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  • 1
    ISSN: 1365-2621
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: The ESR spectra of the stalks and skins of a number of non-irradiated and γ-irradiated citrus fruits suggest that ESR spectroscopy could be used to establish the irradiation history. Two major spectral changes occur up on irradiation. Two additional features appear and are only observed in irradiated specimens (Features B and D, the latter separated by c. 5.9mT) and these are accompanied by an increase in the intensity of the main central signal (Feature A). Observations on the stability of Features A and D indicate that they arise from different radicals. Experiments on the meso- and exo-carps indicate that Features B and D are located mainly in the former and Feature A mainly in the latter.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1420-9055
    Keywords: Key words: Sulfide, iron, iron sulfide, speciation, solubility, solubility product, stability constant, seawater, freshwater.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract: A wide range of stoichiometries has been previously proposed for soluble iron sulfide species and there is no general agreement on their importance in natural waters. The solubility of Fe(II) in 0.1 M NaClO4 equilibrated at 20 ± 0.1°C with various partial pressures of H2S (0.1, 0.001, 0.0001, 0.00001 MPa) was measured in the pH range 3.1-7.9. Equilibrium was established within 1-6 h when amorphous FeS was the solid phase. The results could all be fitted using values for the solubility product constant (I = 0) of p*Ks = 3.00 ± 0.12 and of the stability constant for a soluble Fe(HS) 2 species (I = 0) of pβ 2 = -6.45 ± 0.12 where *Ks = aFe2+· aHS-/aH+ and β 2 = aFe(HS) 2/aFe2+· (aHS-)2. Any soluble species of the form Fex (HS) 2x where x = (1 ?∞) would fit the data equally well. Measurements at different partial pressures are inconsistent with labile species of the form FexSx. There was no evidence for a Fe(HS) + species. When a solution is saturated with respect to amorphous FeS, Fe(HS) 2 will only be a significant proportion of Fe(II) when S(-II) is higher than 0.2mmoll-1. The constants for Fe(HS) 2 or Fex (HS) 2x (x ≥ 2) are consistent with all freshwater data where constant values of measured ion activity products provide no evidence for soluble complex formation. For marine waters with high sulfide concentrations (≥ 6mmol l-1), measured concentrations of Fe(II) are consistent with there being negligible soluble iron sulfide. The data are better fitted if the dissolved species are polymeric as predicted concentrations of the monomer Fe(HS) 2 are significant. These findings suggest that rather than the dissolved species being Fe(HS) 2, it is probably polymeric, that is Fex (HS) 2x (x ≥ 2).
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  • 3
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Electron spin resonance (ESR) spectroscopy was used to demonstrate that free radicals are formed in O3-fumigated plant leaves prior to the formation of visible leaf injury. ESR signals with a g-value of 2.0037 to 2.0043, were observed in pea (Pisum sativum L. cv. Feltham first) and bean (Phaseolus vulgaris L. cv. Pinto) plants that had been fumigated for 4 h with 70–300 nl l−1 of ozone after they had been treated with the spin-trap N-t-butyl-α-phenylnitrone (PBN). The size of the ESR signals increased with the concentration of ozone used but the nature of the trapped radicals could not be identified. However, further experiments using an inhibitor of ethylene biosynthesis, arninoethoxyvinyl glycine (AVG), showed that the reaction between ozone and ethylene is the cause for ozone toxicity.
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  • 4
    ISSN: 0749-1581
    Keywords: ESR ; Cation migration ; Line-width variation ; 2-Pivaloyl-1,4-benzoquinone ; Radical anion ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2-pivaloyl-1,4-benzoquinone radical anion has been prepared by alkali metal reduction in tetrahydrofuran in the presence of dibenzo-18-crown-6, 15-crown-5, or 12-crown-4, and its ESR spectrum in each system has been recorded over a range of temperatures. Line-width variation in the ESR spectrum is observed in some systems. This line-width variation has been attributed to cation migration between sites adjacent to the non-equivalent carbonyl groups rather than to restricted rotation of the pivaloyl group. In some systems, however, the rate of migration is too fast and in others too slow, compared with the time-scale of the ESR experiment, for line-width variation to be observed. The influence of each crown ether upon the rate of cation migration has been found to depend upon the size of the crown ether ‘cavity’ compared with the size of the alkali metal counter-ion.
    Additional Material: 1 Ill.
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  • 5
    ISSN: 0749-1581
    Keywords: ESR ; Spin Trapping ; Occluded radicals ; Polyacrylonitrile ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An ESR spectrum is observed when a sample of polyacrylonitrile powder is dissolved in a dimethyl sulphoxide solution of nitrosobenzene at room temperature. However, the spectrum is not associated with the trapping of occluded radicals from within the polymer latex, but with the hydrogen atom adduct. [Similarly, when an aqueous emulsion of poly(methyl methacrylate) is added in place of the polyacrylonitrile powder the spectrum of the hydrogen atom adduct is again observed.] Experiments in dimethyl-d6 sulphoxide indicate that the hydrogen atom does not originate from the solvent. At higher temperatures (383 K) the spectrum of a mixture of the hydrogen atom and methyl radical adducts is observed. Experiments in dimethyl-d6 sulphoxide show that the latter radical originates from the solvent.
    Additional Material: 6 Ill.
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  • 6
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
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  • 7
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 2 Ill.
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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: In dimethylformamide the ESR spectra of the radical anions of dibenzo[f,h]quinoxaline and dibenzo[a,c]phenazine both exhibit line broadening due to slow molecular tumbling over a wide temperature range. Similar effects are also observed in the spectra of the radical anions of quinoxaline and phenazine. The ESR spectra of the radical anions of dibenzo[f,h]quinoxaline and dibenzo[a,c]phenazine have been interpreted by computer reconstruction and the hyperfine splitting constants assigned with the aid of Hückel unpaired electron density calculations.
    Additional Material: 5 Ill.
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