NMR measurement methods

Calculations of nuclear shielding normally provide values for each of the nine components of the second-order shielding tensor. Thus theoretical estimates are available for the principal components of the tensor as well as its anisotropy and the isotropic value of the nuclear shielding, the latter of which is usually available from high-resolution CP/MAS NMR measurements. Methods for experimentally determining the principal tensor components, and its anisotropy, are described in the previous section. 

The nonnal mode NMR refinement method of Brueschweiler and Case [50] can be applied to experimentally measurable quantities such as order parameters or nuclear Overhauser spectroscopy (NOSEY) intensities. Unlike the X-ray case, the expression of these quanti-... 

The formation of acyl halide-Lewis acid complexes have been observed by several methods. For example, both 1 1 and 1 2 complexes of acetyl chloride, with AICI3 can be observed by NMR spectroscopy. The existence of acylium ions has been demonstrated by X-ray diffraction studies on crystalline salts. For example, crystal structure determinations have been reported for /i-methylphenylacylium and acetylium ions as SbFg salts. There is also a good deal of evidence from NMR measurements which demonstrates that acylium ions can exist in nonnucleophilic solvents. " The positive charge on acylium ions is delocalized onto the oxygen atom. This delocalization is demonstrated in particular by the short O—C bond lengths in acylium ions, which imply a major contribution from the structure having a triple bond ... 

Let us note that cross-sections aE, obtained from optical data and verified by NMR measurements, exceed the corresponding cross-sections found by acoustic methods (c 4 3 A2) [168]. A similar disagreement between the data obtained by NMR and molecular spectroscopy with the acoustic data exists for linear molecules as well. 

As it was mentioned in Section 9.4.1, 3D structures generated by DG have to be optimized. For this purpose, MD is a well-suited tool. In addition, MD structure calculations can also be performed if no coarse structural model exists. In both cases, pairwise atom distances obtained from NMR measurements are directly used in the MD computations in order to restrain the degrees of motional freedom of defined atoms (rMD Section 9.4.2.4). To make sure that a calculated molecular conformation is rehable, the time-averaged 3D structure must be stable in a free MD run (fMD Sechon 9.4.2.5J where the distance restraints are removed and the molecule is surrounded by expMcit solvent which was also used in the NMR measurement Before both procedures are described in detail the general preparation of an MD run (Section 9.4.2.1), simulations in vacuo (Section 9.4.2.2) and the handling of distance restraints in a MD calculation (Section 9.4.2.3) are treated. Finally, a short overview of the SA technique as a special M D method is given in Sechon 9.4.2.6. 

Modern NMR software covers all facets of MR applications and assists the laboratory staff and the research groups not only in the standard procedures of scan preparation, data acquisition, reconstruction and analysis, but also offers an appropriate development environment for user defined measurement methods and data analysis algorithms and provides easy-to-use tools for data management, documentation, export and archiving. The software allows the user to run complex NMR machines in a routine manner and to integrate the spectrometer into the laboratory infrastructure [7]. 

Research users need full access to the functional elements of the spectrometer system and require the most efficient and flexible tools for MR sequence and application development. If the measurement methods delivered with the software do not adequately address the specific investigational requirements of a research team, modem NMR software is an open architecture for implementing new and more sophisticated functionality, with full direct access to all hardware controlling parameters. After evaluation, the new functionality can be developed with the help of toolbox functions that allow rapid prototyping and final builds, to enable the new sequence to be executed by non-experienced personnel and then used in routine applications. These toolboxes provide application oriented definitions and connect to standard mechanisms and routine interfaces, such as the geometry editor, configuration parameters or spectrometer adjustments. 

The inherent sensitivity of NMR signals to the fluid-substrate interactions via a large number of mechanisms provides a direct connection between the NMR measurables, the pore structure and the motional characteristics of the imbibed fluid. While the large number of potential NMR variables makes the experimental design and analysis complex, it also provides the potential for a measurement method capable of measuring and spatially resolving the parameters of interest to functionalized ceramics. 

NMR signals are highly sensitive, via a number of different mechanisms, to the physical and chemical properties of porous materials. Using the set of NMR-based measurement methods that we have developed, it is possible to non-invasively and non-destructively characterize both the microstructural properties of the materials and relaxation properties of fluids imbibed into these materials. 

Rheo-NMR [86] methods have been shown to be well-suited to emulsion rheology studies [28] and could be combined with any of the topics described above. The combination of structural and rheological measurements is a promising area for further research. 

Transferred NMR Measurements to Detect Ligand Binding and Related Methods.132... 

The logical approach to problem solving for rubber analysis at Polysar Ltd was described by Chu [73] (cf. Schemes 2.4 and 2.5). Systematic analysis involves sampling, elimination of interference and measurement. Methods employed include chromatography (GC, HS-GC, HPLC, SEC, IC), spectroscopy (AAS, UV/VIS, IR, NMR), MS, microscopy and thermal analysis. The specific role of each of these techniques for the analysis of rubber compounds with or without... 

In order to work out in more detail Harada and coworkers took a step further by preparing fluorescence-labeled bis(l-naphthylacetyl)-PEG (PEG-1N2) and bis(2-naphthylacetyl)-PEG (PEG-2N2). The complexes of these compounds with y-CD were isolated by standard methods and subjected to NMR measurement. The results also conformed to the conclusion that four ethylene glycol units are included in one y-CD. 

The RM of the dried product was measured at 50 °C over P205 or in an oven with circulating air at 50 °C, or in the same oven at 90 °C over silica gel. Identical measurements were made with fresh bones. For NMR measurements, a known amount of D20 was added to the bone in a glass container. After equilibrium between DzO and H20 was reached, a known amount of the product was taken from the solution and studied in a Perkin Elmer NMR-spectrometer. In Fig. 3.23 the water contents of fresh and freeze dried bones are listed measured by NMR and the gravimetric methods at 90 °C. The data show that only a certain amount of the total water can be removed at 90 °C, while another amount is so... 

In order to perform the various tasks mentioned in Section 11.1.2, it is necessary to use one or several methods to gather information by NMR spectroscopy. Typically, chemical shift and coupling constant information, 2D-NMR measurements, variable temperature or pressure studies are used. If appropriate, specific examples of the particular topic as applied in homogeneous hydrogenation research are detailed below. 

The objectives of this review are to discuss the fundamental and more recently discovered properties of water alone and to critically examine the system properties and measurement methods used to measure the mobility of water and solids in foods—specifically water activity, nuclear magnetic resonance (NMR), and the glass transition. 

The continued use of aw in foods does not preclude the use of other concepts or measurement methods, such as the food polymer science approach proposed by Slade and Levine (1991) or rotational and translation mobility as measured by NMR. Rather, it may be most useful to combine these various approaches, recognizing the strengths, perspective (i.e., distance and time scales), and limitations of each. Then, each approach can be utilized where it is most applicable so as to build a multilevel understanding of the workings of specific food systems. 

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