Transverse Nuclear Magnetic Resonance Research Articles

1H, 13C, and 15N resonance assignments of the amyloidogenic peptide SEM2(49-107) by NMR spectroscopy.

It has been shown that human seminal fluid is a major factor in enhancing HIV activity. The SEM2(49-107) peptide is a product of cleavage after ejaculation by internal prostheses of the semenogelin 2 protein, expressed in seminal vesicles. It is established that the peptide SEM2(49-107) forms amyloid fibrils, which increase probability of contracting HIV infection. In this nuclear magnetic resonance (NMR) study, we present almost complete (86%) resonance assignments for the 1H 15N and 13C atoms of the backbone and side-chain of the SEM2(49-107) peptide (BioMagResBank accession number 52356). The secondary structure of SEM2(49-107) peptide was estimated by using two approaches, secondary chemical shifts analysis (CSI) and TALOS-N prediction. Analysis of the secondary structure of the SEM2(49-107) peptide using both methods revealed that the peptide contains helical segments at the C-terminus. Also in this work, we used phase-sensitive 2D HSQC 1H- 15N experiments measuring longitudinal T1 and transverse T2 NMR relaxation times to report predicted secondary structure and backbone dynamics of the SEM2(49-107) peptide. This resonance assignment will form the basis of future NMR research, contributing to a better understanding of the peptide structure and internal dynamics of the molecule.

Longitudinal and Transverse 1H Nuclear Magnetic Resonance Relaxivities of Lanthanide Ions in Aqueous Solution up to 1.4 GHz/33 T.

The longitudinal and transverse nuclear magnetic resonance relaxivity dispersion (NMRD) of 1H in water induced by the paramagnetic relaxation enhancement (PRE) of dissolved lanthanide ions (Ln3+) can become very strong. Longitudinal and transverse 1H NMRD for Gd3+, Dy3+, Er3+ and Ho3+ were measured from 20 MHz/0.47 T to 1382 MHz/32.5 T, which extended previous studies by a factor of more than two in the frequency range. For the NMRD above 800 MHz, we used a resistive magnet, which exhibits reduced field homogeneity and stability in comparison to superconducting and permanent NMR magnets. These drawbacks were addressed by dedicated NMRD methods. In a comparison of NMRD measurements between 800 MHz and 950 MHz performed in both superconducting and resistive magnets, it was found that the longitudinal relaxivities were almost identical. However, the magnetic field fluctuations of the resistive magnet strongly perturbed the transverse relaxation. The longitudinal NMRDs are consistent with previous work up to 600 MHz. The transverse NMRD nearly scales with the longitudinal one with a factor close to one. The data can be interpreted within a PRE model that comprises the dipolar hyperfine interactions between the 1H and the paramagnetic ions, as well as a Curie spin contribution that is dominant at high magnetic fields for Dy3+, Er3+ and Ho3+. Our findings provide a solid methodological basis and valuable quantitative insights for future high-frequency NMRD studies, enhancing the measurement accuracy and applicability of PRE models for paramagnetic ions in aqueous solutions.

Observation of magnetic structural universality and jamming transition with NMR

Nuclear magnetic resonance (NMR) has been instrumental in deciphering the structure of proteins. Here we show that transverse NMR relaxation, through its time-dependent relaxation rate, is distinctly sensitive to the structure of complex materials or biological tissues at the mesoscopic scale, from micrometers to tens of micrometers. Based on the ideas of universality, we show analytically and numerically that the time-dependent transverse relaxation rate approaches its long-time limit in a power-law fashion, with the dynamical exponent reflecting the universality class of mesoscopic magnetic structure. The spectral line shape acquires the corresponding non-analytic power law singularity at zero frequency. We experimentally detect the change in the dynamical exponent as a result of the transition into maximally random jammed state characterized by hyperuniform correlations. The relation between relaxational dynamics and magnetic structure opens the way for noninvasive characterization of porous media, complex materials and biological tissues

DNA base order parameter determination without influence of chemical exchange.

Nuclear magnetic resonance (NMR) spectroscopy is a versatile tool used to investigate the dynamic properties of biological macromolecules and their complexes. NMR relaxation data can provide order parameters S2, which represent the mobility of bond vectors reorienting within a molecular frame. Determination of S2 parameters typically involves the use of transverse NMR relaxation rates. However, the accuracy in S2 determination can be diminished by elevation of the transverse relaxation rates through conformational or chemical exchange involving protonation/deprotonation or non-Watson-Crick base-pair states of nucleic acids. Here, we propose an approach for determination of S2 parameters without the influence of exchange processes. This approach utilizes transverse and longitudinal 13C chemical shift anisotropy (CSA) - dipole-dipole (DD) cross-correlation rates instead of 13C transverse relaxation rates. Anisotropy in rotational diffusion is taken into consideration. An application of this approach to nucleotide base CH groups of a uniformly 13C/15N-labeled DNA duplex is demonstrated.

A laboratory study of the effect of clay, silt, and sand content on low-field nuclear magnetic resonance relaxation time distributions

We have developed a laboratory nuclear magnetic resonance (NMR) study to investigate the effect of clay, silt, and sand content on the NMR relaxation time distribution. Transverse NMR relaxation times ([Formula: see text]) are determined for water-saturated unconsolidated sediment mixtures of 1%–60% kaolinite clay, 5%–85% silt-size glass beads, and 8%–94% quartz sand by mass. Nearly all of the mixtures are characterized by a unimodal [Formula: see text] distribution. When clay is present in quantities greater than 10%, the clay content dominates the response. For these samples, the mean-log relaxation times ([Formula: see text]) range from 0.03 to 0.06 s, regardless of silt or sand content. For mixtures with [Formula: see text] clay, [Formula: see text] decreases with increasing clay content. When the clay content is kept the same, [Formula: see text] decreases with increasing silt content and increases with the increasing sand content. The strong effect of the clay content on the NMR response is due to the high specific surface area of the clay and the distribution of clay throughout the samples. These results will help improve the interpretation of NMR field data in soils and unconsolidated sediments.

Estimation of the permeability of hydrocarbon reservoir samples using induced polarization and nuclear magnetic resonance methods

We have evaluated several published models using induced polarization (IP) and nuclear magnetic resonance (NMR) measurements for the estimation of permeability of hydrocarbon reservoir samples. IP and NMR measurements were made on 30 samples (clean sands and sandstones) from a Persian Gulf hydrocarbon reservoir. We assessed the applicability of a mechanistic IP-permeability model and an empirical IP-permeability model recently proposed. The mechanistic model results in a broader range of permeability estimates than those measured for sand samples, whereas the empirical model tends to overestimate the permeability of the samples that we tested. We also evaluated an NMR permeability prediction model that is based on porosity [Formula: see text] and the mean of the log transverse relaxation time ([Formula: see text]). This model provides reasonable permeability estimations for the clean sandstones that we tested but relies on calibrated parameters. We also examined an IP-NMR permeability model, which is based on the peak of the transverse relaxation time distribution, [Formula: see text] and the formation factor. This model consistently underestimates the permeability of the samples tested. We also evaluated a new model. This model estimates the permeability using the arithmetic mean of log transverse NMR relaxation time ([Formula: see text]) and diffusion coefficient of the pore fluid. Using this model, we improved estimates of permeability for sandstones and sand samples. This permeability model may offer a practical solution for geophysically derived estimates of permeability in the field, although testing on a larger database of clean granular materials is needed.

Intelligent methods for predicting nuclear magnetic resonance of porosity and permeability by conventional well-logs: a case study of Saharan field

In the well-log data processing, the principal advantage of the nuclear magnetic resonance (NMR) method is the measurement of fluid volume and pore size distribution without resorting to parameters such as rock resistivity. Preliminary processing of the well-log data allowed first to have the petrophysical parameters and then to evaluate the performances of the transverse relaxation time T 2 NMR. Petrophysical parameters such as the porosity of the formation as well as the effective permeability can be estimated without having recourse the fluid type. The well-log data of five wells were completed during the construction of intelligent models in the Saharan oil field Oued Mya Basin in order to assess the reliability of the developed models. Data processing of NMR combined with conventional well data was performed by artificial intelligence. First, the support vector regression method was applied to a sandy clay reservoir with a model based on the prediction of porosity and permeability. NMR parameters estimated using intelligent systems, i.e., fuzzy logic (FL) model, back propagation neural network (BP-NN), and support vector machine, with conventional well-log data are combined with those of NMR, resulting in a good estimation of porosity and permeability. The results obtained during the processing are then compared to the FL and NN regression models performed by the regression method during the validation stage. They show that the correlation coefficients R 2 estimated vary between 0.959 and 0.964, corresponding to the root mean square error values of 0.20 and 0.15.

Restricted lithium ion dynamics in PEO-based block copolymer electrolytes measured by high-field nuclear magnetic resonance relaxation.

The intrinsic ionic conductivity of polyethylene oxide (PEO)-based block copolymer electrolytes is often assumed to be identical to the conductivity of the PEO homopolymer. Here, we use high-field 7Li nuclear magnetic resonance (NMR) relaxation and pulsed-field-gradient (PFG) NMR diffusion measurements to probe lithium ion dynamics over nanosecond and millisecond time scales in PEO and polystyrene (PS)-b-PEO-b-PS electrolytes containing the lithium salt LiTFSI. Variable-temperature longitudinal (T1) and transverse (T2) 7Li NMR relaxation rates were acquired at three magnetic field strengths and quantitatively analyzed for the first time at such fields, enabling us to distinguish two characteristic time scales that describe fluctuations of the 7Li nuclear electric quadrupolar interaction. Fast lithium motions [up to O(ns)] are essentially identical between the two polymer electrolytes, including sub-nanosecond vibrations and local fluctuations of the coordination polyhedra between lithium and nearby oxygen atoms. However, lithium dynamics over longer time scales [O(10 ns) and greater] are slower in the block copolymer compared to the homopolymer, as manifested experimentally by their different transverse 7Li NMR relaxation rates. Restricted dynamics and altered thermodynamic behavior of PEO chains anchored near PS domains likely explain these results.

Characterization of the exhaustion profile of activated carbon in industrial rum “filters” based on TGA, TD-GC/MS, colorimetry and NMR relaxometry

Spectrophotometric measurements applied on saturated granular activated carbons have been barely explored. Although Nuclear Magnetic Resonance (NMR) relaxation studies proved to be suitable to explore pore characteristics in different porous materials, characterization of granular activated carbons used in rum production have not been addressed yet. In this work, the feasibility of using NMR relaxometry and colorimetry in order to characterize the exhaustion degree of granular activated carbon (GAC) from a target rum “filter” is evaluated. Colorimetric measurements and the transverse NMR relaxation time distribution have been correlated with the amount of adsorbed organic compounds on these GAC. Samples from eight consecutive GAC layers of the rum filter have been assessed. The exhaustion profile for the rum “filter” is correlated with the colorimetric results, the 1H NMR T2-relaxometry measurements, the TD-GC/MS chromatograms and the CHNS-O elemental analysis. The proposed methods are not only of general use in GAC characterization but open possibilities for the rum producers to improve the management and economical use of the activated carbon at industrial scale.

A textural and diagenetic assessment of the Zechstein Limestone carbonates, Poland using the transverse Nuclear Magnetic Resonance relaxometry

As a consequence of carbonate pore system ambiguity, only two basic carbonate textures, i.e. mudstone and completely contrasting grainstone have thus far been found to be separable using Nuclear Magnetic Resonance (NMR) relaxometry. Therefore, a new methodology of NMR-derived carbonate facies and diagenetic alteration recognition was prepared and experimentally launched. As many ancient carbonates have often experienced a meteoric exposure stage, this approach focuses on such conditions. Especially the paleoreef carbonate reservoirs are of the main interest of the authors. The Wielichowo Reef (western Poland), developed on an uplifted pre-Zechstein horst structure - the Wolsztyn Ridge - was chosen for the study object. The reef is representative for its region because it is characterized by both high textural and diagenetic variability, often repeatable in case of other objects present on the Wolsztyn Ridge. Consequently, twenty one Zechstein Limestone (Ca1) carbonate core samples from the chosen object were qualitatively studied using a low-field, 50 [mT] NMR spectrometer. Corresponding thin section samples were carefully investigated using both polarizing and electron microscopy, cathodoluminescence and sample staining to obtain a full overview of their petrography and enable further comparisons between NMR and the remaining data. As shown by the obtained results, various carbonate facies can be distinguished on the basis of few criteria. These include: (1) the changeability of the signal's amplitude, (2) the values of clay-bound (MCBW), capillary (BVI) and freely moving (FFI) water, and (3) – the width of the main T2 peak, defined as the first peak occurring directly after the BVI, whose average amplitude exceeds or equals at least 75% of the maximal average amplitude encountered within MCBW or BVI systems. Similarly, it seems possible to separate dissolution vugs from other pore systems. The wider the main peak, the higher the probability of finding irregularly-shaped vugs, as diameter size variances account for elevating signal's amplitude, corresponding to various relaxation times. Furthermore, fractures and increased cementation have a significant impact on final T2 distribition's appearance, as well - hence making the low-field NMR an invaluable tool in the evaluation of carbonate reservoirs influenced by the meteoric exposure.

Interaction of two magnetic resonance modes in the polar phase of superfluid 3He

We report results of low frequency nuclear magnetic resonance (NMR) experiments in the superfluid polar phase of 3He which is stabilized by a new type of "nematic" aerogel - nafen. We have found that an interaction between transverse and longitudinal NMR modes may essentially influence the spin dynamics. Theoretical formulas for NMR resonant frequencies are derived and applied for interpretation of the experimental results.

Fractal dimension of pore-space geometry of an Eocene sandstone formation

The geometry of pore structure of reservoir rock is described by the shape, size, distribution and connection of pores, and pore throats of rocks. Pore-space properties are important for the description and characterization of fluid storage and transport in reservoir rocks. We used the fractal concept to describe the geometric structure of the pores of 24 samples from an Eocene sandstone formation in China. The fractal behavior of pore volume distribution was investigated by capillary pressure curves and nuclear magnetic resonance (NMR). Additionally, the fractal dimension of the pore surface was determined based on data of the specific surface area per unit pore volume ([Formula: see text]). The comparison of fractal dimensions determined by three different methods indicates a clear differentiation into the “surface dimension” and “volume dimension.” The fractal dimension resulting from longer transverse NMR relaxation times and lower capillary pressure reflects the volume dimension of larger pores. The fractal dimension derived from the short NMR relaxation times is similar to the fractal dimension of the internal surface. The surface dimension increases with rising [Formula: see text]. The average value of surface dimension was determined to be 2.31 for the set of Eocene sandstones. This value of fractal dimension was successfully applied in a model of permeability prediction that is based on formation factor and specific surface area ([Formula: see text]).

Nuclear Magnetic Resonance Relaxivities: Investigations of Ultrahigh‐Spin Lanthanide Clusters from 10 MHz to 1.4 GHz

Paramagnetic relaxation enhancement is often explored in magnetic resonance imaging in terms of contrast agents and in biomolecular nuclear magnetic resonance (NMR) spectroscopy for structure determination. New ultrahigh-spin clusters are investigated with respect to their NMR relaxation properties. As their molecular size and therefore motional correlation times as well as their electronic properties differ significantly from those of conventional contrast agents, questions about a comprehensive characterization arise. The relaxivity was studied by field-dependent longitudinal and transverse NMR relaxometry of aqueous solutions containing Fe(III)(10)Dy(III)(10) ultrahigh-spin clusters (spin ground state 100/2). The high-field limit was extended to 32.9 T by using a 24 MW resistive magnet and an ultrahigh-frequency NMR setup. Interesting relaxation dispersions were observed; the relaxivities increase up to the highest available fields, which indicates a complex interplay of electronic and molecular correlation times.

Measurement of the true transverse nuclear magnetic resonance relaxation in the presence of field gradients

A measure of the nuclear spin transverse relaxation time T2, as determined using the nuclear magnetic resonance Carr-Purcell Meiboom-Gill (CPMG) experiment, provides unique information characterizing the microstructure of porous media which are themselves ubiquitous across fields of petrophysics, biophysics, and chemical engineering. However, the CPMG measurement is sensitive to diffusion in large magnetic field gradients. Under such conditions an effective relaxation time T2,eff is observed instead, described by a combination of relaxation and diffusion exponents. The relaxation exponent always varies as nte (where n is the number, and te is the temporal separation, of spin echoes). The diffusion exponent varies as nte (k), where 1 < k ≤ 3, although the exact analytic form is often unknown. Here we present a general approach to separating the influence of relaxation and diffusion by utilizing a composite diffusion exponent. Any T2,eff component with a power of k > 1 is removed to provide a measure of the true T2 relaxation time distribution from CPMG data acquired in the presence of a strong background gradient. We apply the technique to discriminate between the effects of relaxation and diffusion in porous media using catalysts and rocks as examples. The method is generally applicable to any CPMG measurements conducted in the presence of a static magnetic field gradient.

Microscale Simulations of NMR Relaxation in Porous Media Considering Internal Field Gradients

Longitudinal and transverse nuclear magnetic resonance (NMR) relaxation signatures in porous rock were simulated on the microscale to examine and quantify how physical hydrologic parameters, such as rock‐surface properties and pore sizes, affect longitudinal and transverse NMR signals of real, complex media. Parameters studied were: magnetic field strength, rock susceptibility, pore coupling, and surface reactivity. Using the finite element method (FEM), simulations of the spatial‐ and time‐dependent magnetization evolution in arbitrary pore geometries, diffusion regimes, and heterogeneous distributions of rock surface properties, i.e., surface relaxivity, were compiled using an adapted generic diffusion model coupled with magnetic gradient field calculations. The numerical simulations were validated using analytical solutions that are available for simple pore geometries. We observed a pore‐size‐dependent ratio of transverse T2 and longitudinal T1 relaxation times, and thus a pore‐size‐related and rock‐susceptibility‐dependent effective transverse surface relaxivity was deduced. This can be used to improve estimates of pore sizes and thus of permeability from transverse NMR relaxometry measurements. Simulations of connected pore systems showed significant influences of interpore coupling at hydrologically relevant pore sizes, e.g., fine sands. Depending on the dominant diffusion regime, the typically heterogeneous distribution of surface relaxivities in rocks and sediments, i.e., geological noise, can lead to a significant underestimation of derived pore sizes and thus of permeability.

Scaling of transverse nuclear magnetic relaxation due to magnetic nanoparticle aggregation

The aggregation of superparamagnetic iron oxide (SPIO) nanoparticles decreases the transverse nuclear magnetic resonance (NMR) relaxation time T2CP of adjacent water molecules measured by a Carr-Purcell-Meiboom-Gill (CPMG) pulse-echo sequence. This effect is commonly used to measure the concentrations of a variety of small molecules. We perform extensive Monte Carlo simulations of water diffusing around SPIO nanoparticle aggregates to determine the relationship between T2CP and details of the aggregate. We find that in the motional averaging regime T2CP scales as a power law with the number N of nanoparticles in an aggregate. The specific scaling is dependent on the fractal dimension d of the aggregates. We find T2CP∝N-0.44 for aggregates with d = 2.2, a value typical of diffusion limited aggregation. We also find that in two-nanoparticle systems, T2CP is strongly dependent on the orientation of the two nanoparticles relative to the external magnetic field, which implies that it may be possible to sense the orientation of a two-nanoparticle aggregate. To optimize the sensitivity of SPIO nanoparticle sensors, we propose that it is best to have aggregates with few nanoparticles, close together, measured with long pulse-echo times.

Numerically Calculated NMR Response from Different Vortex Distributions in Superfluid 3He-B

In static equilibrium situations, the quantized vorticity in a sample of superfluid 3He-B in a cylindrical container rotating around its symmetry axis is distributed in the form of rectilinear lines. Because of the high critical velocity of vortex creation, rotating states with any number of vortices ranging from zero up to the equilibrium number (corresponding to minimum free energy in the rotating system) can be realized. The different vortex states can be identified through the orienting effect of the vortices on the B-phase order parameter, and the resulting frequency shift of continuous-wave transverse nuclear magnetic resonance (NMR). Recently, however, considerable activity has been devoted to vortex studies concerning dynamic situations where the vortex distributions do not consist only of rectilinear lines. Such investigations include those of vortex multiplication, superfluid turbulence, and the propagation of vortices in a long container. In this work, NMR response from different vortex states in 3He-B is discussed in the framework of hydrostatic theory. In particular, we show how this description can be employed to identify the recently discovered state of helically twisted vortices.

The Effects of Crosslinker and Monomer to the Polymerization of Polymethacrylamide Gel Dosimeters by Direct and Indirect Methods

Radiation-induced polymerization in Polymethacrylamide Gels (PMAAGs) potentially used for 3D dose verification in radiotherapy has been studied using both Raman spectroscopy and Nuclear Magnetic Resonance (NMR) method. The dosimeters are composed of aqueous Methacrylamide (MAA) monomer and N, N’ methyelene-bis-acrylamide (BIS) crosslinker at various concentrations from 2 to 6% (w/w) and gelatin at 6% (w/w). The dosimeters were irradiated to doses up to 30 Gy using 60Co teletherapy ?-ray source at a constant dose rate. The formation of the polymer increases with increasing dose and was followed directly by Raman spectroscopic measurement for CH3 stretching mode assigned to polymethacrylamide and indirectly by the transverse spin-echo pulse NMR R2 relaxation rate of water protons within the polymer gel network. The half dose D1/2 values of both direct and indirect methods were used to evaluate the effects of initial concentrations of monomer and crosslinker to the dose required to produce 50% of the polymer in PMAAGs. The PMAAGs containing more crosslinker than monomer show larger D1/2 values, indicating that the crosslinker has a larger effect on the increase in dose required to produce 50% of the polymer. The D1/2 value of the direct method is consistently higher than that of the indirect method, indicating that the indirect method is more sensitive to the dose response, but fundamentally does not measure the amount of polymethacrylamide formed. There is a correlation between D1/2 value and concentrations of monomer and crosslinker. The correlation factor, kC of the crosslinker is always greater than kM of monomer, for both the direct and indirect methods, suggesting the crosslinker reacts more efficiently than monomer to produce 50% of the polymer of polymethacrylamide.

Graded reduction of cerebral blood flow in rat as detected by the nuclear magnetic resonance relaxation time T2: a theoretical and experimental approach.

The ability of transverse nuclear magnetic resonance relaxation time, T2, to reveal acutely reduced CBF was assessed using magnetic resonance imaging (MRI). Graded reduction of CBF was produced in rats using a modification of Pulsinelli's four-vessel occlusion model. The CBF in cerebral cortex was quantified using the hydrogen clearance method, and both T2 and the trace of the diffusion tensor (Dav = 1/3TraceD) in the adjacent cortical tissue were determined as a function of reduced CBF at 4.7 T. A previously published theory, interrelating cerebral hemodynamic parameters, hemoglobin, and oxygen metabolism with T2, was used to estimate the effects of reduced CBF on cerebral T2. The MRI data show that T2 reduces in a U-shape manner as a function of CBF, reaching a level that is 2.5 to 2.8 milliseconds (5% to 6%) below the control value at CBF, between 15% and 60% of normal. This reduction could be estimated by the theory using the literature values of cerebral blood volume, oxygen extraction ratio, and precapillary oxygen extraction during compromised CBF. Dav dropped with two apparent flow thresholds, so that a small 11% to 17% reduction occurred between CBF values of 16% to 45% of normal, followed by a precipitous collapse by more than 20% at CBF below 15% of normal. The current data show that T2 can be used as an indicator of acute hypoperfusion because of its ability to indicate blood oxygenation level-dependent phenomena on reduced CBF.

Quantum diffusion and tunneling in the solid hydrogens (a short review)

The first observations 30 years ago of molecular clustering via quantum diffusion in solid H2 in nuclear magnetic resonance (NMR) and pressure experiments are described. A previous review on quantum diffusion and tunneling up to 1986 is updated to reflect progress in the last ten years. In particular I review the effect of clustering on heat capacity in solid D2 and on the thermal conductivity in solid H2. The configurational relaxation time observed in D2 at 1.75 K is found to scale with that in H2 at the same temperature in terms of the predictions of ortho–para resonant conversion-induced hopping. The relaxation times measured simultaneously on the same sample in NMR and conductivity experiments reflect different configurational processes. The theory of molecular hopping and pairing in solid H2 is outlined and compared with experiments. The tunneling frequency of HD in solid H2 deduced from transverse and longitudinal NMR relaxation experiments between 0.03 and 14 K is discussed. The hopping of ortho-H2, invoked as a mechanism in the enhanced ortho–para conversion in presence of O2 impurities, is mentioned. Finally, recent tunneling results for H, D and H2− anions in solid H2 during the studies of low temperature reaction dynamics are also briefly described. In the Appendix, the hopping frequency determination in HD from NMR transverse relaxation time measurements is reviewed.