Pulsed fields

Many other pulsed NMR experiments are possible, and some are listed in the final sections. Most can be canied out using the standard equipment described above, but some require additions such as highly controllable, pulsed field gradients, shaped RF pulses for (for example) single-frequency irradiations, and the combined use of pulses at several different frequencies. 

B1.14.4.4 RESTRICTED DIFFUSION PULSED FIELD GRADIENT MICROSCOPY... 

A successful modification to the technique involves delayed pulsed-field extraction which allows discrimination between zero and near-zero kinetic energy electrons. About 1 ps after the laser pulse has produced photoelectrons, a small voltage pulse is applied. This has the effect of amplifying the differences in fhe velocities of fhe phofoelecfrons and allows easy discrimination befween fhem as a resulf of fhe differenf times of arrival af fhe defector. In fhis way only fhe elections which originally had zero kinetic energy following ionization can be counted to give fhe ZEKE-PE specfmm. 

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... 

W. Brown, R. Johnsen, P. Stilbs, B. Lindman. Size and shape of nonionic amphiphile (Ci2Eg) micelles in dilute aqueous solutions as derived from quasielastic and intensity of light scattering, sedimentation and pulsed-field-gradient nuclear magnetic resonance self-diffusion data. J Phys Chem 87 4548-4553, 1983. 

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. 

Group 2 Radiotracer pulsed field gradient NMR measurements (PFG NMR) ... 

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... 

Johnson et al. [186] measured diffusion of fluorescein-labeled macromolecules in agarose gels. Their data agreed well with Eq. (85), which combined the hydrodynamic effects with the steric hindrance factors. Gibbs and Johnson [131] measured diffusion of proteins and smaller molecules in polyacrylamide gels using pulsed-field gradient NMR methods and found their data to fit the stretched exponential form... 

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. 

Duke, TAJ Austin, RH Cox, EC Chan, SS, Pulsed-field Electrophoresis in Microligho-graphic Arrays, Electrophoresis 17, 1075, 1996. 

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

Hadden, DA, Master of Science Thesis, Florida State University, Tallahassee, FL, 1999. Hadden, D Rill, RL McFadden, L Locke, BR, Oligonucleotide and Water Self-Diffusion in Pluronic Triblock Copolymer Gels and Solutions by Pulsed Field Gradient Nuclear Magnetic Resonance, Macromolecules 33, 4235, 2000. 

Hinton, DP Johnson, CS, Diffusion Coefficients, Electrophoretic Mobilities, and Morphologies of Charged Phospholipid Vesicles by Pulsed Field Gradient NMR and Electron Microscopy, Journal of Colloid and Interface Science 173, 364, 1995. 

Kim, Y Morris, MD, Pulsed Field Capillary Electrophoresis of Multikilobase Length Nucleic Acids in Dilute Methyl Cellulose Solutions, Analytical Chemistry 66, 3081, 1994. 

Use of pulsed-field gel electrophoresis (PFGE) to separate large DNA fragments Permits isolation of large DNA fragments obtained by use of restriction endonucleases (rare cutters) that result in very limited cutting of DNA. 

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. 

Pulse Field Gradient Spin Echo-Nuclear Magnetic Spectroscopy Pyridyl... 

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. 

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