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  • Chemistry  (40,868)
  • Wiley-Blackwell  (40,868)
  • American Chemical Society
  • American Meteorological Society
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  • 1
    Electronic Resource
    Electronic Resource
    Points to be considered in thermogravimetry (1993)
    Weinheim [u.a.] : Wiley-Blackwell
    Materials and Corrosion/Werkstoffe und Korrosion 44 (1993), S. 345-350 
    Details
    ISSN: 0947-5117
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Bei der Thermogravimetrie zu berücksichtigende HinweiseKontinuierliche Thermogravimetrie ist eine verbreitete Methode, um Werkstoffe in korrosiven Gasen bei hohen Temperaturen zu prüfen und um Kinetik und Mechanismen der Hochtemperaturkorrosion aufzuklären. Hier werden Empfehlungen zur Durchführung thermogravimetrischer Tests zusammengestellt, Hinweise gegeben betreffend Probengröße und -form, Oberflächenpräparation, Reaktionsrohr, Start des Experiments, besonders empfindliche Messungen und Gasströmung und -regelung. Die Veröffentlichung ist als Grundlage und Startpunkt für zu entwickelnde Richtlinien für die Hochtemperaturkorrosionsforschung gedacht.
    Notes: Continuous thermogravimetry is a common method to test materials in gaseous corrosive environments at high temperatures and to elucidate kinetics and mechanisms of high temperature corrosion. Recommendations how to conduct thermogravimetric tests are collected here, points to be considered including sample size and form, surface preparation, reaction chamber, starting procedure, sensitive measurements, gas supply and dosing. This study is meant as a starting foundation for establishing guidelines in high temperature corrosion research.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/maco.19930440805
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  • 2
    Electronic Resource
    Electronic Resource
    An XPS valence band study of alkane chains secondary structure (1994)
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 22 (1994), S. 507-510 
    Details
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Valence XPS studies of well oriented polyethylene mats, deposited on a gold substrate, provide direct evidence of the existence of the fold structure at the sample surface and confirm earlier suggestions that conformation is directly fingerprinted in that energy region of the spectra. These results also provide new insight into the origin of the valence XPS spectra differences, so far unexplained, of n-tridecane recorded in gas and solid phase.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/sia.7402201107
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  • 3
    Electronic Resource
    Electronic Resource
    Electrophoric labelling of nucleosides for sensitive analysis by negative ion chemical ionization gas chromatography/mass spectrometry (1992)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 21 (1992), S. 441-450 
    Details
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formation and analytical utility of several electrophone derivatives of native and oxidatively modified nucleosides of deoxythymidine and deoxyguanosine were studied. Derivatives include the incorporation of trimethylsilyl, acetyl or perfluoroacyl groups together with pentafluorobenzyl. Acetylation followed by pentafluorobenzylation was the most favourable method. In general, the combined information from the electron impact, positive ion chemical ionization and negative ion chemical ionization spectra was well suited for structure elucidation purposes. The acetyl-pentafluorobenzyl derivative of deoxythymidine was prepared in quantitative yield and was very sensitive on analysis by gas chromatography negative ion chemical ionization. Injection of 0.45 fmol of 3′,5′-bis(O-acetyl)-3-pentafluorobenzyl-deoxythymidine, in multiple ion detection experiments, gave a response with a signal-to-noise ratio larger than 10.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200210905
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  • 4
    Electronic Resource
    Electronic Resource
    Surface characterization of silanized glass fibers by labeling with environmentally sensitive fluorophores (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 375-384 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Glass fibers have been treated with γ-aminopropyl-triethoxysilane (APES) through different silanizating procedures, which include APES aqueous solutions and APES vapor adsorption. Transmission Fourier transform IR (FTIR) measurements have been performed on the silanized samples to characterize the silanization reaction. Dansyl-sulfonamide conjugates have then been formed by reaction of dansyl chloride in dimethylformamide solution with the amine functionality's immobilized on the glass fiber surface. Steady-state and time-resolved fluorescence measurements have been performed on dansylated samples. A dependence of the fluorescence intensity and the wavelength of the maximum emission on the silanization procedure has been observed. Good fits of the fluorescence decays of dansyl labels are found when biexponential functions are used for deconvolution, whereas the decay of dansylamides in fluid solution is single exponential. A two-state model for the solid solvent relaxation seems to apply for this samples. Several surface structural changes produced by the different silanization methods have been proposed. FTIR results support the conclusions drawn from fluorescence measurements. © 1996 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Simple dissolution-reaction model for enzymatic conversion of suspension of solid substrate (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 56 (1997), S. 433-440 
    Details
    ISSN: 0006-3592
    Keywords: simple dissolution-reaction model ; enzymatic conversion ; solid substrate suspension ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Although reactions in substrate suspension are employed in industry for several bioconversion processes, there appears to be no quantitative model available in the literature to rationalize the optimization of these processes. We present a simple model that incorporates the kinetics of substrate dissolution and a simultaneous enzymatic reaction. The model was tested in the α-chymotrypsin-catalyzed hydrolysis of an aqueous suspension of dimethyl benzylmethylmalonate to a homogeneous solution of enantiomerically pure monoester. This reaction occurs in the bulk phase, so catalysis by enzyme absorbed at the solid-liquid interface plays no role. The value of the parameters in the model (i.e., the mass transfer coefficient of substrate dissolution (kL), the substrate solubility, and the rate constant for the enzymatic reaction) were determined in separate experiments. Using these parameter values, the model gave a good quantitative prediction of the rate of the overall dissolution-reaction process. When the particle size distribution is known, kL may also be calculated instead. The model seems to be applicable also for other poorly soluble substrates, other enzymes, and other solvents. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 56: 433-440, 1997.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Letters to the editor (1992)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 38 (1992), S. 635-640 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690380421
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  • 7
    Electronic Resource
    Electronic Resource
    Effects of oxygen and nutrients limitation on ajmalicine production and related enzyme activities in high density cultures of Catharanthus roseus (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 461-468 
    Details
    ISSN: 0006-3592
    Keywords: Catharanthus roseus ; ajmalicine production ; enzyme activities ; dissolved oxygen ; nutrients concentration ; high density culture ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Oxygen and nutrient limitation was investigated in order to identify the origin of a lower specific ajmalicine production in Catharanthus roseus cultures at high cell densities in an induction medium. The effect of oxygen limitation was explored by comparing two identically aerated and agitated high cell density bioreactor cultures with dissolved oxygen (DO) concentration of 15% and 85% of air saturation, with respect to alkaloid formation and related enzymes activities. Oxygen had an evident effect on ajmalicine production: in the high DO cultures production was more than 5 times higher than in the low DO cultures. The difference in ajmalicine production between high and low DO could not be explained by the enzyme activity profiles. Moreover, the productivity in the high density culture could not restored to the level of a low density culture (at a high DO) by increasing the DO alone. The effect of nutrient limitation was studied with response surface methodology in shake flask cultures. Nutrient limitation could not be demonstrated to be responsible for the productivity loss. Alkaloid and enzyme measurements in the shake flask cultures supported previous findings that the tryptamine pathway may regulate alkaloid production, provided that the terpenoid pathway is sufficiently active. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260440409
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  • 8
    Electronic Resource
    Electronic Resource
    Relation between dissolved oxygen concentration and ajmalicine production rate in high-density cultures of Catharanthus roseus (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 45 (1995), S. 435-439 
    Details
    ISSN: 0006-3592
    Keywords: Catharanthus roseus ; ajmalicine production rate ; dissolved oxygen concentration ; kinetic model ; high-density culture ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The relation between dissolved oxygen (DO) and the ajmalicine production rate of Catharanthus roseus was investigated in 15-L tank reactors at constant stirrer speed and gas flow rate. Below a DO concentration of 29% of air saturation the ajmalicine production rate was less than 0.06 μmol/g/d. Above a DO of 43% the ajmalicine production rate was constant at 0.21 μmol/g/d. Between a DO of 29% and 43% there was a strong relation between the ajmalicine production rate and the DO concentration. After a period of at least 12 days at DO ≤29% the culture lacked the ability to adapt to a DO ≥57%. A kinetic equation is proposed for the relation between DO and the specific ajmalicine production rate. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260450508
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  • 9
    Electronic Resource
    Electronic Resource
    The role of glucose in ajmalicine production by catharanthus roseus cell cultures (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 47 (1995), S. 525-534 
    Details
    ISSN: 0006-3592
    Keywords: glucose ; osmotic pressure ; ajmalicine production ; catharanthus roseus ; kinetic model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The role of glucose in ajmalicine production by Catharanthus roseus was investigated in the second stage of a two-stage batch process. Activities of tryptophan decar-boxylate (TDC) and anthranilate synthase (AS), two enzymes In the pathway leading to ajmalicine, were higher after induction with 40 g/L glucose than after induction with 60 or 80 g/L glucose. Experiments with different media containing mixtures of glucose and the nonpermeating osmotic agent xylose, and using an already induced culture as inoculum, revealed that a minimum amount of glucose is required to support ajmalicine production after enzyme induction. This requirement was not an osmotic effect. The relation between the glucose concentration and the specific ajmalicine production rate, qp, was investigated in seven (fed-)batch cultures with constant glucose concentrations: 23, 29, 35, 53, 57, 75, and 98 g/L. In the cultures with a low glucose concentration (23, 29, and 35 g/L) the qp was 2.7-times higher than the cultures with 53 and 57 g/L, and almost six times higher than the cultures with a high glucose concentration (75 and 98 g/L). A glucose perturbation experiment (from 53 to 32 g/L) demonstrated that the ajmalicine production rate was adjusted without much delay. A kinetic equation is proposed for the relationship between the glucose concentration and qp. Differences in enzyme induction and ajmalicine production at different glucose levels could not be explained by the intracellular concentrations of glucose, fructose, sucrose, or starch. © 1995 John Wiley & Sons Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260470504
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetic analysis of enzymatic chiral resolution by progress curve evaluation (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 411-422 
    Details
    ISSN: 0006-3592
    Keywords: enzyme kinetics ; progress curve ; enantioselectivity ; covariance ; kinetic resolution ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The present study deals with kinetic modeling of enzyme-catalyzed reactions by integral progress curve analysis, and shows how to apply this technique to kinetic resolution of enantiomers. It is shown that kinetic parameters for both enantiomers and the enantioselectivity of the enzyme may be obtained from the progress curve measurement of a racemate only.A parameter estimation procedure has been established and it is shown that the covariance matrix of the obtained parameters is a useful statistical tool in the selection and verification of the model structure. Standard deviations calculated from this matrix have shown that progress curve analysis yields parameter values with high accuracies.Potential sources of systematic errors in (multiple) progress curve analysis are addressed in this article. Amongst these, the following needed to be dealt with: (1) the true initial substrate concentrations were obtained from the final amount of product experimentally measured (mass balancing); (2) systematic errors in the initial enzyme concentration were corrected by incorporating this variable in the fitting procedure as an extra parameter per curve; and (3) enzyme inactivation is included in the model and a first-order inactivation constant is determined.Experimental verification was carried out by continuous monitoring of the hydrolysis of ethyl 2-chloropropionate by carboxylesterase NP and the α-chymotrypsin-catalyzed hydrolysis of benzoylalanine mathyl ester in a pH-stat system. Kinetic parameter values were obtained with high accuracies and model predictions were in good agreement with independent measurements of enantiomeric excess values or literature data. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430509
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