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Query: UMLS:C0155339 (Brown)
 12,436 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We investigated the contents of polycyclic aromatic hydrocarbons (PAHs) in the food web organisms included in the diet of brown trout from a remote mountain lake. The preferential habitat and trophic level of the component species have been assessed from the signature of stable isotopes (delta13C and delta15N). Subsequently, the patterns of accumulation and transformation of these hydrocarbons in the food chain have been elucidated. Most of the food web organisms exhibit PAH distributions largely dominated by phenanthrene, which agrees with its predominance in atmospheric deposition, water, and suspended particles. Total PAH levels are higher in the organisms from the littoral habitat than from the deep sediments or the pelagic water column. However, organisms from deep sediments exhibit higher proportions of higher molecular weight PAH than those in other lake areas. Distinct organisms exhibit specific features in their relative PAH composition that point to different capacities for uptake and metabolic degradation. Brown trout show an elevated capacity for metabolic degradation because they have lower PAH concentrations than food and they are enriched strongly in lower molecular weight compounds. The PAH levels in trout highly depend on organisms living in the littoral areas. Fish exposure to PAH, therefore, may vary from lake to lake according to the relative contribution of littoral organisms to their diet.
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PMID:Distribution of polycyclic aromatic hydrocarbons in the food web of a high mountain lake, Pyrenees, Catalonia, Spain. 1611 9

Sublimation was developed by Alley and Brown (2000) in order to isolate bacterial strains that were capable of degrading water insoluble compounds. In this study, sublimation was modified by the use of nutritional agar plates, instead of mineral salt agar, to isolate phenanthrene-degrading bacteria from a mixed culture that had been enriched under the selective pressure of high phenanthrene content. Five strains were obtained with different morphology and degradation ability. Based on the 16S rDNA sequence, two of them were classified as species of the genus Sphingomonas; the others as species of the genus Burkholderia. Denaturing gradient gel electrophoresis (DGGE) was introduced to detect dynamic changes in the bacterial community during enrichment batch culture, and to determine any correlation between the five isolates and the phenanthrene-degrading consortium. The DGGE profile indicated that these five isolates corresponded to four dominant bands of the consortium. Compared to traditional means of isolation, we concluded that modified sublimation is effective and more convenient.
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PMID:Modified sublimation to isolate phenanthrene-degrading bacteria of the genera Sphingomonas and Burkholderia from Xiamen oil port. 1850 49

Mechanistic pathways for high-temperature rearrangements of 2-ethynylbiphenyl have been investigated by calculations at the B3LYP/6-31G(d) level of theory, with free energy estimates at 625 degrees C. Two different routes for high temperature thermal rearrangement can lead to phenanthrene, which was the major product observed by Brown and co-workers (J. Chem. Soc. Chem. Commun. 1974, 123). 1,2-Hydrogen shift (Hopf type B mechanism) affords a vinylidene which proceeds to the major product by sequential electrocyclic closure and a 1,2-shift, rather than the expected aryl C-H insertion. Alternatively, insertion of the vinylidene into a ring double bond would lead directly to the observed minor product, benzazulene. Along a competitive pathway, electrocyclic closure to an isophenanthrene is predicted to be nearly isoenergetic. This intermediate should have a planar allene structure, with substantial diradical character. Sequential hydrogen shifts lead to phenanthrene but with higher cumulative barriers than for the vinylidene route. Calculation of 625 degrees C free energies shows that the carbene mechanism is of lower energy, primarily because of the lower entropic cost. Predictions are made for the unusually facile hydrogen atom dissociation from isoaromatics at high temperature, a consequence of aryl radical formation. Isophenanthrene, isobenzene (1,2,4-cyclohexatriene) and several isonaphthalenes are also predicted to have unusually low C-H bond dissociation energies. Potential significance as a source of aryl radicals in high temperature and combustion chemistry is discussed.
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PMID:Thermal rearrangements of 2-ethynylbiphenyl: a DFT study of competing reaction mechanisms. 1906 66