NMR Spin-spin Relaxation Times Research Articles

Microstructure, rheological and water mobility behaviour of plant-based protein isolates (pea and quinoa) and locust bean gum mixtures

This work reports the impact of locust bean gum (LBG) in the continuous phase of plant-based proteins, i.e. quinoa protein (QPI) and pea protein isolates (PPI). Experimental measurements such as confocal microscopy, rheological analysis and water mobility via nuclear magnetic resonance (nmr) spin-spin relaxation time (T2) were carried out. The influence of LBG on the rheological properties of QPI and PPI is consistent with an exchange-based nmr interpretation of T2 for biopolymer and water. Addition of LBG increased the viscoelastic properties (storage and loss modulus) and shear viscosities of the mixtures. LBG interacted with both plant proteins, resulting in the formation of more dense protein networks and protein coacervates. A stronger interaction between the PPI and LBG was observed, resulting in higher shear viscosities with lower water mobility as compared to QPI:LBG formulations. Results indicated that the interaction between the protein and polysaccharide played a significant role in the microstructure, its rheological properties and consequently water mobility.

Elucidating the Impact of Hydrophilic Segments on 19F MRI Sensitivity of Fluorinated Block Copolymers.

A major challenge in the preparation of polymeric 19F magnetic resonance imaging (MRI) contrast agents (CAs) is signal attenuation caused by reduced segmental mobility of partly fluorinated polymers possessing large numbers of fluorine atoms. Previous studies have thus mainly focused on the development of fluorinated segments for improved 19F MRI; however, detailed investigations of the role of hydrophilic segments on imaging performance remain scarce. In this study, three hydrophilic and biocompatible monomers, i.e., 2-(methylsulfinyl)ethyl acrylate (MSEA), oligo(ethylene glycol) methyl ether acrylate (OEGA), and oligo(2-methyl-2-oxazoline) acrylate (OMOXA), were used to prepare perfluoropolyether (PFPE)-containing amphiphilic block polymers through reversible addition-fragmentation chain-transfer (RAFT) polymerization. The effect of the different hydrophilic segments on 19F imaging performance was explored. The three polymers could be readily dissolved in aqueous solutions, forming assemblies with the hydrophobic PFPE as the core and the hydrophilic chains as the shell. Molecular dynamics simulations demonstrate that the POMOXA chains adopt a rigid, extended conformation, leading to a relatively short 19F NMR spin-spin relaxation time (T2), lower NMR detectable 19F spins (i.e., visibility), and the least intense 19F MRI signal. In contrast, although PMSEA-PFPE has a shorter 19F NMR T2 than POEGA-PFPE, the much higher 19F spin visibility enhances its MRI signal intensity. The result confirms the importance of maintaining both high fluorine visibility and long T2 relaxation time to prepare effective CAs and highlight the key role of the nonfluorinated hydrophilic segments in determining these parameters.

Elucidation of rheological, microstructural, water mobility, and noodle-making properties of rice flour affected by turanose.

The effects of turanose on the physicochemical properties of rice flour systems (aqueous suspension, dough, and noodles) were investigated in terms of rheology, microstructure, and water mobility. Inclusion of turanose increased the pasting viscosities of rice flour by maintaining a closely-packed structure at high temperatures that was confirmed by the real-time microscopic measurements during heating. The elevated probability of intergranular interactions by turanose apparently raised both storage (G') and loss (G″) moduli of the rice flour pastes as well as their respective viscosities. NMR spin-spin relaxation times showed two distinct water populations in the turanose-rice flour samples. The Mixolab experiments demonstrated that the rice doughs with higher levels of turanose exhibited greater dough stability as well as higher degrees of starch gelatinization and retrogradation. Furthermore, the extruded rice noodles containing turanose exhibited a higher expansion ratio and a firmer texture that contributed to lowering the cooking loss by 24.5%.

Changes in secondary structure of myofibrillar protein and its relationship with water dynamic changes during storage of battered and deep-fried pork slices.

Fourier transform infrared spectroscopy was used to analyze the changes of secondary structure of myofibrillar proteins in short-term storage of battered and deep-fried pork slices. These changes were combined with low-field NMR analysis results to analyze the correlation between secondary structure and dynamic changes of water content. The results showed that the number of α-helix and β-sheet decreased by 22.90 and 16.54% respectively, and the orderly structure changed to the disorder structure. The correlation results show that NMR spin-spin relaxation time (T21) has a high negative correlation with α-helix, β-sheet, and has a high positive correlation with irregular curl and β-turn. The population of immobile water (P22) has a very high positive correlation with α-helix, β-sheet, and has a relatively high negative correlation with irregular curl and β-turn. The immobilized water plays an important role in maintaining the secondary structure.

Characterization of poly-d-mannuronate and poly-l-guluronate block fractions from sodium alginate and preparation of hydrogels with poly(vinylalcohol)

Sodium salts of homopoly-d-mannuronic acid (MM) and of homopoly-l-guluronic acid (GG) from sodium alginates were characterized by NMR relaxometry. Determination of NMR spin-lattice and spin-spin relaxation times of water proton in homopolymeric block solutions and hydrogels indicated differences in homopolymeric blocks tertiary structure. Hydrogels of MM or GG blocks and poly(vinyl alcohol) (PVA) were prepared by freeze-thawing cycles method; their swelling properties and sensitivity to pH stimuli were assayed in control delivery of a model drug. MM/PVA hydrogels show better metformin release characteristics than GG/PVA hydrogels. It was found that release of the drug at pH 1.2 from hydrogels was minor to 5%. At the release equilibrium, 60 and 55% of the drug encapsulated were release from MM/PVA and GG/PVA hydrogels, respectively. Also, the release of metformin from hydrogels was studied by 1H NMR spectroscopy showing that 40 and 36% of drug were released after 4 h from MM/PVA and GG/PVA hydrogels, respectively.

The pseudo 2-D relaxation model for obtaining [formula omitted]–[formula omitted] relationships from 1-D [formula omitted] and [formula omitted] measurements of fluid in porous media

NMR spin-lattice (T1) and spin-spin (T2) relaxation times and their inter-relation possess information on fluid behaviour in porous media. To elicit this information we utilize the pseudo 2-D relaxation model (P2DRM), which deduces the T1–T2 functional relationship from independent 1-D T1 and T2 measurements. Through model simulations we show empirically that the P2DRM accurately estimates T1–T2 relationships even when the marginal distributions of the true joint T1–T2 distribution are unknown or cannot be modeled. Estimates of the T1:T2 ratio for fluid interacting with pore surfaces remain robust when the P2DRM is applied to simulations of rapidly acquired data. Therefore, the P2DRM can be useful in situations where experimental time is limited.

PH-Responsive Intra- and Inter-Molecularly Micelle Formation of Anionic Diblock Copolymer in Water

Poly(sodium2-(acrylamido)-2-methylpropanesulfonate)-block-poly(sodium11-(acrylamido)undecanoate) (PAMPS–PAaU) was synthesized via reversible addition-fragmentation chain transfer (RAFT)-controlled radical polymerization. The “living” polymerization of PAaU was evidenced by the fact that the molecular weight distribution was narrow (Mw/Mn = 1.23). The pH-induced association behavior of PAMPS–PAaU in 0.1 M NaCl aqueous solutions as a function of solution pH was investigated by 1H NMR spin-spin relaxation time, dynamic light scattering (DLS), static light scattering (SLS), and fluorescence probe techniques. These results indicated that PAMPS–PAaU formed polymer micelles in 0.1 M NaCl aqueous solutions at pH < 9. At pH = 8–9, the polymer formed the micelles intramolecularly due to hydrophobic self-association of the PAaU block within the single polymer chain. On the other hand, at pH < 8, micellization occurred intermolecularly to form polymer micelles comprising hydrophobic PAaU cores and hydrophilic PAMPS shells.

Phase Behavior, Diffusion, Structural Characteristics, and pH of Aqueous Hydrophobic Ionic Liquid Confined Media: Insights into Microviscosity and Microporsity in the [C4C4im][NTf2] + Water System

We present our studies on the physicochemical properties of water confined in Dibutylimidazolium bis(trifluoromethanesulfonylimide) ([C4C4im][NTf2]) reverse micelles through the NMR relaxation measurements that provide us an understanding of microviscosity and pH in the confined condition. We present experimental results on phase behavior, diffusion, structural characteristics and pH in aqueous ionic liquid-confined media. The ternary phase diagram was constructed by the cloud point measurements and the microheterogeneous regions were detected by the measurement of bulk viscosity and diffusion coefficients of K4[Fe(CN)6] inside the homogeneous microemulsion systems through the cyclic voltammetric (CV) measurements. The size of the microemulsion systems was characterized by the dynamic light scattering (DLS) method. The (1)H NMR spectra of homogeneous microemulsion systems were taken which indicates the presence of bound and free water molecules inside the microemulsion system. The NMR spin-lattice relaxation time (T1) of water molecules in its homogeneous microemulsion systems were measured and the reorientational correlation time (τc) of water molecules obtained from it indicates that the fluidity of homogeneous confined media decreases with the decrease in the composition of water. Microviscosity of the aqueous confined media was calculated from the measured T1 relaxation time values by applying the Debye-Stokes equation and correlated with the bulk viscosity of the samples. It was observed that both the microviscosity and bulk viscosity show inverse relationship. The fraction of bound and free water molecules were calculated from the measured T1 values. NMR spin-spin relaxation time (T2) of water molecules in its homogeneous microemulsion systems were measured with the varying pH of the aqueous core. A change in the T2 relaxation time of the water proton was observed proposing an exchange of proton between the H2O and -OH group of the TX-100 molecules. Finally, methyl orange (MO) was used as a UV-vis spectrophotometric molecular probe and the measured λmax values of the probe were used for the detection of micropolarity of the homogeneous aqueous confined media and was found to be increase with the increase in the size of the confined media.

Dynamic properties of polyampholyte hydrogel elucidated by proton NMR spin-spin relaxation time

1H spin-spin relaxation time(T 2) measurement of polyampholyte hydrogel poly(methylacrylic acidacryloyloxyethyl trimethylammonium chloride)[P(MA-DAC)] in different pH, ionic strength and temperature was carried out to reveal the molecular mobility. Spontaneous volume transition of the polyampholyte hydrogel was also investigated by spin-spin relaxation time measurement. Meanwhile T 2 and the proton component fraction were acquired to study the swelling behaviour of the hydrogel. Moreover the changes of T 2 characterized the molecular mobility of polyampholyte hydrogel in various swelling states. And the results suggest that the mobility of the main chains and a few free side chains(the long T 2) of P(MA-DAC) was dominated by the mesh size in the hydrogel network, depending on the swelling ratio(Q) and the mobility of the side chains(the short T 2) was influenced by electrostatic interaction between different charges in polymer side chains. Finally the T 2 measurements of P(MA-DAC) hydrogel in the spontaneous swelling-deswelling process demonstrated the electrostatic interaction of the charged side chains caused deswelling behavior. At the same time, the mobility state transition temperature of the charged side chains was also studied by the 1H spin-spin relaxation time measurements, and the transition activation energy of the side chains is 2.72 kJ.

Preparation and Characterization of Polyion Complex Micelles with Phosphobetaine Shells

A pair of oppositely charged diblock copolymers, poly(2-(methacryloyloxy)ethyl phosphorylcholine)-block-poly((3-(methacryloylamino)propyl)trimethylammonium chloride) (PMPC-b-PMAPTAC) and poly(2-(methacryloyloxy)ethyl phosphorylcholine)-block-poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PMPC-b-PAMPS), was prepared via reversible addition-fragmentation chain transfer radical polymerization using a PMPC-based macro chain transfer agent. The pendant phosphorylcholine group in the hydrophilic PMPC block has anionic phosphate and cationic quaternary amino groups, which are neutralized within the pendant group. Therefore, the mixing of aqueous solutions of PMPC-b-PMAPTAC and PMPC-b-PAMPS leads to the spontaneous formation of simple core-shell spherical polyion complex (PIC) micelles comprising of a segregated PIC core and PMPC shells. The PIC micelles were characterized using (1)H NMR spin-spin (T2) and spin-lattice relaxation times (T1), diffusion-ordered NMR spectroscopy, static light scattering, dynamic light scattering (DLS), and transmission electron microscopy techniques. The hydrodynamic size of the PIC micelle depended on the mixing ratio of PMPC-b-PMAPTAC and PMPC-b-PAMPS; the maximum size occurred at the mixing ratio yielding stoichiometric charge neutralization. The PIC micelles disintegrated to become unimers with the addition of salts.

As75NMR of Ba(Fe0.93Co0.07)2As2in high magnetic field

The superconducting state of an optimally doped single crystal of Ba(Fe$_{0.93}$Co$_{0.07}$)$_2$As$_2$ was investigated by $^{75}$As NMR in high magnetic fields from 6.4 T to 28 T. It was found that the Knight shift is least affected by vortex supercurrents in high magnetic fields, $H>11$ T, revealing slow, possibly higher order than linear, increase with temperature at $T \lesssim 0.5 \, T_c$, with $T_c \approx 23 \, K$. This is consistent with the extended s-wave state with $A_{1g}$ symmetry but the precise details of the gap structure are harder to resolve. Measurements of the NMR spin-spin relaxation time, $T_2$, indicate a strong indirect exchange interaction at all temperatures. Below the superconducting transition temperature vortex dynamics lead to an anomalous dip in $T_2$ at the vortex freezing transition from which we obtain the vortex phase diagram up to $H = 28$ T.

NMR Studies of Quantum Rotors Confined in Zeolite

We report the results of NMR studies of methane trapped in zeolite at low temperatures. Samples were prepared to contain 1.0±0.2 molecules per α-sodalite cage of zeolite-13X. The NMR spin-spin and spin-lattice relaxation times were measured for 4<T<95 K to determine the rotational dynamics of the molecules and the dependence on the concentration of the A, T and E-molecular species. The results are discussed relative to recent Monte Carlo calculations that show that the molecules are localized but free to tumble in the large α-cages at low temperatures. At higher temperatures there is an effective melting of the translational degrees of freedom for the lattice formed by the centers of the supercages. A sharp definitive jump in the NMR spin-spin relaxation is seen at this “melting” transition.

Swelling and pressure-volume relationships in the dermis measured by osmotic-stress technique

Water transfer across the extracellular matrix (ECM) involves interstitial osmotic forces in as yet unclear ways. In particular, the traditional values of Starling forces cannot adequately explain fluid transfer rates. Here, we reassess these forces by analyzing fluid transfer in live pig and human dermal explants. Pressure potentials were controlled with inert polymers adjusted by membrane osmometry (range = 3-219 mmHg), and fluid transfer in and out of the explants was followed by sequential precision weighing. Water motional freedom in the dermis was examined by NMR. In pigs, mean hydration pressure (HP; the pressure at which volume did not change) was 107 +/- 22 and 47 +/- 12 (SE) mmHg at 4 degrees C and 37 degrees C (P = 0.012, paired t-test, n = 7). Volume changes observed in response to pressure potential were reversible. The equation, Volume change = V(max)/[1+(time/T(1/2))(d)], where V(max) is maximal volume change; T(1/2), time at volume = 1/2 V(max); and d, a rate parameter, was fitted to experimental progression curves (r(2) > 0.9), yielding V(max) values linearly related to pressure, with mean slopes -3.5 +/- 0.28 and -2.6 +/- 0.21(SE) mul.g(-1).mmHg(-1) at 4 degrees C and 37 degrees C. NMR spin-spin relaxation times (T(2)) varied within 200- to 400-mum distances in directions perpendicular to the epidermis, with slopes reaching 0.03 ms/mum. Results support a mechanism in which fluid transport across the ECM is locally regulated at micrometer scales by cell- and fiber-gel-dependent osmomechanical forces. The large HP helps to explain the fast interstitial in/out flow rates observed clinically.

Unusual Dynamic Behavior in the Isotropic Phase of Banana Mesogens Detected by 2H NMR Line Width and T2 Measurements

In this work the first experimental observation of a peculiar behavior in the isotropic phase of liquid crystals by means of 2H NMR is reported. In particular, two five-ring banana-shaped mesogens, the 1,3-phenylenebis{4,4'-(11-undecenyloxy)benzoyloxy}benzoate (Pbis11BB) and its 4-chloro homologue (ClPbis11BB), selectively deuterium labeled on their central rings, are the subject of our investigation. The dynamic behavior of the two liquid crystals was studied in their isotropic phases and in the nematic phase of ClPbis11BB by means of 2H NMR line width and spin-spin relaxation time (T2) analysis. The results obtained reveal that the unusual line broadening observed in the 2H NMR spectra in the isotropic phase, even far above the isotropic phase-mesophase transition, has a homogeneous nature, thus indicating the presence of reorientational motions much slower than in conventional isotropic liquid-crystalline phases.

H NMR Relaxation Study of Thermotropic Phase Transition in Poly(vinyl methyl ether)/D2O Solutions

1H NMR line shapes and spin-spin relaxation times T 2 have shown that in PVME/D 2 O solutions the LCST transition results in limited mobility of most PVME units, evidently in connection with formation of compact globular-like structures. The minority mobile component, which does not take part in the phase transition, mostly consists of low-molecular-weight fraction of PVME, as shown by SEC. Measurements of spin-spin relaxation times of PVME methylene protons have shown that globular structures are more compact in dilute solutions in comparison with semidilute and concentrated solutions where globules contain a certain amount of water. A certain portion of water molecules bound at elevated temperatures in PVME globular structures in semidilute and concentrated solutions was revealed also from measurements of spin-spin and selective and nonselective spin-lattice relaxation times of residual HDO molecules. While the phase separation in dilute PVME solutions is associated with rapid dehydration of polymer chains, for semidilute and concentrated solutions T 2 measurements evidence that with time the originally bound water is slowly released from globular-like structures, and the character of the globules is changed from the spongelike to a rather compact one. From results obtained on D 2 O solutions of PVME/poly(N-isopropylmethacrylamide) (PIPMAAm) mixtures it follows that this process is significantly slower for more rigid globular-like structures of PIPMAAm in comparison with globules of the flexible PVME.

Role of water during AlN-hydrolysis-assisted solidification in ceramic suspensions studied by proton nuclear magnetic resonance T2 relaxation

Using proton nuclear magnetic resonance (1H-NMR), we have studied the thermally activated hydrolysis of aluminum nitride admixed into Al2O3 aqueous suspensions. We paid special attention to the formation of aluminum hydroxide and its role in binding the host ceramic particles into a stiff solid matrix. The water–proton NMR spin-spin relaxation time (T2) was continuously measured as a function of the time of the AlN hydrolysis in the host Al2O3 ceramic suspension. T2 was found to correlate with an increasing fraction of bound water at the surface of the formed hydrogel and so provided us with information about the gel-surface growth during the hydrolysis process. These results are in good agreement with the observed time- and composition-related increases in high-frequency impedance for the analyzed suspensions.

NMR in magnetite below and around the Verwey transition

NMR on ${}^{57}\mathrm{Fe}$ nuclei was measured in two single crystals of magnetite between 4.2 and 135 K (temperature of the Verwey transition ${T}_{V}=121.5$ and 123.9 K). We were able to register all lines detected at 4.2 K also at higher temperatures up to ${T}_{V}.$ The spectra are compatible with the space group $Cc,$ which predicts 8 and 16 lines for iron on tetrahedral (A) and octahedral (B) sites, respectively. One of the $\mathrm{Fe}(A)$ lines is doubly degenerate for all $T&lt;{T}_{V},$ which restricts the possible models of the ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ ordering on the B sites. Above ${T}_{V}$ no remnant of the low-temperature spectrum was detected. At 4.2 K the NMR spin-spin and spin-lattice relaxation times were determined.

Effects of brain membranes on 1H nuclear magnetic resonance signal intensity of ethanol in vitro.

In vivo proton nuclear magnetic resonance (1H NMR) studies of ethanol in animal and human brains have shown that only a fraction of ethanol in brain is visible by NMR. The goals of these in vitro 1H NMR experiments were to determine: (1) whether the interaction of ethanol with brain membranes in vitro diminishes ethanol visibility; and (2) if a magnetization transfer (MT) effect can be observed for the interaction of ethanol with brain membranes in vitro. Furthermore, pilot studies were performed to determine if the brain membranes from rats chronically exposed to ethanol had a different effect on ethanol NMR visibility and spin-spin relaxation time (T2) than brain membranes obtained from control rats. Results show that the NMR visibility of ethanol is lower in rat brain membrane suspensions in vitro as compared to ethanol in saline solutions. The factors decreasing ethanol NMR visibility are T2 relaxation, water presaturation time, and off-resonance saturation by a frequency-dependent MT pulse. One-pulse NMR measurements without water presaturation showed that ethanol visibility was significantly increased by 15% in brain membrane suspensions of ethanol-fed rats, suggestive of decreased ethanol partitioning compared to controls. Furthermore ethanol in brain membrane suspensions from ethanol-fed rats showed smaller MT effects than from control rats. These results provide a mechanism for decreased NMR visibility of ethanol in brain, and suggest that chronic exposure to ethanol produces membrane changes which result in increased NMR visibility.

NMR Imaging of Immiscible Displacements in Porous Media

Summary We introduce a rapid, quantitative nuclear magnetic resonance imaging (NMRI) technique to resolve and measure multiple fluid phases in porous media. Liquids are resolved on the basis of their NMR spin-spin (T2) relaxation times, and their intensities are corrected by attenuation analysis. The phase-resolved and corrected NMRI intensities are normalized to yield fluid saturations. We present the procedure and limitations of this technique. We present in-situ saturation measurements for three immiscible (oil and water) displacements in the same Berea sandstone core. We compared NMRI and effluent recovery methods. T2 of the displacement fluids were sensitive to displacement conditions.

Measurement of Aperture and Multiphase Flow in Fractures With NMR Imaging

Summary Nuclear magnetic resonance imaging (NMRI) techniques were used for the measurement of the spatial distribution of apertures and two-phase fluid distributions in rock fractures. Rock models of known apertures were used to validate the NMRI technique. NMRI aperture values were in good agreement with nominal and hydraulic aperture values. The fracture signal in porous rock was isolated by NMR spin-spin relaxation times. Areal distributions of oil and water in an immiscible fracture flow were resolved on the basis of their NMR spin-lattice relaxation times.