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1

Catalytic conversion CCI3F and CCI2F2 over metal supported catalysts

100%
Kirszensztejn P., Wachowski L., Szymkowiak A., Marciniak P., Czajka B., Skupinski W.
Polish Journal of Environmental Studies
|
2003
|
tom 12
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nr 3
A comparison of the catalytic properties of metals (Pt, Pd and Ru) supported on carbon in the process of catalytic hydrogenolysis of the C-halogen bond in CCl₂F₂ (CFC-12) and CCl₃F (CFC-11) was made. The mechanism of the halogen substitution in the catalytic conversion of CCl₃F was found to differ from that proposed for CCl₂F₂. The catalysts with Ru as the active phase were characterized by much lower activity than those with Pt or Pd, and the main products of conversion in the two reactions were CHClF₂ and CHCl₂F, so the products of substitution of only one chlorine atom in the molecule were obtained, in contrast to the case when Pt or Pd were used.
2
Artykuł dostępny w postaci pełnego tekstu - kliknij by otworzyć plik
Content available

Oxidation of a lignin model compound of benzyl-ether type linkage in water with H2O2 under an oxygen atmosphere catalyzed by Co(Salen)

63%
Zhou X. F., Qin J. X., Wang S. R.
Drewno. Prace Naukowe. Doniesienia. Komunikaty
|
2011
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tom 54
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nr 186
The catalytic properties of Cobalt salen? complex in the oxidation of a lignin model compound [veratrylglycerol-β-guaiacyl-α,γ-dimethylether, VGD] have been investigated in order to obtain the mechanistic aspects of the reaction between Co(salen) and VGD under an oxygen atmosphere using hydrogen peroxide as an oxidant. VGD was found to undergo structural changes in response to the catalytic reaction as characterised by different analytical techniques (FT-IR, H-1 NMR and GC-MS), yielding 2-methoxy phenol and biphenyl. A mechanism for the oxidation of VGD was postulated.
3

Catalytic properties of Ag-SnO2 catalysts applied in low-temperature methane oxidation

63%
Lewandowska A., Kocemba I., Rynkowski J.
Polish Journal of Environmental Studies
|
2008
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tom 17
|
nr 3
433-437
This paper focuses on the catalytic properties of Ag/SnO₂ for low-temperature methane oxidation. The influences of the metal loading (0.2-20 wt.% Ag), support (Al₂O₃, TiO₂, SiO₂) and methane concentration (0.375-1.5%) in the oxidized mixture were investigated. It was observed that the optimal amount of silver in Ag/SnO₂ was 1 wt.%. Lower or higher amounts cause a loss in catalytic activity. SnO₂ was found to be undoubtedly the best support for the title reaction among all tested oxides. A mechanism of methane oxidation over Ag/SnO₂ was proposed.
4

Tea extracts influence on catalytical properties of Fe2plus in lipids

63%
Gramza A., Korczak J., Hes M., Jedrusek-Golinska A.
Polish Journal of Environmental Studies
|
2004
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tom 13
|
nr Suppl.2, Part 1
Lipid oxidation process can be catalyzed by the presence of metal ions. The Fe2+ addition to the unsaturated fatty acid leads to creating of active oxygen forms initiating the lipid oxygenation process. It was stated, that the plant extracts addition, possessing metal chelating proprieties, can inhibit these processes. Research investigations were conducted in sunflower oil and lard in Rancimat test conditions. The Yunan tea extracts (Camelia sinensis L.) metal ions chelating and antioxidative activity in presence of Fe2+ was quantified. Strong Fe2+ chelating properties of tea extracts were affirmed, highest for green tea ethanol extract. The oxidative stability analysis of lipids with tea extracts addition showed the tea and solvent as well as extracts concentration dependency, and was higher for green and black tea ethanol extracts. The correlation among Fe2+ chelating ability and tea extracts properties in protection of lipids in Rancimat test was affirmed.
5
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Content available

Characterization of catalytic properties of Pisum seed beta-amylases

63%
Zimniak-Przybylska Z.
Genetica Polonica
|
1992
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tom 33
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nr 3
6

Conserved Cys residue influences catalytic properties of potato endo-[1-3]-beta-glucanase GLUB20-2

51%
Witek A. I., Witek K., Hennig J.
Acta Biochimica Polonica
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2008
|
tom 55
|
nr 4
791-797
The synthesis and degradation of (1->3)-β-glycosidic bonds between glucose moieties are essential metabolic processes in plant cell architecture and function. We have found that a unique, conserved cysteine residue, positioned outside the catalytic centre of potato endo-(1->3)-β-glucanase — product of the gluB20-2 gene, participates in determining the substrate specificity of the enzyme. The same residue is largely responsible for endo-(1->3)-β-glucanase inhibition by mercury ions. Our results confirm that the spatial adjustment between an enzyme and its substrate is one of the essential factors contributing to the specificity and accuracy of enzymatic reactions.
7

Amino acid substitutions of His296 alter the catalytic properties of Zymomonas mobilis 10232 levansucrase

51%
Li S. Y., Chen M., Li G., Yan Y. L., Yu H. Y., Zhan Y. H., Peng Z. X., Wang J., Lin M.
Acta Biochimica Polonica
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2008
|
tom 55
|
nr 1
His296 of Zymomonas mobilis levansucrase (EC 2.4.1.10) is crucial for the catalysis of the transfructosylation reaction. The three-dimensional structures of levansucrases revealed the His296 is involved in the substrate recognition and binding. In this study, nine mutants were created by site-directed mutagenesis, in which His296 was substituted with amino acids of different polarity, charge and length. The substitutions of His296 with Arg or Trp retained partial hydrolysis and transfructosylation activities. The positively charged Lys substitution resulted in a 2.5-fold increase of sucrose hydrolysis. Substitutions with short (Cys or Ser), negatively charged (Glu) or polar (Tyr) amino acids virtually abolished both the activities. Analysis of transfructosylation products indicated that the mutants synthesized different oligosaccharides, suggesting that amino acid substitutions of His296 strongly affected both the enzyme activity and transfructosylation products.
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