NMR pulsed field gradient technique

The M-S approach allows the prediction of the mixture diffusion based on the pure component M-S diffusivities, along with the mixrnre isotherms (i.e., estimated using the ideal adsorbed solution theory [LAST] of Myers and Prausnitz) [68]. Experimentally, the NMR pulse field gradient technique has been used to calculate the mixture diffusion coefficients. 

Transport Properties of Molecular Sieves Studied by the NMR Pulsed Field Gradient Technique... 

In contrast to the traditional method, the nmr pulsed field gradient technique (4-10) is applied to samples under macroscopic equilibrium. By monitoring the precessional phases of the nuclear spins around an external magnetic field, this technique allows the determination of the displacements r(A> of the individual molecules of the sample during an observation time A of typically 1...100 ms. Using Einstein s relation... 

Figure 8 Corrected diffiisivUies of methane, ethane and propane at various temp tures and sorbate concentrations as determined by single-step FR method (open symbols) and self-diffusion coefficients measured by the NMR pulsed-field gradient technique (filled symbols).

Jobic, H., Bee, M. Karger, J., Vartapetian, R.S., Balzer, C., and Julbe, A. 1995. Mobility of cyclohexane in a microporous sihca sample A quasielastic neutron scattering and NMR pulsed-field gradient technique... 

G. Fleischer, D. Geschke, J. Karger and W. Heink, "Peculiarities of Self-diffusion Studies on Polymer Systems by the NMR Pulsed Field Gradient Technique, J. Magn. Reson.. 65. 429-443 (1985). 

Heink W, Karger J, Pfeifer H, Stallmach F. Measurement of the intracrystaUine self-diffusion of xenon in zeolites by the NMR pulsed field gradient technique. J Am Chem Soc 1990 112 2175-8. 

The basic principles of both the nmr pulsed field gradient and nmr tracer desorption techniques are presented. It is shewn that these methods allow the measurement of the coefficients of intracrystalline and of long-range self-diiiusion as well as or the intracrystalline mean life times of the adsorbate molecules. By combining this information, a unique possibility for the direct proof of the existence of surface barriers is provided. The nmr methods are applied to study the transport properties of adsorbate molecules in zeolite NaX, NaCaA and ZSlf-5, with particular emphasis on the existence of surface barriers. 

In addition to the conventional application of nmr pulsed field gradient experiments to self-diffusion studies, it is also possible to determine the intracrystalline molecular life times. Referring to the corresponding classical experiment, this method has been termed nmr tracer desorption technique (7). Together with the self-diffusion measurements it provides an excellent tool for characterizing the transport properties in the intra- and intercrystalline spaces, as well as at the interface between them. So far, the nmr techniques provide the only possibility for a direct determination of the existence and of the intensity of transport resistances at this... 

Diffusivity of adsorbates may be determined by different techniques. In static conditions, molecules are jumping or hopping from one site to the other as detected by NMR pulse field gradient (47) or neutron diffusion (48) which are satisfactory techniques. In dynamic conditions adsorption rate may be determined by thermogravimetry (46) or volumetry (but heat transfer due to adsorption should be avoided). However in the latter cases compared to the former ones and diffusion coefficient values are then 2 to 4 orders of... 

A review entitled New phosphorus-tellurium heterocycles in the quasi-binary system RP/Te , which contains and Te NMR data, has appeared. H/ H isotope effect on the translational and rotational motion of liquid water and ammonia has been assessed by NMR measurements.The diffusion of ammonia in binary mixtures has been investigated using the pulsed-field gradient technique. A quantitative structure-property relationship of the P NMR chemical shifts has been developed for a large set of phosphines.The NMR spectrum of [P(CF3)2] has been analysed as X3MAY3 and determined.An iterative lineshape analysis of N NMR spectra of [N3] has been described. and P NMR studies of a liquid-crystalline cyclotriphos-... 

We finish this section by comparing our results with NMR and incoherent neutron scattering experiments on water dynamics. Self-diffusion constants on the millisecond time scale have been measured by NMR with the pulsed field gradient spin echo (PFGSE) method. Applying this technique to oriented egg phosphatidylcholine bilayers, Wassail [68] demonstrated that the water motion was highly anisotropic, with diffusion in the plane of the bilayers hundreds of times greater than out of the plane. The anisotropy of... 

There are a number of NMR methods available for evaluation of self-diffusion coefficients, all of which use the same basic measurement principle [60]. Namely, they are all based on the application of the spin-echo technique under conditions of either a static or a pulsed magnetic field gradient. Essentially, a spin-echo pulse sequence is applied to a nucleus in the ion of interest while at the same time a constant or pulsed field gradient is applied to the nucleus. The spin echo of this nucleus is then measured and its attenuation due to the diffusion of the nucleus in the field gradient is used to determine its self-diffusion coefficient. The self-diffusion coefficient data for a variety of ionic liquids are given in Table 3.6-6. 

Advances in experimental techniques, including pulsed-field gradient NMR, and theoretical methods, including volume averaging, macrotransport, and variational methods, that may lead to the resolution of a number of the fundamental issues in gel electrophoresis and to improvements in the practical application of electrotransport in polymeric media... 

While the nuclear magnetic resonance (NMR) technique has widely been used to study diffusion processes of normal liquids, solids, or colloidal systems, there are only a few applications to molten salts. The spin echo self-diffusion method with pulsed field gradients was applied to molten salts by Herdlicka et al. "" There is no need to set up or maintain a concentration gradient. 

A wide variety of ID and wD NMR techniques are available. In many applications of ID NMR spectroscopy, the modification of the spin Hamiltonian plays an essential role. Standard techniques are double resonance for spin decoupling, multipulse techniques, pulsed-field gradients, selective pulsing, sample spinning, etc. Manipulation of the Hamiltonian requires an external perturbation of the system, which may either be time-independent or time-dependent. Time-independent... 

Zhang O, Kay LE, Olivier JP, Forman-Kay JD. Backbone 11 and 15N resonance assignments of the N-terminal SFI3 domain of drk in folded and unfolded states using enhanced sensitivity pulsed field gradient NMR techniques. J Biol NMR 1994 4 845-858. 

Nafion absorbs MeOH more selectively than water, and the MeOH diffusion flow is higher than the osmotic water flow in Nafion membranes. Diffusion coefficients of Nafion 117 determined by different techniques have been reported. Ren et al. measured MeOH diffusion coefficients in Nafion 117 membranes exposed to 1.0 M MeOH solutions using pulsed field gradient (PPG) NMR techniques. The MeOH self-diffusion coefficient was 6 x 10 cm S and roughly independent of concentration over the range of 0.5-8.0 M at 30°C. A similar diffusion coefficient was obtained for Nafion 117 at 22°C by Hietala, Maunu, and Sundholm with the same technique. Kauranen and Skou determined the MeOH diffusion coefficient of 4.9 x 10 cm for Nafion... 

The pulsed field gradient nuclear magnetic resonance (PFG NMR) technique is experimentally distinct from the radiotracer technique but the principle is very similar. A fraction of the nuclei of each constituent is labelled by flipping their spins and monitoring the diffusion of these species. Both techniques are influenced by the presence of neutral associates unlike the Hittorf/Tubandt method. 

Lateral diffusion of phospholipids in model membranes at ambient pressure has been studied over the years by a variety of techniques including fluorescence recovery after photobleaching (FRAP), spin-label ESR, pulse field gradient NMR (PFG-NMR), quasielastic neutron scattering (QENS), excimer fluorescence and others.In general, the values reported for the lateral diffusion coefficient (D) range from 10 to 10 cm /s in the... 

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