Nuclear magnetic resonance carbon-13 labeling

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 assembly of the carbon skeletons of these unusual hydrocarbons was first studied in Carpophilus freemani Dobson, through careful GC-MS and Nuclear Magnetic Resonance (NMR) studies of the incorporation of 2H or 13C-labeled precursors (Petroski et al., 1994). Assembly of the carbon skeleton of the aggregation pheromone of C. freemani, (2 , 4 , 6ii)-5-ethyl-3-methyl-2,4,6-nonatriene, involves initiation with acetate elongation with first propionate (to provide the methyl branch), then butyrate (to provide the ethyl branch) and chain termination with a second butyrate (Figure 6.7). At some point, loss of C02 from one of the butyrate units occurs to yield the appropriate hydrocarbon, but Petroski et al. (1994) were unable to determine which of the butyrate units loses its carboxyl group. Bartelt and Weisleder (1996) studied the biosynthesis of 15 additional methyl- and/or ethyl-branched, tri- and tetraenes in the related... 

Eakin, R.T., Morgan, L.O., Gregg, C.T., Matwiyoff, N.A. (1972). Carbon-13 nuclear magnetic resonance spectroscopy of living cells and their metabolism of a specifically labeled 13C substrate. FEBS Lett. 28,259-264. 

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. 

Over 100 spectra created specifically for Organic Chemistry are presented throughout the text. The spectra are color-coded by type and generously labeled. Mass spectra are green infrared spectra are red and proton and carbon nuclear magnetic resonance spectra are blue. 

The carbon skeleton of isoprenoids is derived from the branched C5 skeleton of isoprene. Isopentenyl diphosphate and dimethylallyl diphosphate represent the biologic equivalents of isoprene. From research on cholesterol biosynthesis in liver tissues and on ergosterol in yeast, mevalonate was accepted as the universal precursor of isoprenoids. However this assertion is inaccurate. Incorporation of labeled acetate and glucose isotopomers into bacterial isoprenoids and into diterpenes of ginkgo embryos indicated fortuitously the existence of an alternative mevalonate-independent route. Its full elucidation required experiments using and H-labeled precursors followed by extensive nuclear magnetic resonance analyses as well as a combination of biochemical and molecular biology methods. These additional studies revealed a complete set of novel unsuspected enzymes. 

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... 

All but the smallest proteins studied by nuclear magnetic resonance (NMR) need to be labeled with isotopes of hydrogen, nitrogen, or carbon ( H, C), or combi-... 

In E. coir. The conversion of pimelate into pimeloyl-CoA does not take place in E. coli. Preliminary labeling experiments with " C02, which ruled out the symmetrical pimelate as intermediate, were confirmed by further studies using C-labeled acetate, with E. coli strains overexpressing the biotin operon. Nuclear magnetic resonance (NMR) analysis of DTB or biotin revealed that carbons 3, 5, 7 and 2,4,6 were obtained from C-1 and C-2 of acetate, respectively (Figure 5). Sanyal etal confirmed using [l,2- C]acetate that intact acetate units were incorporated, consistent with a classical fatty acid or polyketide pathway. The results of the two groups differ, however, on an important point. Sanyal etal did not observe C incorporation at C-1 or C-10 with 1- or... 

Since no intermediates could be detected in the in vitro studies of the oxidation of acetylenic derivatives, it was assumed that very short-lived intermediates were probably formed. In order to further characterize this pathyway, studies with deuterium and labeled biphenylacetylene (acetylenic hydrogen and internal acetylenic carbon, respectively) were initiated. The mass and nuclear magnetic resonance spectra of the resulting biphenyl acetic acid derivative showed that ... 

In more recent years, it has become less essential to use radioactivity, which, though very useful, is also hazardous. As we have mentioned, there are also stable, rare isotopes. In the case of hydrogen we have deuterium in the case of carbon we have carbon 13 (seven neutrons). It is also possible to label a biochemical compound with a stable isotope. Some of these isotopes ( C being one) can be monitored by nuclear magnetic resonance (NMR) all of them can be detected by mass spectrometry, which, as the name implies, relies on measuring the differences in mass of different molecules or fragments of molecules. The improved sensitivity of these two techniques in recent years has enhanced the usefulness of stable isotopes. 

The composition of carbon-chain polymers with monomeric units having widely differing analytical composition, characteristic elements or groups, or radioactive labels can be readily determined. Chemical (microanalysis, functional group determination, etc.) and spectroscopic methods (infrared, ultraviolet, nuclear magnetic resonance, etc.), as well as the determination of radioactivity, yield the average composition of the polymer. The mean composition can also be determined from the refractive indices of solid samples. The composition can be calculated from the principle that the copolymer is considered to be a solution of one unipolymer (from one of the monomeric units) in the other. The composition can also be found by means of the refractive index increment dw/dc in solution, which gives the variation in refractive index with concentration. The mass fraction of the monomeric unit A can be calculated from... 

Abstract. Economical CO separation is a voy hnportant process, not only for the production isotopic labels fiw nuclear magnetic resonance chemical analysis and medical diagnosis, but also to provide a means of removing and fixing radioactive carbon (cartion-14) in the nuclear power industry. is normally sefnaaled from C/ CO or from C/ Y CH4 Iv cryogenic processes. As the separation factor is small, the cost of separation is very hi so that the application of Y is limited to use in the laboratory as a chemical reagem. It is not viable to use it for industrial purposes. A marked difference was observed between the adsorption equilibrium coefficients of CO and Y O on a low-SKVAI Os-ratio Na-X type zeolite (Na-LSX) at low temperatures, so this phenomenon could be used to separate CO from YX). 

Mclnnes AG, Smith DG, Walker JA, Vining LC, Wright JLC (1975) Homonuclear Carbon-13 Decoupling in Carbon-13 Nuclear Magnetic Resonance Study of Eiosynthesis Using Doubly Labeled Precursors. Assembly Pattern of the Acetate Units in Eikaverin. J Chem Soc Chem Commun 66... 

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