Labelled with isotopic oxidation

Citric acid, II, 148 III, 238, 242, 248 Iahelled with C11, III, 238 labelled with isotopic C, III, 241 from molasses, IV, 336 from sucrose, IV, 322, 324 Citric acid cycle, in carbohydrate oxidation, III, 238... 

Formic acid, cellulose ester, I, 310 from inositol oxidation, III, 52 labelled with C1, III, 237 labelled with isotopic C, III, 231, 232 starch ester, I, 300 from sucrose, IV, 309 Formose, IV, 27... 

Three 5a-androst-6-ene derivatives have been recorded as intermediates for labelling with isotopic hydrogen.50 Reaction of 3/3-acetoxyandrost-5-en-17-one with N-bromosuccinimide-perchloric acid followed by oxidation of the intermediate 5,6-bromohydrin gave the diketone (133 R1 = Br, R2 = H), which on treatment with... 

Substitution of deuterium for hydrogen at the a carbon atom of an aldehyde or a ketone is a convenient way to introduce an isotopic label into a molecule and is readily carried out by treating the carbonyl compound with deuterium oxide (D2O) and base... 

An important advance on these studies was the possibility of isolating AORs from Fe enriched media with obvious interest for an iron-sulfur center site labeling, with enhanced sensitivity of the Mossbauer studies. The work developed with bacterial systems is advantageous as compared with mammalian systems for isotopic labeling and opens the possibility of a direct measurement of substrate binding. Spectra of the enzyme in oxidized, partially reduced, benzaldehyde-reacted, and fully reduced states were recorded at different temperatures and with variable externally applied magnetic fields (222). In the oxidized enzyme, the clusters are diamag-... 

Yeom and Frei [96] showed that irradiation at 266 nm of TS-1 loaded with CO and CH3OH gas at 173 K gave methyl formate as the main product. The photoreaction was monitored in situ by FT-IR spectroscopy and was attributed to reduction of CO at LMCT-excited framework Ti centers (see Sect. 3.2) under concurrent oxidation of methanol. Infrared product analysis based on experiments with isotopically labeled molecules revealed that carbon monoxide is incorporated into the ester as a carbonyl moiety. The authors proposed that CO is photoreduced by transient Ti + to HCO radical in the primary redox step. This finding opens up the possibility for synthetic chemistry of carbon monoxide in transition metal materials by photoactivation of framework metal centers. 

The oxidation reactions were performed in a 25 mL ronnd bottom flask. In a typical reaction the catalyst (0.5 % Fe mol) was added to 0.125 M olefin solntion in acetone then dry TBHP (3.5 M in CH2CI2 or in PhCl) was added in one step, and the reaction mixture was stirred and heated in an oil bath at 40°C for 7 h. For the allyhc oxidation of cyclohexene with isotopically labelled oxygen ( 02) the following procedure was carried out the suspension of the catalyst (0.5% Fe mol) in cyclohexene (4 mL, 0.125 M) was frozen and the air in the reactor was evacuated and replaced by an oxygen (21% mol) - argon (79% mol) mixture. Then, the suspension was allowed to warm at room temperatnre and 1.3 mmol of degasified TBHP was added to the solution and the reaction mixtnre was stirred at 40°C for 3 h. 

Retention of configuration is expected for conversion of 3 to 59a. It is curious, however, for the rearrangement of 59a to 60a, since the most obvious pathway—opening of the O—O bond followed by rotation and reclosing—should lead to inversion of configuration. Double isotopic labeling with, 80 was used to show that the rearrangement of 59a to 61a, as well as the initial oxidation of 3 to 59a, is fully intramolecular. 

The authors have also synthesized134 fatty acids labelled with deuterium and carbon-11 in order to investigate if kinetic isotope effects related to fatty acid metabolism can be observed in vivo by pet133,135-137. In vitro, the large kinetic deuterium isotope effects are observed in the oxidation of deuteriated aliphatic carboxylic acids with alkaline permanganate and manganate135-139. 

Tributyltin chloride labelled with a metastable tin-117 isotope has been prepared by Imura and Suzuki36. This artificial isotope was made by irradiating tin-118 labelled bis(tributyltin) oxide with 30-MeV /-rays for six hours (equation 36). 

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...

New derivatives of 4-amino and 2,4-diaminopteridines have been synthesized and their capability to inhibit neuronal nitric oxide synthase evaluated <99JMC4108>. The synthesis of folic acid multiply labeled with stable isotopes, for bioavailability studies in human nutrition, has been reported <99JCS(P1)1311>, Synthesis and antiviral evaluation of several 6-(methylenecarbomethoxy)pteridine-4,7-diones have been described <99JHC435>. Synthesis and biochemical evaluation of bis(6,7-dimethyl-8-D-ribityllumazines) as potential bisubstrate analog inhibitors of riboflavin synthase have been reported <99JOC4635>. Synthesis and cyclization of novel lumazine-enediyne chimeras have been reported <99H13>. 

The Re- Os method was first applied to extraterrestrial samples in the early 1960s when Hirt et al. (1963) reported a whole-rock isochron for 14 iron meteorites that gave an age of 4 Ga. Further development of this system was hindered by several technical difficulties. Rhenium and osmium each exist in multiple oxidation states and can form a variety of chemical species, so complete digestion of the samples, which is required to chemically separate rhenium and osmium for mass spectrometry, is difficult. In addition, accurate determination of rhenium abundance and osmium isotopic composition requires spiking the samples with isotopically labeled rhenium and osmium, and equilibration of spikes and samples is challenging. A third problem is that osmium and, particularly, rhenium are very difficult to ionize as positive ions for mass spectrometry. These problems were only gradually overcome. 

The mechanism of reaction (9a) has been examined by isotope techniques using nitrous oxide labelled with 15N (Clusius et al. [66,67]). The course of the reaction... 

Direct evidence about the first step of activation of butane was obtained on a V-P oxide catalyst in the butane oxidation to maleic anhydride based on deuterium kinetic isotope effect (34). It was found that when a butane molecule was labeled with deuterium at the second and third carbon, a deuterium kinetic isotope effect of 2 was observed. No kinetic isotope effect was observed, however, if the deuterium label was at the first or fourth carbon. By comparing the observed and theoretical kinetic isotope effects, it was concluded that the first step of butane activation on this catalyst was the cleavage of a secondary C—H bond, and this step was the rate-limiting step. 

Later experiments using isotopic labeling with 13C verified Knoop s proposals/but study of isolated enzymes was not possible until after the discovery of coenzyme A in 1950. Then, studies of fatty acid oxidation by extracts from isolated mitochondria established the details of the pathway/... 

Back and Mui17 studied the reaction with isotopically labeled nitric oxide to test the proposal that active nitrogen contained vibra-tionally excited molecules capable of dissociating nitric oxide. This reaction was proposed by Winkler and his co-workers133,435... 

The structure assignment problem, which offers difficulties similar to those discussed for the alkylation products, was solved by means of mass spectrometry in combination with isotope labeling at position 2 with 15N. ESCA (X-ray photoelectron) spectroscopy and IR spectra are in agreement with the assignment as a 3-oxide.23... 

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