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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 7 (1990), S. 16-31 
    ISSN: 0887-3585
    Keywords: BPTI ; dithiothreitol ; DTT-sensitive mutants ; protein folding ; random mutagenesis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: A genetic screening procedure has been developed to identify mutant forms of bovine pancreatic trypsin inhibitor (BPTI) that can fold to an active conformation but are inactivated more rapidly than the wild type protein. Small cultures of Escherichia coli containing plasmids with mutagenized BPTI genes were grown in microtiter plates, lysed, and treated with dithiothreitol (DTT). Under these conditions, unfolding and inactivation of wild-type protein has a half-time of about 10 hours. Variants of BPTI that are inactivated within 1 hour were identified by adding trypsin and a chromogenic substrate. Approximately 11,000 mutagenized clones were screened in this way and 75 clones that produce proteins that can fold but are inactivated by DTT were isolated. The genes coding for 68 “DTT-sensitive” mutant proteins were sequenced, and 25 different single amino acid substitutions at 15 of the 58 residues of the protein were identified. Most of the altered residues are largely buried in the core of the naive wild-type structure and are highly conserved among proteins homologous to BPTI. These results indicate that a large fraction of the sequence of the protein contributes to the kinetic stability of the active conformation, but it also appears that substitutions can be tolerated a most sites without completely preventing folding Because this genetics, further studies of the isolated mutants are expected to provide information about the roles of the altered residues in folding and unfolding.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 15 (1993), S. 322-329 
    ISSN: 0887-3585
    Keywords: unfolded proteins ; mutations ; BPTI ; gel electrophoresis ; disulfide-formation kinetics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The effects of amino acid replacements on the hydrodynamic volume of reduced and unfolded bovine pancreatic trypsin inhibitor (BPTI) have been examined by gel electrophoresis. The electrophoretic mobilities of the reduced forms of 46 BPTI variants were compared at room temperature in the absence of denaturants. The single substitutions examined include many different types of replacements at sites throughout the polypeptide, and, collectively, alter 22 of the 58 residues of the wild-type protein. The only substitutions found to alter the electrophoretic mobility of the reduced protein by more than ∼3% are those that change the net charge of the protein. For nine mutants, the rates of disulfide formation in the reduced protein were also examined and found to be very similar to that of the wild-type protein. These results suggest that any structure that may be present in the reduced protein is either relatively insensitive to amino acid replacements or does not greatly influence the averaged properties of the polypeptide chain. © 1993 Wiley-Liss, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2441-2451 
    ISSN: 0887-624X
    Keywords: fluorinated diaminobiphenyls ; poly(amic acid)s ; polyimides ; spin-coated films ; physical property characterization ; thermal expansion coefficient ; electronics applications ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two new fluorinated diamine monomers, 3,3′-diamino-5,5′-bis(trifluoromethyl)biphenyl and 3,3′-diamino-6,6′-bis(trifluoromethoxy)biphenyl, as well as a known nonfluorinated analog, 3,3′-diaminobiphenyl, were synthesized. Reaction of these diamines with rigid, highly rod-like dianhydrides produced poly(amic acid)s and polyimides, which were spin coated and thermally treated to produce polyimide films for evaluation in electronics applications. It was hoped that these polyimide films would exhibit an ideal combination of low thermal expansion, reduced water absorption, and low dielectric constant but with improved elongation due to the “crankshaft” nature of the 3,3′-biphenyl unit. Unlike polyimide films from analogous 4,4′-diaminobiphenyls, however, the 3,3′-diaminobiphenyl-based polyimides did not yield low in-plane thermal expansion coefficient in spin-coated films. In some cases high elongation was achieved, but with high thermal expansion. These new diamines may nevertheless find utility in polyimides and polyaramides for membrane, fiber, and other applications. Additionally, they may be useful in modifying the properties of polymer backbones via copolymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2441-2451, 1997
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0887-3585
    Keywords: electrospray ionization mass spectrometry ; noncovalent complexes ; protease ; integrase ; nucleocapsid protein ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Mass spectrometry (MS) with electrospray ionization (ESI) has shown utility for studying noncovalent protein complexes, as it offers advantages in sensitivity, speed, and mass accuracy. The stoichiometry of the binding partners can be easily deduced from the molecular weight measurement. In many examples of protein complexes, the gas phase-based measurement is consistent with the expected solution phase binding characteristics. This quality suggests the utility of ESI-MS for investigating solution phase molecular interactions. Complexes composed of proteins from the human immunodeficiency virus (HIV) have been studied using ESI-MS. Multiply charged protein dimers from HIV integrase catalytic core (F185K) and HIV protease have been observed. Furthermore, the ternary complex between HIV protease dimer and inhibitor pepstatin A was studied as a function of solution pH. Zinc binding to zinc finger-containing nucleocapsid protein (NCp7) and the NCp7-psi RNA 1:1 stoichiometry complex was also studied by ESI-MS. No protein-RNA complex was observed in the absence of zinc, consistent with the role of the zinc finger motifs for RNA binding. Proteins Suppl. 2:28-37, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 647-651 
    ISSN: 0935-6304
    Keywords: Supercritical fluid chromatography (SFC) ; Stationary-phase phenomena ; Mobile-phase modifier ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A significant uptake of supercritical mobile phases into immobilized stationary phases has been observed. The phase swelling effect has been evaluated hydrodynamically for SE-30, SE-54, and cyanopropyl silicone phases with respect to the mobile-phase density of supercritical butane, column temperature, and the presence of a polar retention moderator. Some kinetic and retention consequences of the swelling phenomena are discussed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 127-133 
    ISSN: 1040-7685
    Keywords: supercritical fluid chromatography ; retention mechanism ; selectivity tuning ; stationary phase swelling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: When temperature programming is performed in supercritical fluid chromatography (SFC) under conditions where the solute-mobile phase interactions are approximately fixed, that is, with the use of constant mobile phase density, then positive temperature programs can be used. The results resemble those in temperature-programmed gas chromatography (GC) except that chromatograms are compressed and solutes elute at lower temperatures. For a given temperature-program rat, the extent of this compression effect is controlled by the (fixed) mobile phase density. When a methylsilicone stationary phase is used along with CO2 mobile phase, the compression occurs with little change in selectivity. However, with a biphenyl-substituted polysiloxane stationary phase, selectivity shifts occur for some solutes (vs. hydrocarbons) as the density is varied. The effect is even greater and affects more solutes when a cyanopropyl-substituted polysiloxane stationary phase is used.This selectivity behavior differs from the temperature-dependent selectivity behavior known in GC. In GC only the forces between solutes and the stationary phase are involved. But in SFC, mobile phase interactions with both the solutes and the stationary phase are also important. The large selectivity shifts we observe in SFC most likely arise because of stationary phase swelling by the mobile phase. This is a function of the temperature and mobile phase density (or pressure) and can be tuned without changing the composition of the mobile phase. It is possible to use either temperature or density to adjust or fine-tune selectivity between a pair of solutes while using the other parameter to adjust retention of the pair.These experiments further suggest that GC is not only a special case of SFC (where the solute-mobile phase interactions are essentially zero), but that SFC possesses an additional and extremely powerful selectivity adjustment mechanism not available in GC.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectral data for the primary fragmentation of partially ethylated alditol acetates have been tabulated in order to allow easy reference for the identification of these polysaccharide derivatives. Sodium borodeuteride is used in all the aldose to alditol reductions, since the presence of a single deuterium label on C-1 greatly increases the information available in the mass spectrum and allows some identifications to be made which would not otherwise be possible. The primary fragmentations of these derivatives are analogous to those of the partially methylated alditol acetates, with each fragment shifted to a higher m/e value by fourteen mass units for each ether linkage contained in the fragment. The secondary fragmentation is also very similar, being characterized by the loss of acetic acid or ketene, or, less frequently, by the loss of ethanol or acetaldehyde. Coupled with the chromatographic retention time data for the partially ethylated alditol acetates tabulated elsewhere, the unambiguous mass spectral identification makes this derivative an excellent choice as a complementary derivative to the partially methylated alditol acetates for polysaccharide analysis. The utility of the partially ethylated alditol as a routine analytical derivative is further enhanced by the almost identical procedures required for synthesis of the ethyl and methyl derivatives. Through the combined use of these derivatives, most of the possible linkage isomers of the seven common aldoses of plant cell wall polysaccharides can be resolved, identified and quantitated.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 703-706 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A detector array has been designed which integrates all pulse sensing, data logging, control and interface circuitry on a single silicon chip. In conjunction with a microchannel-plate electron multiplier (MCP) the array can be used to measure dispersed spectra of ions, electrons and photons (UV and higher energies). In order to increase the sensitivity of the pulse sensing circuitry, non-standard steps are introduced into the fabrication process which increase cost and prototype development time. In the present work it is shown that by reducing the separation between the MCP output and the array to about 4.5 microns an improvement in performance is achieved which should enable the production of high performance devices using a standard fabrication process.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 441-449 
    ISSN: 1040-7685
    Keywords: open-tubular columns ; supercritical fluid chromatography ; retention ; selectivity ; pressure ; temperature ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied solute retention for n-hydrocarbons, (low-molecular-weight) polystyrenes, an ethoxylated surfactant, and a selectivity test mix on open-tubular columns with methyl-, biphenyl-, and cyanopropyl-substituted stationary phases for pressures up to 680 atm and temperatures up to 240°C. The solute elution range varied tremendously with column choice, with the least retentive stationary phases providing the highest elution range. However, the best resolution and largest analysis range were obtained with the most retentive stationary phase and the highest pressures. Increasing the temperatures above 160°C did not cause a large increase in elution pressure for the solutes used in this study. Exceptionally large shifts in selectivity with temperatures up to about 160°C occurred for the biphenyl and cyanopropyl stationary phases. The availability of pressures higher than 680 atm, coupled with adequately retentive stationary phases used at optimal temperatures, would further increase the analysis scope of opentubular supercritical fluid chromatography.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 5 (1993), S. 261-273 
    ISSN: 1040-7685
    Keywords: open-tubular columns ; supercritical fluid chromatography ; direct injection ; phase behavior ; critical mixture curves ; retention gap ; solvent effect ; phase-ratio focusing ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Open-tubular supercritical fluid chromatography (SFC) is a useful technique for many analyses, but is somewhat limited, in current practice, with respect to trace analysis of liquid samples. Direct injection of the volumes required for trace analysis with ordinary detectors creates a meter or more length of flooded zone and may lead to unacceptable band broadening. We studied solvent mass transfer on short, uncoated columns for several solvents forming Type I binary mixtures with CO2, and found evidence in the solvent peak shapes of distinct liquid and vapor phases, with the liquid present as a dynamically formed film. This study suggests that selecting an injection temperature and pressure to reduce, but not eliminate, the surface tension of the liquidvapor interface, and increasing the mobile phase velocity during injection increase the liquid film thickness and reduce the length of the resulting flooded zone. When a separate uncoated inlet tube (that is, a retention gap) is used to connect the injector with the column, decreasing the inlet tube radius improves the ratio of maximum effective injection volume to inlet tube volume.Just as in GC, dynamically formed films function as pseudo-stationary phases during injection. Without a liquid film, solutes can be transported by injection-solvent-modified mobile phase well beyond the length of a typical film, increasing the difficulty of refocusing the solutes before separation. Refocusing solutes from film-coated flooded zones is easily accomplished using either a solvent effect (specifically, solvent trapping) or phase-ratio focusing.We recommend the use of solvents with phase behavior like toluene and carbon tetrachloride, both of which form films at convenient temperatures and pressures. We discourage the use of solvents with phase behavior like n-pentane which tend to make single-phase, supercritical mixtures with CO2 under typical SFC injection conditions.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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