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Correlative geochemical study of crude oils from southeastern and southern parts of the Pannonian Basin
Full text linkSeveral crude oils from the southeastern Yugoslav part of the Pannonian Basin are correlated for the first time on the basis of many bulk and specific parameters. The investigations involved 15 oils from oil-gas fields A and B and oil field C from the Banat depression and oil field D from South Bačka depression, and four oils from recently discovered oil shows E (the Kostolac depression). On the basis of structural group analysis and other bulk parameters such as API gravity, contents of asphaltenes and sulfur, as well as content of n-alkanes and pristane to phytane ratio, the examined oils are classified into four groups. However, the distributions and relative abundances of n-alkanes, isoprenoids (C19, C20), steranes, tricyclic terpanes and pentacyclic triterpanes, obtained by capillary GC and computerized GC-MS analysis, suggest classification of the examined oils into only two genetic types: A-D and E1-E4. The oils are of relatively high maturity. They are not biodegraded, except for both oils from field D and the oil A9. © 1987
Electrochemical reactivity of biologically active quinone/hydroquinone sesquiterpenoids on glassy carbon electrodes
Full text linkThe redox reactivity of avarone and avarol, a quinone/hydroquinone couple isolated from the marine sponge Dysidea avara, was investigated by cyclic voltammetry, using a glassy carbon electrode. Both oxidation of avarol and reduction of avarone in aqueous ethanol (1:1 V/V) take place by a 2 e- process at a wide range of pH values; in acetonitrile, however, the reduction of avarone occurs as a stepwise electron transfer process. The mechanisms, as well as the scope and limitations of the method are discussed with reference to the biological activity of the two sesquiterpenoids. © 1987
Avarol-induced DNA strand breakage in vitro and in Friend erythroleukemia cells
No full textThe hydroquinone-containing cytostatic compound avarol inhibits predominantly growth of those cell lines which have a low level of superoxide dismutase. The substrate of this enzyme, the superoxide anion, was found to be formed during the in vitro oxidation reaction of avarol to its semiquinone radical in the presence of oxygen. Under the same incubation conditions plasmid DNA (pBR322) was converted from the fully supercoiled circular form mainly to the nicked circular form, indicating that the compound causes primarily single-strand breaks. Using Friend erythroleukemia cells (FLC) it was found that avarol induces a dose-dependent DNA damage; the maximum number of DNA strand breaks was observed at 5 h after addition of the compound to the cells. Removal of avarol resulted in a rapid DNA rejoining with biphasic repair kinetics [first half-time, 8 min (90% of the breaks) and a second half-time, 40 min (10% of the breaks)]. When the degree of avarol-induced DNA damage in FLC was compared with the drug-caused inhibition of cell growth a close correlation was established. Avarol displayed no effect on dimethyl sulfoxide-induced erythrodifferentiation of FLC as determined by the benzidine reaction and by dot blot hybridization experiments. From incubation studies of FLC with [3H]avarol no hint was obtained for the formation of an adduct between DNA and the compound. The subcellular distribution of [3H]avarol was studied in liver cells after i.v. application of the compound. The predominant amount of the compound was present in the cytosolic fraction; little avarol was associated with plasma membranes, nuclei, and mitochondria. Using (a) oxidative phosphorylation and (b) oxygen uptake as parameters for mitochondrial function, no effect of the compound on the activity of this organelle was determined. These results suggest that avarol forms superoxide anions (and in consequence possibly also hydroxyl radicals) especially in those cells which have low levels of superoxide dismutase. Moreover, evidence is provided that the active oxygen species cause DNA damage resulting in the observed cytotoxic effect
Free radical carbocyclic ring reconstruction
Full text linkAlkenyl radical generated by β-fragmentation of tertiary cyclohexyloxy radical with carbocyclic ring opening, possessing a suitably located olefinic double bond, undergoes to the intramolecular 5-exo-trigonal cyclization and a new carbocyclic ring was formed. © 1986
Free radical annulation of cyclopentane ring
Full text linkHomoallyl radical, e.g. 2, reacts with an electron-deficient olefinic bond 1 with a new CC bond forming and arising of a 5-hexenyl radical 3 which further undergoes to 5-exo-trigonal cyclization with a cyclopentane ring (4) annulation. © 1986
Esca and Empa in the Analysis of Sulphides.
No full textThe purpose of the work was to determine the dependence of parameters describing XPS and XES spectra of sulfur on physico-chemical properties of some sulfides. The discussion considers chemical shifts of spectra correlated to oxidation, hybridization, spin state of the metal, electronegativity and properties of the ligand field. FeS//2 (pyrite), ZnS (sphalerite) and BaSO//4 (barite) were the subject of investigation
Determination of Fluorine Ions Penetration Degree Into Enamel by Empa.
No full textExogen of different preparations was applied to completely healthy teeth of children up to 11 years. A month after application of fluorine, teeth were extracted and prepared by standard methods for investigation by electron microprobe ARL, type SEMQ. The results obtained showed that the highest degree of fluorine ions migration was stimulated by organic fluorite' (amin fluoride). Very poor results were obtained by NaF, while the values obtained by 'fluor-protector' ranges between these two preparates. All up to date investigations showed that protective characteristics of fluorine against caries formation were reached only in case when enamel surface contained fluorine concentration of 10**3, mu g. Thus, our results proved that the first condition for good prophylaxy is obtained by application of aminofluoride and then by 'fluor-protector'
