An NMR study of restricted diffusion of water in Douglas-fir wood was undertaken using the pulsed field gradient method. The measurements were performed at 25 C and at two different moisture contents. Analysis of the results shows that the restricted diffusion of water molecules in this sample can be adequately described using a restricted diffusion model that considers diffusion to occur between infinite planar barriers. Two different barrier separations were incorporated into the model in order to obtain a good correspondence between the calculated and experimental results. Excellent agreement exists between parameters deduced from the NMR measurements and known anatomical data.

The proton spin-lattice relaxation parameters in natural and deuterated lysozyme solutions have been measured as a function of temperature (0-50 degrees C). The variation of the apparent magnitudes of the water proton magnetizations in the solutions with temperature indicates that magnetic coupling mixes protein and water proton magnetizations. The results are consistent with an exchange cross-relaxation model (Hills, B. P., Mol Phys 1992, 76, 489-508) in which the cross-relaxation acts between the labile and nonlabile protons, rather than between water and protein protons. Although this cross-relaxation pathway clearly affects the observed magnetization fractions in this protein solution, its influence on the relaxation rates is less apparent.

A nuclear magnetic resonance spin-lattice relaxation dispersion study of the relaxation of several magnetization components in both natural and deuterated lysozyme solutions was undertaken at 20 degrees C. Proton and deuteron resonances were employed. The two-dimensional time evolution of the magnetization and the spin-spin relaxation were analyzed. In addition, an isotopic dilution study was performed at 5 and 30.6 MHz. The results indicate that the water proton spin-lattice relaxation rate which arises from intermolecular relaxation between the water protons and the lysozyme protons represents a relatively strong relaxation mechanism. A model for the dynamics of the water molecules, consistent with the proton and deuteron dispersions as well as with the isotopic dilution results, is presented.

Proton and deuterium spin–lattice relaxation times (T1), spin–spin relaxation times (T2), and rotating frame spin–lattice relaxation times (T1ρ) and Fluorine T1 and T2 were measured as a function of hydration and temperature in hydrated Nafion. The proton and deuterium data display an apparent dynamical transition which we have attributed to a change in the degree of order within the aqueous phase. The temperature at which this transition occurs, Tt, is a function of the level of hydration, increasing for decreasing hydration. Above Tt, the relaxation processes are similar to those observed in bulk water.

The dynamical characteristics of water absorbed in Nafion are investigated using n.m.r. At temperatures below the dynamical transition temperature, Tt, relaxation rates indicate mobility associated with a fluid but the derived motional activation energies are similar to those of ice. This indicates a well ordered supercooled fluid consisting of hydrogen bonded water structures. The correlation time τc is found to have a Gaussian dependence on the surface area to volume ratio, unlike simple porous systems. We have shown that the surface area depends on r2.5. We feel that this is due to the irregular nature of the surfaces of the clusters.

A microprocessor‐based pulse programmer for pulsed nuclear‐magnetic resonance (NMR) based on the Intel 8086 has been developed. The pulse sequences are specified using a programming language developed specifically for this purpose. Pulse and delay timing is generated by a single timebase operating at 20 MHz, controlled by a state memory. The pulse programmer offers a high degree of flexibility at a moderate cost.

Proton nuclear magnetic resonance relaxation investigations of water dynamics in hydrated protein powders have the serious drawback that protein-water intermolecular dipolar interactions make the unambiguous interpretation of the results difficult. To circumvent this difficulty, deuteron spin-lattice and spin-spin relaxation times in lysozyme powder hydrated with deuterium oxide were measured as a function of temperature and at two frequencies. Although the deuteron relaxation results are compatible with a water molecule dynamics model based on either a bimodal distribution of correlation times or anisotropic motion, a comparison of the present results with proton data suggests than an anisotropic motion model is more likely to provide a reasonable description of the water molecule motion. An analysis based on an anisotropic motion model that uses two correlation times to characterize the motion shows that most of the water molecules rotate about their twofold axis of symmetry at a rate that is only approximately 100 times smaller than the rate of isotropic diffusion in the bulk liquid. The reorientation of the twofold axis of symmetry itself is characterized by a correlation time of approximately 10(-7) s.

A pulsed n.m.r. study of relaxation in the rotating reference frame was performed on cellulose samples with moisture contents ( MC ) ranging from 20.5% to 218%. The dependence of the spin-lattice relaxation time ( T 1 ρ ) in the rotating frame on temperature in a sample hydrated to approximately the fibre saturation point ( FSP ) indicates that in this case water exists in two different environments or phases. The first phase consists of a small number of water molecules (<1% of adsorbed water molecules in sample) tightly bonded to cellulose whereas the second phase consists of the remaining adsorbed water molecules which are more loosely attached. At room temperature exchange occurs between these phases at an intermediate exchange rate. For samples with MC > FSP a third water phase was identified. From the dependence of T 1 ρ on the rotating field strength information about water molecule dynamics was deduced.

In wet hen egg white lysozyme (HEWL), the molecular dynamics at the lysozyme–water interface was studied using a proton NMR line-shape-relaxation correlation approach that employed selective inversion of the proton magnetization. The intrinsic lysozyme proton spin-lattice relaxation rate, the intrinsic water proton spin-lattice relaxation rate, and the lysozyme proton – water proton cross-relaxation rate were determined. The lysozyme proton – water proton intermolecular interaction couples these protons and contributes to spin-lattice relaxation as well. The results suggest that a minimum of three different correlation times are needed to characterize the water molecule dynamics in wet HEWL.

En vue d'une meilleure comprehension des interactions entre le bois et les materiaux de revetements, on developpe une technique de RMN pulsee pour la determination precise des teneurs en huile de lin dans le bois de Populus tremuloides

Molecular motions of the fully deuterated sulfolan molecule (C4D8O2S) have been studied in the solid state by NMR measurements of the deuteron spin-lattice relaxation times in the laboratory (T1) and rotating (T1ρ) frame. In the crystalline phase, it has been found that the relaxation is determined by the ring puckering motion of the molecule. The plastic crystal phase is found to exhibit effects from both isotropic reorientation and translational diffusion. The modified nature of this phase and the plastic–crystalline transition of the deuterated as compared to the undeuterated solid is discussed in terms of the C–H—O hydrogen bonding between molecules.

The less known properties of cross relaxation between detectable spins I and fast relaxing spins S, such as the two types of H1 dispersion and the occurrence of two minima of the rotating frame Zeeman relaxation time T1x(I), when γH1T1(S)min<1, or the occurrence of two minima of the dipolar relaxation time T1d(I), when γHL, eff(I) T1(S)min<1 and T1(S)min≪T2(IS), are briefly discussed in the framework of the Blinc–Pirš–Žumer theory. The experimental results on cross relaxation between detectable spins I (protons or deuterons) and fast relaxation spins S (bromine, iodine, and chlorine) in the cubic phases of solid NH4Br, NH4I, and NH4Cl, and their deuterated analogs, are presented and explained.

Sulfolan has been studied by pulsed NMR measurements of laboratory frame spin–lattice relaxation T1 and rotating frame spin–lattice relaxation times T1ρ in the temperature range from 186 to 339 K. The previously reported phase transition at 288 K has been observed, but the data also show the presence of two additional, as yet unreported, phase transitions. The two crystalline phases are characterized by twofold rotations of the sulfolan molecules while the two plastic phases are both characterized by isotropic rotation and translational diffusion. It is suggested that the lower temperature plastic phase involves monovacancy diffusion while the higher temperature one involves relaxed vacancy diffusion. The relaxation times at most temperatures in the solid phases are dependent on the previous thermal history of the sample, with the transitions being sluggish and displaying hysteresis effects.

The transverse NMR relaxation times of hydrogen nuclei of water absorbed in white spruce sapwood [Picea glauca (Meunch) Voss] were measured for moisture contents in the range from 5 to 176%. The spin echo amplitudes resulting from the Carr–Purcell sequence decay nonexponentially suggesting the possibility of at least two different relaxation times for water in wood. A simplified structural model of the wood–water mixture is used to estimate the rates of chemical exchange at room temperature of hydrogen nuclei between various sites in the system. The high-resolution NMR line shape is discussed briefly in terms of this proposed model.

Pulsed nuclear magnetic resonance techniques have been used to measure the moisture content of sugar maple and white spruce sapwood in the range from 0 to 176%. The technique is found to be complementary to other methods of measuring moisture content in wood-cellulose systems.

The properties of ammonium perchlorate were investigated in the temperature range between 1.3 and 50 K by nuclear magnetic resonance and relaxation experiments. The observed increase in the proton second moment from its high temperature value of ~ 1.18 G2 to the value of 4.30 G2 below 4.2 K was associated with a characteristic activation energy of ~ 4 × 10−21 J molecule−1 (~ 0.6 kcal mole−1). No evidence could be found for nuclear spin conversion between the symmetry species of the ammonium ion from measurements of the static proton magnetic susceptibility above 1.3 K. An asymptotic analysis of the low temperature proton lineshapes identified the broad wings of the lines with ammonium ions of T type symmetry. Measurements of the proton relaxation times T1 and T1ρ agreed with previous work by others on NH4ClO4, and were similar to observations on other ammonium compounds having low reorientational barriers.

The temperature dependence and thermal hysteresis of proton and deuteron spin—lattice relaxation times at high fields and a study of the recovery of the proton and deuteron magnetizations in ammonium halides are reported. The anomalies occurring near the order—disorder phase transition are related to structural, dielectric and Raman data. The hysteresis effect and the establishment of long range order are shown to be related.

The frequency dependence of the proton spin dipolar relaxation time was measured in the range 24–32 MHz at 123, 127, and 131 °C in the nematic phase of the liquid crystal para-azoxyanisole. The experiment shows that in this liquid crystal a relaxation mechanism, too slow to relax the Zeeman energy, contributes to the relaxation of the dipolar energy. The experiment also shows that this relaxation rate does not depend on temperature or frequency within the range studied.