Carbon-13 enrichment parameter

Our studies with C NMR in relation to cardiac metabolism have focussed primarily on the development of a mathematical model that allows flux parameters to be calculated from a knowledge of the specific carbon enrichments of metabolic intermediates resolvable by high resolution C NMR spectroscopy (Chance et al., 1983). The concentrations of most intermediates in tissues are below the level necessary for adequate detection of the C resonances, even... 

They indicated that the softness parameter may reasonably be considered as a quantitative measure of the softness of metal ions and is consistent with the HSAB principle by Pearson (1963, 1968). Wood et al. (1987) have shown experimentally that the relative solubilities of the metals in H20-NaCl-C02 solutions from 200°C to 350°C are consistent with the HSAB principle in chloride-poor solutions, the soft ions Au" " and Ag+ prefer to combine with the soft bisulfide ligand the borderline ions Fe +, Zn +, Pb +, Sb + and Bi- + prefer water, hydroxyl, carbonate or bicarbonate ligands, and the extremely hard Mo + bonds only to the hard anions OH and. Tables 1.23 and 1.24 show the classification of metals and ligands according to the HSAB principle of Ahrland et al. (1958), Pearson (1963, 1968) (Table 1.23) and softness parameter of Yamada and Tanaka (1975) (Table 1.24). Compari.son of Table 1.22 with Tables 1.23 and 1.24 makes it evident that the metals associated with the gold-silver deposits have a relatively soft character, whereas those associated with the base-metal deposits have a relatively hard (or borderline) character. For example, metals that tend to form hard acids (Mn +, Ga +, In- +, Fe +, Sn " ", MoO +, WO " ", CO2) and borderline acids (Fe +, Zn +, Pb +, Sb +) are enriched in the base-metal deposits, whereas metals that tend to form soft acids... 

Rotational-echo double-resonance (REDOR)(75,79) is a new solid-state NMR technique which is sensitive to through-space carbon-nitrogen interactions between selectively 13C and 15N-enriched sites separated by up to 5A (20-22). The parameter directly measured in a REDOR experiment is the heteronuclear dipolar coupling constant DCN, which is in itself proportional to the inverse third power of the intemuclear distance, rCN. It is this dependence on (icn)3 which accounts both for REDOR s ability to accurately measure short distances and its insensitivity to longer-range interactions. As a technique which can probe, in detail, intermolecular interactions over a distance range of 5A, REDOR is well suited to studying the distribution of small selectively-labeled molecules in polymer delivery systems. 

Beginning at 850 K and higher, heating of a methoxylated silica sample is accompanied by the sequential formation of the carbon-centered =Si- CH2 (900 K), =Si-HC -Si= (1100K), and (=Si-)3C (1300 K) radicals. With a rise in pyrolysis temperature, the concentration of radicals increases. Their EPR spectra parameters are reported in Table 7.15. The answer to the question of the chemical structure of these radicals was obtained in the experiments on samples enriched with magnetic isotopes of the H(D), C(13C), and Si(29Si) nuclei. The (=Si-)3C radicals EPR spectra are shown in Figure 7.30. 

To confirm this conclusion, traversianal was isolated from cultures of the fungus on liquid potato-dextrose medium supplemented with [1, 2-1 2]acetate, 10 mL 0.041 M solution being added to each 100 mL of cultures on days 10 and 13. The l Cmr spectrum of the compound isolated on day 16 showed that all carbons were highly enriched (4.4% specific incorporation), in a pattern that was in precise accord with expectation. The relevant parameters are indicated... 

An essential step in the homogeneous catalyzed water gas shift reaction involves nucleophilic attack of hydroxide ion at the carbon atom of a metal-bound CO, with a subsequent process leading to the extrusion of COu These two processes have been studied for the reaction of oxygen-18 enriched NaOH with Cr(CO)e in a biphasic medium in the presence of a phase-transfer catalyst. Oxygen exchange was observed to occur at a faster rate than metal hydride, fi-H[Cr(CO)s]2, formation with concomitant production of C02- The kinetic parameters for the reaction of fji-H[Cr(CO)5]2 with CO in alcoholic solvent to afford Cr(CO)e and H2 have been determined. 

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