Search

The very rapid benzene oxide/oxepin equilibrium plays an important role in the metabolism of benzene by cytochrome P450. Although it is the benzene oxide valence tautomer that is attacked by nucleophiles and rearranges to phenols in acidic media, it is the oxepin valence isomers that suffer one-electron oxidation. However, some other reactions are more competitive and also furnish useful illustrations of the Curtin–Hammett principle. For example, while oxepin and benzene oxide are comparable in energy, the only reaction product with maleic anhydride is the Diels–Alder adduct with benzene oxide. Density function theory (B3LYP/6-31G*) calculations are employed for study of three sets of benzene oxide/oxepin equilibria and Diels–Alder reactions with maleic anhydride and dimethylazodicarboxylate as well as epoxidation by dioxirane. Comparisons are made between theory and published experimental data. [ABSTRACT FROM AUTHOR]

This paper deals with a technology of coal beneficiation focusing on the process of flotation. It reviews and describes practices applied by the Coal Beneficiation Plant of Paskov. Samples of raw sludge were subject of flotation tests conducted at the laboratories of the VSB-Technical University of Ostrava. The objective of the testing was to compare effectiveness of the flotation agents utilized. The paper provides for the statistics of the flotation test results. [ABSTRACT FROM AUTHOR]

A reaction of a lithiated derivative of 4,4,5,5-tetramethyl-3-oxido-4,5-dihydro-1 H-imidazole 1-oxyl with 3,6-di- tert-butyl- o-benzoquinone at −80 °C predominantly gave spin-labeled dihydrooxepine via nucleophilic 1,2-addition of the paramagnetic carbanion to the CO group of the benzoquinone followed by insertion of the O atom into the ring. At lower temperatures, this reaction was accompanied by 1,4-addition of the organolithium compound to the benzoquinone followed by oxidation of the resulting adduct into spin-labeled o-benzoquinone. This 'one pot' process is a novel approach to organic derivatives that can further be converted into di- and polyradicals combining nitronyl nitroxide and semiquinolate fragments. [ABSTRACT FROM AUTHOR]

series of 4-aroyl-1 H-benzo[ c]oxepin-4-ones have been prepared by heating ethyl 2-aroyl-3-(2-bromophenyl)propenoates. The synthesized compounds possess higher analgesic activity than the reference drug (analgin) and exhibit low toxicity. [ABSTRACT FROM AUTHOR]

Zinc enolates formed from the substituted 1-aryl-2,2-dibromoalkan-1-ones and zinc react with 4-aroyl-1 H-benzo[ c]oxepin-3-ones to form 1-alkyl-1-aroyl-1a -aroyl-1,1a,4,8b-tetrahydro-3-oxabenzo[ a]cyclopropa c]cyclohepten-2-ones. [ABSTRACT FROM AUTHOR]

Substrate channeling is a mechanism for the internal transfer of hydrophobic, unstable or toxic intermediates from the active site of one enzyme to another. Such transfer has previously been described to be mediated by a hydrophobic tunnel, the use of electrostatic highways or pivoting and by conformational changes. The enzyme PaaZ is used by many bacteria to degrade environmental pollutants. PaaZ is a bifunctional enzyme that catalyzes the ring opening of oxepin-CoA and converts it to 3-oxo-5,6-dehydrosuberyl-CoA. Here we report the structures of PaaZ determined by electron cryomicroscopy with and without bound ligands. The structures reveal that three domain-swapped dimers of the enzyme form a trilobed structure. A combination of small-angle X-ray scattering (SAXS), computational studies, mutagenesis and microbial growth experiments suggests that the key intermediate is transferred from one active site to the other by a mechanism of electrostatic pivoting of the CoA moiety, mediated by a set of conserved positively charged residues. The bacterial enzyme PaaZ is involved in the breakdown of environmental pollutants via the aerobic-anaerobic hybrid pathway but its substrate transfer mechanism is not fully understood. Here, the authors present cryoEM structures of free and ligand-bound PaaZ that suggest a mechanism for internal substrate channeling. [ABSTRACT FROM AUTHOR]