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  • 1975-1979  (9)
  • 1905-1909  (2)
  • Chemistry  (9)
  • synergism  (2)
  • Allelopathy
  • Biochemistry and Biotechnology
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 3 (1977), S. 197-205 
    ISSN: 1573-1561
    Keywords: synergism ; ferulic acid ; p-coumaric acid ; allelopathy ; phytotoxicity ; inhibition ; sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The data support the hypothesis that there is a synergistic phytotoxic effect whenp-coumaric and ferulic acids are found together. Equimolar mixtures of both acids showed greater reduction in sorghum seed germination, shoot elongation, and total seedling growth than either phytotoxin caused when alone. Repeated experiments showed mixtures containing 5×10−3 Mp-coumaric and 5×10−3 M ferulic acids reduced germination to 34% of controls after 24 hr and 59% by 48 hr. The same concentration of either phenol-treated seeds alone showed 69 and 92% germination at comparable times. The phytotoxic action of the combination approximated the inhibitory effect on germination of 10−2 M ferulic acid and was a greater reduction than caused by 10−2 Mp-coumaric treatments. Sorghum seedling growth was more sensitive than germination, with an equimolar mixture of 2.5×10−4 Mp-coumaric and 2.5×10−4 M ferulic acids reducing seedling dry weight significantly below weights of seedlings treated separately with 2.5×10−4 Mp-coumaric or ferulic acids. Further dilutions showed a 1.25×10−4 M concentration of either phenol was stimulatory to seedling growth, whereas a mixture of these two produced inhibition.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of chemical ecology 4 (1978), S. 425-436 
    ISSN: 1573-1561
    Keywords: synergism ; vanillic acid ; p-hydroxybenzoic acid ; allelopathy ; inhibition ; sorghum ; radish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Radish and grain sorghum germination and sorghum growth were inhibited in a synergistic manner by combinations of vanillic andp-hydroxybenzoic acids. At threshold inhibition levels, 2.5 × 10−3 M vanillic acid-treated radish seeds had 71 % of control germination after 24 hr and 2.5 × 10−3 Mp-hydroxybenzoic acid-treated radish yielded 95% germination. A mixture of 2.5 × 10−3 M of each of these two phytotoxins showed 52% germination after 24 hr. Equimolar mixtures of 5 × 10−3 M vanillic andp-hydroxybenzoic acids allowed sorghum germination of 60% of untreated seeds after 24 hr, whereas separate treatments of individual phenols had 93% and 96% of control seed germination. Sorghum root and shoot elongation and total seedling growth were more sensitive than germination to vanillic andp-hydroxybenzoic acid treatments, and synergistic effects also were apparent. A combination of 5 × 10−3 M vanillic with 5 × 10−3 Mp-hydroxybenzoic reduced root length more than either did individually, and a mixture of 5 × 10−4 M vanillic with 5 × 10−4 Mp-hydroxybenzoic acid reduced sorghum seedling growth to approximately that resulting from a 10−3 M concentration of either phenol alone. Phytotoxin levels inhibitory to sorghum growth caused small increases in lower leaf surface diffusive resistance, but did not close stomates, and this effect was not judged to be the cause of reduced sorghum growth.
    Type of Medium: Electronic Resource
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  • 3
    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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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Described herein are proton nmr experiments on chemically modified derivatives of ribonuclease A designed to elucidate the origin of an exchangeable resonance, assigned previously to a histidine ring N proton that titrates between 11 to 13 ppm with a pKa of 6.1 in H2O solution. Histidines 48 and 105, which are distant from the active site, are eliminated as candidates for this resonance from inhibitor binding studies on the enzyme in acetate-water solutions. This exchangeable resonance titrates with modified pKa's and constant area over the above pH range in His-119-N1-carboxymethylated-RNase A and des-(121-124)-RNase A, thus eliminating the imidazole N3 proton in the His 119-Asp 121 hydrogen bond. In His-12-N1-carboxymethylated-RNase A, this resonance is also observable, but broadens on raising the pH above 7 and at elevated temperatures above neutrality. It exhibits a pH-independent chemical shift characteristic of the protonated state of histidine. On the basis of these findings, this exchangeable resonance, designated a, is assigned to the imidazole N1 proton of His 12, which is hydrogen-bonded to the carbonyl oxygen of Thr 45 in the crystal.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 14 (1975), S. 987-997 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The C2H resonance of the active site histidine residue designated AS-2, which has the lower pKa of the two active site histidines, has been correlated in both RNase A and RNase S by comparing the pH 3 to 5.5 regions of the chemical shift titration curves, the effect of the inhibitor CMP-3′ on the chemical shifts at pH 4.0, and the effect of Cu II on the line widths at pH 3.6. It has been demonstrated that resonance AS-2 is absent in the spectrum of RNase S′ reconstituted using S-peptide deuterated at the C2 of His 12, and in that of the RNase S′-CMP-3′ complex. We thus demonstrate that histidine AS-2 is in fact His 12 in both enzymes. This finding is in agreement with out previous assignment of the exchangeable NH proton in RNase A to His 12, but reverses the assignments of the active site histidine C2H resonances made earlier by other authors.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 12 (1979), S. 362-364 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 251 MHz 1H and the natural-abundance 63.1 MHz 13C NMR spectra of N,N'-dimethylimidazolidine have been measured from -50 to -170°C. Below about -140°C. nitrogen inversion in the compound becomes slow on the NMR time scale and both the 1H and the 13C spectra indicate that it exists in solution as a mixture of cis and trans conformations having nearly the same energies. The free-energy barrier (ΔG≠) for nitrogen inversion in N,N'-dimethylimidazolidine is 6.4 kcal mol-1, a value which is 1.5 kcal mol-1 lower than that for N-methylpyrrolidine.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 8 (1976), S. 327-328 
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C n.m.r. chemical shifts of the sp-hybridized carbons in dialkylcarbodiimides have values of δc ≃ 140. These shifts are compared with those of similarly hybridized carbons occuring in other classes of compounds.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The natural-abundance 13C NMR spectra of cis,cis-1,5-cyclooctadiene monoepoxide and cis,syn,cis-1,5-cyclooctadiene diepoxide have been investigated over the temperature range of - 10 to - 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free-energy barrier (ΔG≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol-1 from a line-shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis-1,5-cyclooctadiene diepoxide exists in solution in chair (major) and in twist-boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist-boat conformation that is rapidly pseudorotating via a boat conformation even at - 180°C.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 8 (1976), S. 817-824 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br2- in the surrounding aqueous medium. The reaction 3Pmic + Br2aq- → Pmic+ + 2 Br- was followed by optical absorption measurements in the 10-8-10-4-sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 106 sec-1 and 1 × 109M-1 · sec-1.The fast component is related to the probability of a Br2- radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br2- radical-micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br2- radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this electron transfer reaction are also presented.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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