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  • Chemistry  (4)
  • 2015-2019
  • 1990-1994  (4)
  • 1994  (4)
  • 1
    Electronic Resource
    Electronic Resource
    Crystal structure and nmr conformation of a cyclic pseudotetrapeptide containing urethane backbone linkages (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 403-414 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Urethane bonds, derived from the hydroxyl group of the tyrosine side chain, have been investigated as a new type of amide bond mimetic in the design of pseudopeptides. The structure of a representative cyclic pseudotetrapeptide that consists of an  -  Ala  -  Tyr(urethane) Ala  -  Tyr (urethane) sequence fused into a rigid ring has been studied in the solid state by x-ray crystallography and in solution by two-dimensional nmr techniques. The cyclic pseudotetrapeptide has an oblong shape. The backbone urethane bonds assume a trans-trans conformation. The carbonyl groups in the ring have an alternating pattern of down, up, down, up with respect to the average ring plane. Solution nmr studies give observed nuclear Overhauser effects and coupling constants largely in agreement with the crystal structure. However, in solution the observed structure is likely to be conformationally averaged, and in the averaged structure, the urethane bond is perpendicular to the plane of the aromatic ring of the tyrosine, while in the crystal it is close to this plane. These differences may be explained by intermolecular hydrogen-bonding interactions. Four aspects of the conformation of the cyclic pseudotetrapeptide were investigated in detail: the tyrosine residue with the attached side-chain urethane bond (the tyrosine-urethane unit), the conformation of the two urethane backbone linkages, the conformation of the two conventional peptide bonds within this unusual ring structure, and the tight turns within the cyclic pseudotetrapeptide. The conformation of the tight turns present in the cyclic pseudotetrapeptide is very similar to that of a β-bend of type II. Intermolecular hydrogen bonding, joining adjacent layers of the cyclic pseudotetrapeptide in the solid state, resemble a parallel β-pleated sheet. The presence of these structural motifs in the cyclic pseudotetrapeptide indicates that the tyrosine urethane unit may find applications in peptide and protein engineering. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340312
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  • 2
    Electronic Resource
    Electronic Resource
    Photocrosslinked hydrogels based on copolymers of poly(ethylene glycol) and lysine (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 1271-1281 
    Details
    ISSN: 0887-624X
    Keywords: L-lysine ; poly(ether urethane) ; photocrosslinked ; poly(ethylene glycol) ; hydrogel (s) ; drug release ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A group of new, water-soluble poly(ether-urethane)s, derived from poly(ethylene glycol) and the amino acid L-lysine, provide pendent carboxylic acid groups along the polymer backbone at regular intervals. The carboxylic acid groups were utilized for the attachment of acrylate and methacrylate pendent chains (hydroxyethyl acrylate, hydroxyethyl methacrylate, aminoethyl methacrylate, and aminoethyl methacrylamide), leading to functionalized polymers. The pendent chains were attached via ester and/or amide bonds having different degrees of hydrolytic stability. The attachment reactions proceeded with high yields (up to 95%). The functionalized polymers were subsequently photopolymerized (UV irradiation) to obtain crosslinked hydrogels. Crosslinked membranes with the highest degree of mechanical strength were obtained when the crosslinking reaction was performed in dioxane with benzoin methyl ether (0.1 wt %) as the initiator. the crystallinity, thermomechanical properties, and hydrolytic stability of the crosslinked membranes were studied. All membranes were transparent and highly swellable (equilibrium water content: 64-88%). The tensile strength in the swollen state ranged from 0.15 to 1.09 MPa. Under physiological conditions (phosphate buffered water, 0.1M, pH 7.4, 37°C) the hydrolytic stability of the hydrogels varied depending on the bonds used in the attachment of the acrylate pendent chains: Hydrogels with hydroxyethyl acrylate pendent chains dissolved within 30 days, while hydrogels containing aminoethyl methacrylamide pendent chains remained unchanged throughout a 30 day period. Using high molecular weight FITC-dextrans as model compounds, complete release from the swollen hydrogels required between 60 and 150 h. Overall, the evaluation of poly(ethylene glycol)-lysine derived, photocrosslinked hydrogels indicated that these materials provide a range of potentially useful properties. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080320708
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  • 3
    Electronic Resource
    Electronic Resource
    Fabrication of composite hollow fibers for air separation (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 701-708 
    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: By using microporous polyacrylonitrile (PAN) hollow fibers as the substrate, we developed two types of composite fibers for air-separation. One was a poly(4-vinyl pyridine) (4-PVP)/(hexafluoro propane dianhydride)-durene (6FDA)/PAN composite hollow fiber, and the other was a 6FDA-3,5-diaminobenzonitrile/6FDA-durene/PAN composite hollow fiber. The asymmetric PAN fiber was prepared using dry-jet wet-spinning technology, and the deposition of a thin gutter layer of 6FDA-durene on PAN was carried out by prewetting PAN fibers with Fluorinert® before solution coating. The topcoating of a thin layer (200-300 Å) of PVP or 6FDA-3,5-diaminobenzonitrile on PAN/6FDA-durene fibers was conducted using a conventional solution coating method. The selectivity of 0.7% 4-PVP/2% 6F-durene/PAN composite fibers for O2/N2 was 5.6 with an O2 permeance of 32.2 × 10-6 cc(STP)/cm2 s cmHg, whereas the selectivity of 0.5% 6FDA-3,5-diaminobenzonitrile/2% 6F-durene/PAN fibers was 5.1 with an O2 permeance greater than 37.2 × 10-6 cc(STP)/cm2 s cmHg. Both fiber selectivities can be further improved by increasing the thicknesses of the selective layer. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070530520
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  • 4
    Electronic Resource
    Electronic Resource
    Evaluation of a series of tyrosine-derived polycarbonates as degradable biomaterials (1994)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 919-930 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A series of four polycarbonates derived from the ethyl, butyl, hexyl, and octyl esters of desaminotyrosyl-tyrosine was prepared by condensation polymerization. The resulting polymers had weight average molecular weights ranging from 120,000-450,000, and their chemical structure was confirmed by elemental analysis, nuclear magnetic resonance, and Fourier transform infrared spectroscopy. The polycarbonates were evaluated as degradable biomaterials. Their surface properties were determined by electron spectroscopy for chemical analysis, attenuated total reflectance-Fourier transformed infrared spectroscopy, and contact angle measurement. The degree of surface hydrophobicity was related to the length of the alkyl ester pendent chain. The tensile properties were dependent on the chemical structure of the polymers: For thin, solvent cast film specimens, the tensile modulus varied from 1.2-1.6 GPa, and the strength at break from 60-220 MPa. The degradation of polymeric films was followed in vitro by measuring changes in mechanical strength for up to 40 weeks, and the decrease in molecular weight and changes in surface chemistry for up to 80 weeks. The length of the pendent chain affected the degradation behavior and strength retention; the polymers with short pendent chains were more readily hydrolyzable. For sterilization, ethylene oxide treatment was less destructive, as judged by molecular weight retention, than γ-irradiation. Spin-cast films of all tested polycarbonates were not cytotoxic toward cultured rat lung fibroblasts. The cell response was influenced by the chemical structure of the polymer. The least hydrophobic polycarbonate (having a short ethyl ester pendent chain) was a more stimulating substrate for cell growth than the more hydrophobic polymers (carrying longer alkyl ester pendent chains).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820280811
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