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  • Polymer and Materials Science  (30)
  • Wiley-Blackwell  (30)
  • EMBO Press
  • Public Library of Science
  • 1
    Electronic Resource
    Electronic Resource
    Eine spektroskopische Methode zur Messung der Ammoniak-Permeabilität in PolymerfilmenHerrn Prof. Dr. Herward Pietsch zum 60. Geburtstag gewidmet (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 179 (1990), S. 5-19 
    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: A new spectroscopic method for determining the permeability of ammonia in transparent polymer layers is presented. It is based on the quantitative proof of the ammonia passing the test layer into a sensor layer, containing 4-nitrophenol as an NH3-sensitive probe, which is placed under the test film. The permeability (P) of the test layer is calculated from the slope of extinction with time in the sensor layer. The lag time (t1) gives the diffusion coefficient (D). The suitability of this method is confirmed by comparison with literature values. Diffusion coefficients obtained from t1 correspond well to those obtained by the sorption method.The temperature dependence of P and D in more than five different polymers (CDA, PVB, PVAc, PVC and different polyvinyl alcohols) demonstrates that peculiarities in the temperature dependence of the permeability result from the behaviour of the NH3-solubility (P/D) which is strongly dependent on the polymer structure.
    Notes: Es wird eine neuartige spektroskopische Methode zur Messung der Ammoniak-Permeabilität in transparenten Polymerfilmen vorgestellt. Sie beruht auf dem quantitativen Nachweis des den Testfilm durchdringenden Ammoniaks in einer darunter befindlichen Sensorschicht mit Hilfe der NH3-empfindlichen Sonde 4-Nitrophenol. Aus dem Anstieg der Extinktion mit der Zeit (ΔE/Δt) in der Sensorschicht wird die Permeabilität (P) und aus der Verzögerungszeit (lag time (t1)) der Diffusionskoeffizient (D) berechnet. Die Eignung der Methode wird durch Vergleich mit Literaturwerten belegt. Die aus t1 zugänglichen Diffusionskoeffizienten stimmen sehr gut mit denen überein, die mit der Sorptionsmethode gefunden werden.Die Temperaturabhängigkeiten von P und D in mehr als fünf verschiedenen Polymeren (CDA, PVB, PVAc, PVC und in verschiedenen Polyvinylalkoholen) zeigen, daß Besonderheiten im Temperaturgang der Permeabilität aus dem vom Aufbau des Polymeren stark abhängigen Verhalten der NH3-Löslichkeit (P/D) resultieren.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051790102
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  • 2
    Electronic Resource
    Electronic Resource
    Relations between physical parameters and kinetics of photo-induced radical polymerization in polymer binders: Radical polymerization of acrylamide (1992)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 201 (1992), S. 49-62 
    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: Die photoinduzierte radikalische Polymerisation von Acrylamid in Kombinationen von zwei Polymeren, die Carbonsäuregruppen enthalten, wurde untersucht. Die kinetischen Parameter dieser Polymerisation, gemessen mit Hilfe einer kalorimetrischen Methode, hängen vom Mischungsverhältnis der beiden Polymeren im System ab. In Gemischen mit der niedrigsten Glasübergangstemperatur ist die Polymerisationsgeschwindigkeit am hochsten. Diese Ubergangstemperaturen wurden mit Hilfe einer speziellen Fluoreszenztechnik unter Benutzung von Kristallviolett bestimmt. Die gemessenen Effekte werden wahrscheinlich durch die stark polaren Wechselwirkungen zwischen den Carboxygruppen der beiden Polymeren verursacht.
    Notes: The photo-induced radical polymerization of acrylamide has been investigated in combinations of two polymers containing carboxy groups. The kinetic parameters of this polymerization, measured with a calorimetric method, depend on the proportion of the two polymers in the system. In mixtures with the lowest glass transition temperature, the polymerization rates are the highest. These transition temperatures have been determined with a special fluorescene technique using crystal violet as probe. Presumably, the effects measured in the systems are based on the strong polar interactions between the carboxy groups of both polymers.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1992.052010105
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical conformational analysis of a μ-selective cyclic opioid peptide analog (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 1431-1444 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The allowed conformations of the μ-receptor-selective cyclic opioid peptide analog were determined using a grid search through the entire conformational space. Energy minimization of the 13-membered ring structure lacking the exocyclic Tyr1 residue and the Phe3 side chain using the molecular mechanics program Maximin resulted in only four low-energy conformations. These four ring structures served as templates for a further energy minimization study with the Tyr1 residue and Phe3 side chain added to the molecule. The results indicated that the Tyr1 and Phe3 side chains enjoy considerable orientational freedom, but nevertheless, only a limited number of low-energy side-chain configurations were found. The obtained low-energy conformers are discussed in relation to various proposed models of the bioactive conformation of enkephalins and morphiceptin.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360260817
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  • 4
    Electronic Resource
    Electronic Resource
    Conformational studies of diastereomeric cyclic enkephalins by 1H-NMR and computer simulations (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 1573-1586 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report the solid-phase synthesis and conformational analysis of a 14-membered, cyclic enkephalin analog, H—Tyr—c[—D—A2bu—Gly—Phe—D—Leu—] (where A2bu represents α,γ-diaminobutyric acid). The results from the guinea pig ileum (GPI) and mouse vas deferens (MVD) assays show that the analog, though active, has little selectivity for the μ or δ opioid receptors. Conformational analysis is carried out using 1H-nmr and computer simulations, including molecular dynamics and energy minimizations. The results obtained here are compared with the findings of our studies carried out on the μ-receptor-selective diastereomer, H—Tyr—c[—D—A2bu—Gly—Phe—Leu—] [N. Mammi, M. Hassan, and M. Goodman (1985) J. Am. Chem. Soc. 107, 4008-4013]. This comparison allows for insight into the regiospecificity of these cyclic enkephalin analogs.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360260909
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  • 5
    Electronic Resource
    Electronic Resource
    Enkephalin analogues containing β-naphthylalanine at the fourth position (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 179-196 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To examine the importance of the aromatic side chains of enkephalin on opiate activity, we report the synthesis and conformational analysis of a series of analogues related to enkephalin with β-naphthylalanine in place of phenylalanine at the fourth position. Three linear analogues (Tyr-D-Ala-Gly-(L and D)-β Nal(1)-Leu-NH2 and Tyr-D-Ala-Gly-β Nal(2)-Leu-NH2) were initially synthesized to examine the effect of the substitution on biological activity. The increased activity of these peptides at the μ-opiate receptor, compared to native Leu-enkephalin, prompted us to examine the more conformational constrained analogues, Tr-c[D-A2bu-Gly-(L and D)-β Nal(1)-Leu], incorporating a α,γ-diaminobutyric acid at the second position and cyclization to the carboxylic end of the leucine. These two cyclic analogues provide insight into the necessity for the L chirality of the aromatic residue at position 4. The Tyr-c[D-A2bu-Gly-L-β Nal(1)-Leu] analogue is highly potent and displays a slight preference for the μ receptor. The conformational analysis indicates that despite the high flexibility of the tyrosine side chain, the aromatic rings of the tyrosine and naphthylalanine are relatively distant from each other. The presence of two intramolecular hydrogen bonds help maintain the conformation of the 14-membered backbone ring that keeps the side chains directed away from each other. These findings are in agreement with our model of an extended structure required for μ selectivity and a folded form with close aromatic ring placement for δ selectivity.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290123
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  • 6
    Electronic Resource
    Electronic Resource
    Comparative analysis of various proposed models of the receptor-bound conformation of H-tyr-Tic-Phe OH related δ-opioid antagonists (1995)
    New York : Wiley-Blackwell
    Biopolymers 37 (1995), S. 391-400 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular mechanics study (grid search and energy minimization) was performed with six δ opioid peptide antagonists containing a tetrahydroisoquinoline-3-carboxylic acid (Tic) residue in the 2-position of the peptide sequence. Compounds examined were the highly potent and selective T1P(P) peptides H-Tyr-Tic-Phe-OH (TIP). H-Tyr-TicΨ[CH2-NH]Phe-OH (TIP[Ψ]). H-Tyr-Tic-Phe-Phe-OH (TIPP). and H-Tyr-TicΨ[CH2-NH]Phe-Phe-OH (TlPP[Ψ]), and the weakly active analogues H-Tyr-Tic-NH2 and H-Tyr-Tic-Ala-OH. Low energy conformers of the peptides were examined for their compatibility with three proposed model of the δ receptor-bound conformation. Model 1, based on spatial overlap of the Tyr1 and Phe3 aromatic rings and N-terminal amino group of the peptides with the corresponding aromatic rings and nitrogen atom of the nonpeptide δ-antagonist naltrindole, was ruled out because of the demonstrated importance of the Tic2 aromatic ring for δ antagonism and because of the somewhat elevated energies of the conformers consistent with this model. Models of the receptor-bound conformation based on superimposition of the Tyr1 and Tic2 aromatic rings and N-terminal amino group of the peptides with the corresponding moieties in naltrindole included an all-trans peptide bond conformer [model 2, proposed by B. C. Wilkes and P. W. Schiller (1994) Biopolymers. Vol. 34. pp. 1213-1219] and a conformer with a cis peplide bond between the Tyr1 and Tic2 residues (model 3), originally proposed by P. A. Temussi et al. [(1994) Biochemical and Biophysical Research Communications. Vol. 198, pp. 933-939]. For all six peptides low energy conformers consistent with both model 2 and model 3 were identified: however, peptide conformers corresponding to model 2 showed better coplanarity of the Tyr1 aromatic ring and the phenol ring in naltrindole than peptide conformers corresponding to model 3. Both models remain plausible candidate structures for the receptor-bound conformation of δ antagonists of the TIP(P) class. TIP(P) analogues containing additional conformational constraints need to be developed in order to arrive at a unique model. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360370606
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  • 7
    Electronic Resource
    Electronic Resource
    Ammoniakdiffusion in Polymerfilmen (1989)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 173 (1989), S. 69-84 
    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: With the help of a novel test method, diffusion-coefficients of ammonia were determined in 22 transparent, filmforming polymers at room temperature. This method is based upon the UV-VIS-spectroscopically followable reversible reaction of ammonia with 4-nitro phenol to a Meisenheimer-complex.The dye-building reaction was studied and analyzed by a simple approximation of the diffusion equation. Diffusion coefficients obtained are in good agreement with the few available data in the literature.The dependence of the NH3-diffusion coefficients upon the polymer structure corresponds with the obtained diffusion coefficients, which are known for permanent gases.The described method allows the measurement of diffusion coefficients, which are distinguished up to three orders of magnitude, without any problem (ethylcellulose: 1,07 · 10-7 cm2 · s-1; poly(vinylalcohol): 0.9 · 10-10 cm2 · s-1).
    Notes: Mit Hilfe einer neuartigen Untersuchungsmethode wurden die Diffusionskoeffizienten von Ammoniak (NH3) in 22 transparenten filmbildenden Polymeren bei Raumtemperatur bestimmt. Die Methode beruht auf der UV-VIS-spektroskopisch verfolgbaren reversiblen Reaktion von Ammoniak mit 4-Nitrophenol zu einem 4-Nitrophenolat-Ammoniak-Meisenheimer-Komplex.Die Farbbildungsreaktion im Polymerfilm wurde untersucht und anhand einer einfachen Näherung der Diffusionsgleichung ausgewertet. Die erhaltenen Diffusionskoeffizienten stimmen sehr gut mit den wenigen verfügbaren Literaturwerten überein.Die Abhängigkeit der NH3-Diffusionskoeffizienten von der Polymerstruktur ist weitgehend der für permanente Gase bekannten analog.Die beschriebene Methode erlaubt problemlos, Diffusionskoeffizienten zu messen, die sich bis zu drei Größenordnungen unterscheiden (Ethylcellulose: 1,07 · 10-7 cm2 · s-1; Polyvinylalkohol: 0,9 · 10-10 cm2 · s-1).
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1989.051730106
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  • 8
    Electronic Resource
    Electronic Resource
    Oxygen permeability in polymers, IIIPart I see ref.5; part II see ref.4.. Dependence of the oxygen permeability on the chemical structure of styrene-maleic acid-copolymers (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 93-101 
    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: Die Sauerstoffpermeabilität von Halbestern und Halbamiden der Styrol-Maleinsäure-Copolymeren und weiterer carboxygruppenhaltiger Polymerer wurde im Vergleich mit kommerziellen glasbildenden Polymeren bei Raumtemperatur untersucht. Die Löschung der verzögerten Fluoreszenz von Pyronin B diente zum Nachweis des Sauerstoffs im Polymerfilm.Die Sauerstoffpermeabilität des Styrol-Maleinsäureanhydrid-Copolymeren und der Halbester und Halbamide (Pox = 2…7°10-14 cm2/Pa·s) ist vergleichbar mit der von Polymeren ohne Carboxygruppen wie Polymethylmethacrylat (PMMA) oder Polyvinylacetat (PVAc) und liegt damit etwa eine Größenordnung über der von Polyacrylsäure (PAAc), Styrol-Maleinsäure-Copolymeren (SMAc) oder Carboxymethylcellulose (CMC). Vermutlich konkurrieren intramolekulare H-Brücken in den Halbestern/Halbamiden erfolgreich mit der intermolekularen Wechselwirkung und bewirken damit ebenso wie raumfüllende Substituenten eine Erhöhung der Permeabilität. Zusatz von Basen wie Dimethylaminopropanol (DMAP) und Dimethylaminopropylacrylamid (DMAPAA) senkt die Permeabilität auf bis zu 1/40 des Ausgangswertes ab, was der niedrigen Permeabilität von Polymeren mit vorherrschender ionischer Wechselwirkung (Na-Polyacrylat (NaPAAc), Na-Carboxymethylcellulose (NaCMC) nahekommt.
    Notes: The paper gives a report on the oxygen permeability in films of poly(styrene-comaleic acid) halfesters and halfamides as well as other polymers containing carboxylic groups in comparison with commercially available glass forming polymers at room temperature. The presence of oxygen in the polymer layers was proved by the quenching of the delayed fluorescence of pyronin B. The permeability of the halfesters/halfamides (Pox = 2…7.10-14 cm2/Pa .s) corresponds to that of common polymers like poly(methyl methacrylate) (PMMA) or poly(vinyl acetate) (PVAc), and is nearly one order of magnitude higher than that of poly(acrylic acid) (PAAc), poly(styrene-comaleic acid) (SMAc) and carboxymethylcellulose (CMC). Presumably, intramolecular hydrogen bonds in the halfester/halfamides compete successfully with the intermolecular interactions and hence cause an increase in permeability as also do bulky substituents. Addition of bases like dimethyl aminopropanol (DMAP) and dimethyl aminopropyl acrylamide (DMAPAA) decreases the permeability to about 1/40 of the initial value. The permeability is then similar to the low permeability of polymers with predominant ionic interaction sodium polyacrylate (NaPAAC), sodium carboxymethylcellulose (NaCMC)).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920108
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  • 9
    Electronic Resource
    Electronic Resource
    A conformational comparision of two stereoisomeric cyclic dermorphin analogues employing nmr and computer simulations (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 943-952 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a continuation of our program to study the structure-activity relationship of peptide opiates, we report the conformational analysis of two cyclic tetrapeptides related to dermorphin - Tyr-c[D-Orn-Phe-Asp]-NH2 and Tyr-c[D-Asp-Phe-Orn]-NH2. These analogues have similar binding properties marked by a high selectivity for the μ-opioid receptors because of a drastic decrease in the affinity for the δ-opioid receptor. The conformational preferences of these analogues of dermorphin determined from proton nmr, molecular dynamics, and energy minimizations are quite similar. The constraint of the 13-membered ring formed from cyclization is quite evident from the conformational analysis. The constrained ring system acts as a template maintaining the relative orientation of the exocyclic tyrosine and side chain of phenylalanine. Two intramolecular hydrogen bonds measured for the D-Orn analogue in DMSO were disrupted upon the addition of water. For the D-Asp analogue, two intramolecular hydrogen bonds were found stable in DMSO and water. The global conformations of the two peptides determined from nuclear Overhauser effects did not change with the solvent titration. The difference in the hydrogen bonding within the 13-membered ring may account for the slight differences observed in the efficacy of the analogues at the μ-opioid receptors.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290607
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  • 10
    Electronic Resource
    Electronic Resource
    Theoretical conformational analysis of the opioid δ antagonist H-Tyr-Tic-Phe-OH and the μ agonist H-Tyr-D-Tic-Phe-NH2 (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1213-1219 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular mechanics study (grid search and energy minimization) of the highly δ receptor-selective δ opioid antagonist H-Tyr-Tic-Phe-OH (TIP; Tic: tetrahydroisoquinoline-3-car-boxylic acid) resulted in four low energy conformers with energies within 2 kcal/mol of that of the lowest energy structure. These four conformers contain trans peptide bonds only and represent compact structures showing various patterns of aromatic ring stacking. The centrally located Tic residue imposes several conformational constraints on the N-terminal dipeptide segment; however, the results of molecular dynamics simulations indicated that this tripeptide still shows some structural flexibility, particularly at the Phe3 residue. Analogous studies performed with the structurally related μ receptor-selective μ agonist H-Tyr-D-Tic-Phe-NH2 resulted in low energy structures that were also compact but showed patterns of ring stacking different from those obtained with TIP. Superim-position of low energy conformers of TIP and H-Tyr-D-Tic-Phe-NH2 revealed that the Phe3 residues of the L-Tic- and the D-Tic peptide were always located on opposite sides of the plane defined by the Tic residue, thus providing an explanation for the distinct activity profiles of the two compounds in structural terms. Attempts to demonstrate spatial overlap between the pharmacophoric moieties of low energy conformers of TIP and the nonpeptide δ antagonist naltrindole were made by superimposing either the Tyr1 and Tic2 aromatic rings and the N-terminal amino group or the Tyr1 and Phe3 aromatic rings and the N-terminal amino group of the peptide with the corresponding aromatic rings and nitrogen atom in the alkaloid structure. In each case a low energy structure of TIP was found that showed good spatial overlap of all three specified pharmacophoric groups. These two conformers may represent candidate structures for the δ receptor-bound conformation of TIP. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340909
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