The NMR Technique

Since oligosaccharides in general fail to crystallize, the only technique that is able reliably to offer information on the structure of oligosaccharides in solution at atomic resolution is nuclear magnetic resonance (NMR) spectroscopy [12-15]. There are three NMR parameters that are relevant to the structural analysis of oli- 

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Although these nmr results offer convincing support for the fl-form of 4GT taking the structure proposed by Hall and Pass as their model 7, in the case of the a-form none of the proposed structures were in good agreement with the nmr measurements. This discrepancy highlights the sensitivity of the nmr technique to the exact conformation of the methylene chain, in contrast to the X-ray diffraction technique which is more sensitive to the terephthalolyl residue. 

The NMR techniques discussed so far provide information about proton-proton interactions (e.g., COSY, NOESY, SECSY, 2D y-resolved), or they allow the correlation of protons with carbons or other hetero atoms (e.g., hetero COSY, COLOC, hetero /resolved). The resulting information is very useful for structure elucidation, but it does not reveal the carbon framework of the organic molecule directly. One interesting 2D NMR experiment, INADEQUATE (Incredible Natural Abundance Double Quantum Transfer Experiment), allows the entire carbon skeleton to be deduced directly via the measurement of C- C couplings. 

The intensity of the absorption of microwave energy is a measure the abundance of that isotope. The potency of the NMR spectroscopy is not only its ability to quantify the concentration of an isotope, but to check the enviromnent into which an isotope is embedded. This is possible because the magnetic resonance and thus the absorption frequency prove to be sensitive to the spins of neighboring atoms and to structural features of the probe. Therefore, NMR spectroscopy is more a tool for scientific structural analyses than for daily food (colorant) inspection. For a detailed study of the NMR techniques used in food science we recommend books by Macomber and Pochapsky. - ... 

Fig. 2.9.6 Comparison of maps of the magrfiDEJe of the flow velocity (a) and of the flow acceleration (b). The maps have been determined with the NMR techniques outlined in the text. A photograph of the model object is shown in (c).

Section 3, the main section of this paper, deals with the NMR of bulk semiconductors. Section 3.1 lists the various relevant terms in the NMR spin Hamiltonian. The NMR techniques and strategies that can be employed to obtain the individual NMR parameters of the spin Hamiltonian and theoretical calculations of NMR parameters will be discussed in Sect. 3.2. The remaining subsections will provide examples from the important classes of semiconductors that illustrate the measurement and interpretation of each of the spin Hamiltonian parameters, with an emphasis on what information about semiconductors the parameters convey. 

A solution structure of French Bean plastocyanin has been reported by Wright and co-workers,19 using nuclear magnetic resonance techniques described in Section 3.5 of Chapter 3. The structure, determined from a plastocyanin molecule in solution rather than in a solid-state crystal, agrees well with that of reduced poplar plastocyanin X-ray crystallographic structure reported above. Conformations of protein side chains constituting the hydrophobic core of the French bean plastocyanin are well-defined by the NMR technique. Surface side chains show... 

It is this relative insensitivity that is usually considered as the major drawback of NMR spectroscopy. However, the flexibility of the NMR technique, with the ability to obtain structural information, quantitative data (e.g. kinetic parameters), as well as an indication of molecular volume, using pulsed gradient spin echo (PGSE) NMR diffusion methods [6], makes NMR a most valuable tool. 

Owing to signal overlap, only partial assignment H (6.55-7.99 ppm) and 13C resonances were possible for anions 6-9. Of course, most of the compounds described in this chapter were well characterized mainly due to the NMR techniques. 

In order to better understand the NMR techniques described in this paper, let us first briefly review some fundamental concepts in NMR. (For more details, see Reference 8.) Throughout the discussion, we will use a classical treatment. 

The NMR technique makes use of the property of spin (angular momentum and its associated magnetic moment) possessed by nuclei whose atomic number and mass number are not both even. Such nuclei include the isotopes of hydrogen and 13C, 15N, 170, and 19F. Application of a strong magnetic field to material containing... 

Traditionally, HPLC, GC-MS, or LC-MS methods were used to monitor the clearance of small-molecule impurities. These analytical techniques often require unique solvents, columns, methods, reagents, detectors, and buffers for each analyte to be quantified. The NMR method, albeit not the most sensitive technique, normally does not have these problems. In this chapter, some examples will be used to demonstrate that NMR is a fast, generic, and reliable analytical technique for solving analytical problems encountered in the development of biopharmaceutical products. The NMR techniques described here require minimal sample handling and use simple standard NMR methods. They can easily be implemented and used for process development and validation purposes. 

As discussed above, it appears from physical studies, especially with the NMR technique, that the tertiary structure of ribosomal proteins isolated in the presence of 6 M urea and then carefully renatured under appropriate conditions is very similar to those proteins prepared in the complete absence of urea. 

The usefulness of the NMR technique in solid state physics stems from the fact that the widths, splittings, and shifts of the magnetic resonance of nuclei in solids often depend in a sensitive manner on the magnetic and electrical environment of the nucleus in the solid. In this sense the nucleus can be considered as a probe by which one may ascertain certain details of the nuclear and electronic structure of the solid under investigation. Considerable attention has been given by numerous authors to the theory of the magnetic resonance phenomenon, and it is considered to be in a satisfactory state at the present time. 

The aims of this study were to observe isotropically shifted signals for metal ions like copper(II), which usually give signals broadened beyond detection, and to relate the observed shifts and relaxation times to those of the uncoupled ions in order to understand the phenomena in theoretical terms. This approach allows the power of the NMR technique to fully exploit paramagnetic species and obtain information on spin delocalization, chemical bonding and so on. It is likely that the theory also applies to coupled metal ion-H adical systems like those proposed for derivatives of peroxidases (compound I), which contain iron(IV) and a heme radical (44). 

In addition, the NMR technique provides kinetic measurements for reversible proton transfers that are fast and occur on the NMR time scale (i.e., for processes... 

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