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  • 1
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 108 (1986), S. 976-982 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 54 (1998), S. 991-993 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The plant aspartic proteinase cardosin A was crystallized using vapour diffusion. Crystals belong to the monoclinic space group C2, cell dimensions a = 116.9 (2), b = 87.2 (8), c = 81.3 (1) Å, β = 104.4 (4)°, and contain two molecules in the asymmetric unit related by a non-crystallographic twofold axis. Diffraction data were collected at room temperature with radiation from a synchrotron source up to 2.85 Å resolution. When the crystals were flash cooled to 110 K in a nitrogen stream the same resolution limit could also be obtained on a rotating-anode source. Recently, synchrotron radiation together with flash cooling led to an improvement of the diffraction data to 1.72 Å resolution.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] RNA degradation is a determining factor in the control of gene expression. The maturation, turnover and quality control of RNA is performed by many different classes of ribonucleases. Ribonuclease II (RNase II) is a major exoribonuclease that intervenes in all of these fundamental processes; it ...
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1072-8368
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Desulfovibrio gigas is a strict anaerobe that contains a well-characterized metabolic pathway that enables it to survive transient contacts with oxygen. The terminal enzyme in this pathway, rubredoxin:oxygen oxidoreductase (ROO) reduces oxygen to water in a direct and safe way. The 2.5 Å ...
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-1327
    Keywords: Key words Dimeric cytochrome c3 ; Ab initio structure ; Disulfide bridges ; Thiosulfate reduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract  The 1.2 Å resolution crystal structure of the 29 kDa di-tetrahaem cytochrome c 3 from the sulfate reducing bacterium Desulfovibrio gigas was solved by ab initio methods, making this the largest molecule to be solved by this procedure. The actual refined model of the cysteine-linked dimeric molecule reveals that this molecule is very similar to the non-covalently linked symmetrical dimer of the di-tetrahaem cytochrome c 3 from Desulfomicrobium norvegicum. Each monomer has the typical polypeptide fold, haem arrangement and iron coordination found for the tetrahaem cytochrome c 3 molecules. The interface between the covalently linked monomers in the asymmetric unit of the crystal shows a pseudo two-fold arrangement, disturbed from symmetry by crystal packing forces. The fact that D. gigas contains a dimeric tetrahaem cytochrome with solvent accessible disulfide bridges and that this cytochrome specifically couples hydrogen oxidation to thiosulfate reduction in bacterial extracts provides an interesting aspect related to disulfide exchange reactions in this microorganism.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 259-263 
    ISSN: 0009-2940
    Keywords: Hydrophosphorylation ; Phosphines, alkenyl- ; Phosphines, allenyl- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Contribution to the Synthesis and Structural chemistry of some Alkenyl- and Allenylphosphines1,3-Diphenylpropyne, obtained through an improved synthesis, undergoes base-catalyzed hydrophosphorylation with Ph2PH to give 2-(diphenylphosphino)-1,3-diphenyl-1-propene (1). The structure of 1 has been established by single-crystal X-ray diffraction. Regioisomeric 1-(diphenylphosphino)-1,3-diphenyl-1-propene (2) is a minor byproduct of the reaction. Metallation of 1 with n-BuLi followed by treatment with Ph2PCl yields (R,S)-2,3-bis(diphenylphosphino)-1,3-diphenyl-1-propene (3). Methylation of 1 with MeI gives the phosphonium salt 4. Double lithiation of PhCH2C≡CPh and reaction of the intermediate with two equivalents of Ph2PCl affords 1,3-bis(diphenylphosphino)-1,3-diphenylallene (5). This bisterminal phosphino-functionalized allene is converted into an oxide, sulfide, or selenide (5a-c) with the appropriate oxidant. Dephosphorylation of 5 with n-BuLi and subsequent hydrolysis lead to 1-(diphenylphosphino)-1,3-diphenylallene (6). Hydrophosphorylation of 5 with Ph2PH gives 3 by an alternative route.
    Notes: Durch basenkatalysierte Hydrophosphorylierung von 1,3-Diphenylpropin mit Ph2PH wird 2-(Diphenylphosphino)-1,3-diphenyl-1-propen (1) erhalten, dessen Stereochemie durch Röntgenstrukturanalyse aufgeklärt wurde. Als Nebenprodukt werden auch geringe Mengen des regioisomeren 1-(Diphenylphosphino)-1,3-diphenyl-1-propens (2) isoliert. Deprotonierung von 1 mit n-BuLi und nachfolgende Umsetzung mit Chlordiphenylphosphan liefert das doppelt-phosphorylierte Produkt (R,S)-2,3-Bis(diphenylphosphino)-1,3—diphenyl-1-propen (3). Durch Methylierung von 1 läßt sich das entsprechende Phosphoniumsalz 4 darstellen. Ebenfalls ausgehend von 1,3-Diphenylpropin wird nach doppelter Lithiierung, gefolgt von der Umsetzung mit Chlordiphenylphosphan, das erste 1,3′Diphosphino-substituierte Allen 5 synthetisiert. Aus diesem läßt sich durch starke Basen (RLi) eine Phosphinogruppe abspalten, wobei das Monophosphinoallen 6 entsteht. Oxidation sowie Addition von Schwefel und Selen ergeben die zugehörigen Dichalkogenide 5a-c, Hydrophosphorylierung von 5 führt auf einem anderen Weg zu 3.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 2213-2218 
    ISSN: 0009-2940
    Keywords: Conformational analysis ; Electron diffraction ; Organosilanes ; Silane, tetra(isopropyl)- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Darstellung und Molekülstruktur von Tetra(isopropyl)silan1Tetra(isopropyl)silan wurde nach Literaturvorschriften hergestellt, deren einzelne Stufen aber durch veränderte Reaktionsbedingungen verbessert werden konnten. Das Schlüsselreagens 2-Lithiopropen wurde ausgehend von 1-Methacrylsäure über 1,3-Dibrom-1-methylpropionsäure und 2-Brompropen durch Metallierung des letzteren mit ultraschallaktiviertem Lithium erhalten. Die Lösungen enthalten noch Mono- und Dilithiopropin, wie durch Silylierung mit Chlortrimethylsilan bestätigt werden konnte. Mit SiCl4 entsteht Tetra(isopropenyl)silan, das nach Reinigung katalytisch zur Titelverbindung hydriert werden kann.  -  Die Molekülstruktur von [CH3)2CH]4Si in der Gasphase wurde durch Elektronenbeugung bestimmt. Eine Verfeinerung der Parameter war mit einem Modell der Punktgruppe S4 erfolgreich. Die Bindungslängen Si—C, C—C und C—H zeigen ebenso wie die Winkel Si—C—C und C—C—H die Beengung der vier Substituenten an. Die sterische Spannung wird durch Herausdrehen der Methylgruppen und der Isopropylgruppen aus den jeweiligen gestaffelten Konformationen sowie durch Aufweitung zweier C—Si—C-Winkel vermindert. Die vier restlichen C—Si—C-Winkel sind entsprechend kleiner als der Tetraederwinkel. Die Gesamtstruktur unterscheidet sich in den Drehwinkeln C—Si—C—H deutlich von der des Tetra(isopropyl)phosphonium-Kations in [(CH3)2CH]4P+ [B(C6H5)4]-, die viel größere Winkel C—P—C—H aufweist. Sie ist aber den Strukturen des Tetra-(cyclohexyl)silans und sogar des Tri(isopropyl)phosphonium-isopropylids sehr ähnlich, in dem die pyramidale Konfiguration am ylidischen C-Atom zu einer pseudo-homoleptischen Ligandenanordnung führt.
    Notes: Tetra(isopropyl)silane has been prepared using literature methods, with the individual steps improved by changes in some of the experimental conditions. The key reagent 2-lithiopropene, which can now be obtained in good yields from 1-methacrylic acid via 1,2-dibromo-1-methylpropionic acid and 2-bromopropene by treatment of the latter with ultrasound-activated lithium metal, was shown to contain mono- and dilithiopropyne. The reaction with chlorotrimethylsilane led to the corresponding silylated derivatives, while with silicon tetrachloride tetra(isopropenyl)silane was obtained, which after purification is easily converted into the title compound by catalytic hydrogenation.  -  The gas phase molecular structure of [(CH3)2CH]4Si has been determined by electron diffraction. The parameters could be successfully refined for a model of S4 symmetry. Bond distances Si—C, C—C, and C—H as well as bond angles Si—C—C and C—C—H show the steric compression of the four isopropyl substituents. Steric strain is minimized by twists of the methyl groups and the isopropyl groups away from the fully staggered conformations, but also by an increase of two of the C—Si—C angles as compared to the remaining four, which are decreased relative to the tetrahedral standard. The structure differs strongly (mainly in the twist angles) from that of the isoelectronic tetra(isopropyl)phosphonium cation in [(CH3)2CH]4P+[B(C6H5)4]-, but is very similar to those of tetra(cyclohexyl)silane and of tri(isopropyl)phosphonium isopropylide, where the pyramidal configuration of the ylidic carbon atoms leads to a pseudo homoleptic array of the substituents at phosphorus.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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