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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 33 (1989), S. 1010-1020 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cell growth and enzyme (α-amylase) production characteristics of Bacillus subtilis TN106 containing the recombinant plasmid pAT5 are investigated in batch and continuous cultures using a defined medium with glucose as the limiting nutrient. The batch culture studies demonstrate that the recombinant plasmid, reported earlier1 to be stably maintained in the host, suffers from segregational and structural instabilities. The structural instability of this strain occurred during culture storage and can be eliminated in bioreactor experiments by using a modified inoculum preparation procedure. Such elimination allows an unbiased investigation of segregational instability via continuous culture studies. Such studies conducted with this fast growing microorganism, in the absence of antibiotic selection pressure, indicate a very efficient glucose utilization (very low residual glucose concentrations) over a wide range of dilution rates (0.16 h-1 - 0.94 h-1). The nearly time-invariant and low residual glucose concentrations at each such dilution rate enable convenient estimation of growth parameters of the host and recombinant cells and frequency of segregational instability from transients in the resulting mixed cultures. The specific α-amylase activity exhibits an inverse relationship to the specific growth rate of recombinant cells. The growth of recombinant cells is not affected by the presence of antibiotic (kanamycin). The growth advantage of host cells over recombinant cells diminishes with increasing dilution rate.
    Additional Material: 11 Ill.
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  • 2
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 3
    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: The current understanding of the electrical properties of polyethylene and poly(viny1idenc fluoride) scrviug as model substances or nonpolar and polar polymers is rcviewed. Experimental results on the chargc transport process in PE and field induced structure transitions as well as pyroclectric and piezoelectric properties of poly(viny1idenc fluoride) are presented.
    Notes: Nach einem Überblick über das gegenwärtige Verständnis elektrischer Eigenschaften zweier als Modell substanzen für nichtpolare bzw. polare Strukturen dienender Polymere werden experimentelle Resultate zum Ladungstransportprozeß in Polyethylen und zu feldinduzierten Strukturübergängen in Poly(vinylidenfluorid) sowie dessen pyro- und piezoelektrischen Eigenschaften vorgestellt.
    Additional Material: 5 Ill.
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  • 4
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 38 (1989), S. 1535-1547 
    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: The reaction of α,ω-bis(dimethylamino) polytetramethylene oxide with various dihalides provided a series of elastomeric ionenes. The influence of dihalide structure on the reaction was studied and a number of substituents were found which dramatically increased the rate of polymerization and ultimate molecular weights achieved. These ionene elastomers were thermoplastic and it was shown that in some cases this result was due at least in part to a depolymerization reaction via a dequaternization of the ammonium links. Again, structural features in the dihalide were important not only for the reverse reaction, but for the repolymerization to high molecular weight elastomer as well. An uncharged “analogue” was also prepared to address the feature of microphase separation and compared with the above ionene materials.
    Additional Material: 2 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 38 (1989), S. 1549-1565 
    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: A series of segmented ionene polymers based on the reaction of α,ω-bis(dimethyl amino)polytetramethylene oxide with various dihalide compounds were investigated with respect to their structure-property behavior. The placement of quaternary ammonium ions and halide counterions along the polymer chains was varied by changing the molecular weight of the PTMO soft segment and the structure of the dihalide linking agent. The techniques of dynamic mechanical spectroscopy, thermal analysis, small angle X-ray scattering, and stress-strain behavior analysis were applied. For the case when the PTMO soft segment was amorphous, the ambient temperature properties of these materials displayed low modulus, high strength, and high elongation elastomeric behavior with tensile strength enhanced by the strain-induced crystallization of the PTMO. A high level of phase separation existed between the dihalide component relative to the PTMO soft segment. Due to the Coulombic association of the ionene species, these materials displayed many similarities to the segmented urethane ionomers. In particular, distinct domain structure was noted by SAXS, whose dimensional scale was similar to the segmented urethanes. It was also shown, however, that the driving forces for the microphase separation was caused by favorable electrostatic or Coulombic interactions in contrast to segment-segment incompatibility features as in the segmented urethanes.
    Additional Material: 9 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 1717-1731 
    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: The effects of absorbed moisture on the cure reactions and subsequent solid-state properties of a high-performance epoxy system were investigated in this study. The resin systems investigated were a model system, TGDDM-Novalac-DDS-BF3:MEA (TNDB), and its commercial analog, Hercules 3501-6. The samples were exposed to three environments: a liquid water environment at 50°C; an 85% relative humidity vapor environment at 50°C; and an evacuated, desiccated atmosphere at 22°C. Differential scanning calorimetry (DSC) thermograms were obtained for the Hercules 3501-6 formulation as well as various compositions of the TNDB system for samples exposed to each of the three environments. Moisture was found to accelerate the cure especially for formulations exposed to the vapor environment. Dynamic mechanical experiments were also performed on cured, thin film samples. The “wet” samples were produced by adding water to the resin mixture prior to B-staging. The moisture was shown to increase the extent of reaction, but produce a slightly lower degree of crosslinking as related to the sample's glass transition. This has been attributed to chain-extension reactions, such as the hydroxyl-epoxide etherification reaction, which are favored in the presence of hydroxyl groups from water.
    Additional Material: 12 Ill.
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  • 9
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 34 (1989), S. 309-319 
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The characteristics of growth and synthesis of plasmid-encoded protein were studied for strains of recombinant E. coli JM103 which carried the β-lactamase gene on plasmids of different sizes. The plasmids used included the vector pUC8 and its recombinant derivatives containing varying-sized inserts of Drosophila DNA (not expressed in E. coli). Luria broth (LB) and a minimal medium (M9) supplemented in some cases with additional inorganic phosphate were used as growth media. There was no evidence of segregational instability in these experiments, where no antibiotic selection pressure was employed. Responses of the recombinant strains to variations in environmental parameters including pH, phosphate concentration in the medium, and aeration rate were examined. While the cell growth rate in LB decreased with pH in the range 7.0-8.0, the bulk β-lactamase activity was maximized at an intermediate pH. The recombinant cell growth rate decreases with increasing plasmid size in the minimal medium, while such decrease is not significant when a rich medium such as LB is used. There is an intermediate plasmid size in the range studied (2.7-8.7 kb), at which β-lactamase activity is maximum. While reduction in aeration rate (which determines the dissolved oxygen level) is detrimental for cell growth, it is beneficial for β-lactamase synthesis. The bulk β-lactamase activity therefore exhibits a maximum with respect to aeration rate. Cell growth and β-lactamase production are affected in a similar manner by phosphate concentration in the minimal medium and therefore both are maximized at the same phosphate concentration. This investigation demonstrates clearly how the production of a recombinant plasmid-encoded protein can be maximized by proper manipulation of culture conditions and how it is affected by plasmid size.
    Additional Material: 9 Ill.
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