Spin-echo NMR Technique Research Articles

Diffusion Coefficients in Cold Sulfuric Acid Solution

The diffusion coefficients of dimethyl sulfoxide, dimethyl sulfone, 15N-labeled DNO3, and 17O-labeled D2O in solutions of 0.6−0.8 weight fraction D2SO4 in D2O were studied at temperatures from 248 to 298 K by the pulsed gradient spin-echo NMR technique. Diffusion coefficients for these compounds are reported, and an empirical technique for extrapolating the results to sulfuric acid of stratospheric compositions and temperatures is discussed. The viscosity of 0.7 weight fraction D2SO4 in D2O at temperatures from 248 to 298 K is also reported.

Transverse spin relaxation in liquid 129Xe in the presence of large dipolar fields.

Using spin-echo NMR techniques we study the transverse spin relaxation of hyperpolarized liquid 129Xe in a spherical cell. We observe an instability of the transverse magnetization due to dipolar fields produced by liquid 129Xe, and find that imperfections in the pi pulses of the spin-echo sequence suppress this instability. A simple perturbative model of this effect is in good agreement with the data. We obtain a transverse spin relaxation time of 1300 sec in liquid 129Xe, and discuss applications of hyperpolarized liquid 129Xe as a sensitive magnetic gradiometer and for a permanent electric dipole moment search.

Formula omitted] NMR study of Gd–Ni intermetallic compounds

The spin-echo NMR technique was used to study the magnetic properties of the following intermetallic compounds of the Gd–Ni series: Gd 2Ni 17, GdNi 5, GdNi 3, GdNi 2 and GdNi, with 155 Gd and 157 Gd nuclei as local probes. These compounds have different crystal structures and order ferri- or ferromagnetically. The NMR measurements were performed at 4.2 and 1.5 K. The NMR spectra were compared to computed line positions obtained from the diagonalization of the complete hyperfine Hamiltonian. The RKKY contribution to the hyperfine field was computed for Gd 2Ni 17 and GdNi 3, and differences in the values of B hf at the two sites of Gd, of the order, respectively, of 18 and 6 T, were thus justified. An intense quadrupole interaction was observed at the Gd sites in the compounds GdNi 5, Gd 2Ni 17, and in one of the sites of the compound GdNi 3; in all these cases, the values of V zz are of the order of 10 22 V/m 2. The NMR results in GdNi are consistent with a direction of magnetization along the b-axis for this compound. The present study presents the first systematics of hyperfine interactions in Gd–Ni compounds.

NMR determination of 2D electron spin polarization at nu = 1/2

Using a "standard" NMR spin-echo technique we determined the spin polarization P of two-dimensional electrons, confined to GaAs quantum wells, from the hyperfine shift of Ga nuclei located in the wells. Concentrating on the temperature ( 0.05 less, similarT less, similar10 K) and magnetic field ( 7 less, similarB less, similar17 T) dependencies of P at Landau level filling factor nu = 1/2, we find that the results are described well by a simple model of noninteracting composite fermions, although some inconsistencies remain when the two-dimensional electron system is tilted in the magnetic field.

NMR measurements of self diffusion in polymer gel electrolytes

The pulsed field gradient NMR spin-echo technique has been used to measure the self diffusion coefficients of solvent molecules, Li+ cations and CF3SO3−1 anions in polyvinylidene fluoride (PVDF) gel electrolytes incorporating liquid electrolytes based on either N,N-dimethylformamide (DMF) or tetraglyme (TG) and lithium triflate (LiT). Using the Nernst–Einstein equation with the NMR diffusivities, calculated values for the ionic conductivity were obtained and compared with those determined by ac conductivity measurements to provide estimates of ionic association. These results for the gel electrolytes are compared with those for the corresponding liquid electrolytes, over a range of salt concentrations and temperatures. In general terms, the comparisons support the simple conclusion that regions of liquid electrolyte exist within the gel electrolytes, consistent with limited measurements of the transverse relaxation time T2 on these systems, which are also reported. There are, however, some small but significant differences between the behaviours of the gel electrolytes and the liquid electrolytes and these are discussed.

Study of the self‐diffusion of poly(ethylene glycol)s in poly(vinyl alcohol) aqueous systems

We have measured the self-diffusion coefficients of a series of oligo- and poly(ethylene glycol)s with molecular weights ranging from 150 to 10,000, in aqueous solutions and gels of poly(vinyl alcohol) (PVA), using the pulsed-gradient spin-echo NMR techniques. The PVA concentrations varied from 0 to 0.38 g/mL which ranged from dilute solutions to polymer gels. Effects of the diffusant size and polymer concentration on the self-diffusion coefficients have been investigated. The temperature dependence of the self-diffusion coefficients has also been studied for poly(ethylene glycol)s with molecular weights of 600 and 2,000. Several theoretical models based on different physical concepts are used to fit the experimental data. The suitability of these models in the interpretation of the self-diffusion data is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2396–2403, 1999

Study of the self-diffusion of poly(ethylene glycol)s in poly(vinyl alcohol) aqueous systems

We have measured the self-diffusion coefficients of a series of oligo- and poly(ethylene glycol)s with molecular weights ranging from 150 to 10,000, in aqueous solutions and gels of poly(vinyl alcohol) (PVA), using the pulsed-gradient spin-echo NMR techniques. The PVA concentrations varied from 0 to 0.38 g/mL which ranged from dilute solutions to polymer gels. Effects of the diffusant size and polymer concentration on the self-diffusion coefficients have been investigated. The temperature dependence of the self-diffusion coefficients has also been studied for poly(ethylene glycol)s with molecular weights of 600 and 2,000. Several theoretical models based on different physical concepts are used to fit the experimental data. The suitability of these models in the interpretation of the self-diffusion data is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2396–2403, 1999

Self-Diffusion Studies of Water and Poly(ethylene glycol) in Solutions and Gels of Selected Hydrophilic Polymers

To test the effect of the matrix polymer on diffusion, we have measured the self-diffusion coefficients of water and poly(ethylene glycol) of a molecular weight of 600 (PEG-600) in aqueous systems of selected polymers using the pulsed-gradient spin-echo NMR technique. The polymers used in this study include poly(vinyl alcohol) (PVA), hydroxypropyl methyl cellulose (HPMC), poly(N,N-diethylacrylamide) (PNNDEA), and poly(N-isopropylacrylamide) (PNIPA). The polymer concentrations varied from 0 to 0.38 g/mL. The effect of the polymer network on the self-diffusion coefficients of the solvent (water) and a solute (PEG-600) was investigated by analyzing the diffusion data with the use of the free volume model of Yasuda et al. [Yasuda, H.; Lamaze, C. E.; Ikenberry, L. D. Makromol. Chem. 1968, 118, 19], the diffusion model proposed by Phillies [Phillies, G. D. J. Macromolecules 1986, 19, 2367], and the model of Petit et al. [Petit, J.-M.; Roux, B.; Zhu, X. X.; Macdonald, P. M. Macromolecules 1996, 29, 6031]. The re...

NMR STUDIES ON SELF DIFFUSION COEFFICIENTS OF LITHIUM IONS IN PAN-BASED GEL POLYMER ELECTROLYTES

The self diffusion coefficients D of lithium ions in PAN-EC/PC-LiClO4 gel polymer electrolytes with different compositions and at different temperatures have been directly measured by field gradient NMR spin echo technique. The results indicated that self diffusion coefficients D of lithium ions were dependent on the mass ratio x% of lithium salt, and had a maxiumum at x=10 in the range of x=5 to 20. It was suggested that this was probably involved with transport mechanisms of the hopping of lithium ions, and with two kinds of interactions: the interaction between Li+ ions and plasticizer EC, and the interaction between Li+ ions and network polymer PAN.

Expression of aquaporins in Xenopus laevis oocytes and glial cells as detected by diffusion-weighted 1H NMR spectroscopy and photometric swelling assay

Expression of aquaporins (AQP) and water permeability were studied in Xenopus laevis oocytes and immobilized glial cells by a pulsed-field gradient spin echo NMR technique and a photometric swelling assay. Oocytes injected with poly(A) RNA from C6-BU-1 cells showed increased swelling behavior under hypoosmotic stress due to expressed water channels as compared to control oocytes. The swelling could be reversibly inhibited by HgCl 2. Furthermore, the intracellular relaxation time and the apparent intracellular diffusion coefficient of water in oocytes were determined by diffusion-weighted 1H NMR experiments to be T 2=36 ms and D app,intra=0.18×10 −3 mm 2/s. In immobilized C6 and F98 cells the mean exchange time of intracellular water was found to be 51 ms which increased to 75 ms upon chronic treatment (4 days) in hypertonic medium. Additional hybrid depletion experiments with antisense oligonucleotides directed against AQP1 were performed on oocytes and C6 cells. Moreover, different water channel subtypes of glial cells were assessed by a reverse transcriptase polymerase chain reaction assay. With this, the mRNA encoding AQP1 could be detected in primary cultures and glial cell lines, whereas AQP4 mRNA was found in astroglia-rich primary cultures, but not in F98 and C6 cells. Our results show that water permeability in glial cells is mainly mediated by water channels which play an important role in the regulation of water flow in brain under normal and pathological conditions.

63Cu NMR Evidence for Magnetic Dimensional Crossover in La2-xSrxCuO4

We found a nearly \(\sqrt {T}\) dependence of the planar 63 Cu nuclear spin-lattice relaxation rate 1/ T 1 for the 63 Cu-enriched overdoped La 2- x Sr x CuO 4 ( x =0.23; T c ∼20 K), using the 63 Cu NMR spin-echo technique. Considering both the transport and the magnetic properties, we conclude that the overdoped compound with x =0.23 is a three-dimensional nearly antiferromagnetic metal. The results indicate that a crossover in the antiferromagnetic spin fluctuation spectrum from two to three dimensions occurs as the Sr content increases beyond x ∼0.20. This is consistent with the dimensional crossover in conduction suggested from the results of electrical resistivity measurements.

Cu NMR Study of Bilayer HgBa2CaCu2O6+δ–Variation of Pseudo Spin-Gap Spectrum

We observed the pseudo spin-gap behavior in the T -dependences of 63 Cu Knight shift and NMR relaxation rates, as well as electrical resistivity, over a wide doping range for the bilayer high- T c HgBa 2 CaCu 2 O 6+δ using 63 Cu NMR spin-echo technique. We found a difference in the doping dependence of the pseudo spin-gap behavior between HgBa 2 CaCu 2 O 6+δ and the previous monolayer HgBa 2 CuO 4+δ . The results indicate that the pseudo spin-gap behavior strongly depends on the underlying electronic states.

Restricted diffusion and exchange of intracellular water: theoretical modelling and diffusion time dependence of 1H NMR measurements on perfused glial cells.

Intracellular diffusion properties of water in F98 glioma cells immobilized in basement membrane gel threads, are investigated with a pulsed-field-gradient spin-echo NMR technique at diffusion times from 6 to 2000 ms and at different temperatures. In extended model calculations the concept of 'restricted intracellular diffusion at permeable boundaries' is described by a combined Tanner-Kärger formula. Signal components in a series of ct experiments (constant diffusion time) are separated due to different diffusion properties (Gaussian and restricted diffusion), and physiological as well as morphological cell parameters are extracted from the experimental data. The intracellular apparent diffusion coefficients strongly depend on the diffusion time and are up to two orders of magnitude smaller than the self diffusion constant of water. Propagation lengths are found to be in the range of 4-7 microns. Hereby intracellular signals of compartments with a characteristic diameter could be selected by an appropriate gradient strength. With cg experiments (constant gradient) a mean intracellular residence time for water is determined to be about 50 ms, and the intrinsic intracellular diffusion constant is estimated to 1 x 10(-3)mm2/s. Studying the water diffusion in glial cells provides basic understanding of the intracellular situation in brain tissue and may elucidate possible influences on the changes in the diffusion contrast during ischemic conditions.

Self-diffusion of water in thermoreversible gels near volume transition: Model development and PFG NMR investigation

Pulsed filed gradient spin echo (PFG-SE) NMR technique has been used to measure the self-diffusion coefficient ( D self) of water in a thermoreversible hydrogel, Poly(N-isopropylacrylamide). D self, was measured as a function of temperature (−5–50°C) and hydration level. A theoretical model to predict D self was built by using a combination of lattice fluid hydrogen bond theory and free volume theory. The fully swollen gel did not show any discontinuous change in D self with temperature, Whereas, a partially swollen gel, showing the existence of two kinds of water having diffusivities differing by order of magnitude, exhibits a discontinuous change in D self. These results were explained within the theoretical framework developed by us. The present work thus enables an elucidation of diffusion phenomenon at the volume transition point for the first time.

Pseudo Spin-Gap Spectrum in the Monolayer HgBa2CuO4+δ

We report the doping dependence of the planar 63 Cu Knight shift ( 63 K ), the nuclear spin-lattice relaxation rate 63 (1/ T 1 T ) and the Gaussian spin-echo decay rate 63 (1/ T G ) for the high- T c monolayer HgBa 2 CuO 4+δ over a wide doping range [ T c =50, 72, 82 K (underdoping), 96 K (optimal doping) and 30 K (overdoping)], measured by the Cu NMR spin-echo technique. We found the following new facts; (1) both the static and the dynamical spin susceptibilities exhibit the pseudo spin-gap behavior over a wide q region around the staggered mode Q , (2) the dynamical pseudo spin-gap in 1/ T 1 T can mainly be ascribed to the static one in 1/ T G , and (3) a spin fluctuation amplitude probed by the empirical ratio T 1 T /( T G ) 2 is a monotonic decreasing function of the doping level but not proportional to T c . From comparison with La 2- x Sr x CuO 4 , we discussed the role of the pseudo spin-gap in the high- T c superconductivity.

Molecular motion and solvation of benzene in water, carbon tetrachloride, carbon disulfide and benzene: A combined molecular dynamics simulation and nuclear magnetic resonance study

Benzene, dissolved in several solvents of varying viscosities and as a neat liquid, is investigated using both MD simulation techniques and NMR spectroscopy. Molecular motions—linear translation, angular rotation and reorientational motion—are studied and related to intermolecular interactions and to the microscopic solvation structure obtained from MD simulation. Self-diffusion coefficients are measured by Fourier transform pulse-gradient spin–echo NMR techniques. The reorientational rotational motion of benzene is studied using 2H NMR T1 relaxation measurements. The 2H T1 measurements also include benzene in solvents: hexane, cyclohexane, chloroform, dodecane and hexadecane. A special emphasis is on the anisotropy of benzene. Attempts are made to interpret the anisotropic behavior in terms of specific solute–solvent interactions and the solvation structure around benzene. Concerning the three solvents—water, carbon tetrachloride and carbon disulfide—a fairly clear and consistent picture emerges from both experimental and theoretical studies. The reorientational motion of benzene is found to be highly anisotropic in water, slightly less anisotropic in carbon tetrachloride, while it is nearly isotropic in carbon disulfide solution. MD simulations show some evidence for hydrogens of water approaching the ring region of benzene.

Diffusion of Li+ ions in concentrated solutions of LiNO3 in 1,3-diaminopropane

The temperature and composition dependences of the self-diffusion coefficient of Li+ ions were investigated for concentrated solutions of LiNO3 in 1,3-diaminopropane by means of the NMR spin-echo technique from 20 to 50°C. The composition dependence of the activation energy shows a bend around 30 mol % LiNO3. This is consistent with the previous results obtained from the electrical conductivity and the correlation time of the rotational motion of the solvating ions, and suggests that solvent molecules may act as bridges between Li+ ions at higher concentrations of LiNO3.

1H MAS and 1H[ 23Na] double resonance NMR studies on the modification of surface hydroxyl groups of γ-alumina by sodium

The modification of surface hydroxyl groups with sodium in a series of Na 2CO 3-γ-Al 2O 3 catalysts was investigated as a function of both the Na 2CO 3 loading and the calcination temperature by means of 1H magic angle spinning (MAS) and 1H[ 23Na] spin-echo double resonance NMR techniques. The 1H NMR experiments revealed that sodium ions are homogeneously distributed over the alumina surface and closely coordinated with the surface hydroxyl groups. In the catalysts calcined at 250 °C, the acidic hydroxyl groups (with a chemical shift of 2.0 ppm) are preferentially associated with sodium ions at low Na 2CO 3 coverages (5 and 10%), while both the acidic and the basic (0 ppm) hydroxyl groups are accessible for sodium ions at high coverages (15 and 20%). The coordination causes a low-field shift of about 2 ppm in the 1H MAS spectra, and a broad signal at 4.5 ppm appears. It is interesting that the 4.5 ppm signal is completely suppressed in the 1H[ 23Na] MAS experiments, providing direct evidence that a strong interaction exists between adsorbed sodium ions and the surface hydroxyl groups. Increasing the calcination temperature to 450 °C results in preferential removal of the acidic hydroxyl groups, and only the most basic hydroxyl groups remain when the calcination temperature is raised to 600 °C. This is attributed to the formation of the coordinated species ▪ which enhances the acidity of the surface hydroxyl groups and prompts their dehydroxylation, especially at high calcination temperature. Correlation of the 1H MAS NMR results and catalytic activity measurements indicates that the basic hydroxyl groups are essential for the carbonyl sulfide hydrolysis reaction.

Dynamic properties of aqueous solutions of ethylene glycol oligomers as measured by the pulsed gradient spin-echo NMR technique at 25[deg

Self-diffusion coefficients for binary systems containing water and an oligomer of ethylene glycol [HO–(CH2CH2–O)nH, n=1–5], have been measured at 25°C in the whole concentration range by the pulsed gradient spin-echo NMR technique. Upon adding oligomer to pure water, both the oligomer and water self-diffusion coefficients decrease until a certain composition is reached, after which they remain approximately constant. This evidence is interpreted in terms of molecular interactions, especially hydrogen-bond formation. A relation between mutual and self-diffusion coefficients for these systems is found and commented upon.

Pseudo Spin-Gap in Single-Layer High-TcCu OxideHgBa2CuO4+δ

We observed the pseudo spin-gap behavior of spin excitations in lightly doped single- CuO 2 -layer HgBa 2 CuO 4+δ ( T c =50, 72 and 80 K) using the Cu NMR spin-echo technique. The results indicate that lightly doped high- T c Cu oxide inherently possesses the pseudo spin-gap.