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  • Chemical Engineering  (3)
  • 4-Hydroxyphenylacetate  (1)
  • 2020-2021
  • 1990-1994  (4)
  • 1960-1964
  • 1945-1949
  • 1
    Electronic Resource
    Electronic Resource
    Anaerobic oxidation of phenylacetate and 4-hydroxyphenylacetate to benzoyl-coenzyme A and CO2 in denitrifying Pseudomonas sp. (1993)
    Springer
    Archives of microbiology 159 (1993), S. 563-573 
    Details
    ISSN: 1432-072X
    Keywords: Phenylacetate ; 4-Hydroxyphenylacetate ; Phenylglyoxylate ; Alpha-Oxidation ; Pseudomonas ; Oxidoreductase ; CoA ligase ; Benzoyl-CoA ; Anaerobic aromatic metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Anaerobic degradation of (4-hydroxy)phenylacetate in denitrifying Pseudomonas sp. was investigated. Evidence is presented for α-oxidation of the coenzyme A (CoA)-activated carboxymethyl side chain, a reaction which has not been described. The C6−C2 compounds are degraded to benzoyl-CoA and furtheron to CO2 via the following intermediates: Phenylacetyl-CoA, phenylglyoxylate, benzoyl-CoA plus CO2; 4-hydroxyphenylacetyl-CoA, 4-hydroxyphenylglyoxylate, 4-hydroxybenzoyl-CoA plus CO2, benzoyl-CoA. Trace amounts of mandelate possibly derived from mandelyl-CoA were detected during phenylacetate degradation in vitro. The reactions are catalyzed by (i) phenylacetate-CoA ligase which converts phenylacetate to phenylacetyl-CoA and by a second enzyme for 4-hydroxyphenylacetate; (ii) a (4-hydroxy)-phenylacetyl-CoA dehydrogenase system which oxidizes phenylacetyl-CoA to (4-hydroxy)phenylglyoxylate plus CoA; and (iii) (4-hydroxy)phenylglyoxylate: acceptor oxidoreductase (CoA acylating) which catalyzes the oxidative decarboxylation of (4-hydroxy)phenylglyoxylate to (4-hydroxy)benzoyl-CoA and CO2. (iv) The degradation of 4-hydroxyphenylacetate in addition requires the reductive dehydroxylation of 4-hydroxybenzoyl-CoA to benzoyl-CoA, catalyzed by 4-hydroxybenzoyl-CoA reductase (dehydroxylating). The whole cell regulation of these enzyme activities supports the proposed pathway. An ionic mechanism for anaerobic α-oxidation of the CoA-activated carboxymethyl side chain is proposed. Phenylacetic acids are plant constituents and in addition are formed from a large variety of natural aromatic compounds by microorganisms; their degradation therefore plays a significant role in nature, as illustrated in the preceding paper (Mohamed and Fuchs 1993). We have investigated and purified an enzyme which catalyzes the first step in the anaerobic degradation of phenylacetate in a denitrifying Pseudomonas sp. Phenylacetate is converted to phenylacetyl-CoA by phenylacetate-CoA ligase (AMP forming). The postulated function of this enzyme is corroborated by the strict regulation of its expression. 4-Hydroxyphenylacetate appears to be similarly activated by an independent enzyme prior to further degradation. We have suggested before that phenylacetyl-CoA is anaerobically converted by α-oxidation of the side chain to phenylglyoxylate1, which is oxidatively decarboxylated to benzoyl-CoA plus CO2 (Seyfried et al. 1991; Dangel et al. 1991). 4-Hydroxyphenylacetate was proposed to be similarly oxidized to 4-hydroxybenzoyl-CoA plus CO2, followed by reductive dehydroxylation to benzoyl-CoA. The evidence was not presented in full, and the crucial α-oxidation was not demonstrated in vitro. We present here ample evidence for this pathway. A hypothetical mechanism is proposed by which the oxidation of the α-methylene group to an α-carbonyl group may occur.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00249036
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  • 2
    Electronic Resource
    Electronic Resource
    Catalytic dehydrogenation of ethylbenzene to styrene in membrane reactors (1994)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 40 (1994), S. 2055-2059 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690401215
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  • 3
    Electronic Resource
    Electronic Resource
    Competitive hydrodesulfurization and hydrogenation in a monolithic reactor (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 746-752 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Competitive liquid-phase hydrodesulfurization of thiophene and hydrogenation of cyclohexene on a monolithic CoMo/γ-Al2O3 catalyst were studied. The flow pattern in the monolithic catalyst reactor was segmented gas-liquid flow (slug flow). The hydrogen pressure and the temperature were varied between 30-40 bar and 509-523 K, respectively. The experimental data are consistent with rate expressions of the Langmuir-Hinshelwood type where the reactions proceed on two different types of active sites. This kinetic model is based on hydrogenation of the thiophene ring prior to sulfur elimination.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690360511
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the effect of fumed silica on rigid PVC properties (1993)
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 15 (1993), S. 17-21 
    Details
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: This study seeks to substitute fumed silica for chlorinated polyethylene (CPE) within a rigid PVC formulation intended for profile extrusion such as doors and window frames. The effect of fumed silica on both mechanical (tensile and impact) and thermal (Vicat point, HDT, and linear thermal expansion coefficient) properties were investigated. Five rigid PVC formulations were prepared, including a reference one (F1), then F1 with CPE, F1 with untreated silica, F1 with heat treated silica, and finally F1 with dried silica and a coupling agent. The effect of CPE on mechanical properties was very modest. On the other hand, CPE showed its inefficiency, in that HDT and Vicat point were decreased. Heat treated silica showed the greatest improvement in both mechanical and thermal properties. Untreated silica showed a small effect on both properties. Finally, the incorporation of coupling agent gave considerable improvement in both mechanical and thermal properties.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/vnl.730150106
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