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  • 1
    Electronic Resource
    Electronic Resource
    Solvent effects on biocatalysis in organic systems: Equilibrium position and rates of lipase catalyzed esterification (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 38 (1991), S. 1137-1143 
    Details
    ISSN: 0006-3592
    Keywords: organic-phase biocatalysis ; equillibrium ; reaction rates ; log P ; solvent choice ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260381004
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of immiscible organic solvents on activity/stability of native chymotrypsin and immobilized-stabilized derivatives (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 39 (1992), S. 75-84 
    Details
    ISSN: 0006-3592
    Keywords: chymotrypsin ; enzymes in water-immiscible solvents ; effect of phase interface on enzymes ; fully dispersed enzyme in biphasic system ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have developed different activity/stability tests to evaluate the possibilities of fully dispersed chymotrypsin derivatives as industrial catalysts in biphasic systems. We have tested different immiscible organic solvents (log P ranged from 0.65 to 2.8) and used different enzyme derivatives (soluble chymotrypsin and one-point and multipoint covalent attached derivatives). Special emphasis has been given to the role of the “exact composition of the aqueous phase.”High phosphate concentrations largely protect every hymotrypsin derivative from the distorting effects of dissolved solvent molecules. The effects on the activity and stability of soluble chymotrypsin due to saturating solvent concentrations in an aqueous solution, and the much more severe effects of contact with the phase interface in a stirred biphasic system, all show the opposite trend for the influence of solvent polarity to that generally observed for biocatalysts. For example, deleterious effects decline in the order chloroform, dichloromethane, ethyl acetate. On the contrary, with or without stirring, our stabilized chymotrypsin-agarose derivatives are much more stable against these water-immiscible solvents, and their relative effects follow the normal trend. From these integrated activity and stability tests we can conclude that fully dispersed immobilized-stabilized derivatives seem to be an interesting alternative to develop industrial biphasic processes catalyzed by chymotrypsin.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260390112
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  • 3
    Electronic Resource
    Electronic Resource
    The equilibrium and kinetics of N-acetyl-tryptophan phenylethyl ester synthesis by agarose-chymotrypsin in organic media (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 1092-1096 
    Details
    ISSN: 0006-3592
    Keywords: agarose-chymotrypsin ; enzymes in organic media ; esterification ; peptide synthesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The synthesis of N-acetyl tryptophan phenylethyl ester in organic media is catalyzed by suspended agarose beads with multipoint covalently attached chymotrypsin. A dilute aqueous phase is trapped within the gel beads and may be manipulated separately from the organic phase. The equilibrium position becomes more favorable as the solvent polarity decreases, with Keq increasing 38 times between 2-butanone and 1,1,1-trichloroethane. The more apolar solvents also give faster kinetics. Addition of cosolvents (up to 10% dimethylformamide or 20% acetonitrile) does not affect the rate but does substantially reduce the equilibrium yield, presumably also by making the organic phase more polar. With trichloroethane as solvent the enzyme appears to be kinetically saturated with 1M phenylethanol. Doubling this concentration also does not cause the expected increase in equilibrium conversion, probably again because Keq is reduced in the more polar organic phase. Increased temperature raises the reaction rate as expected but has little effect on the equilibrium. © 1992 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260400913
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  • 4
    Electronic Resource
    Electronic Resource
    Solvation of CBZ-amino acid nitrophenyl esters in organic media and the kinetics of their transesterification by subtilisin (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 1081-1086 
    Details
    ISSN: 0006-3592
    Keywords: solvation ; organic media ; kinetics ; subtilisin ; thermodynamics ; solubility ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Subtilisin Carlsberg adsorbed on silica particles has been used to catalyze the transesterification of CBZ-Ala-ONp and CBZ-Leu-ONp with 1-butanol in organic systems preequilibrated to water activity of 0.93. Initial reaction rates are conveniently followed by extraction of the released nitrophenol into an alkaline aqueous phase. Kinetic parameters were determined for varied ester concentrations in toluene, isopropyl ether, and hexane. The effect of solvent on substrate solvation was determined by solubility measurements. Much of the observed effect of solvent on Vm/Km may be accounted for by solvation differences. The residual effect of solvent on Km, after discounting solvation differences, is completely opposite to the apparent trend. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260431111
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  • 5
    Electronic Resource
    Electronic Resource
    Immiscible organic solvent inactivation of urease, chymotrypsin, lipase, and ribonuclease: Separation of dissolved solvent and interfacial effects (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 1355-1361 
    Details
    ISSN: 0006-3592
    Keywords: enzyme inactivation ; immiscible organic solvents ; interfacial area ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new technique with controlled interface generation allows separation and quantitation of enzyme inactivation by both solvent/aqueous interface and dissolved solvent. This has now been used in n-butanol, isopropylether, 2-octanone, n-hexane, n-butylbenzene, and n-tridecane. Ribonuclease was stable with all the solvent/aqueous interfaces studied. Chymotrypsin was mainly inactivated by the more hydrophobic solvent/aqueous interfaces, whereas lipase was only inactivated by the less hydrophobic solvent/aqueous interfaces. Urease was inactivated by some interfaces, but not all, without an obvious trend. Thus, the commonly expected simple relationship with solvent polarity (e.g., log P) does not apply when interfacial inactivation is determined specifically. Greater dissolved solvent inactivation occurred with the more polar solvents, though only a general trend was apparent with log P. A better correlation was noted with the Hilde-brand solubility parameter. Interfacial effects are discussed with reference to enzyme molecular weight, denaturation temperature, hydrophobicity, and adiabatic compressibility. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260441112
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of water and enzyme concentration on thermolysin-catalyzed solid-to-solid peptide synthesis (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 59 (1998), S. 68-72 
    Details
    ISSN: 0006-3592
    Keywords: enzymatic ; solid-to-solid conversion ; peptide synthesis ; proteases ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We have studied a thermolysin-catalyzed solid-to-solid dipeptide synthesis using equimolar amounts of Z-Gln-OH and H-Leu-NH2 as model substrates. The high substrate concentrations make this an effective alternative to enzymatic peptide synthesis in organic solvents. Water content was varied in the range of 0 to 600 mL water per mol substrate and enzyme concentration in the range of 0.5 to 10 g/mol of substrates. High yields around 80% conversion and initial rates from 5 to 20 mmol s-1 kg-1 were achieved. The initial rate increases 10-fold on reducing the water content, to reach a pronounced optimum at 40 mL water per mol substrate. Below this, the rate falls to much lower values in a system with no added water, and to zero in a rigorously dried system. This behavior is discussed in terms of two factors: At higher water contents the system is mass transfer limited (as shown by varying enzyme content), and the diffusion distances required vary. At low water levels, effects reflect the stimulation of the enzymatic activity by water. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:68-72, 1998.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Inactivation of enzymes by organic solvents: New technique with well-defined interfacial area (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 43 (1994), S. 331-336 
    Details
    ISSN: 0006-3592
    Keywords: enzyme inactivation ; organic solvents ; urease ; interfacial area ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A liquid-liquid bubble column apparatus allows exposure of enzyme solutions to water-immiscible organic solvents with a known total interfacial area and welldefined time scales and flow. It allows clear distinction of the different classes of inactivation mechanism. With urease as a model enzyme, octan-2-one and butylbenzene act only through the effects of solvent molecules dissolved in the aqueous phase, giving first-order inactivation at 0.34 and 0.21 h-1, respectively. Hexane and tridecane act only through exposure to the interface. The amount of urease inactivated is proportional to the total area of interface exposed, rather than to elapsed time, and may be characterized by a rate of about 0.5 μkat m-2. This is consistent with the formation and (partial) inactivation of a complete adsorbed monolayer of protein. With butan-1-ol, both mechanisms contribute significantly to the observed inactivation. The presence of O2 increases the rate of interfacial inactivation, but not that by dissolved solvent. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260430410
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  • 8
    Electronic Resource
    Electronic Resource
    Solvent selection for biocatalysis in mainly organic systems: Predictions of effects on equilibrium position (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 35 (1990), S. 691-701 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Predictions may be made for the influence of solvent choice on the equilibrium position of biocatalyzed reactions, based on data for the liquid-liquid distribution of the reactants. The most reliable predictions are probably for dilute systems, based on partition coefficients or correlations derived from them. The effective equilibrium constant for esterification reactions is predicted to alter by more than four orders of magnitude on changing between different water-immiscible solvents. The equilibrium constant correlates well with the solubility of water in the solvent, and is most favorable for synthesis in the least polar solvents (aliphatic hydrocarbons). Similar effects seem to apply for other reactions, including oxidation of alcohols and hydrolysis of chlorides. Predictions can be made for nondilute systems using the UNIFAC system of group contributions, but the reliability of these is more questionable.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260350706
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  • 9
    Electronic Resource
    Electronic Resource
    How dry are anhydrous enzymes? Measurement of residual and buried 18O-labeled water molecules using mass spectrometry (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 313-321 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: There is continual debate over the central role of water in protein folding, structure, stability, and dynamics. Catalytic activity has been demonstrated in organic media with, apparently “anhydrous” enzymes. Hence there is considerable discussion over whether there are a few residual water molecules or if the enzymes are demonstrating activity in the complete absence of water. Here we present measurements designed to test this hypothesis based on the detection of 18O-labeled water by mass spectrometry. This extremely sensitive technique avoids many of the potential errors associated with published methods for measuring water content such as gravimetry or Karl Fischer titrations. We have also explored the mass spectrometric detection of 2H-enriched water and found that lyophilization of deuteron-labeled protein can lead to extensive loss of the isotopic label during the drying process.“Anhydrous” protein was produced by extended drying, over P2O5, of lyophilized powders hydrated through the vapor phase with 18O-labeled water. Redissolution in standard water released the remaining protein-bound 18O-labeled water molecules, and the isotopic enrichment of the water was used to calculate the number of bound molecules per mole of protein. In the cases of lysozyme and subtilisin Carlsberg, 4 ± 2 and 15 ± 2 waters per mole were found, respectively. Comparisons with crystal structures showed these values correspond closely to the expected number of buried water molecules in these proteins. This is consistent with the idea that water physically entrapped within the rigid protein structure is retained but all the other more accessible surface-bound hydration molecules can be removed by the drying process. Such anhydrous subtilisin Carlsberg preparations have been found to be weakly catalytic and therefore it appears that additional water molecules on the surface of the enzyme are not essential for this level of enzyme activity. © 1997 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Protease-Catalyzed peptide synthesis in low-water organic two-phase systems and problems affecting it (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 33 (1989), S. 1489-1494 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: No. Abstract.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260331117
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