Relaxation Properties Of Water Research Articles

Spin-lattice relaxation time in water/graphene-oxide dispersion.

We present the results of the calculations of the spin-lattice relaxation time of water in contact with graphene oxide by means of all-atom molecular dynamics simulations. We fully characterized the water-graphene oxide interaction through the calculation of the relaxation properties of bulk water and of the contact angle as a function of graphene oxide oxidation state and comparing them with the available experimental data. We then extended the calculation to investigate how graphene oxide alters the dynamical and relaxation properties of water in different conditions and concentrations. We show that, despite the diamagnetic nature of the graphene oxide, the confining effects of the bilayers strongly affect the longitudinal relaxation properties of interfacial water, which presents a reduced dynamics due to hydrogen bonds with oxygen groups on graphene oxide. This property makes graphene oxide an interesting platform to investigate water dynamics in confined geometries and an alternative contrast-agent for magnetic resonance imaging applications, especially in view of the possibility to functionalize graphene oxide from theranostic perspectives.

Low-field and variable-field NMR relaxation studies of H2O and D2O molecular dynamics in articular cartilage.

Osteoarthritis (OA) as the main degenerative disease of articular cartilage in joints is accompanied by structural and compositional changes in the tissue. Degeneration is a consequence of a reduction of the amount of macromolecules, the so-called proteoglycans, and of a corresponding increase in water content, both leading to structural weakening of cartilage. NMR investigations of cartilage generally address only the relaxation properties of water. In this study, two-dimensional (T1-T2) measurements of bovine articular cartilage samples were carried out for different stages of hydration, complemented by molecular exchange with D2O and treatment by trypsin which simulates degeneration by OA. Two signal components were identified in all measurements, characterized by very different T2 which suggests liquid-like and solid-like dynamics. These measurements allow the quantification of separate hydrogen components and their assignment to defined physical pools which had been discussed repeatedly in the literature, i.e. bulk-like water and a combination of protein hydrogens and strongly bound water. The first determination of 2H relaxation dispersion in comparison to 1H dispersion suggests intramolecular interactions as the dominating source for the pronounced magnetic field dependence of the longitudinal relaxation time T1.

Disruption of Hydrogen-Bonding Network Eliminates Water Anomalies Normally Observed on Cooling to Its Calorimetric Glass Transition.

The calorimetric glass-transition temperature of water is 136 K, but extrapolation of thermodynamic and relaxation properties of water from ambient temperature to below its homogeneous nucleation temperature TH = 235 K predicts divergence at TS = 228 K. The "no-man's land" between the TH and glassy water crystallization temperature of 150 K, which is encountered on warming up from the vitrified state, precludes a straightforward reconciliation of the two incompatible temperature dependences of water properties, above 235 K and below 150 K. The addition of lithium chloride to water allows bypassing both TH and TS on cooling, resulting in the dynamics with no features except the calorimetric glass transition, still at 136 K. We show that lithium chloride prevents hydrogen-bonding network completion in water on cooling, as manifested, in particular, in changing microscopic diffusion mechanism of the water molecules. Thus thermodynamic and relaxation peculiarities exhibited by pure water on cooling to its glass transition, such as the existence of the TH and TS, must be associated specifically with the hydrogen-bonding network.

Probing water migration in Mozzarella cheese during maturation and heating utilizing magnetic resonance techniques

Immediately following manufacture, Mozzarella undergoes significant structural rearrangement. During this maturation process, free water occupying the interstitial area around the fat channels is absorbed into the protein matrix. Magnetic resonance techniques allow the evaluation of molecular mobility within the porous cheese matrix. A 3 week maturation trial was conducted in which the relaxation and diffusion properties of water and fat were assessed at room and elevated temperatures. Relaxation measurements at 20 °C highlighted the progressive change in the mobility of water as it became more associated with the casein gel matrix over the trial period. Heating was found to cause an increase in molecular mobility as the association between the casein and water lessened at elevated temperatures. This work illustrated that the diffusion and relaxation properties of water within Mozzarella on heating changed over a three week maturation period. The data also indicates that the diffusion of water at low temperatures was dominated by free water, while the diffusion at elevated temperatures was likely dictated by the degree of connectivity within the protein matrix.

Dielectric permittivity spectra of oil-water-saturated sandy-clayey rocks of different mineralogical compositions and relaxation properties of water in these rocks

Experimental measurements of the dielectric permittivity and equivalent conductivity of sandy-clayey samples (a mixture of river sand with bentonite or kaolin) saturated with salt-solution-diesel-fuel emulsions were performed in the frequency range from 10 kHz to 1 GHz at temperatures of 25-65 °C. It is shown that when the content of the salt solution in the saturating fluid does not exceed 10%, the dielectric permittivity in the frequency range from 1 MHz to 1 GHz depends little on the mineral composition of the sample and on the concentration of the saturating solution. When the portion of water is 33.3% or higher, increasing the concentration of the salt solution leads to an increase in the equivalent conductivity and the real part of the complex dielectric permittivity. Using the refractive model of the complex dielectric permittivity, we have estimated the dielectric properties of bound water, which depend on temperature and the type of clay (bentonite or kaolin) in the sand-clay mixture but are independent of the water saturation and the amount of clay in the sample.

Optimized in-phase and opposed-phase MR imaging for accurate detection of small fat or water fractions: theoretical considerations and experimental application in emulsions

To optimize strategies and measurement parameters for quantification of small fat and water fractions (<10%) in mixtures of both components by 4-point in-phase and opposed-phase gradient-echo imaging and to compare theoretical results with in-vitro experiments using emulsions. Theoretical analysis was based on steady-state signal equations for spoiled GRE-sequences and on relaxation properties of water and fat components. For quantification, signals were corrected for T2*-decay, T1-decay, and signal contributions from double bonds. Theoretical results were exemplarily compared to measurements at 1.5T on emulsions with either low water or fat fractions (0.5-10%) using spoiled 2D- and 3D-GRE-sequences. Excitation flip angle was varied in order to determine suitable values for sensitive detection of small fat/water fractions. Theoretical results and measurements correlated well, especially for 3D-sequences. Maximal sensitivity to a small signal fraction (S (fat) and S (water), respectively), was provided at the Ernst angle of the lower concentrated component. For 2D-sequences, the nominal flip angle had to be increased for compensation of slice profile effects and B(1) inhomogeneities. IP- and OP-echoes are recommended to be acquired in separate measurements with smallest possible receiver bandwidth to increase SNR/unit-time. Lowest detectable fat/water concentration in emulsions under typical conditions regarding spatial resolution and measuring time was approximately 1%. Using IP/OP-imaging with optimized parameters and post-processing, a sensitive and reliable detection of small fat/water fractions larger than 1% is possible in emulsions.

Quantification of water compartmentation in cell suspensions by diffusion-weighted and T2-weighted MRI

When studying water diffusion in biological systems, any specific signal attenuation curve may be reproduced by a broad range of mathematical functions. Our goals were to quantify the diffusion and T(2) relaxation properties of water in a simple biological system and to study the changes that occur in osmotically stressed cells. Human breast cancer cells were incubated in isotonic or hypotonic osmotic buffers. Diffusion-weighted and T(2)-weighted magnetic resonance images were acquired during sedimentation over 12 h. Diffusion-weighted imaging (DWI) data were analyzed with a biexponential fit, the Kärger model for exchange between two freely diffusing populations and the Price-modified Kärger model accounting for restricted diffusion in spherical geometry. We found that only the Price model provided an accurate quantitative description for water diffusion in both cell systems, independent of acquisition parameters, over the entire density range. Model-derived cell radii, intracellular volume fractions and transmembrane water exchange times were in good agreement with results calculated from light microscopy and with model-free exchange times. T(2) data indicated two populations in fast exchange, with volume fractions clearly different from DWI populations. Hypotonic stress led to higher slow apparent diffusion coefficient, longer T(2) and lower membrane permeability. The tortuosity in a hypotonic cell suspension complied with the Wang model for spherical geometry. Quantitative characterization of biological systems is obtainable by DWI, using appropriate modeling, accounting for water restriction and exchange between compartments.

3P150 ポリアクリル酸水溶液のマイクロ波誘電緩和特性のpHおよびNaCl濃度依存性(水・水和/電解質))

3P150 ポリアクリル酸水溶液のマイクロ波誘電緩和特性のpHおよびNaCl濃度依存性(水・水和/電解質))

Permeability of Porous Core

The relaxation properties of water saturated in porous core are discussed and the distribution of proton transverse relaxation time and bi-exponential model of longitudinal relaxation time are obtained, which provide an illustration for two-model of fluids saturated in porous media. The cutoff value of T-1 based on relaxation specific property of fluids in porous core is adopted to improve the correlation between permeability and Phi(4)T(1b)(2).

T1 and T2 relaxation times of the major 1H‐containing metabolites in rat brain after focal ischemia

The relaxation properties of water and metabolites were measured in rat brain following the occlusion of the middle cerebral artery (MCA) with localized 1H MRS. The PRESS sequence was employed to select volumes of 39 microL in the ischemic and the contralateral hemisphere. T1 and T2 relaxation times and peak intensities of water, choline containing compounds (Cho), creatine and phosphocreatine (Cre) and N-acetyl aspartate (NAA) in both hemispheres were determined at 3-6 h, 1 day and 3 or 4 days after occlusion. Lactate in the ischemic hemisphere was also quantified. The relaxation properties and peak intensities of NAA, Cre and Cho remained unchanged in the ischemic volume during the first 3-6 h of ischemia as compared to the contralateral volume. Water T2 was slightly increased in the ischemic volume. After 24 h the T1 and T2 of water and Cre and the T1 of Cho had increased significantly in the ischemic volume, while the peak intensities of Cho, Cre and NAA were reduced. It appears therefore that tissue changes which occur in the early phase of ischemia have no significant effects on the relaxation behaviour of the metabolites. However, ischemic brain damage affects the relaxation behaviour and concentration of the metabolites and water at later stages.