Oxygen 19 labelling studies

A somewhat similar catalytic acetoxylation of ethylene to vinyl acetate by 02 has been carried out in acetic acid in the presence of a Pd(OAc)2-pyCo(TPP)N02 system.472 A stoichiometric epoxidation of alkenes such as 1-octene or propene by cobalt-nitro complexes has been shown to occur in the presence of thallium(III) benzoate. Oxygen labeling studies showed that the epoxide oxygen atom comes only from the nitro ligand (equation 197).473... 

Scheme 1.2 Alternative mechanisms for the acid-catalysed decomposition of N1 -adamantyl-N2 hydroxydiazenium oxide (1) distinguished by an oxygen labelling study [7, 8].

This paper reports oxygen-labeling studies directed toward identifying the mechanisms for CO2 interaction with zirconia. The mechanism of bicarbonate formation and its subsequent conversion to the formate either directly or via the intermediate formation of CO were explored. 

Bilirubin and carbon monoxide are always produced in equimolar proportions under normal conditions of heme catabolism the process is oxidative and requires molecular oxygen. Labelling studies using 02 show that the labelled oxygen ends up in the bilirubin at the terminal lactam positions, and in the carbon monoxide that is liberated (by removal of the C-5 carbon). The overall process is shown in Figure 5.5. 

Both reactions proceed through e transfer with no other change in the ruthenium complex. In contrast/ " [Au "(0)(py)(bpy)2] and [Ru (OH)(py)(bpy)2] oxidize phenol and alkylated phenols to the corresponding quinones via a detectable intermediate. Oxygen labeling studies show that quantitative oxygen transfer occurs. Ferrocenium ion reacts via a photoinduced pathway with benzylic alcohol, benzhydrol, and 1-propanol. Reaction products are dependent upon the choice... 

The complex [(bpy)20Ru—O—RuO(bpy)2] containing ruthenium(V) oxidizes water. Oxygen labeling studies etablish that the mechanism does not involve oxidation of noncoordinated water as a dominant pathway, but that some coupling of the coordinated aqua ligands is involved. 

Wasserman demonstrated with 0 labeling studies that the amide carbonyl oxygen is incorporated into the oxazole ring upon cyclization... 

The mechanism shown in Figure 21.7 is supported by isotope-labeling studies. When ethyl propanoate labeled with lsO in the ether-like oxygen is hydrolyzed in aqueous NaOH, the l80 label shows up exclusively in the ethanol product. None of the label remains with the propanoic acid, indicating that saponification occurs by cleavage of the C-OR bond rather than the CO—R bond. 

A study of the chlorine oxidation of 2-hydroxyethyl octyl sulphoxide92 (equation 28) showed that a cyclic intermediate is probably involved in the process which gives the sulphone in good yield. Labelling studies have shown that the hydroxyl group is replaced by a chlorine atom whilst the hydroxyl oxygen atom is transferred to the sulphur atom. A similar result was obtained for 3-hydroxypropyl and 4-hydroxybutyl alkyl sulphoxides93. 

Recently, Nam, Fukuzumi, and coworkers succeed in an iron-catalyzed oxidation of alkanes using Ce(IV) and water. Here, the generation of the reactive nonheme iron (IV) 0x0 complex is proposed, which subsequently oxidized the respective alkane (Scheme 16) [104]. With the corresponding iron(II) complex of the pentadentate ligand 31, it was possible to achieve oxidation of ethylbenzene to acetophenone (9 TON). 0 labeling studies indicated that water is the oxygen source. 

Ligeza A, Tikhonov AN, Hyde JS, Subczynski WK. 1998. Oxygen permeability of thylakoid membranes Electron paramagnetic resonance spin labeling study. Biochim Biophys Acta 1365 453. 

Subczynski, W. K., J. S.Hyde, and A. Kusumi. 1991. Effect of alkyl chain unsaturation and cholesterol intercalation on oxygen transport in membranes A pulse ESR spin labeling study. Biochemistry 30 8578-8590. 

Subczynski, W. K., E. Markowska, and J. Sielewiesiuk. 1991. Effect of polar carotenoids on the oxygen diffusion-concentration product in lipid bilayers. An EPR spin label study. Biochim. Biophys. Acta 1068 68-72. 

In contrast to the metabolism of BA and BaP, the 5,6-dihydrodiols formed in the metabolism of DMBA by liver microsomes from untreated, phenobarbital-treated, and 3-methylcholanthrene-treated rats are found to have 5R,6R/5S,6S enantiomer ratios of 11 89, 6 94, and 5 95, respectively (7.49 and Table II). The enantiomeric contents of the dihydrodiols were determined by a CSP-HPLC method (7.43). The 5,6-epoxide formed in the metabolism of DMBA by liver microsomes from 3MC-treated rats was found to contain predominantly (>97%) the 5R,6S-enantiomer which is converted by microsomal epoxide hydrolase-catalyzed hydration predominantly (>95%) at the R-center (C-5 position, see Figure 3) to yield the 5S,6S-dihydrodiol (49). In the metabolism of 12-methyl-BA, the 5S,6S-dihydrodiol was also found to be the major enantiomer formed (50) and this stereoselective reaction is similar to the reactions catalyzed by rat liver microsomes prepared with different enzyme inducers (unpublished results). Labeling studies using molecular oxygen-18 indicate that 5R,68-epoxide is the precursor of the 5S,6S-dihydrodiol formed in the metabolism of 12-methyl-BA (51). 

Marshall et al. noted that under the catalysis of Ag+ or Rh+, 1,2-allenyl ketone or aldehyde 417 may undergo cycloisomerization to afford furans 418. The reaction proceeded via the interaction of Ag+ or Rh+ with the relatively electron-rich C=C bond in the allene moiety followed by nucleophilic attack of the carbonyl oxygen [187]. Through a labeling study, it was found that the reaction proceeds by the mechanism shown in Scheme 10.162 [188]. 

Isotopic labeling studies have shown that H202 formed in irradiated suspensions of ZnO contained oxygen atoms derived exclusively from 02. 

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