Labeling, with heavy water

Furan has also been labeled with heavy water on supported catalysts (chromium, zinc, and manganese oxides promoted with K2C03) at a temperature of 350°.117 Deuterated furan has also been obtained from the vapor phase decarbonylation of furfural over mixed oxide catalysts in the presence of heavy water. Both of these systems utilize extreme experimental conditions and the methods outlined in Table XII are to be preferred for preparative labeling. 

Little was known of the mechanisms of action of aconitase because all attempts at purification failed until it was demonstrated that the enzyme requires iron and cysteine for activity. It has since become evident that the mechanism of the reaction catalyzed by aconitase is extremely complex. C/.y-aconitate was thought to be an intermediate, but the compound could not be isolated. This led Speyer and Dickman [78] to suggest that a common intermediate exists between citrate on the one hand, and aconitate and isocitrate on the other (see Fig. 1-17). These authors found that when citric acid labeled with heavy water was used as a substrate, the isocitrate was extensively labeled, while only traces of deuterium were found in cw-aconitate. This suggested that cw-aconitate is not on the pathway leading from isocitric to citric acid. To explain these results, the authors postulated an intermediate common to c/.y-aconitate and isocitrate consisting of a tricarboxylic acid forming a complex with iron and cysteine. Such a complex would then be capable of intramolecular hydrogen transfer between the carbonium... 

One of the most important methods for specific incorporation of single deuterium atoms into both aliphatic and aromatic hydrocarbons employs compounds containing a carbon-metal bond. Most such substances are extremely sensitive to hydrolysis and it is thus a simple matter to label them by treatment with heavy water. 

In the case of micellar solutions, it is not possible to separate the diffusivity of the surfactant as a whole from singly dispersed amphiphiles and micelles. Lindman and Brun (1973), using radiolabeled tracer studies, and Lindman et al. (1984), using magnetic resonance with C labeling and heavy water as a solvent, showed that... 

Labeling with 2H, 13C, 15N and/or lsO can be introduced via peptide synthesis, cell culture, or hydrolysis in labeled water [88]. The heavy isotope-labeled peptide can be used as an IS to obtain quantitative measurements of the protein concentration. Typically, the protein sample of interest is digested with trypsin, and the isotope-labeled control peptides are added to the mixture. The signature peptides in the digest can be separated and quantified by HPLC-ESI-MS/MS. Alternatively, MALDI-MS can also be used for tryptic peptide determinations after some separation steps such as gel electrophoresis [89]. 

A number of isotopically different forms of water can be prepared, which greatly facilitates experimental studies. Replacing both of the usual hydrogen atoms with deuterium (2H) results in heavy water, or deuterium oxide, with a molecular weight of 20. The role of water in chemical reactions can then be studied by analyzing the deuterium content of substances involved as reactants or products. Tritium (3H), a radioactive isotope with a half-life of 12.4 years, can also be incorporated into water. Tritiated water has been used to measure water diffusion in plant tissues. Another alternative for tracing the pathway of water is to replace the usual 160 isotope with lsO. This labeling of water with lsO helped determine that the O2 evolved in photosynthesis comes from H20 and not from CO2 (Chapter 5, Section 5.5A). 

This mechanism was tested by use of C-labeled carbon dioxide (Barker, 1943 Buswell and Sollo, 1948 Stadtman and Barker, 1949, 1951 Pine and Barker, 1956 Baresi et al, 1978). Essentially none of the methane was found to be derived from carbon dioxide. Methane is derived entirely from the methyl carbon atoms and carbon dioxide is derived exclusively from carboxyl carbon atoms. Van Neil s mechanism is clearly not valid because the methyl carbon atom is not oxidized to carbon dioxide. Other work has been done to ascertain whether hydrogen atoms are removed during the fermentation of acetic acid, and whether the methyl group is incorporated intact into methane (Pine and Barker, 1954). Water and heavy water were used with deuterated and nondeuterated acetic acid. Acetic acid labeled in the methyl group, when used as the substrate, showed that the isotopic content of acetic acid and methane are the same. Unlabeled acetic acid fermented in the presence of heavy water indicated that about one atom of deuterium per molecule of methane formed is derived from heavy water. It was concluded that the methyl group is transferred from acetic acid to methane as a unit without the loss of attached hydrogen or deuterium atoms. 

To further increase the profiling depth of this technique the use of this reaction was combined with a position scanned He ion microbeam. The resulting technique has been used to study molecular ingress/ diffusion into various materials by labeling the molecules of interest with deuterium. Water molecules are labeled by adding heavy water (D2O) and other... 

Water is poorly soluble in hydrocarbons and determination of its solubility by ordinary chemical analysis requires a large amount of hydrocarbon samples. The solubility of water in benzene (Joris and Taylor 1948) and other hydrocarbons (Black et al. 1948) was determined with the use of tritium ( H, T) as tracer. These studies give an example where correction for the mass difference between an element of natural isotopic composition and its radioactive tracer is necessary. Water labeled with T was prepared by bombardment of heavy water (D2O) with... 

When deutero-water is fed to animals, it becomes distributed throughout the body tissues. Body fats become labeled, and the amount of deuterium found in the fatty acid chain suggests that the fatty acids have been built from smaller units. This suggestion is reasonable, since, as already noted above, the deuterium of heavy water does not normally exchange with the stably bound hydrogens on the carbons of a fatty acid... 

Heavy water is the cheapest available deuterium source. However, it has one inconvenience. Being inevitably employed in excess, it necessitates extraction or at least drying of the reaction mixture as part of the workup protocol. In contrast, deuterium chloride in diethyl ether can be employed in stoichiometric doses. But also this reagent suffers from a drawback. It reacts, if slowly, with the ethereal solvent. Therefore, the indefinitely storable phenylacetylene-ry-c may often become the deuteration reagent of choice. Due to its high intrinsic acidity and its needle-like slim shape, this terminally deuterated acetylene transfers the isotope label most effectively and in general irreversibly. 

The NDIS difference methods were initially applied to concentrated solutions of nickel chloride in heavy water. Both Ni " " and Cl possess isotopes of sufficient number and variation in neutron coherent scattering lengths and results were obtained for all aspects of the Ni + and Cl hydration as a function of concentration (Figs. 1 and 2) and with variations of temperature and pressure.Results were also obtained to determine the extent of the preferential hydration of NP+ regarding the number of H2O and D2O molecules in its first hydration shell (Fig. 2) as far as it could be ascertained, at ambient conditions there is no preference for the heavier molecule over the lighter one. From a complete set of six experiments on six isotopically labelled samples of a 4.3 molal solution of NiCb in heavy water, all three r.d.f.s of the solute were calculated ftom sets of double difference (Fig. 3). 

The oxygen in water is primarily (99.8%) l60, but water enriched with the heavy isotope, 80 is also available. When an aldehyde or ketone is dissolved in 180-enriched water, the isotopic label becomes incorporated into the carbonyl group. Explain. 

Figure 2.3 Changes in the heavy isotope content of oxygen and hydrogen in the urine with time after administration of The and 0 are diluted by the formation of H2O from oxidation of fuels and particularly that ingested in food and drink. The 0 in water is diluted from the production of CO2 via the oxidation of the fuels. The difference in the slopes indicates the rate of CO2 production. The label heavy isotope content is actually the isotopic enrichment. Physical activity, for example, increases fuel oxidation (i.e. respiration) and therefore greater dilution of...

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