Nuclear magnetic resonance isotopic labeling

The mechanism outlined above is supported by experimental findings. An intermediate 5 has been isolated, " and has been identified by and N-nuclear magnetic resonance spectroscopy. Side-products have been isolated, which are likely to be formed from intermediate 4. N-isotope labeling experiments have shown that only the nitrogen remote from the phenyl group is eliminated as ammonia. 

Probably, one of the most valuable advances in this field has dealt with the first chemoenzymatic synthesis of the stable isotope-enriched heparin from a uniformly double labelled 13C, 15N /V-acetylheparosan from E. coli K5. Heteronuclear, multidimensional nuclear magnetic resonance spectroscopy was employed to analyze the chemical composition and solution conformation of N-acety 1 hcparosan, the precursors, and heparin. Isotopic enrichment was found to provide well-resolved 13C spectra with the high sensitivity required for conformational studies of these biomolecules. Stable isotope-labelled heparin was indistinguishable from heparin derived from animal tissues and might be employed as a novel tool for studying the interaction of heparin with different receptors.30... 

Hunger and Wang provide an account of advances in the characterization of solid catalysts in the functioning state by nuclear magnetic resonance spectroscopy. Examples include investigations of zeolite-catalyzed reactions with isotopic labels that allow characterization of transition states and reaction pathways as well as characterization of organic deposits, surface complexes, and reaction intermediates formed in catalyst pores. 

Self diffusion coefficients can be obtained from the rate of diffusion of isotopically labeled solvent molecules as well as from nuclear magnetic resonance band widths. The self-diffusion coefficient of water at 25°C is D= 2.27 x 10-5 cm2 s 1, and that of heavy water, D20, is 1.87 x 10-5 cm2 s 1. Values for many solvents at 25 °C, in 10-5 cm2 s 1, are shown in Table 3.9. The diffusion coefficient for all solvents depends strongly on the temperature, similarly to the viscosity, following an Arrhenius-type expression D=Ad exp( AEq/RT). In fact, for solvents that can be described as being globular (see above), the Stokes-Einstein expression holds ... 

Dioxiranes 4 have equivalent oxygens (attested by isotopic labeling and 170 NMR NMR - nuclear magnetic resonance) and an t/)3-hybridized carbon (of course, the exact hybridization is influenced by the 3-membered ring), whereas carbonyl oxides 1-3 have an r/)Z-hybridized carbon atom and give rise to diastereomers la and lb when R yf R1. 

The reader is referred to articles by Barrow,12 Garson,1314 and Moore15 for background information on the field of marine secondary metabolite biosynthesis. Early work in this field used radiochemical tracers such as 14C or 3H recently, studies with 13C have proved popular because of the ease of detection of this stable isotope by nuclear magnetic resonance (NMR). In particular, our understanding of marine microbial biosynthesis and of de novo biosynthesis in marine molluscs has progressed significantly as a consequence of the use of 13C-labeled precursors. 

As the glucose is metabolized, the metabolic derivatives become enriched with the isotopic carbon label and are detected using advanced technologies such as mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Importantly, incorporation of isotopes into molecules can alter reaction mechanisms including the rate of a reaction-this is termed isotopic substitution and forms the basis of the kinetic isotope effect. 

The study of biological macromolecules by nuclear magnetic resonance (NMR) spectroscopy has been greatly expanded with the use of isotopic labeling (51). 

Incorporation studies of C-labeled precursors require extensive nuclear magnetic resonance (NMR) measurements. The signals of C-NMR-spectra of the analyzed metabolites must be assigned fully. The C-NMR spectra of the reference compound of natural abundance (1.1%) and of the labeled metabolite must be recorded in the same conditions. A comparison between the relative signal intensities of the two spectra indicates that the carbon atom is labeled and indicates the magnitude of the isotope enrichment. 

Abstract. Economical CO separation is a very important process, not only for the production of isotopic labels for nuclear magnetic resonance chemical analysis and medical diagnosis, but also to provide a means of removing and fixing radioactive carbon (carbon-14) in the nuclear power industiy. C is normally separated from CO or fiom CHt by cryogenic processes. As the separation factor is small, the cost of... 

The elucidation of PrP structure and function often necessitates the incorporation of biophysical probes. These monitors can be fluorescent dyes which enable one to study protein function both in vivo and in vitro by modem fluorescence methods. The incorporation of nuclear magnetic resonance (NMR) sensitive isotopes or spin labels opens the route to NMR and electron paramagnetic resonance (EPR) methodology. In the following these three methods will be briefly discussed in respect of their application in prion research. 

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