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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 14 (1988), S. 1821-1828 
    ISSN: 1573-1561
    Keywords: Allelopathy ; bioassay ; mechanism of action ; seed germination ; radicle growth ; seedling growth ; Lemna bioassay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The bioassay has been one of the most widely used tests to demonstrate allelopathic activity. Often, claims that a particular plant species inhibits the growth of another are based entirely on the seed germination response to solvent extracts of the suspected allelopathic plant; few of these tests are of value in demonstrating allelopathy under natural conditions. The veracity of the bioassay for evaluating naturally occurring compounds for phytotoxicity depends upon the physiological and biochemical response capacity of the bioassay organism and the mechanism(s) of action of the allelochemicals. The possibility that more than one allelochemical, acting in concert at very low concentrations, may be responsible for an observed allelopathic effect makes it imperative that bioassays be extremely sensitive to chemical growth perturbation agents. Among the many measures of phytotoxicity of allelochemicals, the inhibition (or stimulation) of seed germination, radicle elongation, and/or seedling growth have been the parameters of choice for most investigations. Few of these assays have been selected with the view towards the possible mechanism of the allelopathic effect.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 15 (1989), S. 951-960 
    ISSN: 1573-1561
    Keywords: Allelopathy ; grain sorghum ; Sorghum bicolor ; weed inhibition ; weed management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Three years of field data in northeastern Nebraska demonstrate that a grain sorghum crop reduces weediness in the following crop year. Weed growth was consistently lower in sorghum areas the year after strip-cropping fields with sequences of four-row bands of grain sorghum, soybeans, and corn. Percentage weed cover was significantly lower early in the year, and midsummer weed biomass was well below that found after corn and soybeans. Weed biomass in June and July following corn was two to four times that of grain sorghum strips. Inhibitory effects of grain sorghum were primarily on broadleaf weeds, often showing no action on grass weeds. No obvious differences were noted in the weed species present after the three crops. Allelopathy provides a logical explanation for the sorghum-mediated weed inhibition found in this study. The data have implications for weed management strategies in agriculture.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 98 (1987), S. 99-109 
    ISSN: 1573-5036
    Keywords: Allelopathy ; Ferulic acid ; Magnesium ; Mineral content ; Phosphorus ; PotassiumSorghum bicolor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two week old sorghum seedlings (Sorghum bicolor L. Moench) were treated with ferulic acid added to the nutrient solution. Effects on tissue concentration of P, K, Mg, Ca, Fe, and Zn were evaluated after 3 and 6 days. Treatemnts of 0.25 mM ferulic acid approximated the growth inhibition threshold, and after 6 days 0.5 mM treated plants weighed less than controls. Both treatments reduced the P content of the roots and shoots at the 3- and 6-day harvests in three replicate experiments. Roots of treated plants at both harvests had a lower concentration of K and Mg. These reductions in P, K, and Mg were most extensive from the 0.5 mM ferulic acid regime. In some cases at both harvests, shoot K was lower and Mg was higher than control tissue. Ferulic acid effects at the 3-day harvest included an elevation of Ca and depression of Fe in shoots. Changes in nutrient content preceded measurable differences in plant weight. These data indicate that one mechanism of growth inhibition by this allelochemical may be an alteration of nutrient balance.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Letters Edition 25 (1987), S. 426-427 
    ISSN: 0887-6258
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 13 (1969), S. 851-865 
    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: Untreated and fire-retardant-treated white α-cellulose samples were isothermally pyrolyzed in a fluidized bath in a nitrogen environment at 298-360°C. Results were reported in terms of volatilization (based on weight loss-time measurements) and the degradation products (based on gas chromatographic-mass spectrometric analysis). The findings products (based on gas chromatographic-mass spectrometric analysis). The findings on untreated cellulose indicate that: (1) pyrolysis occurs in three distinct phases in the temperature range 276-360°C; (2) there is a single activation energy of 42 kcal/mole over this temperature range; (3) the initial rapid weight loss is not due to the desoprtion of water, but primarily to decomposition of the cellulose; molecules: (4) there is little difference in either the quality or relative quantity of the volatiles generated during the three different phases of pyrolysis. The findings on treated cellulose show that the fire retardant, KHCO3, does not markedly change the types of degradation products having molecular weights below about 110, althought it does change their relative concentrations. Furthermore, the rate of product generation and the quantity of residual char are increased.
    Additional Material: 11 Ill.
    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 15 (1971), S. 835-851 
    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 typical gas chromatogram of the volatile pyrolysis products of untreated α-cellulose contains 39 peaks; however, mass spectral data indicate that at least 59 compounds, with molecular weights less than about 150, are present. A total of 37 compounds have been identified, 13 of which have not been previously reported. Most of the newly identified compounds contain a benzene ring, indicating that these compounds may be products of reactions between initial volatiles. A comparison of the products generated in the temperature range of 330°-440°C indicates that the formation of pyrolysis products is essential independent of temperature. Comparisons of the chromatograms obtained for untreated levoglucosan and cellulose indicate that most of the decomposition of cellulose probably forms levoglucosan which then decomposes to yield the observed pyrolysis products. In addition, the products of flame retardant-treated levoglucosan are essentially the same as those of cellulose with the same retardant treatment. This suggests that the retardants act on the levoglucosan formed in the decomposition of the cellulose rather than on the cellulose directly.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 1 (1975), S. 227-234 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: IR-spektroskopische Untersuchungen von Polyäthylen-Proben, dargestellt durch Reduktion von Polyvinylchlorid mit Lithiumaluminiumhydrid, ließen darauf schließen, daß Polyvinylchlorid Seitenketten enthält, die seine Morphologie und Festkörpereigenschaften wesentlich beeinflussen. Die Natur dieser Seitenketten war bisher unbekannt. Es wird anhand von 13C-NMR Spektren gezeigt, daß die Verzweigungen in reduziertem Polyvinylchlorid aus Methylgruppen bestehen, die vermutlich aus Chlormethylgruppen des ursprünglichen Polymeren entstanden sind. Die untersuchte Probe enthielt ca. 3 CH3-Gruppen pro 1000 CH2-Gruppen, jedoch is dieses Verhältnis vermutlich von der Polymerisationstemperatur abhängig. Zusätzlich wurden Anzeichen für längere Seitenketten gefunden, die allerdings nur in einem Ausmaß von weniger als 1 pro 1000 CH2-Gruppen vorhanden sein dürften.
    Notes: The presence of branches in poly(vinyl chloride) as indicated by previous IR measurements on the polymer reduced to polyethylene by means of lithium aluminum hydride is believed to affect materially the morphology and solid state properties of poly(vinyl chloride); however, up to the present, the nature of these branches has not been known. By use of 13C-NMR on reduced poly(vinyl chloride) it is demonstrated that the brances are methyl groups, presumably corresponding to chloromethyl groups in the original polymer. In the sample studied, the frequency is ca. 3 methyl groups per 1000 CH2 groups, but this is expected to depend on the temperature of polymerization. There is also some evidence for long branches, probably not exceeding 1 per 1000 CH2 groups.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Polymer Science 18 (1955), S. 417-421 
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of seven vinyl esters of perfluoro acids has been prepared by the mercury catalyzed reaction of the acids with acetylene. Certain physical properties of the monomers are given. Homopolymers gave clear, flexible films with the exception of vinyl caprylate and caprate, which formed waxy films. Copolymerization of vinyl perfluorobutyrate proceeded readily with vinyl acetate and methyl methacrylate, but less readily with styrene, maleic anhydride, and acrylonitrile.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0022-3832
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crosslinking and degradation of seven polyacrylates by 1000 kvp. electrons has been investigated. Gel content-radiation dose analysis reveals the energy dissipation per main-chain fracture, Ed, to be the same (530 ± 100 electron volts) for methyl, n-butyl, sec-butyl, isobutyl, and tert-butyl acrylate polymers. The energy dissipation per crosslinked unit formation, Ec, is 80-90 e.v. for methyl, n-butyl, isobutyl and neopentyl acrylate polymers. Ec may be slightly higher for poly-sec-butyl acrylate. Poly-tert-butyl acrylate possesses a uniquely high Ec of 300 e.v. The presence of hydrogen atoms alpha to the alcoholic oxygen of the ester group is believed to contribute strongly to the crosslinking reactions of polyacrylates under ionizing radiations. Poly-1,1-dihydroperfluorobutyl acrylate exhibits an initial Ec of ∼45 e.v. and an Ed of ∼450 e.v. Beyond 15 megareps the ration of main-chain fracture to crosslink formation increases.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Energy pathways between the αR, β′, C7eq, and β-regions of the conformational energy surface of N-acetyl-N′-methylalanyl amide were obtained by SCF ab initio calculations on the 4-21G level, with gradient geometry optimization at each point. The calculations indicate that no barrier exists at this computational level between αR and β′. The variation of geometry (bond distances and bond angles) with conformation is analyzed in detail, and the most important geometrical parameters that should be treated as variables in both empirical energy calculations and in the fitting of polypeptide chains in proteins by x-ray methods are identified. In addition to the φ,ψ correlation discussed previously for the helical state, a correlation of these dihedral angles in the β-region is described.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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