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  • Physics  (3)
  • Key words Urea decomposition  (2)
  • (-)-2-(1,2,2-trimethyl)-cyclopentyl-6-methyl-1,4-quinone  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Phytochemistry 30 (1991), S. 325-328 
    ISSN: 0031-9422
    Keywords: (-)-2-(1,2,2-trimethyl)-cyclopentyl-6-methyl-1,4-quinone ; Hepaticae ; Jungermanniales ; Radula javanica ; bibenzyls ; cuparene-type sesquiterpene quinone. ; cyclopropanochromans ; radulanins I, J and K
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1439-863X
    Keywords: Key words Urea decomposition ; Size fraction ; Phytoplankton ; Lake Nakaumi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of brackish phytoplankton cell classes upon the response of urea decomposition was investigated in Lake Nakaumi. The urea decomposition rate was 5 to 350 μmol urea m−3 h−1 in the light and 3 to 137 μmol urea m−3 h−1 in the dark. The urea decomposition rates in the light were obviously higher than in the dark. An extremely high rate (350 μmol urea m−3 h−1) was observed in Yonago Bay. The rate in the smaller fraction (〈5 μm) exceeded that in the middle (5–25 μm) and larger fractions (〉25 μm). The chlorophyll- and photosynthesis-specific rates for urea decomposition in the light were 0.5 to 3.9 μmol urea mg chl.a −1 h−1 and 0.3 to 1.3 μmol urea mg photo.C−1. The specific urea decomposing activities were higher in the smaller fraction than in the other two fractions. The present results suggest that in brackish waters urea decomposition occurred with coupling to the standing crop and photosynthetic activity of phytoplankton.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1439-863X
    Keywords: Key words Urea decomposition ; Diel variation ; Lake Nakaumi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Diel variations in urea decomposing activity in the euphotic zone of brackish Lake Nakaumi were measured under fixed light intensity. The decomposition rate of urea was 17 to 44 μ mol urea m−3 h−1 in the light and 10 to 27 μ mol urea m−3 h−1 in the dark. Higher decomposition rates were obtained in the upper euphotic zone. A clear diel periodicity in the urea decomposition rate was observed, with high rates from 1200 to 1600 and low rates from 0000 to 0400. Chlorophyll a specific decomposing activity ranged from 12 to 21 μg urea C mg chl.a −1 h−1 in the light and 7 to 13 μg urea C mg chl.a −1 h−1 in the dark. In the light, high values were obtained from 1600 to 2000 and low values from 0400 to 0800. The diel change in specific decomposing activity exhibited a similar pattern to that of the photosynthetic assimilation number, following the diel change in photosynthetic activity.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 15 (1977), S. 2059-2065 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oxidation of hydroquinone catalyzed by copper(II) complexes of poly-1-vinylimidazole, vinylamine-vinylacetamide copolymer, and polyethyleneimine was studied in aqueous solution at 25°C. The rate of oxidation was determined spectrophotometrically over several pH values. The rate of copper(II) reduction was evaluated from copper(I)-cuproin complex formation, and the reoxidation of copper(I) to copper(II) was observed by visible spectroscopy. Among the copper(II) complexes, poly-1-vinylimidazole complex exhibited excellent catalytic activity, which amounted to over 20 times that of aqueous copper(II) ion solution, while the reduction of copper(II) in the former system was slower than that in the latter system. The reoxidation of copper(I) to copper(II) was found to be completed immediately in the presence of polymer ligands such as poly-1-vinylimidazole, while copper(I) ion was only slowly reoxidized. The discussion of the reaction mechanism emphasizes the importance of the reoxidation process.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 17 (1979), S. 2729-2737 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The autoxidation of Cu(I) complexes with imidazole and polyvinylimidazole derivatives was studied by observing the formation of the corresponding Cu(II) complexes with a stopped-flow technique. The reaction was second order and proportional to the concentrations of Cu(I) and oxygen. In the Cu(I)-imidazole complex pH variation was without effect in the range of 7.5-8.6. The oxidation rate of Cu(I).polyvinylimidazole complexes, on the other hand, decreased with a rise in pH. The activation parameters of the Cu(I)·polyvinylimidazole complexes, compared with those of the Cu(I).imidazole complex, were characterized by large enthalpic requirements coupled with favorable entropies of activation. This was explained by the fact that a conformational change in the polymeric ligands took place during oxidation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 18 (1980), S. 101-107 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Cu(II) complexes of copolymers having pendant sulfide and imidazolyl groups were prepared by a free radical copolymerization of ethylvinylsulfide with vinylimidazole, and their properties and function were studied spectrophotometrically in comparison with those of poly[4(5)-vinylimidazole]. The complexes were found to be effective as catalysts for the oxidation of hydroquinone. Visible and ESR spectra of the Cu(II)-copolymer complexes were similar to those of the Cu(II)-homopolymer complexes, while the catalytic activity for the oxidation was different between these complex systems. A rapid reaction followed by a slow reaction, particularly at high ethylvinylsulfide content in the copolymers, was observed in the Cu(II)-copolymer complex systems, but a continuous reaction proportional to the reaction time was observed in the Cu(II)-homopolymer complex systems. The reoxidation rate of Cu(I) to Cu(II) complex, which was little affected by the concentration of imidazolyl group, decreased with a rise of the ethylvinylsulfide content in the copolymer. It was suggested that the sulfur atom of the sulfide group was weakly coordinated to Cu(II) but strongly to Cu(I), and an electron transfer reaction from substrate to the Cu(II) complex was increased, while reoxidation reaction of the Cu(I) complex was decreased in the copolymer complex systems.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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