Determination by high-resolution NMR

Fig. 15. Stereo drawing of the most likely conformer of the cation as-Pt(NH3)2(d(GG-lV7,JV7))+ in solution as determined by high-resolution NMR techniques...

Elastomeric poly acetaldehyde is amorphous and atactic. High resolution NMR studies were carried out in order to determine the actual tacticity of the polymer (4, 5, 23). Poly acetaldehyde consists mainly of heterotactic sequences isotactic sequences are also present in the polymer. The ratio of heterotactic to isotactic varies, but it is usually between 2-3 1. A detailed description of the tacticity determination by high resolution NMR will be given in a subsequent paper by Goodman and Brandrup (23). 

Watts CR, Tessmer MR, Kallick DA (1995) Stmc-ture of Leu -Enkephalin Bound to a Model Membrane as Determined by High-Resolution NMR. Lett Peptide Sci 2 59—70... 

Since the first protein solution structure was determined by high resolution NMR spectroscopy about 25 years ago [166], NMR has been estabhshed as the only experimental method that provides both structural and dynamical information at atomic resolution close to physiologically relevant conditions. Protein structure determination in living cells has also been achieved recently by in-cell NMR [18]. However, the limitation of this technique in structural studies hes in low sensitivities and poor resolution when the size of macromolecules increases. Some proteins, in particular metalloproteins, might not be stable for a period of time (days or weeks) or have limited solubility. Moreover, new challenges in fife science have also promoted development of new NMR methods which will improve sensitivities and reduce acquisition times to fulfil the requirement of characterization of these proteins and their complexes. 

The extent of reversed monomeric units is routinely determined by high-resolution NMR methods, using predominately F spectra and, less frequently, C spectra [580-582]. F-NMR can also be used to measure chain branching in head to-tail sequences. Plasma polymerized samples yield more complex spectra as a result of extensive cross-linking, branching, and unsaturation [554]. 

The incidence of these defects is best determined by high resolution F nmr (111,112) infrared (113) and laser mass spectrometry (114) are alternative methods. Typical commercial polymers show 3—6 mol % defect content. Polymerization methods have a particularly strong effect on the sequence of these defects. In contrast to suspension polymerized PVDF, emulsion polymerized PVDF forms a higher fraction of head-to-head defects that are not followed by tail-to-tail addition (115,116). Crystallinity and other properties of PVDF or copolymers of VDF are influenced by these defect stmctures (117). 

The degradation of 2,6-xylenol (2,6-dimethylphenol) by bacteria produces a metabolite with elemental composition C8///0O2 as determined by high-resolution mass spectrometry Which carbon skeleton and which relative configuration are deducible from the NMR experiments 44, all obtained from one 1.5 mg sample ... 

The C NMR spectrum of the metabolite shows 16 signals instead of 8 as expected from the elemental composition determined by high-resolution mass spectrometry. Moreover, aromaticity of the 2,6-xylenol is obviously lost after metabolism because two ketonic carbonyl carbon atoms (5c = 203.1 and 214.4) and four instead of twelve carbon signals are observed in the shift range of trigonal carbon nuclei (5c = 133.1, 135.4, 135.6 and 139.4) in the C NMR spectra. To conclude, metabolism involves oxidation of the benzenoid ring. 

Both compounds were non-fluorescent. Compound KM-1 was similar to PMs in the absorption maximum (A.max 488 nm) but not in the spectral shape, whereas KM-2 was similar to PMs in the spectral shape but not in the absorption maximum at 515 nm (Fig. 9.10). The chemical structures of KM-1 and KM-2 have been determined by high-resolution mass spectrometry and NMR spectrometry (Fig. 9.11 Stojanovic, 1995). 

Monomer reactivity ratios are generally but not always independent of the reaction medium in radical copolymerization. There is a real problem here in that the accuracy of r values is often insufficient to allow one to reasonably conclude whether r or rx varies with changes in reaction media. The more recent determinations of r values by high-resolution NMR are much more reliable than previous data for this purpose. It has been observed that the... 

Yoshioka, S. Aso, Y. Kojima, S. Sakurai, S. Fujiwara, T. Akutsu, H. Molecular mobility of protein in lyophilized formulations linked to the molecular mobility of polymer excipients, as determined by high resolution C sohd-state NMR. Pharm. Res. 1999, id (10), 1621-1625. 

Nuclear Magnetic Resonance. The successful study of polymers in solution by high resolution NMR spectroscopy started with the pioneering work on the sequence structure of poly methyl methacrylate in 1960. Since then, an ever-increasing number of investigations have been carried out ranging from the elucidation of the statistics of homopolymer and copolymer structure to the study of conformation, relaxation and adsorption properties of polymers. The aspects of sequence length determination and tacticity have received considerable attention (Klesper 84, for example, reports more than 500 entries). Therefore, a detailed review will not be attempted. (For a detailed description of the NMR Theory and statistics of polymer structure, see Bovey 59, Randall 23, and Klesper 84). 

D. Uhrin J.-R. Brisson, Structure Determination of Microbial Polysaccharides by High Resolution NMR Spectroscopy. In NMR in Microbiology Theory and Applications, J. N. Barotin, J. C. Portais, Eds. Horizon Scientific Press Wymonden, 2000 165-190. 

Figure Bl.13.4. The inversion-recovery determination of the carbon-13 spin-lattice relaxation rates in melezitose. (Reproduced by permission of Elsevier from Kowalewski J and Maler L 1997 Methods for Structure Elucidation by High-Resolution NMR ed Gy Batta, K E Kover and Cs Szantay (Amsterdam Elsevier) pp 325-47.)...

Tellurophene derivatives may be considered as organic intermediates. Indeed the treatment of tellurophene <84CC6i7> with Grignard reagents in the presence of nickel catalysts affords 88% of Z,Z-1,3-butadiene (6), as determined by high resolution H and C NMR spectroscopy. This yield decreases from Te to O in the series. 

Compound 3 had a molecular formula of C16H14O4, as determined by high resolution mass spectrum. The NMR spectrum was similar to those observed for pterocarpans (13). Compound 3 was identified as (-)-Medicarpin by comparing its m.p. and NMR, IR, UV, and MS with those of an authentic sample (Dr. H. D. Van Etton, Cornell University). 

Gunstone, F. D. The Composition of Hydrogenated Fats Determined by High Resolution 13C NMR Spectroscopy. Chem. Ind. 1991, (Nov 4), 802. 

The imidazole alkaloid 4,6-dehydro-l,2,4,5-tetrahydro-2,5-dioxopilocarpine (34) was isolated from P. grandiflorus Engl, stems, as a yellowish oil. Its structure was determined by high-resolution mass spectroscopy miz 238) and and NMR that indicated a change in the structure of pilocarpine due to the signals at 177.7, 162.4, 152.4, 132.2, and 112.3 ppm, associated to two additional carbonyl groups and a double bond [33]. 

Monomer composition and comonomer sequence distribution were determined by high resolution and NMR spectroscopy. In the NMR spectrum, MATRIF a-CH3 resonance pattern is observed in 0.82-1.67 ppm (Figure 20.6), three signals were observed and can be associated to the (M) centered VMV, MMV, and MMM triads (where V and M stand for VCN and MATRIF, respectively) [86]. Integration of the three sets of resonances yields the following ratio VMV/MMV/MMM = 37/55/8. 

It is also worth noting that for caffeine solutions a thermodynamic parameter such as the enthalpy of dimerization of caffeine in water can be determined comparatively by dissolution calorimetry and by high resolution NMR [118,119]. 

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