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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of low-molecular-weight oligomers in recycled poly(ethylene terephthalate) (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 225 (1995), S. 109-122 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Poly(ethylenterephthalat)-(PET)-Rezyklat aus gebrauchten Getränkeflaschen wurde bei 150-220°C im Vakuum behandelt oder bei mehreren Temperaturen mit zwei unterschiedlichen Durchsatzgeschwindigkeiten extrudiert. Nach anschließender Extraktion wurden die erhaltenen niedermolekularen Verbindungen mittels Hochleistungs-Flüs-sigchromatographie (HPLC), Größenausschlußchromatographie (SEC) und Massenspektrometrie mit chemischer Ionisierung (DCI/MS) untersucht. Die Verteilung von cyclischen und linearen Oligomeren mit Polymerisationsgraden von 2 bis 6 im Extrakt wurde bestimmt. Als Folge der Vakuumbehandlung des PET nimmt der Oligomergehalt mit steigenden Temperaturen ab. Umgekehrt führt die Extrusion bei ansteigenden Temperaturen (ebenso bei längeren Aufbewahrungszeiten) zu höheren Oligomerkon-zentrationen. Außerdem wurden bei zunehmenden Aufbewahrungstemperaturen und -zeiten breitere Molekulargewichtsverteilungen beobachtet, d. h. es wurden in zunehmendem Maße größere Ringe und längere Ketten gebildet. Eine bedeutende Menge an Oligomeren mit mittlerem Molekulargewicht wurde ebenfalls nachgewiesen.
    Notes: Low-molecular-weight compounds extracted from recycled poly(ethylene terephthalate) (PET) from post-consumer soft-drink bottles, treated at 150-220°C in vacuo or extruded at several temperatures and two different mass flow rates, were characterized by high performance liquid chromatography (HPLC), size exclusion chromatography (SEC) and desorption chemical ionization/mass spectrometry (DCI/MS). Among these products, cyclic and linear oligomers (polymerization degree 2-6) were identified, and their distribution was determined.As a consequence of vacuum treatment of PET, the overall oligomer content decreases with increasing temperatures. Conversely, the extrusion at crescent temperatures causes an increase of the oligomer concentration; the same effect was observed by increasing the residence time. A further effect was represented by the enlargement of molecular weight distributions, i.e. larger rings and longer chains were formed in greater amounts at higher temperatures and residence times; a significant fraction of medium-molecular-weight oligomers (M̄n = 1400-1900) was also formed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052250110
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  • 2
    Electronic Resource
    Electronic Resource
    Preferred conformation of the terminally blocked (Aib)10 homo-oligopeptide: A long, regular 310-helixThis is part 229 of the Linear Oligopeptides series. For part 228, see Ref. 1. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 129-138 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decapeptide pBrBz- (Aib)10-OtBu, synthesized by the 5(4H)-oxazolone method, crystallizes in the monoclinic space group C2/c with a = 43.901(2), b = 9.289(2), and c = 34.746(3) A; β = 114.69(3)°; and Z = 8. The crystals contain one molecule of water associated with each peptide. The structure has been solved by the Patterson method and refined to an R value of 0.073 for 6819 observed reflections. The peptide adopts a regular 310-helical structure stabilized by eight N—H … O=C intramolecular 1 ← 4 (or C10) H bonds. This study has allowed us to characterize this important peptide secondary structure in great detail. The crystal-state conformation agrees well with proposals made on the basis of an ir absorption and 1H-nmr study in solution.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360310112
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis and biological activity of tripeptide FR113680 analogues containing unconventional amino acidsSymbols and abbrevations are in accord with recommendations from Ref. 1. (1995)
    New York : Wiley-Blackwell
    Biopolymers 36 (1995), S. 409-414 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to further develop structure-activity relationships and to get information about the biological active conformations we synthetized analogues tripeptide to the FR 113680 [Ac- Thr-D-Trp(CHO)-PheNMeBzl; Ac: acethyl], in which the phenylalanine residue was replaced by unconventional amino acids [1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic); (3aS, 7aS)-octahydroindole-2-carboxylic acid (Oic); (S,S,S)-2-azabiciclo[3.3.0]octane-3-carboxylic acid (Aoc); 3-(1′-naphthyl) alanine (Nap) phenylglicine (Phg); thienylalanine (Thi)]. The biological activity of the peptides was performed on guinea pig ileumfar neurokinin 1 (NK-1) and on rat colon for neurokinin 2 (NK-2). In particular, the replacement of the Phe3 by the Oic (8a) gave an higher antagonist activity in both NK-1 and NK-2 receptors, but no improvement in selectivity with respect to reference tripeptide (FR113680) The compound (8a) represent the first example of highly potent peptides that do not contain an aromatic mi no acid of the third position as had been previously considered essential. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360360404
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis and antinociceptive activity of peptides related to interleukin-1β193-195 Lys-Pro-Thr (1996)
    New York : Wiley-Blackwell
    Biopolymers 40 (1996), S. 479-484 
    Details
    ISSN: 0006-3525
    Keywords: structure-activity relationships ; analgesic peptides ; antinociceptive activity ; interleukin-1β193-195 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To obtain information about the structure-activity relationships of analgesic peptides, we modified the previously reported tripeptide, H-Lys-Pro-Thr-OH (C). The proline part in C was replaced with various analogues of unconventional amino acids {(3aS, 7aS)-octahydroindole-2-carboxylic acid (Oic), (S,S,S,)-2-azabiciclo [3.3.0] octane-3-carboxylic acid (Aoc), D-Aoc, and (2S, 4R)-hydroxyproline (Hyp)} with varying lipophilic, steric, and conformational properties, and alternatively with Lys and Orn in the lysine part. Moreover, the threonine part was changed to various natural amino acids (Ser, Thr, Val, Leu). All the compounds were screened in vivo for their analgesic effects in mouse writhing test. Compound 24 (H-Orn-Hyp-Val-OH), the most active compound within the series, showed an ED50 value of 10 mg/kg, which is comparable with the ED50 values exhibited by indometacin (4.1 mg/kg) and the dipeptide H-Lys-D-Pro-OH (6.9 mg/kg), both used as reference drugs. © 1997 John Wiley & Son's, Inc. Biopoly 40: 479-484, 1996
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Preferred conformation of peptides rich in alicyclic Cα,α-disubstituted glycines (1996)
    New York : Wiley-Blackwell
    Biopolymers 40 (1996), S. 519-522 
    Details
    ISSN: 0006-3525
    Keywords: conformational analysis, of peptides ; disubstituted glycines, peptides rich in ; Fourier transform ir absorption, of peptides ; 310-helical conformation, in peptides ; Cα-methylated α-amino acids, peptides rich in ; nmr, of peptides ; peptide conformation ; x-ray diffraction, of peptides ; β-turn conformation, in peptides ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational preferences of the alicyclic Cα,α-disubstituted glycines Acnc (1-amino-1-cycloalkane-carboxylic acid; n = 4, 7, 9, 12) were assessed in selected model compounds, including homopeptides and Ala (or Aib, α-aminoisobutyric acid)/Acnc peptides containing a small total number of residues, by Fourier transform ir absorption, 1H-nmr, and x-ray diffraction analyses. The results obtained indicate that β-turn and 310-helical structures are preferentially adopted by short peptides rich in these cycloaliphatic α-amino acids. © 1997 John Wiley & Sons, Inc. Biopoly 40: 519-522, 1996
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Helical screw sense of peptide molecules: The pentapeptide system (Aib)4/L-Val[L-(αMe)Val] in the crystal state (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 433-443 
    Details
    ISSN: 0006-3525
    Keywords: Aib peptides ; crystal state structure ; helical peptides ; peptide helices ; x-ray crystallography ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal-state preferred conformations of six Nα-blocked pentapeptide esters, each containing four helicogenic, achiral α-aminoisobutyric acid (Aib) residues followed by one chiral L-valine (L-Val) or Cα-methyl-L-valine [(αMe)Val] residue at the C-terminus, have been assessed by x-ray diffraction analysis. In all of the compounds the —(Aib)4— sequence is folded in a regular 310-helical conformation. In the four pentapeptides characterized by the L-(αMe)Val residue two conformationally distinct molecules occur in the asymmetric unit. Conversely, only one molecule is observed in the asymmetric unit of two pentapeptides with the C-terminal L-Val residue. In the L-Val based peptides the helical screw sense of the —(Aib)4— sequence is right-handed, whereas in the L—(αMe)Val— analogues both right- and left-handed helical screw senses concomitantly occur in the two crystallographically independent molecules. © 1998 John Wiley & Sons, Inc. Biopoly 46: 433-443, 1998
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Structural versatility of peptides from Cα,αdialkylated glycines: Linear Ac3c homo-oligopeptides (1989)
    New York : Wiley-Blackwell
    Biopolymers 28 (1989), S. 175-184 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal-state molecular structures of five linear Ac3c homo-oligopeptides to the tetramer were determined by x-ray diffraction. The oligomers are H-(Ac3c)2-OMe, Fmoc-(Ac3c)2-OMe MeOH, Ac-(Ac3c)2-OMe, pBrBz-(Ac3c)3-OMe · H2O, and t-Boc-(Ac3c)4-OMe · 2H2O. The results indicate the propensity of the tri- and tetrapeptides to fold into type I β-bends and distorted 310-helices, respectively, in partial contrast to Aib, Ac5c, and Ac6c homo-peptides of comparable main-chain length, where regular type III β-bends and 310-helical structures were found. When the influence of the constraints produced by the intramolecular H bonds of the C10-type is absent, other less common structural features may be observed. The average geometry of the cyclopropyl group of the Ac3c residue is found to be asymmetric and the N—Cα—C′ bond angle significantly expanded from the regular tetrahedral value.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360280119
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  • 8
    Electronic Resource
    Electronic Resource
    Polylysine induces changes in membrane electrical properties of K562 cells (1997)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 35 (1997), S. 165-174 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The ionic environment of the cell membrane is of extreme importance in maintaining cell integrity and the numerous functions necessary for cell growth, differentiation, etc., as well as in cell-biomaterial interactions. In this study, the effects of polylysine (a basic poly-amino acid with a net positive charge which is often used to coat biomaterials surfaces) on the erythroleukemic K562 cell membrane were investigated. In particular, the effects of this polycation were evaluated using dielectric relaxation studies in the radiofrequency range with which it is possible to measure both active ionic transport across the cell membrane (membrane conductivity) and the static charge distribution present on the cell surface due to the structural components of the cell membrane (membrane permittivity). The conductivity of the cytosol can also be determined. The results demonstrate that while the conductivity of the cytosol is not significantly altered, both the conductivity and permittivity of the K562 cell membrane are varied by exposure of these cells to polylysine. These observations indicate that both active ionic transport and the type, quantity, or distribution of membrane components such as lipids, proteins, and polysaccharides may also be altered. Although the precise mechanisms by which these variations in K562 cells occur are unknown, it can be hypothesized that changes in the growth characteristics of these cells may be in part responsible. In particular, as demonstrated by light microscopic examination of K562 cells directly in the culture flasks, the cells in polylysinecoated flasks do not grow in suspension as do the controls, but rather show anchorage-dependent-like behavior. It is this important change from suspension to monolayer growth induced by polylysine that may be responsible for the changes in membrane electrical parameters. © 1997 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Effects of hyaluronan viscous materials on cell membrane electrical properties (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 41 (1998), S. 211-220 
    Details
    ISSN: 0021-9304
    Keywords: hyaluronan (hyaluronic acid) ; K562 cells ; Maxwell-Wagner effect ; membrane electrical properties ; viscous materials ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Hyaluronan [hyaluronic acid (HA)] has been implicated in various cellular processes such as proliferation, adhesion, migration, and differentiation. The secondary and tertiary structures of HA give it very important and unique viscoelastic properties. HA-composed materials are currently used intraocularly during ophthalmological surgery to facilitate surgical procedures and prevent tissue damage. To examine the effects of three viscous biomaterials composed of hyaluronan (Healon™, IAL™, and Biolon™) used in ophthalmological surgery, the membrane electrical properties of the erythroleukemic K562 cell line exposed to these materials were investigated. Membrane conductivity, membrane permittivity, and the conductivity of the cytosol were evaluated using dielectric relaxation measurements in the radiofrequency range and fitting the experimental results to the general equations of the Maxwell-Wagner effect. The results demonstrate that while membrane permittivity and the conductivity of the cytosol are not significantly altered, the membrane conductivity of K562 cells exposed to all three biomaterials increases substantially and in a time-dependent manner with respect to untreated cells. These observations seem to indicate that hyaluronan perturbs ionic transport while it does not vary the type, quantity, or distribution of membrane components. In addition, the variations induced by these substances on the cell membrane are not dependent upon the molecular weight or on the biological origin of hyaluronan. These results may aid in elucidating the mechanisms involved in hyaluronan/cell membrane interaction and thus may provide a deeper understanding of the complications related to their use in ophthalmological surgery. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 211-220, 1998.
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