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  • Polymer and Materials Science  (5)
  • Aircraft Design, Testing and Performance
  • Analytical Chemistry and Spectroscopy
  • Astronomy
  • SPACECRAFT PROPULSION AND POWER
  • 1995-1999  (5)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    A simple assay for screening translational activity of non-natural amino acids. Implications for polymer synthesis on messenger RNA templates (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 1267-1274 
    Details
    ISSN: 0887-624X
    Keywords: unnatural amino acids ; 5,5,5-trifluoroleucine ; azetidine-2-carboxylic acid ; thiazolidine-4-carboxylic acid ; mono-fluorophenylalanine (o,m,p) ; thienylalanine ; cellfree protein synthesis ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ability to incorporate unnatural amino acids into biologically synthesized proteins will greatly extend the impact of protein engineering on polymer materials science. The present report describes the use of a rapid cell-free assay to assess the incorporation potential of unnatural amino acids in Escherichia coli. The assay features a coupled transcription-translation system (‘Zubay system’) to screen incorporation of amino acid analogs into plasmid-encoded proteins. Activity estimates are based on the ability of an analog to compete with a radiolabeled natural amino acid, and toxicity effects are screened by monitoring incorporation of a second, unrelated amino acid. The assay was established with analogs known to be active in vivo, using a common bacterial expression vector as template DNA. Positive results were obtained with the leucine analog 5,5,5-trifluoroleucine, the proline analogs azetidine-2-carboxylic acid and thiazolidine-4-carboxylic acid, and three isomers of mono-fluorophenylalanine (o,m,p). No activity was observed for the phenylalanine analogs 2-thienylalanine and 3-thienylalanine. The results suggest that the cell-free assay will be a useful predictor of in vivo incorporation and a useful tool in the design and synthesis of genetically engineered materials. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080330809
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  • 2
    Electronic Resource
    Electronic Resource
    Visible light photopolymerization employing 2,4-diiodo-6-butoxy-3-fluorone and tetraorganylborate salts as photoinitiators (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 2817-2824 
    Details
    ISSN: 0887-624X
    Keywords: visible light photopolymerization ; tetraorganylborates ; fluorone dyes ; acrylic monomers ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several new tetraorganylborate salts have been synthesized and tested as coinitiators with 2,4-diiodo-6-butoxy-3-fluorone (DIBF) for the photopolymerization of acrylic monomer mixtures. The rate of photopolymerization has been found to be a function of chemical structure of the borates. Stability, solubility, and reactivity of these borates as coinitiators for photopolymerization have been investigated. Diphenyldialkylborates have been found to be the best among the tested coinitiators. © 1996 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis and study of iodonium borate salts as photoinitiators (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 36 (1998), S. 1667-1677 
    Details
    ISSN: 0887-624X
    Keywords: photoinitiator ; iodonium borate salts ; photoinduced radical polymerization ; fluorone dye ; visible polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Iodonium butyltriphenylborate salts (A—I+—Ar′Ph3B-—R), (=Bu) were found to be more efficient than iodonium tetraphenylborate salts (R=Ph) when used as photoinitiators for the polymerization of acrylates. Relative photodecomposition rates were also different. It was found from a study of the photoreaction of iodonium borate salts with a model monomer, methyl methacrylate, that iodonium butyltriphenylborate salts simultaneously produce a butyl radical from the borate anion and an aryl radical from the iodonium cation upon irradiation. Both radicals initiate polymerization. Iodonium tetraphenylborate salts were found to release an aryl radical, but only from the iodonium cation. Iodonium borate salts exhibit strong absorption below 300 nm with a tail absorption above 400 nm. Thus, iodonium butyltriphenyl borate salts are efficient photoinitiators even when used with visible light. When a photosensitizer such as 5,7-diiodo-3-butoxy-6-fluorone is employed, iodonium butyltriphenylborate salts are rendered much more efficient for visible light photopolymerization. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1667-1677, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Small structural ensembles for a 17-nucleotide mimic of the tRNA TΨC-loop via fitting dipolar relaxation rates with the quadratic programming algorithm (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 329-342 
    Details
    ISSN: 0006-3525
    Keywords: dynamic nmr refinement ; MD with time-averaged restraints ; PDQPRO ; quadratic programming algorithm ; TΨC-loop, tRNA ; tRNA (m5U54)-methyltransferase ; RNA/protein recognition ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solution structures are typically average structures determined with the help of nmr-derived distance and torsion angle information. However, when a biomolecule populates significantly different conformations, the average structure might be prone to artifacts, and other refinement strategies are necessary. For example, when experimental restraints are used in molecular dynamics simulations in a time-averaged fashion (MDtar), the experimental structural information does no longer need to be satisfied at each step of the simulation; instead, the whole trajectory must agree with the restraints. However, the resulting structural ensembles are large and not unique and it is not trivial to extract the essential dynamic features for a system. Here we demonstrate that large MDtar ensembles can be simplified substantially by reducing the number of members to just a few on the basis of adjusting the individual probabilities of the members with the PDQPRO program [N. B. Ulyanov et al. Biophysical Journal (1995), Vol. 68, p. 13]. This algorithm finds the global minimum for a search function that represents the best match of a given ensemble with the experimental dipolar interproton relaxation rates. We have applied this strategy to a 17-residue RNA hairpin, whose loop exhibited considerable flexibility evident from nmr data. This 17mer is a mimic of the TΨC-loop of tRNA, where nucleotide 54 is usually a ribosylthymidine. The methylation of U54, which is completely buried in transfer ribonucleic acid, is administered by tRNA (m5U54)-methyltransferase (RUMT). Since the 17mer is a good substrate for RUMT, we previously concluded that the flexibility of the 17mer's loop is a key to how RUMT gains access to the methylation site [L. J. Yao et al. Journal of Biomolecular NMR (1996) Vol. 9, p. 229]. Application of the PDQPRO algorithm to the previously acquired MDtar trajectories allowed us to reduce the number of conformations from several hundred to one major and five or six minor conformations with individual populations from ∼ 5% to ∼ 50% without any deterioration in the match with the experimental data. The major conformation exhibits a continuation of A-form helicity through part of the loop, involving C60 and U59. In this and most other conformations the methylation site in U54 is no longer buried. © 1998 John Wiley & Sons, Inc. Biopoly 46: 329-342, 1998
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Structure and properties of a photosensitive polyimide: Effect of photosensitive group (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 33 (1995), S. 453-465 
    Details
    ISSN: 0887-6266
    Keywords: photosensitive polyimide ; thermal imidization ; in-plane orientation ; microvoid ; mechanical properties ; optical properties ; dielectric constant ; residual stress ; water diffusion ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photosensitive poly(p-phenylene biphenylteracarboximide) (BPDA-PDA) precursor was synthesized by attaching photocross-linkable 2-(dimethylamino)ethyl methacrylate (DMAEM) monomer to its poly(amic acid) through acid/base complexation. The polyimide thin films were prepared by a conventional cast/softbake/thermal imidization process from the photosensitive precursors with various concentrations of DMAEM. The structure and properties of the polyimide films were investigated by small-angle and wide-angle x-ray scattering, refractive indices and birefringence analysis, residual stress and relaxation analysis, stress-strain analysis, and dynamic mechanical thermal analysis. In comparison with the polyimide film from the poly(amic acid), the films, which were imidized from the photosensitive precursors, exhibited a better molecular order and microstructure; however, they exhibited less molecular orientation in the film plane. Despite the enhancement in both the molecular order and microstructure, the film properties (i.e., mechanical properties, thermal expansion, residual stress, optical properties, dielectric constant, and water sorption) degraded overall due to both the decrease in molecular in-plane orientation and the formation of microvoids caused by the bulky photosensitive group during thermal imidization. That is, on one hand, the PSPI precursor formation provides an advantageous, direct patternability to the BPDA-PDA precursor, and on the other hand, it results in degraded properties to the resulting polyimide film. © 1995 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1995.090330314
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