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  • 1990-1994  (7)
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 978-984 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Oligopyrroles with increasing chain length and polypyrroles were recently synthesized with new chemical methods. In this paper, we analyze their infrared and Raman spectra. The spectra can be nicely interpreted in terms of recent theoretical concepts of vibrational dynamics of polyconjugated systems. The spectra thus become a tool for deriving information on the structure of these materials.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 58 (1993), S. 6497-6498 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: An open reading frame from Rhizobium leguminosarum bv. viciae strain VF39, previously identified and found to be similar to Escherichia coli fnr and Rhizobium meliloti fixK (orf240, thereafter called fnrN), was further analysed. Analysis of the expression of an fnrN-lacZ transcriptional fusion revealed that fnrN is preferentially expressed under oxygen limitation. Using R. meliloti fixN-lacZ fusions it was shown that the fnrN gene product only mediates transcriptional activation under microaerobiosis, indicating that the FnrN protein responds, directly or indirectly, to oxygen. Plasmids which expressed fnrN under the control of an E. coli promoter were able to complement an E. coli fnr mutant with respect to anaerobic growth on nitrate but not fumarate, and to promote anaerobic but not aerobic activation of the Fnr-dependent E. coli genes narGHJI, nirB and fdnGHI coding for nitrate reductase, NADH-dependent nitrite reductase and formate dehydrogenase-N, respectively. Fumarate and DMSO reductase activities were not induced by FnrN. The E. coli fnr gene substituted for fnrN in oxygen-regulated transcription of nirB- and fixN-lacZ fusions in R leguminosarum. The results indicate that Fnr and FnrN are functionally very similar and share a common mode of oxygen-dependent transcriptional activation. From hybridization studies, it appeared that fnrN-like genes are present in a number of different R. leguminosarum strains.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 368 (1994), S. 831-834 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Each five-membered ring in the target polymer la (Fig. 1) is joined to three six-membered rings as shown. The polymer should, therefore, have a planar, board-like structure. There is no doubt that the well known and often applied method to increase the solubility of conformationally rigid polymers ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 44 (1993), S. 50-53 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Synthese eines Diels-Alder-Leiterpolymers mit Imino- und Etherbrücken wird beschrieben. Der Strukturnachweis wird durch hochaufgelöste 13C-NMR-Spektroskopie geführt, wobei Modellverbindungen eine wichtige Rolle zukommt. Die Molekulargewichte erreichen Werte bis zu M̄n = 52000. Dies sind die höchsten, die bisher für doppelsträngige Polymere erreicht wurden. Schließlich wird die Einkristallstrukturanalyse der Modellverbindung 8 vorgestellt.
    Notes: The synthesis of a Diels-Alder ladder polymer with imino and ether bridges is described. The structure proof is based upon a comparison of its high resolution 13C-NMR spectrum with those of model compounds. The molecular weights can reach values as high as M̄n = 52000 which are the highest ones observed so far for a double stranded polymer. The X-ray structure of model compound 8 is also presented.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 44 (1993), S. 59-69 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In diesem Artikel wird ein Überblick über ein neues und einfach durchzuführendes, mit Nickel oder Palladium katalysiertes Polykondensationsverfahren für verschiedene homo- und heteroaromatische Monomere gegeben. Diese Methode ermöglicht die regiospezifische Verknüpfung der Monomere an vorgegebenen Stellen, um so die entsprechenden strukturell perfekten Polyarylene zu gewinnen, die bisher nur als schlecht definierte, im allgemeinen unlösliche und unschmelzbare Substanzen bekannt waren. Die Verträglichkeit der Methode gegenüber funktionellen Gruppen ist ausgezeichnet. Die erreichbaren Polymerisationsgrade liegen bei 20 bis 60. Die Löslichkeit und Charakterisierbarkeit der Polymere wird, wenn erforderlich, durch Anknüpfung von flexiblen Alkyl-, tert.-Butyl- oder Alkoxyketten an die Monomere gewährleistet. Die Ergebnisse von vorläufigen physikochemischen Messungen an einigen der Polymere beziehungsweise an ihren Modellsubstanzen werden kurz diskutiert. Sie liefern nicht nur wichtige Anhaltspunkte für die Eigenschaften der Poly- und Oligoarylene, sondern auch Hinweise auf interessante, völlig neuartige Eigenschaften dieser Materialien.
    Notes: This article provides an overview on a new and easy to perform Ni-and Pd-catalyzed polycondensation of various kinds of homo- and heteroaromatic monomers. It allows the regiospecific coupling of these monomers at predetermined positions to furnish the corresponding structurally perfect polyarylenes, which up to now have only been known as ill-defined, generally insoluble and infusible materials. The compatibility of this method towards functional groups is excellent. The achievable degrees of polymerization range from 20 to 60. The solubility and characterizability of the polymers is ensured, if necessary, by the attachment of flexible alkyl, tert.-butyl, or alkoxy chains to the monomers. Results of initial physicochemical measurements with some of the polymers and their respective model compounds are briefly discussed. They do not only give vital clues to the intrinsic properties of poly- and oligoarylenes but also disclose exciting, unprecedented properties of these materials.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Acta Polymerica 45 (1994), S. 389-391 
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The chain stiffness of a methoxypropyl-substituted poly[1.1.1]propellane in solution is investigated by static and dynamic light scattering. The Kuhn statistical segment length is determined as lk=150Å utilizing the Kratky-Porod wormlike chain model. It is, however, not yet clear whether the derived Kuhn length characterizes the chain stiffness of a perfect polypropellane chain or rather originates from “kinks” in the polymer backbone due to the presence of possible side reactions during polymerization.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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