Of 13C-enriched

The latter mechanism is supported by evidence obtained from the initiation and termination steps in the syndiospecific polymerization of styrene [190]. The 13C-enriched titanium catalyst afforded polystyrene with a CH(Ph)CH213CH3 end group, which indicates that the initiation step proceeded by secondary insertion (2,1-insertion) of styrene into the Ti-13C bond of the active species (Eq. 10). In contrast to this mechanism, termination by the addition of 13C-enriched methanol or tert-butyl alcohol afforded polymers without 13CH30 or tertbutoxy end groups. 

Homologation of 13C-Enriched Acetic Acid CataIyst RuO2-10CH3I... 

The HBA/HNA system provides a more suitable system for study, since it is prepared by melt polymerization of the two monomers and is far more stable at elevated temperatures compared to the PHBA/PET. The HBA/HNA copolymers are soluble in pentafluorophenol permitting use of NMR techniques to characterize diad sequences. In Fig. 13b,c the 13CNMR spectrum of the carboxyl carbon region of the HBA/HNA copolyesters of the 73/27 and 48/52 systems is shown [34]. Also shown in Fig. 13a,d are the spectra of 13C enriched HBA and HNA containing copolymers permitting unique identification of the diad sequences. As a result of this technique it was possible to determine the reactivity ratios of the two monomers by analyzing the 50/50 copolymer after polymerization to a molar mass value of 2000 [35]. Examination of the copolymer by 13C NMR showed the same ratio of monomers as in the starting... 

A simple, quantitative, vacuum-line method for the preparation of millimole quantities of 13C-enriched difluoromethane and chlorofluoromethane by heating (13C)dichloromethane with mercury(II) fluoride at 230 C for 1 hour is known. The volatile product is estimated to be 75% difluoromethane 2 and 25% chlorofluoromethane l.54... 

Some help with the complexity can be obtained by incorporation of 13C-enriched methyl groups into... 

Fig. 2.20. Nuclear Overhauser effect observed on proton broad-band decoupling of 13C-enriched formic acid [33]. (Reproduced by permission of the copyright owner from K.F. Kuhlmann and D.M. Grant, J. Am. Chem. Soc. 90, 7355 (1968).)...

A trend of 13C enrichment developed in POM as the summer progressed, especially in the fertilized side, where 813C values increased to around -25% (Table I). The 13C content of zooplankton in the fertilized side mirrored this trend, but the absolute 13C enrichment was less than that found in POM. The trend in POM is caused in small part by increasing 813C-DIC values over the same time period (Table II). More importantly, increasing algal biomass and uptake of CO lowered dissolved CO concentrations to... 

Figure 8.2.12 (a) RF circuitry and layout of a dual-channel 13C probe, (b) Proton-coupled 13C NMR spectra acquired simultaneously by using this probe. Both spectra were acquired by using single 90° pulses and 50 kHz bandwidths. The top trace is the spectrum obtained from 4 jl1 of 13C-enriched methanol using a commercial receiver, while the bottom trace is obtained from 4 ul1 of 13C-labelled carbon tetrachloride from a home-built receiver. Reproduced by permission of Academic Press from Oldfield, E., J. Magn. Resort., A, 1994,107, 255... 

Proteins that are to be studied by NMR must be specially prepared. Natural proteins almost exclusively contain 12C and 14N, neither of which is an NMR-active isotope. For analysis, the protein must be enriched with 13C and 15N. Isotopically-enriched proteins can be isolated from bacteria that are grown in the presence of 13C-enriched glucose and 15NH4C1. The resulting proteins are then handed off to the NMR experts. 

Chanton, J.P., Crill, P.M., Baertlett, K.B., and Martens, C.S. (1989b) Amazon Capims (floating grassmats) a source of 13C-enriched methane to the troposphere. Geophys. Res. Lett. 16, 799-802. 

IV lines and a two-hour infusion, high cost of 13C-enriched substrates, and sample size considerations studies with healthy volunteers had N < 10, but this may not be enough to detect differences in the metabolic models between groups of patients and healthy volunteers. 

Compounds 80, 81 and 82 have been used to assign correctly the 13C-NMR spectra of the covalent adducts which result from nucleophilic attack of bisulphite anion on them66. Previously, uracil labelled with 13C at C(4) has been applied67 to study its incorporation into transfer ribonucleic acid (tRNA) by taking the 13C NMR spectra of 13C-enriched tRNA. The fluidity of the fatty acids within biological membranes has been investigated68 by feeding 13C-labelled acetate. 

The spectrum of 13C enriched protein before and after addition of DOTP is shown in Fig. 10.37. It is seen that resonances 1,2 and 5 shifted to higher frequency while resonances 3 and 4 shifted to lower frequency, throughout the titration until one equivalent of chelate per protein dimer had been added. 

C MAS-NMR spectroscopy was used to quantify the different carbon species in synthetically produced nanodiamonds.430 A 13C study has been reported to study the modification of the electronic properties of SWCNT by alkali intercalation.431,432 13C MAS-NMR data were used to study the structure of 13C-enriched SWCNT, prepared by catalytic decomposition of CH4.433 H, 13C and 15N MAS-NMR spectra of amorphous carbon nitride (a-CNx) films were consistent with sp2 hybridised nitrogen atoms in an aromatic carbon... 

With increasing availability of 13C-enriched saccharides, additional 13C- H and 13C-13C coupling constants have provided valuable information to confirm and/or extend structural conclusions based on the traditional proton-based NMR data. 

By means of 13C-enrichment studies on 1,2 5,6-di-O-isopropyl-idene-a-D-glucofuranose, Schwarcz and Perlin70 have accounted for fragments at mle 131 and 129 (see 21). 

M Bardet, D Gagnaire, R Nardin, D Robert, M Vincendon. Use of 13C enriched wood for structural NMR investigation of wood and wood components, ceUulose and hgnin, in solid and in solution. Flolzforschung 40 (Suppl) 17-24, 1986. 

The achievements concerning reaction mechanisms of ot-olefin polymerizations are summarized. The contributions of 13c NMR in this field, particularly concerning the stereochemical structure of 13c enriched end groups, are discussed. 

Price, N. P. (2006). Acylic sugar derivatives for GC/MS analysis of 13C-enrichment during carbohydrate metabolism. Analytical Chemistry, 76, 6566-6574. 

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