Studying pulsed field gradient

Brown, W Stilbs, P Lindstrom, T, Self-Diffusion of Small Molecules in Cellulose Gels using FT-Pulsed Field Gradient NMR, Journal of Applied Polymer Science 29, 823,1984. Brownstein, KR Tarr, CE, Importance of Classical Diffusion in NMR Studies of Water in Biological Cells, Physical Review A 19, 2446, 1979. 

Gibbs, SJ Johnson, CS, Pulsed Field Gradient NMR Study of Probe Motion in Polyacrylamide Gels, Macromolecules 24, 6110, 1991. 

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. 

W. S. Price 1997, (Pulsed-field gradient nuclear magnetic resonance as a tool for studying translational diffusion Part 1. Basic theory), Concepts Magn. Reson. 9, 299-336. 

A. Pampel, R. Reszka, D. Michel 2002, (Pulsed field gradient MAS NMR studies of the mobility of carboplatin in cubic liquid crystalline phases), Chem. Phys. Lett. 357, 131-136. 

Diffusion-relaxation correlation has been utilized to study biological tissues, e.g., compartmentalization in tissues [32-35]. In many reports, a sequence that combines a stimulated echo-type sequence with a pulsed field gradient and a CPMG as a detection has been described [35]. Other pulses sequences have also been used to study the diffusion-relaxation correlation, e.g., Ref. [36]. 

U.Tallarek, E. Bayer, G. Guiochon 1998, (Study of dispersion in packed chromatographic columns by pulsed field gradient nuclear magnetic resonance), J. Am. Chem. Soc. 120, 1494. 

P. T. Callaghan, K. W. Jolley, R. S. J. Humphrey 1983, (Diffusion of fat and water in cheese as studied by pulsed field gradient nuclear magnetic-resonance), Colloid Interface Sci. 93, 521. 

Pulsed field gradient NMR has become a standard method for measurement of diffusion rates. Stilbs [272] and others have exploited in particular the FT version for the study of mixtures. An added advantage of PFG-NMR is that it can be employed to simplify complex NMR spectra. This simplification is achieved by attenuation of resonances based on the differential diffusion properties of components present in the mixture. 

SJ Gibbs, EN Lightfoot, TW Root. Protein diffusion in porous gel filtration chromatography media studied by pulsed field gradient NMR spectroscopy. J Phys Chem 96 7458-7462, 1992. 

Price, W.S. 1998a. Pulsed-field gradient nuclear magnetic resonance as a tool for studying translational diffusion. II. Experimental aspects. Basic theory. Concepts in Magn. Reson. 10, 197-237. Price, W.S. 1998b. NMR imaging. In Annual Reports on NMR Spectroscopy (G.A. Webb, ed.), Vol. 34, pp. 140-216. Academic Press, New York. 

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... 

The D-HMBC pulse sequence can also be used in combination with the pulse field gradient (PFG) technique [12]. Figure 5(c) shows the successful observation of cross peaks between the methyl group at C-5 of an oxazole unit and adjacent carbons in promothiocin. These cross peaks are hidden by the strong t noise of the solvent peak in the HMBC and D-HMBC spectra. The above results clearly indicate that D-HMBC is a quite useful technique for structural studies of complicated natural products. 

The idea of back transformation of a three-dimensional NMR experiment involving heteronuclear 3H/X/Y out-and-back coherence transfer can in principle be carried to the extreme by fixing the mixing time in both indirect domains. Even if one-dimensional experiments of this kind fall short of providing any information on heteronuclear chemical shifts, they may still serve to obtain isotope-filtered 3H NMR spectra. A potential application of this technique is the detection of appropriately labelled metabolites in metabolism studies, and a one dimensional variant of the double INEPT 111/X/Y sequence has in fact been applied to pharmacokinetics studies of doubly 13C, 15N labelled metabolites.46 Even if the pulse scheme relied exclusively on phase-cycling for coherence selection, a suppression of matrix signals by a factor of 104 proved feasible, and it is easily conceivable that the performance can still be improved by the application of pulsed field gradients. 

When pulsed magnetic field gradients are applied to study diffusive processes, the MR technique is often referred to as pulsed field gradient or pulsed gradient spin echo (PGSE) MR. Application of PGSE MR techniques to quantify molecular diffusion was pioneered by Stejskal and Tanner 17,18), and the techniques typically probe molecular displacements of 10 -10 m over time scales of the order 10 M s. 

Diffusional behavior of sorbed species is studied by NMR using one of three approaches the van Vleck method of moments, relaxation measurements, and the pulsed-field-gradient method. An example of the use of the method of moments is the work of Stevenson (194) on H resonances in zeolite H-Y (see Section III,K). Another is the study by Lechert and Wittem (284) of C6H6 and C6H3D3 adsorbed on zeolite Na-X. Analysis of second moments of H resonances allowed the intra- and intermolecular contributions to the spectra to be extracted. Similarly, second moments of H and 19F spectra of cyclohexane, benzene, fluorobenzene, and dioxane on Na-X provided information about orientation of molecules within zeolitic cavities (284-287). 

Pulsed-field-gradient studies of methane sorbed on zeolite (Ca,Na)-A and n-butane and n-heptane on zeolite Na-X (259,293-294) under the conditions of case 1 above showed that Defr decreases with increasing hydrocarbon chain length and with the fractional saturation of crystals, 8. At 20°C and 8 = 0.8, Dcff (= D ) is 1.4 x 10-5 and 6.3 x 10-6 cm2 sec-1 for n-butane and n-heptane, respectively, which is similar to the values measured in bulk liquids. 

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