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  • 1
    Electronic Resource
    Electronic Resource
    Orientation and relaxation of nonlinear elastic dumbbells in electric fields: Modeling transient electric birefringence (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5943-5949 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The orientation and extension of a finitely extensible nonlinearly elastic (FENE) dumbbell in an electric field is analyzed to model the nonlinear phenomena observed during orientation and relaxation of flexible polymer molecules in transient electric birefringence measurements. In the model the dumbbell interacts with the electric field via an induced dipole with a dipole moment proportional to the end-to-end separation of the dumbbell. The electric field produces a strong "elongational'' deformation of the molecule which has analogies with the deformations produced by elongational flow. The steady state birefringence, as a function of field strength, is calculated in two ways: first using matched expansions around low and high field conditions, and then using Peterlin's approximation of preaveraging the connector force law. Both techniques yield similar results: Kerr law behavior is observed at low field strengths and saturation of birefringence at high field strengths. Birefringence relaxation after the field is removed shows a strong field dependence on the initial rate of relaxation. Previously proposed means of analyzing birefringence relaxation data for flexible molecules are discussed in light of this observation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455545
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  • 2
    Electronic Resource
    Electronic Resource
    Transient electric birefringence of flexible polymers: Orientation and relaxation dynamics (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 3212-3219 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The orientation and relaxation dynamics of flexible polymers in an electric field is analyzed by following the change in electric birefringence with time. The polymer chain is represented by two beads (dipole) connected by a Hookean spring and interacts with the electric field through a local induced dipole which is proportional to the end-to-end distance between the beads. Equations of motion are written for the beads taking into account (a) the hydrodynamic drag force, (b) the Brownian force, (c) the spring force, and (d) the electric force acting on the molecule. The electric field produces a strong anisotropic orientation of the polymer chain. Thus, equations are derived and analytically solved to yield the time dependence of the rise of birefringence in the electric field, the relaxation of the birefringence from a nonequilibrium state, and the change in the mean-squared end-to-end distance of the molecule with time. The dynamics are found to be governed by the dimensionless number μ0E2/H, where μ0 is a constant related to the polarizability of the molecule, E is the electric field strength, and H the Hookean spring constant. A merit of this analysis lies in the fact that expressions for the time course of the birefringence rise in the presence of an orienting field of strength E as well as relaxation in the presence of a reduced electric field, Er (Er〈E) can be readily derived; hence cases other than the field-free decay (Er=0) can be interpreted. Moreover, for a biological system, a state of equilibrium with Er=0 may never be reached. Finally, the field dependence of the birefringence and the orientation and relaxation time constants has been obtained using the model and comparison of the steady state and relaxation behavior of Hookean and finitely extensible nonlinear elastic (FENE) polymer chains has been carried out. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470253
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  • 3
    Electronic Resource
    Electronic Resource
    Application of continuous zone electrophoresis to preparative separation of proteins (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 42 (1993), S. 829-835 
    Details
    ISSN: 0006-3592
    Keywords: preparative separation ; proteins ; continuous zone electrophoresis ; ion-exchange chromatography ; surface charge ; electrophoretic mobility ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A comprehensive study of the application of continuous zone electrophoresis to preparative separation of proteins in free solution is presented. First, the influence of electric field strength, buffer residence time in the chamber, sample flow rate, and sample concentration on separation resolution and throughput were studied. Using multiple injections of sample into the electrophoresis chamber, a throughput of 500 mg protein/h was achieved for partially purified model proteins. Experiments on Escherichia coli crude extracts yielded a fivefold purification of β-galactosidase along with a simultaneous separation of proteins from cell debris in a single step. Experiments correlating the electrophoretic mobility in continuous electrophoresis with the elution behavior in ion-exchange chromatography were performed on more than a dozen proteins which conclusively showed that separation of proteins in continuous zone electrophoresis is governed by net surface charge. Based on these results, the fraction numbers in which the proteins eluted could be correctly predicted. Proteins and enzymes with differences 〉0.5 M elution molarities in ion-exchange chromatography were separated by continuous zone electrophoresis on a preparative scale (mg/h or g/h) with 〉90% recovery. This corresponds to a preparative scale separation of proteins and enzymes which differ in apparent electrophoretic mobility by only 0.70 × 10-5 cm2/V · s. © 1993 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260420707
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  • 4
    Electronic Resource
    Electronic Resource
    A rapid method for determining kinetic parameters of enzymes exhibiting nonlinear thermal inactivation bahavior (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 49 (1996), S. 106-110 
    Details
    ISSN: 0006-3592
    Keywords: inactivation ; thermal inactivation ; enzymes ; alcohol dehydrogenase ; kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A rapid method is developed to analyze the kinetics of thermal inactivation of enzymes that exhibit a nonlinear biphasic log(activity)-time relationship. Thermal destruction experiments on alcohol dehydrogenase from baker's yeast demonstrate the applicability of the method. The method is based on physical considerations (as opposed to mathematical curve fitting/regression methods) and also serves as a quick check of results obtained using nonlinear regression. It is superior to fitting nonlinear enzyme inactivation data by first-order kinetics or taking the initial and final slopes of the inactivation data. In fact, the method is of general validity and can be applied to any decay process that can be represented by a sum of exponentials. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Separation of enzymes from microorganism crude extracts by free-flow zone electrophoresis (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 51 (1996), S. 15-22 
    Details
    ISSN: 0006-3592
    Keywords: preparative separation ; continuous ; free-flow zone electrophoresis ; electrophoretic mobility ; net charge ; enzymes ; proteins ; crude extract ; cell debris ; Candida boidinii ; Escherichia coli ; formate dehydrogenase ; formaldehyde dehydrogenase ; methanol oxidase ; β-galactosidase ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Continuous, single-step, state-of-the-art preparative separations of enzymes from microorganism crude extracts by free-flow zone electrophoresis are presented. In the first example, the enzymes formate dehydrogenase, formaldehyde dehydrogenase, and methanol oxidase were continuously separated from Candida boidinii crude extract. Yields of 85% to 95% and purification factors between 3 and 7 were obtained along with a simultaneous separation of the finer cell debris from the enzymes. Using multiple injections of sample, a throughput of 46.2 mg protein/h was recorded. In the second example, a fivefold purification of β-galactosidase from Escherichia coli was achieved along with complete, simultaneous cell debris separation from the enzyme. The yield of the enzyme was greater than 90%. The preparative free-flow zone electrophoresis experiments were run continuously for a period of 12 h and the separations were found to be stable; i.e., the enzymes and the cell debris eluted at their respective fraction numbers during the entire period. In both examples, choice of the type of buffer played a critical role and had to be investigated and optimized experimentally. Scale-up aspects of the separations are also discussed. Recently, by comparison of free-flow zone electrophoresis with ion-exchange chromatography, we have presented evidence that free-flow electrophoresis separations are governed by net surface charge (S. Nath et al., Biotechnol. Bioeng. 1993, 42: 829-835). Here, we offer further confirmation of this evidence by comparison of preparative free-flow zone electrophoresis experiments at various pHs on a mixture of two model proteins with analytical electrophoretic titration curves of the proteins. We are thus in a position to predict separations in free-flow zone electrophoresis. © 1996 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Forced oscillations in continuous flow stirred tank reactors with nonlinear step growth polymerization (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 30 (1985), S. 557-569 
    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: The self-step growth polymerization of RAf monomers in homogeneous, continuous flow stirred tank reactors (HCSTRs) is simulated under conditions of periodic feed concentration (with frequency ω and amplitude α). By having periodic operation, the polydispersity index of the polymer is found to increase by about 35% over the values at steady state. Periodic operation of HCSTRs is found to lead to gelation only for certain values of the frequency and the dimensionless residence time τ*. Gelling envelopes have been obtained to give conditions under which HCSTRs should be operated. These envelopes can be described in terms of two critical dimensionless residence times, τc,1* and τc,2* such that nongelling operation is always ensured when τ* 〈 τc,1*. For τ* 〉 τc,2*, periodic operation always leads to gelation, and HCSTRs cannot be used. For τc,1* 〈 τ* 〈 τc,2*, the gelling behavior is found to depend on the functionality f, amplitude α, and the dimensionless residence time τ*.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1985.070300209
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  • 7
    Electronic Resource
    Electronic Resource
    Separation of enzymes from Candida boidinii crude extract by continuous flow zone electrophoresis (1990)
    Weinheim : Wiley-Blackwell
    Electrophoresis 11 (1990), S. 937-941 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Separation of the enzymes formate dehydrogenase, formaldehyde dehydrogenase and methanol oxidase from Candida boidinii crude extract has been explored using continuous flow zone electrophoresis in the VaP-22 and the scaled-up VaP-220 electrophoresis apparatus. Yields up to 95 % and purification factors between 3 and 7 were obtained, together with separation of cell debris from the enzymes. Multiple injections of sample were used to obtain a protein throughput of 46.2 mg/h in the VaP-22. A tenfold higher throughput was achieved using the VaP-220. Correlation of the electrophoretic mobility in continuous flow zone electrophoresis with the elution behavior in ion-exchange chromatography confirmed the primary role of net surface charge in the separation of biological molecules. Proteins and enzymes with differences 〉 0.05 M elution molarities in ion-exchange chromatography can be separated. This corresponds to a preparative scale (mg/h or g/h) separation of proteins and enzymes whose difference in apparent electrophoretic mobility is 〉 0.70 x 10-5cm2/(V.s).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150111110
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  • 8
    Electronic Resource
    Electronic Resource
    Correlation of migration behavior in free-flow zone electrophoresis and electrophoretic titration curve (1990)
    Weinheim : Wiley-Blackwell
    Electrophoresis 11 (1990), S. 612-616 
    Details
    ISSN: 0173-0835
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The correlation of electrophoretic migration behavior in free-flow zone electrophoresis (FFZE) and electrophoretic titration curve (ETC) has been explored. It is shown that the ETC of a protein or a mixture of proteins can be used to predict the fraction numbers at which those proteins elute in a preparative scale FFZE experiment. The ETC is a quick and effective way to choose optimal buffer conditions in FFZE. FFZE is employed to determine the isoelectric points (pI) of proteins whose pIs lie beyond the range of IEF 3-9 gels. It is found that separations in FFZE are governed by the net surface charge of the proteins.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150110805
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  • 9
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    Transient electric birefringence of flexible polymers: Orientation and relaxation dynamics (1995)
    American Institute of Physics
    Details
    Publication Date: 1995-08-22
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics
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  • 10
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    Orientation and relaxation of nonlinear elastic dumbbells in electric fields: Modeling transient electric birefringence (1988)
    American Institute of Physics
    Details
    Publication Date: 1988-11-01
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics
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