Nuclear magnetic resonance phase sensitive

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

On the other hand, the spectroscopic techniques probe individual ionic species which build up the ionic aggregates. These techniques permit the investigation of the immediate chemical environments, the mobility of cations and water-ions Interactions. Metal nuclear magnetic resonance and Mossbauer spectroscopy are sensitive probes of counter cations and provide valuable information on the cations and their environment. Infrared spectroscopy is complementary to the above methods and addresses itself to the bound SO3" anions or water and the interaction of water molecules with the various species with which it is in contact. A common conclusion that is reached in the above mentioned studies is that four or five water molecules are needed to complete the hydration process. Reducing the level of moisture content (which surrounds the ionic species) below four water molecules per unit SOj site enhances the Coulombic interaction between the ionic species. This eventually leads to the formation of ion pairs in the dry membranes. These ion pairs do not necessarily disperse homogeneously in the fluorocarbon matrix but tend to form aggregates, phase separated from the matrix materials as demonstrated in the scattering studies. 

Most of the metal alkoxides of interest for electrooptical ceramics are solids (less often liquids) that can be purified by recrystallization, sublimation, or distillation. They are all moisture sensitive, and handling under an inert atmosphere and with anhydrous solvents is thus required. Their unequivocal characterization and formulation are best achieved by x-ray diffraction studies (on monocrystals). Studies on solutions (molecular weight data, nuclear magnetic resonance, NMR, with H, or metal nuclei) are a means either to establish whether the solid-state structure is retained or, in the absence of x-ray data, to establish the molecular structure and eventually stereolability [48]. Mass spectrometry provides information on the stability of the oligomers or the het-erometallic species in the vapor phase. The information gained by infrared spectroscopy is limited the technique is mostly useful for the identification of solvates M(OR) (ROH)x (vOH absorption 3400-3100 cm-l or of chemically modified (heteroleptic) alkoxides (probe for the vCO stretching of P-diketonate or carboxylate ligands, for instance). 

The mass spectrometer is now widely accepted as a crucial analytical tool for organic molecules in the pharmaceutical industry. Although usually treated as a spectroscopic technique, it does not rely on the interaction with electromagnetic radiation (light, infrared, etc.) for the analysis. Rather it is a micro-chemical technique relying on the production of characteristic ions in the gas phase, followed by the separation and acquisition of those ions. By its operation, it destroys the sample unlike other techniques, such as nuclear magnetic resonance (NMR), infrared (IR) and Raman/UV spectroscopies. Nonetheless, mass spectrometry is so sensitive that molecular weight and structural information can be provided on very small samples (attomolar (10" molar) quantities). 

Nuclear magnetic resonance (NMR) spectroscopy is at present one of the most widely applied physical techniques in biology, and its potential applications increase day by day, as more sophisticated instrumentation becomes available and deeper theoretical knowledge is obtained. The phenomenon of NMR was discovered simultaneously by Purcell and his associates at Harvard University and by Bloch and co-workers at Stanford University, for which they were jointly awarded the Nobel prize in physics in 1952. In the lipid field there are two main types of NMR spectroscopy that are of interest broad-line experiments, concerned mainly with the spectra obtained from samples in the solid state, or from oriented phases, and narrow-line, or high-resolution, experiments carried out with samples in the liquid, solution or gas phases. Both types of NMR spectroscopy are extremely useful in the study of the lipids. In addition, Fourier transform (FT) NMR has helped increase the sensitivity of the technique and the so-called pulse method of recording spectra has literally widened the prospect of NMR applications in the field of lipid research and industry. The application of NMR to solid fats is still in its infancy (Pines et aL, 1973 Schaefer and Stejskal, 1979 BocieketaL, 1985). 

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