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  • Chemistry  (7)
  • Atomic and molecular collisions and interactions
  • Nuclear Reactions
  • 1995-1999  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 239 (1996), S. 33-41 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der neuartige dikationische Komplex [dppfNi(MeCN)4][BF4]2 (dppf = 1,1′-Bis(diphenylphosphin)ferrocen) zeigte in Anwesenheit von Diethylaluminiumchlorid (AIEt2CI) hohe Aktivität für die Polymerisation von 1,3-Butadien. Reaktionsdauer, Temperatur und das Aluminium/Nickel-Verhältnis wurden auf maximale Aktivität und Selektivität optimiert. Umsätze über 90% konnten erreicht werden. Im Vergleich zu Polybutadienen, die mit anderen Nickel-Phosphin-Systemen hergestellt wurden, zeigten die synthetisierten Polybutadiene höhere cis-1,4-Anteile (〈80%) und eine geringe Bildung von 1,2-Einheiten (2%). Alle Polymeren hatten niedrige mittlere Molekulargewichte (Mw 〉 11 800).
    Notes: The new dicationic nickel complex [dppfNi(MeCN)4][BF4]2 (dppf = 1,1′-bis(diphenylphosphino)ferrocene) in the presence of diethylaluminium chloride (AIEt2CI) exhibited high activity on the 1,3-butadiene polymerization. Reaction time, temperature and aluminium/nickel molar ratio were optimized in order to achieve maximum activity and selectivity. Conversions higher than 90% were obtained in contrast to other nickel-based systems using phosphine ligands, the resulting polybutadiene showed high cis-1,4 (〈80%) content and only small amount of 1,2-units (2%). All polymers presented low molecular weights (Mw 〉 11 800).
    Additional Material: 2 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 403-415 
    ISSN: 0006-3525
    Keywords: molecular dynamics ; DNA curvature ; DNA flexibility ; TATA box functionality ; TATA box binding protein (TBP) ; TBP recognition ; TBP binding ; TBP transcriptional activation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four 1.5 ns molecular dynamics (MD) simulations were performed on the d(GCTATAAAAGGG) · d(CCCTTTTATAGC) double helix dodecamer bearing the Adenovirus major late promoter TATA element and three iso-composition mutants for which physical and biochemical data are available from the same laboratory. Three of these DNA sequences experimentally induce tight binding with the TATA box binding protein (TBP) and induce high transcription rates; the other DNA sequence induces much lower TBP binding and transcription. The x-ray crystal structures have previously shown that the duplex DNA in DNA-TBP complexes are highly bent. We performed and analyzed MD simulations for these four DNAs, whose experimental structures are not available, in order to address the issue of whether inherent DNA structure and flexibility play a role in establishing these observed preferences. A comparison of the experimental and simulated results demonstrated that DNA duplex sequence-dependent curvature and flexibility play a significant role in TBP recognition, binding, and transcriptional activation. © 1998 John Wiley & Sons, Inc. Biopoly 46: 403-415, 1998
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 19 (1998), S. 409-411 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: RuHCl(CO)(PCy3)2 (1) dissolved in 1-butyl-3-methylimidazolium tetrafluoroborate (2) molten salt is able to reduce selectively NBR to HNBR under hydrogen partial pressures between 10 and 40 bar at 100-160°C in a typical two-phase catalytic reaction. Reaction rates between 0.059 (mmol Ru)-1 · min-1 and 1.65 (mmol Ru)-1 · min-1 were obtained depending on the reaction parameters and increasing with the volume of the molten salt. The overall process has an apparent activation energy of 47 ± 3 kJ · mol-1. The recovered ionic catalyst solution can be reused several times without significant changes in the catalytic performance (selectivity and activity).
    Additional Material: 5 Ill.
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  • 4
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The complex [η3-methallyl-nickel-dad]PF6 is a new catalyst precursor for ethylene polymerization. The system is active in the presence of usual organoaluminium compounds like diethylaluminium chloride, at low Al/Ni ratios and under mild reaction conditions (temperatures between -10°C and 25°C, ethylene partial pressure from 1 to 15 atm). The polymers show extensive methyl branching, whose content is controlled by reaction parameters like temperature and ethylene pressure.
    Additional Material: 2 Ill.
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  • 5
    ISSN: 0894-3230
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A theoretical study on the structures and internal rotations of methyl N,N-dimethylcarbamate and its sulphur, selenium and tellurium homologues [Me2NC(O)YMe, 1 (Y = O), 2 (Y = S), 3 (Y = Se), 4 (Y = Te)] was performed by means of ab initio molecular orbital calculations at the MP2/3-21G(*)//HF/3-21G(*) level. These calculations indicate that 1-4 are all planar with Z-conformation with respect to the central bonds of their O(DOUBLE BOND)C(SINGLE BOND)Y(SINGLE BOND)Me units, whereas the corresponding E-forms are transition states for rotation about Y(SINGLE BOND)C(O) bonds which have energies higher than the E-forms by 20·6, 15·4, 13·9, and 9·6 kcal mol-1, respectively. The energy of 1 increases monotonically from the Z-form to the E-form with rotation about the Y(SINGLE BOND)C(O) bond, but in 2-4 a transition state and a local minimum were found between the two forms. This different phenomenon for 1 compared with its homologues 2-4 arise mainly from the large steric repulsion between a methyl group on the nitrogen and that on the oxygen in E-1. Optimization of the transition states (TSa and TSs) for rotation about N(SINGLE BOND)C(O) bonds showed that TSa is favoured by 2-4 but disfavoured by 1 owing to the repulsion between lone pairs on the nitrogen and oxygen atoms in its TSa. The barriers for rotation about N(SINGLE BOND)C(O) bonds were estimated to be 16·1, 14·7, 14·7, and 15·7 kcal mol-1 for 1,2,3,4, respectively.
    Additional Material: 5 Ill.
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  • 6
    ISSN: 0935-6304
    Keywords: high temperature gas chromatography ; flavonoids ; propolis ; high molecular weight compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The underivatized acetone and hexane fractions from propolis samples (predominant flora Citrus spp. and Vernonia polyanthes) were analyzed by HT-HRGC (high temperature high resolution gas chromatography) and HT-HRGC coupled to mass spectrometry (HT-HRGC-MS). Several compounds, including flavonoid aglycones, phenolic acids, and high molecular weight compounds were characterized in crude extracts by HT-HRGC-MS. HT-HRGC and HT-HRGC-MS were shown to be quick and informative tools for rapid analysis of crude extracts without need for prior derivatization and purification.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Cell Biochemistry and Function 16 (1998), S. 253-259 
    ISSN: 0263-6484
    Keywords: dietary fatty acids ; lymphocyte proliferation ; glucose oxidation ; glutamine oxidation ; enzyme activity ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effect of diets enriched with fat containing different fatty acids on glucose and glutamine metabolism of mesenteric lymph nodes lymphocytes, spleen, and thymus and lymphocyte proliferation was examined. The following fat-rich diets were tested: (1) standard chow (CC); (2) medium chain saturated fatty acids (MS) - coconut fat oil; (3) long chain saturated fatty acids (LS) - cocoa butter; (4) monounsaturated fatty acids (MU) - canola oil (n-9); (5) polyunsaturated fatty acids (PU) - soybean oil (n-6). Of the fat-rich diets tested, MS was the one to present the least pronounced effect. Lymphocyte proliferation was reduced by LS (64 per cent), MU (55 per cent), and PU (60 per cent). Hexokinase activity was enhanced in lymph node lymphocytes by PU (67 per cent), in the spleen by MS (42 per cent), and in the thymus by PU (30 per cent). This enzyme activity was reduced in the spleen (33 per cent) by LS and MU (35 per cent). In the thymus, this enzyme activity was reduced by LS (26 per cent) and MU (13 per cent). Maximal phosphate-dependent glutaminase activity was raised in lymphocytes by MS (70 per cent) and MU (20 per cent). This enzyme activity, however, was decreased in lymphocytes by PU (26 per cent), in the spleen by LS (15 per cent), and in the thymus by MU (44 per cent). Citrate synthase activity was increased in lymphocytes by MU (35 per cent), in the spleen by LS (56 per cent) and MU (68 per cent), and in the thymus by LS (42 per cent). This enzyme activity was decreased in lymphocytes by PU (24 per cent) only. [U-14C]-Glucose decarboxylation was raised by all fat-rich diets; MS (88 per cent), LS (39 per cent), MU (33 per cent), and PU (50 per cent), whereas [U-14C]-glutamine decarboxylation was increased by LS (53 per cent) and MU (55 per cent) and decreased by MS (17 per cent). The results presented indicate that the reduction in lymphocyte proliferation due to LS, LU and PU could well be a consequence of changes in glucose and glutamine metabolism. Copyright © 1998 John Wiley & Sons, Ltd.
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