Proton NMR Relaxation Times Research Articles

An insight into the beginning stage of the aqueous ring opening metathesis polymerization of exo,exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid with RuIII compounds: the consumption of RuIII species in the presence of carboxylic acids monitored by ESR spectroscopy

The presence of paramagnetic species in the aqueous ring opening metathesis polymerizations of the exo,exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid monomer with RuCl3 and K2[RuCl5H2O] compounds was studied using ESR techniques. It was observed that the intensities of the RuIII signals in the ESR spectra decrease on the time scale of the induction period so that the ROMP can take place. The intensity of the RuIII signal almost disappeared 50 min after reacting with K2[RuCl5H2O] and after 100 min in the case of RuCl3. Reactions of the cis-[Ru(NH3)4(H2O)2](tfms)3 and [Ru(NH3)5H2O](tfms)3 complexes with the monomer and different organic compounds representing the organic functions in the monomer (furan, norbornene, but-2-ene-1,4-diol and formic, acetic, oxalic and maleic acids) were also monitored by ESR and UV/vis spectra. It was deduced that the organic acids provide the disappearance of the RuIII signal. The proton NMR relaxation times of the residual water in D2O for reactions with oxalic acid suggested that the presence of paramagnetic ions in the solution decreases along with the disappearance of the ESR signal for RuIII. It was suggested that diamagnetic Ru species were indeed produced in the medium.

Detection of pH in Microemulsions, without a Probe Molecule, Using Magnetic Resonance

Proton NMR relaxation times have been used to probe the pH of water inside reverse micelles of a cetyltrimethylammonium bromide (CTAB)-hexanol-aq microemulsion. T(2) relaxation times were found to change with pH; however, T(1) relaxation times remained unaffected. This behavior was attributed to acid-catalyzed exchange between protons of water and hydroxyl protons of the cosurfactant hexanol. The rate of exchange and its influence on the T(2) relaxation time of water, inside the reverse micelle, were investigated as a function of water-to-surfactant ratio (ω(0)) and ionic strength. This exchange behavior and pH-dependent T(2) relaxation time were also observed for two other microemulsions--CTAB-hexane-pentanol-aq and Triton X-100-cyclohexane-hexanol-aq. Using this pH-dependent T(2) relaxation time, it was possible to monitor pH changes in the bromate-sulfite reaction inside a CTAB-hexanol-aq microemulsion.

1H and 23Na MRI studies of Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) fillet pieces salted in different brine concentrations

Applicability of magnetic resonance imaging (MRI) to quantitative analysis of sodium in salted fish products is usually impaired by the partial (23)Na MRI 'invisibility' phenomena as well as high investment costs of the MRI equipment. Salmon and cod fillet pieces, unsalted and brine salted (50, 100, 150, 200 and 250 g kg(-1) NaCl) for 48 h, were studied using (1)H and (23)Na MRI. Based on MRI results, T(1) and T(2) relaxation times were calculated for (1)H and the T(2) time for (23)Na nuclei. In addition, water diffusion images for all fillet samples and reference brine solutions were obtained. Variation of the nuclear magnetic resonance relaxation times and water diffusion constants with brine concentration is discussed in terms of the muscle structural changes. Sodium MRI visibility factors for the MRI method used were determined for all fish samples. Observed changes in proton and sodium NMR relaxation times with the salt content reflect complex counteraction of several factors related to the muscle structural changes. Sodium MRI visibility factors appear to be dependent on a number of experimental factors in a complex matter, making quantitative sodium analysis by the MRI technique used non-trivial. Copyright © 2007 Society of Chemical Industry.

Influence of Aging and Salting on Protein Secondary Structures and Water Distribution in Uncooked and Cooked Pork. A Combined FT-IR Microspectroscopy and 1H NMR Relaxometry Study

Fourier transform infrared (FT-IR) microspectroscopy and low-field (LF) proton NMR transverse relaxation measurements were used to study the changes in protein secondary structure and water distribution as a consequence of aging (1 day and 14 days) followed by salting (3%, 6%, and 9% NaCl) and cooking (65 degrees C). An enhanced water uptake and increased proton NMR relaxation times after salting were observed in aged meat (14 days) compared with nonaged meat (1 day). FT-IR bands revealed that salting induced an increase in native beta-sheet structure while aging triggered an increase in native alpha-helical structure before cooking, which could explain the effects of aging and salting on water distribution and water uptake. Moreover, the decrease in T2 relaxation times and loss of water upon cooking were attributed to an increase in aggregated beta-sheet structures and a simultaneous decrease in native protein structures. Finally, aging increased the cooking loss and subsequently decreased the final yield, which corresponded to a further decrease in T2 relaxation times in aged meat upon cooking. However, salting weakened the effect of aging on the final yield, which is consistent with the increased T2 relaxation times upon salting for aged meat after cooking and the weaker effect of aging on protein secondary structural changes for samples treated with high salt concentration. The present study reveals that changes in water distribution during aging, salting, and cooking are not only due to the accepted causal connection, i.e., proteolytic degradation of myofibrillar structures, change in electrostatic repulsion, and dissolution and denaturation of proteins, but also dynamic changes in specific protein secondary structures.

Estimation of τ value in proton NMR relaxation times of dibenzo diaza 18-crown-6 ether derivative in solution

Spin–lattice ( T 1) and spin–spin ( T 2) relaxation times of seven peaks in dibenzo diaza 18-crown-6 ether derivative were measured at 300K with a Bruker 400 MHz NMR spectrometer. An equation was derived for correlation time τ from the ratio of the (1/ T 1)/2(1/ T 2) using relaxation formulas pertaining to dipolar interactions. The correlation time was calculated from the equation for each peak using experimental data for (1/ T 1)/2(1/ T 2) ratio. The estimated τ values ranged from 0.7 ns to 2 ns. The similarity of τ values of the peaks belonging to the different parts of the molecule suggested that overall molecular tumbling may be responsible for relaxation mechanism of all the groups.

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

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

Site Specific Proton and Deuteron NMR Relaxation Dispersion in Selectively Deuterated Polyisoprene Melts

AbstractSummary: The frequency dependence of proton and deuteron NMR relaxation times was determined in selectively deuterated and undeuterated polyisoprene melts and compared to polybutadiene melts. Master curves were generated by the Williams‐Landel‐Ferry (WLF) formalism which resulted in very similar dispersions for all samples with a high and a low frequency branch following characteristic power laws. The results show a consistently weaker frequency dependence than any reported so far for other polymer melts. The reason for this finding is identified in the distribution of intramolecular motion modes, while intermolecular contributions are ruled out.Master curves for 1H relaxation dispersions obtained from measurements between 223 K and 348 K shifted relative to a reference temperature of 296 K.magnified imageMaster curves for 1H relaxation dispersions obtained from measurements between 223 K and 348 K shifted relative to a reference temperature of 296 K.

NMR detection of thermal damage in carbon fiber reinforced epoxy resins

Composite materials of epoxy resins reinforced by carbon fibers are increasingly being used in the construction of aircraft. In these applications, the material may be thermally damaged and weakened by jet blast and accidental fires. The feasibility of using proton NMR relaxation times T 1, T 1 ρ , and T 2 to detect and quantify the thermal damage is investigated. In conventional spectrometers with homogeneous static magnetic fields, T 1 ρ is readily measured and is found to be well correlated with thermal damage. This suggests that NMR measurements of proton T 1 ρ may be used for non-destructive evaluation of carbon fiber-epoxy composites. Results from T 1 ρ measurements in the inhomogeneous static and RF magnetic fields of an NMR-MOUSE are also discussed.

Cross‐linking of polybutadiene: correlation between solid‐state 1H NMR spectroscopy, thermoporosimetry, densimetry and crystallinity measurements

AbstractT2 proton NMR relaxation times were used to follow the changes in the macromolecular chain mobility of a chemically (by dicumyl peroxide) cross‐linked polybutadiene matrix. The same phenomenon was also studied by an investigation of the ability of the polymer to crystallize using DSC measurements. The solubility of the elastomer depends on the size of its macromolecular chains. Cross‐linking, leading to an increase in the size of macromolecules, provokes an insolubility of the elastomer. By densimetry measurements, it was possible to follow the changes in the solubility of the polymer up to its gel‐point. Beyond the gel‐point, the swelling solvent, cyclohexane, was used as a textural probe. Using the shift of its solid‐solid thermal transition points, it was possible to calculate the distribution of the distances between the cross‐links as a function of the curing times by thermoporosimetry analysis. Copyright © 2003 Society of Chemical Industry

Self-Diffusion of Hydrophilic Poly(propyleneimine) Dendrimers in Poly(vinyl alcohol) Solutions and Gels by Pulsed Field Gradient NMR Spectroscopy

Pulsed-field gradient NMR spectroscopy was used to study the diffusion of three different poly(propyleneimine) dendrimers with hydrophilic triethylenoxy methyl ether terminal groups (generations 2, 4, and 5) in poly(vinyl alcohol) aqueous solutions and gels. The effects of the diffusant size, polymer concentration (from 0 to 0.26 g/mL), and temperature on the self-diffusion coefficients have been studied, and the model of Petit et al. [Macromolecules 1996, 29, 6031] was used to fit the experimental data. The Stokes−Einstein hard-sphere radii were also calculated in the zero concentration limit and were compared with those of the linear poly(ethylene glycol)s under the same conditions. The proton NMR relaxation times (T1 and T2) were measured to study the mobility of the dendrimer core part and terminal group as a function of the dendrimer size.

1HNMR Study on the Motion of NH4 + in Ferroelectric NH4H(ClH2CCOO)2 and Mixed (NH4)1-xRbxH(ClH2CCOO)2 (x = 0.15)

Temperature-dependent proton NMR relaxation time measurements have been performed at 60 MHz in order to study the NH4 + dynamics in ferroelectric NH4H(ClH2CCOO)2 and mixed Rbx(NH4)1-x(ClH2CCOO)2, where x = 0.15. The data indicate that the dominant relaxation mechanism for the NMR spin-lattice relaxation time T 1 in both crystals involves simultaneous NH4 group reorientation about their C2 and C3 symmetry axis in the paraelectric phase. Details of the NH4 +reorientation have been inferred from analysis of temperature dependence of T1 assuming the Watton model. The activation parameters of the motionshave been determined.It has been found that the substitution of Rb does not change the activation parameters of the NH4 group dynamics.

High Pressure Study of Dynamics in Tetraphenyltin

Measurements of proton NMR relaxation times as well as inelastic and elastic neutron scattering of tetraphenyltin (C 6 H 5 ) 4 Sn as a function of temperature and pressure were performed in the work. It allowed to determine activation volume j V * for a small amplitude reorientation/oscillation of the phenyl rings. The values of activation volume is very small and the ratio of j V */ V M ( V M is molar volume) is less than 1%.

Non Invasive Quantification of Manganese Deposits in the Rat Brain by Local Measurement of NMR Proton T1 Relaxation Times

Up to now, there is no reliable non invasive biomarker for the concentration of manganese (Mn) in the brain after intoxication to this metal. The aim of the present experimental study was to determine the predictive value of the localized measurement of the proton NMR relaxation time T 1 as a quantitative estimation of the concentration of Mn in brain. The relationship of the proton relaxation rates (1/ T 1) was established in rat brain homogenates as a function of the Mn, iron, and copper concentration. Subsequently, an experimental model of Mn neurotoxicity was used: rats were stereotactically injected with increasing amounts of Mn 2+ (as MnCl 2) in the ventricles. After 3 weeks, local measurements of T 1 were carried out in live rats. They were then sacrificed in order to sample the striatum, the cortex, and the cerebellum from the brain and to perform a quantitative determination of the concentration of Mn in these tissues by atomic absorption spectrometry (AAS). The results indicate excellent correlation coefficients between relaxation rates and tissue Mn concentrations (r = 0.84, 0.77 and 0.92 for the striatum, the cortex and the cerebellum, respectively). This methodology offers a unique tool for monitoring the degree of Mn concentration in different areas of the brain in animal models of Mn intoxication. It will be useful for evaluating the efficacy of treatments aimed at decreasing the metal in the brain. The method could be potentially useful for being transposed in the clinical situation for monitoring Mn-exposed workers.

Flexible Structures of SIBLING Proteins, Bone Sialoprotein, and Osteopontin

Bone sialoprotein (BSP) and osteopontin (OPN) are two members of the SIBLING (Small Integrin-Binding LIgand, N-linked Glycoprotein) family of genetically related proteins that are clustered on human chromosome 4. We present evidence that this entire family is the result of duplication and subsequent divergent evolution of a single ancient gene. The solution structures of these two post-translationally modified recombinant proteins were solved by one dimensional proton NMR and transverse relaxation times. The polypeptide backbones of both free BSP and OPN rapidly sample an ensemble of conformations consistent with them both being completely unstructured in solution. This flexibility appears to enable these relatively small glycoproteins to rapidly associate with a number of different binding partners including other proteins as well as the mineral phase of bones and teeth. These proteins often function by bridging two proteins of fixed structures into a biologically active complex.

Molecular Dynamics of Cellulose-Water Systems Investigated by NMR Relaxation Method

Summary On the basis of the proton NMR relaxation time dependencies on temperature and frequency in cellulose pulp a simple two-motion model of molecular dynamics has been proposed. The parameters, activation energies and correlation times, describing the model may be correlated with structure features such as level of crystallinity of cellulose with different origin, as well as degree of paper devastation.

Relationship between Proton NMR Relaxation Time and Viscosity of Saccharide Solutions.

Proton relaxation was measured in 1H-NMR for saccharide solutions. The proton relaxation curve for saccharide solutions was almost mono-exponential and spin-lattice (T1) and spin-spin relaxation (T2) times were determined from the curve. T1 and T2 were described well by the second order function of solute molality with the correlation coefficient over 0.994. The B-coefficients for T1 and T2 correlated well with the B-coefficient of viscosity and also with the number of equatorial OH groups of saccharide molecules, suggesting that the saccharide solution structure was reflected in these parameters in spite of the effect of proton exchange between water and solute.

Proton NMR relaxation studies of solid tyrosine derivatives and their mixtures with l-leucinamide

Proton NMR relaxation time measurements were carried out on solid tyrosine derivatives: acetyl- l-tyrosine ethyl ester (Ac-Tyroet), N-carbobenzyloxy- l-tyrosine ethyl ester (CBZ-Tyroet), N-trifluoroacetyl- l-tyrosine ethyl ester (TFAc-Tyroet) and their mixtures with l-leucinamide. It was found that spin-lattice relaxation was driven mainly by methyl group rotation at low temperature for the pure solids and the mixtures. Benzene ring flipping motion and a third motion (possibly whole molecule tumbling) were found to be responsible for relaxing Ac-Tyroet and CBZ-Tyroet at high temperature. However, these motions were highly hindered in TFAc-Tyroet. Molecular tumbling motion was detected in the supercooled liquid mixtures of l-leuNH/CBZ-Tyroet and l-leuNH/Ac-Tyroet, while this motion is absent in the mixture l-leuNH/TFAc-Tyroet. The hindered motion in TFAc-Tyroet may be one of the factors affecting its ability to form a supercooled liquid with l-leucinamide.

Proton and carbon NMR measurements of the effects of hydration on the wheat protein ω-gliadin

The wheat protein ω-gliadin consists of a simple repeat sequence composed mainly of proline and glutamine. It thus represents a simple model for many cereal proteins and other proline and glutamine rich sequences which occur in multiple repeats. The behaviour on hydration has been examined by the measurement of proton NMR relaxation times. Sidechain motions (methyl and amino group rotation, proline ring puckering) were largely responsible for T 1 relaxation. It was found that the glass transition does not affect T 1 and T 1 ρ relaxation and only affects transverse relaxation. Magic angle spinning experiments have been used to observe line narrowed proton spectra as well as carbon cross polarisation spectra. In the proton spectra, at high levels of hydration, backbone and sidechain NH groups are observed indicating that whole segments of the protein chain are in the mobile regime. The carbon spectra are characterised by a loss of the proline C δ signal intensity at high levels of hydration indicating the involvement of proline in the hydration process. It is concluded that the behaviour of ω-gliadin on hydration may be explained by the formation of mobile protein loops together with residual regions of strong interprotein interaction.

Proton NMR relaxation studies of solid L-leucinamide

Proton NMR relaxation time measurements were carried out on solid L-leucinamide. Transverse relaxation, spin-lattice relaxation in the laboratory and rotating frame, and spin lattice relaxation in the dipolar field were measured. The effects of deuteration of the amino groups were also examined. It was found that, unusually for a simple solid, transverse relaxation consisted of two Gaussian components which could be assigned separately to aliphatic and amino groups. Spin-lattice relaxation was driven mainly by methyl group rotation at low temperatures and amino group rotation at high temperatures.

Water binding to biopolymers in different cereals and legumes: proton NMR relaxation, dielectric and water imbibition studies

Proton NMR relaxation time (T1), dielectric properties by means of the thermally stimulated depolarization currents (TSDC) method, and water imbibition were measured in cereal and legume grains (wheat, triticale, maize, pea, chick pea, horsebean, white lupin, lentil and beans) having different chemical composition (proteins, carbohydrates, lipids). T1 versus water content in the range 0.05–1.40 g water/g dry matter showed characteristic V-shaped curves with a sharp or a broad minimum depending on the species. Water content at T1 min was in high positive correlation with protein content of the grains (r=0.90) and in high negative correlation with soluble carbohydrates (r=−0.92), while lipids gave a very low correlation (r=0.38). The water content at T1 min (0.18–0.47 g water/g dry matter) was assigned to a primary hydration sphere around the macromolecules, since, when T1 was plotted versus per cent maximum hydration, the T1 min values for all grains fell between 25–30% of maximum hydration. The extrapolated value for zero protein content was 0.08 g water/g dry matter, which coincided with data in the literature for the water monolayer on starch. The TSDC measurements enabled us to determine the amount of tightly (irrotationally) bound water at primary hydration sites to 0.18±0.02 g water/g dry matter for beans, pea and chickpea, and, tentatively, to about 0.10 g water/g dry matter for wheat. Water imbibition data for 11 cereal and legume species gave total water hydration capacity in the range a=0.44–1.82 g water/g dry matter. This value divided by the water content of the primary hydration sphere (swelling index) was also in high positive correlation with the protein content of the grains (r=0.84).