Nuclear Magnetic Resonance Spin-spin Relaxation Research Articles

Finite Element Simulation of NMR spectra and spin-spin relaxation of confined fluids under intense magnetic field gradients

Magnetic field gradients, generated as the magnetic response of solids and liquids to an applied field, directly affect the lineshapes and spin-spin relaxation time (T2) in Nuclear Magnetic Resonance (NMR) experiments and, therefore, the interpretation of fluid content in porous rocks. This paper presents a numerical study of pulse NMR spectra and T2 relaxation of fluids under realistic magnetic field gradients using the software COMSOL. Two physics sections are coupled: first, the internal magnetic field gradient is calculated in the whole system, comprising the solid matrix and a fluid mixture of brine and oil inside. Then, in the second, the NMR signal of the liquids, the Free Induction Decay (FID), is obtained by solving the Bloch–Torrey–MacConnell equations over the pore volume. The calculation of the NMR spectrum follows from the FID Fourier Transform (FFT). For the T2 calculations, a CPMG sequence is built by concatenating different studies. The obtained T2 reproduces the bulk value of the relaxation time, the dependence on the pore radii, and the relaxivity value correctly. Different magnetic properties, coupling parameters, pore sizes, and geometries are considered.

The effect of ultrasound treatment on the interaction of brine with pork meat proteins.

The objective of the study is to elucidate the effect of ultrasound treated salt solution on curing of pork meat. The interactions of salt (NaCl) solutions of 3 and 25% with the proteins of pork meat are studied. High intensity ultrasound operating at 20 kHz was used. The differential scanning calorimetry (DSC), NMR spin-spin relaxation time, unfrozen water and water diffusion coefficient measurements were carried out in meat cured with ultrasound treated and untreated salt solutions. The effect of ultrasonication was most evident from measured spin-spin relaxation times T21, the rate of chemical exchange of water protons k and the amount of unfrozen water Wunf in the meat. The measured diffusion coefficient of water Dw in meat cured with ultrasound treated and control salt solution did not show significant difference. The nuclear magnetic resonance (NMR) relaxation data, differential scanning calorimetry (DSC) and the diffusion coefficient data reliably show that the possible action of ultrasound to salt solution was manifested on the first 2 days of the experiment with a 3% salt solution.

Structural and magnetic properties of a new cubic spinel LiRhMnO4

We report the structural and magnetic properties of a new system LiRhMnO$_{4}$ (LRMO) through x-ray diffraction, bulk magnetization, heat capacity and $^{7}$Li nuclear magnetic resonance (NMR) measurements. LRMO crystallizes in the cubic space group $\mathit{Fd}$$\bar{3}$$\mathit{m}$. From the DC susceptibility data, we obtained the Curie-Weiss temperature $\mathrm{\theta}_{\mathrm{CW}}$ = -26 K and Curie constant $\mathit{C}$ = 1.79 Kcm$^{3}$/mol suggesting antiferromagnetic correlations among the magnetic Mn$^{4+}$ ions with an effective spin $\mathit{S}$ = $\frac{3}{2}$. At $\mathit{H}$ = 50 Oe, the field cooled and zero-field cooled magnetizations bifurcate at a freezing temperature, $T_{f}$ = 4.45 K, which yields the frustration parameter $\mathit{f=\frac{\mid\theta_{CW}\mid}{T_{f}}}>$5. AC susceptibility, shows a cusp-like peak at around $T_{f}$, with the peak position shifting as a function of the driving frequency, confirming a spin-glass-like transition in LRMO. LRMO also shows typical spin-glass characteristics such as memory effect, aging effect and relaxation. In the heat capacity, there is no sharp anomaly down to 2 K indicative of long-range ordering. The field sweep $^{7}$Li NMR spectra show broadening with decreasing temperature without any spectral line shift. The $^{7}$Li NMR spin-lattice and spin-spin relaxation rates also show anomalies due to spin freezing near $T_{f}$.

Improving the Colloidal Stability of Temperature-Sensitive Poly(N-isopropylacrylamide) Solutions Using Low Molecular Weight Hydrophobic Additives.

Poly(N-isopropylacrylamide) (PNIPAM) is an important polymer with stimuli-responsive properties, making it suitable for various uses. Phase behavior of the temperature-sensitive PNIPAM polymer in the presence of four low-molecular weight additives tert-butylamine (t-BuAM), tert-butyl alcohol (t-BuOH), tert-butyl methyl ether (t-BuME), and tert-butyl methyl ketone (t-BuMK) was studied in water (D2O) using high-resolution nuclear magnetic resonance (NMR) spectroscopy and dynamic light scattering. Phase separation was thermodynamically modeled as a two-state process which resulted in a simple curve which can be used for fitting of NMR data and obtaining all important thermodynamic parameters using simple formulas presented in this paper. The model is based on a modified van’t Hoff equation. Phase separation temperatures Tp and thermodynamic parameters (enthalpy and entropy change) connected with the phase separation of PNIPAM were obtained using this method. It was determined that Tp is dependent on additives in the following order: Tp(t-BuAM) > Tp(t-BuOH) > Tp(t-BuME) > Tp(t-BuMK). Also, either increasing the additive concentration or increasing pKa of the additive leads to depression of Tp. Time-resolved 1H NMR spin–spin relaxation experiments (T2) performed above the phase separation temperature of PNIPAM revealed high colloidal stability of the phase-separated polymer induced by the additives (relative to the neat PNIPAM/D2O system). Small quantities of selected suitable additives can be used to optimize the properties of PNIPAM preparations including their phase separation temperatures, colloidal stabilities, and morphologies, thus improving the prospects for the application.

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.

Effect of hydration of microparticulated whey protein ingredients on their gelling behaviour in a non-fat milk system

Two types of microparticulated whey protein ingredients with different particle characteristics were added to a non-fat milk system and allowed to hydrate for different periods of time prior to heat treatment. Differences during acidification of the milk systems were investigated by rheology and 1H nuclear magnetic resonance spin-spin relaxation. The amounts of more or less mobilised water were shown to differ depending on the type of microparticulated whey protein. Large protein microparticles did not actively participate in gel network formation and showed an increased fraction of more mobilised water, and thus higher syneresis upon storage. An enhanced surface reactivity was shown in small microparticles which may also be related to the increased interaction potential of the native whey proteins present.

Comparison of spin dynamics and magnetic properties in antiferromagnetic closed and open molecular Cr-based rings

We present magnetization and 1H nuclear magnetic resonance (NMR) measurements performed in both closed Cr8 and open Cr8Zn antiferromagnetic molecular rings in the temperature range 1.65 < T < 300 K at different external magnetic fields. The magnetization measurements on Cr8Zn are consistent with a small decrease of the exchange constant JCr-Cr and a much smaller gap between the singlet ground state and the first magnetic excited state when compared with the same properties of the closed ring Cr8, in agreement with previous inelastic neutron scattering results. The temperature dependence of the 1H NMR nuclear spin lattice relaxation rate (NSLR), 1/T1(T), was found to be similar in both open and closed rings with a magnetic field dependent peak centered at a temperature of the order of the corresponding exchange constant JCr-Cr. Such main peak in the NSLR could be fitted with a single correlation frequency ωc1 as in most molecular magnets. At low temperature T < 4 K, a new feature not observed in previous NMR measurements on antiferromagnetic rings and consisting in a smaller peak of 1/T1(T) which is well resolved only in Cr8Zn, was singled out. This low-T peak indicates the presence of a second correlation frequency ωc2 of the magnetization, found to be quite different between the two rings and thus possibly reflecting the different low temperature level structure associated with the different spin topology. The presence of ωc2 is confirmed by the NMR spin-spin relaxation rate enhancement, which generates a two-steps wipe-out effect of the NMR signal intensity.

Effects of Oxidation on Water Distribution and Physicochemical Properties of Porcine Myofibrillar Protein Gel

The effects of hydroxyl radicals induced oxidation on water distribution of porcine myofibrillar protein (MP) gels were investigated using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI), and relationship between MP gel properties and water distribution was analyzed with Pearson’s correlation. Results of NMR spin-spin relaxation time (T2) and MRI suggested that, comparing with unoxidized MP gel, the population of immobile water of gel (P22) decreased by 18.81 %, while that of free water (P23) increased by 85.56 %, and grey scale value decreased by 18.52 %, after being oxidized with 20 mM H2O2, respectively. Images of scanning electron microscope (SEM) showed the highest degree of oxidation led to the most coarse and porous gel-network. Gel properties including WHC, whiteness and strength of MP gels decreased by 14.65 %, 2.83 % and 52.74 % after being oxidized with 20 mM H2O2 (p < 0.05), respectively. Pearson’s correlation analysis showed oxidation, gel-properties and NMR results were highly correlated (p < 0.05). Therefore, we hypothesized that hydroxyl radicals induced oxidation resulted in immobile water shifting to free water partly, thus reduced the abundance of water and gel properties of gels.

Nuclear Magnetic Resonance (NMR) Characterization of a Polymerized Ionic Liquid Electrolyte Material

ABSTRACTSolid electrolyte materials have the potential to improve performance and safety characteristics of lithium-ion batteries by replacing conventional solvent-based electrolytes. A candidate solid polymer electrolyte, AMLi/PEGDM, has been synthesized by crosslinking an anionic monomer AMLi, with poly(ethylene glycol) dimethacrylate. The main goal of the synthesis is to produce a single-ion conducting polymer network where lithium cations can move freely and fluorinated anions are immobilized as part of the polymer network. A comprehensive characterization of anion and cation mobility in the resulting material is therefore required. Using pulsed-field gradient nuclear magnetic resonance (PFG-NMR), we are able to measure and quantify the individual diffusion coefficients of mobile species in the material (19F and 7Li) and confirm the extent to which the fluorinated anionic component is immobilized. We have characterized dry (σ~3.0 x10-7 S/cm at 30°C) and propylene carbonate (PC) saturated gel (σ~1.0x10-4 S/cm at 30°C) samples. Experimental results include NMR spin-spin and spin-lattice relaxation times in addition to diffusion coefficient measurements over a temperature range up to 100°C. Practically, the diffusion measurements are extremely challenging, as the spin-spin (T2) relaxation times are very short, necessitating the development of specialized pulsed-field gradient apparatus. Diffusion coefficients for the most mobile components of the lithium cations and fluorinated anions at 100°C in dry membranes have been found to be 3.4 x10-8 cm2/s and 2.1 x10-8 cm2/s respectively. These results provide valuable insight into the conduction mechanisms in these materials, and will drive further optimization of solid polymer electrolytes.

1H Nuclear Magnetic Resonance of a Ferroelectric Liquid Crystalline System

We used <TEX>$^1H$</TEX> nuclear magnetic resonance (NMR) to study the phase transitions and molecular dynamics in a characteristic ferroelectric liquid crystal with a carbon number n = 7, S-2-methylbutyl 4-n-heptyloxybiphenyl-4'-carboxylate (C7). The results were compared with those of our recent work on S-2-methylbutyl 4-n-octanoyloxybiphenyl-4'-carboxylate (C8), with a carbon number n = 8. While the recrystallization and isotropic phase transitions exhibited a first-order nature in the <TEX>$^1H$</TEX> NMR spin-lattice and spin-spin relaxation measurements, a second-order nature was shown at the Sm-A - Sm-<TEX>$C^*$</TEX> liquid crystalline phase transition. A soft-mode anomaly arising from the tilt angle amplitude fluctuation of the director, of which only a hint had been noticed in the C8 system, was manifested in the C7 system at this transition.

Nuclear magnetic resonance study of ultrananocrystalline diamonds

We report on a nuclear magnetic resonance (NMR) study of ultrananocrystalline diamond (UNCD) materials produced by detonation technique. Analysis of the 13C and 1H NMR spectra, spin-spin and spin-lattice relaxation times in purified UNCD samples is presented. Our measurements show that UNCD particles consist of a diamond core that is partially covered by a sp 2-carbon fullerene-like shell. The uncovered part of outer diamond surface comprises a number of hydrocarbon groups that saturate the dangling bonds. Our findings are discussed along with recent calculations of the UNCD structure. Significant increase in the spin-lattice relaxation rate (in comparison with that of natural diamond), as well as stretched exponential character of the magnetization recovery, are attributed to the interaction of nuclear spins with paramagnetic centers which are likely fabrication-driven dangling bonds with unpaired electrons. We show that these centers are located mainly at the interface between the diamond core and shell.

Detection of Pre-Harvest Sprouting in Rice Seeds by Using 1H-NMR

Pre-harvest sprouting (PHS) is a serious source of costly yield and grade losses for producers. Unreleased test lines of cereals should be screened for resistance to PHS. However, screening large numbers of test lines is relatively time-consuming or expensive. In this study, nuclear magnetic resonance (NMR) was used to characterize PHS as a nondestructive method. The water content in the rice grains of ‘TC65’ and ‘Notched’ gradually decreased until 21 days after pollination (DAP) . After 21 DAP, the water content in both lines remained constant. In PHS at this time, none of the ‘TC65’ seeds germinated while 15% of the ‘Notched’ seeds had germinated. At 14 DAP when PHS was not confirmed, NMR spin-spin relaxation time (T2) in ‘TC65’ and ‘Notched’ seeds were about 40 ms and 20 ms, respectively. These results indicated that the T2 is effective to screen resistance to PHS at early stage. In addition, T2s in germinating seeds linearly increased to 165 ms as germination advanced during 10-day treatment period. On the contrary, T2s in nongerminating seeds were about 20 ms and they remained constant during the treatment period. Thus, 1H-NMR relaxation times were measured as a way to screen both resistance to PHS and germination process.

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.

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.

Characterisation of Soybean and Wheat Seeds by Nuclear Magnetic Resonance Spectroscopy

The effects of equilibration under different air relative humidities (RH, 1 - 90 %) and temperatures (35 and 45 °C) on soybean (Glycine max) and wheat (Triticum aestivum) seeds were studied using different techniques. Seed moisture content, electrical conductivity (EC) of seed leachate and per cent seed germination were measured following standard procedures, and compared with nuclear magnetic resonance spin-spin relaxation time (T2) measurements. Moisture contents of soybean and wheat seeds, following the reverse sigmoidal trend, were greater at 35 than at 45 °C at any particular RH. Changes in T2 were related to the changes in germination percentage and leachate EC of both soybean and wheat seeds. Equilibrating soybean seeds at RH ≤ 11 % decreased germination percentage with corresponding decrease in T2. On the contrary, EC of seed leachate increased. In wheat seeds equilibrated at 45 °C, T2 was maximal at RH 5.5 %. T2 declined in seeds equilibrated at high RH (> 80 %) together with low germination percentage.

Advanced 13C Nuclear Magnetic Resonance Investigation of Metal-Ligand Interactions in Monolayer-Protected Gold Nanoparticles: NMR Shifts and Relaxations

ABSTRACTWhile self-assembled monolayer (SAM) systems have been intensively investigated since the seminal work of Nuzzo and others in the later 1980s, the detailed nature of the interactions between thiol and gold in terms of surface bonding and ligand motion, a central theme crucial for any further advancements in the field of SAMs, is still elusive and subject to controversy. Nuclear magnetic resonance (NMR) spectroscopy, a canonical technique of chemistry and physics, has the unique ability of providing insightful chemical bonding and ligand motional information. Recent advances in wet chemistry in terms of synthesizing alkanethiol-protected, very stable and almost monodispersed, gold nanoparticles, due to Schriffin and co-workers, enable this feature of NMR to be harnessed in the study of thiol-metal bonding and ligand motions on gold surfaces. Here, we report a detailed 13C NMR shift and relaxation investigation of monolayer-protected gold nanoparticles as a function of metal particle size, by using selectively 13C1-labelled octanethiol. Several interesting results are obtained for the first time: as the gold particle size increases from ca. 1.5 to 4.0 nm, the 13C1 NMR shift moves down-field from ca. 39 to 50 ppm (with respect to TMS), the spin-lattice relaxation rate 1/T1 decreases, and the spin-spin relaxation rate 1/T2 increases. For a given particle size, the 1/T2 varies across the heterogeneously broadened line shape, being higher at the lower field, while there is no clear trend shown in 1/T1. All these results suggest that while particle tumbling may be the dominant spin-lattice relaxation mechanism, the physical properties of the metal core, i.e., more metallic vs. less metallic, are most probably the dominant factors influencing the 13C1 NMR shift and spin-spin relaxation. Now new doors are opened up for more detailed NMR investigations of metal-ligand interactions in SAM systems.

Polaronic effects on lithium motion in intercalated perovskite lithium lanthanum titanate observed by 7Li NMR and impedance spectroscopy

The long-range and short-range motion of lithium ions into an electrochemically intercalated Li3xLa2/3-xTiO3 (LLTO) sintered pellet has been studied by ac impedance spectroscopy and 7Li solid state nuclear magnetic resonance (NMR). The temperature dependence of the dc conductivity and the intercalation ratio dependence of the chemical shift, the relative intensity of the resonance line, the spin-lattice and the spin-spin relaxation times of 7Li NMR experiments are indicative of polaron formation at the initial stage of intercalation. The total dc conductivity measured in the temperature range 45-600 K and the shape of the impedance diagrams show that after intercalation the conductivity is both ionic and electronic in nature. However for temperatures lower than 300 K the total conductivity is mainly dominated by the electronic one and for temperatures higher than 400 K the total conductivity is dominated by the ionic one. Moreover at low temperatures, when electronic conductivity dominates, the temperature dependence of the conductivity agrees well with a polaron model for conduction in these intercalated oxides. The NMR experiments clearly show that the resonance peak decreases strongly as intercalation occurs. This is explained by a coupling between the electronic and the Li+ nuclear spins leading to an unobservability of some Li+ nuclei in NMR. The other Li+ nuclei, which do not interact directly with the electronic spins, are responsible for the observed NMR signal. If the static effect of the intercalation is weak and leads to a very small chemical shift variation, variable temperature 7Li NMR spin-lattice and spin-spin relaxation measurements show that the presence of electrons acts essentially on the dynamics of the Li+ nuclei through the lattice modification induced by the polaron formation. At the beginning of the intercalation the inverse of the relaxation time T1 of the observed Li+ nuclei decreases by one order of magnitude. At the same time the linewidth of the resonance peak (1/T2) decreases abruptly. The motion of the lithium ions is sharply enhanced. For further intercalation, 1/T1 decreases and the linewidth of the central peak increases indicating that the variations of the relaxation times are mostly governed by the variations of the spectral densities of the Li+ motion. Consequently, the lithium motion decreases gradually as intercalation proceeds. These results are in good agreement with a lattice modification due to polaron formation during intercalation.

Phase separation inLa0.5Ca0.5MnO3observed by55Mnand139LaNMR

We studied zero-field ${}^{55}\mathrm{Mn}$ and ${}^{139}\mathrm{La}$ nuclear magnetic resonance (NMR) in ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_{3}.$ The ${}^{55}\mathrm{Mn}$ and ${}^{139}\mathrm{La}$ NMR intensities, resonance frequencies, and spin-spin relaxation times showed thermal hystereses upon cooling and warming. The analysis of the result shows that there are two distinct phase regions below ${T}_{C}:$ a stable metallic ferromagnetic (FM) region and a region where metallic FM and insulating antiferromagnetic phases compete. The two metallic FM phases are distinguished by mobile ${e}_{g}$ electron density. The ${e}_{g}$ electron density of the stable FM phase is 0.5, but that of the FM phase in the competition region is lower than that.

Superconducting Fluctuation Effects on the Spin-Lattice Relaxation Rate inYBa2Cu3O6.95

We report 63Cu(2) spin-lattice relaxation rate measurements of YBa_2Cu_3O_{6.95} in magnetic fields from 2.1 T to 27.3 T obtained from 17O(2,3) nuclear magnetic resonance spin-spin relaxation. For T < 120 K, the spin-lattice rate increases with increasing magnetic field. We identify this magnetic field dependence with the change in the low-energy spectral weight originating from d-wave pairing fluctuation corrections to the density of states.

Isothermal and non-isothermal crystallization of PP: effect of annealing and of the addition of HDPE

In this report, we present the results of our investigation into the crystallization behaviour of polyproplene. The crystallization process was followed by hot-stage optical microscopy, differential scanning calorimetry, and dynamic mechanical methods. As well, nuclear magnetic resonance spin-spin relaxation techniques were employed to probe the morphology of the polypropylene. Nucleation in this isotactic polypropylene was athermal and appeared to be heterogeneous. The dependence of the onset temperature of crystallization on the annealing temperature and on the annealing time indicated that PP nuclei were able to survive the melting process. Nuclear magnetic resonance spin-spin relaxation experiments indicated that the PP melt contained a significant proportion of regions of high segment density. It was postulated that these ‘ordered’ regions acted as nucleation sites for PP crystallization, and that the number and size of these regions was determined by the annealing time and temperature. Addition of HDPE to PP resulted in melting-point depression and plasticization of the PP phase at lower HDPE contents. HDPE was able to penetrate the PP phase sufficiently at lower HDPE contents to reduce the number and size of regions of high segment density, thereby delaying the nucleation and subsequent crystallization of the PP phase.