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  • Chemistry  (17)
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  • 04. Solid Earth::04.05. Geomagnetism::04.05.06. Paleomagnetism
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  • 1991  (16)
  • 1
    Electronic Resource
    Electronic Resource
    Some fundamental studies of the reaction of poly(vinyl alcohol) with alkyl chlorophosphates (1991)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 192 (1991), S. 1733-1739 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The modification reaction of poly(vinyl alcohol) with diethyl chlorophosphate and ethyl dichlorophosphate is studied in homogeneous phase using tertiary amines as catalysts. The structure of the modified polymers was determined by means of 1H and 31P{1H} nuclear magnetic resonance (NMR) spectroscopy as well as by chemical analysis. The structure of the polymers resulting from the reaction with diethyl chlorophosphate greatly depends on the reaction temperature as well as the catalyst. For lower reaction temperatures (≤25°C) only acyclic phosphate ester groups were observed. The activation energy was found to be 24,9 kJ/mol. The presence of cyclic phosphate ester groups was found, when higher reaction temperatures (〉25°C) were used. These results can be interpreted considering the existence of transesterification reactions. Crosslinking structures were obtained in case ethyl dichlorophosphate was used instead of diethyl chlorophosphate.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1991.021920807
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  • 2
    Electronic Resource
    Electronic Resource
    Albumin denaturation during ultrafiltration: Effects of operating conditions and consequences on membrane fouling (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 528-534 
    Details
    ISSN: 0006-3592
    Keywords: albumin denaturation ; ultrafiltration ; protein denaturation ; membrane fouling ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Ultrafiltration of high-purity grade bovine serum albumin has been carried out under various temperature between 5 and 30°C and at various cross-flow velocities, pressures, and concentrations with the aim of studying protein denaturation and its consequences on the process. Three different pump heads have been tested. Denaturation of proteins in solution has been monitored by laser light scattering and size exclusion chromatography. The rate of protein denaturation increases with temperature, cross-flow, and time. It is observed that membrane fouling is different whether denaturation has occurred or not. Under high-concentration polarization, denaturation can occur in the boundary layer if the wall concentration exceeds 400 g/L. It is shown how the residence time, operating temperature, and pressure play an important part in membrane fouling. This can provide guidelines for process design and control.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260380511
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  • 3
    Electronic Resource
    Electronic Resource
    Peroxidase-ferrocene modified carbon paste electrode as an amperometric sensor for the hydrogen peroxide assay (1991)
    Weinheim : Wiley-Blackwell
    Electroanalysis 3 (1991), S. 281-285 
    Details
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new enzymatic amperometric sensor for hydrogen peroxide based on a modified carbon paste electrode is described. Horseradish peroxidase and ferrocene mediator were immobilized by dissolution or dispersion in a graphite-paraffin oil paste. To prevent losses of immobilized chemicals under operational conditions, the electrode surface was coated with a Nafion membrane. The device exhibits a relatively fast response time (42 s for 95% of the steady-state response) and yields currents linearly related to the hydrogen peroxide concentration over the 10-7 to 10-5 mol/L range in both static and flow injection operations. The slope of the calibration plot remained constant for more than 20 days. Flow injection assays of hydrogen peroxide at a sampling rate of about 70 injections per hour, with a relative standard deviation of 1.4%, are possible. An easy and low cost preparation procedure is described.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140030407
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  • 4
    Electronic Resource
    Electronic Resource
    Study of the radial and axial distribution of heavy metals in oak growth rings by stripping voltammetry (1991)
    Weinheim : Wiley-Blackwell
    Electroanalysis 3 (1991), S. 325-329 
    Details
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The concentrations of the heavy metals (Cd, Pb, Cu, and Zn) have been determined in oak growth rings from the polluted region of Königstein, Germany, by differential pulse anodic stripping voltammetry and compared to those in soil. The radial distribution was found to be the same for all four metals studied and features a distinct increase in the recent growth rings and a marginal increase in the transition zone between sapwood and heartwood. The toxic metals cadmium and lead are preferentially bound to lower parts of the tree, whereas for essential metals copper and zinc, monotonous axial distribution has been found in the range 0-5 m. This points to different degrees of mobility of heavy metal complexes in wood material.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140030413
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of talc surface treatment on the mechanical properties of composites based on PP/LDPE blend matrices (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 245-252 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 has been made of property optimization of a composite based on low density polyethylene and polypropylene (PP) blend matrices with talc modified by a titanate coupling agent. Analysis shows that the flexural properties improve with increasing content of both talc and polypropylene. However, the tensile moduli show a different behavior. Tensile strength is hardly affected by the filler content at PP percentages in the matrix above 50 percent. The surface modified talc gives rise to higher mechanical properties than the unmodified talc. This improvement is more noticeable as talc and PP percentages in the composite is increased. Scanning electron microscopy has shown the effect of the coupling agent at the filler/polymer matrix interphase and the greater affinity between talc and polypropylene.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760310407
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  • 6
    Electronic Resource
    Electronic Resource
    Thermospray mass spectrometry of phosphorothionate pesticides and their oxygen analogues (1991)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 20 (1991), S. 3-10 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positive and negative ion modes thermospray mass spectrometry were used for the characterization of the phosphorothionate pesticides parathion-ethyl, fenchlorphos, bromophos-ethyl and fenitrothion and their oxygen analogues. A convenient and easy procedure using dimethyldioxirane has been developed for the preparation of the triester phosphates from the corresponding phosphorothionates. The spectra reported from paraoxon-ethyl and fenitrooxon are compared with those of standards available. For the first time, the characterization of the oxygen analogues of fenchlorphos and bromofos-ethyl by any mass spectrometric technique is reported.By employing the positive ion mode, the base peak was [M + NH4]+ for all the studied pesticides with a second abundant ion corresponding to [M + H]+ whereas in the negative ion mode typical negative chemical ionization mechanisms involving electron capture, dissociative electron capture and anion attachment have been observed. The corresponding specific fragments were: [M - R]-, R being a methyl or ethyl; [FG]-, FG being the functional group fragment which contains the phosphorus moiety; M-, [M - Cl]-, phenolate and thiophenolate anions and adducts with the ionizing additive. Special emphasis is given to the changes in the spectra of the phosphorothionate pesticides as compared to their oxygen analogues. With the positive ion mode, sensitivity was about one and a half orders of magnitude better for the oxygen analogues than for the parent pesticides, whereas in the negative ion mode identical sensitivities were observed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200200104
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  • 7
    Electronic Resource
    Electronic Resource
    Vanadium(V) determination through a catalytic polarographic method (1991)
    Weinheim : Wiley-Blackwell
    Electroanalysis 3 (1991), S. 715-719 
    Details
    ISSN: 1040-0397
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for determining trace level of vanadium(V) has been developed. The reaction is the polarographic reduction of the bromate, catalyzed by this metal ion, in the presence of cupferron, in acetic-acetate medium. The peak current obtained is proportional to the vanadium(V) concentration between 2.10-8 and 3.10-7 M, with a detection limit of 6.10-9 M. The procedure is very selective and has been successfully applied to a certified steel sample after extraction of iron wit ethyl ether.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140030720
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of rac-allocoronamic acid hydrochloride (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 1099-1100 
    Details
    ISSN: 0170-2041
    Keywords: Aminocyclopropanecarboxylic acids ; Amino acid, dehydro ; Diazomethane, addition of ; Oxazolone ; Cyclopropanecarboxylic acid ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new method is reported for the synthesis of rac-allocoronamic acid hydrochloride (5), from the readily available oxazolone 1 via the 1,3-dehydro amino acid derivative 2, diazomethane addition, photolysis and acid hydrolysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101190
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  • 9
    Electronic Resource
    Electronic Resource
    Die Nickel-katalysierte Cyclotrimerisierung von Malonitril und der Dicyanmethanid-überbrückte anionische NiII-Komplex [{Ni(C6F5)2(μ-NCCHCN)}2]2⊖Diese Arbeit wurde von der Dirección General de Investigación Cientifica y Técnica (Projekt PB87-0690) gefördert. J. G. dankt der Dirección Regional de Educación y Universidad de Murcia für ein Forschungsstipendium. (1991)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 103 (1991), S. 733-735 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19911030632
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  • 10
    Electronic Resource
    Electronic Resource
    Dependence of XRF intensity on the tilt of the propagation plane: Experimental (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 20 (1991), S. 163-169 
    Details
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The geometrical properties of the x-ray fluorescence (XRF) intensity related to the α-parameterization were confirmed experimentally. A special sample stage was built to allow the rotation of the sample with the propagation plane (the plane defined by the incident and take-off beam directions) and was coupled to an energy-dispersive spectrometer. The device and the way in which it was carefully aligned with the collimated x-ray beams are described. The fluorescence spectra of three NBS standard samples were measured for 16 different positions of the α angle. The incident and take-off angles were both 45° for sample rotations between α = 0 and the maximum angle of 86°. XRF intensities from non-enhanced lines do not show any dependence on α as predicted by theory. Enhanced lines, on the contrary, decrease in intensity when α increases, allowing the isolation of the primary emission by extrapolation to the limiting case α = π/2.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/xrs.1300200403
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