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  • Chemistry  (3)
  • disintegration time  (1)
  • 1985-1989  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Kinetics of Release from Enteric-Coated Tablets (1988)
    Springer
    Pharmaceutical research 5 (1988), S. 550-565 
    Details
    ISSN: 1573-904X
    Keywords: Enteric coating ; release kinetics ; film model ; disintegration time ; formulation design
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Controlled and localized release of drugs in the intestine can be achieved by enteric coating. The design of enteric-coated tablets has so far remained empirical, in part because of the lack of a quantitative description of the drug release kinetics. In this paper, a mathematical model is presented that describes the dissolution of the polymer coating and release kinetics of weakly acidic drugs from enteric-coated tablets in buffered media. This model can also be used to predict the time of onset of core disintegration. The model assumes that the release rate is limited by diffusion, and furthermore, all the reactions are considered as reversible and instantaneous. Dissolution and reaction are assumed to take place in the polymer layer and a hypothetical stagnant liquid film adjacent to the polymer layer (the classical film theory approach). The dissolution of the enteric coating is found to depend on the intrinsic solubilities and pK a's of the drug and polymer and the medium properties. The release rate of the drug is found to depend on the intrinsic solubilities and pK a's of drug and polymer, the medium properties, i.e., pH and buffer capacity, and a mass transfer coefficient. Explicit relationships between the release rates and all these factors are derived. Successful prediction of experimental data indicates that the model provides an adequate description of release from enteric coated tablets. Limitations of the model and its potential application to the design of appropriate in vitro testing conditions and to the formulation of enteric coated tablets are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1015937912504
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  • 2
    Electronic Resource
    Electronic Resource
    Escherichia coil growth dynamics: A three-pool biochemically based description (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 31 (1988), S. 102-116 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A three-pool growth model of an individual Escherichia coli cell is described herein. The model is based on a previously developed chemically structured complex single cell growth model. The reduction in model complexity and the identification of the essential modes of motion, over the time scale of growth, is achieved by temporal decomposition and analysis of hierarchy in relaxation times. The three-pool model faithfully simulates the changes in cell size, cell shape, cell macromolecular composition, DNA initiation and termination periods, and the dependence of cell growth under abiotic glucose limitation. The predictions made by the reduced model compare favorably with both the experimental data and those of the full single cell model (SCM) without any parameter adjustments. The three-pool model has very few significant parameters and has the potential to find immediate practical use in bioreactor design and process control strategies. The model development illustrates the use of modal analysis to yield reduced physiologically realistic dynamic model of complex microbial system such as E. coll.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260310203
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  • 3
    Electronic Resource
    Electronic Resource
    On the dynamic order of structured Escherichia coli growth models (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 789-792 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Reliable dynamic descriptions of cellular growth are important for many practical applications including bioreactor design and control. A chemically structured growth model of Escherichia coli has been formulated and herein we focus on finding the essential dynamic order of the metabolic part of this model. Standard linear analysis is applied and the main finding is that the model contains three essential modes of motion over the time scale of growth. The doubling time is successfully predicted from an unstable growth motion and the metabolite composition of the three modes of motion suggests that only a three pool metabolic model is necessary. The three pools correspond to important groups of macromolecules; protein, nucleic acids and cell wall constituents.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260290623
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  • 4
    Electronic Resource
    Electronic Resource
    Control of interspecies electron transfer flow during anaerobic digestion: Dynamic diffusion reaction models for hydrogen gas transfer in microbial flocs (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 33 (1989), S. 745-757 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Dynamic reaction diffusion models were used to analyze the consequences of aggregation for syntrophic reactions in methanogenic ecosystems. Flocs from a whey digestor were used to measure all model parameters under the in situ conditions of a particular defined biological system. Fermentation simulations without adjustable parameters could precisely predict the kinetics of H2 gas production of digestor flocs during syntrophic methanogenesis from ethanol. The results demonstrated a kinetic compartmentalization of H2 metabolism inside the flocs. The interspecies electron transfer reaction was mildly diffusion controlled. The H2 gas profiles across the flocs showed high H 2 concentrations inside the flocs at any time. Simulations of the syntrophic metabolism at low substrate concentrations such as in digestors or sediments showed that it is impossible to achieve high H2 gas turnovers at simultaneously low steady-state H2 concentrations. This showed a mechanistic contradiction in the concept of postulated low H2 microenvironments for the anaerobic digestion process. The results of the computer experiments support the conclusion that syntrophic H2 production may only be a side reaction of H2 independent interspecies electron transfer in methanogenic ecosystems.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260330612
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