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  • Wiley-Blackwell  (55)
  • Geological Society of America (GSA)
  • 1
    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 starch-polyacrylonitrile graft copolymer prepared from gelatinized wheat starch with ceric ammoninm nitrate as the initiator has been freed of ungrafted polyacrylonitrile and separated into fractions by extraction with dimethylformamide, γ-butyrolactone, and dimethyl sulfoxide. The copolymer fractions obtained differed appreciably in level of add-on, molecular weights of grafted chains, and grafting frequency. To determiue the molecular weights of grafted chains, the starch part of the copolymer was effectively removed by hydrolysis with α-amylase. It was necessary to dissolve or swell the polymer in dimethyl sulfoxide and freshly precipitate it by addition to water before enzymatic hydrolysis. In studying the effect of reaction medium on copolymer composition, there was less ungrafted homopolymer formed and a higher yield of graft copolymer possessing more frequent grafts with water than with aqueous dimethylformamide or aqueous ethylene glycol. Polymer solubility, the results of control polymerizations of acrylonitrile in the absence of starch, and the detection of glucose endgroups on the polyacrylonitrile liberated from the fractionated polymer by hydrolysis are presented as evidence that the copolymers obtained are true grafts rather thau intimate mixtures.
    Additional Material: 1 Ill.
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  • 2
    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 study was made of the influence of selected chain modifiers on both the molecular weight of grafted polyacrylonitrile and the grafting frequency of the starch-polyacrylo-nitrile graft copolymer. Gelatinized wheat starch was used with ceric ammonium nitrate as the initiator. The organic chain modifiers investigated were ethyl mercaptan, 1-dodecanethiol, methyl ethyl ketone, acetaldehyde, and chloroform. Sodium chromate, cupric bromide, cupric nitrate, cupric acetate, and cupric chloride were also tested as chain modifiers. In the presence of cupric chloride, there was a tenfold reduction in the molecular weight of grafted polyacrylonitrile; however, fewer chains were grafted to the starch backbone than were observed without cupric chloride.
    Additional Material: 4 Tab.
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  • 3
    ISSN: 0192-253X
    Keywords: C/EBP ; thyroid hormone ; metamorphosis ; gene expression ; Rana cafesbeiana ; bZlP proteins ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Tissue-specific changes in gene expression occur in the liver of Rana cafesbeiana tadpoles undergoing metamorphosis. Many of these changes can be induced precociously by administration of thyroid hormone (TH) to a tadpole or to cultured tadpole liver. While the precise molecular means by which TH exerts a tissue-specific response is unknown, recent studies suggest that the expression of genes which are liver-specific and characteristic of the adult liver phenotype may rely on TH-induction of tissue-specific transcription factors, as well as the thyroid hormone receptor proteins. Guided by this notion, we screened our Rana catesbeiana liver cDNA library and isolated clones, RcC/EBP-1 and -2, encoding Rana homologues of a mammalian transcription factor, C/EBP (CCAAT/enhancer core binding protein), implicated in the expression of liver-specific genes and terminal differentiation of hepatocytes. Gel mobility shift assays demonstrate that the proteins synthesized from these cDNAs bind specifically to the consensus binding site for C/EBP-related proteins. Characterization of the amino acid sequence in the bZlP DNA-binding domains of these proteins suggests that RcC/EBP-1 and -2 encode Rana homologues of C/EBPα and δ, respectively. Hybridization analyses demonstrate that the amount of RcC/EBP-2 mRNAs in tadpole liver remains constant throughout metamorphosis, whereas RcC/EBP-1 mRNAs are up-regulated during both spontaneous and TH-induced metamorphosis. The TH-induced up-regulation of RcC/ EBP-1 mRNAs precedes the up-regulation of liver-specific urea cycle enzyme mRNAs by 6 to 12 hours. These results, coupled with in situ hybridization studies, suggest that RcC/EBP-1 mRNAs encode a transcription factor which may play an early role(s) in the terminal differentiation and/or reprogramming of gene expression in this tadpole's liver cells during both spontaneous and TH-induced metamorphosis. ©1994 WiIey-Liss, Inc.
    Additional Material: 8 Ill.
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  • 4
    ISSN: 0192-253X
    Keywords: Thyroid hormone ; carbamyl phosphate synthetase ; Rana catesbeiana ; metamorphosis ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: During both spontaneous and thyroid hormone (TH)-induced metamorphosis, the Rana catesbeiana tadpole undergoes postembryonic developmental changes in its liver which are necessary for its transition from an ammonotelic larva to a ureotelic adult. Although this transition ultimately results from marked increases in the activities and/or de novo synthesis of the urea cycle enzymes, the precise molecular means by which TH exerts this tissue-specific response are presently unknown. Recent reports, using RNA from whole Xenopus laevis tadpole homogenates and indirect means of measuring TH receptor (TR) mRNAs, suggest a correlation between the up-regulation of TRβ-mRNAs and the general morphological changes occurring during amphibian metamorphosis. To assess whether or not this same relationship exists in a TH-responsive tissue, such as liver, we isolated and characterized a cDNA clone containing the complete nucleotide sequence for a R. catesbeiana urea cycle enzyme, ornithine transcarbamylase (OTC), as well as a genomic clone containing a portion of the hormone-binding domain of a R. catesbeiana TRβ gene. Through use of these homologous sequences and a heterologous cDNA fragment encoding rat carbamyl phosphate synthetase (CPS), we directly determined the relative levels of the TRβ, OTC, and CPS mRNAs in liver from spontaneous and TH-induced tadpoles. Our results establish that TH affects an up-regulation of mRNAs for its own receptor prior to up-regulating CPS and OTC mRNAs. Moreover, results with cultured tadpole liver demonstrate that TH, in the absence of any other hormonal influence, can affect an up-regulation of both the TRβ and OTC mRNAs. © 1992 Wiley-Liss, Inc.
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  • 5
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 15 (1994), S. 313-319 
    ISSN: 0192-253X
    Keywords: Metamorphosis ; postembryonic development ; thyroid hormones ; ecdysteroids ; amphibians ; insects ; fish ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Additional Material: 1 Ill.
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  • 6
    ISSN: 0192-253X
    Keywords: Heat shock protein ; maize ; mi-crosporogenesis ; gametogenesis ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The small (18-kDa) heat shock proteins (hsps) of maize are encoded by a complex multigene family. In a previous report, we described the genetic information from cDNAs encoding two different members of the family. In this communication, we report the isolation and characterization of cDNA and genomic clones encoding information for a third member of this hsp family (c/gMHSP18-1). DNA fragments containing nucleotide sequences common to, or specific for, each of these characterized 18-kDa genes were prepared and used as probes to assess the expression of these genes during microsporogenesis and development of the gametophyte in an inbred line of maize (Oh43). Our results demonstrate (1) that mRNA transcripts encoding the 18-kDa hsps are expressed and/or accumulate during microsporogenesis, and (2) that genes encoding two of the characterized 18-kDa hsps are expressed and/or accumulate independently, in a stage-specific manner during microsporogenesis. These observations imply that the stage-specific expression of particular 18-kDa hsp genes results from gene-specific regulation during microsporogenesis and gametophyte development rather than from an overall activation of the heat shock or stress response. © 1993Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 1 (1980), S. 21-34 
    ISSN: 0197-8462
    Keywords: radiofrequency radiation ; microwaves ; rhesus monkey dosimetry ; microwave dosimetry ; cranial structures ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Temperature increases due to absorption of 1.2 GHz, CW, 70 mW/cm2, radio frequency (RF) energy, were measured in 3.3-cm-radius homogeneous muscle-equivalent spheres, M. mulatta cadaver heads (both detached from and attached to the body) and living, anesthetized M. mulatta heads. Temperatures were measured with a Vitek, Model 101 Electrothermia Monitor and temperature distributions were compared to theoretical predictions from a thermal-response model of a simulated cranial structure. The results show that the thermal response model accurately predicts the temperature distribution in muscle-equivalent spheres, the distribution of temperature in detached M. mulatta heads when exposed from the back of the head, and the distribution of temperature in attached M. mulatta cadaver heads for animals oriented with body parallel to the H-field. The temperature distribution in the detached M. mulatta heads varies markedly with exposure orientation, ie, facing forward, backward, or to the side. The orientation of the M. mulatta cadaver body significantly affects the temperature distribution in the head - with H-field orientation showing high, nonuniform values, and E-field orientation showing low, uniform values. In live animals blood flow produces a significant short-term effect on the temperature distribution in the midbrain, but not the cortex. Midbrain temperatures are both significantly higher and lower than the comparable cadaver measurements, depending on location.
    Additional Material: 10 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 2095-2100 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starch-g-polyacrylonitrile (starch-g-PAN) copolymers were prepared by ceric ammonium nitrate initiation, and the major portion of the starch in these graft copolymers was then removed by acid hydrolysis to yield PAN with oligosaccharide end groups. Although these PAN-oligosaccharide samples reacted with methyl methacrylate in the presence of ceric ammonium nitrate, the resulting products were largely graft copolymers rather than the expected PAN-poly(methyl methacrylate) (PMMA) block copolymers. The following evidence is presented for a PAN-g-PMMA structure: (i) PAN without oligosaccharide end groups also produced a copolymer with methyl methacrylate under our reaction conditions. (ii) Starch-g-PAN (51 or 37% add-on) was a less reactive substrate toward ceric-initiated polymerization than PAN with oligosaccharide end groups. (iii) Low-add-on (18%) starch-g-PAN reacted with methyl methacrylate to give a final graft copolymer in which a large percentage of PMMA was grafted to the PAN component rather than to starch.
    Additional Material: 2 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 2205-2209 
    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
    Additional Material: 1 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 24 (1979), S. 2015-2023 
    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: Mixtures of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid (AASO3H) were graft polymerized onto starch by cobalt-60 irradiation, and the water absorbency and water solubility of the resulting products were determined. The conversion of monomers to polymer was nearly quantitative when pregelatinized wheat starch and a water solution of the two monomers were simultaneously irradiated (simultaneous irradiation conditions). Products with high water absorbency were obtained with equal weights of starch and total monomers when acrylamide:AASO3H ratios ranged from 9:1 to 1:3. Water solubility of these polymers was over 50%. Neither of the two monomers gave absorbent polymers when graft polymerized individually onto starch. Although highly absorbent products were also obtained at a total monomer:starch ratio of 2:5, ratios of 1:5 and lower gave products with poor absorbency. Neutralization of AASO3H with sodium hydroxide before graft polymerization drastically reduced both the water solubility and absorbency of the final products. A reaction with granular starch was also carried out under simultaneous irradiation with a total monomer:starch ratio of 2:5 and with equal weights of the two monomers. Conversion of monomers to polymer was once again nearly quantitative. To obtain good water absorbency from this granular product, it was necessary to first neutralize the AASO3H portion with alkali, then disperse the polymer in hot water, and finally dry the resulting water dispersion. Graft copolymers with good water absorbency were also obtained by adding preirradiated starch to a water solution of acrylamide and AASO3H, although only partial conversions of monomers to polymer were realized. Selected products from the various graft polymerizations were fractionated by extraction with either water or a 1% solution of sodium chloride. The synthetic polymer content of the resulting fractions and the percentage of AASO3H in the synthetic portion of each polymer were determined. The Mn of some of the synthetic polymers was also determined after removal of carbohydrate by enzymatic hydrolysis.
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