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  • 1
    ISSN: 0935-6304
    Keywords: Chiral discrimination ; 2,3,6-Tri-O-methyl)-β-cyclodextrin ; Capillary Gas Chromatography ; ?-Alkyl-5-methylhydantoin ; Thermodynamic parameters ; Molecular modeing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Permethylated β-cyclodextrin (hereafter designated perMe-β-CD), dililuted or not in polysiloxane, is an efficient chiral discriminant for native, 3-methylated, and 1,3-dimethylated series of 5-methyl-5-(CnH2n + 1)hydantoins. From thermodynamic data obtained with pure perMe-β-CD and with the aid of molecular modeling, it is concluded that: (i) For native hydantoin derivatives having a carbon chain at the 5-position varying from ethyl to nonyl (2≤n≤9), the retention time is related to their H-bonding capability. The resolution is poor for derivatives with n≤4. For n≤5, the resolution is considerably improved and this increase in resolution is attributed to the long alkyl chain being capable of being buried inside the cyclodextrin cavity. (ii) For 1,3-dimethylhydantion derivatives having a carbon chain at the 5-position varying from ethyl to hexyl(2≤n≤6), the retention time is mainly determined by a steric fit between the solute and the inner volume of the macrocyclic cavity. For n = 2, a particular behavior is observed, consistent with a total inclusion of the solutes inside the cavity. By contrast with the native hydantoins, the selectively is high for light derivatives. Thus, the selectivity does not correlate with a strong docking energy (such as the presence of H-bonds postulated with native derivatives). (iii) For 3-methylhydantoin derivatives having a carbon chain at the 5-position varying from ethyl to octyl (2≤n≤8), as expected, retension time and selectivity are intermediate between that of native hydantoins and 1,3-dimethylhydantoins. For all three series, where n≤5, the increase in chain length (n) does not bring about substantial changes in the chromatographic results. Therefore, for these long alkyl chain derivatives, similar dominant interactions with perMe-β-CD are postulated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0930-7516
    Keywords: Chemistry ; Industrial Chemistry and Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Local mass transfer studies have been carried out in an external loop airlift reactor and indicated the existence of significant non-uniformities in aeration capacity in the various sections of the reactor. The traditional assumption of a single well mixed unit with a single kL a value for external loop airlift reactors was found to be poor and cannot represent adequately the reactor as a whole. The liquid head in the gas/liquid separator was found to have a significant negative negative effect on the local mass transfer coefficient kL a. Visualization of flow patterns showed the existence of strong vortices in the riser and downcomer which contributed to a reduction in local aeration capacity. Mass transfer experiments in an aerated tank showed that the aeration capacity can be reduced by half in viscous media but improved significantly in the presence of salts.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0570-0833
    Keywords: bridging ligands ; magnetic properties ; manganese ; metalloenzymes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Highly active Ziegler-Natta catalysts have been synthesized using an electrochemical process in their preparation, with the aim of producing selectively titanium(III) species from TiCl4. The use of an undivided cell, an aluminium anode and a halogenated solvent (dichloromethane or 1,2-dichloroethane), has allowed the production in situ of chloroalkyl aluminium species, by cathodic reduction of TiCl4, thus giving rise to a new Ziegler-Natta catalytic combination. The possibility of scale up for this lectrochemical synthesis has been clearly shown. The Ti/Al system was modified so as to enhance its activity, first by adding a soluble dialkylmagnesium compound and then a soluble vanadium compound such as VOCl3. This Ti/Al/Mg/V highly active system was used under different conditions: in a hydrocarbon medium at low (80°C) and high (200°C) temperature and also under supercritical conditions in a continuous high-pressure autoclave reactor, to produce homoor copolymers of ethylene with α-olefins. Compared to similar heterogeneous catalysts obtained by comilling, the observed activities are shown to be very much improved, especially under high pressure and high temperature conditions. This may be related to the very narrow granular distribution centered at 2,5-3 μm, compared to a much broader distribution (centered at 6 μm) obtained with the comilled catalyst.
    Additional Material: 14 Ill.
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  • 5
    ISSN: 0044-8249
    Keywords: Brückenliganden ; Magnetische Eigenschaften ; Mangan ; Metalloenzyme ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0029-5981
    Keywords: linear viscoelasticity ; discrete creep spectrum ; incremental constitutive law ; strain history ; damping analysis ; thin structures ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mathematics , Technology
    Notes: This paper is concerned with the development of an incremental formulation in the time domain for the displacement and stress analysis of quasistatic, linear, thin viscoelastic structures undergoing mechanical deformation. By representing the viscoelastic behaviour of a material by a discrete creep spectrum and by an incremental constitutive equations, the difficulty of retaining the stress history in computer solutions is avoided. A complete general formulation of linear viscoelastic stress analysis is developed in terms of increments of midsurface strains and curvatures and corresponding stress resultants.
    Additional Material: 15 Ill.
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  • 7
    ISSN: 0749-503X
    Keywords: Heterologous gene expression ; levansucrase ; signal peptide ; B. subtilis ; S. cerevisiae ; Life Sciences ; Life Sciences (general)
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We compared the ability of signal sequences from various Bacillus or yeast secreted proteins to direct Bacillus subtilis levansucrase into the secretion pathway of the yeast Saccharomyces cerevisiae. The efficiency of these sequences correlated with the overall hydrophobicity of their h-domain and was independent of their origin. Furthermore, the net charge of the proximal protein sequence downstream from the signal sequence contributed to the competence of the heterologous proteins to be secreted by yeast. Modification of this net charge allowed the protein to be translocated under the control of the yeast invertase signal sequence. Moreover, glycosylation of levansucrase did not modify significantly the fructosyl polymerase activity.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0021-9304
    Keywords: total hip arthroplasty ; ceramic and polyethylene particles ; macrophage response ; flow cytometry ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Using the J774 macrophage cell line, we designed an in vitro model to analyze by flow cytometry the effects of size, concentration, and composition of ceramic (Al2O3 and ZrO2) and high density polyethylene (HDP) particles on phagocytosis and cell mortality. Inflammatory mediator (TNF-α) also was measured by ELISA. Kinetic studies revealed that phagocytosis of the particles begins very early after cell exposure, increasing with time and particle concentration and reaching a plateau after 15 h. This implies that the optimum period to evaluate cellular response to particulate debris is between 15 and 24 h of incubation. Results also showed that phagocytosis increases with concentration for particles up to 2 μm. For larger particles (up to 4.5 μm), phagocytosis seems to reach a plateau independent of size and concentration, which suggests a saturation of phagocytosis that is most likely dependent on overall particle volume ingested. We did not detect any significant difference in phagocytosis between Al2O3 and ZrO2 at 0.6 μm. Al2O3 seems to be more easily phagocytosed than HDP at the same size (4.5 μm) and concentrations. Cytotoxicity studies revealed that macrophage mortality increases with particle size and concentration for sizes greater than 2 μm. Smaller particles (0.6 μm) cause cell mortality only at higher concentrations (from 1,250 particles per cell), but the mortality is still very low (10%). No significant difference in cell mortality and TNF-α release was found between Al2O3 and ZrO2. Effects of Al2O3 and HDP at 4.5 μm were compared by measuring TNF-α release. Results showed that TNF-α release increases with particle concentrations and is higher with HDP than with Al2O3. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 600-607, 1998.
    Additional Material: 7 Ill.
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