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  • 1
    Digitale Medien
    Digitale Medien
    The effect of radical trapping reagents upon formation of poly(α-tetrahydrothiophenio para-xylylene) polyelectrolytes by the wessling soluble precursor method (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2223-2231 
    Details
    ISSN: 0887-624X
    Schlagwort(e): poly(arylene vinylene) ; poly(1,4-phenylene vinylene) ; poly(para-phenylene vinylene) ; para-xylylene ; 1,4-benzoquinodimethane ; radical polymerization ; conducting polymers ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Molecular weights were studied by gel permeation chromatography of derivatized poly(α-tetrahydrothiophenio para-xylylene) chloride produced by aqueous or methanolic base-induced polymerization of 1,4-bis(tetrahydrothiopheniomethyl) benzene dichloride, both with and without a variety of added polymerization inhibiting agents. Efficient radical scavenging agents such as 2,2,6,6-tetramethylpiperidinoxyl and hydrogen atom donor 2,4,6-tri-tert-butylaniline reduced the degree of polymerization of the reactive α-(tetrahydrothiophenium chloride)-para-xylylene intermediate produced in this chemistry, and in some cases completely suppressed formation of high polymer. These two traps did not affect the equilibrium production of the para-xylylene by UV-Vis spectral analysis; hence they must affect the subsequent polymerization chain propagation steps in the mechanism. Electron spin resonance studies of polymerization in the presence of 0.00025 equiv of TEMPO showed disappearance of the spin label, a result consistent with a radical scavenging process. The results suggest that production of high molecular weight poly(α-tetrahydrothiophenio para-xylylene) chloride proceeds through a radical chain propagation sequence. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1992.080301018
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  • 2
    Digitale Medien
    Digitale Medien
    Para-Xylylenes and analogues by base-induced elimination from 1,4-bis-(dialkylsulfoniomethyl)arene salts in poly(1,4-arylene vinylene) synthesis by the wessling soluble precursor method (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 2233-2240 
    Details
    ISSN: 0887-624X
    Schlagwort(e): para-xylylenes ; 1,4-benzoquinodimethanes ; conducting polymers ; poly(arylene vinylene)s ; poly(phenylene vinylene)s ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: para-Xylylenes are generated by treatment of various 1,4-bis(dialkylsulfoniomethyl)arene dihalides with base in water, methanol, and aqueous acetonitrile, as shown by UV-Vis spectroscopy. This procedure allows the monitoring of the transient xylylene monomers that yield polyelectrolyte precursor polymers for poly(arylene vinylene)s, formed by variations of the chemistry developed originally by Wessling and co-workers. Alkoxy, alkyl, and halogen ring substituents on the sulfonium salt precursors do not greatly affect the ability to generate and observe the growth and decay of steady-state concentrations of the para-xylylene intermediates. Use of strong resonance-acceptor substituents - such as cyano or nitro - on the ring reduces production of a strong para-xylylene absorption, possibly due to reluctance of the ylides initially formed from the bis-sulfonium salts to eliminate to the xylylenes. By variation of UV-Vis conditions, it was found that use of 20% aqueous acetonitrile rather than water allowed formation of low to modest molecular weight polyelectrolytes in cyano-substituted cases (Mw = 8000-37,000). Use of UV-Vis test experiments should be useful for screening of bis sulfonium salt precursors that may be expected to give high molecular weight polyelectrolytes - in cases where para-xylylene formation is easy - as well as for finding reaction conditions that will optimize polymer formation. © 1992 John Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1992.080301019
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  • 3
    Digitale Medien
    Digitale Medien
    Solid-state photochemical generation of polymeric polyradicals: Poly(4-vinylphenoxy) and copolymers with styrene (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 30 (1992), S. 1335-1345 
    Details
    ISSN: 0887-624X
    Schlagwort(e): polyradicals ; magnetism ; phenoxyl radicals ; high-spin molecules ; organic ferromagnetism ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Synthesis of poly(4′-vinyl-2,4,6-tri-tert-butyl-diphenyloxalate) and its 65 : 35 and 19 : 81 copolymers with styrene are described. Rigid phase broad-band photolysis of the homopolymer with a quartz filtered xenon arc at 77 K results in production of up to 25% of the theoretical number of spins/mol expected for quantitative production of pendant phenoxyl radicals, and shows no major loss of radical signal in the ESR at temperatures below 100 K. Curie law analysis of the temperature dependence of the ESR radical signal intensity for the neat photolyzed homopolymer 1 shows curvature consistent with antiferromagnetic pairing of radical spins at low temperatures. Since through-bond conjugation of radical spins is not possible in this system, the antiferromagnetic interaction is interpreted in terms of intrachain and/or interchain through-space exchange interactions.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1992.080300711
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  • 4
    Digitale Medien
    Digitale Medien
    Synthesis and characterization of novel epoxy monomers and liquid crystal thermosets (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 2249-2260 
    Details
    ISSN: 0887-624X
    Schlagwort(e): liquid crystalline ; liquid crystal polymer ; liquid crystal thermoset ; thermoset ; epoxy ; thermotropic ; networks ; nematic ; smectic ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Four new epoxy monomers have been synthesized and characterized as part of a program to prepare novel liquid crystal thermoset (LCT) materials. Three of the new epoxy monomers contained a biphenyl mesogen and were not liquid crystalline (LC). The remaining epoxy monomer, which contained a 1,4-dibenzoyloxybenzene mesogen, was synthesized in an overall yield of 30% and displayed a broad (83°C) nematic liquid crystalline phase. The new liquid crystalline epoxy monomer was cured at 120°C and postcured at 175°C with a stoichiometric amount of 1,4-phenylenediamine. The thermal transitions of the resulting LCT were studied by differential scanning calorimetry (DSC), polarized light optical microscopy (POM), thermomechanical analysis (TMA), and wide angle x-ray diffraction (WAXD) as a function of cure time and temperature. A process characterization diagram was constructed which shows that LCTs based on this new LC monomer can be processed in the liquid crystalline phase over a broad range of times and temperatures. Qualitative agreement with previous epoxy LCT results was found, as LCT's with smectic phases and without clearing temperatures were observed at long cure times (high crosslink densities), whereas nematic phases with clearing temperatures predominated in networks at short cure times (low crosslink densities). © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1993.080310908
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  • 5
    Digitale Medien
    Digitale Medien
    Syntheses of new poly (arylene vinylene) analogues: Poly (4,7-benzofuran vinylene) and poly (4,7-benzothiophene vinylene) (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 65-71 
    Details
    ISSN: 0887-624X
    Schlagwort(e): poly(arylene vinylene)s ; conducting polymers ; soluble precursor polymers ; polyelectrolytes ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of bis(4,7-tetrahydrothiopheniomethyl) benzofuran dibromide with aqueous tetramethylammonium hydroxide leads to a water-soluble polyelectrolyte which can be film cast and thermolytically eliminated to give poly(4,7-benzofuran vinylene) (PBFV). Subjection of bis(4,7-tetrahydrothiopheniomethyl) benzothiophene dibromide to the same reaction sequence gives poly(4,7-benzothiophene vinylene) (PBTV). UV-VIS studies show that PBFV has a band gap of 2.76 eV, while PBTV has a band gap of 2.92 eV. These polymers are members of a new class of conjugated poly (arylene vinylene)s, in which heterocyclic pseudoaromatic rings are fused onto a poly(1,4-phenylene vinylene) backbone. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pola.1994.080320108
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  • 6
    Digitale Medien
    Digitale Medien
    The effect of the dilution rate on CHO cell physiology and recombinant interferon-γ production in glucose-limited chemostat culture (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 42 (1993), S. 1077-1085 
    Details
    ISSN: 0006-3592
    Schlagwort(e): chemostat ; glucose limitation ; glycosylation ; CHO cells ; interferon-γ ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The physiology of a recombinant Chinese hamster ovary cell line in glucose-limited chemostat culture was studied over a range of dilution rates (D = 0.008 to 0.20 h-1). The specific growth rate (μ) deviated from D at low dilution rates due to an increased specific death rate. Extrapolation of these data suggested a minimum specific growth rate of 0.011 h-1 (μmax = 0.025 h-1) The metabolism at each steady state was characterized by determining the metabolic quotients for glucose, lactate, ammonia, amino acids, and interferon-γ (IFN-γ). The specific rate of glucose uptake increased linearly with μ, and the saturation constant for glucose (Ks) was calculated to be 59.6 μM. There was a linear increase in the rate of lactate production with a higher yield of lactate from glucose at high growth rates. The decline in the rate of production of lactate, alanine, and serine at low growth rate was consistent with the limitation of the glycolytic pathway by glucose. The specific rate of IFN-γ production increased with μ in a manner indicative of a growth-related product. Despite changes in the IFN-γ production rate and cell physiology, the pattern of IFN-γ glycosylation was similar at all except the lowest growth rates where there was increased production of nonglycosylated IFN-γ. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260420909
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  • 7
    Digitale Medien
    Digitale Medien
    Modeling linear and variable growth in phosphate limited suspension cultures of Opium poppy (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 371-379 
    Details
    ISSN: 0006-3592
    Schlagwort(e): plant tissue culture ; Papaver somniferum ; linear growth ; phosphate limitation ; modeling ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: In examining the growth kinetics of cell suspensions of opium poppy (Papaver somniferum), the increase in biomass with time was observed to be linear over the entire batch growth period of up to 20 days. Although batch growth profiles were reproducible utilizing the same inoculum, growth rates varied tremendously when experiments were inoculated with cells from different flasks. Both of these phenomena are difficult to explain with conventional batch growth models. In a series of a experiments, phosphate was determined to be the growth-rate-limiting substrate. By expressing growth rate in terms of the intracellular reserves of phosphorus, a growth model which expresses kinetics in terms of the intracellular phosphorus contents of the cells is shown to predict both linear growth character and inoculum dependent variability in growth. The stationary phase phosphate content of seven plant suspension cultures of different plant species was found to be comparable to phosphorus levels of phosphate-starved poppy cells, which suggests that phosphate limitation may be common for plant tissue culture. The applicability of this model to other biological systems which display similar batch growth patterns when subjected to inorganic nutrient deprivation is discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260380407
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  • 8
    Digitale Medien
    Digitale Medien
    Estimation of Growth Yield and Maintenance Coefficient of Plant Cell SuspensionsJournal article 12859 of the Purdue University Agricultural Experiment Station. (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1131-1136 
    Details
    ISSN: 0006-3592
    Schlagwort(e): plant cell suspensions ; carbon utilization ; growth yield ; maintenance coefficient ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Methodology is presented for the determination of growth yield (Yg) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Yg and m requires measurements of specific growth rate (µ) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Yg and m because µ is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the Km for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the Km, the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Yg and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of µ and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260381003
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  • 9
    Digitale Medien
    Digitale Medien
    Glucose-limited chemostat culture of chinese hamster ovary cells producing recombinant human interferon-γ (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 327-335 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Chinese hamster ovary ; interferon-γ ; chemostat culture ; glycosylation ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A Chinese hamster ovary (CHO) cell line expressing recombinant human interferon-γ (IFN-γ) was grown under glucose limitation in a chemostate at a constant dilution rate of 0.015 h-1 with glucose feed concentrations of 2.75 mM and 4.25 mM. The changes in cell concentration that accompanied changes in the glucose feed concentration indicated that the cells were glucose-limited. The cell yield on glucose remained constant, but there was a decline in residual glucose concentration and a reduced lactate yield from glucose in the latter stages of the culture. The consumption rates for many of the essential amino acids were increased later in the culture. The volumetric rate of interferon-γ production was maintained throughout the course of this culture, indicating that IFN-γ expression was stable under these conditions. However, the specific rate of IFN-γ production was significantly lower at the higher glucose feed concentration. Under glucose limitation, the proportion of fully glycosylated IFN-γ produced by these cells was less than that produced in the early stages of batch cultures. The proportion of fully glycosylated IFN-γ increased during transient periods of glucose excess, suggesting that the culture environment influences the glycosylation of IFN-γ.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260390311
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  • 10
    Digitale Medien
    Digitale Medien
    Determining metabolic sensitivity coefficients directly from experimental data (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 41 (1993), S. 1027-1038 
    Details
    ISSN: 0006-3592
    Schlagwort(e): sensitivity coefficients ; metabolic sensitivity coefficients ; elasticities ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The application of metabolic control theory (MCT), or other methods of determining metabolic sensitivity to the rates of specific cellular processes, such as enzymatic reactions, requires knowledge of the elasticity coefficients (system partial derivatives) for the processes under study. Although rate equations are available in the literature for some enzymatic reactions, there are many reactions and processes for which this is not the case. Although one could perform the experiments necessary to determine the rate equations for a given system, these equations are, in fact, not required for the calculation of sensitivities-only the elasticities (the derivatives) are needed. A more direct and efficient approach would be to compute elasticities directly from experimental data. Errors can analysis and alternative regression techniques are presented which not only allow one to eliminate data components with excessive noise, but also provide guidance as to what additional data may be require for accurate sensitivity analysis. This information indicates which measurements require more accuracy and what additional experiments should be conducted to reduce errors in calculated metabolic sensitivity coefficients. © 1993 Wiley & Sons, Inc.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260411105
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