Nuclear magnetic resonance isotopic enrichment

Stable isotope ratio analysis (SIRA, GC-IRMS [Gas Chromatography-Isotope Ratio Mass Spectrometry], and Site Specific Isotope Fractionation — Nuclear Magnetic Resonance [SNIF-NMR]) have proven useful in many adulteration situations. In nature, and exist at relative proportions of 1.11 98.89 [27]. The photosynthetic process selectively enriches the plant in dependent upon the type of photosynthetic process used by the plant. Plants using the Hatch-Slack pathway (e.g., com, sugar cane, millet, and lemon grass) give 8 C values the closest to the standard, i.e., 5 C values of ca. -10. The 5 C value is calculated as ... 

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... 

Example Isotopic enrichment is a standard means to enhance the response of an analyte in nuclear magnetic resonance (NMR). Such measures gain importance if extremely low solubility is combined with a large number of carbons, as is often the case with [60]fullerene compounds. [19] The molecular ion signals, IVT, of Qo with natural isotopic abundance and of C-enriched Cgo are shown below (Fig. 3.11 for EI-MS of [60]fullerenes cf. Refs. [20-22]). From these mass spectra, the enrichment can be determined by use of Eq. 3.1. For Qo of natural isotopic abundance we obtain Mrceo = 60 x 12.0108 u = 720.65 u. Applying Eq. 

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. 

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. 

Solvents for nuclear magnetic resonance (NMR) spectroscopy, enriched in deuterium to an extent of >99%, are commercially available. The separation of deuterium from naturally occurring hydrogen is achieved electrol5fiically with the isotope in the form of D2O. When an aqueous solution of NaOH (natural isotopic abundances) is electrolysed (equation 2.36) using an Ni electrode, the separation factor defined in equation 2.37 is The choice of electrode is critical to the... 

While not as convenient, direct monitoring of a nitrosyl group can be carried out by nuclear magnetic resonance (NMR) spectroscopy, since both " N and N have nuclear spins which allow NMR detection. In N NMR spectra, the chemical shift observed for bent and bridging M-NO groups typically appears in the range of 300 to 900 ppm, while for hnear M-NO moieties, resonances occur from -100 to 200 ppm (referenced to nitromethane) [12]. Isotopically enriched nitrosyl complexes are often prepared to simphfy mechanistic investigations or to facilitate the collection of the spectra. 

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