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  • Polymer and Materials Science  (5)
  • directional turnover  (1)
  • Wiley-Blackwell  (6)
  • Public Library of Science
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  • Wiley-Blackwell  (6)
  • Public Library of Science
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  • 1
    Electronic Resource
    Electronic Resource
    Microtubule-dependent transport of secretory granules during stalk secretion in a peritrich ciliate (1982)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 2 (1982), S. 47-71 
    Details
    ISSN: 0886-1544
    Keywords: microtubules ; transport ; secretion ; peritrich ciliate ; directional turnover ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of microtubules in secretory granule translocation was studied during stalk secretion in the peritrich ciliate, Zoothamnium arbuscula. In each cell, the release of stalk-forming secretory materials is restricted to a specialized region of the cytoplasm, the scopula. Many of the membrane-bound secretory granules that dominate the scopular cytoplasm appear to be aligned along cortical microtubules that converge on the scopular surface. This arrangement is consistent with the hypothesis that microtubules transport granules relative to the sites of exocytosis. To establish the role of microtubules in stalk secretion, telotrochs were exposed to agents with different disruptive effects on microtubule function. Exocytosis itself is not prevented by these drugs, and granules positioned for secretion prior to treatment are released. Maytansine and isopropyl-n-phenyl carbamate (IPC) completely inhibit stalk elongation. In maytansine-treated cells, microtubules are absent from the scopular cytoplasm, and granules are absent from the scopular surface. Microtubules are present in IPC-treated cells, but the granules are misdirected to the cytoplasm lateral to the scopula where no secretory sites exist. Even though the rate of stalk secretion is decreased by deuterium oxide (D2O), a control length stalk is eventually produced. In D2O-treated cells microtubules are present and in their normal orientation. The inhibition of secretion when microtubules are absent (maytansine) or misdirected (IPC) and the retardation of secretion when microtubule turnover is reduced (D2O) supports a mechanism of granule transport based on the directional turnover of microtubule subunits.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970020105
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  • 2
    Electronic Resource
    Electronic Resource
    Methyl α-cyanoacrylate. I. Free-radical homopolymerizationPresented in part at the 136th Meeting of the American Chemical Society, Atlantic City, New Jersey, September 1959. (1960)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 4 (1960), S. 231-236 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Methyl α-cyanoacrylate, when suitably inhibited by Lewis acids against anionic polymerization, can be polymerized readily with free-radical initiators to form hard, clear, high molecular weight polymers. The ratio of kp2/kt is approximately 0.021 at 60°C. if 100% efficiency of initiation by azobisisobutyronitrile is assumed. Acceleration occurs at very low conversion to polymer during bulk polymerizations. The homopolymer is thermally unstable at temperatures only slightly above the glass temperature (estimated to be 165-170°C.). Degradation of the polymer under gamma irradiation is pronounced, only 18 e.v. being required per main-chain scission.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1960.070041116
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  • 3
    Electronic Resource
    Electronic Resource
    Crystalline acrylic polymers. II. Mechanism studies (1960)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 47 (1960), S. 75-89 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The polymerization of methyl methacrylate and isopropyl acrylate in toluene with phenyl-H3-magnesium bromide has been studied at 0 and -70°C., respectively. Comparison of number-average molecular weights calculated from measurement of radioactivity and from measurements of appropriate colligative properties has shown that there is one and only one phenyl group per chain. Thus, initiation in this system is by 1,4-addition of the organomagnesium compound to the monomer. Methyl methacrylate, isopropyl acrylate, ethyl acrylate, and methyl acrylate were polymerized in toluene with phenylmagnesium bromide as the initiator. Isolation and identification of all the products have shown that, in addition to polymer, there are formed small amounts of two ketones and a hydrocarbon. Data are presented indicating that the principal mode of termination is via an intramolecular cyclization to give chains having a β-ketoester group on the end (arising from intramolecular reaction). A rationale for the stereospecificity, the termination reaction, and the large ratios of weight-average to number-average molecular weight in these polymerizations is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1960.1204714908
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  • 4
    Electronic Resource
    Electronic Resource
    Anionic polymerization. Mechanism of methyl methacrylate polymerizations initiated by metal amides in liquid ammoniaPresented in part at the 131st Meeting of the American Chemical Society, Miami, April, 1957. (1960)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 42 (1960), S. 367-382 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Polymerizations of methyl methacrylate initiated by potassium and sodium amides in liquid ammonia solution proceed extremely rapidly even at low temperatures. The resulting polymers have relatively narrow molecular weight distributions M̄v/M̄n ∼ 1.5 and, unlike polymers of styrene prepared similarly, do not contain terminal amine groups. The molecular weight of poly(methyl methacrylate) prepared with potassium amide is independent of the monomer concentration and of the concentrations of potassium amide, potassium ion, and amide ion. The absence of terminal amine groups suggests that methoxide ion, produced by 1,2-addition of amide ion to the monomer, is the actual initiating species. The substantial absence of a termination step is indicated by the narrow distribution of molecular weights. Several minor variations of this general reaction sequence may give the experimentally observed independence of molecular weight on reactant concentrations. One such modification is considered by way of illustration, although final selection of a detailed mechanism is not possible on the basis of the present results.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1960.1204214008
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature dependence of the stereospecificity in the free radical polymerization of methyl methacrylate (1958)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 31 (1958), S. 173-177 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1958.1203112218
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  • 6
    Electronic Resource
    Electronic Resource
    Crystalline acrylic polymers. I. Stereospecific anionic polymerization of methyl methacrylatePresented in part at the 135th Meeting of the American Chemical Society, Boston, April 1959. (1960)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 46 (1960), S. 317-331 
    Details
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Isotactic (type II)polymers of methyl methacrylate are obtained from anionic polymerizations initiated by organolithium compounds at low temperature ( -70°)in toluene solution. The presence of small amounts of various ethers leads to polymers of reduced isotacticity; the effectiveness of these ethers in disrupting stereospecificity can be related semiquantitatively to their Lewis base strength. Certain Grignard reagents also produce highly isotactic polymer of methyl methacrylate, while others lead to less stereospecific results. The nature of the inorganic component of such initiators appears to determine the steric course of the addition reaction. The formation of a magnesium halide-monomer complex may be involved.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1960.1204614803
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