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  • 1
    ISSN: 1436-5073
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Zwei neue chromogene Kronenetherreagenzien, 22-Kosh und 21-Kosh wurden durch Kondensation von Cryptand-22 bzw. -21 mit 2-Hydroxy-5-nitrobenzylbromid synthetisiert. Die Extraktion der Erdalkalimetallionen mit einer Dichlorethanlösung von 22-Kosh oder 21-Kosh wurde untersucht und ihre Extraktionskonstanten wurden bestimmt. Für die Leichtigkeit der Extrahierbarkeit mit den beiden Reagenzien ergibt sich folgende Reihenfolge: Mg《Ba〈Sr〈Ca. Die Extraktion mit 22-Kosh ist wirksamer, die Selektivität für Erdalkalimetallionen mit 21-Kosh jedoch ausgeprägter als mit 22-Kosh. 22-Kosh erwies sich als vielversprechendes Reagens für die photometrische Bestimmung von Calcium in Blutserum. Der molare Extinktionskoeffizient des Calciumkomplexes beträgt 5,5×104 bei 406 nm.
    Notes: Summary Two new chromogenic crown reagents, 22-Kosh and 21-Kosh, have been synthesized by the condensation of Cryptand-22 and -21, respectively, with 2-hydroxy-5-nitrobenzyl bromide. Extraction of alkaline-earth metal ions with a dichloroethane solution of 22-Kosh or 21-Kosh has been investigated and their extraction coefficients have been evaluated. The relative ease of extraction is Mg《Ba〈Sr〈Ca for both reagents. The extraction is more effective with 22-Kosh than with 21-Kosh, and the selectivities for alkaline-earth metal ions are more pronounced with 21-Kosh than 22-Kosh. 22-Kosh is found to be a very promising reagent for the extraction-photometric determination of calcium in blood serum. The molar absorptivity of the calcium complex is 5.5×104 l·mole−1·cm−1 at 406 nm.
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  • 2
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitrogen-containing five-membered heterocycles, N-methylpyrrole 2, N-methylpyrazole 4, N-methylimidazole 6, 4-methylthiazole 11, N-methylindole 14, benzothiazole 16, N-methylbenzimidazole 18, and benzoxazole 20 were lithiated with BuLi and LDA in THF and reacted with the polymerization-resistant 1,2-dithiolane 1. All of the corresponding lithioheterocycles cleaved the S-S bond of the 1,2-dithiolane 1 to give the ring-opened products in line with the carbanion mechanism proposed for the enzyme-reductive acylations of lipoic acid. The ring-opened products 8, 9, 13, 22, and 23 were isolated in good yields and high purity. The ring-opened products from benzothiazole and N-methylbenzimidazole were decomposed by the action of excess lithioheterocycles. The lithiobenzoxazole was less reactive than the other lithioheterocycles. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:289-294, 1998
    Additional Material: 1 Tab.
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  • 3
    ISSN: 1042-7163
    Keywords: Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithiated furans have been found to cleave the S-S bond of polymerization-resistant 1,2-dithiolanes to give the ring opened products in good yields. In the case of lithiated benzofuran, the excess reagent reacted with the normal product to give a mixture. Lithiated dihydrofuran and dihydropyran gave the corresponding ring-opened products that rearranged to spiro-1,3-dithianes during acidic workup. The reaction was applied to the selective synthesis of substrates for intramolecular Diels-Alder reactions. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:281-287, 1998
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  • 4
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract An ethylene-forming enzyme which forms ethylene from 2-oxo-4-methylthiobutyric acid (KMBA) was purified to an electrophoretically homogeneous state from a cell-free extract of Cryptococcus albidus IFP 0939. The presence of KMBA, NADH, Fe(III) chelated to EDTA and oxygen were essential for the formation of ethylene. When ferric ions, as Fe(III)EDTA, in the reaction mixture were replaced by Fe(II)EDTA under aerobic conditions, the non-enzymatic formation of ethylene was observed. Under anaerobic conditions in the presence of Fe(III)EDTA and NADH, the enzyme reduced 2 mol of Fe(III) with 1 mol of NADH to give 2 mol of Fe(II) and 1 mol NAD+, indicating that the ethylene-forming enzyme is an NADH-Fe(III)EDTA oxidoreductase. The role of NADH:Fe(III)EDTA oxidoreductase activity in the formation in vivo ethylene from KMBA is discussed.
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  • 5
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract A novel ethylene-forming enzyme that forms ethylene from α-ketoglutarate was purified from the cell-free extract of Penicillium digitatum IFO 9372. The purified enzyme was confirmed to be homogenous on polyacrylamide disc gel electrophoresis, and the molecular weight of the enzyme consisting of a single polypeptide was estimated to be about 42 kDa by gel filtration column chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The presence of α-ketoglutarate, l-arginine, ferrous ion, dithiothreitol and oxygen were essential for the enzyme reaction. Substrate and cofactor specificity of the enzyme was highly specific for α-ketoglutarate and l-arginine, respectively. Some properties of the purified enzyme were surveyed and compared with those of the ethylene-forming system in higher-plants.
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