Spin echoes, NMR studies

The exact nature of the NO-releasing reaction and the other products of reaction in mammalian tissue are still unclear. The matter has been discussed by a number of authors and a reductive mechanism in rat hepatocytes and human erythrocytes has been suggested in the presence of NADH and NADPH. Nitroprusside can pass through cell membranes and so there is no intrinsic difficulty with this suggestion. There is direct evidence from spin echo NMR studies to show the conversion, by nitroprusside, of glutathione into glutathione disulfide within erythrocytes [49]. 

Toonkool, P., Regan, D. G., Kuchel, P. W., Morris, M. B., and Weiss, A. S. (2001a). Thermodynamic and hydrodynamic properties of human tropoelastin. Analytical ultracentrifuge and pulsed field-gradient spin-echo NMR studies. / Biol. Chem. 276, 28042-28050. 

A. Allerhand, F.-M. Chen and H. S. Gutowsky, Spin-echo NMR studies of chemical exchange. HI. Conformational isomerization of cyclohexane and dn-cyclohexane. J. Chem. Phys., 1965, 42(9),... 

Diffusion coefficients derived from pulsed gradient spin echo NMR-studies show lower values for the encapsulated guest identical to those of the host, see Frish, L. Matthews, S. E. Bohmer, V. Cohen, Y. J. Chem. Soc., Perkin Trans. 2 1999, 669-671. 

Ud constant which can be determined experimentally for spin echo NMR studies ... 

Frish L, Matthews SE, Bohmer V, Cohen Y. A pulsed gradient spin echo NMR study of guest encapsulation by hydrogen-bonded tetraurea calix[4]arene dimers. J Chem Soc Perkin Trans 1999 2 669-72. 

C. Ferrero, D. MassueUe, D. Jeannerat and E. Doelker, Towards elucidation of the drug release mechanism from compressed hydrophihc matrices made of cellulose ethers. I. Pulse-fleld-gradient spin-echo NMR study of sodium salicylate diffusMty in swollen hydrogels with respect to polymer matrix physical structure,/. Control. Release, 128 (1) 71-79, 2008. 

TITLE Analysis of Amino Acids at the Active Site of Chloroplast Coupling Factor One A Spin-Echo nmr Study. 

Mis] Misawa, M., Tanaka, Y., Nagai, H., Tsujimura, A., Spin-Echo NMR Study of Co-Hyperfine Field Distributions in Amorphous (C,T)-B Alloys (T = Fe, Ni, Mn) , J. Non-Crystalline Solids, 117/118, 344—346 (1990) (Magn. Prop., Experimental, 6) [1990Ste] Stergioudis, G.A., Polychroniadis, E.K., Induced Crystallization in Fe-Co-B Amorphous Alloys by Heat-Treatment and Electron-Beam Irradiation , Mater. Res. Bull, 25(10) 1287-1290 (1990) (Experimental, 15)... 

In electron spin echo relaxation studies, the two-pulse echo amplitude, as a fiinction of tire pulse separation time T, gives a measure of the phase memory relaxation time from which can be extracted if Jj-effects are taken into consideration. Problems may arise from spectral diflfrision due to incomplete excitation of the EPR spectrum. In this case some of the transverse magnetization may leak into adjacent parts of the spectrum that have not been excited by the MW pulses. Spectral diflfrision effects can be suppressed by using the Carr-Purcell-Meiboom-Gill pulse sequence, which is also well known in NMR. The experiment involves using a sequence of n-pulses separated by 2r and can be denoted as [7i/2-(x-7i-T-echo) J. A series of echoes separated by lx is generated and the decay in their amplitudes is characterized by Ty. ... 

Brown FF, Campbell ID, Kuchel PW, Rabenstein DC (1977) Human erythrocyte metabolism studies by H-l spin-echo NMR. FEBS Lett 82 12-16... 

The solvent mobility in atactic polystyrene-toluene solutions has been studied as a function of temperature using NMR. The local reorientation of the solvent was studied using deuterium NMR relaxation times on the deuterated solvent. Longer range motions were also probed using the pulsed-gradient spin-echo NMR method for the measurement of diffusion coefficients on the protonated solvent. The measurements were taken above and below the gel transition temperatures reported by Tan et al. (Macromolecules, 1983. 16, 28). It was found that both the relaxation time measurements and the diffusion coefficients of the solvent varied smoothly through the reported transition temperature. Consequently, it appears that in this system, the solvent dynamics are unaffected by gel formation. This result is similar to that found in other chemically crossed-linked systems. 

Pulse field gradient (PFG) NMR spectroscopy is now generally regarded as the method of choice for measuring the translational diffusion coefficients of molecules of virtually any type under many conditions (48). H, H, F, and P variants of this method have been used successfully to study lateral diffusion of cholesterol, phospholipids, and water in model membranes (49,50). This technique introduces two identical gradient pulses of the external magnetic field into the standard spin-echo NMR... 

Generally, we will use spin-echo NMR to study systems for which more... 

Diffusion of Water in poly[PFSA] Membranes To describe diffusion of water through the membrane in the presence of a water activity gradient, an appropriate interdiffusion coefficient must be determined. Experimental methods used to study diffusion of water in these polymers, such as radiotracer and pulsed gradient spin-echo NMR techniques, probe intrad-iffusion coefficients, often referred to as tracer or self-diffusion coefficients, determined in the absence of a chemical potential gradient. Intra- and interdiffusion coefficients are related for the case of diffusion of a small molecule in a polymeric matrix as follows [28] ... 

Topgaard, D., Malmborg, C. and Soderman, O. Restricted self-diffusion of water in a highly concentrated W/O emulsion studied using modulated gradient spin-echo NMR, /. Magn. Reson., 156, 195, 2002. 

With the advent of Fourier-transform NMR and powerful superconducting magnets, spin-echo NMR is now the method of choice for high-pressure intradiffusion measurements. Individual measurements take of the order of few (2-30) minutes to collect rather than the 24-50 h needed for diaphragmcell measurements. Because of the higher sensitivity and the faster collection of data it is now possible to study by NMR systems with diffusion coefficients which are as low as 10 s whereas the time scale for diaphragm-cell mea-... 

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