NMR Relaxation Times T1 Research Articles

Analysis of discreteT2 components of NMR relaxation for aqueous solutions in hollow fiber capillaries

An analysis is presented of proton NMR T2 relaxation times measured for aqueous solutions in simple bundles of hollow fibers. The relaxation times are calculated with a two-compartment diffusive exchange model using the known relaxation times of the aqueous solutions and the fiber geometry. When the relaxation time outside the fibers is short (approximately 1 ms), three or more relaxation components are observed from this two compartment system, in agreement with the calculation. The amplitude and relaxation times of the third component are consistent with those of a diffusion-mediated mode, as suggested theoretically by Brownstein and Tarr (Phys. Rev. A 19, 2446 (1979)). The possible contribution of such modes to the multicomponent relaxation observed in tissues is discussed.

Reduction in myocardial high energy phosphate spin lattice relaxation times using manganese.

Paramagnetic contrast agents are being widely used in proton magnetic resonance imaging. The present study demonstrates the potential usefulness of paramagnetic contrast agents in 31P NMR spectroscopy. Using the Langendorff perfused rat heart, manganese chloride (Mn2+) at a concentration of 50 microM/L was added to the perfusate for 10 or 30 min. 31P NMR T1 relaxation times were subsequently measured at 121.5 MHz. After the 10 min exposure to Mn2+, 31P NMR T1 measurements of phosphocreatine and ATP were reduced by ca 25 and 50%, respectively, with no significant change in linewidths. A small additional decrease in T1 relaxation times after infusion of Mn2+ for 30 min was not significantly different from the values at 10 min. Potential uses of Mn2+ in 31P NMR spectroscopy include improving the S/N ratio of spectra and assessment of calcium ion channel activity.

Evidence for Steric Enhancement of Resonance in 2-Alkylanisoles from 13C NMR T1 Relaxation Times of Methoxy-carbons and from Atomic Charges on Methoxy -oxygens

Evidence for Steric Enhancement of Resonance in 2-Alkylanisoles from 13C NMR T1 Relaxation Times of Methoxy-carbons and from Atomic Charges on Methoxy -oxygens

Resorption of peritumoural oedema in cerebral gliomas during dexamethasone treatment evaluated by NMR relaxation time imaging.

Peritumoural brain oedema is a prominent feature of malignant brain tumours. Glucocorticoids diminish the neurological symptoms and signs caused by the oedema and reduce the abnormally high cerebral water content. The exact mechanisms of action of the glucocorticoids are unknown. The present study investigates the influence of dexamethasone on NMR relaxation time T1 in peritumoural oedema in 13 patients with gliomas. It is shown that NMR T1 images can be used as a potent monitor of brain oedema, and that dexamethasone significantly reduces mean T1 after 1, 3, and 7 days of treatment by 2%, 6%, and 13% respectively. Using an image histogram analysis technique the term "super-oedema" was defined as the 50% of the total oedema area with the highest T1, corresponding to the highest water content. It is shown, that with this technique the treatment effect of steroids on super-oedema was a reduction of 13%, 33%, and 57% after 1, 3, and 7 days of treatment respectively. The mean change after 24 hours of treatment was statistically significant (p < 0.01). The method can be used in all situations where the anti-oedematous effect of a given treatment is to be monitored.

The synthesis and characterization of a mesomorphic brush type polycarbosilane: poly[1,1-bis(4?-biphenyl)silabutane

Poly[1,1-bis(4′-biphenyl)silabutane] (II) has been prepared by the anionic ring opening polymerization of 1,1-bis(4′-biphenyl)silacyclobutane. II shows mesomorphic behavior by DSC. The13C NMR T1 relaxation times have been measured. These are found to be smaller than those of poly(1,1-dimethylsilabutane)by an order of magnitude. This may result from interaction of the highly rigid biphenyl side chain moieties. The thermal stability of II is higher than that for other 1,1-disubstituted polysilabutanes.

Mutal interactions between hydrogen bonds in alcohols ‐ nuclear magnetic relaxation study

AbstractProton NMR relaxation times T1 and T2 were measured in methonal, ethanol, propanol and butanol at a temperature of 37°C and at an RF frequency of 20 MHz. The hydrogen bond energies of the above alcohols are in the range 2.33‐4.56 Kcal/mole. The relaxation time T1 is found to decrease with increase of hydrogen bond energy in these alcohols and this is explained by postulating mutal interactions between adjacent hydrogen bonds.

Phase behaviour of monoglyceride/water systems

Studies on the gel and lamellar phases formed by C16–18 saturated monoglyceride, C16–18SMG (Hymono 8903, a commercial distilled monoglyceride) in contact with water are described. Optical microscopy was used to study the mesomorphic behaviour as a function of temperature. Differential scanning calorimetry was utilised to determine the transition enthalpies between the mesophases. Surfactant mobility was studied by measuring proton NMR T2 relaxation times for samples comprising C16–18SMG/2H2O. Molecular ordering was also studied by measuring 2H and 17O quadrupole splittings (by NMR) for systems comprising C16–18SMG/2H2O and C16–18SMG/H217O (10% H217O in H216O).Over the temperature range studied (0–90 °C), gel, lamellar and cubic mesophases were found. For the gel phase, separate 2H NMR spectra, representing the 2H2O solvent and the monoglyceride O2H groups, were observed. Two signals were also observed for the lamellar phase. From the relative intensities, one signal was assigned to the O2H group on the terminal carbon atom of the monoglyceride molecule, whilst the other signal arose from the 2H2O solvent and the other monoglyceride O2H group. Analysis of these results demonstrate that there are about three bound water molecules per surfactant molecule for the lamellar phase at maximum hydration. Unusually, the degree of ordering of the water in the gel phase is much smaller than that of the water in the lamellar phase.

Hydrated clearance of gadolinium-DTPA as a measurement of glomerular filtration rate

Technetium (99mTc)-diethylene triamine pentaacetic acid (DTPA) hydrated clearance studies are accurate for determining GFR but require special facilities for handling and measuring samples. We investigated the potential of a non-radioactive paramagnetic analog, Gadolinium (Gd)-diethylene triamine pentaacetic acid (DTPA), an approved NMR contrast agent, as a glomerular filtration marker. Instead of relying on the radioactivity of technetium, this test is based on the fact that gadolinium induces alterations in the NMR T1 relaxation times in blood and urine samples. Ninety patients underwent simultaneous determinations of GFR using 1 mCi of Tc-DTPA and 0.05 mmol/kg Gd-DTPA (Berlex Labs) IV. The patients were hydrated with oral and intravenous fluid. Following a one hour equilibrium period, three or four consecutive urine collections were obtained; plasma samples were acquired at the beginning and end of each approximately 20-minute interval. 99mTc-DTPA radioactivity was determined with a scintillation counter. T1 relaxation times were measured on a 10 MHz NMR spectrometer. These were converted to Gd-DTPA concentration by comparison with standard solutions. The Gd-DTPA derived GFR closely approximated the 99mTc-DTPA derived GFR which ranged from 15 to 147 ml/min. The equation and correlation coefficient of the regression line is y = 1.04 x -2.2, r = 0.94. Thus, Gd-DTPA is a safe, non-radioactive indicator of GFR that may provide an alternative renal clearance method for clinical studies of progressive renal disease and nephrotoxicity.

Effects of micellization and surface adsorption on deuterium NMR T1 relaxation times of n-alkylphosphocholine surfactants

Effects of micellization and surface adsorption on deuterium NMR T1 relaxation times of n-alkylphosphocholine surfactants

Functional MR of the kidney

A bolus injection of Gadopentetate Dimeglumine with dynamic gradient echo MR imaging has allowed for the visualization of normal and abnormal renal function. Following an injection of gadopentetate dimeglumine, NMR T1 relaxation times obtained on serial collections of serum and urine at timed intervals were used to derive the glomerular filtration rate. The merger of dynamic contrast-enhanced MRI with an in vitro NMR-derived GFR provides for assessment of renal function without the use of radioactive agents.

Temperature dependence of the NMR line shifts and T1 relaxation times of tellurium-125 in the semiconductor alloys mercury cadmium telluride

The {sup 125}Te NMR spectra of the semiconductor alloys Hg{sub 1{minus}x}Cd{sub x}Te are studied. The temperature dependence between 15 and 300 K of the frequency shifts and the T{sub 1} relaxation times of the five tellurium lines in the spectra of a set of Hg{sub 1{minus}x}Cd{sub x}Te polycrystalline samples with a large variety of x values are measured. In addition to those for samples prepared stoichiometrically, NMR results are recorded for samples containing an excess and a deficiency of metal atoms. The results are reported, and qualitative conclusions are made concerning the electronic interaction, chemical shift, and Knight shift contributions governing the NMR experimental parameters. This study demonstrates the ability of NMR spectroscopy to monitor and characterize the clusters Hg{sub 4{minus}n}Cd{sub n}Te with n = 0-4 in the alloys separately.

Model for the structure of the lipid bilayer.

A detailed model for the structure and dynamics of the interior of the lipid bilayer in the liquid crystal phase is presented. The model includes two classes of motion: (i) the internal dynamics of the chains, determined from Brownian dynamics simulations with a continuous version of the Marcelja mean-field potential, and (ii) noncollective reorientation (axial rotation and wobble) of the entire molecule, introduced by a cone model. The basic unit of the model is a single lipid chain with field parameters adjusted to fit the 2H order parameters and the frequency-dependent 13C NMR T1 relaxation times of dipalmitoyl phosphatidylcholine bilayers. The chain configurations obtained from the trajectory are used to construct a representation of the bilayer. The resulting lipid assembly is consistent with NMR, neutron diffraction, surface area, and density data. It indicates that a high degree of chain disorder and entanglement exists in biological membranes.

1H and 19F NMR Relaxations of Electroconducting Polypyrrole and Polythiophene Trifluoromethanesulfonates

Abstract The NMR relaxation time T1 of 1H and that of 19F were determined for polypyrrole and polythiophene doped with trifluoromethanesulfonate (triflate) or perchlorate ions. The 1H T1 is governed by the paramagnetism of the polymer chains. The 19F T1 of the triflate ions is explained by the combined effect of the F–F dipolar interaction and the electron–nucleus coupling. The activation energy for CF3 reorientation about the C3 axis was 7.5 kJ mol−1 for polypyrrole triflate and 15 kJ mol−1 for the corresponding polythiophene.

Hydrogen bond dynamics in isotopically substituted benzoic acid dimers

The hydrogen pair transfer in the hydrogen-bonded dimers of benzoic acid and its carboxyl-deuterated species is investigated in the solid. Measurements are reported for the temperature-dependent NMR relaxation time T1 in single crystals containing dimers with one or two carboxylic deuterons. Combined with previous data, the temperature dependence of the measurements is analyzed in terms of a master-equation description for a one- or two-dimensional quantum-mechanical model of the transfer motion. The description by a one-dimensional model is found to be inadequate as it yields unrealistic isotope effects in the model parameters. On the other hand, reasonable results are obtained for a two-dimensional model which includes, apart from the transfer motion of the hydrogens, a heavy atom mode with properties suggested by x-ray structural data. This model explains the thermal activation of the transfer process mainly as a result of promotion of tunneling by heavy atom rocking. Activation energies remain considerably smaller than the barrier height and indicate predominance of tunneling even at room temperature.

1H NMR visibility of mammalian glycogen in solution.

High-resolution 1H NMR spectra of rabbit liver glycogen in 2H2O were obtained at 500 MHz, and several resonances were assigned by comparison with the chemical shifts of alpha-linked diglucose molecules. The NMR relaxation times T1 and T2 of glycogen in 2H2O were determined to be 1.1 and 0.029 s, respectively. The measured natural linewidth of the carbon-1 proton (12 +/- 2 Hz) is in excellent agreement with that calculated from T2. The visibility measurements made by digesting glycogen and comparing glucose and glycogen signal intensities demonstrate that in spite of the very high molecular weight, all of the proton nuclei in glycogen contribute to the NMR spectrum. The result is not unexpected, since 100% NMR visibility was previously observed from the carbon nuclei of glycogen, due to the rapid intramolecular motions.

13C NMR spectroscopic studies on polyanion‐polycation complexes and their component polyelectrolytes

AbstractPosition and intensities of the 13C NMR signals and relaxation times T1 of several anionic and cationic polyelectrolytes in the solid state were compared with those of the appropriate polyanion‐polycation complexes. At a high charge density of the components, the most significant changes of the parameters in question due to complex formation are observed for the C atoms adjacent to the charge centers, indicating a strong Coulombic interaction. At lower charge density, conformational changes of the polymer chains have also to be taken into consideration.

Investigations concerning the potential for using 1h nmr relaxometry or high‐resolution spectroscopy of plasma as a screening test for malignant lung disease

In 158 plasma samples, obtained from patients with lung carcinoma, lung metastases, and infectious or inflammatory lung diseases and from healthy controls, the NMR relaxation times T1 and T2 of water protons were measured at a resonance frequency of 20 MHz by pulsed NMR techniques and adjusted to a standardized total plasma protein concentration. For one-third of these samples water-suppressed 500-MHz 1H NMR spectroscopy at 37 degrees C was used (a) to determine the widths of the composite lipid methyl and methylene signals, and (b) to quantitate individual lipid methylene signal components that could be detected in resolution-enhanced spectra. In addition, hematological parameters and the plasma levels of several acute phase proteins and apolipoprotein-A were monitored. No diagnostically significant differences between lung carcinoma patients and patients with nonmalignant lung disease could be found for any of the plasma NMR parameters, nor could T1 or lipid linewidth data distinguish between any patient group and healthy controls. However, the mean T2 was significantly shortened by about 15% for any kind of lung disease compared to healthy controls. Similar but less significant results were found for apolipoprotein-A levels. A linear discriminant function, calculated from the apolipoprotein-A and T2 data, did not improve the differentiation between malignant and nonmalignant lung disease but did improve the discrimination between tumor patients and healthy controls up to a sensitivity and specificity of 80 and 96.5%, respectively. T2 correlates inversely with plasma fibrinogen levels and the blood sedimentation rate and, therefore, appears to monitor a general inflammatory status of a tumor patient rather than the presence or absence of cancer. For all groups except healthy pregnant women, the lipid methylene composite signal linewidth correlates inversely with the fraction of mobile triglyceride present (mainly as VLDL), as estimated from resolution-enhanced spectra.

NMR T1 relaxation time of the brain during alcohol withdrawal and its lack of relationship with symptom severity.

A significant fall in brain T1 relaxation time, consistent with a reduction in brain water of approximately 0.3%, occurred in 19 chronic alcoholic patients admitted for detoxification. There was no correlation between T1 and the severity of withdrawal symptoms and hence no evidence that changes in brain water levels contributed to the abstinence syndrome.

Polymer‐Water Interaction of Maltodextrins. Part II: NMR Study of Bound Water in Liquid Maltodextrin‐Water Systems

AbstractThe NMR relaxation times T1 and T2 for starch polysaccharides in solution were employed for the characterization of bound and free water. The “Solomon equations” were taken for the calculation of the amount of bound water in maltodextrin‐water systems. The amount of monomolecular bound water in maltodextrin solutions and gels is independent on the state in the same order of magnitude as estimated for maltodextrin powders from water vapour sorption isotherms. With increasing temperature between 1°C and 60°C a slight decrease of bound water was found.

Magnetic resonance studies on neutron irradiated quartz and amorphous silica

NMR and ESR experiments were performed on samples of neutron irradiated quartz and amorphous silica. MAS NMR and static NMR spectra (on 29Si) were acquired. Longitudinal NMR relaxation times T1 (of 29Si) were measured, both under MAS and static conditions. ESR was used to observe the paramagnetic centers in these samples, which are thought to be the main agent responsible for longitudinal NMR relaxation. Densities of these paramagnetic centers were derived from ESR spectra and the results were compared with the T1 results.