Nuclear Spin-spin Relaxation Times Research Articles

NMR studies of the dynamics of HD adsorbed in MCM-41

Abstract The motion of hydrogen deuteride molecules adsorbed on MCM-41 at monolayer coverages has been explored using NMR techniques. The nuclear spin-spin and nuclear spin-lattice relaxation times show an abrupt change at 8.8 K, consistent with the formation of small clusters below that temperature. The molecular tunneling times deduced from the NMR measurements are consistent with the values determined by neutron scattering [Coulomb et al., Micro Meso Matls 101,270 (2007)].

Effect of autoclaving on the mechanical properties and structure of the giant squid hydrolysate‐polysaccharide gel

Fish hydrolysates are an attractive option for preparing composite gel foods. However, not much is known regarding their gel properties. Here, we investigated the effect of the autoclaving treatment (121°C, 10 min) on the microstructure and properties of the giant squid hydrolysate-konjac glucomannan-κ-carrageenan-locust bean gum gel (GSH-P gel). The nuclear magnetic resonance proton spin-spin relaxation time (T2 ) measurements indicated that autoclaving led to stronger water-binding ability of the GSH-P gel. The rheological measurements indicated that autoclaving led to significantly higher viscoelastic modulus and gel strength. The results of confocal laser scanning microscopy and small-angle X-ray scattering indicated that the phase separation of polysaccharides and proteins/peptides was enhanced by autoclaving, and the polysaccharides swelled better, resulting in less, but ordered, network structures. Autoclaving had a similar, but insignificant, positive effect on the polysaccharide (P) gel. Thus, GSH seems to play an important role in the process of polysaccharide gelation. This study shows that autoclaving can alter the structure and improve the properties of the GSH-P gel.

Probing the dynamics of 3He atoms adsorbed on MCM-41 with pulsed NMR

We report measurements of the nuclear spin-spin and spin-lattice relaxation times for 3He adsorbed on MCM-41 for temperatures 0.08 < T < 1.2 K. Deviations from Curie behavior are observed at low temperatures. The relaxation times exhibit a two-component behavior representing the differing dynamics of the mobile quasi-free molecules in the center of the tubes compared to the adsorbed layer on the walls. The amplitudes of the two components provide an accurate measure of the number of fluid-like molecules traveling in the center of the nanotubes.

Gelling properties of myosin as affected by L-lysine and L-arginine by changing the main molecular forces and microstructure

ABSTRACTThis paper investigated the effects of l-lysine (Lys) and l-arginine (Arg) on the water-holding capacity (WHC) and hardness of myosin gel as well as the mechanism of these effects. The results showed that Lys, Arg, and KOH increased the WHC but decreased the hardness in all cases. At pH 6.32, the WHC increased in the order control < KOH < Lys ≈ Arg, while the hardness decreased in the order control > KOH > Lys > Arg. Lys shortened low field nuclear magnetic resonance spin-spin relaxation times (T2), while Arg and KOH slightly affected T2. Lys, Arg, and KOH had different influences on the molecular forces in myosin gels and the distribution of myosin size. Lys formed a gel with porous clusters, while Arg generated a gel with fine caves. Therefore, both Lys and Arg changed the microstructure of myosin gel by changing the distribution of the myosin size as well as the molecular forces that form and/or maintain myosin gel, ultimately contributing to the differences in the WHC, hardness, and T2.

Application of Nuclear Magnetic Resonance to Detect Toxigenic Clostridium difficile from Stool Specimens: A Proof of Concept

We evaluated the performance of an early prototype core molecular mirroring nuclear magnetic resonance detection platform (Mentor-100) to detect toxigenic Clostridium difficile from stool. This technology uses customized nanoparticles bound to target specific oligonucleotide probes that form binaries in the presence of nucleic acid from the target microorganism. Liquid patient stool specimens were seeded with C. difficile or other Clostridium species to determine the analytical sensitivity and specificity. Samples underwent nucleic acid extraction and target amplification with probes conjugated with iron nanoparticles. Signal from nuclear magnetic resonance spin-spin relaxation time was measured to detect the presence or absence of toxigenic C. difficile. The limit of detection was <180 colony forming units per reaction of toxigenic C. difficile. No cross-reactivity was observed with nontoxigenic C. difficile, Clostridium sordellii, Clostridium perfringens, Bacillus subtilis, or Paenibacillus polymyxa at 108 colony forming units/mL. Correlation studies using frozen stool samples yielded a sensitivity of 88.4% (61 of 69) and a specificity of 87.0% (40 of 46) as compared with a commercial PCR assay for C. difficile. The area under the curve in the receiver operating characteristic curve analysis was 0.922. The prototype molecular mirroring platform showed promising performance for pathogen detection from clinical specimens. Theplatform design has the potential to offer a novel, low-cost alternative to currently available nucleic acid-based tests.

NMR studies of methane and hydrogen in microporous materials

We review the results of nuclear magnetic resonance studies of the molecular dynamics of the quantum gases HD and CH4 adsorbed in the cages of microporous structures. Measurements of the variation of the nuclear spin-lattice and nuclear spin-spin relaxation times with temperature provide detailed information about the translational and rotational dynamics of the adsorbed molecules over a wide temperature range.

1H-NMR Study of Spin-1/2 Triple-chain Magnet Cu3(OH)4MoO4

We have studied a natural mineral Cu3(OH)4MoO4 (mineral name: szenicsite), which is characterized as S = 1/2 triple-chain antiferromagnet, by measurements of the magnetic susceptibility χ and 1H-NMR in order to determine the low temperature magnetic state from a microscopic viewpoint. χ(T) was fitted fairly well by the sum of isolated uniform antiferromagnetic chains and a small amount of paramagnetic impurities. The width of 1H-NMR spectrum increased with decreasing temperature, suggesting inhomogeneous broadening due to impurity moments. The shift of the spectrum showed a maximum at approximately 70K and continuously decreased with decreasing temperature to the lowest temperature of 1.5K. 1D nature of this compound was also suggested from temperature and field dependences of the nuclear spin-lattice relaxation time T1. We also found that the nuclear spin-spin relaxation time T2 depended on the RF pulse power, which suggests that a relaxation process among proton spins contributes significantly to the T2. No magnetic long-range ordering was found. These results suggest that the intrinsic magnetic properties of Cu3(OH)4MoO4 in the temperature range down to 1.5K are close to those of uniform antiferromagnetic chains without a spin gap.

Ultrafast Two‐Dimensional NMR Relaxometry for Investigating Molecular Processes in Real Time

Nuclear spin-lattice (T1) and spin-spin (T2) relaxation times provide versatile information about the dynamics and structure of substances, such as proteins, polymers, porous media, and so forth. Multidimensional experiments increase the information content and resolution of NMR relaxometry, but they also multiply the measurement time. To overcome this issue, we present an efficient strategy for a single-scan measurement of a 2D T1-T2 correlation map. The method shortens the experimental time by one to three orders of magnitude as compared to the conventional method, offering an unprecedented opportunity to study molecular processes in real-time. We demonstrate that, despite the tremendous speed-up, the T1-T2 correlation maps determined by the single-scan method are in good agreement with the maps measured by the conventional method. The concept of the single-scan T1-T2 correlation experiment is applicable to a broad range of other multidimensional relaxation and diffusion experiments.

Nuclear magnetic resonance relaxometry of water in two and quasi-two dimensions

Molecular dynamics (MD) and Monte Carlo (MC) methods are used to determine the spin-pair correlation function G(*)(t) for the diffusion of bulk water in three dimensions (3D) and pore water in two dimensions (2D) and quasi-two dimensions (Q2D). The correlation function is required for the determination of the nuclear magnetic resonance spin-lattice and spin-spin relaxation times T(1) and T(2). It is shown that the analytic form of the powder-average correlation function, introduced by Sholl [Sholl, J. Phys. C: Solid State Phys. 7, 3378 (1974)] for the diffusion of spins on a 3D lattice, is of general validity. An analytic expression for G(*)(t) for a uniform spin fluid is derived in 2D. An analytic expression for the long-time behavior of G(*)(t) is derived for spins diffusing on 3D, 2D, and Q2D lattices. An analytic correction term, which accounts for spin pairs outside the scope of the numerical simulations, is derived for 3D and 2D and shown to improve the accuracy of the simulations. The contributions to T(1) due to translational and rotational motion obtained from the MD simulation of bulk water at 300 K are 7.4 s and 10±1 s, respectively, at 150 MHz, leading to an overall time of 4.3±0.4 s compared to the experimental value of 3.8 s. In Q2D systems, in which water is confined by alpha-quartz surfaces to thicknesses of 1-5 nm, T(1) for both translational and rotational relaxation is reduced due to the orientation and adsorption of spins at the surfaces. A method of parametrizing the MC lattice-diffusion simulations in 3D, 2D, and Q2D systems is presented. MC results for G(*)(t) for 3D and 2D systems are found to be consistent with an analytic uniform fluid model for t~/>40 ps. The value of TT(1) for translational diffusion obtained from the MC simulation of bulk water is found to be 4.8 s at 15 MHz. G(*)(t) obtained from MC simulations of Q2D systems, where water is confined by hard walls, is found to execute a distinct transition from 3D to 2D behavior. The T(1) is found to be similar to the 3D bulk water result at all pore thicknesses.

NMR investigation of the low-temperature dynamics of solid4He doped with3He impurities

The lattice dynamics of solid ${}^{4}$He has been explored using pulsed NMR methods to study the motion of ${}^{3}$He impurities in the temperature range (0.05--0.20 K) where experiments have revealed anomalies attributed to superflow or unexpected viscoelastic properties of the solid ${}^{4}$He lattice. We report the results of measurements of the nuclear spin-lattice and spin-spin relaxation times that measure the fluctuation spectrum at high and low frequencies, respectively, of the ${}^{3}$He motion that results from quantum tunneling in the ${}^{4}$He matrix. The measurements were made for ${}^{3}$He concentrations $16&lt;{x}_{3}&lt;2000$ ppm. For ${}^{3}$He concentrations ${x}_{3}=16$ and 24 ppm, large changes are observed for both the spin-lattice relaxation time ${T}_{1}$ and the spin-spin relaxation time ${T}_{2}$ at temperatures close to those for which the anomalies are observed in measurements of torsional oscillator responses and the shear modulus. These changes in the NMR relaxation rates were not observed for higher ${}^{3}$He concentrations.

Nuclear Spin Relaxation of Very Dilute 3He impurities in Solid 4He

We report measurements of the nuclear spin-lattice and spin-spin relaxation times of very dilute 3He in solid 4He in the temperature range 0.01 ≤ T ≤ 0.5 K for densities where anomalies have been observed in torsional oscillator and shear modulus measurements. We compare the results with the values of the relaxation times reported by other observers for higher concentrations and the theory of Landesman that takes into account the elastic properties of the 4He lattice. A sharp increase in the magnitude of the nuclear spin-lattice relaxation times compared to the the classical Landesman theory is observed close to the temperatures where the torsional and shear modulus anomalies are observed. The NMR results suggest that the tunneling of 3He impurities in the atomic-scale elastic distortion is affected by the same processes that give rise to the macroscopic elastic dissipation anomalies.

NMR Study of HD Adsorbed in a Z-type Metal-Organic Framework

We report the results of measurements of the nuclear spin-lattice and spin-spin relaxation rates of hydrogen deuteride trapped in the mesoporous cages of a metal organic framework (MOF) for temperatures 2.2 < T < 50 K There is considerable interest in the use of this class of materials for hydrogen storage because of the high density of adsorption. NMR studies can provide important information about the molecular interactions and dynamics inside the cages of the MOF structure. Samples were studied with filling factors of 0.1 and 1.0 molecules per cage as determined by the adsorption isotherm at 77 K The results show strong peaks in the relaxation times at several well defined temperatures that are very different from the adsorption energy levels. The origin of these peaks is discussed in terms of the quantization of the translational degrees of freedom of the molecules inside the cages and the associated discrete energy levels. Measurements of the nuclear spin-spin relaxation times also provide an important measure of the diffusivity of hydrogen through the MOF structure which is a critical parameter for the use of MOFs for storage and transport.

Assessment of Disease Severity in Late Infantile Neuronal Ceroid Lipofuscinosis Using Multiparametric MR Imaging

LINCL is a uniformly fatal lysosomal storage disease resulting from mutations in the CLN2 gene that encodes for tripeptidyl peptidase 1, a lysosomal enzyme necessary for the degradation of products of cellular metabolism. With the goal of developing quantitative noninvasive imaging biomarkers sensitive to disease progression, we evaluated a 5-component MR imaging metric and tested its correlation with a clinically derived disease-severity score. MR imaging parameters were measured across the brain, including quantitative measures of the ADC, FA, nuclear spin-spin relaxation times (T2), volume percentage of CSF (%CSF), and NAA/Cr ratios. Thirty MR imaging datasets were prospectively acquired from 23 subjects with LINCL (2.5-8.4 years of age; 8 male/15 female). Whole-brain histograms were created, and the mode and mean values of the histograms were used to characterize disease severity. Correlation of single MR imaging parameters against the clinical disease-severity scale yielded linear regressions with R2 ranging from 0.25 to 0.70. Combinations of the 5 biomarkers were evaluated by using PCA. The best combination included ADC, %CSF, and NAA/Cr (R2=0.76, P<.001). The multiparametric disease-severity score obtained from the combination of ADC, %CSF, and NAA/Cr whole-brain MR imaging techniques provided a robust measure of disease severity, which may be useful in clinical therapeutic trials of LINCL in which an objective assessment of therapeutic response is desired.

The Use of Solid State NMR to Evaluate EVA/Silica FILMs

Nanocomposites based on ethylene-co-vinyl acetate (EVA) and silica oxide (SiO2), with nanometric size (40nm) were prepared by solution process, employing chloroform as solvent. The nanocomposites were mainly characterized by solid state nuclear magnetic resonance spectroscopy (NMR). From the methodology employed polymer matrix was evaluated by the determination of proton nuclear spin-lattice relaxation time (T1H) and spin-spin relaxation time (T2H) employing low field NMR spectrometer and also applying carbon-13 (13C) solid-state NMR techniques and proton spin-lattice relaxation time in the rotating frame (T1pH) by high field NMR. The nanoparticle, silica oxide, was analyzed by silicon-29 (29Si) NMR MAS spectrum. The evaluation of relaxation time showed an increase in the proton spin-lattice relaxation time, because of silicon nucleus interaction with polymer chains promoting an increase in the sample rigidity, which is a result of good silica oxide dispersion in the polymeric matrix. The nanomaterial with 5% of SiO2presented good dispersion of silica oxide in the polymeric matrix, because of the formation of strong intermolecular interaction.

On the thermodynamic equilibrium in the 3He-aerogel system at low temperatures

At the present work we propose a new method for studying the processes of thermodynamic equilibrium setting in the adsorbed 3He film in a porous media. By this method we have studied the thermalization of the adsorbed 3He on the silica aerogel surface at the temperature 1.5 K. The process of the thermodynamic equilibrium setting was controlled by measuring of the pressure in the experimental cell, the amplitude of the NMR signal and the time of the nuclear spin-spin and spin-lattice relaxation times of an adsorbed 3He. The thermodynamic equilibrium setting in the system "adsorbed helium-3 - aerogel" has the characteristic time 26 min.

The influence of Fe, Cu, SiO2, TiO2, and Al2O3 nanoparticles in aqueous solution on proton relaxation times

Measurements of proton nuclear spin-spin and spin-lattice relaxation times are applied for determining the concentration of solid-phase nanoparticles in nanofluids. This approach is tested for metal oxides SiO2, TiO2, Al2O3 and metal-carbon nanoparticles of 3d-metals Fe and Cu. It is shown that the sensitivity of the method for determining concentrations of 3d-metals is much higher than for oxides (by 2–4 orders of magnitude). It is revealed that measurement of the proton spin-spin relaxation time allows one to determine the concentration of Cu nanoparticles to 0.0001 mg/ml and that of Fe nanoparticles to 0.00001 mg/ml.

Dynamics of HD Molecules Trapped in Cages of Zeolite

There is considerable interest in the use of mesoporous structures (e.g. zeolites and metal organic frameworks) for hydrogen storage but little is known about the molecular interactions and the dynamics of molecules inside the cages of these structures. In order to determine these properties we have measured the nuclear magnetic spin-lattice and spin-spin relaxation times of HD molecules trapped in the α-cages of zeolite 13X for a wide temperature range 1.6 12 K, corresponding to the onset of intercage diffusion.

Magnetic quantum tunneling inFe8with excited nuclei

We investigate the effect of dynamic nuclear spin fluctuation on quantum tunneling of the magnetization (QTM) in the molecular magnet Fe8 by increasing the nuclei temperature using radio frequency (RF) pulses before the hysteresis loop measurements. The RF pulses do not change the electrons spin temperature. Independently we show that the nuclear spin-spin relaxation time T2 has strong temperature dependence. Nevertheless, we found no effect of the nuclear spin temperature on the tunneling probability. This suggests that in our experimental conditions only the hyperfine field strength is relevant for QTM. We demonstrate theoretically how this can occur.

Nuclear quadrupole spin-lattice relaxation in Bi4Ge3O12 single crystals doped with atoms of d or f elements. Crystal field effects in compounds exhibiting anomalous magnetic properties

The nuclear quadrupole spin-lattice relaxation was studied in the range 4.2–300 K for single crystals of Bi4Ge3O12 doped with minor amounts (the tenth fractions of mol%) of paramagnetic atoms of Cr, Nd, and Gd. Unusual spin dynamic features were recently found for these crystals at room temperature: a dramatic (up to 8-fold) increase in the effective nuclear quadrupole spin-spin relaxation time T2* occurred upon doping the pure Bi4Ge3O12 sample. Unlike T2*, the effective spin-lattice relaxation time T1* at room temperature differs insignificantly for both doped and pure samples. But at lower temperatures, the samples exhibit considerably different behavior of the spin-lattice relaxation with temperature, which is caused by different contributions to the relaxation process of the dopant paramagnetic atoms. The distinctive maximum in the temperature dependence of the spin-lattice relaxation time for the Nd-doped crystal is shown to result from the crystal electric field effects.

Measurements of the nuclear spin-spin relaxation times for commensurate 3He-Ne films adsorbed on hexagonal boron nitride

Measurements of the 3He nuclear spin-spin relaxation time, T2, have been carried out for commensurate layers of 3He-Ne mixtures adsorbed on hexagonal boron nitride for temperatures 0.2< T <10 K. A temperature independent relaxation is observed at low temperatures and is interpreted in terms of the effective exchange frequencies for 3He particle exchange on the surface. The results show a strong dependence on the fraction of neon in the adsorbed layer. This variation is discussed in terms of a multiple spin exchange model for 3He in a monolayer. The contributions to T2 from different components of the exchange, 2-spin exchange (J2), 3-spin exchange (J3), 4-spin exchange (J4) and higher exchange permutations depend on the 3He coverage and thus permit the separation of the amplitudes of the different exchange rates, and in particular allow one to deduce the relative strengths of 2-atom and 3-atom exchange where other methods are sensitive only to the effective two-particle term Jeff = J2 - 2J3.