Proton NMR Relaxation Research Articles

Ammonium ion dynamics in NH4Br at high pressure - type of reorientation

Proton NMR relaxation measurements were performed for ammonium bromide at pressures up to 800 MPa. The correlation functions for ammonium ion reorientation were calculated by Monte Carlo method. Knowledge of these functions allow calculation of the NMR relaxation times T1. Comparison between experimental and calculated values of relaxation times gives some insight into the model of ammonium ion reorientation.

Application of fast field cycling proton NMR relaxation spectroscopy to a crystalline solid

Fast field cycling (FFC) NMR has been relatively little used for solids. This is partly due to instrumental problems and because normal perturbation theory no longer applies when Zeeman fields are of the order of local dipolar fields. Measurements of proton relaxation of solid l-leucinamide over a Larmor frequency range (24 kHz–100 MHz) are described. It is shown that good experimental data can be obtained in the rigid lattice condition and that the results may be explained by modifying conventional perturbation theory to take account of the effects of dipolar relaxation.

NMR proton relaxation measurements of water associated with high methoxy and low methoxy pectins

Nuclear magnetic resonance was used to study water proton relaxation in high (HMP) and low methoxy pectins (LMP). In solution, on the order of 40% of the water molecules may be affected by interactions with pectin molecules, dependent upon pectin type and concentration. Transverse relaxation rates were greater for HMP than LMP, and were attributed to decreased mobility of water protons and the lesser number of methoxyl groups in LMP. Plots of relaxation rates ( R 2=1/ T 2) versus the 90–180° pulse spacing were used to calculate the proton exchange rate ( k b). HMP and LMP has k b values of 128 and 135 s −1 at pH 2.5. For LMP k b increased to 280 s −1 at pH 6.5, but decreased for HMP above pH 6.5. Dry samples were equilibrated to water activity values between 0.11 and 0.75. Proton relaxation was quite rapid in these systems, suggesting limited water mobility. At higher moisture levels, R 2 values were progressively lower and more evenly spread over a wider pulse spacing range, indicating additional populations of more mobile water. Studies on LMP which were gelled with Ca 2+, showed a substantial increase in relaxation rates and little dispersion behavior, and this was attributed to the decreased mobility of pectin biopolymers.

NMR studies of calcium induced alginate gelation. Part II. The internal bead structure

Proton NMR relaxation, diffusion and microimaging techniques were used to investigate the internal structure of calcium alginate gel beads formed by dripping a sodium alginate solution into a calcium chloride solution. It is shown that many of the pore structures previously reported are probably artefacts of sample preparation. Evidence is presented for a non-uniform calcium alginate concentration profile even in beads that have been ‘equilibrated’ in calcium chloride solution for over 24 h. It is found that the internal structure depends on the ratio of calcium and alginate concentrations and a microstructural phase diagram can be constructed. Copyright © 2000 John Wiley & Sons, Ltd.

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.

Anomalous proton NMR relaxation behavior of cell wall materials from Chinese water chestnuts

Proton T1 NMR relaxation of the cell wall materials from Chinese water chestnuts (CWC) is an order of magnitude more efficient than those from potatoes, even though both the major relaxation pathways and the relative proton population of the relaxation groups are similar. This anomalous behavior of CWC can be explained by the detection of a strong ESR signal, which is an order of magnitude larger than that in samples from potatoes. The estimated free radical concentration is about 60 µM. Spectral properties of the radicals (g = 2.00599, linewidth 10.75 G) are consistent with that of semiquinone radicals derived from wall-bound polyphenols in cell wall materials. Hydration led to the drastic reduction of the ESR signal; it virtually disappeared when as little as 13% water was added to CWC in the vapor phase. Redrying over phosphorus pentoxide under vacuum followed by exposure to air resulted in some recovery of the free radical signals. Paradoxically, 1H T1 relaxation of a wet CWC (21% D2O) showed sustained efficiency at T > 300 K. T1ρ relaxation was only moderately affected by the presence of free radicals and transverse relaxation showed no effects. All the relaxation behavior could be accounted for by a spin diffusion model involving low concentration of unpaired electron spins. Copyright © 2000 John Wiley & Sons, Ltd.

Investigation of partially deuterated poly(butadiene) elastomers. Part 1. 1H and 2H nmr transverse relaxation data

It is well known that deuteron nmr is a very sensitive tool for the investigation of order and orientation. 1H and 2H nmr measurements of partially deuterated poly(butadiene) elastomers with systematically varied elastic properties are presented. A combined study of proton and deuteron nmr relaxation and the behavior under mechanical deformation was performed. 2H nmr transverse magnetization data are compared to the predictions of a model describing elastomer deuterium transverse magnetization data as a linear superposition of contributions from elastic chains and free dangling chain ends. The structural parameters are compared with results from mechanical and swelling measurements. The influence of microstructure, precursor chain length and their molar mass distribution as well as of the crosslink density on the transverse relaxation and the deformation behavior were studied.

Proton NMR Study of the Molecular Motions in Smectic-C* Ferri and Anti-Ferroelectric Mesophases

We report the first study of molecular dynamics in S*Cγ (ferrielectric) and S*CA (anti-ferroelectric) mesophases of a liquid crystal, by means of proton NMR relaxation. The relaxation dispersion detected in both S*Cγ and S*CA mesophases is compared with the observed for the SA and S*C phases of the same compound, which is similar to those observed in previous studies. However, to describe the relaxation behaviour detected in both S*Cγ and S*CA mesophases we had to include an additional relaxation mechanism. Considering the frequency range where it is observed, this mechanism may be related to the antiphase azimuihal mode previously detected by dielectric permittivity studies.

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.

Solid state 1H NMR studies of cell wall materials of potatoes

Cell wall materials from potatoes ( Solanum tuberosum) prepared by two different methods have been studied using NMR proton relaxation times. Spin lattice relaxation in both the rotating and laboratory frames as well as transverse relaxation have been measured over a range of temperatures and hydration levels. It was observed that the sample prepared using a DMSO extraction showed anomalous behaviour of spin lattice relaxation in the laboratory frame probably due to residual solvent in the sample. Spin lattice relaxation in the laboratory frame is the result of hydroxymethyl rotation and another unidentified high frequency motion. In the rotating frame relaxation is adequately explained by hydroxymethyl rotation alone. In neither experiment is methyl group rotation observed, calculation suggests that this is due to the low density of methyl groups in the sample. Non-freezing water in potato cell walls, α-cellulose and pectin was found about 0.2, 0.04 and 0.18 g per gram dry matter, indicating preferable hydration of pectin compared to cellulose. The effects of hydration are most noticeable in the measurements that reflect low frequency motions, particularly transverse relaxation, where both second moments and the relative intensity of signals arising from immobile material are reduced by hydration.

Water‐polysaccharides interactions during apples drying process

AbstractIn this work the state of water in samples of a food (apple) during the drying process was analyzed.Low resolution NMR, differential scanning calorimetry (DSC) and sorption measurements were performed on differently dried samples.It was possible to correlate the NMR proton relaxation time to the water activity aw=P/P0, in order to have an independent method for measuring this parameter. The calorimetric curves showed the thermal transitions of different water populations and the sorption measurements on dry apple gave the fraction of water tightly bond to the structure, which resulted about 30%.

The effect of excipients on the molecular mobility of lyophilized formulations, as measured by glass transition temperature and NMR relaxation-based critical mobility temperature.

The dependence of the molecular mobility of lyophilized formulations on pharmaceutical polymer excipients was studied. Molecular mobility as determined by NMR relaxation-based critical temperature of molecular mobility (Tmc) and glass transition temperature (Tg) is discussed in relation to the plasticizing effect of water in formulations. The Tmc and Tg of lyophilized gamma-globulin formulations containing 6 different polymer excipients such as dextran, polyvinylpyrrolidone (PVP) and methylcellulose (MC) was determined by NMR and DSC. The molecular mobility of water in the formulations was determined by proton NMR and dielectric relaxation spectrometry (DRS). Tmc varied with polymer excipients. Tmc increased as the ratio of bound water to mobile water increased and as the molecular mobility of mobile water decreased. The formulation containing MC exhibited a lower Tmc than the formulation containing dextran because of the smaller ratio of bound water and the higher molecular mobility of mobile water. The Tmc of the formulation containing PVP was higher than that expected from the higher T2 values of water because of the lower molecular mobility of mobile water regardless of the higher ratio of mobile water. The Tmc of these lyophilized formulations was higher than their T(g) by 23 degrees C to 34 degrees C, indicating that the formulations became a NMR-detected microscopically liquidized state below their T(g). The quantity and the molecular mobility of mobile water in lyophilized formulations can be considered to affect the T(mc) of lyophilized formulations, which in turn governs their stability.

Ageing of Starch Based Systems as Observed with FT-IR and Solid State NMR Spectroscopy

The retrogradation and physical ageing of model starch systems with respect to their glass transition temperatures Tg have been investigated by Fourier transform infrared Spectroscopy and solid state NMR spectroscopy. Diffuse reflectance Fourier transform infrared (DRIFT) spectra demonstrate the commencing retrogradation of starch materials stored above their Tg by changes in peak lineshapes and intensities in the characteristic area between 995 cm−1 and 1020 cm−1. Solid state NMR proton relaxation times in the rotating frame (proton T1ρ) show a characteristic course in relation to the storage conditions (time, humidity), for which a distinction is made between physical ageing which occurs below the Tg, and recrystallisation (retrogradation) which takes place above Tg. The proton T1ρ's of materials stored below Tg increase asymptotically in time due to physical ageing, whereas the proton T1ρ's of materials stored above Tg increase until a moisture content is reached that rises them above Tg, decrease due to further water absorption and then increase due to recrystallisation (retrogradation).

Relaxation rates of blood with osmotically modified red cell volume: application of the two-compartment fast exchange model.

Blood has been considered as a simplified tissue model, both physiologically and physically consisting in two compartments, extra-cellular and intra-cellular. In the physiologic condition (300 mOsm), the relaxation rates of red cell suspensions in saline increased linearly with the hematocrit in the range 0-0.80 according to Fullerton's model of fast proton exchanges between the two compartments (Fullerton GD, Potter JL, Dornbluth NC. NMR relaxation of protons in tissues and other macromolecular water solutions. Magn Reson Imaging 1982; 1:209-228). In experiments of osmotic variations, between 200 and 900 mOsm at three constant red cell numbers in the samples, non-linear variations of relaxation rates with red cell volume were observed. In the hyperosmotic domain, the particularly high increase in blood transverse relaxation rate with the decreasing cell volume has been attributed to the progressive water-protein organization in the cellular compartment. A generalised form of the fast exchange model has been applied to extended experimental conditions of red cells, by introducing the red cell volume ratio of modified to iso-osmotic values, and the volume fraction of iso-osmotic red cells.

Molecular Dynamics in Dilute Aqueous Solutions of Ethyl(hydroxyethyl)cellulose and Sodium Dodecyl Sulfate As Investigated by Proton NMR Relaxation

Dilute aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) and sodium dodecyl sulfate (SDS) have been investigated by 1H NMR shift and relaxation measurements. The shift measurements indicate no presence of EHEC at the core of the SDS micelles but at and just inside the micellar surface. Both the spin−lattice relaxation time (T1) and the spin−spin relaxation time (T2) imply that molecular motions slow as the system aggregates. T1 measured at both 270 and 400 MHz indicates nonextreme narrowing conditions with molecular motions on the nanosecond time scale. T2 monitors slower dynamics of the EHEC/SDS/water as compared to both of the systems polyethylene oxide (PEO)/SDS/water and SDS/water, attributed to the rigid EHEC backbone as compared to the more flexible PEO chain. An important observation is that the NMR relaxation data correlate well with the microviscosity in the EHEC/SDS/water system as measured by intramolecular excimer formation of the fluorescent probe 1,3-di(1-pyrenyl)propane (P3P).

Water Binding of PolysaccharidesNMR and ESR Studies

In this paper proton and deuteron NMR relaxation data of water in various physiologically important polysaccharides are presented as a function of the water content. The relaxation times are analyz...

A method for analysing proton NMR relaxation data from motionally heterogeneous polymer systems

Historically, the results of studies of the motional processes present in polymers above the glass transition temperature ( T g) by proton NMR spin-lattice relaxation in either the laboratory or rotating frames ( T 1 or T 1ρ) have shown poor agreement with the results from similar studies carried out using other techniques such as dielectric or mechanical relaxation. We believe that this is mainly because of the complication of the NMR results due to magnetisation transport, either by spin diffusion or by bulk diffusion of the polymer. We suggest a novel approach to the analysis of proton NMR relaxation data from a motionally heterogeneous polymer, and show that the results of such an analysis are intrinsically reasonable and of the form expected for dielectric or mechanical relaxation.

Proton NMR Study of Rouse Dynamics and Ideal Glass Transition Temperature of Poly(ethylene oxide) LiCF3SO3 Complexes.

A range of low-molecular-weight linear poly(ethylene oxide) chains with LiCF3SO3 have been examined via the transverse proton NMR relaxation. From the measured relaxation functions it is shown that the chains obey Rouse dynamics. This analysis gives the molecular weight of a Rouse statistical subunit and the fundamental Rouse relaxation time. It was found that varying the temperature and salt concentration had no effect on the size of a Rouse statistical segment and therefore none on the conformation of the chains. The temperature dependence of the fundamental Rouse relaxation time was found to be well modeled by the Vogel-Tamman-Fulcher equation. The NMR-measured correlation times were then successfully used to predict the glass transition temperature as measured by DSC. The main conclusion of this paper is that under the addition of salt the ideal glass transition temperature T0 is found to remain constant or indeed to slightly decrease.

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.

Nuclear Magnetic Resonance Study of theS=1/2Heisenberg LadderCu2(C5H12N2)2Cl4: Quantum Phase Transition and Critical Dynamics

We present an extensive NMR study of the spin-1/2 antiferromagnetic Heisenberg ladder Cu2(C5H12N2)2Cl4 in a magnetic field range 4.5 - 16.7 T. By measuring the proton NMR relaxation rate 1/T_1 and varying the magnetic field around the critical field H_c1 = Delta / g\mu_B = 7.5 T, we have studied the transition from a gapped spin liquid ground state to a gapless magnetic regime which can be described as a Luttinger liquid. We identify an intermediate regime T > |H-H_c1|, where the spin dynamics is (possibly) only controlled by the T=0 critical point H_c1.