxation time constant of (127)I in CsI powder can be used to accurately measure sample temperature under MAS within a reasonable experimental time down to 10 K.

  13. [Natural polymers according to NMR data: cross-relaxation in hydrated collagen macromolecules from two connective tissues].

    PubMed

    Rodin, V V; Foucat, L; Renou, J P

    2004-01-01

    Spin-lattice relaxation and cross-relaxation in oriented and randomly oriented collagen fibers from two connective tissues (15-month-old calf and 8-year-old steer) at a water content of 0.6 g H2O/g dry matter were studied. Collagens were chosen according to different numbers of covalent nonreducible cross-links, which increase during the life of the animal. The spin-lattice relaxation curves for all the collagens after a 180 degree-tau-90 degree pulse sequence were described by two exponential components. The dependences of two components of spin lattice relaxation time and their populations on the length of the 180 degree-pulse were obtained. On the basis of data of Goldman-Shen sequence and the two-phase model, the populations of proton fractions (p(w) and p(c)) as well as the rates of transfer of magnetization between water protons and collagen protons (k(w) and k(c)) were calculated. No significant difference between k(w) (k(c)) in oriented and randomly oriented fibers as well as in fibers with different cross-linking was found. The estimates of the cross-relaxation times for low cross-link collagen and high cross-link one were done. The correlation times of dipole-dipole interactions for both connective tissues were calculated using the cross-relaxation theory.

  14. Paramagnetic NMR Relaxation and Molecular Mechanics Studies of Chloroperoxidase-Indole Complex: Insights into the Mechanism of Chloroperoxidase-Catalyzed Regioselective Oxidation of Indole

    PubMed Central

    Zhang, Rui; He, Qinghao; Chatfield, David; Wang, Xiaotang

    2013-01-01

    To unravel the mechanism of CPO-catalyzed regioselective oxidation of indole, the structure of the CPO-indole complex was studied using NMR relaxation measurements and computational techniques. The dissociation constant (KD) of the CPO-indole complex was calculated to be approximately 21 mM. The distances (r) between protons of indole and the heme iron calculated from NMR relaxation measurements and molecular docking revealed that the pyrrole ring of indole is oriented toward the heme with its 2-H pointing directly at the heme iron. Both KD and r values are independent of pH in the range of 3.0–6.5. The stability and structure of the CPO-indole complex are also independent of the concentration of chloride/iodide ion. Molecular docking suggests the formation of a hydrogen bond between the N–H of indole and the carboxyl O of Glu 183 in the binding of indole to CPO. Simulated annealing of the CPO-indole complex using r values from NMR experiments as distance restraints reveals that the van der Waals interactions were much stronger than the Coulomb interactions in indole binding to CPO, indicating that the association of indole with CPO is primarily governed by hydrophobic rather than electrostatic interactions. This work provides the first experimental and theoretical evidence for the long-sought mechanism that leads to the “unexpected” regioselectivity of CPO-catalyzed oxidation of indole. The structure of the CPO-indole complex will serve as a lighthouse in guiding the design of CPO mutants with tailor-made activities for biotechnological applications. PMID:23634952

  15. Long-range Li+ dynamics in the lithium argyrodite Li7PSe6 as probed by rotating-frame spin-lattice relaxation NMR.

    PubMed

    Epp, V; Gün, O; Deiseroth, H-J; Wilkening, M

    2013-05-21

    Lithium-rich argyrodites belong to a relatively new group of fast ion conducting solids. They might serve as powerful electrolytes in all-solid-state lithium-ion batteries being, from a medium-term point of view, the key technology when safe energy storage systems have to be developed. Spin-lattice relaxation (SLR) nuclear magnetic resonance (NMR) measurements carried out in the rotating frame of reference turned out to be the method of choice to study Li dynamics in argyrodites. When plotted as a function of the inverse temperature, the SLR rates log10(R1ρ) reveal an asymmetric diffusion-induced rate peak. The rate peak contains information on the Li jump rate, the activation energy of the hopping process as well as correlation effects. In particular, considering the high-temperature flank of the SLR NMR rate peak recorded in the rotating frame of reference, an activation energy of approximately 0.49 eV is found. This value represents long-range lithium jump diffusion in crystalline Li7PSe6. As an example, at 325 K the Li jump rate determined from SLR NMR is in the order of 1.4 × 10(5) s(-1). The pronounced asymmetry of the rate peak R1ρ(1/T) points to correlated Li motion. It is comparable to that which is typically found for structurally disordered materials showing a broad range of correlation times.

  16. Relaxation time: a proton NMR-based approach as a metric to measure reactivity of engineered nanomaterials

    NASA Astrophysics Data System (ADS)

    Paruthi, Archini; Misra, Superb K.

    2017-08-01

    The toxicological impact of engineered nanoparticles in environmental or biological milieu is very difficult to predict and control because of the complexity of interactions of nanoparticles with the varied constituents in the suspended media. Nanoparticles are different from their bulk counterparts due to their high surface area-to-volume ratio per unit mass, which plays a vital role in bioavailability of these nanoparticles to its surroundings. This study explores how changes in the spin-spin nuclear relaxation time can be used to gauge the availability of surface area and suspension stability of selected nanoparticles (CuO, ZnO, and SiO2), in a range of simulated media. Spin-spin nuclear relaxation time can be mathematically correlated to wetted surface area, which is well backed up by the data of hydrodynamic size measurements and suspension stability. We monitored the change in spin-spin relaxation time for all the nanoparticles, over a range of concentrations (2.5 -100 ppm) in deionized water and artificial seawater. Selective concentrations of nanoparticle suspensions were subjected for temporal studies over a period of 48 hrs to understand the concept of spin-spin nuclear relaxation time-based reactivity of nanoparticle suspension. The nanoparticles showed high degree of agglomeration, when suspended in artificial seawater. This was captured by a decrease in spin-spin nuclear relaxation time and also an increment in the hydrodynamic size of the nanoparticles.

  17. NMR paramagnetic relaxation due to the S=5/2 complex, Fe(III)-(tetra-p-sulfonatophenyl)porphyrin: central role of the tetragonal fourth-order zero-field splitting interaction.

    PubMed

    Schaefle, Nathaniel; Sharp, Robert

    2005-05-08

    The metalloporphyrins, Me-TSPP [Me=Cr(III), Mn(III), Mn(II), Fe(III), and TSPP=meso-(tetra-p-sulfonatophenyl)porphyrin], which possess electron spins S=3/2, 2, 5/2, and 5/2, respectively, comprise an important series of model systems for mechanistic studies of NMR paramagnetic relaxation enhancement (NMR-PRE). For these S>1/2 spin systems, the NMR-PRE depends critically on the detailed form of the zero-field splitting (zfs) tensor. We report the results of experimental and theoretical studies of the NMR relaxation mechanism associated with Fe(III)-TSPP, a spin 5/2 complex for which the overall zfs is relatively large (D approximately = 10 cm(-1)). A comparison of experimental data with spin dynamics simulations shows that the primary determinant of the shape of the magnetic relaxation dispersion profile of the water proton R1 is the tetragonal fourth-order component of the zfs tensor. The relaxation mechanism, which has not previously been described, is a consequence of zfs-induced mixing of the spin eigenfunctions of adjacent Kramers doublets. We have also investigated the magnetic-field dependence of electron-spin relaxation for S=5/2 in the presence of a large zfs, such as occurs in Fe(III)-TSPP. Calculations show that field dependence of this kind is suppressed in the vicinity of the zfs limit, in agreement with observation.

  18. An inversion method of 2D NMR relaxation spectra in low fields based on LSQR and L-curve

    NASA Astrophysics Data System (ADS)

    Su, Guanqun; Zhou, Xiaolong; Wang, Lijia; Wang, Yuanjun; Nie, Shengdong

    2016-04-01

    The low-field nuclear magnetic resonance (NMR) inversion method based on traditional least-squares QR decomposition (LSQR) always produces some oscillating spectra. Moreover, the solution obtained by traditional LSQR algorithm often cannot reflect the true distribution of all the components. Hence, a good solution requires some manual intervention, for especially low signal-to-noise ratio (SNR) data. An approach based on the LSQR algorithm and L-curve is presented to solve this problem. The L-curve method is applied to obtain an improved initial optimal solution by balancing the residual and the complexity of the solutions instead of manually adjusting the smoothing parameters. First, the traditional LSQR algorithm is used on 2D NMR T1-T2 data to obtain its resultant spectra and corresponding residuals, whose norms are utilized to plot the L-curve. Second, the corner of the L-curve as the initial optimal solution for the non-negative constraint is located. Finally, a 2D map is corrected and calculated iteratively based on the initial optimal solution. The proposed approach is tested on both simulated and measured data. The results show that this algorithm is robust, accurate and promising for the NMR analysis.

  19. 11B and 27Al NMR spin-lattice relaxation and Knight shift of Mg1-xAlxB2: Evidence for an anisotropic Fermi surface

    NASA Astrophysics Data System (ADS)

    Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.

    2002-10-01

    We report a detailed study of the 11B and 27Al NMR spin-lattice relaxation rates (1/T1) and the 27Al Knight shift (K) in Mg1-xAlxB2, 0<=x<=1. The evolution of (1/T1T) and K with x is in excellent agreement with the prediction of ab initio calculations of a highly anisotropic Fermi surface, consisting mainly of hole-type two-dimensional (2D) cylindrical sheets from bonding 2px,y boron orbitals. The density of states at the Fermi level also decreases sharply on Al doping and the 2D sheets collapse at x~0.55, where the superconducting phase disappears.

  20. H-1 Relaxation Times of Metabolites in Biological Samples Obtained with Nondestructive Ex-vivo Slow-MAS NMR

    SciTech Connect

    Hu, Jian Zhi; Wind, Robert A.; Rommereim, Donald N.

    2006-03-01

    Methods suitable for measuring 1H relaxation times such as T1, T2 and T1p, in small sized biological objects including live cells, excised organs and tissues, oil seeds etc., were developed in this work. This was achieved by combining inversion-recovery, spin-echo, or spin lock segment with the phase-adjusted spinning sideband (PASS) technique that was applied at slow sample spinning rate. Here, 2D-PASS was used to produce a high-resolution 1H spectrum free from the magnetic susceptibility broadening so that the relaxation parameters of individual metabolite can be determined. Because of the slow spinning employed, tissue and cell damage due to sample spinning is minimized. The methodologies were demonstrated by measuring 1H T1, T2 and T1p of metabolites in excised rat livers and sesame seeds at spinning rates of as low as 40 Hz.

  1. Fast Li ion dynamics in the solid electrolyte Li7 P3 S11 as probed by (6,7) Li NMR spin-lattice relaxation.

    PubMed

    Wohlmuth, Dominik; Epp, Viktor; Wilkening, Martin

    2015-08-24

    The development of safe and long-lasting all-solid-state batteries with high energy density requires a thorough characterization of ion dynamics in solid electrolytes. Commonly, conductivity spectroscopy is used to study ion transport; much less frequently, however, atomic-scale methods such as nuclear magnetic resonance (NMR) are employed. Here, we studied long-range as well as short-range Li ion dynamics in the glass-ceramic Li7 P3 S11 . Li(+) diffusivity was probed by using a combination of different NMR techniques; the results are compared with those obtained from electrical conductivity measurements. Our NMR relaxometry data clearly reveal a very high Li(+) diffusivity, which is reflected in a so-called diffusion-induced (6) Li NMR spin-lattice relaxation peak showing up at temperatures as low as 313 K. At this temperature, the mean residence time between two successful Li jumps is in the order of 3×10(8) s(-1) , which corresponds to a Li(+) ion conductivity in the order of 10(-4) to 10(-3) S cm(-1) . Such a value is in perfect agreement with expectations for the crystalline but metastable glass ceramic Li7 P3 S11 . In contrast to conductivity measurements, NMR analysis reveals a range of activation energies with values ranging from 0.17 to 0.26 eV, characterizing Li diffusivity in the bulk. In our case, through-going Li ion transport, when probed by using macroscopic conductivity spectroscopy, however, seems to be influenced by blocking grain boundaries including, for example, amorphous regions surrounding the Li7 P3 S11 crystallites. As a result of this, long-range ion transport as seen by impedance spectroscopy is governed by an activation energy of approximately 0.38 eV. The findings emphasize how surface and grain boundary effects can drastically affect long-range ionic conduction. If we are to succeed in solid-state battery technology, such effects have to be brought under control by, for example, sophisticated densification or through the preparation

  2. Magnetic hyperthermia efficiency and 1H-NMR relaxation properties of iron oxide/paclitaxel-loaded PLGA nanoparticles

    NASA Astrophysics Data System (ADS)

    Ruggiero, Maria R.; Geninatti Crich, Simonetta; Sieni, Elisabetta; Sgarbossa, Paolo; Forzan, Michele; Cavallari, Eleonora; Stefania, Rachele; Dughiero, Fabrizio; Aime, Silvio

    2016-07-01

    Magnetic iron oxide nanoparticles (Fe-NPs) can be exploited in biomedicine as agents for magnetic fluid hyperthermia (MFH) treatments and as contrast enhancers in magnetic resonance imaging. New, oleate-covered, iron oxide particles have been prepared either by co-precipitation or thermal decomposition methods and incorporated into poly(lactic-co-glycolic acid) nanoparticles (PLGA-Fe-NPs) to improve their biocompatibility and in vivo stability. Moreover, the PLGA-Fe-NPs have been loaded with paclitaxel to pursue an MFH-triggered drug release. Remarkably, it has been found that the nanoparticle formulations are characterized by peculiar 1H nuclear magnetic relaxation dispersion (NMRD) profiles that directly correlate with their heating potential when exposed to an alternating magnetic field. By prolonging the magnetic field exposure to 30 min, a significant drug release was observed for PLGA-Fe-NPs in the case of the larger-sized magnetic nanoparticles. Furthermore, the immobilization of lipophilic Fe-NPs in PLGA-NPs also made it possible to maintain Néel relaxation as the dominant relaxation contribution in the presence of large iron oxide cores (diameters of 15-20 nm), with the advantage of preserving their efficiency when they are entrapped in the intracellular environment. The results reported herein show that NMRD profiles are a useful tool for anticipating the heating capabilities of Fe-NPs designed for MFH applications.

  3. Inhomogeneous 1H NMR spin-lattice relaxation in the organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br

    NASA Astrophysics Data System (ADS)

    Gezo, Joseph Christopher

    The two-dimensional superconductors based on the organic molecule "ET" have been an active area of research since their discovery over two decades ago. The member of this family with the highest critical temperature, kappa-(ET)2Cu[N(CN)2]Br ( Tc=11.7 K), has seen renewed interest since the observation of an anomalous Nernst signal by Nam et al in 2007 [51]. A similar effect was seen earlier by Ong's group in some of the high-temperature cuprate superconductors by [78,84]. This is interpreted to be evidence of a picture of superconductivity in which the resistive transition is driven by thermal fluctuations in the phase of the superconducting order parameter. Below Tc, these fluctuations take the form of bound vortex-antivortex pairs that have no long-range effect on the phase. At Tc, they undergo a Kosterlitz-Thouless unbinding transition; the unbound vortices destroy long-range phase coherence. Previously reported proton NMR measurements on this material have shown a high sensitivity to vortex motion, but reported no interesting behavior above the phase transition [15,25,42]. In this thesis, we revisit the 1H NMR properties of kappa-(ET)2Cu[N(CN)2]Br, paying specific attention to the spin-lattice relaxation, to look for some fingerprint of the phenomenon observed by Nam et al.

  4. Conformational stability and thermal pathways of relaxation in triclosan (antibacterial/excipient/contaminant) in solid-state: combined spectroscopic ((1)H NMR) and computational (periodic DFT) study.

    PubMed

    Latosińska, Jolanta Natalia; Latosińska, Magdalena; Tomczak, Marzena Agnieszka; Medycki, Wojciech

    2015-05-21

    The mechanism of molecular dynamics in the antibacterial/antifungal agent, triclosan (5-chloro-2-(2',4'-dichlorophenoxy)-phenol), in solid state was studied by (1)H NMR spectroscopy and periodic density functional theory (DFT) calculations. Temperature dependencies of the proton spin-lattice relaxation time (T1) in the ranges 86-293 and 90-250 K (at 15 and 24.667 MHz, respectively) and the second moment (M2) of the (1)H NMR resonant line in the range 103-300 K were measured. Two minima in the temperature dependence of T1 revealed a classical Arrhenius governed activation processes. The low temperature shallow minimum T1(T) of 71 s at 115 K, 15 MHz, which shifts with frequency, was assigned to classical hindered jumps of hydroxyl group around OC axis and with respect to a 5-chloro-2-phenol ring. The activation energy of this motion estimated on the basis of the fit of the theoretical model to the experimental points is 9.68 kJ/mol. The pointed high temperature minimum T1(T) of 59 s at 190 K, 15 MHz, which also shifts with frequency, was assigned to the small angle librations by Θlib= ± 9° between two positions of equilibrium differing in energy by 7.42 kJ/mol. The activation energy of this motion estimated on the basis of the fit of the theoretical model to the experimental points is 31.1 kJ/mol. Both motions result in a negligible reduction in the (1)H NMR line second moment, thus the second moment delivers an irrelevant description of the molecular motions in triclosan.

  5. Effective Forces Between Diamagnetic and Paramagnetic Ions in D 2 O at Low and Moderate Ionic Strengths: An NMR Relaxation Study

    NASA Astrophysics Data System (ADS)

    Sacco, A.; Belorizky, E.; Jeannin, M.; Gorecki, W.; Fries, P. H.

    1997-09-01

    The dynamical behaviour of several pairs of dissociated, attractive and repulsive, ions is investigated in aqueous solutions for ionic strengths up to 1 mol l^{-1}. The experimental information is provided by the NMR longitudinal relaxation rates of the protons on the diamagnetic ions. The ionic solutions were chosen so that the main relaxation mechanism of these protons is due to the time fluctuations of their dipolar magnetic coupling with the electronic spins on the paramagnetic ions. This coupling strongly depends on the ion-ion potential of mean force (PMF) and on the ion self-diffusion coefficients. The interionic spatial correlations and the associated PMF are derived from a new approximation of the integral equations of the statistical mechanics of liquids. This formalism, which treats all the ions as discrete particles, rests on the infinite dilution PMF of the various ion pairs. It mixes a Born-Oppenheimer theory at infinite dilution with a sort of McMillan-Mayer approximation to take the ionic concentration into account. It goes beyond the Debye-Hückel screening theory, in which a continuous screening charge distribution approximates the effects of the discrete surrounding ions. It is related to the concept of the local dielectric constants which replace the usual macroscopic dielectric constant and depend on the interionic distances. The self-diffusion coefficients of the diamagnetic ions were measured by the NMR pulsed magnetic field gradient (PMFG) techniques applied to the resonant protons. In paramagnetic solutions, where several protonated species coexist, special caution is required and this is discussed in detail. For all the investigated solutions the theory well accounts for the observed variation of the NMR relaxation as a function of the ion charges, of the ionic strength and of the NMR proton resonance frequency. The relaxation results predicted by the new approximation of the ion-ion PMF are compared with those derived from the simple

  6. Interaction between reduced glutathione and PEO-PPO-PEO copolymers in aqueous solutions: studied by 1H NMR and spin-lattice relaxation.

    PubMed

    Jia, Lianwei; Guo, Chen; Yang, Liangrong; Xiang, Junfeng; Tang, Yalin; Liu, Huizhou

    2011-03-17

    In order to investigate the effect of PEO-PPO-PEO copolymers on the glutathione (GSH)/glutathione-S-transferase (GST) detoxification system, interaction between the copolymers and GSH is studied by NMR measurements. Selective rotating-frame nuclear Overhauser effect (ROE) experiment confirms that glutamyl (Glu) α-H of GSH has spatial contact with EO methylene protons. Spin-lattice relaxation times of GSH Glu α-H show a decrease when PEO-PPO-PEO copolymers are added, and the decrease is greater with copolymers possessing more EO units. Other protons of GSH show little change in the presence of the copolymers. The addition of GSH promotes the dehydration of PEO-PPO-PEO copolymers. This results from the breaking of hydrogen bonds between water and the polymers and the forming of hydrogen bonds between Glu α-carboxylate protons and oxygen atoms of EO units. The dissociation constant between GSH and P85 copolymer is determined by spin-lattice relaxation measurements, which shows the binding is of low affinity and the two molecules are in fast dissociation kinetics. This study suggests that GSH transporting or utilizing systems may be affected by treatment of PEO-PPO-PEO copolymers.

  7. 31P NMR Relaxation of Cortical Bone Mineral at Multiple Magnetic Field Strengths and Levels of Demineralization

    PubMed Central

    Seifert, Alan C.; Wright, Alexander C.; Wehrli, Suzanne L.; Ong, Henry H.; Li, Cheng; Wehrli, Felix W.

    2013-01-01

    Purpose Recent work has shown that solid-state 1H and 31P MRI can provide detailed insight into bone matrix and mineral properties, thereby potentially enabling differentiation of osteoporosis from osteomalacia. However, 31P MRI of bone mineral is hampered by unfavorable relaxation properties. Hence, accurate knowledge of these properties is critical to optimizing MRI of bone phosphorus. Methods In this work, 31P MRI signal-to-noise ratio (SNR) was predicted on the basis of T1 and T2* (effective transverse relaxation time) measured in lamb bone at six field strengths (1.5 – 11.7 T) and subsequently verified by 3-D ultra-short echo-time and zero echo-time imaging. Further, T1 was measured in deuterium-exchanged bone and partially demineralized bone. Results 31P T2* was found to decrease from 220.3 ± 4.3 μs to 98.0 ± 1.4 μs from 1.5 to 11.7 T, and T1 to increase from 12.8 ± 0.5 s to 97.3 ± 6.4 s. Deuteron substitution of exchangeable water showed that 76% of the 31P longitudinal relaxation rate is due to 1H-31P dipolar interactions. Lastly, hypomineralization was found to decrease T1, which may have implications for 31P MRI based mineralization density quantification. Conclusion Despite the steep decrease in the T2*/T1 ratio, SNR should increase with field strength as Bo0.4 for sample-dominated noise and as Bo1.1 for coil-dominated noise. This was confirmed by imaging experiments. PMID:23505120

  8. Dynamic regulation of GDP binding to G proteins revealed by magnetic field-dependent NMR relaxation analyses

    PubMed Central

    Toyama, Yuki; Kano, Hanaho; Mase, Yoko; Yokogawa, Mariko; Osawa, Masanori; Shimada, Ichio

    2017-01-01

    Heterotrimeric guanine-nucleotide-binding proteins (G proteins) serve as molecular switches in signalling pathways, by coupling the activation of cell surface receptors to intracellular responses. Mutations in the G protein α-subunit (Gα) that accelerate guanosine diphosphate (GDP) dissociation cause hyperactivation of the downstream effector proteins, leading to oncogenesis. However, the structural mechanism of the accelerated GDP dissociation has remained unclear. Here, we use magnetic field-dependent nuclear magnetic resonance relaxation analyses to investigate the structural and dynamic properties of GDP bound Gα on a microsecond timescale. We show that Gα rapidly exchanges between a ground-state conformation, which tightly binds to GDP and an excited conformation with reduced GDP affinity. The oncogenic D150N mutation accelerates GDP dissociation by shifting the equilibrium towards the excited conformation. PMID:28223697

  9. Dynamic regulation of GDP binding to G proteins revealed by magnetic field-dependent NMR relaxation analyses.

    PubMed

    Toyama, Yuki; Kano, Hanaho; Mase, Yoko; Yokogawa, Mariko; Osawa, Masanori; Shimada, Ichio

    2017-02-22

    Heterotrimeric guanine-nucleotide-binding proteins (G proteins) serve as molecular switches in signalling pathways, by coupling the activation of cell surface receptors to intracellular responses. Mutations in the G protein α-subunit (Gα) that accelerate guanosine diphosphate (GDP) dissociation cause hyperactivation of the downstream effector proteins, leading to oncogenesis. However, the structural mechanism of the accelerated GDP dissociation has remained unclear. Here, we use magnetic field-dependent nuclear magnetic resonance relaxation analyses to investigate the structural and dynamic properties of GDP bound Gα on a microsecond timescale. We show that Gα rapidly exchanges between a ground-state conformation, which tightly binds to GDP and an excited conformation with reduced GDP affinity. The oncogenic D150N mutation accelerates GDP dissociation by shifting the equilibrium towards the excited conformation.

  10. Complex mechanism of relaxation in solid chloroxylenol (antibacterial/antifungal agent) studied by ¹H NMR spectroscopy and density functional theory calculations.

    PubMed

    Latosińska, Jolanta Natalia; Latosińska, Magdalena; Tomczak, Marzena Agnieszka; Medycki, Wojciech

    2014-03-27

    Molecular relaxation in antibacterial/antifungal agent: chloroxylenol (4-chloro-3,5-dimethylphenol, PCMX) in the solid state was studied by the (1)H NMR and quantum chemistry calculations. The temperature dependencies of the proton spin-lattice relaxation time (T1) in the ranges 15-273 K (at 24.667 MHz), 77-295 K (at 15 MHz), and 112-291 K at 90 MHz and the second moment (M2) of (1)H NMR resonant line in the range 106-380 K were measured. The two minima in the temperature dependence of T1 revealed two activation processes, whereas the M2 dependence in the studied range was quite flat and revealed the only significant reduction at 380 K. The low temperature part of T1(T) dependence indicated the occurrence of two processes characteristic of methyl bearing solids; the quantum mechanics governed incoherent tunneling (responsible for the low temperature flattening of T1) and the classical Arrhenius dependence governed hindered rotation (related to the wide low temperature minimum of 0.066 s at 57 K, 24.667 MHz). The 2D potential energy surface obtained using DFT/B3LYP/6-311++G(2d,p) calculations revealed the inequivalence of methyl groups and the lack of their interplay/coupling. The activation energies of classical hindered rotation are 3.35 and 2.5 kJ/mol, whereas temperatures at which the proton tunneling T(tun) finally ceases are 52 and 63 K, for inequivalent methyl groups. C(p)(T) required for the estimation of T(tun) was calculated purely theoretically on the basis of the Einstein and Debye models of specific heat and 51 modes of atomic vibrations, 4 internal rotations, and 3 torsions calculated by DFT. The -CH3 motion (tunneling and classical) results in the reduction in the (1)H NMR line second moment from 17.3 G(2) (rigid) to approximately 11.05 G(2). The pointed high temperature minimum T1(T) of 0.109 s at 89 K, 24.667 MHz, which shifts with frequency, was assigned to small-angle libration jumps, by the Θ2 = ±15° between two positions of equilibrium. The

  11. Temperature Dependence of NMR Relaxation Times of Nucleoside Triphosphates and Inorganic Phosphate in the Isolated Perfused Rat Liver. Effect on Pi Compartmentation

    NASA Astrophysics Data System (ADS)

    Dufour, Sylvie; Thiaudière, Eric; Vidal, Giovanni; Gallis, Jean-Louis; Rousse, Nicole; Canioni, Paul

    1996-11-01

    The effect of temperature on31P NMR spectra from isolated perfused rat livers was studied at 9.4 T. Relaxation times (T1andT2) of nucleoside triphosphates (NTP) and inorganic phosphate (Pi) were determined at 37, 25, 15, and 4°C. Under hypothermic conditions, an unexpected apparent line sharpening in the Pi spectral region and a clear emergence of an additional Pi resonance were observed. This additional signal was assigned to mitochondrial Pi.T1values obtained for cytosolic and mitochondrial Pi at 4°C were 1.14 ± 0.24 s (n= 5) and 0.71 ± 0.18 s (n= 5), respectively. No significant mitochondrial contribution to the Pi resonance was observed at 37°C. Quantification of Pi and NTP liver contents at 37 and 4°C was performed by comparing the perfused liver spectrum and the corresponding perchloric acid extract spectrum. Under experimental conditions of low external Pi (0.12 mM), it was concluded that intracellular Pi was completely NMR-visible at 4 and 37°C. The observation of the mitochondrial Pi signal at 4°C was well explained by an increase in the Pi level within the matrix, in response to the mitochondrial swelling induced by hypothermia, as observed by electron microscopy.T2values for the cytosolic Pi at 37 and 4°C were 17 ± 4 ms (n= 8) and 22 ± 4 ms (n= 10), respectively. Comparison with measured linewidths indicated that line broadening for the main phosphorylated metabolites-including matrix Pi-was the result ofB0field inhomogeneity. The additional broadening of the cytosolic Pi resonance at 4 and 37°C was attributed to pH heterogeneity within the liver.

  12. Competition between Na + and Li + for Unsealed and Cytoskeleton-Depleted Human Red Blood Cell Membrane: A 23Na Multiple Quantum Filtered and 7Li NMR Relaxation Study

    NASA Astrophysics Data System (ADS)

    Srinivasan, Chandra; Minadeo, Nicole; Toon, Jason; Graham, Daniel; Mota de Freitas, Duarte; Geraldes, Carlos F. G. C.

    1999-09-01

    Evidence for competition between Li+ and Na+ for binding sites of human unsealed and cytoskeleton-depleted human red blood cell (csdRBC) membranes was obtained from the effect of added Li+ upon the 23Na double quantum filtered (DQF) and triple quantum filtered (TQF) NMR signals of Na+-containing red blood cell (RBC) membrane suspensions. We found that, at low ionic strength, the observed quenching effect of Li+ on the 23Na TQF and DQF signal intensity probed Li+/Na+ competition for isotropic binding sites only. Membrane cytoskeleton depletion significantly decreased the isotropic signal intensity, strongly affecting the binding of Na+ to isotropic membrane sites, but had no effect on Li+/Na+ competition for those sites. Through the observed 23Na DQF NMR spectra, which allow probing of both isotropic and anisotropic Na+ motion, we found anisotropic membrane binding sites for Na+ when the total ionic strength was higher than 40 mM. This is a consequence of ionic strength effects on the conformation of the cytoskeleton, in particular on the dimer-tetramer equilibrium of spectrin. The determinant involvement of the cytoskeleton in the anisotropy of Na+ motion at the membrane surface was demonstrated by the isotropy of the DQF spectra of csdRBC membranes even at high ionic strength. Li+ addition initially quenched the isotropic signal the most, indicating preferential Li+/Na+ competition for the isotropic membrane sites. High ionic strength also increased the intensity of the anisotropic signal, due to its effect on the restructuring of the membrane cytoskeleton. Further Li+ addition competed with Na+ for those sites, quenching the anisotropic signal. 7Li T1 relaxation data for Li+-containing suspensions of unsealed and csdRBC membranes, in the absence and presence of Na+ at low ionic strength, showed that cytoskeleton depletion does not affect the affinity of Na+ for the RBC membrane, but increases the affinity of Li+ by 50%. This clearly indicates that cytoskeleton

  13. Adiabatic fast passage application in solid state NMR study of cross relaxation and molecular dynamics in heteronuclear systems

    NASA Astrophysics Data System (ADS)

    Baranowski, M.; Woźniak-Braszak, A.; Jurga, K.

    2016-01-01

    The paper presents the benefits of using fast adiabatic passage for the study of molecular dynamics in the solid state heteronuclear systems in the laboratory frame. A homemade pulse spectrometer operating at the frequency of 30.2 MHz and 28.411 MHz for protons and fluorines, respectively, has been enhanced with microcontroller direct digital synthesizer DDS controller [1-4]. This work briefly describes how to construct a low-cost and easy-to-assemble adiabatic extension set for homemade and commercial spectrometers based on recently very popular Arduino shields. The described set was designed for fast adiabatic generation. Timing and synchronization problems are discussed. The cross-relaxation experiments with different initial states of the two spin systems have been performed. Contrary to our previous work [5] where the steady-state NOE experiments were conducted now proton spins 1H are polarized in the magnetic field B0 while fluorine spins 19F are perturbed by selective saturation for a short time and then the system is allowed to evolve for a period in the absence of a saturating field. The adiabatic passage application leads to a reversal of magnetization of fluorine spins and increases the amplitude of the signal.

  14. 1H and 2H NMR spin-lattice relaxation probing water: PEG molecular dynamics in solution.

    PubMed

    Clop, Eduardo M; Perillo, María A; Chattah, Ana K

    2012-10-04

    Nuclear magnetic resonance spin-lattice relaxation times (T(1)) measurements were performed in aqueous solutions of poly(ethylene glycol) (PEG) of 6000 Da molecular mass to study the dynamical relation between PEG and water molecules at different solute concentrations. (1)H-T(1) experiments were carried on at a low magnetic field in the time domain (20 MHz) and at a high field (400 MHz) to obtain spectral resolution. Two contributing components were identified in each proton system, PEG and water, presenting values of T(1) with very different orders of magnitude. The approximate matching between the shorter (1)H-T(1) values associated with water and PEG has lead us to conclude that there exists a network of interactions (hydrogen bonds) between the solute and the solvent, which results in the presence of an ordered and dehydrated structure of PEG folded or self-assembled in equilibrium with a more flexible monomer structure. Dynamic light scattering results were consistent with the formation of PEG aggregates, showing a mean size between 40 and 100 nm.

  15. Ionic liquid containing microemulsions: probe by conductance, dynamic light scattering, diffusion-ordered spectroscopy NMR measurements, and study of solvent relaxation dynamics.

    PubMed

    Pramanik, Rajib; Sarkar, Souravi; Ghatak, Chiranjib; Rao, Vishal Govind; Sarkar, Nilmoni

    2011-03-17

    Room-temperature ionic liquid (RTIL), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([P(13)][Tf(2)N]), was substituted for polar water and formed nonaqueous microemulsions with benzene by the aid of nonionic surfactant TX-100. The phase behavior of the ternary system was investigated, and microregions of [P(13)][Tf(2)N]-in-benzene (IL/O), bicontinuous, and benzene-in-[P(13)][Tf(2)N] (O/IL) were identified by traditional electrical conductivity measurements. Dynamic light scattering (DLS) revealed the formation of these IL microemulsions because with gradual increase of RTIL contents the droplet sizes of the microemulsions are also gradually increasing. Pulsed-field gradient spin-echo NMR have been studied to measure the diffusion coefficients of neat [P(13)][Tf(2)N] and [P(13)][Tf(2)N] in microemulsions which indicate ionic liquid containing microemulsions is formed. Moreover, the dynamics of solvent relaxation have been investigated in [P(13)][Tf(2)N]/TX100/benzene microemulsions using steady-state and time-resolved fluorescence spectroscopy using coumarin 153 (C-153) and coumarin 480 (C-480) fluorescence probe with variation of RTIL contents in microemulsions. For both of the probes with increasing amount of ionic liquids in microemulsions the relative contribution of the fast components increases and the slow components contribution decreases; therefore the average solvation time decreases. © 2011 American Chemical Society

  16. High-resolution NMR field-cycling device for full-range relaxation and structural studies of biopolymers on a shared commercial instrument.

    PubMed

    Redfield, Alfred G

    2012-02-01

    Improvements are described in a shuttling field-cycling device (Redfield in Magn Reson Chem 41:753-768, 2003), designed to allow widespread access to this useful technique by configuring it as a removable module to a commercial 500 MHz NMR instrument. The main improvements described here, leading to greater versatility, high reliability and simple construction, include: shuttling provided by a linear motor driven by an integrated-control servomotor; provision of automated bucking magnets to allow fast two-stage cycling to nearly zero field; and overall control by a microprocessor. A brief review of history and publications that have used the system is followed by a discussion of topics related to such a device including discussion of some future applications. A description of new aspects of the shuttling device follows. The minimum round trip time to 1T and above is less than 0.25 s and to 0.002 T is 0.36 s. Commercial probes are used and sensitivity is that of the host spectrometer reduced only by relaxation during travel. A key element is development of a linkage that prevents vibration of the linear motor from reaching the probe.

  17. N15: the linear phage-plasmid.

    PubMed

    Ravin, Nikolai V

    2011-03-01

    The lambdoid phage N15 of Escherichia coli is very unusual among temperate phages in that its prophage is not integrated into chromosome but is a linear plasmid molecule with covalently closed ends. Upon infection the phage DNA circularises via cohesive ends, then phage-encoded enzyme, protelomerase, cuts at an inverted repeat site and forms hairpin ends (telomeres) of the linear plasmid prophage. Replication of the N15 prophage is initiated at an internally located ori site and proceeds bidirectionally resulting in formation of duplicated telomeres. Then the N15 protelomerase cuts duplicated telomeres generating two linear plasmid molecules with hairpin telomeres. Stable inheritance of the plasmid prophage is ensured by partitioning operon similar to the F factor sop operon. Unlike F sop, the N15 centromere consists of four inverted repeats dispersed in the genome. The multiplicity and dispersion of centromeres are required for efficient partitioning of a linear plasmid. The centromeres are located in N15 genome regions involved in phage replication and control of lysogeny, and binding of partition proteins at these sites regulates these processes. Two N15-related lambdoid Siphoviridae phages, φKO2 in Klebsiella oxytoca and pY54 in Yersinia enterocolitica, also lysogenize their hosts as linear plasmids, as well as Myoviridae marine phages VP882 and VP58.5 in Vibrio parahaemolyticus and ΦHAP-1 in Halomonas aquamarina. The genomes of all these phages contain similar protelomerase genes, lysogeny modules and replication genes, as well as plasmid-partitioning genes, suggesting that these phages may belong to a group diverged from a common ancestor.

  18. Probing microsecond time scale dynamics in proteins by methyl (1)H Carr-Purcell-Meiboom-Gill relaxation dispersion NMR measurements. Application to activation of the signaling protein NtrC(r).

    PubMed

    Otten, Renee; Villali, Janice; Kern, Dorothee; Mulder, Frans A A

    2010-12-01

    To study microsecond processes by relaxation dispersion NMR spectroscopy, low power deposition and short pulses are crucial and encourage the development of experiments that employ (1)H Carr-Purcell-Meiboom-Gill (CPMG) pulse trains. Herein, a method is described for the comprehensive study of microsecond to millisecond time scale dynamics of methyl groups in proteins, exploiting their high abundance and favorable relaxation properties. In our approach, protein samples are produced using [(1)H, (13)C]-d-glucose in ∼100% D(2)O, which yields CHD(2) methyl groups for alanine, valine, threonine, isoleucine, leucine, and methionine residues with high abundance, in an otherwise largely deuterated background. Methyl groups in such samples can be sequence-specifically assigned to near completion, using (13)C TOCSY NMR spectroscopy, as was recently demonstrated (Otten, R.; et al. J. Am. Chem. Soc. 2010, 132, 2952-2960). In this Article, NMR pulse schemes are presented to measure (1)H CPMG relaxation dispersion profiles for CHD(2) methyl groups, in a vein similar to that of backbone relaxation experiments. Because of the high deuteration level of methyl-bearing side chains, artifacts arising from proton scalar coupling during the CPMG pulse train are negligible, with the exception of Ile-δ1 and Thr-γ2 methyl groups, and a pulse scheme is described to remove the artifacts for those residues. Strong (13)C scalar coupling effects, observed for several leucine residues, are removed by alternative biochemical and NMR approaches. The methodology is applied to the transcriptional activator NtrC(r), for which an inactive/active state transition was previously measured and the motions in the microsecond time range were estimated through a combination of backbone (15)N CPMG dispersion NMR spectroscopy and a collection of experiments to determine the exchange-free component to the transverse relaxation rate. Exchange contributions to the (1)H line width were detected for 21 methyl

  19. Cooperative binding of midazolam with testosterone and alpha-naphthoflavone within the CYP3A4 active site: a NMR T1 paramagnetic relaxation study.

    PubMed

    Cameron, Michael D; Wen, Bo; Allen, Kyle E; Roberts, Arthur G; Schuman, Jason T; Campbell, A Patricia; Kunze, Kent L; Nelson, Sidney D

    2005-11-01

    Recent studies have indicated that CYP3A4 exhibits non-Michaelis-Menten kinetics for numerous substrates. Both homo- and heterotropic activation have been reported, and kinetic models have suggested multiple substrates within the active site. We provide some of the first physicochemical data supporting the hypothesis of allosteric substrate binding within the CYP3A4 active site. Midazolam (MDZ) is metabolized by CYP3A4 to two hydroxylated metabolites, 1'- and 4-hydroxymidazolam. Incubations using purified CYP3A4 and MDZ showed that both alpha-naphthoflavone (alpha-NF) and testosterone affect the ratio of formation rates of 1'- and 4-hydroxymidazolam. Similar to previous reports, alpha-NF was found to promote formation of 1'-hydroxymidazolam, while testosterone stimulated formation of 4-hydroxymidazolam. NMR was used to measure the closest approach of individual MDZ protons to the paramagnetic heme iron of CYP3A4 using paramagnetic T(1) relaxation measurements. Solutions of 0.2 microM CYP3A4 with 500 microM MDZ resulted in calculated distances between 7.4 and 8.3 A for all monitored MDZ protons. The distances were statistically equivalent for all protons except C3-H and were consistent with the rotation within the active site or sliding parallel to the heme plane. When 50 microM alpha-NF was added, proton-heme iron distances ranged from 7.3 to 10.0 A. Consistent with kinetics of activation, the 1' position was situated closest to the heme, while the fluorophenyl 5-H proton was the furthest. Proton-heme iron distances for MDZ with CYP3A4 and 50 microM testosterone ranged from 7.7 to 9.0 A, with the flourophenyl 5-H proton furthest from the heme iron and the C4-H closest to the heme, also consistent with kinetic observations. When titrated with CYP3A4 in the presence of MDZ, testosterone and alpha-NF resonances themselves exhibited significant broadening and enhanced relaxation rates, indicating that these effector molecules were also bound within the CYP3A4 active

  20. My starting point: the discovery of an NMR method for measuring blood oxygenation using the transverse relaxation time of blood water.

    PubMed

    Thulborn, Keith R

    2012-08-15

    This invited personal story, covering the period from 1979 to 2010, describes the discovery of the dependence of the transverse relaxation time of water in blood on the oxygenation state of hemoglobin in the erythrocytes. The underlying mechanism of the compartmentation of the different magnetic susceptibilities of hemoglobin in its different oxygenation states also explains the mechanism that underlies blood oxygenation level dependent contrast used in fMRI. The story begins with the initial observation of line broadening during ischemia in small rodents detected by in vivo 31P NMR spectroscopy at high field. This spectroscopic line broadening or T2* relaxation effect was demonstrated to be related to the oxygenation state of blood. The effect was quantified more accurately using T2 values measured by the Carr-Purcell-Meiboom-Gill method. The effect was dependent on the integrity of the erythrocytes to compartmentalize the different magnetic susceptibilities produced by the changing spin state of the ferrous iron of hemoglobin in its different oxygenation states between the erythrocytes and the suspending solution. The hematocrit and magnetic field dependence, the requirement for erythrocyte integrity and lack of T1 dependence confirmed that the magnetic susceptibility effect explained the oxygenation state dependence of T2* and T2. This T2/T2* effect was combined with T1 based measurements of blood flow to measure oxygen consumption in animals. This blood oxygenation assay and its underlying magnetic susceptibility gradient mechanism was published in the biochemistry literature in 1982 and largely forgotten. The observation was revived to explain evolving imaging features of cerebral hematoma as MR imaging of humans increased in field strength to 1.5 T by the mid 1980s. Although the imaging version of this assay was used to measure a global metabolic rate of cerebral oxygen consumption in humans at 1.5-T by 1991, the global measurement had little clinical value

  1. Crystal structure, NMR study, dielectric relaxation and AC conductivity of a new compound [Cd3(SCN)2Br6(C2H9N2)2]n

    NASA Astrophysics Data System (ADS)

    Saidi, K.; Kamoun, S.; Ayedi, H. Ferid; Arous, M.

    2013-11-01

    The crystal structure, the 13C NMR spectroscopy and the complex impedance have been carried out on [Cd3(SCN)2Br6(C2H9N2)2]n. Crystal structure shows a 2D polymeric network built up of two crystallographically independent cadmium atoms with two different octahedral coordinations. This compound exhibits a phase transition at (T=355±2 K) which has been characterized by differential scanning calorimetry (DSC), X-rays powder diffraction, AC conductivity and dielectric measurements. Examination of 13C CP/MAS line shapes shows indirect spin-spin coupling (14N and 13C) with a dipolar coupling constant of 1339 Hz. The AC conductivity of this compound has been carried out in the temperature range 325-376 K and the frequency range from 10-2 Hz to 10 MHz. The impedance data were well fitted to two equivalent electrical circuits. The results of the modulus study reveal the presence of two distinct relaxation processes. One, at low frequency side, is thermally activated due to the ionic conduction of the crystal and the other, at higher frequency side, gradually disappears when temperature reaches 355 K which is attributed to the localized dipoles in the crystal. Moreover, the temperature dependence of DC-conductivity in both phases follows the Arrhenius law and the frequency dependence of σ(ω,T) follows Jonscher's universal law. The near values of activation energies obtained from the conductivity data and impedance confirm that the transport is through the ion hopping mechanism.

  2. Site-specific protonation kinetics of acidic side chains in proteins determined by pH-dependent carboxyl (13)C NMR relaxation.

    PubMed

    Wallerstein, Johan; Weininger, Ulrich; Khan, M Ashhar I; Linse, Sara; Akke, Mikael

    2015-03-04

    Proton-transfer dynamics plays a critical role in many biochemical processes, such as proton pumping across membranes and enzyme catalysis. The large majority of enzymes utilize acid-base catalysis and proton-transfer mechanisms, where the rates of proton transfer can be rate limiting for the overall reaction. However, measurement of proton-exchange kinetics for individual side-chain carboxyl groups in proteins has been achieved in only a handful of cases, which typically have involved comparative analysis of mutant proteins in the context of reaction network modeling. Here we describe an approach to determine site-specific protonation and deprotonation rate constants (kon and koff, respectively) of carboxyl side chains, based on (13)C NMR relaxation measurements as a function of pH. We validated the method using an extensively studied model system, the B1 domain of protein G, for which we measured rate constants koff in the range (0.1-3) × 10(6) s(-1) and kon in the range (0.6-300) × 10(9) M(-1) s(-1), which correspond to acid-base equilibrium dissociation constants (Ka) in excellent agreement with previous results determined by chemical shift titrations. Our results further reveal a linear free-energy relationship between log kon and pKa, which provides information on the free-energy landscape of the protonation reaction, showing that the variability among residues in these parameters arises primarily from the extent of charge stabilization of the deprotonated state by the protein environment. We find that side-chain carboxyls with extreme values of koff or kon are involved in hydrogen bonding, thus providing a mechanistic explanation for the observed stabilization of the protonated or deprotonated state.

  3. Solution structure of a DNA decamer containing the antiviral drug ganciclovir: combined use of NMR, restrained molecular dynamics, and full relaxation matrix refinement.

    PubMed

    Foti, M; Marshalko, S; Schurter, E; Kumar, S; Beardsley, G P; Schweitzer, B I

    1997-05-06

    The nucleoside analog 9-[(1,3-dihydroxy-2-propoxy)methyl]guanine (ganciclovir, DHPG) is an antiviral drug that is used in the treatment of a variety of herpes viruses in immunocompromised patients and in a gene therapy protocol that has shown promising activity for the treatment of cancer. To probe the structural effects of ganciclovir when incorporated into DNA, we determined and compared the solution structure of a modified ganciclovir-containing decamer duplex [d(CTG)(ganciclovir)d(ATCCAG)]2 and a control duplex d[(CTGGATCCAG)]2 using nuclear magnetic resonance techniques. 1H and 31P resonances in both duplexes were assigned using a combination of 2-D 1H and 31P NMR experiments. Proton-proton distances determined from NOESY data and dihedral angles determined from DQF-COSY data were used in restrained molecular dynamics simulations starting from canonical A- and B-form DNA models. Both the control and ganciclovir sets of simulations converged to B-type structures. These structures were subjected to full relaxation matrix refinement to produce final structures that were in excellent agreement with the observed NOE intensities. Examination of the final ganciclovir-containing structures reveals that the base of the ganciclovir residue is hydrogen bonded to its complementary dC and is stacked in the helix; in fact, the base of ganciclovir exhibits increased stacking with the 5' base relative to the control. Interestingly, some of the most significant distortions in the structures occur 3' to the lesion site, including a noticeable kink in the sugar-phosphate backbone at this position. Further examination reveals that the backbone conformation, sugar pucker, and glycosidic torsion angle of the residue 3' to the lesion site all indicate an A-type conformation at this position. A possible correlation of these structural findings with results obtained from earlier biochemical studies will be discussed.

  4. Flexibility at a glycosidic linkage revealed by molecular dynamics, stochastic modeling, and (13)C NMR spin relaxation: conformational preferences of α-L-Rhap-α-(1 → 2)-α-L-Rhap-OMe in water and dimethyl sulfoxide solutions.

    PubMed

    Pendrill, Robert; Engström, Olof; Volpato, Andrea; Zerbetto, Mirco; Polimeno, Antonino; Widmalm, Göran

    2016-01-28

    The monosaccharide L-rhamnose is common in bacterial polysaccharides and the disaccharide α-L-Rhap-α-(1 → 2)-α-L-Rhap-OMe represents a structural model for a part of Shigella flexneri O-antigen polysaccharides. Utilization of [1'-(13)C]-site-specific labeling in the anomeric position at the glycosidic linkage between the two sugar residues facilitated the determination of transglycosidic NMR (3)JCH and (3)JCC coupling constants. Based on these spin-spin couplings the major state and the conformational distribution could be determined with respect to the ψ torsion angle, which changed between water and dimethyl sulfoxide (DMSO) as solvents, a finding mirrored by molecular dynamics (MD) simulations with explicit solvent molecules. The (13)C NMR spin relaxation parameters T1, T2, and heteronuclear NOE of the probe were measured for the disaccharide in DMSO-d6 at two magnetic field strengths, with standard deviations ≤1%. The combination of MD simulation and a stochastic description based on the diffusive chain model resulted in excellent agreement between calculated and experimentally observed (13)C relaxation parameters, with an average error of <2%. The coupling between the global reorientation of the molecule and the local motion of the spin probe is deemed essential if reproduction of NMR relaxation parameters should succeed, since decoupling of the two modes of motion results in significantly worse agreement. Calculation of (13)C relaxation parameters based on the correlation functions obtained directly from the MD simulation of the solute molecule in DMSO as solvent showed satisfactory agreement with errors on the order of 10% or less.

  5. The structural plasticity of heparan sulfate NA-domains and hence their role in mediating multivalent interactions is confirmed by high-accuracy 15N-NMR relaxation studies

    PubMed Central

    Mobli, Mehdi; Nilsson, Mathias

    2007-01-01

    Considering the biological importance of heparan sulfate (HS) and the significant activity of its highly-sulfated regions (S-domains), the paucity of known functions for the non-sulfated NA-domains is somewhat puzzling. It has been suggested that chain dynamics within the NA-domains are the key to their functional role in HS. In this study, we investigate this hypothesis using state-of-the-art nuclear magnetic resonance (NMR) experiments at multiple frequencies. To resolve the problem of severe overlap in 1H-NMR spectra of repetitive polysaccharides from proteoglycans, we have prepared oligosaccharides with the chemical structure of HS NA-domains containing the 15N nucleus, which has enough chemical shift dispersion to probe the central residues of octasaccharides at atomic resolution using 600 MHz NMR. By performing NMR relaxation experiments at three magnetic-field strengths, high quality data on internal dynamics and rotational diffusion was obtained. Furthermore, translational diffusion could also be measured by NMR using pulse field gradients. These experimental data were used, in concert with molecular dynamics simulations, to provide information on local molecular shape, greatly aiding our relaxation analyses. Our results, which are more accurate than those presented previously, confirm the higher flexibility of the NA-domains as compared with reported data on S-domains. It is proposed that this flexibility has two functional roles. First, it confers a greater area of interaction from the anchoring point on the core protein for the bioactive S-domains. Secondly, it allows multiple interactions along the same HS chain that are dynamically independent of each other. Electronic Supplementary Material The online version of this article (doi:10.1007/s10719-007-9081-9) contains supplementary material, which is available to authorized users. PMID:18080183

  6. Interactions of Human Nucleotide Excision Repair Protein XPA with DNA and RPA70ΔC327: Chemical Shift Mapping and 15N NMR Relaxation Studies†

    PubMed Central

    Buchko, Garry W.; Daughdrill, Gary W.; de Lorimier, Robert; K., Sudha Rao B.; Isern, Nancy G.; Lingbeck, Jody M.; Taylor, John-Stephen; Wold, Marc S.; Gochin, Miriam; Spicer, Leonard D.; Lowry, David F.; Kennedy, Michael A.

    2014-01-01

    Human XPA is an essential component in the multienzyme nucleotide excision repair (NER) pathway. The solution structure of the minimal DNA binding domain of XPA (XPA-MBD: M98-F219) was recently determined [Buchko et al. (1998) Nucleic Acids Res. 26, 2779–2788, Ikegami et al. (1998) Nat. Struct. Biol. 5, 701–706] and shown to consist of a compact zinc-binding core and a loop-rich C-terminal subdomain connected by a linker sequence. Here, the solution structure of XPA-MBD was further refined using an entirely new class of restraints based on pseudocontact shifts measured in cobalt-substituted XPA-MBD. Using this structure, the surface of XPA-MBD which interacts with DNA and a fragment of the largest subunit of replication protein A (RPA70ΔC327: M1-Y326) was determined using chemical shift mapping. DNA binding in XPA-MBD was highly localized in the loop-rich subdomain for DNA with or without a lesion [dihydrothymidine (dhT) or 6-4-thymidine-cytidine (64TC)], or with DNA in single- or double-stranded form, indicating that the character of the lesion itself is not the driving force for XPA binding DNA. RPA70ΔC327 was found to contact regions in both the zinc-binding and loop-rich subdomains. Some overlap of the DNA and RPA70ΔC327 binding regions was observed in the loop-rich subdomain, indicating a possible cooperative DNA-binding mode between XPA and RPA70ΔC327. To complement the chemical shift mapping data, the backbone dynamics of free XPA-MBD and XPA-MBD bound to DNA oligomers containing dhT or 64TC lesions were investigated using 15N NMR relaxation data. The dynamic analyses for the XPA-MBD complexes with DNA revealed localized increases and decreases in S2 and an increase in the global correlation time. Regions of XPA-MBD with the largest increases in S2 overlapped regions having the largest chemical shifts changes upon binding DNA, indicating that the loop-rich subdomain becomes more rigid upon binding DNA. Interestingly, S2 decreased for some residues in

  7. Rotary echo nutation NMR

    NASA Astrophysics Data System (ADS)

    Janssen, R.; Tijink, G. A. H.; Veeman, W. S.

    1988-01-01

    A two-dimensional solid state NMR experiment which combines rotary echoes and nutation NMR is investigated and used to study different sodium sites in zeolite NaA. It is shown that with this technique sodium ions with different relaxation rates in the rotating frame can be distinguished.

  8. Sub-millisecond 125Te NMR spin-lattice relaxation times and large Knight shifts in complex tellurides: Validation of a quadratic relation across the spectrum

    SciTech Connect

    Levin, E. M.; Cui, J. -F.; Schmidt-Rohr, K.

    2016-07-16

    125Te NMR spectra and spin-lattice relaxation times, T1, have been measured for several GeTe-based materials with Te excess. In this paper, the spectra show inhomogeneous broadening by several thousand ppm and a systematic variation in T1 relaxation time with resonance frequency. The quadratic dependence of the spin-lattice relaxation rate, 1/T1, on the Knight shift in the Korringa relation is found to be valid over a wide range of Knight shifts. This result confirms that T1 relaxation in GeTe-based materials is mostly dominated by hyperfine interaction between nuclei and free charge carriers. In GeTe with 2.5% excess of Te, about 15% of the material exhibits a Knight shift of ≥4500 ppm and a T1 of only 0.3 ms, indicating a high hole concentration that could correspond to close to 50% vacancies on the Ge sublattice in this component. Lastly, our findings provide a basis for determining the charge carrier concentration and its distribution in complex thermoelectric and phase-change tellurides, which should lead to a better understanding of electronic and thermal transport properties as well as chemical bonding in these materials.

  9. Dosimetry of {sup 60}Co and {sup 192}Ir gamma-irradiated agarose gels by proton relaxation time measurement and NMR imaging, in a 0-100 Gy dose range

    SciTech Connect

    Chalansonnet, A.; Briguet, A.; Bonnat, J.L.

    1997-05-01

    Localized irradiation of the skin and subcutaneous tissues with large single doses of gamma rays can induce immediate effects characterized by erythema, desquamation, and necrosis. Correlations between the evolution of the lesions and dosimetry studies have to be established by biophysical methods. NMR studies of the effects of an irradiated Fricke solution might be a means of controlling the delivered irradiation doses. After exposition to ionizing radiations, ferrous ions are transformed into ferric ions. Both are paramagnetic ions, and proton spin-lattice relaxation is accelerated depending on the oxidation reaction. In this study, solution of ammonium ferrous sulfate in an acid environment was incorporated into a gelling substance made with agarose, so that T{sub 1} weighted image contrast could be used to detect ferric ion formation. Experiments with {sup 192}Ir and {sup 90}Co gamma rays with doses in the 0 to 100 Gy range were conducted with Fe{sup 2+} concentrations of 0.5, 1, 1.5, and 2 mM in a gelling substance containing 4% agarose. A relationship was established between the amount of Fe{sup 3+} created and the spin-lattice proton relaxation rate, which led to a straightforward dose-effect relation. The use of such high doses allowed us to reproduce realistic conditions of accidental overexposure. A linear relationship was obtained between the doses absorbed and the NMR parameters measured (T{sub 1} and relative image intensity). 17 refs., 3 figs., 1 tab.

  10. Folding of the KIX domain: characterization of the equilibrium analog of a folding intermediate using 15N/13C relaxation dispersion and fast 1H/2H amide exchange NMR spectroscopy.

    PubMed

    Schanda, Paul; Brutscher, Bernhard; Konrat, Robert; Tollinger, Martin

    2008-07-18

    The KIX domain of the transcription co-activator CBP is a three-helix bundle protein that folds via rapid accumulation of an intermediate state, followed by a slower folding phase. Recent NMR relaxation dispersion studies revealed the presence of a low-populated (excited) state of KIX that exists in equilibrium with the natively folded form under non-denaturing conditions, and likely represents the equilibrium analog of the folding intermediate. Here, we combine amide hydrogen/deuterium exchange measurements using rapid NMR data acquisition techniques with backbone (15)N and (13)C relaxation dispersion experiments to further investigate the equilibrium folding of the KIX domain. Residual structure within the folding intermediate is detected by both methods, and their combination enables reliable quantification of the amount of persistent residual structure. Three well-defined folding subunits are found, which display variable stability and correspond closely to the individual helices in the native state. While two of the three helices (alpha(2) and alpha(3)) are partially formed in the folding intermediate (to approximately 50% and approximately 80%, respectively, at 20 degrees C), the third helix is disordered. The observed helical content within the excited state exceeds the helical propensities predicted for the corresponding peptide regions, suggesting that the two helices are weakly mutually stabilized, while methyl (13)C relaxation dispersion data indicate that a defined packing arrangement is unlikely. Temperature-dependent experiments reveal that the largest enthalpy and entropy changes along the folding reaction occur during the final transition from the intermediate to the native state. Our experimental data are consistent with a folding mechanism where helices alpha(2) and alpha(3) form rapidly, although to different extents, while helix alpha(1) consolidates only as folding proceeds to complete the native state-structure.

  11. Integrated computational approach to the analysis of NMR relaxation in proteins: application to ps-ns main chain 15N-1H and global dynamics of the Rho GTPase binding domain of plexin-B1.

    PubMed

    Zerbetto, Mirco; Buck, Matthias; Meirovitch, Eva; Polimeno, Antonino

    2011-01-20

    An integrated computational methodology for interpreting NMR spin relaxation in proteins has been developed. It combines a two-body coupled-rotator stochastic model with a hydrodynamics-based approach for protein diffusion, together with molecular dynamics based calculations for the evaluation of the coupling potential of mean force. The method is applied to ¹⁵N relaxation of N-H bonds in the Rho GTPase binding (RBD) domain of plexin-B1, which exhibits intricate internal mobility. Bond vector dynamics are characterized by a rhombic local ordering tensor, S, with principal values S₀² and S₂², and an axial local diffusion tensor, D₂, with principal values D(2,||) and D(2,⊥). For α-helices and β-sheets we find that S₀² ~ -0.5 (strong local ordering), -1.2 < S₂² < -0.8 (large S tensor anisotropy), D(2,⊥) ~ D₁ = 1.93 × 10⁷ s⁻¹ (D₁ is the global diffusion rate), and log(D(2,||)/D₁) ~ 4. For α-helices the z-axis of the local ordering frame is parallel to the C(α)-C(α) axis. For β-sheets the z-axes of the S and D₂ tensors are parallel to the N-H bond. For loops and terminal chain segments the local ordering is generally weaker and more isotropic. On average, D(2,⊥) ~ D₁ also, but log(D(2,||)/D₁) is on the order of 1-2. The tensor orientations are diversified. This study sets forth an integrated computational approach for treating NMR relaxation in proteins by combining stochastic modeling and molecular dynamics. The approach developed provides new insights by its application to a protein that experiences complex dynamics.

  12. 1H NMR spin-spin relaxation and imaging in porous systems: an application to the morphological study of white portland cement during hydration in the presence of organics.

    PubMed

    Gussoni, M; Greco, F; Bonazzi, F; Vezzoli, A; Botta, D; Dotelli, G; Natali Sora, I; Pelosato, R; Zetta, L

    2004-07-01

    Proton nuclear magnetic resonance (NMR) spin-spin relaxation and imaging have been applied to investigate white Portland cement pastes during hydration in the absence and in the presence of organic solvents. The main organic solvent investigated was methanol, alone or together with the organic waste 2-chloroaniline (2-CA), an aromatic amine representative of an important class of highly toxic compounds. For all the analysed samples, prepared with a solvent-to-cement ratio of 0.4, the decay of the echo magnetization has been fitted by adopting a model that combines an exponential component with a gaussian one. The calculated independent relaxation parameters have been discussed in terms of morphological and dynamical changes that occur during the cement hardening process and pore formation. Three kinds of water molecules: "solid-like" (chemically and physically bound), "liquid-like" (porous trapped) and "free" water, endowed with anisotropic, near isotropic and isotropic motion, respectively, were identified. Spin-echo images collected on the same samples during the hydration kinetics, allowed the changes of water and solvents spatial distribution in the porous network to be monitored, showing percolation phenomena and confirming the multimodal open channels structure of the hardened cement system. Both T(2) relaxation and imaging data indicated that a pronounced delay occurs in the cement hardening when organics are present.

  13. Magnetic Field-Independent ^17O and ^63, 65Cu Normal State Spin Lattice Relaxation as Inferred by ^17O T2 NMR up to 28 T in YBa_2Cu_3O_7

    NASA Astrophysics Data System (ADS)

    Mitrovic, V. F.; Bachman, H. N.; Halperin, W. P.

    1998-03-01

    ^17O spin-spin relaxation NMR (T_2) is a powerful probe of vortex fluctuations in high Tc cuprates.(H. N. Bachman et al)., Bull. Am. Phys. Soc., 41, 467 (1996). It is important to understand the normal state T2 relaxation in order to extract the vortex field fluctuations.^1,(C. H. Recchia et al)., Phys. Rev. Lett. 78, 3543 (1997). The study of T2 in YBCO has shown that, in the normal state, copper and oxygen spin fluctuations (T1 processes) dominate the time scales for T_2, the spin-echo height decay. Thus, measurements of T2 as a function of magnetic field are an indicator of ^17O and ^63, 65Cu T1 behavior. We report new T2 measurements taken in the normal state from 3.2 T up to 28.2 T in which the spin-spin relaxation rate is observed to be completely field independent. By comparison with the predicted spin echo height decay given by the Gaussian Phase Approximation model we show that T1 of ^63, 65Cu and ^17O must not deviate from their published low-field values, within experimental error, over the entire magnetic field range. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity. The NHMFL is supported through the NSF and the state of Florida.

  14. Pulsed NMRON relaxation measurements and thermometric NMR in the quasi-2 dimensional femomagnet: Mn(COOCH 3) 2·4H 2O

    NASA Astrophysics Data System (ADS)

    Le Gros, M.; Kotlicld, A.; Turrell, B. G.

    1990-08-01

    The measurement of the field dependence of the nuclear spin-lattice relaxation time of 54Mn in the two manganese sites in the quasi-2 dimensional ferromagnet Mn(COOCH 3) 2·4H 20 obtained by the pulsed NMRON technique is reported. This technique allows the observation in low fields of the higher frequency resonance which previously could not be measured by CW methods. The anomaly in the 54Mn relaxation time observed in the 55Mn level crossing regime is discussed, and the thermometric observation of the field dependence and lice width of the resonance lines from the abundant 55Mn spin systems is reported and related to the 54Mn spin-lattice relaxation behavior.

  15. NMR T1 relaxation time measurements and calculations with translational and rotational components for liquid electrolytes containing LiBF4 and propylene carbonate

    NASA Astrophysics Data System (ADS)

    Richardson, P. M.; Voice, A. M.; Ward, I. M.

    2013-12-01

    Longitudinal relaxation (T1) measurements of 19F, 7Li, and 1H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.

  16. NMR T1 relaxation time measurements and calculations with translational and rotational components for liquid electrolytes containing LiBF4 and propylene carbonate.

    PubMed

    Richardson, P M; Voice, A M; Ward, I M

    2013-12-07

    Longitudinal relaxation (T1) measurements of (19)F, (7)Li, and (1)H in propylene carbonate/LiBF4 liquid electrolytes are reported. Comparison of T1 values with those for the transverse relaxation time (T2) confirm that the measurements are in the high temperature (low correlation time) limit of the T1 minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T1 from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.

  17. High resolution NMR study of T1 magnetic relaxation dispersion. III. Influence of spin 1/2 hetero-nuclei on spin relaxation and polarization transfer among strongly coupled protons.

    PubMed

    Korchak, Sergey E; Ivanov, Konstantin L; Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Kaptein, Robert; Vieth, Hans-Martin

    2012-09-07

    Effects of spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 129, 234513 (2008); S. E. Korchak, K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, ibid. 133, 194502 (2010)], spin-spin interactions have a pronounced effect on the relaxivity tending to equalize the longitudinal relaxation times once the spins become strongly coupled at a sufficiently low magnetic field. In addition, we have found influence of (19)F nuclei on the proton NMRD, although in the whole field range, studied protons and fluorine spins were only weakly coupled. In particular, pronounced features in the proton NMRD were found; but each feature was predominantly observed only for particular spin states of the hetero-nuclei. The features are explained theoretically; it is shown that hetero-nuclei can affect the proton NMRD even in the limit of weak coupling when (i) protons are coupled strongly and (ii) have spin-spin interactions of different strengths with the hetero-nuclei. We also show that by choosing the proper magnetic field strength, one can selectively transfer proton spin magnetization between spectral components of choice.

  18. NMR T{sub 1} relaxation time measurements and calculations with translational and rotational components for liquid electrolytes containing LiBF{sub 4} and propylene carbonate

    SciTech Connect

    Richardson, P. M. Voice, A. M. Ward, I. M.

    2013-12-07

    Longitudinal relaxation (T{sub 1}) measurements of {sup 19}F, {sup 7}Li, and {sup 1}H in propylene carbonate/LiBF{sub 4} liquid electrolytes are reported. Comparison of T{sub 1} values with those for the transverse relaxation time (T{sub 2}) confirm that the measurements are in the high temperature (low correlation time) limit of the T{sub 1} minimum. Using data from pulsed field gradient measurements of self-diffusion coefficients and measurements of solution viscosity measured elsewhere, it is concluded that although in general there are contributions to T{sub 1} from both translational and rotational motions. For the lithium ions, this is mainly translational, and for the fluorine ions mainly rotational.

  19. A carbon-13 NMR spin-lattice relaxation study of the molecular conformation of the nootropic drug 2-oxopyrrolidin-1-ylacetamide

    NASA Astrophysics Data System (ADS)

    Baldo, M.; Grassi, A.; Guidoni, L.; Nicolini, M.; Pappalardo, G. C.; Viti, V.

    The spin-lattice relaxation times ( T1) of carbon-13 resonances of the drug 2-oxopyrrolidin- 1-ylacetamide ( 2OPYAC) were determined in CDCl 3 + DMSO and H 2O solutions to investigate the internal conformational flexibility. The measured T1s for the hydrogen-bearing carbon atoms of the 2-pyrrolidone ring fragment were diagnostic of a rigid conformation with respect to the acetamide linked moiety. The model of anisotropic reorientation of a rigid body was used to analyse the measured relaxation data in terms of a single conformation. Owing to the small number of T1 data available the fitting procedure for each of the possible conformations failed. The structure corresponding to the rigid conformation was therefore considered to be the one that is strongly stabilized by internal hydrogen bonding as predicted on the basis of theoretical MO ab initio quantum chemical calculations.

  20. Superconducting fluctuations and {sup 63}Cu NQR-NMR relaxation in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}: Effect of magnetic field and a test for the pairing-state symmetry

    SciTech Connect

    Carretta, P.; Livanov, D.V.; Rigamonti, A.; Varlamov, A.A. |

    1996-10-01

    Evidence is presented of superconducting fluctuations in the {sup 63}Cu NQR-NMR relaxation rate in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}, as obtained from a careful comparison of measurements carried out in the absence and in the presence of a field parallel to the {ital c} axis. It is shown that the field causes a reduction of the relaxation rate {ital W} in a range of about 10 K above {ital T}{sub {ital c}}. This effect is related to the suppression by the magnetic field of the phase-sensitive positive Maki-Thompson contribution while the negative contribution from the DOS fluctuations is almost field independent. Furthermore, it is argued how the fluctuation effects on {ital W} can be used to discuss the pairing state symmetry, at variance with the insensitivity of the transport measurements. It is pointed out that the existence of the Maki-Thompson contribution to {ital W} evidences an {ital s}-wave symmetry component for the pairing in YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}. {copyright} {ital 1996 The American Physical Society.}

  1. Oxygen Mapping within Healthy and Acutely Infarcted Brain Tissue in Humans Using the NMR Relaxation of Lipids: A Proof-Of-Concept Translational Study.

    PubMed

    Colliez, Florence; Safronova, Marta M; Magat, Julie; Joudiou, Nicolas; Peeters, André P; Jordan, Bénédicte F; Gallez, Bernard; Duprez, Thierry

    2015-01-01

    The clinical applicability of brain oxygenation mapping using the MOBILE (Mapping of Oxygen By Imaging Lipids relaxation Enhancement) magnetic resonance (MR) technique was assessed in the clinical setting of normal brain and of acute cerebral ischemia as a founding proof-of-concept translational study. Changes in the oxygenation level within healthy brain tissue can be detected by analyzing the spin-lattice proton relaxation ('Global T1' combining water and lipid protons) because of the paramagnetic properties of molecular oxygen. It was hypothesized that selective measurement of the relaxation of the lipid protons ('Lipids T1') would result in enhanced sensitivity of pO2 mapping because of higher solubility of oxygen in lipids than in water, and this was demonstrated in pre-clinical models using the MOBILE technique. In the present study, 12 healthy volunteers and eight patients with acute (48-72 hours) brain infarction were examined with the same clinical 3T MR system. Both Lipids R1 (R1 = 1/T1) and Global R1 were significantly different in the infarcted area and the contralateral unaffected brain tissue, with a higher statistical significance for Lipids R1 (median difference: 0.408 s-1; p<0.0001) than for Global R1 (median difference: 0.154 s-1; p = 0.027). Both Lipids R1 and Global R1 values in the unaffected contralateral brain tissue of stroke patients were not significantly different from the R1 values calculated in the brain tissue of healthy volunteers. The main limitations of the present prototypic version of the MOBILE sequence are the long acquisition time (4 min), hampering robustness of data in uncooperative patients, and a 2 mm slice thickness precluding accurate measurements in small infarcts because of partial volume averaging effects.

  2. PEG Coating Reduces NMR Relaxivity of Mn0.5Zn0.5Gd0.02Fe1.98O4 Hyperthermia Nanoparticles

    PubMed Central

    Issa, Bashar; Qadri, Shahnaz; Obaidat, Ihab M.; Bowtell, Richard W.; Haik, Yousef

    2011-01-01

    Purpose To investigate both T1 and T2 MR relaxation enhancement of Gd substituted Zn-Mn ferrite magnetic nanoparticles. Both uncoated and polyethylene glycol (PEG) coated particles were used. Materials and Methods Chemical co-precipitation was used to synthesize particles in the form Mn0.5Zn0.5Gd0.02Fe1.98O4 suitable for hyperthermia applications. Physical characterization of the magnetic nanoparticles included SEM, TEM, ICP, and SQUID. T1 and T2 measurements were performed at 1.5 T. Results The saturation magnetization was 12.86 emu/g while the particle’s magnetic moment was 1.86 × 10−19 J/T. The particle size increased due to coating, while 1/T1 and 1/T2 relaxivities (26 °C) decreased from 2.5 to 0.7 and from 201.3 to 76.6 s−1 mM−1, respectively at a magnetic field 1.5 T. Conclusion The reduction in both 1/T1 and 1/T2 is attributed to increased distance of closest approach between the protons and the magnetic core caused by the shielding provided by the high molecular weight PEG. 1/T2 data is compared to existing theoretical models using a modified radius that takes into account both possible agglomeration of the particles and increased inter-particle separation induced by PEG coating. PMID:21928382

  3. Novel DNA packaging recognition in the unusual bacteriophage N15

    SciTech Connect

    Feiss, Michael; Geyer, Henriette; Klingberg, Franco; Moreno, Norma; Forystek, Amanda; Maluf, Nasib Karl; Sippy, Jean

    2015-08-15

    Phage lambda's cosB packaging recognition site is tripartite, consisting of 3 TerS binding sites, called R sequences. TerS binding to the critical R3 site positions the TerL endonuclease for nicking cosN to generate cohesive ends. The N15 cos (cos{sup N15}) is closely related to cos{sup λ}, but whereas the cosB{sup N15} subsite has R3, it lacks the R2 and R1 sites and the IHF binding site of cosB{sup λ}. A bioinformatic study of N15-like phages indicates that cosB{sup N15} also has an accessory, remote rR2 site, which is proposed to increase packaging efficiency, like R2 and R1 of lambda. N15 plus five prophages all have the rR2 sequence, which is located in the TerS-encoding 1 gene, approximately 200 bp distal to R3. An additional set of four highly related prophages, exemplified by Monarch, has R3 sequence, but also has R2 and R1 sequences characteristic of cosB–λ. The DNA binding domain of TerS-N15 is a dimer. - Highlights: • There are two classes of DNA packaging signals in N15-related phages. • Phage N15's TerS binding site: a critical site and a possible remote accessory site. • Viral DNA recognition signals by the λ-like bacteriophages: the odd case of N15.

  4. 3D NMR Experiments for Measuring 15N Relaxation Data of Large Proteins: Application to the 44 kDa Ectodomain of SIV gp41

    NASA Astrophysics Data System (ADS)

    Caffrey, Michael; Kaufman, Joshua; Stahl, Stephen J.; Wingfield, Paul T.; Gronenborn, Angela M.; Clore, G. Marius

    1998-12-01

    A suite of 3D NMR experiments for measuring15N-{1H} NOE,15NT1, and15NT1ρvalues in large proteins, uniformly labeled with15N and13C, is presented. These experiments are designed for proteins that exhibit extensive spectral overlap in the 2D1H-15N HSQC spectrum. The pulse sequences are readily applicable to perdeuterated samples, which increases the spectral resolution and signal-to-noise ratio, thereby permitting the characterization of protein dynamics to be extended to larger protein systems. Application of the pulse sequences is demonstrated on a perdeuterated13C/15N-labeled sample of the 44 kDa ectodomain of SIV gp41.

  5. Sorption isotherm measurements by NMR.

    PubMed

    Leisen, Johannes; Beckham, Haskell W; Benham, Michael

    2002-01-01

    An experimental setup is described for the automated recording of sorption isotherms by NMR experiments at precisely defined levels of relative humidity (RH). Implementation is demonstrated for a cotton fabric; Bloch decays. T1 and T2* relaxation times were measured at predefined steps of increasing and decreasing relative humidities (RHs) so that a complete isotherm of NMR properties was obtained. Bloch decays were analyzed by fitting to relaxation functions consisting or a slow- and a fast-relaxing component. The fraction of slow-relaxing component was greater than the fraction of sorbed moisture determined from gravimetric sorption data. The excess slow-relaxing component was attributed to plasticized segments of the formerly rigid cellulose matrix. T1 and T2* sorption isotherms exhibit hysteresis similar to gravimetric sorption isotherms. However, correlating RH to moisture content (MC) reveals that both relaxation constants depend only on MC, and not on the history of moisture exposure.

  6. Different structure of the complexes of two cytochrome P-450 isozymes with acetanilide by 1H-NMR relaxation and spectrophotometry.

    PubMed

    Woldman YaYu; Weiner, L M; Lyakhovich, V V

    1993-05-28

    The functional and spectral characteristics of the interaction of acetanilide with phenobarbital- and methylcholanthrene- induced rat liver microsomes, as well as with corresponding major isozymes (cytochromes P-450b and P-450c) have been compared. The magnitude of the reverse 1st type binding spectra proved to be negatively correlated with the acetanilide oxidation on isozymes under study. The data on paramagnetic relaxation of acetanilide protons in the presence of P-450 have shown the structure of the enzyme-substrate complex to be different for two isozymes, acetanilide molecule being closer to Fe ion in the active site in the case of P-450c, which is active towards acetanilide oxidation. For the P-450c-acetanilide complex the group oxidized (phenyl) is the closest to Fe ion.

  7. NMR spin-lattice relaxation study of 7Li and 93Nb nuclei in Ti- or Fe-doped LiNbO3:Mg single crystals

    NASA Astrophysics Data System (ADS)

    Yeom, Tae Ho; Lim, Ae Ran

    2016-04-01

    In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO3, LiNbO3:Mg, LiNbO3:Mg/Ti, LiNbO3:Mg/Fe, and LiNbO3:Mg/Fe (thermally treated at 500°C) single crystals. The results for the LiNbO3:Mg single crystals doped with Fe3+ or Ti3+ are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO3:Mg/Fe single crystals were examined based on the T1 analysis of 7Li and 93Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  8. Enhanced NMR Relaxation of Tomonaga-Luttinger Liquids and the Magnitude of the Carbon Hyperfine Coupling in Single-Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Kiss, A.; Pályi, A.; Ihara, Y.; Wzietek, P.; Simon, P.; Alloul, H.; Zólyomi, V.; Koltai, J.; Kürti, J.; Dóra, B.; Simon, F.

    2011-10-01

    Recent transport measurements [Churchill et al. Nature Phys.NPAHAX1745-2473 5, 321 (2009)10.1038/nphys1247] found a surprisingly large, 2-3 orders of magnitude larger than usual C13 hyperfine coupling (HFC) in C13 enriched single-wall carbon nanotubes. We formulate the theory of the nuclear relaxation time in the framework of the Tomonaga-Luttinger liquid theory to enable the determination of the HFC from recent data by Ihara et al. [Europhys. Lett. 90, 17 004 (2010)EULEEJ0295-507510.1209/0295-5075/90/17004]. Though we find that 1/T1 is orders of magnitude enhanced with respect to a Fermi-liquid behavior, the HFC has its usual, small value. Then, we reexamine the theoretical description used to extract the HFC from transport experiments and show that similar features could be obtained with HFC-independent system parameters.

  9. High-field 1H T1 and T2 NMR relaxation time measurements of H2O in homeopathic preparations of quartz, sulfur, and copper sulfate

    NASA Astrophysics Data System (ADS)

    Baumgartner, Stephan; Wolf, Martin; Skrabal, Peter; Bangerter, Felix; Heusser, Peter; Thurneysen, André; Wolf, Ursula

    2009-09-01

    Quantitative meta-analyses of randomized clinical trials investigating the specific therapeutic efficacy of homeopathic remedies yielded statistically significant differences compared to placebo. Since the remedies used contained mostly only very low concentrations of pharmacologically active compounds, these effects cannot be accounted for within the framework of current pharmacology. Theories to explain clinical effects of homeopathic remedies are partially based upon changes in diluent structure. To investigate the latter, we measured for the first time high-field (600/500 MHz) 1H T1 and T2 nuclear magnetic resonance relaxation times of H2O in homeopathic preparations with concurrent contamination control by inductively coupled plasma mass spectrometry (ICP-MS). Homeopathic preparations of quartz (10 c-30 c, n = 21, corresponding to iterative dilutions of 100-10-100-30), sulfur (13 x-30 x, n = 18, 10-13-10-30), and copper sulfate (11 c-30 c, n = 20, 100-11-100-30) were compared to n = 10 independent controls each (analogously agitated dilution medium) in randomized and blinded experiments. In none of the samples, the concentration of any element analyzed by ICP-MS exceeded 10 ppb. In the first measurement series (600 MHz), there was a significant increase in T1 for all samples as a function of time, and there were no significant differences between homeopathic potencies and controls. In the second measurement series (500 MHz) 1 year after preparation, we observed statistically significant increased T1 relaxation times for homeopathic sulfur preparations compared to controls. Fifteen out of 18 correlations between sample triplicates were higher for controls than for homeopathic preparations. No conclusive explanation for these phenomena can be given at present. Possible hypotheses involve differential leaching from the measurement vessel walls or a change in water molecule dynamics, i.e., in rotational correlation time and/or diffusion. Homeopathic preparations

  10. Superoxygenated Water as an Experimental Sample for NMR Relaxometry

    ERIC Educational Resources Information Center

    Nestle, Nikolaus; Dakkouri, Marwan; Rauscher, Hubert

    2004-01-01

    The increase in NMR relaxation rates as a result of dissolved paramagnetic species on the sample of superoxygenated drinking water is demonstrated. It is concluded that oxygen content in NMR samples is an important issue and can give rise to various problems in the interpretation of both spectroscopic and NMR imaging or relaxation experiments.

  11. Superoxygenated Water as an Experimental Sample for NMR Relaxometry

    ERIC Educational Resources Information Center

    Nestle, Nikolaus; Dakkouri, Marwan; Rauscher, Hubert

    2004-01-01

    The increase in NMR relaxation rates as a result of dissolved paramagnetic species on the sample of superoxygenated drinking water is demonstrated. It is concluded that oxygen content in NMR samples is an important issue and can give rise to various problems in the interpretation of both spectroscopic and NMR imaging or relaxation experiments.

  12. Molecular determinants for drug-receptor interactions. 8. Anisotropic and internal motions in morphine, nalorphine, oxymorphone, naloxone and naltrexone in aqueous solution by carbon-13 NMR spin-lattice relaxation times

    NASA Astrophysics Data System (ADS)

    Grassi, Antonio; Perly, Bruno; Pappalardo, Giuseppe C.

    1989-02-01

    Carbon-13 NMR spin-lattice relaxation times ( T1) were measured for morphine, oxymorphone, nalorphine, naloxone and naltrexone as hydrochloride salts in 2H 2O solution. The data refer to the molecules in the N-equatorial configuration. The experimental T1 values were interpreted using a model of anisotropic reorientation of a rigid body with superimposed internal motions of the flexible N-methyl, N-methyl-allyl and N-methyl-cyclopropyl fragments. The calculated internal motional rates were found to markedly decrease on passing from agonists to mixed (nalorphine) and pure (naloxone, naltrexone) antagonists. For these latter the observed trend of the internal flexibility about NC and CC bonds of the N-substituents is discussed in terms of a correlation with their relative antagonistic potencies. In fact, such an evidence of decreasing internal conformational dynamics in the order nalorphine, naloxone, naltrexone, appeared interestingly in line with the "two-state" model of opiate receptor operation mode proposed by Snyder.

  13. The therapeutically anti-prion active antibody-fragment scFv-W226: paramagnetic relaxation-enhanced NMR spectroscopy aided structure elucidation of the paratope-epitope interface.

    PubMed

    Mangels, Christian; Kellner, Ruth; Einsiedel, Jürgen; Weiglmeier, Philipp R; Rosch, Paul; Gmeiner, Peter; Schwarzinger, Stephan

    2010-08-01

    Antibodies have become indispensable reagents with numerous applications in biological and biotechnical analysis, in diagnostics as well as in therapy. In all cases, selective interaction with an epitope is crucial and depends on the conformation of the paratope. While epitopes are routinely mapped at high throughput, methods revealing structural insights on a rather short timescale are rare. We here demonstrate paramagnetic relaxation-enhanced (PRE) NMR spectroscopy to be a powerful tool unraveling structural information about epitope-orientation in a groove spanned by the complementary determining regions. In particular, we utilize the spin label TOAC, which is fused to the peptidic epitope using standard solid-phase chemistry and which is characterized by a reduced mobility compared to, e.g., spin labels attached to the side-chain functionalities of cysteine or lysine residues. We apply the method to determine the orientation of helix 1 of the prion protein, which is the epitope for the therapeutically anti-prion active scF(v) fragment W226.

  14. Studies of DNA-binding properties of lafutidine as adjuvant anticancer agent to calf thymus DNA using multi-spectroscopic approaches, NMR relaxation data, molecular docking and dynamical simulation.

    PubMed

    Yang, Hongqin; Tang, Peixiao; Tang, Bin; Huang, Yanmei; He, Jiawei; Li, Shanshan; Li, Hui

    2017-06-01

    The interactions between lafutidine (LAF) and calf thymus DNA (ctDNA) have been investigated both experimentally and theoretically. UV-vis absorption studies confirmed that LAF binds to ctDNA through non-covalent interactions. Fluorescence quenching and time-resolved fluorescence spectroscopy studies showed that the binding of LAF with ctDNA occurred through static quenching mechanism, resulting in the formation of a LAF-ctDNA complex. The binding constants (K) of the complex were found to be around 10(3)M(-1) via NMR relaxation rates and fluorescence data, and the calculated thermodynamic parameters indicated that hydrogen bonds and van der Waals forces played major roles in the binding of LAF to ctDNA. The changes in CD spectra indicated that LAF induced a slight perturbation on the base stacking and helicity of B-DNA. A comparative study of the LAF-ctDNA complex with respect to potassium iodide quenching experiments and competition displacement assays with ethidium bromide, acridine orange, and Hoechst 33258 probes suggested that LAF interacted with ctDNA by minor groove mode. Molecular docking analysis further supported the minor groove binding. Molecular dynamics simulation indicated that LAF depart from the C-G region of DNA, but it can steadily bind with the middle part of DNA composed by A-T base pairs. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. Synthesis of C13- and N15-Labeled DNAN

    DTIC Science & Technology

    2014-07-24

    relaxation time T2 Transverse relaxation time T2* Observed transverse relaxation time TNT 2,4,6-Trinitrotoluene TLC Thin layer chromatography IHTR...heterogeneous, we decided to double the amount of sulfuric acid to improve both the mixing efficiency and the thermal control of the reaction. 2...chlorodinitrobenzene by the simple displacement of chloride using methanol and sodium hydroxide at 60 °C (Fedoroff et al., 1960). Recrystallization

  16. Replication and Maintenance of Linear Phage-Plasmid N15.

    PubMed

    Ravin, Nikolai V

    2015-02-01

    The lambdoid phage N15 of Escherichia coli is very unusual among temperate phages in that its prophage is not integrated into the chromosome but is a linear plasmid molecule with covalently closed ends (telomeres). Upon infection, the phage DNA circularizes via cohesive ends, and then a special phage enzyme of the tyrosine recombinase family, protelomerase, cuts at another site and joins the ends, forming hairpin telomeres of the linear plasmid prophage. Replication of the N15 prophage is initiated at an internally located ori site and proceeds bidirectionally, resulting in the formation of duplicated telomeres. The N15 protelomerase cuts them, generating two linear plasmid molecules with hairpin telomeres. Stable inheritance of the plasmid prophage is ensured by a partitioning operon similar to the F factor sop operon. Unlike the F centromere, the N15 centromere consists of four inverted repeats dispersed in the genome. The multiplicity and dispersion of centromeres are required for efficient partitioning of a linear plasmid. The centromeres are located in the N15 genome regions involved in phage replication and control of lytic development, and binding of partition proteins at these sites regulates these processes. The family of N15-like linear phage-plasmids includes lambdoid phages ɸKO2 and pY54, as well as Myoviridae phages ΦHAP-1, VHML, VP882, Vp58.5, and vB_VpaM_MAR of marine gamma-proteobacteria. The genomes of these phages contain similar protelomerase genes, lysogeny control modules, and replication genes, suggesting that these phages may belong to a group diverged from a common ancestor.

  17. Soils, Pores, and NMR

    NASA Astrophysics Data System (ADS)

    Pohlmeier, Andreas; Haber-Pohlmeier, Sabina; Haber, Agnes; Sucre, Oscar; Stingaciu, Laura; Stapf, Siegfried; Blümich, Bernhard

    2010-05-01

    Within Cluster A, Partial Project A1, the pore space exploration by means of Nuclear Magnetic Resonance (NMR) plays a central role. NMR is especially convenient since it probes directly the state and dynamics of the substance of interest: water. First, NMR is applied as relaxometry, where the degree of saturation but also the pore geometry controls the NMR signature of natural porous systems. Examples are presented where soil samples from the Selhausen, Merzenhausen (silt loams), and Kaldenkirchen (sandy loam) test sites are investigated by means of Fast Field Cycling Relaxometry at different degrees of saturation. From the change of the relaxation time distributions with decreasing water content and by comparison with conventional water retention curves we conclude that the fraction of immobile water is characterized by T1 < 5 ms. Moreover, the dependence of the relaxation rate on magnetic field strength allows the identification of 2D diffusion at the interfaces as the mechanism which governs the relaxation process (Pohlmeier et al. 2009). T2 relaxation curves are frequently measured for the rapid characterization of soils by means of the CPMG echo train. Basically, they contain the same information about the pore systems like T1 curves, since mostly the overall relaxation is dominated by surface relaxivity and the surface/volume ratio of the pores. However, one must be aware that T2 relaxation is additionally affected by diffusion in internal gradients, and this can be overcome by using sufficiently short echo times and low magnetic fields (Stingaciu et al. 2009). Second, the logic continuation of conventional relaxation measurements is the 2-dimensional experiment, where prior to the final detection of the CPMG echo train an encoding period is applied. This can be T1-encoding by an inversion pulse, or T2 encoding by a sequence of 90 and 180° pulses. During the following evolution time the separately encoded signals can mix and this reveals information about

  18. Spin liquid state in the 3D frustrated antiferromagnet PbCuTe2O6: NMR and muon spin relaxation studies

    SciTech Connect

    Khuntia, P.; Bert, F.; Mendels, P.; Koteswararao, B.; Mahajan, A. V.; Baenitz, M.; Chou, F. C.; Baines, C.; Amato, A.; Furukawa, Y.

    2016-03-11

    In this study, PbCuTe2O6 is a rare example of a spin liquid candidate featuring a three-dimensional magnetic lattice. Strong geometric frustration arises from the dominant antiferromagnetic interaction that generates a hyperkagome network of Cu2+ ions although additional interactions enhance the magnetic lattice connectivity. Through a combination of magnetization measurements and local probe investigations by NMR and muon spin relaxation down to 20 mK, we provide robust evidence for the absence of magnetic freezing in the ground state. The local spin susceptibility probed by the NMR shift hardly deviates from the macroscopic one down to 1 K pointing to a homogeneous magnetic system with a low defect concentration. The saturation of the NMR shift and the sublinear power law temperature (T) evolution of the 1/T1 NMR relaxation rate at low T point to a nonsinglet ground state favoring a gapless fermionic description of the magnetic excitations. Below 1 K a pronounced slowing down of the spin dynamics is witnessed, which may signal a reconstruction of spinon Fermi surface. Nonetheless, the compound remains in a fluctuating spin liquid state down to the lowest temperature of the present investigation.

  19. NMR relaxation rate studies of molecular motions in NaSn, the Laves-phase metal hydride C15-ZrCr(2)H(x) and carbon/epoxy composite materials

    NASA Astrophysics Data System (ADS)

    Stoddard, Ronald Dean

    Here I present studies of molecular motions in three very different systems: NaSn, which exhibits motion characteristic of both a superionic conductor and a rotor crystal; C15-ZrCrsb2Hsbx (x < 0.5), a metal hydride which exhibits unusual characteristics in its hydrogen motion; and, finally a study of the relationship between Tsb2 and the degree of cure of carbon/epoxy materials. NaSn is characterized by Nasp+ ions and stable (Snsb4)sp{4-} tetrahedra. At high temperatures NaSn displays a disordered solid phase (alpha-NaSn). The presence of Nasp+ ions suggests that alpha-NaSn may be a superionic conductor (translationally disordered) and the presence of stable Snsb4 tetrahedra suggests it may be a rotor crystal (organizationally disordered). The purpose of this study is to gain better understanding of the motions in alpha-NaSn by monitoring Na and Sn motion using sp{23}Na and sp{119}Sn NMR, respectively. C15-ZrCrsb2Hsbx (x < 0.5) is a Laves phase metal hydride which displays extremely rapid hydrogen motion and a Tsb1 peak which cannot be explained by a model employing a single correlation time for the motion. A model employing a Gaussian distribution of correlation times has been used to successfully fit Tsb1, but the origin of this distribution in a crystalline solid solution is not known. The purpose of this study is to better understand the low temperature hydrogen motions occurring in C15-ZrCrsb2Hsbx by extending the previous NMR measurements using Tsb1p and Tsb1D, experiments which effectively push the relaxation peak to lower temperatures. New techniques for manufacturing carbon/epoxy components are under development which require partial curing of the material. At present, no method for monitoring partial curing exists. Tsb2 is a promising monitor of degree of cure because of its sensitivity to changes rates of molecular motions. The purpose of this study is to demonstrate the sensitivity of Tsb2 to changes in molecular motion due to curing, and to find a

  20. NMR Imaging of Elastomeric Materials

    DTIC Science & Technology

    1990-11-30

    on ’everse if necessary and identify by block number) FIELD GROUP SUB-GROUP nuclear magnetic resonance , imaging, elastomers, tires, composites, porous...correspondence should be addressed 1i ABSTRACT Nuclear magnetic resonance images have been obtained for four porous glass disks of different porosities...INDEX HEADINGS: NMR imaging Porous materials Spin relaxation 2. I0J INTRODUCTION Nuclear magnetic resonance (NMR) imaging has seen increasing use in the

  1. Relaxed heaps

    SciTech Connect

    Driscoll, J.R. ); Gabow, H.N.; Shrairman, R. ); Tarjan, R.E. )

    1988-11-01

    The relaxed heap is a priority queue data structure that achieves the same amortized time bounds as the Fibonacci heap - a sequence of m decrease key and n delete min operations takes time O(m + n log n). A variant of relaxed heaps achieves similar bounds in the worst case - O(1) time for decrease key and O(log n) for delete min. Relaxed heaps give a processor-efficient parallel implementation of Dijkstra's shortest path algorithm, and hence other algorithms in network optimization. A relaxed heap is a type of binomial queue that allows heap order to be violated.

  2. 14N15N detectability in Pluto’s atmosphere

    NASA Astrophysics Data System (ADS)

    Jessup, Kandis Lea; Gladstone, G. R.; Heays, A. N.; Gibson, S. T.; Lewis, B. R.; Stark, G.

    2013-11-01

    Based on the vapor pressure behavior of Pluto’s surface ices, Pluto’s atmosphere is expected to be predominantly composed of N2 gas. Measurement of the N2 isotopologue 15N/14N ratio within Pluto’s atmosphere would provide important clues to the evolution of Pluto’s atmosphere from the time of formation to its present state. The most straightforward way of determining the N2 isotopologue 15N/14N ratio in Pluto’s atmosphere is via spectroscopic observation of the 14N15N gas species. Recent calculations of the 80-100 nm absorption behavior of the 14N2 and 14N15N isotopologues by Heays et al. (Heays, A.N. et al. [2011]. J. Chem. Phys. 135, 244301), Lewis et al. (Lewis, B.R., Heays, A.N., Gibson, S.T., Lefebvre-Brion, H., Lefebvre, R. [2008]. J. Chem. Phys. 129, 164306); Lewis et al. (Lewis, B.R., Gibson, S.T., Zhang, W., Lefebvre-Brion, H., Robbe, J.-M. [2005]. J. Chem. Phys. 122, 144302), and Haverd et al. (Haverd, V.E., Lewis, B.R., Gibson, S.T., Stark, G. [2005]. J. Chem. Phys. 123, 214304) show that the peak magnitudes of the 14N2 and 14N15N absorption bandhead cross-sections are similar, but the locations of the bandhead peaks are offset in wavelength by ∼0.05-0.1 nm. These offsets make the segregation of the 14N2 and 14N15N absorption signatures possible. We use the most recent N2 isotopologue absorption cross-section calculations and the atmospheric density profiles resulting from photochemical models developed by Krasnopolsky and Cruickshank (Krasnopolsky, V.A., Cruickshank, D.P. [1999]. J. Geophys. Res. 104, 21979-21996) to predict the level of solar light that will be transmitted through Pluto’s atmosphere as a function of altitude during a Pluto solar occultation. We characterize the detectability of the isotopic absorption signature per altitude assuming 14N15N concentrations ranging from 0.1% to 2% of the 14N2 density and instrumental spectral resolutions ranging from 0.01 to 0.3 nm. Our simulations indicate that optical depth of unity is

  3. Protein-Inhibitor Interaction Studies Using NMR

    PubMed Central

    Ishima, Rieko

    2015-01-01

    Solution-state NMR has been widely applied to determine the three-dimensional structure, dynamics, and molecular interactions of proteins. The designs of experiments used in protein NMR differ from those used for small-molecule NMR, primarily because the information available prior to an experiment, such as molecular mass and knowledge of the primary structure, is unique for proteins compared to small molecules. In this review article, protein NMR for structural biology is introduced with comparisons to small-molecule NMR, such as descriptions of labeling strategies and the effects of molecular dynamics on relaxation. Next, applications for protein NMR are reviewed, especially practical aspects for protein-observed ligand-protein interaction studies. Overall, the following topics are described: (1) characteristics of protein NMR, (2) methods to detect protein-ligand interactions by NMR, and (3) practical aspects of carrying out protein-observed inhibitor-protein interaction studies. PMID:26361636

  4. Petrophysical applications of NMR imaging

    SciTech Connect

    Rothwell, W.P.; Vinegar, H.J.

    1985-12-01

    A system for obtaining high-resolution NMR images of oil field cores is described. Separate proton density and T/sub 2/ relaxation images are obtained to distinguish spatial variations of fluid-filled porosity and the physical nature of the pores. Results are presented for typical sandstones.

  5. NMR characterization of shocked quartz

    SciTech Connect

    Boslough, M.B.; Cygan, R.T.; Assink, R.A.; Kirkpatrick, R.J.

    1994-03-01

    We have characterized experimentally and naturally-shocked quartz (both synthetic and natural samples) by solid state nuclear magnetic resonance (NMR) spectroscopy. Relaxation analysis of experimentally-shocked samples provides a means for quantitative characterization of the amorphous/disordered silica component NMR spectra demonstrate that magnetization in both the amorphous and crystalline components follows power-law behavior as a function of recycle time. This observation is consistent with the relaxation of nuclear spins by paramagnetic impurities. A fractal dimension can be extracted from the power-law exponent associated with each phase, and relative abundances can be extracted from integrated intensities of deconvolved peaks. NMR spectroscopy of naturally-shocked sandstone from Meteor Crater, Arizona (USA) led to the discovery of a new amorphous hydroxylated silica phase. Solid state NMR spectra of both experimentally and naturally shocked quartz were unexpectedly rich in microstructural information, especially when combined with relaxation analysis and cross-polarization studies. We suggest solid state NMR as a potentially useful tool for examining shock-induced microstructural changes in other inorganic compounds, with possible implications for shock processing of structural ceramics.

  6. β-NMR

    NASA Astrophysics Data System (ADS)

    Morris, Gerald D.

    2014-01-01

    The β-NMR facility at ISAC is constructed specifically for experiments in condensed matter physics with radioactive ion beams. Using co-linear optical pumping, a 8Li + ion beam having a large nuclear spin polarisation and low energy (nominally 30 keV) can be generated. When implanted into materials these ions penetrate to shallow depths comparable to length scales of interest in the physics of surfaces and interfaces between materials. Such low-energy ions can be decelerated with simple electrostatic optics to enable depth-resolved studies of near-surface phenomena over the range of about 2-200 nm. Since the β-NMR signal is extracted from the asymmetry intrinsic to beta-decay and therefore monitors the polarisation of the radioactive probe nuclear magnetic moments, this technique is fundamentally a probe of local magnetism. More generally though, any phenomena which affects the polarisation of the implanted spins by, for example, a change in resonance frequency, line width or relaxation rate can be studied. The β-NMR program at ISAC currently supports a number of experiments in magnetism and superconductivity as well as novel ultra-thin heterostructures exhibiting properties that cannot occur in bulk materials. The general purpose zero/low field and high field spectrometers are configured to perform CW and pulsed RF nuclear magnetic resonance and spin relaxation experiments over a range of temperatures (3-300 K) and magnetic fields (0-9 T).

  7. Relaxation-relaxation exchange experiments in porous media with portable Halbach-Magnets.

    NASA Astrophysics Data System (ADS)

    Haber, A.; Haber-Pohlmeier, S.; Casanova, F.; Blümich, B.

    2009-04-01

    Mobile NMR became a powerful tool following the development of portable NMR sensors for well logging. By now there are numerous applications of mobile NMR in materials analysis and chemical engineering where, for example, unique information about the structure, morphology and dynamics of polymers is obtained, and new opportunities are provided for geo-physical investigations [1]. In particular, dynamic information can be retrieved by two-dimensional Laplace exchange NMR, where the initial NMR relaxation environment is correlated with the final relaxation environment of molecules migrating from one environment to the other within a so-called NMR mixing time tm [2]. Relaxation-relaxation exchange experiments of water in inorganic porous media were performed at low and moderately inhomogeneous magnetic field with a simple, portable Halbach-Magnet. By conducting NMR transverse relaxation exchange experiments for several mixing times and converting the results to 2D T2 distributions (joint probability densities of transverse relaxation times T2) with the help of the inverse 2D Laplace Transformation (ILT), we obtained characteristic exchange times for different pore sizes. The results of first experiments on soil samples are reported, which reveal information about the complex pore structure of soil and the moisture content. References: 1. B. Blümich, J. Mauler, A. Haber, J. Perlo, E. Danieli, F. Casanova, Mobile NMR for Geo-Physical Analysis and Material Testing, Petroleum Science, xx (2009) xxx - xxx. 2. K. E. Washburn, P.T. Callaghan, Tracking pore to pore exchange using relaxation exchange spectroscopy, Phys. Rev. Lett. 97 (2006) 175502.

  8. Interfaces in polymer nanocomposites - An NMR study

    NASA Astrophysics Data System (ADS)

    Böhme, Ute; Scheler, Ulrich

    2016-03-01

    Nuclear Magnetic Resonance (NMR) is applied for the investigation of polymer nanocomposites. Solid-state NMR is applied to study the modification steps to compatibilize layered double hydroxides with non-polar polymers. 1H relaxation NMR gives insight on the polymer dynamics over a wide range of correlation times. For the polymer chain dynamics the transverse relaxation time T2 is most suited. In this presentation we report on two applications of T2 measurements under external mechanical stress. In a low-field system relaxation NMR studies are performed in-situ under uniaxial stress. High-temperature experiments in a Couette cell permit the investigation of the polymer dynamics in the melt under shear flow.

  9. 224} studied by NMR

    SciTech Connect

    Furukawa, Y; Fang, X; Kögerler, P

    2014-05-14

    7Li nuclear magnetic resonance (NMR) studies have been performed to investigate magnetic properties and spin dynamics of Mn3+ (S = 2) spins in the giant polyoxometalate molecule {Mn40W224}. The 7Li-NMR line width is proportional to the external magnetic field H as expected in a paramagnetic state above 3 K. Below this temperature the line width shows a sudden increase and is almost independent of H, which indicates freezing of the local Mn3+ spins. The temperature dependence of T1 for both 1H and 7Li reveals slow spin dynamics at low temperatures, consistent with spin freezing. The slow spin dynamics is also evidenced by the observation of a peak of 1/T2 around 3 K, where the fluctuation frequency of spins is of the order of ~200 kHz. An explicit form of the temperature dependence of the fluctuation frequency of Mn3+ spins is derived from the nuclear relaxation data.

  10. Rapid sample injection for hyperpolarized NMR spectroscopy.

    PubMed

    Bowen, Sean; Hilty, Christian

    2010-06-14

    Due to its ability to enhance the signal of a single NMR scan by several orders of magnitude, solid-to-liquid state dynamic nuclear polarization (DNP) appears well suited for the analysis of minimal amounts of compounds, as well as for the study of rapid chemical reactions. A key requirement in enabling the application of DNP-NMR to typical small-molecule substances encountered in chemistry and biochemistry is the ability to obtain high-resolution spectra, while at the same time minimizing the loss of polarization due to spin relaxation between the separate steps of DNP polarization and NMR measurement. Here, we present data demonstrating the capability of measuring DNP enhanced NMR spectra of compounds with comparably short relaxation times, with only minimal line broadening attributable to the sample transfer process. We discuss the performance characteristics of a sample injection apparatus specifically designed to provide high-resolution DNP-NMR spectra of small molecule compounds.

  11. sup 31 P and sup 1 H NMR studies of the structure of enzyme-bound substrate complexes of lobster muscle arginine kinase: Relaxation measurements with Mn(II) and Co(II)

    SciTech Connect

    Jarori, G.K.; Ray, B.D.; Rao, B.D.N. )

    1989-11-28

    The paramagnetic effects of Mn(II) and Co(II) on the spin-lattice relaxation rates of {sup 31}P nuclei of ATP and ADP and of Mn(II) on the spin-lattice relaxation rate of the {delta} protons of arginine bound to arginine kinase from lobster tail muscle have been measured. Temperature variation of {sup 31}P relaxation rates in E-MnADP and E-MnATP yields activation energies ({Delta}E) in the range 6-10 kcal/mol. Thus, the {sup 31}P relaxation rates in these complexes are exchange limited and cannot provide structural information. However, the relaxation rates in E-CoADP and E-CoATP exhibit frequency dependence and {Delta}E values in the range 1-2 kcal/mol; i.e., these rates depend upon {sup 31}P-Co(II) distances. These distances were calculated to be in the range 3.2-4.5 {angstrom}, appropriate for direct coordination between Co(II) and the phosphoryl groups. The paramagnetic effect of Mn(II) on the {sup 1}H spin-lattice relaxation rate of the {delta} protons of arginine in the E-MnADP-Arg complex was also measured at three frequencies. From the frequency dependence of the relaxation rate an effective {tau}{sub C} of 0.6 ns has also been calculated, which is most likely to be the electron spin relaxation rate ({tau}{sub S1}) for Mn(II) in this complex. The distance estimated on the basis of the reciprocal sixth root of the average relaxation rate of the {delta} protons was 10.9 {plus minus} 0.3 {angstrom}.

  12. Relaxation System

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Environ Corporation's relaxation system is built around a body lounge, a kind of super easy chair that incorporates sensory devices. Computer controlled enclosure provides filtered ionized air to create a feeling of invigoration, enhanced by mood changing aromas. Occupant is also surrounded by multidimensional audio and the lighting is programmed to change colors, patterns, and intensity periodically. These and other sensory stimulators are designed to provide an environment in which the learning process is stimulated, because research has proven that while an individual is in a deep state of relaxation, the mind is more receptive to new information.

  13. Relaxation Techniques.

    DTIC Science & Technology

    1985-04-01

    FUNDING/SPONSORING 18b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER ORGANIZATION (If applicable) 8c ADDRESS f( t’, State and ZIP Code) 10...inhaling and exhaling to promote a feeling of relaxation that is used in yoga, LaMaze childbirth, and hypnosis . The sccond is progressive muscle

  14. Nuclear Moment Alignment, Relaxation and Detection Mechanisms.

    DTIC Science & Technology

    1983-03-01

    Distribuion/ - Availability Codes• I~Avail and/or SDst special / Edward Phillips Manager , NMR Gyro Project Ln 1.0 GUIDANCE & CONTROL SYSTEMSLikon 5500...06481 OW Cookmwc Woodd, HNK C@Muwdm@1lKU TABLE OF CONTENTS , Paragraph Title Page SECTION I PROGRAM DESCRIPTION ?i1.1 INTRODUCTION ........... * . 1... CONTENTS (cont) Paragraph Title Page SECTION IV - EFFECT OF SEVERAL SURFACE TREATMENTS ON 12 9Xe POLARIZATION AND RELAXATION IN NMR CELLS 4.1 INTRODUCTION

  15. Dynamics of [C{sub 3}H{sub 5}N{sub 2}]{sub 6}[Bi{sub 4}Br{sub 18}] by means of {sup 1}H NMR relaxometry and quadrupole relaxation enhancement

    SciTech Connect

    Masierak, W.; Florek-Wojciechowska, M.; Oglodek, I.; Jakubas, R.; Privalov, A. F.; Kresse, B.; Fujara, F.; Kruk, D.

    2015-05-28

    {sup 1}H spin-lattice field cycling relaxation dispersion experiments in the intermediate phase II of the solid [C{sub 3}H{sub 5}N{sub 2}]{sub 6}[Bi{sub 4}Br{sub 18}] are presented. Two motional processes have been identified from the {sup 1}H spin-lattice relaxation dispersion profiles and quantitatively described. It has been concluded that these processes are associated with anisotropic reorientations of the imidazolium ring, characterized by correlation times of the order of 10{sup −8} s-10{sup −9} s and of about 10{sup −5} s. Moreover, quadrupole relaxation enhancement (QRE) effects originating from slowly fluctuating {sup 1}H-{sup 14}N dipolar interactions have been observed. From the positions of the relaxation maxima, the quadrupole coupling parameters for the {sup 14}N nuclei in [C{sub 3}H{sub 5}N{sub 2}]{sub 6}[Bi{sub 4}Br{sub 18}] have been determined. The {sup 1}H-{sup 14}N relaxation contribution associated with the slow dynamics has been described in terms of a theory of QRE [Kruk et al., Solid State Nucl. Magn. Reson. 40, 114 (2011)] based on the stochastic Liouville equation. The shape of the QRE maxima (often referred to as “quadrupole peaks”) has been consistently reproduced for the correlation time describing the slow dynamics and the determined quadrupole coupling parameters.

  16. Photodissociation dynamics of IBr(-)(CO(2))(n), n<15.

    PubMed

    Sanford, Todd; Han, Sang-Yun; Thompson, Matthew A; Parson, Robert; Lineberger, W Carl

    2005-02-01

    We report the ionic photoproducts produced following photoexcitation of mass selected IBr(-)(CO(2))(n), n=0-14, cluster ions at 790 and 355 nm. These wavelengths provide single state excitation to two dissociative states, corresponding to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states of the IBr(-) chromophore. Excitation of these states in IBr(-) leads to production of I(-)+Br and Br(-)+I( *), respectively. Potential energy curves for the six lowest electronic states of IBr(-) are calculated, together with structures for IBr(-)(CO(2))(n), n=1-14. Translational energy release measurements on photodissociated IBr(-) determine the I-Br(-) bond strength to be 1.10+/-0.04 eV; related measurements characterize the A(') (2)Pi(1/2)<--X (2)Sigma(1/2) (+) absorption band. Photodissociation product distributions are measured as a function of cluster size following excitation to the A(') (2)Pi(1/2) and B 2 (2)Sigma(1/2) (+) states. The solvent is shown to drive processes such as spin-orbit relaxation, charge transfer, recombination, and vibrational relaxation on the ground electronic state. Following excitation to the A(') (2)Pi(1/2) electronic state, IBr(-)(CO(2))(n) exhibits size-dependent cage fractions remarkably similar to those observed for I(2) (-)(CO(2))(n). In contrast, excitation to the B 2 (2)Sigma(1/2) (+) state shows extensive trapping in excited states that dominates the recombination behavior for all cluster sizes we investigated. Finally, a pump-probe experiment on IBr(-)(CO(2))(8) determines the time required for recombination on the ground state following excitation to the A(') state. While the photofragmentation experiments establish 100% recombination in the ground electronic state for this and larger IBr(-) cluster ions, the time required for recombination is found to be approximately 5 ns, some three orders of magnitude longer than observed for the analogous I(2) (-) cluster ion. Comparisons are made with similar experiments carried out on I(2

  17. In situ determination of surface relaxivities for unconsolidated sediments

    NASA Astrophysics Data System (ADS)

    Duschl, Markus; Galvosas, Petrik; Brox, Timothy I.; Pohlmeier, Andreas; Vereecken, Harry

    2015-08-01

    NMR relaxometry has developed into a method for rapid pore-size determination of natural porous media. Nevertheless, it is prone to uncertainties because of unknown surface relaxivities which depend mainly on the chemical composition of the pore walls as well as on the interfacial dynamics of the pore fluid. The classical approach for the determination of surface relaxivities is the scaling of NMR relaxation times by surface to volume ratios measured by gas adsorption or mercury intrusion. However, it is preferable that a method for the determination of average pore sizes uses the same substance, water, as probe molecule for both relaxometry and surface to volume measurements. One should also ensure that in both experiments the dynamics of the probe molecule takes place on similar length scales, which are in the order of some microns. Therefore, we employed NMR diffusion measurements with different observation times using bipolar pulsed field gradients and applied them to unconsolidated sediments (two purified sands, two natural sands, and one soil). The evaluation by Mitra's short-time model for diffusion in restricted environments yielded information about the surface to volume ratios which is independent of relaxation mechanisms. We point out that methods based on NMR diffusometry yield pore dimensions and surface relaxivities consistent with a pore space as sampled by native pore fluids via the diffusion process. This opens a way to calibrate NMR relaxation measurements with other NMR techniques, providing information about the pore-size distribution of natural porous media directly from relaxometry.

  18. Bioagent detection using miniaturized NMR and nanoparticle amplification : final LDRD report.

    SciTech Connect

    Clewett, C. F. M.; Adams, David Price; Fan, Hongyou; Williams, John D.; Sillerud, Laurel O.; Alam, Todd Michael; Aldophi, Natalie L. (New Mexico Resonance, Albuquerque, NM); McDowell, Andrew F.

    2006-11-01

    This LDRD program was directed towards the development of a portable micro-nuclear magnetic resonance ({micro}-NMR) spectrometer for the detection of bioagents via induced amplification of solvent relaxation based on superparamagnetic nanoparticles. The first component of this research was the fabrication and testing of two different micro-coil ({micro}-coil) platforms: namely a planar spiral NMR {micro}-coil and a cylindrical solenoid NMR {micro}-coil. These fabrication techniques are described along with the testing of the NMR performance for the individual coils. The NMR relaxivity for a series of water soluble FeMn oxide nanoparticles was also determined to explore the influence of the nanoparticle size on the observed NMR relaxation properties. In addition, The use of commercially produced superparamagnetic iron oxide nanoparticles (SPIONs) for amplification via NMR based relaxation mechanisms was also demonstrated, with the lower detection limit in number of SPIONs per nanoliter (nL) being determined.

  19. Understanding NMR relaxometry of partially water-saturated rocks

    NASA Astrophysics Data System (ADS)

    Mohnke, O.; Jorand, R.; Nordlund, C.; Klitzsch, N.

    2015-06-01

    Nuclear magnetic resonance (NMR) relaxometry measurements are commonly used to characterize the storage and transport properties of water-saturated rocks. Estimations of these properties are based on the direct link of the initial NMR signal amplitude to porosity (water content) and of the NMR relaxation time to pore size. Herein, pore shapes are usually assumed to be spherical or cylindrical. However, the NMR response at partial water saturation for natural sediments and rocks may differ strongly from the responses calculated for spherical or cylindrical pores, because these pore shapes do not account for water menisci remaining in the corners of desaturated angular pores. Therefore, we consider a bundle of pores with triangular cross sections. We introduce analytical solutions of the NMR equations at partial saturation of these pores, which account for water menisci of desaturated pores. After developing equations that describe the water distribution inside the pores, we calculate the NMR response at partial saturation for imbibition and drainage based on the deduced water distributions. For this pore model, the NMR amplitudes and NMR relaxation times at partial water saturation strongly depend on pore shape, i.e., arising from the capillary pressure and pore shape-dependent water distribution in desaturated pores with triangular cross sections. Even so, the NMR relaxation time at full saturation only depends on the surface-to-volume ratio of the pore. Moreover, we show the qualitative agreement of the saturation-dependent relaxation-time distributions of our model with those observed for rocks and soils.

  20. Partition of the linear plasmid N15: interactions of N15 partition functions with the sop locus of the F plasmid.

    PubMed

    Ravin, N; Lane, D

    1999-11-01

    A locus close to one end of the linear N15 prophage closely resembles the sop operon which governs partition of the F plasmid; the promoter region contains similar operator sites, and the two putative gene products have extensive amino acid identity with the SopA and -B proteins of F. Our aim was to ascertain whether the N15 sop homologue functions in partition, to identify the centromere site, and to examine possible interchangeability of function with the F Sop system. When expressed at a moderate level, N15 SopA and -B proteins partly stabilize mini-F which lacks its own sop operon but retains the sopC centromere. The stabilization does not depend on increased copy number. Likewise, an N15 mutant with most of its sop operon deleted is partly stabilized by F Sop proteins and fully stabilized by its own. Four inverted repeat sequences similar to those of sopC were located in N15. They are distant from the sop operon and from each other. Two of these were shown to stabilize a mini-F sop deletion mutant when N15 Sop proteins were provided. Provision of the SopA homologue to plasmids with a sopA deletion resulted in further destabilization of the plasmid. The N15 Sop proteins exert effective, but incomplete, repression at the F sop promoter. We conclude that the N15 sop locus determines stable inheritance of the prophage by using dispersed centromere sites. The SopB-centromere and SopA-operator interactions show partial functional overlap between N15 and F. SopA of each plasmid appears to interact with SopB of the other, but in a way that is detrimental to plasmid maintenance.

  1. {sup 1}H NMR relaxometry and quadrupole relaxation enhancement as a sensitive probe of dynamical properties of solids—[C(NH{sub 2}){sub 3}]{sub 3}Bi{sub 2}I{sub 9} as an example

    SciTech Connect

    Florek-Wojciechowska, M.; Wojciechowski, M.; Brym, Sz.; Kruk, D.; Jakubas, R.

    2016-02-07

    {sup 1}H nuclear magnetic resonance relaxometry has been applied to reveal information on dynamics and structure of Gu{sub 3}Bi{sub 2}I{sub 9} ([Gu = C(NH{sub 2}){sub 3}] denotes guanidinium cation). The data have been analyzed in terms of a theory of quadrupole relaxation enhancement, which has been extended here by including effects associated with quadrupole ({sup 14}N) spin relaxation caused by a fast fluctuating component of the electric field gradient tensor. Two motional processes have been identified: a slow one occurring on a timescale of about 8 × 10{sup −6} s which has turned out to be (almost) temperature independent, and a fast process in the range of 10{sup −9} s. From the {sup 1}H-{sup 14}N relaxation contribution (that shows “quadrupole peaks”) the quadrupole parameters, which are a fingerprint of the arrangement of the anionic network, have been determined. It has been demonstrated that the magnitude of the quadrupole coupling considerably changes with temperature and the changes are not caused by phase transitions. At the same time, it has been shown that there is no evidence of abrupt changes in the cationic dynamics and the anionic substructure upon the phase transitions.

  2. Scalar operators in solid-state NMR

    SciTech Connect

    Sun, Boqin

    1991-11-01

    Selectivity and resolution of solid-state NMR spectra are determined by dispersion of local magnetic fields originating from relaxation effects and orientation-dependent resonant frequencies of spin nuclei. Theoretically, the orientation-dependent resonant frequencies can be represented by a set of irreducible tensors. Among these tensors, only zero rank tensors (scalar operators) are capable of providing high resolution NMR spectra. This thesis presents a series of new developments in high resolution solid-state NMR concerning the reconstruction of various scalar operators motion in solid C{sub 60} is analyzed.

  3. Natural relaxation

    NASA Astrophysics Data System (ADS)

    Marzola, Luca; Raidal, Martti

    2016-11-01

    Motivated by natural inflation, we propose a relaxation mechanism consistent with inflationary cosmology that explains the hierarchy between the electroweak scale and Planck scale. This scenario is based on a selection mechanism that identifies the low-scale dynamics as the one that is screened from UV physics. The scenario also predicts the near-criticality and metastability of the Standard Model (SM) vacuum state, explaining the Higgs boson mass observed at the Large Hadron Collider (LHC). Once Majorana right-handed neutrinos are introduced to provide a viable reheating channel, our framework yields a corresponding mass scale that allows for the seesaw mechanism as well as for standard thermal leptogenesis. We argue that considering singlet scalar dark matter extensions of the proposed scenario could solve the vacuum stability problem and discuss how the cosmological constant problem is possibly addressed.

  4. NMR imaging techniques and applications: A review

    NASA Astrophysics Data System (ADS)

    Bottomley, Paul A.

    1982-09-01

    Over the past ten years, a variety of techniques have been proposed and demonstrated that enable the spatial discrimination and mapping of nuclear-magnetic-resonance (NMR) signals in heterogeneous objects. These NMR imaging techniques are currently finding useful application in clinical medicine and physiological chemistry, where their noninvasive, apparently hazard-free nature, and the sensitivity of the NMR signal to the state of biological tissue, are key advantages. This article reviews the historical development, the conceptual basis, and the applications of the various NMR imaging techniques. Qualitative descriptions and illustrations of each technique and an outline of imaging instrumentation are provided. Proton NMR imaging, in medicine, of pathological states such as cancer, imaging of relaxation time, chemical shift and flow parameters, imaging of nuclei other than hydrogen, and potential hazards are discussed and demonstrated with examples.

  5. Dynamics in supercooled polyalcohols: Primary and secondary relaxation

    NASA Astrophysics Data System (ADS)

    Döß, A.; Paluch, M.; Sillescu, H.; Hinze, G.

    2002-10-01

    We have studied details of the molecular dynamics in a series of pure polyalcohols by means of dielectric spectroscopy and 2H nuclear magnetic resonance (NMR). From glycerol to threitol, xylitol and sorbitol a systematic change in the dynamics of the primary and secondary relaxation is found. With increasing molecular weight and fragility an increase in the width of the α-peak is observed. Details of the molecular reorientation process responsible for the α-relaxation were exploited by two-dimensional NMR experiments. It is found that in the same sequence of polyalcohols the appearance of the secondary relaxation changes gradually from a wing type scenario to a pronounced β-peak. From NMR experiments using selectively deuterated samples the molecular origin of the secondary relaxation could be elucidated in more detail.

  6. Fluid-Rock Characterization and Interactions in NMR Well Logging

    SciTech Connect

    Hirasaki, George J.; Mohanty, Kishore K.

    2003-02-10

    The objective of this project was to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity.

  7. Relaxation response in femoral angiography.

    PubMed

    Mandle, C L; Domar, A D; Harrington, D P; Leserman, J; Bozadjian, E M; Friedman, R; Benson, H

    1990-03-01

    Immediately before they underwent femoral angiography, 45 patients were given one of three types of audiotapes: a relaxation response tape recorded for this study, a tape of contemporary instrumental music, or a blank tape. All patients were instructed to listen to their audiotape during the entire angiographic procedure. Each audiotape was played through earphones. Radiologists were not told the group assignment or tape contents. The patients given the audiotape with instructions to elicit the relaxation response (n = 15) experienced significantly less anxiety (P less than .05) and pain (P less than .001) during the procedure, were observed by radiology nurses to exhibit significantly less pain (P less than .001) and anxiety (P less than .001), and requested significantly less fentanyl citrate (P less than .01) and diazepam (P less than .01) than patients given either the music (n = 14) or the blank (n = 16) control audiotapes. Elicitation of the relaxation response is a simple, inexpensive, efficacious, and practical method to reduce pain, anxiety, and medication during femoral angiography and may be useful in other invasive procedures.

  8. STRUCTURE ASSIGNMENT OF AMINOCONDURITOLS BY N-15 NMR CORRELATION SPECTROSCOPY; SYNTHESIS OF A POSITIONAL ISOMER OF 7-DEOXYPANCRATISTATIN. (R826113)

    EPA Science Inventory

    The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

  9. La relaxation en pedagogie (Relaxation in Teaching).

    ERIC Educational Resources Information Center

    Dufeu, Bernard

    1989-01-01

    A discussion of the use of relaxation techniques in the language classroom outlines the reasons for their use and specifies procedures for relaxation either lying down or seated as a prelude to instruction. (MSE)

  10. Breathing and Relaxation

    MedlinePlus

    ... Home Health Insights Stress & Relaxation Breathing and Relaxation Breathing and Relaxation Make an Appointment Ask a Question ... level is often dependent on his or her breathing pattern. Therefore, people with chronic lung conditions may ...

  11. NMR phase noise in bitter magnets.

    PubMed

    Sigmund, E E; Calder, E S; Thomas, G W; Mitrović, V F; Bachman, H N; Halperin, W P; Kuhns, P L; Reyes, A P

    2001-02-01

    We have studied the temporal instability of a high field resistive Bitter magnet through nuclear magnetic resonance (NMR). This instability leads to transverse spin decoherence in repeated and accumulated NMR experiments as is normally performed during signal averaging. We demonstrate this effect via Hahn echo and Carr--Purcell--Meiboom--Gill (CPMG) transverse relaxation experiments in a 23-T resistive magnet. Quantitative analysis was found to be consistent with separate measurements of the magnetic field frequency fluctuation spectrum, as well as with independent NMR experiments performed in a magnetic field with a controlled instability. Finally, the CPMG sequence with short pulse delays is shown to be successful in recovering the intrinsic spin--spin relaxation even in the presence of magnetic field temporal instability. Copyright 2001 Academic Press.

  12. Hyperpolarized 131Xe NMR spectroscopy

    NASA Astrophysics Data System (ADS)

    Stupic, Karl F.; Cleveland, Zackary I.; Pavlovskaya, Galina E.; Meersmann, Thomas

    2011-01-01

    Hyperpolarized (hp) 131Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T1 relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent 131Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in 129Xe SEOP. 131Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase 131Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp 131Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp 131Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I⩾1/2 nuclei is presented.

  13. Hyperpolarized 131Xe NMR spectroscopy

    PubMed Central

    Stupic, Karl F.; Cleveland, Zackary I.; Pavlovskaya, Galina E.; Meersmann, Thomas

    2011-01-01

    Hyperpolarized (hp) 131Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T1 relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent 131Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in 129Xe SEOP. 131Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase 131Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp 131Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp 131Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I⩾1/2 nuclei is presented. PMID:21051249

  14. Relaxation Assessment with Varied Structured Milieu (RELAX).

    ERIC Educational Resources Information Center

    Cassel, Russell N.; Cassel, Susie L.

    1983-01-01

    Describes Relaxation Assessment with Varied Structured Milieu (RELAX), a clinical program designed to assess the degree to which an individual is able to demonstrate self-control for overall general relaxation. The program is designed for use with the Cassel Biosensors biofeedback equipment. (JAC)

  15. Relaxation Assessment with Varied Structured Milieu (RELAX).

    ERIC Educational Resources Information Center

    Cassel, Russell N.; Cassel, Susie L.

    1983-01-01

    Describes Relaxation Assessment with Varied Structured Milieu (RELAX), a clinical program designed to assess the degree to which an individual is able to demonstrate self-control for overall general relaxation. The program is designed for use with the Cassel Biosensors biofeedback equipment. (JAC)

  16. Study of correlations in molecular motion by multiple quantum NMR

    NASA Astrophysics Data System (ADS)

    Tang, J. H.

    1981-11-01

    The theoretical background of spin Hamiltonians, the density matrix formalism of multiple quantum NMR are discussed as well as creation and detection of multiple quantum coherence by multiple pulse sequence. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are considered. An oriented methyl group relaxed by paramagnetic impurities is examined and possible correlated motion between two coupled methyl groups is investigated by multiple quantum NMR. For a six spin system it is shown that the four quantum spectrum is sensitive to two body correlations, and serves a ready test of correlated motion. The spin lattice dynamics of orienting or tunneling methyl groups (CH3 and CD3) at low temperatures and the anisotropic spin lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules are described as well as NMR spectrometers.

  17. Interfaces in polymer nanocomposites – An NMR study

    SciTech Connect

    Böhme, Ute; Scheler, Ulrich

    2016-03-09

    Nuclear Magnetic Resonance (NMR) is applied for the investigation of polymer nanocomposites. Solid-state NMR is applied to study the modification steps to compatibilize layered double hydroxides with non-polar polymers. {sup 1}H relaxation NMR gives insight on the polymer dynamics over a wide range of correlation times. For the polymer chain dynamics the transverse relaxation time T{sub 2} is most suited. In this presentation we report on two applications of T{sub 2} measurements under external mechanical stress. In a low-field system relaxation NMR studies are performed in-situ under uniaxial stress. High-temperature experiments in a Couette cell permit the investigation of the polymer dynamics in the melt under shear flow.

  18. Micellar kinetics of a fluorosurfactant through stopped-flow NMR.

    PubMed

    Yushmanov, Pavel V; Furó, István; Stilbs, Peter

    2006-02-28

    19F NMR chemical shifts and transverse relaxation times T2 were measured as a function of time after quick stopped-flow dilution of aqueous solutions of sodium perfluorooctanoate (NaPFO) with water. Different initial concentrations of micellar solution and different proportions of mixing were tested. Previous stopped-flow studies by time-resolved small-angle X-ray scattering (TR-SAXS) detection indicated a slow (approximately 10 s) micellar relaxation kinetics in NaPFO solutions. In contrast, no evidence of any comparable slow (>100 ms) relaxation process was found in our NMR studies. Possible artifacts of stopped-flow experiments are discussed as well as differences between NMR and SAXS detection methods. Upper bounds on the relative weight of a slow relaxation process are given within existing kinetic theories of micellar dissolution.

  19. Multiecho scheme advances surface NMR for aquifer characterization

    NASA Astrophysics Data System (ADS)

    Grunewald, Elliot; Walsh, David

    2013-12-01

    nuclear magnetic resonance (NMR) is increasingly used as a method to noninvasively characterize aquifers. This technology follows a successful history of NMR logging, applied over decades to estimate hydrocarbon reservoir properties. In contrast to logging, however, surface methods have utilized relatively simple acquisition sequences, from which pore-scale properties may not be reliably and efficiently estimated. We demonstrate for the first time the capability of sophisticated multiecho measurements to rapidly record a surface NMR response that more directly reflects aquifer characteristics. Specifically, we develop an adaptation of the multipulse Carr-Purcell-Meiboom-Gill (CPMG) sequence, widely used in logging, to measure the T2 relaxation response in a single scan. We validate this approach in a field surface NMR data set and by direct comparison with an NMR log. Adoption of the CPMG marked a landmark advancement in the history of logging NMR; we have now realized this same advancement in the surface NMR method.

  20. Understanding NMR relaxometry of partially water-saturated rocks

    NASA Astrophysics Data System (ADS)

    Mohnke, O.; Nordlund, C.; Jorand, R.; Klitzsch, N.

    2014-11-01

    Nuclear Magnetic Resonance (NMR) relaxometry measurements are commonly used to characterize the storage and transport properties of water-saturated rocks. These assessments are based on the proportionality of NMR signal amplitude and relaxation time to porosity (water content) and pore size, respectively. The relationship between pore size and NMR relaxation time depends on pore shape, which is usually assumed to be spherical or cylindrical. However, the NMR response at partial water saturation for natural sediments and rocks differs strongly from the response calculated for spherical or cylindrical pores, because these pore shapes cannot account for water menisci remaining in the corners of de-saturated angular pores. Therefore, we consider a bundle of pores with triangular cross-sections. We introduce analytical solutions of the NMR equations at partial saturation of these pores, which account for water menisci of de-saturated pores. After developing equations that describe the water distribution inside the pores, we calculate the NMR response at partial saturation for imbibition and drainage based on the deduced water distributions. For this pore model, NMR amplitude and NMR relaxation time at partial water saturation strongly depend on pore shape even so the NMR relaxation time at full saturation only depends on the surface to volume ratio of the pore. The pore-shape-dependence at partial saturation arises from the pore shape and capillary pressure dependent water distribution in pores with triangular cross-sections. Moreover, we show the qualitative agreement of the saturation dependent relaxation time distributions of our model with those observed for rocks and soils.

  1. Fluid-Rock Characterization and Interactions in NMR Well Logging

    SciTech Connect

    George J. Hirasaki; Kishore K. Mohanty

    2005-09-05

    The objective of this report is to characterize the fluid properties and fluid-rock interactions that are needed for formation evaluation by NMR well logging. The advances made in the understanding of NMR fluid properties are summarized in a chapter written for an AAPG book on NMR well logging. This includes live oils, viscous oils, natural gas mixtures, and the relation between relaxation time and diffusivity. Oil based drilling fluids can have an adverse effect on NMR well logging if it alters the wettability of the formation. The effect of various surfactants on wettability and surface relaxivity are evaluated for silica sand. The relation between the relaxation time and diffusivity distinguishes the response of brine, oil, and gas in a NMR well log. A new NMR pulse sequence in the presence of a field gradient and a new inversion technique enables the T{sub 2} and diffusivity distributions to be displayed as a two-dimensional map. The objectives of pore morphology and rock characterization are to identify vug connectivity by using X-ray CT scan, and to improve NMR permeability correlation. Improved estimation of permeability from NMR response is possible by using estimated tortuosity as a parameter to interpolate between two existing permeability models.

  2. NMR spin-lattice relaxation study of {sup 7}Li and {sup 93}Nb nuclei in Ti- or Fe-doped LiNbO{sub 3}:Mg single crystals

    SciTech Connect

    Yeom, Tae Ho; Lim, Ae Ran E-mail: arlim@jj.ac.kr

    2016-04-15

    In this study, to understand the effects of paramagnetic impurities, we investigated the temperature dependent of the spin-lattice relaxation times of pure LiNbO{sub 3}, LiNbO{sub 3}:Mg, LiNbO{sub 3}:Mg/Ti, LiNbO{sub 3}:Mg/Fe, and LiNbO{sub 3}:Mg/Fe (thermally treated at 500°C) single crystals. The results for the LiNbO{sub 3}:Mg single crystals doped with Fe{sup 3+} or Ti{sup 3+} are discussed with respect to the site distribution and atomic mobility of Li and Nb. In addition, the effects of a thermal treatment on LiNbO{sub 3}:Mg/Fe single crystals were examined based on the T{sub 1} analysis of {sup 7}Li and {sup 93}Nb. It was found that the presence of impurities in the crystals induced systematic changes of activation energies concerning atomic mobility.

  3. Determination of the solution-bound conformation of an amino acid binding protein by NMR paramagnetic relaxation enhancement: use of a single flexible paramagnetic probe with improved estimation of its sampling space.

    PubMed

    Bermejo, Guillermo A; Strub, Marie-Paule; Ho, Chien; Tjandra, Nico

    2009-07-15

    We demonstrate the feasibility of elucidating the bound ("closed") conformation of a periplasmic binding protein, the glutamine-binding protein (GlnBP), in solution, using paramagnetic relaxation enhancements (PREs) arising from a single paramagnetic group. GlnBP consists of two globular domains connected by a hinge. Using the ligand-free ("open") conformation as a starting point, conjoined rigid-body/torsion-angle simulated annealing calculations were performed using backbone (1)H(N)-PREs as a major source of distance information. Paramagnetic probe flexibility was accounted for via a multiple-conformer representation. A conventional approach where the entire PRE data set is enforced at once during simulated annealing yielded poor results due to inappropriate conformational sampling of the probe. On the other hand, significant improvements in coordinate accuracy were obtained by estimating the probe sampling space prior to structure calculation. Such sampling is achieved by refining the ensemble of probe conformers with intradomain PREs only, keeping the protein backbone fixed in the open form. Subsequently, while constraining the probe to the previously found conformations, the domains are allowed to move relative to each other under the influence of the non-intradomain PREs, giving the hinge region torsional degrees of freedom. Thus, by partitioning the protocol into "probe sampling" and "backbone sampling" stages, structures significantly closer to the X-ray structure of ligand-bound GlnBP were obtained.

  4. Metabolism of nonessential N-15-labeled amino acids and the measurement of human whole-body protein synthesis rates

    NASA Technical Reports Server (NTRS)

    Stein, T. P.; Settle, R. G.; Albina, J. A.; Melnick, G.; Dempsey, D. T.

    1991-01-01

    Eight N-15-labeled nonessential amino acids plus (N-15)H4Cl were administered over a 10-h period to four healthy adult males using a primed-constant dosage regimen. The amount of N-15 excreted in the urine and the urinary ammonia, hippuric acid, and plasma alanine N-15 enrichments were measured. There was a high degree of consistency across subjects in the ordering of the nine compounds based on the fraction of N-15 excreted.

  5. Metabolism of nonessential N-15-labeled amino acids and the measurement of human whole-body protein synthesis rates

    NASA Technical Reports Server (NTRS)

    Stein, T. P.; Settle, R. G.; Albina, J. A.; Melnick, G.; Dempsey, D. T.

    1991-01-01

    Eight N-15-labeled nonessential amino acids plus (N-15)H4Cl were administered over a 10-h period to four healthy adult males using a primed-constant dosage regimen. The amount of N-15 excreted in the urine and the urinary ammonia, hippuric acid, and plasma alanine N-15 enrichments were measured. There was a high degree of consistency across subjects in the ordering of the nine compounds based on the fraction of N-15 excreted.

  6. Proteins responsible for lysogenic conversion caused by coliphages N15 and phi80 are highly homologous.

    PubMed Central

    Vostrov, A A; Vostrukhina, O A; Svarchevsky, A N; Rybchin, V N

    1996-01-01

    Lysogenic conversion caused by lambdoid bacteriophage phi80 and that caused by coliphage N15 have similar characteristics, suggesting that similarities in their cor genes and Cor proteins are responsible for this effect. Here we present the nucleotide sequence of the N15 cor gene. The N15 cor gene homolog was found in the phi80 cor region, but in the opposite direction of that of the open reading frame to which the phi80 cor gene had previously been assigned (M. Matsumoto, N. Ichikawa, S. Tanaka, T. Morita, and A. Matsushiro, Jpn. J. Genet. 60:475-483, 1985). PMID:8631731

  7. Water proton relaxation in dilute and unsaturated suspensions of non-porous particles.

    PubMed

    Hills, B P

    1994-01-01

    NMR water proton relaxation times are reported for suspensions of silica powder of varying silica/water ratios. Pore size distributions and pore connectivities are derived from the relaxation time distributions for the water-saturated suspension. Capillary theory appears to explain the relaxation behaviour of the unsaturated, packed suspensions. The relaxation data in suspensions that have lower solid/liquid ratios than the saturated, packed suspension are sensitive to the particular radial distribution function. This is analysed with a simple cluster model.

  8. Clathrate formation and dissociation in vapor/water/ice/hydrate systems in SBA-15, sol-gel and CPG porous media, as probed by NMR relaxation, novel protocol NMR cryoporometry, neutron scattering and ab initio quantum-mechanical molecular dynamics simulation.

    PubMed

    Webber, J Beau W; Anderson, Ross; Strange, John H; Tohidi, Bahman

    2007-05-01

    The Gibbs-Thomson effect modifies the pressure and temperature at which clathrates occur, hence altering the depth at which they occur in the seabed. Nuclear magnetic resonance (NMR) measurements as a function of temperature are being conducted for water/ice/hydrate systems in a range of pore geometries, including templated SBA-15 silicas, controlled pore glasses and sol-gel silicas. Rotator-phase plastic ice is shown to be present in confined geometry, and bulk tetrahydrofuran hydrate is also shown to probably have a rotator phase. A novel NMR cryoporometry protocol, which probes both melting and freezing events while avoiding the usual problem of supercooling for the freezing event, has been developed. This enables a detailed probing of the system for a given pore size and geometry and the exploration of differences between hydrate formation and dissociation processes inside pores. These process differences have an important effect on the environment, as they impact on the ability of a marine hydrate system to re-form once warmed above a critical temperature. Ab initio quantum-mechanical molecular dynamics calculations are also being employed to probe the dynamics of liquids in pores at nanometric dimensions.

  9. Hydrate Shell Growth Measured Using NMR.

    PubMed

    Haber, Agnes; Akhfash, Masoumeh; Loh, Charles K; Aman, Zachary M; Fridjonsson, Einar O; May, Eric F; Johns, Michael L

    2015-08-18

    Benchtop nuclear magnetic resonance (NMR) pulsed field gradient (PFG) and relaxation measurements were used to monitor the clathrate hydrate shell growth occurring in water droplets dispersed in a continuous cyclopentane phase. These techniques allowed the growth of hydrate inside the opaque exterior shell to be monitored and, hence, information about the evolution of the shell's morphology to be deduced. NMR relaxation measurements were primarily used to monitor the hydrate shell growth kinetics, while PFG NMR diffusion experiments were used to determine the nominal droplet size distribution (DSD) of the unconverted water inside the shell core. A comparison of mean droplet sizes obtained directly via PFG NMR and independently deduced from relaxation measurements showed that the assumption of the shell model-a perfect spherical core of unconverted water-for these hydrate droplet systems is correct, but only after approximately 24 h of shell growth. Initially, hydrate growth is faster and heat-transfer-limited, leading to porous shells with surface areas larger than that of spheres with equivalent volumes. Subsequently, the hydrate growth rate becomes mass-transfer-limited, and the shells become thicker, spherical, and less porous.

  10. Application of C30B15N15 heterofullerene in the isoniazid drug delivery: DFT studies

    NASA Astrophysics Data System (ADS)

    Hazrati, Mehrnoosh Khodam; Bagheri, Zargham; Bodaghi, Ali

    2017-05-01

    Using density functional theory, we have investigated the potential application of a C30B15N15 heterofullerene in anti-cancer isoniazid drug delivery. It was found that isoniazid prefers to attach via its -NH2 group to a boron atom of the C30B15N15 with releasing a large energy of about 21.91 kcal/mol. Our partial density of states analysis demonstrates that the boron atoms significantly contribute in generation of virtual orbitals of C30B15N15 fullerene, indicating that these atoms will be suitable for nucleophilic attack rather than carbon atoms. In addition to the large released energy, the electronic properties C30B15N15 are significantly sensitive to the isoniazid attachment which can recognize the drug trajectory by affecting the fluorescence emission properties. Unlike, different nanostructures whose structures need to be manipulated to be suitable for drug delivery, the C30B15N15 fullerene can be used in the pristine form. We proposed a drug release mechanism in cancer tissues, representing that in the low pH of the cancer cells the drug and C30B15N15 fullerene are considerably protonated, thereby separating the drug from the surface of the fullerene. The reaction mechanism of the drug with the fullerene is changed from covalence in natural environment to hydrogen bonding in acidic cancer cells.

  11. Assessment of meat quality by NMR--an investigation of pork products originating from different breeds.

    PubMed

    Straadt, Ida K; Aaslyng, Margit D; Bertram, Hanne C

    2011-12-01

    In the present study, meat obtained from uncommon and novel pig crossings between the rare Iberian and Mangalitza pigs and the more frequent Duroc and Landrace/Yorkshire pigs was characterized by time-domain proton NMR relaxometry and high-resolution proton NMR spectroscopy to elucidate the potential of NMR to assess the meat quality of new-introduced pig breeds. Multivariate data analysis of proton NMR T(2) relaxation curves obtained on fresh meat samples revealed differences in the T(2) relaxation pattern of the different breeds included in the study. Comparison of NMR T(2) relaxation data with gravimetric determination of water-holding capacity (WHC) indicated that this should be ascribed to differences in the WHC of the different meats, and that NMR T(2) relaxation in accordance with previous studies provides unique information about WHC, which may be ascribed to the fact that NMR T(2) relaxation reflects information about intrinsic meat structure. High-resolution proton NMR spectroscopy of freeze exudate and meat extracts also revealed differences in the metabolite profile of the meat between the different breeds studied. The effects of breed on the amount of lactate in the freeze exudate were observed, which could be linked to WHC of the meat. In conclusion, the different NMR techniques applied could provide complementary information about biophysical and biochemical factors of importance for meat quality assessment.

  12. New Designs for NMR Core Scanning

    NASA Astrophysics Data System (ADS)

    Bluemich, B.; Anferova, S.; Talnishnikh, E.; Arnold, J.; Clauser, C.

    2006-12-01

    Within the last ten years, mobile magnetic resonance has moved from the oil field to many new areas of application. While the focus of mobile NMR in the past was on single-sided or inside-out NMR, the advent of tube-shaped Halbach magnets has introduced the conventional outside-in NMR concept to mobile NMR where the object is inside a magnet. Our Halbach magnet is constructed from small magnet blocks at light weight and low cost with a magnetic field sufficiently homogeneous. To automatize NMR measurements, the Halbach magnet is mounted on a sliding table to scan long core sections without human interaction. In homogeneous magnetic fields, the longitudinal relaxation time T1 and even the transverse relaxation time T2 are proportional to the pore diameters of rocks. Hence, the T1 and T2 signals map the pore-size distribution of the studied rock cores. For fully saturated samples the integral of the distribution curve is proportional to porosity. The porosity values from NMR measurements with the Halbach magnet are used to estimate permability. The Halbach magnet can be used for certain sample geometries in combination with exchangeable radio frequency (rf) coils with different diameters from 24 mm up to 80 mm. To measure standard Ocean Drilling Program (ODP)/Integrated Ocean Drilling Program (IODP) cores, which have a standard diameter of 60 mm and are split lengthwise after recovery, we use a surface figure-8 rf coil with an inner diameter of 60 mm. Besides 1D T2 measurements, we perform relaxation-relaxation correlation experiments, where T1 and T2 are measured in parallel. In this way, the influence of diffusion on the shape of the T2 distribution function is probed. A gradient coil system was designed to perform Pulsed Field Gradients (PFG) experiments. As the gradient coils restrict the axial access to the magnet, only cylindrical core plugs with 20 mm in diameter can be analysed by PFG NMR methods. The homogeneity of the magnetic field in the sensitive volume

  13. NMR on cesium intercalated carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Schmid, M.; Goze-Bac, C.; Mehring, M.; Roth, S.; Bernier, P.

    2004-09-01

    Intercalation of single wall carbon nanotube (SWNT) bundles with alkali metals is expected to modify the electronic band structure and to raise the Fermi level. We report results from temperature dependent 13C- and 133Cs-NMR measurements on Cs intercalated SWNT. Cs was reversibly intercalated with different stoichiometries. NMR lineshapes as well as relaxation effects are studied and discussed in context of dynamics of alkali ions in SWNT bundles. The results are compared with structural simulations of Cs-ions intercalated in SWNT.

  14. NMR Characterizations of Properties of Heterogeneous Media

    SciTech Connect

    Uh, Jinsoo; Phan, Jack; Xue, Dong; Watson, A. Ted

    2003-01-28

    The overall goal of this project was to develop reliable methods for resolving macroscopic properties important for describing the flow of one or more fluid phases in reservoirs from formation measurements. During this reporting period, the determination of surface relaxivity from NMR data was investigated. A new method for determining the surface relaxivity from measured data was developed and tested with data obtained from an Exxon sample. The new method avoids the use of a certain mathematical short-time approximation in the data analysis, which has been shown to be unsuitable.

  15. Proton relaxation times in cancer diagnosis

    SciTech Connect

    Santhana Mariappan, S.V.; Subramanian, S.; Chandrakumar, N.; Rajalakshmi, K.R.; Sukumaran, S.S.

    1988-10-01

    Proton nuclear magnetic resonance relaxation parameters (T1, T2) were measured for over 100 malignant and normal tissue samples of various organs of the human body. The purpose of this study was to estimate the reliability of the NMR technique in discriminating normal from malignant tissues. Breast and cervix samples were analyzed by using the malignancy index concept and we were able to distinguish malignant and normal tissue in 17 out of 18 breast samples and 5 out of 7 cervix samples. Since the relaxation data of a normal control population of the other organs were not available, the data for these are reported without any further analysis. The distinction between carcinomas and sarcomas was also made by using the estimated relaxation parameters. Malignancy indices of breast tissue samples for linear least-squares and nonlinear two-parameter and three-parameter least-squares procedures were calculated and used to evaluate the relative efficiencies in discriminating malignant from normal tissues.

  16. [Study of the algorithm for inversion of low field nuclear magnetic resonance relaxation distribution].

    PubMed

    Chen, Shanshan; Wang, Hongzhi; Yang, Peiqiang; Zhang, Xuelong

    2014-06-01

    It is difficult to reflect the properties of samples from the signal directly collected by the low field nuclear magnetic resonance (NMR) analyzer. People must obtain the relationship between the relaxation time and the original signal amplitude of every relaxation component by inversion algorithm. Consequently, the technology of T2 spectrum inversion is crucial to the application of NMR data. This study optimized the regularization factor selection method and presented the regularization algorithm for inversion of low field NMR relaxation distribution, which is based on the regularization theory of ill-posed inverse problem. The results of numerical simulation experiments by Matlab7.0 showed that this method could effectively analyze and process the NMR relaxation data.

  17. Characterization of the Interfacial Regions of Heterogeneous Blends of Immiscible Polymers by Dynamic Nuclear Polarization (13)C NMR

    DTIC Science & Technology

    1990-10-31

    a stable free radical, we can generate a dynamic nuclear polarization ( DNP ) enhanced 13C NMR signal from chains of the undoped component which are...within 100 A of the interface. DNP - enhanced NMR relaxation experiments performed on polycarbonate/free-radical-doped- polystyrene blends show that...perform DNP -selected, NMR relaxation experiments on a variety of polycarbonate-polystyrene blends with known thermal histories and solvent exposure. The

  18. Nuclear magnetic resonance relaxation and diffusion measurements as a proxy for soil properties

    NASA Astrophysics Data System (ADS)

    Duschl, Markus; Pohlmeier, Andreas; Galvosas, Petrik; Vereecken, Harry

    2013-04-01

    Nuclear Magnetic Resonance (NMR) relaxation and NMR diffusion measurements are two of a series of fast and non-invasive NMR applications widely used e.g. as well logging tools in petroleum exploration [1]. For experiments with water, NMR relaxation measures the relaxation behaviour of former excited water molecules, and NMR diffusion evaluates the self-diffusion of water. Applied in porous media, both relaxation and diffusion measurements depend on intrinsic properties of the media like pore size distribution, connectivity and tortuosity of the pores, and water saturation [2, 3]. Thus, NMR can be used to characterise the pore space of porous media not only in consolidated sediments but also in soil. The physical principle behind is the relaxation of water molecules in an external magnetic field after excitation. In porous media water molecules in a surface layer of the pores relax faster than the molecules in bulk water because of interactions with the pore wall. Thus, the relaxation in smaller pores is generally faster than in bigger pores resulting in a relaxation time distribution for porous media with a range of pore sizes like soil [4]. In NMR diffusion experiments, there is an additional encoding of water molecules by application of a magnetic field gradient. Subsequent storage of the magnetization and decoding enables the determination of the mean square displacement and therefore of the self-diffusion of the water molecules [5]. Employing various relaxation and diffusion experiments, we get a measure of the surface to volume ratio of the pores and the tortuosity of the media. In this work, we show the characterisation of a set of sand and soil samples covering a wide range of textural classes by NMR methods. Relaxation times were monitored by the Carr-Purcell-Meiboom-Gill sequence and analysed using inverse Laplace transformation. Apparent self-diffusion constants were detected by a 13-intervall pulse sequence and variation of the storage time. We

  19. (129)Xe NMR of Mesoporous Silicas

    SciTech Connect

    Anderson, M.T.; Asink, R.A.; Kneller, J.M.; Pietrass, T.

    1999-04-23

    The porosities of three mesoporous silica materials were characterized with {sup 129}Xe NMR spectroscopy. The materials were synthesized by a sol-gel process with r = 0, 25, and 70% methanol by weight in an aqueous cetyltrimethylammonium bromide solution. Temperature dependent chemical shifts and spin lattice relaxation times reveal that xenon does not penetrate the pores of the largely disordered (r= 70%) silica. For both r = 0 and 25%, temperature dependent resonances corresponding to physisorbed xenon were observed. An additional resonance for the r = 25% sample was attributed to xenon between the disordered cylindrical pores. 2D NMR exchange experiments corroborate the spin lattice relaxation data which show that xenon is in rapid exchange between the adsorbed and the gas phase.

  20. NMR studies of nucleic acid dynamics

    NASA Astrophysics Data System (ADS)

    Al-Hashimi, Hashim M.

    2013-12-01

    Nucleic acid structures have to satisfy two diametrically opposite requirements; on one hand they have to adopt well-defined 3D structures that can be specifically recognized by proteins; on the other hand, their structures must be sufficiently flexible to undergo very large conformational changes that are required during key biochemical processes, including replication, transcription, and translation. How do nucleic acids introduce flexibility into their 3D structure without losing biological specificity? Here, I describe the development and application of NMR spectroscopic techniques in my laboratory for characterizing the dynamic properties of nucleic acids that tightly integrate a broad set of NMR measurements, including residual dipolar couplings, spin relaxation, and relaxation dispersion with sample engineering and computational approaches. This approach allowed us to obtain fundamental new insights into directional flexibility in nucleic acids that enable their structures to change in a very specific functional manner.

  1. Latent Period of Relaxation.

    PubMed

    Kobayashi, M; Irisawa, H

    1961-10-27

    The latent period of relaxation of molluscan myocardium due to anodal current is much longer than that of contraction. Although the rate and the grade of relaxation are intimately related to both the stimulus condition and the muscle tension, the latent period of relaxation remains constant, except when the temperature of the bathing fluid is changed.

  2. UPTAKE OF GLYCINE-N15 BY COMPONENTS OF CELL NUCLEI

    PubMed Central

    Daly, Marie M.; Allfrey, V. G.; Mirsky, A. E.

    1952-01-01

    1. The uptake of glycine-N15 by components of cell nuclei was studied. The nuclear components were derived both from tissues with high metabolic rates-mammalian liver, kidney, and pancreas-and from cells with relatively low rates of metabolism-avian erythrocytes and echinoderm sperm. N15 uptake by nuclear components of liver, kidney, and pancreas was far more rapid than by those of erythrocytes and sperm. 2. The nuclear components of liver, kidney, and pancreas for which measurements were made were DNA, histone, and residual protein of chromatin. Uptake into DNA was low, into histone higher, and into residual protein much higher still, being comparable with that into mixed cytoplasmic protein. 3. A comparison of the uptake of N15 by the chromosomal components, histone and DNA of liver, pancreas, and kidney showed that chromosomal "activity" varies in different cells and also in the same cell depending upon its over-all activity. PMID:13011275

  3. NMR in Copper-Oxide Metals

    SciTech Connect

    Varma, C.M.

    1996-10-01

    The anomalous part of the NMR relaxation rate of copper nuclei in the normal state of copper-oxide metals is calculated using the orbital magnetic parts of the fluctuations derived in a recent theory to explain the long wavelength transport anomalies. Oxygen and yttrium reside on lattice sites at which the anomalous contribution is absent at all hole densities. The frequency, momentum dependence, and the form factor of the fluctuations is predicted. {copyright} {ital 1996 The American Physical Society.}

  4. High-Precision Measurements of 15N15N, 14N15N, and 14N2 in N2 and Potential Applications to Oceanic Nitrogen Cycle Research

    NASA Astrophysics Data System (ADS)

    Li, S.; Yeung, L.; Young, E. D.; Ostrom, N. E.; Haslun, J. A.

    2016-02-01

    The balance of nitrogen fixation and nitrogen loss in the oceans is uncertain. For example, anaerobic ammonia oxidation could account for 50% or more of marine N2 production, although its global importance is still poorly known. Isotopic ratios in fixed nitrogen species (e.g., δ15N and δ18O values of NO2- and NO3-) are widely used to trace preservation and removal of N-bearing compounds and/or isotopic variations of their different sources. However, these approaches in general probe only one side of the nitrogen mass balance—the "fixed" nitrogen reservoir—so they offer few constraints on the ultimate loss of nitrogen from that pool as N2. The rare isotopologue ratio 15N15N/14N2 in N2may provide information about those nitrogen-loss processes directly. We will report the first measurements of Δ30 (the abundance of 15N15N relative to that predicted by chance alone), made on a unique high-resolution mass spectrometer (the Nu Instruments Panorama), and we will discuss the potential utility of Δ30 as an independent tracer of the nitrogen cycle. The parameter Δ30 is insensitive to the bulk 15N/14N isotopic ratio of the reservoir; instead, it reflects isotopic ordering in N2, which is altered when N-N bonds are made or broken. Our preliminary measurements of N2 from denitrifying soils and pure cultures of denitrifiers indicate large kinetic isotopic effects during N-N bond formation that favor 15N15N production during denitrification. We also observed a nonstochastic excess of 15N15N in tropospheric N2 [Δ30 = +19.05 ± 0.12‰ (1σ)]. This excess likely comes from fixed-nitrogen loss processes in the biosphere. Variations in Δ30 of N2 from pure culture experiments (+16.96 to +18.95‰) probably reflect the different isotopic signatures of the enzymes that catalyze denitrification. So, enzyme-specific Δ30 values of dissolved N2 should provide information about the importance of different biochemical pathways of fixed-nitrogen loss (e.g., denitrification vs

  5. Analyzing protein-ligand interactions by dynamic NMR spectroscopy.

    PubMed

    Mittermaier, Anthony; Meneses, Erick

    2013-01-01

    Nuclear magnetic resonance (NMR) spectroscopy can provide detailed information on protein-ligand interactions that is inaccessible using other biophysical techniques. This chapter focuses on NMR-based approaches for extracting affinity and rate constants for weakly binding transient protein complexes with lifetimes of less than about a second. Several pulse sequences and analytical techniques are discussed, including line-shape simulations, spin-echo relaxation dispersion methods (CPMG), and magnetization exchange (EXSY) experiments.

  6. Diamond Deposition and Defect Chemistry Studied via Solid State NMR

    DTIC Science & Technology

    1994-06-30

    same integrated NMR signal, regardless of its chemical environment, provided complete spin-lattice relaxation occurs between averages 3 . Gem -quality...occurs between averages, and broadening from years, a large research effort has been devoted to the study paramagnetic centers is insignificant. Gem ...information on the distribution and motion mond’s durability very attractive. However, while gem - of hydrogen can be obtained from the solid-state NMR

  7. NMR probe of metallic states in nanoscale topological insulators.

    PubMed

    Koumoulis, Dimitrios; Chasapis, Thomas C; Taylor, Robert E; Lake, Michael P; King, Danny; Jarenwattananon, Nanette N; Fiete, Gregory A; Kanatzidis, Mercouri G; Bouchard, Louis-S

    2013-01-11

    A 125Te NMR study of bismuth telluride nanoparticles as a function of particle size revealed that the spin-lattice relaxation is enhanced below 33 nm, accompanied by a transition of NMR spectra from the single to the bimodal regime. The satellite peak features a negative Knight shift and higher relaxivity, consistent with core polarization from p-band carriers. Whereas nanocrystals follow a Korringa law in the range 140-420 K, micrometer particles do so only below 200 K. The results reveal increased metallicity of these nanoscale topological insulators in the limit of higher surface-to-volume ratios.

  8. Asymmetric NMR lineshapes and precision magnetometry

    NASA Astrophysics Data System (ADS)

    Cowan, Brian

    1996-04-01

    In an inhomogeneous magnetic field of asymmetric distribution the observed NMR precession frequency of a liquid will vary with time. We show that the initial frequency corresponds to the mean of the absorption spectrum whereas the final precession frequency corresponds to the peak of the spectrum. Precision magnetometry requires knowledge of the mean so that reliable extrapolation to the zero-time value of the frequency is required. We demonstrate that, as with the narrowing of NMR lines, the effect of atomic motion is to cause the precession frequency to relax in an exponential manner. The importance of these results is discussed in the comparison of proton magnetic resonance in water and NMR in gaseous 0957-0233/7/4/028/img1 for precision magnetometry.

  9. Visualizing transient dark states by NMR spectroscopy.

    PubMed

    Anthis, Nicholas J; Clore, G Marius

    2015-02-01

    Myriad biological processes proceed through states that defy characterization by conventional atomic-resolution structural biological methods. The invisibility of these 'dark' states can arise from their transient nature, low equilibrium population, large molecular weight, and/or heterogeneity. Although they are invisible, these dark states underlie a range of processes, acting as encounter complexes between proteins and as intermediates in protein folding and aggregation. New methods have made these states accessible to high-resolution analysis by nuclear magnetic resonance (NMR) spectroscopy, as long as the dark state is in dynamic equilibrium with an NMR-visible species. These methods - paramagnetic NMR, relaxation dispersion, saturation transfer, lifetime line broadening, and hydrogen exchange - allow the exploration of otherwise invisible states in exchange with a visible species over a range of timescales, each taking advantage of some unique property of the dark state to amplify its effect on a particular NMR observable. In this review, we introduce these methods and explore two specific techniques - paramagnetic relaxation enhancement and dark state exchange saturation transfer - in greater detail.

  10. Hydrogen storage in fragmented carbon nanotubes: 1H NMR

    NASA Astrophysics Data System (ADS)

    Schmid, M.; Krämer, S.; Mehring, M.; Roth, S.; Haluska, M.; Bernier, P.

    2001-11-01

    We report 1H Nuclear Magnetic Resonance (NMR) studies on single walled carbon nanotubes, ball milled under hydrogen atmosphere. We have measured field and temperature dependence of proton spectra, linewidth and spin-lattice relaxation rates (T1-1). The results are interpreted by applying a quantitative model for 1H linewidth and spin-lattice relaxation rates induced by remanent dilute paramagnetic impurities. By using a calibration method with a reference sample we were able to quantify the hydrogen content.

  11. DIFFERENTIATION IN N15 UPTAKE AND THE ORGANIZATION OF AN ARCTIC TUNDRA PLANT COMMUNITY

    EPA Science Inventory

    We used N15 soil-labeling techniques to examine how the dominant species in a N-limited, tussock tundra plant community partitioned soil N, and how such partitioning may contribute to community organization. The five most abundant species were well differentiated with respect to...

  12. DIFFERENTIATION IN N15 UPTAKE AND THE ORGANIZATION OF AN ARCTIC TUNDRA PLANT COMMUNITY

    EPA Science Inventory

    We used N15 soil-labeling techniques to examine how the dominant species in a N-limited, tussock tundra plant community partitioned soil N, and how such partitioning may contribute to community organization. The five most abundant species were well differentiated with respect to...

  13. A Review of the Principles and Applications of the NMR Technique for Near-Surface Characterization

    NASA Astrophysics Data System (ADS)

    Behroozmand, Ahmad A.; Keating, Kristina; Auken, Esben

    2015-01-01

    This paper presents a comprehensive review of the recent advances in nuclear magnetic resonance (NMR) measurements for near-surface characterization using laboratory, borehole, and field technologies. During the last decade, NMR has become increasingly popular in near-surface geophysics due to substantial improvements in instrumentation, data processing, forward modeling, inversion, and measurement techniques. This paper starts with a description of the principal theory and applications of NMR. It presents a basic overview of near-surface NMR theory in terms of its physical background and discusses how NMR relaxation times are related to different relaxation processes occurring in porous media. As a next step, the recent and seminal near-surface NMR developments at each scale are discussed, and the limitations and challenges of the measurement are examined. To represent the growth of applications of near-surface NMR, case studies in a variety of different near-surface environments are reviewed and, as examples, two recent case studies are discussed in detail. Finally, this review demonstrates that there is a need for continued research in near-surface NMR and highlights necessary directions for future research. These recommendations include improving the signal-to-noise ratio, reducing the effective measurement dead time, and improving production rate of surface NMR (SNMR), reducing the minimum echo time of borehole NMR (BNMR) measurements, improving petrophysical NMR models of hydraulic conductivity and vadose zone parameters, and understanding the scale dependency of NMR properties.

  14. NMR of lignins

    Treesearch

    John Ralph; Larry L. Landucci

    2010-01-01

    This chapter will consider the basic aspects and findings of several forms of NMR spectroscopy, including separate discussions of proton, carbon, heteronuclear, and multidimensional NMR. Enhanced focus will be on 13C NMR, because of its qualitative and quantitative importance, followed by NMR’s contributions to our understanding of lignin...

  15. NMR analysis of biodiesel

    USDA-ARS?s Scientific Manuscript database

    Biodiesel is usually analyzed by the various methods called for in standards such as ASTM D6751 and EN 14214. Nuclear magnetic resonance (NMR) is not one of these methods. However, NMR, with 1H-NMR commonly applied, can be useful in a variety of applications related to biodiesel. These include monit...

  16. Evaluation of sandstone surface relaxivity using laser-induced breakdown spectroscopy

    NASA Astrophysics Data System (ADS)

    Washburn, Kathryn E.; Sandor, Magdalena; Cheng, Yuesheng

    2017-02-01

    Nuclear magnetic resonance (NMR) relaxometry is a common technique used to assess the pore size of fluid-filled porous materials in a wide variety of fields. However, the NMR signal itself only provides a relative distribution of pore size. To calculate an absolute pore size distribution from the NMR data, the material's surface relaxivity needs to be known. Here, a method is presented using laser-induced breakdown spectroscopy (LIBS) to evaluate surface relaxivity in sandstones. NMR transverse and longitudinal relaxation was measured on a set of sandstone samples and the surface relaxivity was calculated from the pore size distribution determined with MICP measurements. Using multivariate analysis, it was determined that the LIBS data can predict with good accuracy the longitudinal (R2 ∼ 0.84) and transverse (R2 ∼ 0.79) surface relaxivity. Analysis of the regression coefficients shows significant influence from several elements. Some of these are elements previously established to have an effect on surface relaxivity, such as iron and manganese, while others are not commonly associated with surface relaxivity, such as cobalt and titanium. Furthermore, LIBS provides advantages compared to current methods to calibrate surface relaxivity in terms of speed, portability, and sample size requirements. While this paper focuses on geological samples, the method could potentially be expanded to other types of porous materials.

  17. Evaluation of sandstone surface relaxivity using laser-induced breakdown spectroscopy.

    PubMed

    Washburn, Kathryn E; Sandor, Magdalena; Cheng, Yuesheng

    2017-02-01

    Nuclear magnetic resonance (NMR) relaxometry is a common technique used to assess the pore size of fluid-filled porous materials in a wide variety of fields. However, the NMR signal itself only provides a relative distribution of pore size. To calculate an absolute pore size distribution from the NMR data, the material's surface relaxivity needs to be known. Here, a method is presented using laser-induced breakdown spectroscopy (LIBS) to evaluate surface relaxivity in sandstones. NMR transverse and longitudinal relaxation was measured on a set of sandstone samples and the surface relaxivity was calculated from the pore size distribution determined with MICP measurements. Using multivariate analysis, it was determined that the LIBS data can predict with good accuracy the longitudinal (R(2)∼0.84) and transverse (R(2)∼0.79) surface relaxivity. Analysis of the regression coefficients shows significant influence from several elements. Some of these are elements previously established to have an effect on surface relaxivity, such as iron and manganese, while others are not commonly associated with surface relaxivity, such as cobalt and titanium. Furthermore, LIBS provides advantages compared to current methods to calibrate surface relaxivity in terms of speed, portability, and sample size requirements. While this paper focuses on geological samples, the method could potentially be expanded to other types of porous materials.

  18. HPLC & NMR-based forced degradation studies of ifosfamide: The potential of NMR in stability studies.

    PubMed

    Salman, D; Peron, J-M R; Goronga, T; Barton, S; Swinden, J; Nabhani-Gebara, S

    2016-03-01

    The aim of this study is to conduct a forced degradation study on ifosfamide under several stress conditions to investigate the robustness of the developed HPLC method. It also aims to provide further insight into the stability of ifosfamide and its degradation profile using both HPLC and NMR. Ifosfamide solutions (20mg/mL; n=15, 20mL) were stressed in triplicate by heating (70°C), under acidic (pH 1 & 4) and alkaline (pH 10 & 12) conditions. Samples were analysed periodically using HPLC and FT-NMR. Ifosfamide was most stable under weakly acidic conditions (pH 4). NMR results suggested that the mechanism of ifosfamide degradation involves the cleavage of the PN bond. For all stress conditions, HPLC was not able to detect ifosfamide degradation products that were detected by NMR. These results suggest that the developed HPLC method for ifosfamide did not detect the degradation products shown by NMR. It is possible that degradation products co-elute with ifosfamide, do not elute altogether or are not amenable to the detection method employed. Therefore, investigation of ifosfamide stability requires additional techniques that do not suffer from the aforementioned shortcomings. Copyright © 2015 Académie Nationale de Pharmacie. Published by Elsevier Masson SAS. All rights reserved.

  19. Dynamics of Antibody Domains Studied by Solution NMR

    PubMed Central

    Vu, Bang K.; Walsh, Joseph D.; Dimitrov, Dimiter S.; Ishima, Rieko

    2012-01-01

    Information on local dynamics of antibodies is important to evaluate stability, to rationally design variants, and to clarify conformational disorders at the epitope binding sites. Such information may also be useful for improved understanding of antigen recognition. NMR can be used for characterization of local protein dynamics at the atomic level through relaxation measurements. Due to the complexity of the NMR spectra, an extensive use of this method is limited to small protein molecules, for example, antibody domains and some scFv. Here, we describe a protocol that was used to study the dynamics of an antibody domain in solution using NMR. We describe protein preparation for NMR studies, NMR sample optimization, signal assignments, and dynamics experiments. PMID:19252840

  20. PARAMAGNETIC RELAXATION IN CRYSTALS.

    DTIC Science & Technology

    CRYSTALS, PARAMAGNETIC RESONANCE, RELAXATION TIME , CRYSTAL DEFECTS, QUARTZ, GLASS, STRAIN(MECHANICS), TEMPERATURE, NUCLEAR SPINS, HYDROGEN, CALCIUM COMPOUNDS, FLUORIDES, COLOR CENTERS, PHONONS, OXYGEN.

  1. Ultrafast multidimensional Laplace NMR for a rapid and sensitive chemical analysis

    NASA Astrophysics Data System (ADS)

    Ahola, Susanna; Zhivonitko, Vladimir V.; Mankinen, Otto; Zhang, Guannan; Kantola, Anu M.; Chen, Hsueh-Ying; Hilty, Christian; Koptyug, Igor V.; Telkki, Ville-Veikko

    2015-09-01

    Traditional nuclear magnetic resonance (NMR) spectroscopy relies on the versatile chemical information conveyed by spectra. To complement conventional NMR, Laplace NMR explores diffusion and relaxation phenomena to reveal details on molecular motions. Under a broad concept of ultrafast multidimensional Laplace NMR, here we introduce an ultrafast diffusion-relaxation correlation experiment enhancing the resolution and information content of corresponding 1D experiments as well as reducing the experiment time by one to two orders of magnitude or more as compared with its conventional 2D counterpart. We demonstrate that the method allows one to distinguish identical molecules in different physical environments and provides chemical resolution missing in NMR spectra. Although the sensitivity of the new method is reduced due to spatial encoding, the single-scan approach enables one to use hyperpolarized substances to boost the sensitivity by several orders of magnitude, significantly enhancing the overall sensitivity of multidimensional Laplace NMR.

  2. Using an NMR Spectrometer to Do Magnetic Resonance Imaging: An Undergraduate Physical Chemistry Laboratory Experiment

    ERIC Educational Resources Information Center

    Steinmetz, Wayne E.; Maher, M. Cyrus

    2007-01-01

    A conventional Fourier-transform NMR spectrometer with a triple-axis gradient probe can function as a MRI imager. In this experiment students gain hands-on experience with MRI while they learn about important principles underlying the practice of NMR, such as gradients, multi-dimensional spectroscopy, and relaxation. Students image a biological…

  3. Using an NMR Spectrometer to Do Magnetic Resonance Imaging: An Undergraduate Physical Chemistry Laboratory Experiment

    ERIC Educational Resources Information Center

    Steinmetz, Wayne E.; Maher, M. Cyrus

    2007-01-01

    A conventional Fourier-transform NMR spectrometer with a triple-axis gradient probe can function as a MRI imager. In this experiment students gain hands-on experience with MRI while they learn about important principles underlying the practice of NMR, such as gradients, multi-dimensional spectroscopy, and relaxation. Students image a biological…

  4. Vortex dynamics in Rb3C60 observed by 87Rb and 13C NMR

    NASA Astrophysics Data System (ADS)

    Zimmer, G.; Mehring, M.; Rachdi, F.; Fischer, J. E.

    1996-08-01

    The vortex dynamics in Rb3C60 is investigated by 87Rb and 13C NMR. It is shown that spin-spin relaxation as well as two-dimensional exchange experiments allow an estimation of the time scale of vortex fluctuations. The effective pinning potential is deduced from the temperature dependence of the NMR parameters.

  5. NMR methodologies in the analysis of blueberries.

    PubMed

    Capitani, Donatella; Sobolev, Anatoly P; Delfini, Maurizio; Vista, Silvia; Antiochia, Riccarda; Proietti, Noemi; Bubici, Salvatore; Ferrante, Gianni; Carradori, Simone; De Salvador, Flavio Roberto; Mannina, Luisa

    2014-06-01

    An NMR analytical protocol based on complementary high and low field measurements is proposed for blueberry characterization. Untargeted NMR metabolite profiling of blueberries aqueous and organic extracts as well as targeted NMR analysis focused on anthocyanins and other phenols are reported. Bligh-Dyer and microwave-assisted extractions were carried out and compared showing a better recovery of lipidic fraction in the case of microwave procedure. Water-soluble metabolites belonging to different classes such as sugars, amino acids, organic acids, and phenolic compounds, as well as metabolites soluble in organic solvent such as triglycerides, sterols, and fatty acids, were identified. Five anthocyanins (malvidin-3-glucoside, malvidin-3-galactoside, delphinidin-3-glucoside, delphinidin-3-galactoside, and petunidin-3-glucoside) and 3-O-α-l-rhamnopyranosyl quercetin were identified in solid phase extract. The water status of fresh and withered blueberries was monitored by portable NMR and fast-field cycling NMR. (1) H depth profiles, T2 transverse relaxation times and dispersion profiles were found to be sensitive to the withering.

  6. Radiation damping in microcoil NMR probes

    NASA Astrophysics Data System (ADS)

    Krishnan, V. V.

    2006-04-01

    Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-μL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.

  7. Radiation damping in microcoil NMR probes.

    PubMed

    Krishnan, V V

    2006-04-01

    Radiation damping arises from the field induced in the receiver coil by large bulk magnetization and tends to selectively drive this magnetization back to equilibrium much faster than relaxation processes. The demand for increased sensitivity in mass-limited samples has led to the development of microcoil NMR probes that are capable of obtaining high quality NMR spectra with small sample volumes (nL-microL). Microcoil probes are optimized to increase sensitivity by increasing either the sample-to-coil ratio (filling factor) of the probe or quality factor of the detection coil. Though radiation damping effects have been studied in standard NMR probes, these effects have not been measured in the microcoil probes. Here a systematic evaluation of radiation damping effects in a microcoil NMR probe is presented and the results are compared with similar measurements in conventional large volume samples. These results show that radiation-damping effects in microcoil probe is much more pronounced than in 5 mm probes, and that it is critically important to optimize NMR experiments to minimize these effects. As microcoil probes provide better control of the bulk magnetization, with good RF and B0 inhomogeneity, in addition to negligible dipolar field effects due to nearly spherical sample volumes, these probes can be used exclusively to study the complex behavior of radiation damping.

  8. Stellar Origins of C-13 and N-15-Enriched Presolar SiC Grains

    NASA Technical Reports Server (NTRS)

    Liu, Nan; Nittler, Larry R.; Alexander, Conel M. O’D.; Wang, Jianhua; Pignatari, Marco; Jose, Jordi; Nguyen, Ann

    2016-01-01

    Extreme excesses of 13 C ( C (12 C/ 13 C<10) and 15 N ( N (14 N/ 15 N< 20) in rare presolar SiC 20) in rare presolar SiClar SiC grains have been considered diagnostic of an origin in classical novae [1], though an origin in core-collapse supernovae (CCSNe) has also been proposed [2]. We report multi-element isotopic data for 19 13 C- and 15 N-enriched presolar SiC grains(12 C/13 C<16 and 14 N/ 15 N<150) from an acid resistant residue of the Murchison meteorite. These grains are enriched in 13 C and15 N, but with quite diverse Si isotopic signatures. Four grains with isotopic signatures. Four grains with isotopic signatures. Four grains with isotopic signatures. Four grains with isotopic signatures.

  9. Asymmetric Induction by a Nitrogen 14N/15N Isotopomer in Conjunction with Asymmetric Autocatalysis

    PubMed Central

    Ozaki, Hanae; Harada, Shunya; Tada, Kyohei; Ayugase, Tomohiro; Ozawa, Hitomi; Kawasaki, Tsuneomi

    2016-01-01

    Abstract Chirality arising from isotope substitution, especially with atoms heavier than the hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An N 2 ,N 2 ,N 3 ,N 3‐tetramethyl‐2,3‐butanediamine containing nitrogen (14N/15N) isotope chirality was synthesized and it was revealed that this isotopically chiral diamine compound acts as a chiral initiator for asymmetric autocatalysis. PMID:27754589

  10. Asymmetric Induction by a Nitrogen (14) N/(15) N Isotopomer in Conjunction with Asymmetric Autocatalysis.

    PubMed

    Matsumoto, Arimasa; Ozaki, Hanae; Harada, Shunya; Tada, Kyohei; Ayugase, Tomohiro; Ozawa, Hitomi; Kawasaki, Tsuneomi; Soai, Kenso

    2016-12-05

    Chirality arising from isotope substitution, especially with atoms heavier than the hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An N(2) ,N(2) ,N(3) ,N(3) -tetramethyl-2,3-butanediamine containing nitrogen ((14) N/(15) N) isotope chirality was synthesized and it was revealed that this isotopically chiral diamine compound acts as a chiral initiator for asymmetric autocatalysis.

  11. On the performance of Spin Diffusion NMR Techniques in Oriented Solids: Prospects for Resonance Assignments and Distance Measurements from Separated Local Field Experiments

    PubMed Central

    Traaseth, Nathaniel J.; Gopinath, T.; Veglia, Gianluigi

    2010-01-01

    NMR spin diffusion experiments have the potential to provide both resonance assignment and internuclear distances for protein structure determination in oriented solid-state NMR. In this paper, we compared the efficiencies of three common spin diffusion experiments: proton-driven spin diffusion (PDSD), cross-relaxation driven spin diffusion (CRDSD), and proton-mediated proton transfer (PMPT). As model systems for oriented proteins, we used single crystals of N-acetyl-L-15N-leucine (NAL) and N-acetyl-L-15N-valyl-L-15N-leucine (NAVL) to probe long- and short distances, respectively. We demonstrate that for short 15N/15N distances such as those found in NAVL (3.3 Å), the PDSD mechanism gives the most intense cross-peaks, while for longer distances (> 6.5 Å), the CRDSD and PMPT experiments are more efficient. The PDSD was highly inefficient for transferring magnetization across distances greater than 6.5 Å (NAL crystal sample), due to small 15N/15N dipolar couplings (< 4.5 Hz). Interestingly, the mismatched Hartmann-Hahn condition present in the PMPT experiment gave more intense cross-peaks for lower 1H and 15N spinlock field strengths (32 and 17 kHz, respectively) rather than higher values (55 and 50 kHz), suggesting a more complex magnetization transfer mechanism. Numerical simulations are in good agreement with the experimental findings, suggesting a combined PMPT and CRDSD effect. We conclude that in order to assign SLF spectra and measure short and long-range distances, the combined use of homonuclear correlation spectra, such as the ones surveyed in this work, are necessary. PMID:20936833

  12. On the performance of spin diffusion NMR techniques in oriented solids: prospects for resonance assignments and distance measurements from separated local field experiments.

    PubMed

    Traaseth, Nathaniel J; Gopinath, T; Veglia, Gianluigi

    2010-11-04

    NMR spin diffusion experiments have the potential to provide both resonance assignment and internuclear distances for protein structure determination in oriented solid-state NMR. In this paper, we compared the efficiencies of three spin diffusion experiments: proton-driven spin diffusion (PDSD), cross-relaxation-driven spin diffusion (CRDSD), and proton-mediated proton transfer (PMPT). As model systems for oriented proteins, we used single crystals of N-acetyl-L-(15)N-leucine (NAL) and N-acetyl-L-(15)N-valyl-L-(15)N-leucine (NAVL) to probe long and short distances, respectively. We demonstrate that, for short (15)N/(15)N distances such as those found in NAVL (3.3 Å), the PDSD mechanism gives the most intense cross-peaks, while, for longer distances (>6.5 Å), the CRDSD and PMPT experiments are more efficient. The PDSD was highly inefficient for transferring magnetization across distances greater than 6.5 Å (NAL crystal sample), due to small (15)N/(15)N dipolar couplings (<4.5 Hz). Interestingly, the mismatched Hartmann-Hahn condition present in the PMPT experiment gave more intense cross-peaks for lower (1)H and (15)N RF spinlock amplitudes (32 and 17 kHz, respectively) rather than higher values (55 and 50 kHz), suggesting a more complex magnetization transfer mechanism. Numerical simulations are in good agreement with the experimental findings, suggesting a combined PMPT and CRDSD effect. We conclude that, in order to assign SLF spectra and measure short- and long-range distances, the combined use of homonuclear correlation spectra, such as the ones surveyed in this work, are necessary.

  13. TEACHING NEUROMUSCULAR RELAXATION.

    ERIC Educational Resources Information Center

    NORRIS, JEANNE E.; STEINHAUS, ARTHUR H.

    THIS STUDY ATTEMPTED TO FIND OUT WHETHER (1) THE METHODS FOR ATTAINING NEUROMUSCULAR RELAXATION THAT HAVE PROVED FRUITFUL IN THE ONE-TO-ONE RELATIONSHIP OF THE CLINIC CAN BE SUCCESSFULLY ADAPTED TO THE TEACHER-CLASS RELATIONSHIP OF THE CLASSROOM AND GYMNASIUM, AND (2) NEUROMUSCULAR RELAXATION CAN BE TAUGHT SUCCESSFULLY BY AN APPROPRIATELY TRAINED…

  14. ECG gated NMR-CT for cardiovascular diseases

    SciTech Connect

    Nishikawa, J.; Ohtake, T.; Machida, K.; Iio, M.; Yoshimoto, N.; Sugimoto, T.

    1985-05-01

    The authors have been applying ECG gated NMR-CT to mainly patients with myocardial infarction (MI), and hypertrophic cardiomyopathy (HCM). Thirteen patients with MI, 8 with HCM and 5 without any heart diseases were studied by ECG gated NMR imaging (spin-echo technique, TR: depends on patient heart rate, TE: 35 and 70 msec.) with 0.35 T superconducting magnet. On NMR images (MRI), the authors examined the wall thickness, wall motion and T/sub 2/ relaxation time in the area of diseased myocardium. The lesions of old MI were depicted as the area of thin wall and T/sub 2/ relaxation time of those lesions were similar to the area of non-infarcted myocardium. The lesions of recent MI (up to 3.5 months from the recent attack) were shown as the same wall thickness as the non-infarcted myocardium and the area of prolonged T/sub 2/ relaxation time compared with that of non-infarcted myocardium. MRI demonstrated diffusely thick myocardium in all patients with HCM. T/sub 2/ relaxation time of the areas of HCM was almost the same as that of normal myocardium, and it's difference among each ventricular wall in patients with HCM was not statistically significant. The authors conclude that ECG gated NMR-CT offers 3-D morphological information of the heart without any contrast material nor radioisotopes. ECG gated MRI provides the useful informations to diagnose MI, especially in the differential diagnosis between old and recent MI.

  15. Transverse Spin Relaxation in Liquid X

    SciTech Connect

    Romalis, M. V.; Ledbetter, M. P.

    2001-08-06

    Using spin-echo NMR techniques we study the transverse spin relaxation of hyperpolarized liquid X{sup 129}e in a spherical cell. We observe an instability of the transverse magnetization due to dipolar fields produced by liquid X{sup 129}e , and find that imperfections in the {pi} pulses of the spin-echo sequence suppress this instability. A simple perturbative model of this effect is in good agreement with the data. We obtain a transverse spin relaxation time of 1300sec in liquid X{sup 129}e , and discuss applications of hyperpolarized liquid X{sup 129}e as a sensitive magnetic gradiometer and for a permanent electric dipole moment search.

  16. Relaxation of magnetotail plasmas

    NASA Technical Reports Server (NTRS)

    Bhattacharjee, A.

    1987-01-01

    A quasi-thermodynamic model is presented for the relaxation of magnetotail plasmas during substorms, followed by quiet times. It is proposed that the plasma relaxes to a state of low-potential energy subject to a small number of global constraints. The constraints are exactly preserved by all ideal motions and, approximately, by a wide class of motions of the plasma undergoing magnetic reconnection. A variational principle which minimizes the free energy predicts the relaxed state. Exact, two-dimensional solutions of the relaxed state are obtained. A universal feature of the exact solutions is a chain of magnetic islands along the tail axis. Sufficient conditions for the stability of relaxed states are obtained from the second variation of the free-energy functional.

  17. Diabetes and diastolic function: stiffness and relaxation from transmitral flow.

    PubMed

    Riordan, Matt M; Chung, Charles S; Kovács, Sándor J

    2005-12-01

    To characterize the mechanism by which diabetes affects the heart in diabetic (n = 15) and age-matched control subjects (n = 15), we quantified and compared diastolic function (DF) in terms of chamber stiffness and viscosity/relaxation by analyzing Doppler E- and E'-waves and simultaneous (high-fidelity) hemodynamic data. We compared tau, standard Doppler indexes and indexes of stiffness and viscosity/relaxation computed via the parameterized diastolic filling (PDF) formalism. Three PDF parameters uniquely characterize each E-wave in terms of load (x(o)), viscoelasticity or viscosity/relaxation (c) and stiffness (k). Significant differences for c (p = 0.00004), the peak atrioventricular pressure gradient (kx(o)) (p = 0.02) and the stored elastic energy available for early filling (1/2kx(o)2) (p = 0.04) were found. The only conventional index attaining significance was E-wave acceleration time (p = 0.007). Neither time constant of isovolumic relaxation (tau) nor E-wave deceleration time, E', k or x(o) differentiated between groups. We conclude that PDF based DF assessment differentiates between diabetic and nondiabetic controls better than conventional echo- or cath-based indexes. Our results in humans agree with published results from animal studies. We conclude that diabetes affects the heart via a quantifiable increase in chamber viscoelasticity (c) rather than an increase in chamber stiffness (k) and that phenotypic characterization of diabetic cardiomyopathy is facilitated by DF assessment via the PDF formalism.

  18. T2-Filtered T2 - T2 Exchange NMR

    NASA Astrophysics Data System (ADS)

    d'Eurydice, Marcel Nogueira; Montrazi, Elton Tadeu; Fortulan, Carlos Alberto; Bonagamba, Tito José

    2016-05-01

    This work introduces an alternative way to perform the T2 - T2 Exchange NMR experiment. Rather than varying the number of π pulses in the first CPMG cycle of the T2 - T2 Exchange NMR pulse sequence, as used to obtain the 2D correlation maps, it is fixed and small enough to act as a short T2-filter. By varying the storage time, a set of 1D measurements of T2 distributions can be obtained to reveal the effects of the migration dynamics combined with relaxation effects. This significantly reduces the required time to perform the experiment, allowing a more in-depth study of exchange dynamics and relaxation processes with improved signal-to-noise ratio. These aspects stand as basis of this novel experiment, T2-Filtered T2 - T2 Exchange NMR or simply T2 F-TREx.

  19. NMR studies of protein structure and dynamics

    NASA Astrophysics Data System (ADS)

    Kay, Lewis E.

    2011-12-01

    Recent advances in solution NMR spectroscopy have significantly extended the spectrum of problems that can now be addressed with this technology. In particular, studies of proteins with molecular weights on the order of 100 kDa are now possible at a level of detail that was previously reserved for much smaller systems. An example of the sort of information that is now accessible is provided in a study of malate synthase G, a 723 residue enzyme that has been a focal point of research efforts in my laboratory. Details of the labeling schemes that have been employed and optimal experiments for extraction of structural and dynamics information on this protein are described. NMR studies of protein dynamics, in principle, give insight into the relation between motion and function. A description of deuterium-based spin relaxation methods for the investigation of side chain dynamics is provided. Examples where millisecond (ms) time scale dynamics play an important role and where relaxation dispersion NMR spectroscopy has been particularly informative, including applications involving the membrane enzyme PagP and mutants of the Fyn SH3 domain that fold on a ms time scale, are presented.

  20. NMR CHARACTERIZATIONS OF PROPERTIES OF HETEROGENEOUS MEDIA

    SciTech Connect

    C.T. Philip Chang; Changho Choi; Jeromy T. Hollenshead; Rudi Michalak; Jack Phan; Ramon Saavedra; John C. Slattery; Jinsoo Uh; Randi Valestrand; A. Ted Watson; Song Xue

    2005-01-01

    A critical and long-standing need within the petroleum industry is the specification of suitable petrophysical properties for mathematical simulation of fluid flow in petroleum reservoirs (i.e., reservoir characterization). The development of accurate reservoir characterizations is extremely challenging. Property variations may be described on many scales, and the information available from measurements reflect different scales. In fact, experiments on laboratory core samples, well-log data, well-test data, and reservoir-production data all represent information potentially valuable to reservoir characterization, yet they all reflect information about spatial variations of properties at different scales. Nuclear magnetic resonance (NMR) spectroscopy and imaging (MRI) provide enormous potential for developing new descriptions and understandings of heterogeneous media. NMR has the rare capability to probe permeable media non-invasively, with spatial resolution, and it provides unique information about molecular motions and interactions that are sensitive to morphology. NMR well-logging provides the best opportunity ever to resolve permeability distributions within petroleum reservoirs. We develop MRI methods to determine, for the first time, spatially resolved distributions of porosity and permeability within permeable media samples that approach the intrinsic scale: the finest resolution of these macroscopic properties possible. To our knowledge, this is the first time that the permeability is actually resolved at a scale smaller than the sample. In order to do this, we have developed a robust method to determine of relaxation distributions from NMR experiments and a novel implementation and analysis of MRI experiments to determine the amount of fluid corresponding to imaging regions, which are in turn used to determine porosity and saturation distributions. We have developed a novel MRI experiment to determine velocity distributions within flowing experiments, and

  1. Mg NMR in DNA solutions: Dominance of site binding effects.

    PubMed

    Rose, D M; Bleam, M L; Record, M T; Bryant, R G

    1980-11-01

    (25)Mg NMR spectroscopy is applied to a study of magnesium ion interactions with DNA, which is considered as a model for a linear polyelectrolyte. It is demonstrated that the magnesium ion spectrum is complicated by a non-Lorent-zian line shape and is dominated by the effects of chemical exchange with macromolecule binding sites. A distinction is made between specific-site interactions in which the magnesium ion loses a water molecule from the first coordination sphere on binding and those interactions, referred to as territorial binding, in which the ion maintains its first coordination sphere complement of solvent. The first type of site-binding interactions are shown to dominate the magnesium ion NMR spectrum, based on a consideration of the magnitudes of the observed (25)Mg relaxation rates compared with (23)Na relaxation rates, the clear contributions of chemical exchange-limited relaxation, and an ion displacement experiment employing sodium.

  2. Study of correlations in molecular motion by multiple quantum NMR

    SciTech Connect

    Tang, J.H.

    1981-11-01

    Nuclear magnetic resonance is a very useful tool for characterizing molecular configurations through the measurement of transition frequencies and dipolar couplings. The measurement of spectral lineshapes, spin-lattice relaxation times, and transverse relaxation times also provide us with valuable information about correlations in molecular motion. The new technique of multiple quantum nuclear magnetic resonance has numerous advantages over the conventional single quantum NMR techniques in obtaining information about static and dynamic interactions of coupled spin systems. In the first two chapters, the theoretical background of spin Hamiltonians and the density matrix formalism of multiple quantum NMR is discussed. The creation and detection of multiple quantum coherence by multiple pulse sequence are discussed. Prototype multiple quantum spectra of oriented benzene are presented. Redfield relaxation theory and the application of multiple quantum NMR to the study of correlations in fluctuations are presented. A specific example of an oriented methyl group relaxed by paramagnetic impurities is studied in detail. The study of possible correlated motion between two coupled methyl groups by multiple quantum NMR is presented. For a six spin system it is shown that the four-quantum spectrum is sensitive to two-body correlations, and serves a ready test of correlated motion. The study of the spin-lattice dynamics of orienting or tunneling methyl groups (CH/sub 3/ and CD/sub 3/) at low temperatures is presented. The anisotropic spin-lattice relaxation of deuterated hexamethylbenzene, caused by the sixfold reorientation of the molecules, is investigated, and the NMR spectrometers and other experimental details are discussed.

  3. Whole-core analysis by sup 13 C NMR

    SciTech Connect

    Vinegar, H.J.; Tutunjian, P.N. ); Edelstein, W.A.; Roemer, P.B. )

    1991-06-01

    This paper reports on a whole-core nuclear magnetic resonance (NMR) system that was used to obtain natural abundance {sup 13}C spectra. The system enables rapid, nondestructive measurements of bulk volume of movable oil, aliphatic/aromatic ratio, oil viscosity, and organic vs. carbonate carbon. {sup 13}C NMR can be used in cores where the {sup 1}H NMR spectrum is too broad to resolve oil and water resonances separately. A 5 1/4-in. {sup 13}C/{sup 1}H NMR coil was installed on a General Electric (GE) CSI-2T NMR imager/spectrometer. With a 4-in.-OD whole core, good {sup 13}C signal/noise ratio (SNR) is obtained within minutes, while {sup 1}H spectra are obtained in seconds. NMR measurements have been made of the {sup 13}C and {sup 1}H density of crude oils with a wide range of API gravities. For light- and medium-gravity oils, the {sup 13}C and {sup 1}H signal per unit volume is constant within about 3.5%. For heavy crudes, the {sup 13}C and {sup 1}H density measured by NMR is reduced by the shortening of spin-spin relaxation time. {sup 13}C and {sup 1}H NMR spin-lattice relaxation times were measured on a suite of Cannon viscosity standards, crude oils (4 to 60{degrees} API), and alkanes (C{sub 5} through C{sub 16}) with viscosities at 77{degrees}F ranging from 0.5 cp to 2.5 {times} 10{sup 7} cp. The {sup 13}C and {sup 1}H relaxation times show a similar correlation with viscosity from which oil viscosity can be estimated accurately for viscosities up to 100 cp. The {sup 13}C surface relaxation rate for oils on water-wet rocks is very low. Nonproton decoupled {sup 13}C NMR is shown to be insensitive to kerogen; thus, {sup 13}C NMR measures only the movable hydrocarbon content of the cores. In carbonates, the {sup 13}C spectrum also contains a carbonate powder pattern useful in quantifying inorganic carbon and distinguishing organic from carbonate carbon.

  4. SARA: a software environment for the analysis of relaxation data acquired with accordion spectroscopy

    PubMed Central

    Harden, Bradley J.

    2014-01-01

    We present SARA (Software for Accordion Relaxation Analysis), an interactive and user-friendly MATLAB software environment designed for analyzing relaxation data obtained with accordion spectroscopy. Accordion spectroscopy can be used to measure nuclear magnetic resonance (NMR) relaxation rates in a fraction of the time required by traditional methods, yet data analysis can be intimidating and no unified software packages are available to assist investigators. Hence, the technique has not achieved widespread use within the NMR community. SARA offers users a selection of analysis protocols spanning those presented in the literature thus far, with modifications permitting a more general application to crowded spectra such as those of proteins. We discuss the advantages and limitations of each fitting method and suggest a protocol combining the strengths of each procedure to achieve optimal results. In the end, SARA provides an environment for facile extraction of relaxation rates and should promote routine application of accordion relaxation spectroscopy. PMID:24408364

  5. SARA: a software environment for the analysis of relaxation data acquired with accordion spectroscopy.

    PubMed

    Harden, Bradley J; Frueh, Dominique P

    2014-02-01

    We present SARA (Software for Accordion Relaxation Analysis), an interactive and user-friendly MATLAB software environment designed for analyzing relaxation data obtained with accordion spectroscopy. Accordion spectroscopy can be used to measure nuclear magnetic resonance (NMR) relaxation rates in a fraction of the time required by traditional methods, yet data analysis can be intimidating and no unified software packages are available to assist investigators. Hence, the technique has not achieved widespread use within the NMR community. SARA offers users a selection of analysis protocols spanning those presented in the literature thus far, with modifications permitting a more general application to crowded spectra such as those of proteins. We discuss the advantages and limitations of each fitting method and suggest a protocol combining the strengths of each procedure to achieve optimal results. In the end, SARA provides an environment for facile extraction of relaxation rates and should promote routine application of accordion relaxation spectroscopy.

  6. An introduction to NMR-based approaches for measuring protein dynamics

    PubMed Central

    Kleckner, Ian R; Foster, Mark P

    2010-01-01

    Proteins are inherently flexible at ambient temperature. At equilibrium, they are characterized by a set of conformations that undergo continuous exchange within a hierarchy of spatial and temporal scales ranging from nanometers to micrometers and femtoseconds to hours. Dynamic properties of proteins are essential for describing the structural bases of their biological functions including catalysis, binding, regulation and cellular structure. Nuclear magnetic resonance (NMR) spectroscopy represents a powerful technique for measuring these essential features of proteins. Here we provide an introduction to NMR-based approaches for studying protein dynamics, highlighting eight distinct methods with recent examples, contextualized within a common experimental and analytical framework. The selected methods are (1) Real-time NMR, (2) Exchange spectroscopy, (3) Lineshape analysis, (4) CPMG relaxation dispersion, (5) Rotating frame relaxation dispersion, (6) Nuclear spin relaxation, (7) Residual dipolar coupling, (8) Paramagnetic relaxation enhancement. PMID:21059410

  7. Metabolism of Nonessential N15-Labeled Amino Acids and the Measurement of Human Whole-Body Protein Synthesis Rates

    NASA Technical Reports Server (NTRS)

    Stein, T. P.; Settle, R. G.; Albina, J. A.; Dempsey, D. T.; Melnick, G.

    1991-01-01

    Eight N-15 labeled nonessential amino acids plus (15)NH4Cl were administered over a 10 h period to four healthy adult males using a primed-constant dosage regimen. The amount of N-15 excreted in the urine and the urinary ammonia, hippuric acid, and plasma alanine N-15 enrichments were measured. There was a high degree of consistency across subjects in the ordering of the nine compounds based on the fraction of N-15 excreted (Kendall coefficient of concordance W = 0.83, P is less than 0.01). Protein synthesis rates were calculated from the urinary ammonia plateau enrichment and the cumulative excretion of N-15. Glycine was one of the few amino acids that gave similar values by both methods.

  8. Relaxation Techniques for Health

    MedlinePlus

    ... for posttraumatic stress disorder have had inconsistent results. Rheumatoid Arthritis There’s limited evidence that biofeedback or other relaxation ... might be valuable additions to treatment programs for rheumatoid arthritis. Ringing in the Ears (Tinnitus) Only a few ...

  9. Relaxation techniques for stress

    MedlinePlus

    ... problems such as high blood pressure, stomachaches, headaches, anxiety, and depression. Using relaxation techniques can help you feel calm. These exercises can also help you manage stress and ease ...

  10. Rapid measurement of multidimensional 1H solid-state NMR spectra at ultra-fast MAS frequencies

    NASA Astrophysics Data System (ADS)

    Ye, Yue Qi; Malon, Michal; Martineau, Charlotte; Taulelle, Francis; Nishiyama, Yusuke

    2014-02-01

    A novel method to realize rapid repetition of 1H NMR experiments at ultra-fast MAS frequencies is demonstrated. The ultra-fast MAS at 110 kHz slows the 1H-1H spin diffusion, leading to variations of 1H T1 relaxation times from atom to atom within a molecule. The different relaxation behavior is averaged by applying 1H-1H recoupling during relaxation delay even at ultra-fast MAS, reducing the optimal relaxation delay to maximize the signal to noise ratio. The way to determine optimal relaxation delay for arbitrary relaxation curve is shown. The reduction of optimal relaxation delay by radio-frequency driven recoupling (RFDR) was demonstrated on powder samples of glycine and ethenzamide with one and multi-dimensional NMR measurements.

  11. Extended function of plasmid partition genes: the Sop system of linear phage-plasmid N15 facilitates late gene expression.

    PubMed

    Ravin, Nikolai V; Rech, Jérôme; Lane, David

    2008-05-01

    The mitotic stability of the linear plasmid-prophage N15 of Escherichia coli depends on a partition system closely related to that of the F plasmid SopABC. The two Sop systems are distinguished mainly by the arrangement of their centromeric SopB-binding sites, clustered in F (sopC) and dispersed in N15 (IR1 to IR4). Because two of the N15 inverted repeat (IR) sites are located close to elements presumed (by analogy with phage lambda) to regulate late gene expression during the lytic growth of N15, we asked whether Sop partition functions play a role in this process. In N15, a putative Q antiterminator gene is located 6 kb upstream of the probable major late promoter and two intrinsic terminator-like sequences, in contrast to lambda, where the Q gene is adjacent to the late promoter. Northern hybridization and lacZ reporter activity confirmed the identity of the N15 late promoter (p52), demonstrated antiterminator activity of the Q analogue, and located terminator sequences between p52 and the first open reading frame. Following prophage induction, N15 mutated in IR2 (downstream from gene Q) or IR3 (upstream of p52) showed a pronounced delay in lysis relative to that for wild-type N15. Expression of ir3(-)-p52::lacZ during N15 wild-type lytic growth was strongly reduced relative to the equivalent ir3(+) fusion. The provision of Q protein and the IR2 and SopAB proteins in trans to ir3(+)-p52::lacZ increased expression beyond that seen in the absence of any one of these factors. These results indicate that the N15 Sop system has a dual role: partition and regulation of late gene transcription during lytic growth.

  12. Protein Motions and Folding Investigated by NMR Spectroscopy

    NASA Astrophysics Data System (ADS)

    Palmer, Arthur

    2002-03-01

    NMR spin relaxation spectroscopy is a powerful experimental approach for globally characterizing conformational dynamics of proteins in solution. Laboratory frame relaxation measurements are sensitive to overall rotational diffusion and internal motions on picosecond-nanosecond time scales, while rotating frame relaxation measurements are sensitive to chemical exchange processes on microsecond-millisecond time scales. The former approach is illustrated by ^15N laboratory-frame relaxation experiments as a function of temperature for the helical subdomain HP36 of the F-actin-binding headpiece domain of chicken villin. The data are analyzed using the model-free formalism to characterize order parameters and effective correlation times for intramolecular motions of individual ^15N sites. The latter approach is illustrated by ^13C Carr-Purcell-Meiboom-Gill relaxation measurements for the de novo designed α_2D protein and by ^15N rotating-frame relaxation measurements for the peripheral subunit-binding domain (PSBD) from the dihydrolopoamide acetyltransferase component of the pyruvate dehydrogenase multienzyme complex from Bacillus stearothermophilus. These experiments are used to determine the folding and unfolding kinetic rate constants for the two proteins. The results for HP36, α_2D, and PSBD illustrate the capability of current NMR methods for characterizing dynamic processes on multiple time scales in proteins.

  13. Lectures on pulsed NMR

    SciTech Connect

    Pines, A.

    1988-08-01

    These lectures discuss some recent developments in pulsed NMR, emphasizing fundamental principles with selected illustrative applications. Major topics covered include multiple-quantum spectroscopy, spin decoupling, the interaction of spins with a quantized field, adiabatic rapid passage, spin temperature and statistics of cross-polarization, coherent averaging, and zero field NMR. 32 refs., 56 figs.

  14. Lectures on pulsed NMR

    SciTech Connect

    Pines, A.

    1986-09-01

    These lectures discuss some recent developments in pulsed NMR, emphasizing fundamental principles with selected illustrative applications. Major topics covered include multiple-quantum spectroscopy, spin decoupling, the interaction of spins with a quantized field, adiabatic rapid passage, spin temperature and statistics of cross-polarization, coherent averaging, and zero field NMR. 55 figs.

  15. Some nitrogen-14 NMR studies in solids

    SciTech Connect

    Pratum, T.K.

    1983-11-01

    The first order quadrupolar perturbation of the /sup 14/N NMR spectrum yields information regarding the static and dynamic properties of the surrounding electronic environment. Signal to noise problems caused by long /sup 14/N longitudinal relaxation times (T/sub 1/) and small equilibrium polarizations are reduced by rotating frame cross polarization (CP) experiments between /sup 14/N and /sup 1/H. Using quadrupolar echo and CP techniques, the /sup 14/N quadrupolar coupling constants (e/sup 2/qQ/h) and asymmetry parameters (eta) have been obtained for a variety of tetraalkylammonium compounds by observation of their quadrupolar powder patterns at various temperatures. For choline chloride and iodide the /sup 14/N NMR powder patterns exhibit the effects of anisotropic molecular motion, while choline bromide spectra show no such effects.

  16. NMR logging apparatus

    SciTech Connect

    Walsh, David O; Turner, Peter

    2014-05-27

    Technologies including NMR logging apparatus and methods are disclosed. Example NMR logging apparatus may include surface instrumentation and one or more downhole probes configured to fit within an earth borehole. The surface instrumentation may comprise a power amplifier, which may be coupled to the downhole probes via one or more transmission lines, and a controller configured to cause the power amplifier to generate a NMR activating pulse or sequence of pulses. Impedance matching means may be configured to match an output impedance of the power amplifier through a transmission line to a load impedance of a downhole probe. Methods may include deploying the various elements of disclosed NMR logging apparatus and using the apparatus to perform NMR measurements.

  17. Method of three-dimensional NMR imaging using selective excitation

    SciTech Connect

    Edelstein, W.A.; Bottomley, P.A.

    1984-02-14

    Selective excitation is used to define a thick planar slab of excited nuclear spins in a nuclear magnetic resonance (NMR) imaging sample. The thick slab is selected such that the excited spins are contained well within the optimum sensitive region defined by the radio frequency (RF) transmitter and receiver coils. Three-dimensional spatial information of an NMR imaging parameter, such as nuclear spin density or nuclear spin relaxation time, is collected simultaneously from the excited slab and can be used to construct a series of several tomographic section images of the slab. The spatial information is encoded in the NMR signal by application of pulsed gradient magnetic fields subsequent to excitation. Image picture information is obtained from the NMR signals via three-dimensional Fourier transformation.

  18. UC Merced NMR Instrumentation Acquisition

    DTIC Science & Technology

    2015-06-18

    UC Merced NMR Instrumentation Acquisition For the UC Merced NMR Instrumentation Acquisition proposal, a new 400 MHz and an upgraded 500 MHz NMR ...UC Merced NMR Instrumentation Acquisition Report Title For the UC Merced NMR Instrumentation Acquisition proposal, a new 400 MHz and an upgraded 500...MHz NMR have been delivered, installed, and incorporated into research and two lab courses. While no results from these instruments have been

  19. Understanding NMR T2 spectral uncertainty

    NASA Astrophysics Data System (ADS)

    Prange, Michael; Song, Yi-Qiao

    2010-05-01

    NMR relaxation and diffusion data analysis commonly uses a wide range of methods from simple exponential fitting to Laplace inversions. The pros and cons of these methods are often the subject of intense debate. We show that the ill-conditioned nature of such analysis gives rise to a range of solutions for every method resulting in uncertainty in the spectral solution. Such uncertainty is in fact characteristic of the inversion method. We show a simple method of sparse spectral representation can be used to improve the statistics of multiple-exponential-based inversion schemes.

  20. 3D 15N/15N/1H chemical shift correlation experiment utilizing an RFDR-based 1H/1H mixing period at 100 kHz MAS

    NASA Astrophysics Data System (ADS)

    Nishiyama, Yusuke; Malon, Michal; Ishii, Yuji; Ramamoorthy, Ayyalusamy

    2014-07-01

    Homonuclear correlation NMR experiments are commonly used in the high-resolution structural studies of proteins. While 13C/13C chemical shift correlation experiments utilizing dipolar recoupling techniques are fully utilized under MAS, correlation of the chemical shifts of 15N nuclei in proteins has been a challenge. Previous studies have shown that the negligible 15N-15N dipolar coupling in peptides or proteins necessitates the use of a very long mixing time (typically several seconds) for effective spin diffusion to occur and considerably slows down a 15N/15N correlation experiment. In this study, we show that the use of mixing proton magnetization, instead of 15N, via the recoupled 1H-1H dipolar couplings enable faster 15N/15N correlation. In addition, the use of proton-detection under ultrafast MAS overcomes the sensitivity loss due to multiple magnetization transfer (between 1H and 15N nuclei) steps. In fact, less than 300 nL (∼1.1 micromole quantity) sample is sufficient to acquire the 3D spectrum within 5 h. Our results also demonstrate that a 3D 15N/15N/1H experiment can render higher resolution spectra that will be useful in the structural studies of proteins at ultrafast MAS frequencies. 3D 15N/15N/1H and 2D radio frequency-driven dipolar recoupling (RFDR)-based 1H/1H experimental results obtained from a powder sample of N-acetyla-L-15N-valyl-L-15N-leucine at 70 and 100 kHz MAS frequencies are presented.

  1. From Strong to Fragile Glass Formers: Secondary Relaxation in Polyalcohols

    NASA Astrophysics Data System (ADS)

    Döß, A.; Paluch, M.; Sillescu, H.; Hinze, G.

    2002-03-01

    We have studied details of the molecular origin of slow secondary relaxation near Tg in a series of neat polyalcohols by means of dielectric spectroscopy and 2H NMR. From glycerol to threitol, xylitol, and sorbitol the appearance of the secondary relaxation changes gradually from a wing-type scenario to a pronounced β peak. It is found that in sorbitol the dynamics of the whole molecule contributes equally to the β process, while in glycerol the hydrogen bond forming OH groups remain rather rigid compared to the hydrogens bonded to the carbon skeleton.

  2. Enhancing NMR of Nonrelaxing Species Using a Controlled Flow Motion and a Miniaturized Circuit.

    PubMed

    Carret, Guillaume; Berthelot, Thomas; Berthault, Patrick

    2017-03-07

    In this article we show that circulation of the sample in a closed-loop circuit combined to microsized detection can lead to a significant signal NMR enhancement. We present an optimized NMR device based on a mini bubble-pump associated with fluidics and microdetection that can be installed on a commercial NMR spectrometer. In addition to a significant signal enhancement for slowly relaxing nuclei, we show that it enables more precise and frequent monitoring of chemical reactions. An additional modification leads to a stopped-flow system very efficient for instance for 2D NMR experiments with long mixing times.

  3. Partition operon expression in the linear plasmid prophage N15 is controlled by both Sop proteins and protelomerase.

    PubMed

    Dorokhov, Boris D; Lane, David; Ravin, Nikolai V

    2003-10-01

    The temperate coliphage N15, unlike most low copy-number prokaryotic replicons, is maintained as a linear DNA molecule with covalently closed ends. Accurate partitioning of the plasmid prophage is assured by a close homologue of the sop locus of the F plasmid. However, the region upstream of the N15 sopAB genes contains multiple putative promoters, in contrast to F sop whose expression is driven by one negatively autoregulated promoter. In addition, the centromere of N15 is represented by four inverted repeats located at widely separated sites within the region essential for replication and control of lytic functions. We have analysed expression of N15 sop genes. We find that transcription of N15 sop is driven by two major promoters. The first, P1, is similar in sequence and function to the F sop promoter; it is repressed by Sop proteins. The second promoter, P2, is upstream of P1 and is several times stronger. It is insensitive to regulation by Sop proteins but is tightly repressed by protelomerase, the N15 enzyme that completes prophage replication by generating hairpin telomeres. These results establish a regulatory link between the partition system and other processes of N15 maintenance.

  4. BOOK REVIEW: NMR Imaging of Materials

    NASA Astrophysics Data System (ADS)

    Blümich, Bernhard

    2003-09-01

    Magnetic resonance imaging (MRI) of materials is a field of increasing importance. Applications extend from fundamental science like the characterization of fluid transport in porous rock, catalyst pellets and hemodialysers into various fields of engineering for process optimization and product quality control. While the results of MRI imaging are being appreciated by a growing community, the methods of imaging are far more diverse for materials applications than for medical imaging of human beings. Blümich has delivered the first book in this field. It was published in hardback three years ago and is now offered as a paperback for nearly half the price. The text provides an introduction to MRI imaging of materials covering solid-state NMR spectroscopy, imaging methods for liquid and solid samples, and unusual MRI in terms of specialized approaches to spatial resolution such as an MRI surface scanner. The book represents an excellent and thorough treatment which will help to grow research in materials MRI. Blümich developed the treatise over many years for his research students, graduates in chemistry, physics and engineering. But it may also be useful for medical students looking for a less formal discussion of solid-state NMR spectroscopy. The structure of this book is easy to perceive. The first three chapters cover an introduction, the fundamentals and methods of solid-state NMR spectroscopy. The book starts at the ground level where no previous knowledge about NMR is assumed. Chapter 4 discusses a wide variety of transformations beyond the Fourier transformation. In particular, the Hadamard transformation and the 'wavelet' transformation are missing from most related books. This chapter also includes a description of noise-correlation spectroscopy, which promises the imaging of large objects without the need for extremely powerful radio-frequency transmitters. Chapters 5 and 6 cover basic imaging methods. The following chapter about the use of relaxation and

  5. An NMR database for simulations of membrane dynamics

    PubMed Central

    Leftin, Avigdor; Brown, Michael F.

    2011-01-01

    Computational methods are powerful in capturing the results of experimental studies in terms of force fields that both explain and predict biological structures. Validation of molecular simulations requires comparison with experimental data to test and confirm computational predictions. Here we report a comprehensive database of NMR results for membrane phospholipids with interpretations intended to be accessible by non-NMR specialists. Experimental 13C–1H and 2H NMR segmental order parameters (SCH or SCD) and spin-lattice (Zeeman) relaxation times (T1Z) are summarized in convenient tabular form for various saturated, unsaturated, and biological membrane phospholipids. Segmental order parameters give direct information about bilayer structural properties, including the area per lipid and volumetric hydrocarbon thickness. In addition, relaxation rates provide complementary information about molecular dynamics. Particular attention is paid to the magnetic field dependence (frequency dispersion) of the NMR relaxation rates in terms of various simplified power laws. Model-free reduction of the T1Z studies in terms of a power-law formalism shows that the relaxation rates for saturated phosphatidylcholines follow a single frequency-dispersive trend within the MHz regime. We show how analytical models can guide the continued development of atomistic and coarse-grained force fields. Our interpretation suggests that lipid diffusion and collective order fluctuations are implicitly governed by the viscoelastic nature of the liquid-crystalline ensemble. Collective bilayer excitations are emergent over mesoscopic length scales that fall between the molecular and bilayer dimensions, and are important for lipid organization and lipid-protein interactions. Future conceptual advances and theoretical reductions will foster understanding of biomembrane structural dynamics through a synergy of NMR measurements and molecular simulations. PMID:21134351

  6. Noninvasive testing of art and cultural heritage by mobile NMR.

    PubMed

    Blümich, Bernhard; Casanova, Federico; Perlo, Juan; Presciutti, Federica; Anselmi, Chiara; Doherty, Brenda

    2010-06-15

    Nuclear magnetic resonance (NMR) has many applications in science, medicine, and technology. Conventional instrumentation is large and expensive, however, because superconducting magnets offer maximum sensitivity. Yet NMR devices can also be small and inexpensive if permanent magnets are used, and samples need not be placed within the magnet but can be examined externally in the stray magnetic field. Mobile stray-field NMR is a method of growing interest for nondestructive testing of a diverse range of materials and processes. A well-known stray-field sensor is the commercially available NMR-MOUSE, which is small and can readily be carried to an object to be studied. In this Account, we describe mobile stray-field NMR, with particular attention to its use in analyzing objects of cultural heritage. The most common data recorded are relaxation measurements of (1)H because the proton is the most sensitive NMR nucleus, and relaxation can be measured despite the inhomogeneous magnetic field that typically accompanies a simple magnet design. Through NMR relaxation, the state of matter can be analyzed locally, and the signal amplitude gives the proton density. A variety of stray-field sensors have been designed. Small devices weighing less than a kilogram have a shallow penetration depth of just a few millimeters and a resolution of a few micrometers. Access to greater depths requires larger sensors that may weigh 30 kg or more. The use of these sensors is illustrated by selected examples, including examinations of (i) the stratigraphy of master paintings, (ii) binder aging, (iii) the deterioration of paper, (iv) wood density in master violins, (v) the moisture content and moisture profiles in walls covered with paintings and mosaics, and (vi) the evolution of stone conservation treatments. The NMR data provide unique information to the conservator on the state of the object--including past conservation measures. The use of mobile NMR remains relatively new, expanding

  7. Crude protein extraction protocol for phage N15 protelomerase in vitro enzymatic assays.

    PubMed

    Chen, Qingwen; Narayanan, Kumaran

    2011-07-01

    The phage N15 protelomerase enzyme (TelN) is essential for the replication of its genome by resolution of its telRL domain, located within a telomerase occupancy site (tos), into hairpin telomeres. Isolation of TelN for in vitro processing of tos, however, is a highly complex process, requiring multiple purification steps. In this study a simplified protocol for crude total protein extraction is described that retains the tos-cleaving activity of TelN for at least 4 weeks, greatly simplifying in vitro testing of its activity. This protocol may be extended for functional analysis of other phage and bacterial proteins, particularly DNA-processing enzymes. Copyright © 2011 Elsevier Inc. All rights reserved.

  8. Perspectives on paramagnetic NMR from a life sciences infrastructure.

    PubMed

    Ravera, Enrico; Parigi, Giacomo; Luchinat, Claudio

    2017-09-01

    The effects arising in NMR spectroscopy because of the presence of unpaired electrons, collectively referred to as "paramagnetic NMR" have attracted increasing attention over the last decades. From the standpoint of the structural and mechanistic biology, paramagnetic NMR provides long range restraints that can be used to assess the accuracy of crystal structures in solution and to improve them by simultaneous refinements through NMR and X-ray data. These restraints also provide information on structure rearrangements and conformational variability in biomolecular systems. Theoretical improvements in quantum chemistry calculations can nowadays allow for accurate calculations of the paramagnetic data from a molecular structural model, thus providing a tool to refine the metal coordination environment by matching the paramagnetic effects observed far away from the metal. Furthermore, the availability of an improved technology (higher fields and faster magic angle spinning) has promoted paramagnetic NMR applications in the fast-growing area of biomolecular solid-state NMR. Major improvements in dynamic nuclear polarization have been recently achieved, especially through the exploitation of the Overhauser effect occurring through the contact-driven relaxation mechanism: the very large enhancement of the (13)C signal observed in a variety of liquid organic compounds at high fields is expected to open up new perspectives for applications of solution NMR. Copyright © 2017 Elsevier Inc. All rights reserved.

  9. Study of cultured fibroblasts in vivo using NMR

    SciTech Connect

    Karczmar, G.S.

    1984-08-01

    The goal was to study the compartmentation of phosphorylated glycolytic intermediates in intact Chicken Embryo Fibroblasts (CEFs) using /sup 31/P NMR at 109 MHz. A technique for maintaining functional cells at high densities in an NMR magnet is described. Signals were detected from cytoplasmic inorganic phosphate (P/sub i/), ATP, NAD, NADH, phosphorylcholine and phosphorylethanolamine. The effect of external glucose on cytoplasmic pools of phosphates was studied. When cells were perfused with glucose-free medium the rate of glycolysis decreased, the amplitudes of the ATP resonances decreased, and the P/sub i/ intensity increased. The quantity of NMR-detectable P/sub i/ produced was significantly greater than the quantity of NMR-detectable ATP which was lost. Experiments with /sup 32/P labeled P/sub i/ showed that as the concentration of glucose in the medium was increase, the amount of phosphate sequestered in the cells increased. We conclude that there is a pool of P/sub i/ which is not detected by high resolution NMR and that the size of this pool increases as the rate of glycolysis increase. Longtitudinal relaxation times of intracellular phosphates in normal, transformed, and primary CEFs were measured. The results demonstrate that relaxation times of phosphates are sensitive to structural and metabolic changes which occur when cells are grown in culture. 59 references. 31 figures.

  10. NMR relaxometry as a versatile tool to study Li ion dynamics in potential battery materials.

    PubMed

    Kuhn, A; Kunze, M; Sreeraj, P; Wiemhöfer, H D; Thangadurai, V; Wilkening, M; Heitjans, P

    2012-04-01

    NMR spin relaxometry is known to be a powerful tool for the investigation of Li(+) dynamics in (non-paramagnetic) crystalline and amorphous solids. As long as significant structural changes are absent in a relatively wide temperature range, with NMR spin-lattice (as well as spin-spin) relaxation measurements information on Li self-diffusion parameters such as jump rates and activation energies are accessible. Diffusion-induced NMR relaxation rates are governed by a motional correlation function describing the ion dynamics present. Besides the mean correlation rate of the dynamic process, the motional correlation function (i) reflects deviations from random motion (so-called correlation effects) and (ii) gives insights into the dimensionality of the hopping process. In favorable cases, i.e., when temperature- and frequency-dependent NMR relaxation rates are available over a large dynamic range, NMR spin relaxometry is able to provide a comprehensive picture of the relevant Li dynamic processes. In the present contribution, we exemplarily present two recent variable-temperature (7)Li NMR spin-lattice relaxation studies focussing on Li(+) dynamics in crystalline ion conductors which are of relevance for battery applications, viz. Li(7) La(3)Zr(2)O(12) and Li(12)Si(7).

  11. In situ fluid typing and quantification with 1D and 2D NMR logging.

    PubMed

    Sun, Boqin

    2007-05-01

    In situ nuclear magnetic resonance (NMR) fluid typing has recently gained momentum due to data acquisition and inversion algorithm enhancement of NMR logging tools. T(2) distributions derived from NMR logging contain information on bulk fluids and pore size distributions. However, the accuracy of fluid typing is greatly overshadowed by the overlap between T(2) peaks arising from different fluids with similar apparent T(2) relaxation times. Nevertheless, the shapes of T(2) distributions from different fluid components are often different and can be predetermined. Inversion with predetermined T(2) distributions allows us to perform fluid component decomposition to yield individual fluid volume ratios. Another effective method for in situ fluid typing is two-dimensional (2D) NMR logging, which results in proton population distribution as a function of T(2) relaxation time and fluid diffusion coefficient (or T(1) relaxation time). Since diffusion coefficients (or T(1) relaxation time) for different fluid components can be very different, it is relatively easy to separate oil (especially heavy oil) from water signal in a 2D NMR map and to perform accurate fluid typing. Combining NMR logging with resistivity and/or neutron/density logs provides a third method for in situ fluid typing. We shall describe these techniques with field examples.

  12. 2D relaxation/diffusion correlations in porous media.

    PubMed

    Godefroy, S; Callaghan, P T

    2003-01-01

    2D correlations between NMR relaxation and/or diffusion have been used to investigate water and oil dynamics in food and micro-emulsion systems. In the case of Mozzarella and Gouda cheese samples, a significant change in D/T2 correlation is appearing with cheese aging. In the case of a water/toluene micro-emulsion, some evidence for coalescence effects is suggested by D/D exchange spectra.

  13. [Sop proteins can cause transcriptional silencing of genes located close to the centromere sites of linear plasmid N15].

    PubMed

    Mardanov, A V; Lane, D; Ravin, N V

    2010-01-01

    Stable inheritance of bacterial chromosomes and low copy number plasmids is ensured by accurate partitioning of replicated molecules between the daughter cells at division. Partitioning of the prophage of the temperate bacteriophage N15, which exists as a linear plasmid molecule with covalently closed ends, depends on the sop locus, comprising genes sopA and sopB, as well as four centromere sites located in different regions of the N15 genome essential for replication and the control of lysogeny. We found that binding of SopB to the centromere can silence centromere-proximal promoters, presumably due to subsequent polymerizing of SopB along the DNA. Close to the IR4 centromere site we identified a promoter, P59, able to drive expression of phage late genes encoding the structural proteins of virion. We found that following binding to IR4 the N15 Sop proteins can cause repression of this promoter. The repression depends on SopB and became stronger in the presence of SopA. Sop-dependent silencing of centromere-proximal promoters control gene expression in phage N15, particularly preventing undesired expression of late genes in the N15 prophage. Thus, the phage N15 sop system not only ensures plasmid partitioning but is also involved in the genetic network controlling prophage replication and the maintenance of lysogeny.

  14. Renal transplant NMR

    SciTech Connect

    Velchik, M.G.; Kressel, H.; Thickman, D.; Alavi, A.

    1985-05-01

    The preliminary results of NMR evaluation of renal transplants (Txs) are reported including correlation with nuclear medicine (NM) and ultrasound (US). Thirteen Txs (8 cadaver (Cd), 5 living related doner (LRD) in 13 patients (6M, 7F) ranging in age from 25-47 (x 35) were evaluated by NM (32), NMR (15) and US (5). Clinical diagnoses included: rejection (8), ATN (2), infarction (1), and normal (2). Of the 8 patients with rejection (5) Cd; 3 LRD) pathologic proof was obtained in 3. An experimental 0.12 T resistive magnet (GE) was used with a partial saturation technique with repetition time (TR) of 143 and 286 msec to provide T1 weighting. T2 weighted information was obtained with a spin echo technique with echo times (TE) of 20, 40, 60 and 80 msec. The NMR appearance of normal Txs consisted of a uniform signal intensity (Tx> pelvic musculature), well-defined internal architecture with good cortical medullary differentiation and normal appearing vessels. The NMR appearance of abnormal transplants consisted of a heterogeneous or overall decrease in signal intensity (kidney muscle) with poor cortical medullary differentiation with or without a halo of decreased signal intensity. Although NMR was able to differentiate normal from abnormal, it was unable to clearly discriminate between ATN and rejection. Advantages of NMR included the ability to demonstrate regional anatomy, vasculature, post operative fluid collections and hematomas, and associated avascular necrosis of the hips.

  15. Pulsed NMR spectroscopy

    NASA Technical Reports Server (NTRS)

    Burum, D. P.; Elleman, D. D.; Rhim, W.

    1978-01-01

    Method gives results approximating those of classical continuous-irradiation method but in less time. Method also makes it possible to measure chemical shifts and spin-lattice relaxation times with improved sensitivity. Equipment can be used for adiabatic demagnetization experiments, measurements of rotating-frame spin/lattice relaxation times, and accurate measurements of exact resonance points. When measuring relaxation times, pulse technique can be very effective since pulses may be limited in amplitude and length to prevent spin system from being driven into saturation.

  16. NMR assessment on bone simulated under microgravity

    NASA Astrophysics Data System (ADS)

    Ni, Q.; Qin, Y.

    Introduction Microgravity-induced bone loss has been suggested to be similar to disuse-osteoporosis on Earth which constitutes a challenging public health problem No current non-destructive method can provide the microstructural changes in bone particularly on cortical bone Recently the authors have applied low field nuclear magnetic resonance NMR spin-spin relaxation technique and computational analysis method to determine the porosity pore size distribution and microdamage of cortical bone 1-3 The studies by the authors have shown that this technology can be used to characterize microstructural changes as well as bone water distribution bound and mobile water changes of weightless treated simulating a microgravity condition turkey and mouse cortical bone We further determinate that the NMR spin-spin relaxation time T 2 spectrum derived parameters can be used as descriptions of bone quality e g matrix water distribution and porosity size distributions and alone or in combination with current techniques bone mineral density measurements more accurately predict bone mechanical properties Methods underline Bone sample preparation Two kinds of animal samples were collected and prepared for designed experiments from SUNY Cortical bones of the mid-diaphyses of the ulnae of 1-year-old male turkeys were dissected from freshly slaughtered animals Eight samples were categorized from normal or control and four samples were 4-week disuse treated by functionally isolated osteotomies disuse A total of 12

  17. Quadrupolar relaxation of hyperpolarized krypton-83 as a probe for surfaces.

    PubMed

    Stupic, Karl F; Cleveland, Zackary I; Pavlovskaya, Galina E; Meersmann, Thomas

    2006-02-01

    This work reports the first systematic study of relaxation experienced by the hyperpolarized (hp) noble gas isotope (83)Kr (I=9/2) in contact with surfaces. The spin-lattice relaxation of (83)Kr is found to depend strongly on the chemical composition of the surfaces in the vicinity of the gas. This effect is caused by quadrupolar interactions during brief periods of surface adsorption that are the dominating source of longitudinal spin relaxation in the (83)Kr atoms. Simple model systems of closest packed glass beads with uniform but variable bead sizes are used for the relaxation measurements. The observed relaxation rates depend strongly on the chemical treatment of the glass surfaces and on the surface to volume ratio. Hp (83)Kr NMR relaxation measurements of porous polymers with pore sizes of 70-250 microm demonstrate the potential use of this new technique for material sciences applications.

  18. Relaxation in quantum glasses

    NASA Astrophysics Data System (ADS)

    Ancona Torres, Carlos E.

    The Ising model in transverse field provides the simplest description of a quantum glass. I study two systems that are realizations of the Ising model in transverse field, LiHoxY1-- xF4 and Rb1-- x(NH4)xH2PO 4. In the spin glass LiHoxY1-- xF4, applying a magnetic field Ht transverse to the Ising direction introduces tunneling between the bare Ising eigenstates. In addition, the coupling between the transverse dipolar interaction and the transverse field introduces entanglement or tunable random fields depending on the concentration. By comparing the classical and quantum transitions in LiHo0.198Y0.802F4 and LiHo 0.167Y0.833F4, I characterize the crossover from random field dominated behavior in the 19.8% sample to entanglement dominated behavior in the 16.7% sample. The quantum transition in the 19.8% sample is dominated by the limit on its correlation length caused by the random fields, while the dominant effect in the 16.7% sample is the enhanced tunneling rate introduced by entanglement. The proton glass Rb1--x(NH 4)xH2PO4 relaxes through tunneling of protons in the hydrogen bonds of the crystal, yielding an effective Ising model in transverse field. Since this field cannot be tuned directly, I combine bulk dielectric susceptibility measurements with neutron Compton scattering measurements of the local tunneling potential in two different concentrations, x = 35% and 72%. I find that tunneling drives the fastest relaxation processes at temperatures as high as 20 K and explicitly calculate the tunneling rate from the tunneling potential of the hydrogen bond. Moreover, the structural mechanism for the glassy relaxation allows a real-space picture of the relaxation dynamics to be correlated to the free energy description of aging. I find that the glassy relaxation is driven by the sequential diffusion of defects called Takagi configurations with a classical to quantum crossover in the relaxation at 3 K. I relate the relaxation rate to the quantum action of tunneling

  19. A Comparative Study of T1 and T2 Relaxation in Shale

    NASA Astrophysics Data System (ADS)

    Keating, K.; Obasi, C. C.; Pashin, J. C.

    2015-12-01

    Nuclear magnetic resonance (NMR) relaxation measurement have been used extensively in petroleum and, more recently, in groundwater resource evaluation to estimate the porosity, pore-size distributions, permeability, fluid saturation, and fluid mobility. In shale, the transverse decay rate of NMR signal is sensitive to the microporosity, but is also affected by the paramagnetic contributions of clay and other iron-bearing minerals. Furthermore, contrasts in the magnetic susceptibility of the mineral matrix and pore fluids that result in an inhomogeneous magnetic field within the pore space results in an extra term in transverse relaxation. These issues can cause errors in NMR-based estimates of pore-size distribution and permeability. In this study we compare T1 and T2 relaxation time distributions in order to study the molecular mechanism of relaxation in brine-saturated mixtures of clay and other common minerals. We collected measurements on a range of mixtures of clay minerals common in shale (illite, glauconite, celadonite, chamosite, montmorillonite and kaolinite) and pyrite. To constrain the interpretation of the NMR data, we measured the magnetic susceptibility and surface area of all samples. We are confident that by accounting for the presence and variations of clay and pyrite in shale, we can substantially improve both the NMR estimate of pore-size distribution and permeability.

  20. Robust determination of surface relaxivity from nuclear magnetic resonance DT(2) measurements.

    PubMed

    Luo, Zhi-Xiang; Paulsen, Jeffrey; Song, Yi-Qiao

    2015-10-01

    Nuclear magnetic resonance (NMR) is a powerful tool to probe into geological materials such as hydrocarbon reservoir rocks and groundwater aquifers. It is unique in its ability to obtain in situ the fluid type and the pore size distributions (PSD). The T1 and T2 relaxation times are closely related to the pore geometry through the parameter called surface relaxivity. This parameter is critical for converting the relaxation time distribution into the PSD and so is key to accurately predicting permeability. The conventional way to determine the surface relaxivity ρ2 had required independent laboratory measurements of the pore size. Recently Zielinski et al. proposed a restricted diffusion model to extract the surface relaxivity from the NMR diffusion-T2 relaxation (DT2) measurement. Although this method significantly improved the ability to directly extract surface relaxivity from a pure NMR measurement, there are inconsistencies with their model and it relies on a number of preset parameters. Here we propose an improved signal model to incorporate a scalable LT and extend their method to extract the surface relaxivity based on analyzing multiple DT2 maps with varied diffusion observation time. With multiple diffusion observation times, the apparent diffusion coefficient correctly describes the restricted diffusion behavior in samples with wide PSDs, and the new method does not require predetermined parameters, such as the bulk diffusion coefficient and tortuosity. Laboratory experiments on glass beads packs with the beads diameter ranging from 50 μm to 500 μm are used to validate the new method. The extracted diffusion parameters are consistent with their known values and the determined surface relaxivity ρ2 agrees with the expected value within ±7%. This method is further successfully applied on a Berea sandstone core and yields surface relaxivity ρ2 consistent with the literature. Copyright © 2015 Elsevier Inc. All rights reserved.

  1. N2H+ and N15NH+ toward the prestellar core 16293E in L1689N

    NASA Astrophysics Data System (ADS)

    Daniel, F.; Faure, A.; Pagani, L.; Lique, F.; Gérin, M.; Lis, D.; Hily-Blant, P.; Bacmann, A.; Roueff, E.

    2016-07-01

    Context. Understanding the processes that could lead to an enrichment of molecules in 15N atoms is of particular interest because this may shed light on the relatively strong variations observed in the 14N/15N ratio in various solar system environments. Aims: The sample of molecular clouds where 14N/15N ratios have been measured currently is small and has to be enlarged to allow statistically significant studies. In particular, the N2H+ molecule currently shows the broadest spread of 14N/15N ratios in high-mass star-forming regions. However, the 14N/15N ratio in N2H+ was obtained in only two low-mass star-forming regions (L1544 and B1b). We here extend this sample to a third dark cloud. Methods: We targeted the 16293E prestellar core, where the N15NH+J = 1-0 line was detected. Using a model previously developed for the physical structure of the source, we solved the molecular excitation with a nonlocal radiative transfer code. For this purpose, we computed specific collisional rate coefficients for the N15NH+-H2 collisional system. As a first step of the analysis, the N2H+ abundance profile was constrained by reproducing the N2H+J = 1-0 and 3-2 maps. A scaling factor was then applied to this profile to match the N15NH+J = 1-0 spectrum. Results: We derive a column density ratio N2H+/N15NH. Conclusions: We performed a detailed analysis of the excitation of N2H+ and N15NH+ in the direction of the 16293E core with modern models that solve the radiative transfer and with the most accurate collisional rate coefficients available to date. We obtained the third estimate of the N2H+/N15NH+ column density ratio in the direction of a cold prestellar core. The current estimate ~330 agrees with the typical value of the elemental isotopic ratio in the local interstellar medium. It is lower than in some other cores, however, where values as high as 1300 have been reported.

  2. Quantitative analysis of protein-ligand interactions by NMR.

    PubMed

    Furukawa, Ayako; Konuma, Tsuyoshi; Yanaka, Saeko; Sugase, Kenji

    2016-08-01

    Protein-ligand interactions have been commonly studied through static structures of the protein-ligand complex. Recently, however, there has been increasing interest in investigating the dynamics of protein-ligand interactions both for fundamental understanding of the underlying mechanisms and for drug development. NMR is a versatile and powerful tool, especially because it provides site-specific quantitative information. NMR has widely been used to determine the dissociation constant (KD), in particular, for relatively weak interactions. The simplest NMR method is a chemical-shift titration experiment, in which the chemical-shift changes of a protein in response to ligand titration are measured. There are other quantitative NMR methods, but they mostly apply only to interactions in the fast-exchange regime. These methods derive the dissociation constant from population-averaged NMR quantities of the free and bound states of a protein or ligand. In contrast, the recent advent of new relaxation-based experiments, including R2 relaxation dispersion and ZZ-exchange, has enabled us to obtain kinetic information on protein-ligand interactions in the intermediate- and slow-exchange regimes. Based on R2 dispersion or ZZ-exchange, methods that can determine the association rate, kon, dissociation rate, koff, and KD have been developed. In these approaches, R2 dispersion or ZZ-exchange curves are measured for multiple samples with different protein and/or ligand concentration ratios, and the relaxation data are fitted to theoretical kinetic models. It is critical to choose an appropriate kinetic model, such as the two- or three-state exchange model, to derive the correct kinetic information. The R2 dispersion and ZZ-exchange methods are suitable for the analysis of protein-ligand interactions with a micromolar or sub-micromolar dissociation constant but not for very weak interactions, which are typical in very fast exchange. This contrasts with the NMR methods that are used

  3. NMR Studies of Dynamic Biomolecular Conformational Ensembles

    PubMed Central

    Torchia, Dennis A.

    2015-01-01

    Multidimensional heteronuclear NMR approaches can provide nearly complete sequential signal assignments of isotopically enriched biomolecules. The availability of assignments together with measurements of spin relaxation rates, residual spin interactions, J-couplings and chemical shifts provides information at atomic resolution about internal dynamics on timescales ranging from ps to ms, both in solution and in the solid state. However, due to the complexity of biomolecules, it is not possible to extract a unique atomic-resolution description of biomolecular motions even from extensive NMR data when many conformations are sampled on multiple timescales. For this reason, powerful computational approaches are increasingly applied to large NMR data sets to elucidate conformational ensembles sampled by biomolecules. In the past decade, considerable attention has been directed at an important class of biomolecules that function by binding to a wide variety of target molecules. Questions of current interest are: “Does the free biomolecule sample a conformational ensemble that encompasses the conformations found when it binds to various targets; and if so, on what time scale is the ensemble sampled?” This article reviews recent efforts to answer these questions, with a focus on comparing ensembles obtained for the same biomolecules by different investigators. A detailed comparison of results obtained is provided for three biomolecules: ubiquitin, calmodulin and the HIV-1 trans-activation response RNA. PMID:25669739

  4. Structures and relative stability of neutral gold clusters: Aun (n=15-19)

    NASA Astrophysics Data System (ADS)

    Bulusu, Satya; Zeng, X. C.

    2006-10-01

    We performed a global-minimum search for low-lying neutral clusters (Aun) in the size range of n =15-19 by means of basin-hopping method coupled with density functional theory calculation. Leading candidates for the lowest-energy clusters are identified, including four for Au15, two for Au16, three for Au17, five for Au18, and one for Au19. For Au15 and Au16 we find that the shell-like flat-cage structures dominate the population of low-lying clusters, while for Au17 and Au18 spherical-like hollow-cage structures dominate the low-lying population. The transition from flat-cage to hollow-cage structure is at Au17 for neutral gold clusters, in contrast to the anion counterparts for which the structural transition is at Au16- [S. Bulusu et al., Proc. Natl. Acad. Sci. U.S.A. 103, 8362 (2006)]. Moreover, the structural transition from hollow-cage to pyramidal structure occurs at Au19. The lowest-energy hollow-cage structure of Au17 (with C2v point-group symmetry) shows distinct stability, either in neutral or in anionic form. The distinct stability of the hollow-cage Au17 calls for the possibility of synthesizing highly stable core/shell bimetallic clusters M @Au17 (M =group I metal elements).

  5. ^93Nb NMR investigation of the multiferroic system Ba3NbFe3Si2O14

    NASA Astrophysics Data System (ADS)

    Lumata, Lloyd; Hoch, M. J. R.; Zhou, H. D.; Brooks, J. S.; Kuhns, P. L.; Reyes, A. P.; Wiebe, C. R.

    2009-03-01

    We present ^93Nb nuclear magnetic resonance spectroscopy and relaxation data on the new multiferroic system Ba3NbFe3Si2O14. The spin-lattice relaxation rate ^931/T1 and spin-spin relaxation rate ^931/T2 show a peak at 26 K accompanied by broadening of the NMR lineshapes, characteristic of N'eel ordering. Salient features of ^93Nb NMR lineshapes in the ordered phase and temperature-dependent ^93Nb Knight shifts will be discussed in relation to the possible bulking or tilting of the NbO6 octahedra (caused by magneto-lattice coupling) around the transition.

  6. NMR imaging microscopy

    SciTech Connect

    Not Available

    1986-10-01

    In the past several years, proton nuclear magnetic resonance (NMR) imaging has become an established technique in diagnostic medicine and biomedical research. Although much of the work in this field has been directed toward development of whole-body imagers, James Aguayo, Stephen Blackband, and Joseph Schoeninger of the Johns Hopkins University School of Medicine working with Markus Hintermann and Mark Mattingly of Bruker Medical Instruments, recently developed a small-bore NMR microscope with sufficient resolution to image a single African clawed toad cell (Nature 1986, 322, 190-91). This improved resolution should lead to increased use of NMR imaging for chemical, as well as biological or physiological, applications. The future of NMR microscopy, like that of many other newly emerging techniques, is ripe with possibilities. Because of its high cost, however, it is likely to remain primarily a research tool for some time. ''It's like having a camera,'' says Smith. ''You've got a way to look at things at very fine levels, and people are going to find lots of uses for it. But it is a very expensive technique - it costs $100,000 to add imaging capability once you have a high-resolution NMR, which itself is at least a $300,000 instrument. If it can answer even a few questions that can't be answered any other way, though, it may be well worth the cost.''

  7. Ultralow field NMR spectrometer with an atomic magnetometer near room temperature.

    PubMed

    Liu, Guobin; Li, Xiaofeng; Sun, Xianping; Feng, Jiwen; Ye, Chaohui; Zhou, Xin

    2013-12-01

    We present a Cs atomic magnetometer with a sensitivity of 150fT/Hz(1/2) operating near room temperature. The nuclear magnetic resonance (NMR) signal of 125μL tap water was detected at an ultralow magnetic field down to 47nT, with the signal-to-noise ratio (SNR) of the NMR signal approaching 50 after eight averages. Relaxivity experiments with a Gd(DTPA) contrast agent in zero field were performed, in order to show the magnetometer's ability to measure spin-lattice relaxation time with high accuracy. This demonstrates the feasibility of an ultralow field NMR spectrometer based on a Cs atomic magnetometer, which has a low working temperature, short data acquisition time and high sensitivity. This kind of NMR spectrometer has great potential in applications such as chemical analysis and magnetic relaxometry detection in ultralow or zero fields. Copyright © 2013 Elsevier Inc. All rights reserved.

  8. Ultralow field NMR spectrometer with an atomic magnetometer near room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Guobin; Li, Xiaofeng; Sun, Xianping; Feng, Jiwen; Ye, Chaohui; Zhou, Xin

    2013-12-01

    We present a Cs atomic magnetometer with a sensitivity of 150 fT/Hz1/2 operating near room temperature. The nuclear magnetic resonance (NMR) signal of 125 μL tap water was detected at an ultralow magnetic field down to 47 nT, with the signal-to-noise ratio (SNR) of the NMR signal approaching 50 after eight averages. Relaxivity experiments with a Gd(DTPA) contrast agent in zero field were performed, in order to show the magnetometer's ability to measure spin-lattice relaxation time with high accuracy. This demonstrates the feasibility of an ultralow field NMR spectrometer based on a Cs atomic magnetometer, which has a low working temperature, short data acquisition time and high sensitivity. This kind of NMR spectrometer has great potential in applications such as chemical analysis and magnetic relaxometry detection in ultralow or zero fields.

  9. Indirect use of deuterium in solution NMR studies of protein structure and hydrogen bonding.

    PubMed

    Tugarinov, Vitali

    2014-02-01

    A description of the utility of deuteration in protein NMR is provided with an emphasis on quantitative evaluation of the effects of deuteration on a number of NMR parameters of proteins: (1) chemical shifts, (2) scalar coupling constants, (3) relaxation properties (R1 and R2 rates) of nuclei directly attached to one or more deuterons as well as protons of methyl groups in a highly deuterated environment, (4) scalar relaxation of 15N and 13C nuclei in 15N-D and 13C-D spin systems as a measure of hydrogen bonding strength, and (5) NOE-based applications of deuteration in NMR studies of protein structure. The discussion is restricted to the 'indirect' use of deuterium in the sense that the description of NMR parameters and properties of the nuclei affected by nearby deuterons (15N, 13C, 1H) is provided rather than those of deuterium itself. Copyright © 2013 Elsevier B.V. All rights reserved.

  10. NMR investigation of gaseous SF6 confinement into EPDM rubber.

    PubMed

    Neutzler, Sven; Terekhov, Maxim; Hoepfel, Dieter; Oellrich, Lothar Rainer

    2005-02-01

    The confinement process of gaseous sulphurhexafluoride (SF6) in ethylene-propylene-diene (EPDM) rubber was investigated by spectroscopic and spatially resolved NMR techniques. A strong elongation of T1 relaxation time of SF6 and a decrease of the diffusion coefficient were found. A possible explanation may be the strong restriction of molecular mobility due to interactions between SF6 and active centers of the EPDM.

  11. 7Li NMR on Li intercalated carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Schmid, M.; Goze-Bac, C.; Mehring, M.; Roth, S.

    2005-09-01

    Solid state 7Li Nuclear Magnetic Resonance (NMR) measurements were performed on lithium intercalated single wall carbon nanotubes (SWNT). The temperature dependence of the static spectra, as well as the spin-lattice relaxation behavior of the intercalated Li nuclei reveal two coexisting kinds of Li intercalation sites. Our results can be interpreted in terms of a staging phenomenon similar to graphite intercalation compounds (GIC).

  12. NMR analysis, protonation equilibria and decomposition kinetics of tolperisone.

    PubMed

    Orgován, Gábor; Tihanyi, Károly; Noszál, Béla

    2009-12-05

    The rate constants of spontaneous and hydroxide-catalyzed decomposition and the tautomer-specific protonation constants of tolperisone, a classical muscle relaxant were determined. A solution NMR method without any separation techniques was elaborated to quantitate the progress of decomposition. All the rate and equilibrium constants were determined at four different temperatures and the activation parameters were calculated. The molecular mechanism of decomposition is proposed.

  13. Studying Dynamics by Magic-Angle Spinning Solid-State NMR Spectroscopy: Principles and Applications to Biomolecules

    PubMed Central

    Schanda, Paul; Ernst, Matthias

    2016-01-01

    Magic-angle spinning solid-state NMR spectroscopy is an important technique to study molecular structure, dynamics and interactions, and is rapidly gaining importance in biomolecular sciences. Here we provide an overview of experimental approaches to study molecular dynamics by MAS solid-state NMR, with an emphasis on the underlying theoretical concepts and differences of MAS solid-state NMR compared to solution-state NMR. The theoretical foundations of nuclear spin relaxation are revisited, focusing on the particularities of spin relaxation in solid samples under magic-angle spinning. We discuss the range of validity of Redfield theory, as well as the inherent multi-exponential behavior of relaxation in solids. Experimental challenges for measuring relaxation parameters in MAS solid-state NMR and a few recently proposed relaxation approaches are discussed, which provide information about time scales and amplitudes of motions ranging from picoseconds to milliseconds. We also discuss the theoretical basis and experimental measurements of anisotropic interactions (chemical-shift anisotropies, dipolar and quadrupolar couplings), which give direct information about the amplitude of motions. The potential of combining relaxation data with such measurements of dynamically-averaged anisotropic interactions is discussed. Although the focus of this review is on the theoretical foundations of dynamics studies rather than their application, we close by discussing a small number of recent dynamics studies, where the dynamic properties of proteins in crystals are compared to those in solution. PMID:27110043

  14. [Structural organization and control of expression of the sop-operon of linear plasmid prophage N15].

    PubMed

    Ravin, N V; Dorokhov, B D; Lane, D

    2004-01-01

    Stable inheritance of bacterial chromosomes and low-copy-number plasmids depends on the active partition of replicated molecules between daughter cells. The partition mechanism is well known for circular plasmids F and P1. The mechanism of partition of linear replicons was studied with the example of bacteriophage N15, which persists as a linear plasmid with covalently closed ends on lysogeny, rather than integrating into the Escherichia coli chromosome. Since stable inheritance of N15 is due to the sop operon homologous to sop of the F plasmid, the control of expression of the N15 sop genes was analyzed. The sop promoter (Psop) contains a binding site for bacterial IHF and five CTTTGC copies, which overlap the -35 and -10 elements. The Sop proteins were shown to interact with a Psop-containing DNA fragment in vitro. Transcription of the sop operon is regulated by the Sop proteins: SopA represses Psop, and SopB enhances the repression, having no effect on the promoter activity in the absence of SopA. In N15 lysogenic cells, Psop proved to be repressed. This regulatory mechanism was assumed to ensure production of SopA and SopB in amounts required for the segregation stability of N15 and to neutralize occasional fluctuations of their concentration in the cell.

  15. Relaxation in Physical Education Curricula.

    ERIC Educational Resources Information Center

    Coville, Claudia A.

    1979-01-01

    A theoretical framework for incorporating relaxation instruction in the physical education curriculum is presented based on the assumption that relaxation is a muscular-skeletal skill benefitting general motor skill acquisition. Theoretical principles, a definition of relaxation, and an analysis of stages of skill development are also used in the…

  16. A Comparison of Relaxation Strategies.

    ERIC Educational Resources Information Center

    Matthews, Doris B.

    Some researchers argue that all relaxation techniques produce a single relaxation response while others support a specific-effects hypothesis which suggests that progressive relaxation affects the musculoskeletal system and that guided imagery affects cognitive changes. Autogenics is considered a technique which is both somatic and cognitive. This…

  17. 1H NMR relaxometry, viscometry, and PFG NMR studies of magnetic and nonmagnetic ionic liquids.

    PubMed

    Daniel, Carla I; Chávez, Fabián Vaca; Feio, Gabriel; Portugal, Carla A M; Crespo, João G; Sebastião, Pedro J

    2013-10-03

    A study is presented of the molecular dynamics and of the viscosity in pure [Aliquat][Cl] ionic liquid and in a mixture of [Aliquat][Cl] with 1% (v/v) of [Aliquat][FeCl4]. The (1)H spin-lattice relaxation rate, R1, was measured by NMR relaxometry between 8 and 300 MHz. In addition, the translation self-diffusion, D, was measured by pulse field gradient NMR. The ILs' viscosity was measured as a function of an applied magnetic field, B, and it was found that the IL mixture's viscosity decreased with increasing B, whereas the [Aliquat][Cl] viscosity is independent of B. All experimental results were analyzed taking into account the viscosity's magnetic field dependence, assuming a modified Stokes-Einstein diffusion/viscosity relation. The main difference between the relaxation mechanisms responsible for R1 in the two IL systems is related to the additional paramagnetic relaxation contribution associated with the (1)H spins-[FeCl4] paramagnetic moments' interactions. Cross-relaxation cusps in the R1 dispersion, associated with (35)Cl and (1)H nuclear spins in the IL systems, were detected. The R1 model considered was successfully fitted to the experimental results, and it was possible to estimate the value of D at zero field in the case of the IL mixture which was consistent with the values of D measured at 7 and 14.1 T and with the magnetic field dependence estimated from the viscosity measurements. It was observed that a small concentration of [Aliquat][FeCl4] in the [Aliquat][Cl] was enough to produce a "superparamagnetic"-like effect and to change the IL mixture's molecular dynamics and viscosity and to allow for their control with an external magnetic field.

  18. Relaxation from particle production

    NASA Astrophysics Data System (ADS)

    Hook, Anson; Marques-Tavares, Gustavo

    2016-12-01

    We consider using particle production as a friction force by which to implement a "Relaxion" solution to the electroweak hierarchy problem. Using this approach, we are able to avoid superplanckian field excursions and avoid any conflict with the strong CP problem. The relaxation mechanism can work before, during or after inflation allowing for inflationary dynamics to play an important role or to be completely decoupled.

  19. Relaxation from particle production

    SciTech Connect

    Hook, Anson; Marques-Tavares, Gustavo

    2016-12-20

    Here, we consider using particle production as a friction force by which to implement a “Relaxion” solution to the electroweak hierarchy problem. Using this approach, we are able to avoid superplanckian field excursions and avoid any conflict with the strong CP problem. The relaxation mechanism can work before, during or after inflation allowing for inflationary dynamics to play an important role or to be completely decoupled.

  20. Intermediate valence behavior of Yb2Ni12P7 studied by using 31P NMR

    NASA Astrophysics Data System (ADS)

    Koyama, T.; Sugiura, K.; Ueda, K.; Mito, T.; Kohara, T.; Satoh, R.; Tsuchiya, K.; Nakano, T.; Takeda, N.

    2013-08-01

    The Yb-based heavy-fermion compound Yb2Ni12P7 with a hexagonal Zr2Fe12P7-type crystal structure was investigated by using the 31P nuclear magnetic resonance (NMR) technique. The complicated NMR line changes its shape gradually with decreasing temperature, implying the presence of some Knight shift components. The temperature dependences of the Knight shift and the nuclear spin-lattice relaxation rate 1/ T 1 suggest the delocalization of 4 f electrons.

  1. Optimizing Adiabaticity in NMR

    NASA Astrophysics Data System (ADS)

    Vandermause, Jonathan; Ramanathan, Chandrasekhar

    We demonstrate the utility of Berry's superadiabatic formalism for numerically finding control sequences that implement quasi-adiabatic unitary transformations. Using an iterative interaction picture, we design a shortcut to adiabaticity that reduces the time required to perform an adiabatic inversion pulse in liquid state NMR. We also show that it is possible to extend our scheme to two or more qubits to find adiabatic quantum transformations that are allowed by the control algebra, and demonstrate a two-qubit entangling operation in liquid state NMR. We examine the pulse lengths at which the fidelity of these adiabatic transitions break down and compare with the quantum speed limit.

  2. Shiftless NMR Spectroscopy

    PubMed Central

    Wu, Chin H.; Opella, Stanley J.

    2013-01-01

    The acquisition and analysis of high resolution one- and two- dimensional solid-state NMR spectra without chemical shift frequencies are described. Many variations of Shiftless NMR spectroscopy are feasible. A two-dimensional experiment that correlates 13Cα-15N dipole-dipole and 1H-13Cα dipole-dipole couplings in single crystal and powder samples of the model peptide, 13Cα, 15N-acetylleucine, is demonstrated. In addition to the resolution of resonances from individual sites in a single crystal sample, the bond lengths and angles are characterized by the two-dimensional powder pattern obtained from a polycrystalline sample. PMID:18266429

  3. N-15/N-14 variations in Cretaceous Atlantic sedimentary sequences - Implication for past changes in marine nitrogen biogeochemistry

    NASA Technical Reports Server (NTRS)

    Rau, Greg H.; Arthur, Michael A.; Dean, Walter E.

    1987-01-01

    Unusually low delta N-15 found in early to middle Cretaceous beds rich in marine organic matter from two separate eastern Atlantic Ocean basins is reported. These findings constitute unambiguous evidence that the N contained in these strata is the end result of biogeochemical processes that differed substantially from those that operated on the N contained in intervening organic carbon-poor strata and younger marine sediments. The data indicate that the low N-15 relative abundance is the consequence of pelagic rather than postdepositional processes. Reduced ocean circulation, increased denitrification, and hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N2-fixing blue-green algae, a possible source of the sedimentary N-15 depletion.

  4. In-Phase Ultra High-Resolution In Vivo NMR.

    PubMed

    Fugariu, Ioana; Bermel, Wolfgang; Lane, Daniel; Soong, Ronald; Simpson, Andre J

    2017-04-05

    Although current NMR techniques allow organisms to be studied in vivo, magnetic susceptibility distortions, which arise from inhomogeneous distributions of chemical moieties, prevent the acquisition of high-resolution NMR spectra. Intermolecular single quantum coherence (iSQC) is a technique that breaks the sample's spatial isotropy to form long range dipolar couplings, which can be exploited to extract chemical shift information free of perturbations. While this approach holds vast potential, present practical limitations include radiation damping, relaxation losses, and non-phase sensitive data. Herein, these drawbacks are addressed, and a new technique termed in-phase iSQC (IP-iSQC) is introduced. When applied to a living system, high-resolution NMR spectra, nearly identical to a buffer extract, are obtained. The ability to look inside an organism and extract a high-resolution metabolic profile is profound and should find applications in fields in which metabolism or in vivo processes are of interest.

  5. NMR study of black-phase in SmS

    NASA Astrophysics Data System (ADS)

    Koyama, T.; Yamada, H.; Ueda, K.; Mito, T.; Haga, Y.

    2015-03-01

    We report the result of the 33S nuclear magnetic resonance (NMR) measurement on the nonmagnetic semiconductor SmS at ambient pressure. For this measurement, the 33S isotope enriched powder sample of SmS was prepared to increase the 33S NMR intensity. We have attempted 33S NMR measurement on SmS and successfully observed the signal of it. With decreasing temperature, the spectrum measured at the constant magnetic field shifted to lower frequency and became weakly temperature dependent below 50 K. The presence of the energy gap was microscopically established by the rapid decrease in the nuclear spin-lattice relaxation rate 1/T1. The activation energy was deduced to be 625 K from an Arrhenius plot of T1.

  6. Diffusional Properties of Methanogenic Granular Sludge: 1H NMR Characterization

    PubMed Central

    Lens, Piet N. L.; Gastesi, Rakel; Vergeldt, Frank; van Aelst, Adriaan C.; Pisabarro, Antonio G.; Van As, Henk

    2003-01-01

    The diffusive properties of anaerobic methanogenic and sulfidogenic aggregates present in wastewater treatment bioreactors were studied using diffusion analysis by relaxation time-separated pulsed-field gradient nuclear magnetic resonance (NMR) spectroscopy and NMR imaging. NMR spectroscopy measurements were performed at 22°C with 10 ml of granular sludge at a magnetic field strength of 0.5 T (20 MHz resonance frequency for protons). Self-diffusion coefficients of H2O in the investigated series of mesophilic aggregates were found to be 51 to 78% lower than the self-diffusion coefficient of free water. Interestingly, self-diffusion coefficients of H2O were independent of the aggregate size for the size fractions investigated. Diffusional transport occurred faster in aggregates growing under nutrient-rich conditions (e.g., the bottom of a reactor) or at high (55°C) temperatures than in aggregates cultivated in nutrient-poor conditions or at low (10°C) temperatures. Exposure of aggregates to 2.5% glutaraldehyde or heat (70 or 90°C for 30 min) modified the diffusional transport up to 20%. In contrast, deactivation of aggregates by HgCl2 did not affect the H2O self-diffusion coefficient in aggregates. Analysis of NMR images of a single aggregate shows that methanogenic aggregates possess a spin-spin relaxation time and self-diffusion coefficient distribution, which are due to both physical (porosity) and chemical (metal sulfide precipitates) factors. PMID:14602624

  7. Determining the sizes of micropores in activated charcoals by the pulsed NMR method

    NASA Astrophysics Data System (ADS)

    Gogelashvili, G. Sh.; Khozina, E. V.; Vartapetyan, R. Sh.; Ladychuk, D. V.; Grunin, Yu. B.

    2011-07-01

    The pulsed NMR method was used to measure the nuclear spin-spin relaxation of protons of water adsorbed in micropores of activated charcoal (AC) samples with different porous structures. A correlation was found between the spin-spin relaxation time of water protons in AC with completely filled micropores and the volume density of water primary adsorption centers in the AC samples. An equation for approximating obtained dependences is proposed that allows us to determine the volume of micropores in AC.

  8. Magnetic equivalence of terminal nuclei in the azide anion broken by nuclear spin relaxation

    NASA Astrophysics Data System (ADS)

    Bernatowicz, P.; Szymański, S.

    NMR spectra of water solution of sodium azide selectively 15N labelled in the central position were studied using an iterative least-squares method. In agreement with predictions based on Bloch-Wangsness-Redfield nuclear spin relaxation theory, it is demonstrated that quadrupolar relaxation of the magnetically equivalent terminal 14N (spin-1) nuclei in the azide anion renders the J coupling between these nuclei an observable quantity. In isotropic fluids, this seems to be the first experimental evidence of relaxation-broken magnetic equivalence symmetry.

  9. Electron spin relaxation due to reorientation of a permanent zero field splitting tensor.

    PubMed

    Schaefle, Nathaniel; Sharp, Robert

    2004-09-15

    Electron spin relaxation of transition metal ions with spin S> or =1 results primarily from thermal modulation of the zero field splitting (zfs) tensor. This occurs both by distortion of the zfs tensor due to intermolecular collisions and, for complexes with less than cubic symmetry, by reorientational modulation of the permanent zfs tensor. The reorientational mechanism is much less well characterized in previous work than the distortional mechanism although it is an important determinant of nuclear magnetic resonance (NMR) paramagnetic relaxation enhancement phenomena (i.e., the enhancement of NMR relaxation rates produced by paramagnetic ions in solution or NMR-PRE). The classical density matrix theory of spin relaxation does not provide an appropriate description of the reorientational mechanism at low Zeeman field strengths because the zero-order spin wave functions are stochastic functions of time. Using spin dynamics simulation techniques, the time correlation functions of the spin operators have been computed and used to determine decay times for the reorientational relaxation mechanism for S=1. In the zfs limit of laboratory field strengths (H(Zeem)relaxation time, tau(S) (composite function) approximately 0.53tau(R)((1)), where tau(R)((1)) is the reorientational correlation time of a molecule-fixed vector. The value of tau(S) (composite function) is independent of the magnitude of the cylindrical zfs parameter (D), but it depends strongly on low symmetry zfs terms (the E/D ratio). Other spin dynamics (SD) simulations examined spin decay in the intermediate regime of field strengths where H(Zeem) approximately H(zfs) (composite function), and in the vicinity of the Zeeman limit. The results demonstrate that the reorientational electron spin relaxation mechanism is often significant when H(zfs) (composite function)> or =H(Zeem), and that its neglect

  10. Modern NMR Spectroscopy.

    ERIC Educational Resources Information Center

    Jelinski, Lynn W.

    1984-01-01

    Discusses direct chemical information that can be obtained from modern nuclear magnetic resonance (NMR) methods, concentrating on the types of problems that can be solved. Shows how selected methods provide information about polymers, bipolymers, biochemistry, small organic molecules, inorganic compounds, and compounds oriented in a magnetic…

  11. Modern NMR Spectroscopy.

    ERIC Educational Resources Information Center

    Jelinski, Lynn W.

    1984-01-01

    Discusses direct chemical information that can be obtained from modern nuclear magnetic resonance (NMR) methods, concentrating on the types of problems that can be solved. Shows how selected methods provide information about polymers, bipolymers, biochemistry, small organic molecules, inorganic compounds, and compounds oriented in a magnetic…

  12. Autonomous driving in NMR.

    PubMed

    Perez, Manuel

    2017-01-01

    The automatic analysis of NMR data has been a much-desired endeavour for the last six decades, as it is the case with any other analytical technique. This need for automation has only grown as advances in hardware; pulse sequences and automation have opened new research areas to NMR and increased the throughput of data. Full automatic analysis is a worthy, albeit hard, challenge, but in a world of artificial intelligence, instant communication and big data, it seems that this particular fight is happening with only one technique at a time (let this be NMR, MS, IR, UV or any other), when the reality of most laboratories is that there are several types of analytical instrumentation present. Data aggregation, verification and elucidation by using complementary techniques (e.g. MS and NMR) is a desirable outcome to pursue, although a time-consuming one if performed manually; hence, the use of automation to perform the heavy lifting for users is required to make the approach attractive for scientists. Many of the decisions and workflows that could be implemented under automation will depend on the two-way communication with databases that understand analytical data, because it is desirable not only to query these databases but also to grow them in as much of an automatic manner as possible. How these databases are designed, set up and the data inside classified will determine what workflows can be implemented. Copyright © 2016 John Wiley & Sons, Ltd.

  13. Dynamical properties of confined supercooled water: an NMR study

    NASA Astrophysics Data System (ADS)

    Mallamace, Francesco; Broccio, Matteo; Corsaro, Carmelo; Faraone, Antonio; Liu, Li; Mou, Chung-Yuan; Chen, Sow-Hsin

    2006-09-01

    We report a set of dynamical data of confined water measured in a very deeply supercooled regime (290-190 K). Water is contained in silica matrices (MCM-41-S) which consist of 1D cylindrical pores with diameters d = 14,18 and 24 Å. When confined in these tubular pores, water does not crystallize, and can be supercooled well below 200 K. We use the NMR technique to obtain the characteristic proton relaxation time-constants (the spin-lattice relaxation time-constant T1 and the spin-spin relaxation time-constant T2) and a direct measurement of the self-diffusion coefficient in the whole temperature range. We give evidence of the existence of a fragile-to-strong dynamic crossover (FSC) at TL = 225 K from the temperature dependence of the self-diffusion coefficient. A combination of the NMR self-diffusion coefficient with the average translational relaxation time, as measured by quasi-elastic neutron scattering, shows a well defined decoupling of transport coefficients, i.e. the breakdown of the Stokes-Einstein relation, on approaching the crossover temperature TL.

  14. Anomalous nuclear spin-lattice relaxation of 3He in contact with ordered Al2O3 aerogel

    NASA Astrophysics Data System (ADS)

    Alakshin, E. M.; Zakharov, M. Yu.; Klochkov, A. V.; Kuzmin, V. V.; Safiullin, K. R.; Stanislavovas, A. A.; Tagirov, M. S.

    2016-09-01

    Spin-lattice relaxation of 3He in contact with the ordered Al2O3 fiber aerogel has been studied at the temperature of 1.6 K in fields of 0.1-0.5 T by the pulsed nuclear magnetic resonance (NMR) method. An additional mechanism of the relaxation of 3He in aerogels is found and it is shown that this relaxation mechanism is not associated with the adsorbed layer. A hypothesis about the influence of intrinsic paramagnetic centers on the relaxation of gaseous 3He is proposed.

  15. Simultaneously cycled NMR spectroscopy.

    PubMed

    Parish, David M; Szyperski, Thomas

    2008-04-09

    Simultaneously cycled (SC) NMR was introduced and exemplified by implementing a set of 2-D [1H,1H] SC exclusive COSY (E.COSY) NMR experiments, that is, rf pulse flip-angle cycled (SFC), rf pulse phase cycled (SPC), and pulsed field gradient (PFG) strength cycled (SGC) E.COSY. Spatially selective 1H rf pulses were applied as composite pulses such that all steps of the respective cycles were affected simultaneously in different slices of the sample. This increased the data acquisition speed for an n-step cycle n-fold. A high intrinsic sensitivity was achieved by defining the cycles in a manner that the receiver phase remains constant for all steps of the cycle. Then, the signal resulting from applying the cycle corresponded to the sum of the signals from all steps of the cycle. Hence, the detected free induction decay did not have to be separated into the contributions arising from different slices, and read-out PFGs, which not only greatly reduce sensitivity but also negatively impact lineshapes in the direct dimension, were avoided. The current implementation of SFC E.COSY reached approximately 65% of the intrinsic sensitivity of the conventional phase cycled congener, making this experiment highly attractive whenever conventional data acquisition is sampling limited. Highly resolved SC E.COSY yielding accurate 3J-coupling values was recorded for the 416 Da plant alkaloid tomatidine within 80 min, that is, 12 times faster than with conventional phase cycled E.COSY. SC NMR is applicable for a large variety of NMR experiments and thus promises to be a valuable addition to the arsenal of approaches for tackling the NMR sampling problem to avoid sampling limited data acquisition.

  16. NMR relaxometry study of development of freeze damage in mandarin orange.

    PubMed

    Zhang, Lu; McCarthy, Michael J

    2016-07-01

    Freeze damage to citrus fruit is one of the major causes of the loss of marketable fruit for the citrus industry. Because freeze damage occurs inside citrus fruit, detecting freeze damage is very challenging. This study addresses this problem by using NMR relaxometry to monitor changes at the sub-cellular level in mandarin flesh at two freezing temperatures, -4 °C and -20 °C. The T2 relaxation spectra of mandarin flesh segments displayed three relaxation components, each representing a sub-cellular water compartment. Freezing treatment at -4 °C for 240 min significantly decreased the relative magnitude of the slow relaxation component and increased that of the intermediate relaxation components. These changes are signs of water redistribution between sub-cellular compartments and an increase in membrane permeability. Freezing treatment at -20 °C caused more evident changes in the T2 relaxation spectra. Noticeable changes occurred as early as 120 min of freezing. In addition, NMR relaxometry was performed on cold-stored mandarins. Smaller changes were observed in samples stored at 4 °C than frozen samples. The relative magnitudes of relaxation components are sensitive to sub-cellular changes in mandarin flesh due to freeze damage. Thus, freeze damage in mandarin flesh can be tracked by NMR relaxometry. © 2015 Society of Chemical Industry. © 2015 Society of Chemical Industry.

  17. Molecular factors that determine Curie spin relaxation in dysprosium complexes.

    PubMed

    Caravan, P; Greenfield, M T; Bulte, J W

    2001-11-01

    Dysprosium complexes can serve as transverse relaxation (T(2)) agents for water protons through chemical exchange and the Curie spin relaxation mechanism. Using a pair of matched dysprosium(III) complexes, Dy-L1 (contains one inner-sphere water) and Dy-L2 (no inner-sphere water), it is shown that the transverse relaxation of bulk water is predominantly an inner-sphere effect. The kinetics of water exchange at Dy-L1 were determined by (17)O NMR. Proton transverse relaxation by Dy-L1 at high fields is governed primarily through a large chemical shift difference between free and bound water. Dy-L1 forms a noncovalent adduct with human serum albumin which dramatically lengthens the rotational correlation time, tau(R), causing the dipole-dipole component of the Curie spin mechanism to become significant and transverse relaxivity to increase by 3-8 times that of the unbound chelate. These findings aid in the design of new molecular species as efficient r(2) agents.

  18. Progressive muscle relaxation, yoga stretching, and ABC relaxation theory.

    PubMed