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  • Wiley-Blackwell  (19,958)
  • 1995-1999  (11,407)
  • 1980-1984  (8,551)
  • 1935-1939
  • 1930-1934
  • 1997  (11,407)
  • 1981  (8,551)
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  • 1995-1999  (11,407)
  • 1980-1984  (8,551)
  • 1935-1939
  • 1930-1934
Year
  • 1
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    Habitat Selection and Life Cycle Characteristics of Five Species of the Amphipod Genus Gammarus in the Baltic (1981)
    Wiley-Blackwell
    In:  Oikos, 37 (2). p. 173.
    Details
    Publication Date: 2015-10-06
    Type: Article , PeerReviewed
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  • 2
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    Nutritional condition and vertical distribution of Baltic cod larvae (1997)
    Wiley-Blackwell
    In:  Journal of Fish Biology, 51 (Suppl. A.). pp. 352-369.
    Details
    Publication Date: 2017-09-08
    Description: Newly hatched Baltic cod Gadus morhua larvae are typically found at depths 〉60 m. This is a region of low light and prey availability, hence generating the hypothesis that larvae have to migrate from hatching depth to the surface layer to avoid starvation and improve their nutritional condition. To test this hypothesis, Baltic cod larvae were sampled during the spawning seasons of 1994 and 1995 with depth-resolving multiple opening/closing nets. Each larva was aged by otolith readings and its RNA/DNA ratio was determined as a measure of nutritional condition. The RNA/DNA ratios of these larvae aged 2-25 days (median 10 days) ranged from 0.4 to 6.2, corresponding to levels exhibited by starving and fast-growing larvae in laboratory calibration studies (starvation, protein growth rate, Gpi= -12.2% day−1; fastgrowing larvae, Gpi=14.1%day−1) respectively. Seventy per cent of the field caught larvae had RNA/DNA ratios between the mean values found for starving and fed laboratory larvae. Only larvae aged 8-11 days had higher mean RNA/DNA ratios above 45 m than below (t-test, P〈0.05). However, the instantaneous protein growth rates were significantly higher for all larval age groups in the surface layers (t-test, P〈0.05). Starving larvae were found in all depths sampled (10-85 m), whereas growing larvae (positive Gpi) were restricted to samples taken shallower than 45 m. These superior growth rates above 45 m corroborate the hypothesis and imply that migration to the shallow water layers is a prerequisite for good nutritional condition, growth and survival of Baltic cod larvae. The frequent occurrence of cod larvae older than 8 days in the deep water in poor condition suggests that a proportion of the larvae will die from Starvation in the deep layers of the Baltic Sea.
    Type: Article , PeerReviewed
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  • 3
    Electronic Resource
    Electronic Resource
    Polycarbonat-ein vielseitiger werkstoff mit zukunft (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 244 (1997), S. 43-66 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The market development of bisphenol-A-polycarbonate has shown higher growth than any other engineering thermoplastic. The reasons can be found in the permanent improvement of the cost/performance-relationship and in the technical use of the variability of the basic structure. Incorporation of specific monomer units leads to tailor-made properties for a wide range of applications, as for example medical devices, electronic parts and glazing.This process has not yet slowed down, rather it is accelerated by new results from research and development. The improvement of flaw behavior and pit replication for new grades of materials for the next generation of compact discs, new grades that can be sterilized by γ-radiation without degradation and the microstructuring by low-energy laser systems are examples for the ongoing expansion of polycarbonate applications. Surface modification by hardcoatings with nanosized particles will allow to enter the fast growing market of glazing.
    Additional Material: 27 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052440103
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  • 4
    Electronic Resource
    Electronic Resource
    Polyamide, polyester und polyoxymethylen. Die klassischen technischen kunststoffe und ihre perspektiven (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 244 (1997), S. 67-92 
    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: Polyamide, Polyester und Polyoxymethylen sind mit einem weltweiten Verbrauch von derzeit 2,4 Mio t pro Jahr wichtige technische Kunststoffe. Sie werden aufgrund ihrer besonderen Eigenschaftsprofile überwiegend im Fahrzeugbau und in der Elektroindustrie für hochbelastete Funktionsbauteile eingesetzt. Der vorliegende Beitrag behandelt Polymerisationswege, Eigenschaften und ausgewählte neue Entwicklungen dieser Polymerklassen.Teilaromatische Polyamide stoßen durch ihre Dimensionsstabilität und thermische Belastbarkeit in Anwendungen vor, die bisher Duromeren oder Metallen vorbehalten waren. Glasfaserverstärkte Polyamide mit besonders hoher Dauerwärmebeständigkeit übemehmen wichtige Funktionen im Motorbereich von Fahrzeugen. Polyamid-Blends sind als Karosseriewerkstoffe ein Schlüssel zu leichten Autos mit niedrigem Treibstoffverbrauch. Halogenfrei flammgeschützte Polyamide erhöhen Sicherheit und Umweltverträglichkeit in brandgefährdeten Anwendungsbereichen.Polybutylenterephthalat als technisch wichtigster Polyester eröffnet in Mischung mit amorphen Polymeren neue Perspektiven durch geringerenVerzug und bessere Oberfläche bei glasfaserverstärkten Teilen. Polybutylennaphthalat erweitert den Anwendungsbereich zu höheren Temperaturen. Von Polybutylenterephthalat abgeleitete Copolyester sind biologisch abbaubar und daher vielversprechend für kompostierbare Folien.Polyoxymethylen-Copolymere haben ihre Stärke in der günstigen Kombination aus Steifigkeit, Dimensionsstabilität, Gleit/Reibe-Verhalten und Beständigkeit gegen heißes Wasser und Kraftstoff.Aufgrund ihres hohen und noch weiter steigerungsfähigen Leistungsvermögens werden Polyamide, Polyester und Polyoxymethylen das in den letzten Jahren gezeigte Wachstum in Zukunft weiter ausbauen können.
    Notes: Polyamide, polyester and polyoxymethylene having presently a worldwide sales volume of 2,4 million tons a year are important engineering thermoplastics. Based on their special property profiles they are mainly used in the automotive and electronic industry for high performance functional parts. This contribution presents polymerisation processes, properties, and selected new developments for these polymer classes.Semiaromatic polyamides due to their dimensional stability and thermal resistance lend themselves to applications which were so far reserved for thermosets or metals. Glass fiber reinforce polyamides designed to have the highest possible heat ageing resistance can take important functions under the hood. A polyamide blend used as a material for exterior body parts is key to light weight cars with strongly reduced fuel consumption. Halogene free flame retardant polyamide increases fire safety and environmental safety in flame sensitive applications.Polybutyleneterephthalate as the technically most important polyester offers new perspectives in blends with amorphous polymers leading to lower distortion and better surface quality in glass fiber reinforced parts. Polybutylenenaphthalate is widening the range of application of polyesters towards higher temperatures. Copolyesters derived from polybutyleneterephthalate are biologically degradable and are therefore promising materials for fermentable foils.Polyoxymethylene copolymers show an outstanding combination of stiffness, dimensional stability, friction and wear as well as resistance against hot water and fuel.As a result of their excellent properties and the existing potential for further improvements polyamide, polyester and polyoxymethylene will continue to grow above average in the future.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052440104
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  • 5
    Electronic Resource
    Electronic Resource
    Sind polyurethanwerkstoffe ein reifes gebiet? (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 244 (1997), S. 121-133 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The world-wide production of polyurethanes has exceeded 6 mio. metric tons in 1994. Compared with the produced amounts of large-scale thermoplastics such as PE, PVC, PP and PS, polyurethanes keep the 5th place.Polyurethanes (PUR) are segmented polymers, which can be synthesized from preformed building blocks in a modular unit construction system. The chemical modules and the various possibilities of combination will be discussed here.Tailor-made polyurethane materials can be divided into two main-fields of application: foams and compact PUR.The main constituents of polyurethane materials are diisocyanates and polyols. These key- chemicals are well characterised with respect to their technological, economical and ecological properties. Taking into account the availability, the masses of production and the experiences that have been collected with the PUR main constituents, these PUR precursors seem to be very mature already.In contrast to this, the PUR-materials made from these building blocks still offer numerous novel problem-solutions, resulting from the variability of the diisocyanate-poly-addition reaction: PUR materials are most commonly segmented into several phases. The formation of hard- and softsegments can be easily demonstrated by looking at thermoplastic polyurethanes (TPU). A deeper understanding of this phase separation and the molecular organisation within these materials promises to realize prospectic polymeric architectures with new and improved properties. PUR materials will still be able to offer new answers to future requirements in balancing economical and ecological needs. By looking at the life-cycles of soft and hard-foams, polyurethane-coatings and thermoplastic PUR-elastomers, this contribution will adress the question: “Is PUR-chemsitry still a challenging field?”
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052440106
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  • 6
    Electronic Resource
    Electronic Resource
    Fire-retardant action of potassium nitrate in polyamide 6 (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 23-35 
    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 Zugabe von 10-20 Gew.-% Kaliumnitrat (KN03) zu Polyamid 6 (PA 6) vermindert die Brennbarkeit des Polymeren. Das thermische Verhalten der KN03/PA 6-Mischung wurde mittels Thermogravimetrie, Differentialkalorimetrie und Analyse der fluchtigen Anteile untersucht. Feste Zersetzungsprodukte der Mischung wurden mittels Infrarotspektroskopie, Rontgendiffraktometrie und Elektronenresonanzspek-'troskopie analysiert. Es wurde gefunden, daß KNO3 dem Flielßen und Tropfen der Schmelze vorbeugt und die Karbonisierung auf der Oberflache des Polymeren fordert. Das verringert die Brandgefahr und verbessert die Feuerbestandigkeit. Andererseits geht KNO3 mit PA 6 in der kondensierten Phase eine exotherme Reaktion ein und setzt Sauerstoff frei, der wiederum die Brennbarkeit von PA 6 begiinstigt. Der Mechanismus der chemischen Wechselwirkung van KNO3 mit PA 6 wird diskutiert.
    Notes: The addition of 10-20 wt.-% of potassium nitrate (KNO3) to polyamide 6 (PA 6) improves the fire retardance of the polymer. The thermal decomposition behaviour of the PA 6/KN03-mixture was studied using thermogravimetry, differential scanning calorimetry and thermal volatilisation analysis. Solid products of the thermal decomposition of the mixture were analysed by infrared spectroscopy, X-ray diffraction and electron paramagnetic resonance. It was found that KNO, prevents flowing and dripping of the melt and promotes charring on the surface of the polymer which decreases its fire hazard and improves its fire retardance. On the other hand, KNO3 exothermally reacts with PA 6 in the condensed phase and supplies oxygen to the gas phase which increases the combustibility of PA 6. The mechanism of the chemical interaction of KN03 with PA 6 is discussed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052450103
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of tricalcium phosphate, hydroxyethyl methacrylate, and ethylene glycol dimethacrylate on the mechanical properties of acrylic bone cement (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), 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: Der Einfluß einer Beimischung von Tricalciumphosphat (TCP), Hydroxyethylmethacrylat (HEMA) und Ethylenglycoldimethacrylat (EGDMA) auf die Eigenschaften eines chirurgischen Knochenzements wurde untersucht. Die in Zugversuchen entstandenen Bruchflächen wurden mittels Rasterelektronenmikroskopie charakterisiert. Der Einfluß der Additive auf den Temperaturanstieg während der Polymerisation wurde geprüft. Zug-, Biege- und Druckfestigkeit des ausgehärteten Zements nahmen mit zunehmendem TCP-Gehalt ab, der Elastizitätsmodul stieg dagegen an. Die Zugfestigkeit nahm mit steigendem HEMA-Gehalt geringfügig zu und blieb oberhalb 15 Gew.-% HEMA konstant. Zug-, Biege- und Druckfestigkeit zeigten bei einem EGDMA-Gehalt von 2 Gew.-% (in HEMA) ein Maximum. HEMA und EGDMA beschleunigten die Polymerisation, wogegen TCP retardierend wirkte.
    Notes: The effects of the addition of tricalcium phosphate (TCP), hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate (EGDMA) on the properties of standard surgical Simplex-P radiopaque bone cement have been investigated. The fracture surface after tensile test was studied by scanning electron microscopy. The influence of these components on the temperature rise during polymerization was investigated. It was found that the tensile strength, the bending strength, and the compressive strength decreased with increasing TCP content, whereas the inverse was observed for the Young's modulus. The tensile strength slightly increased with increasing HEMA content and then it levelled off when the HEMA content was higher than 15 wt.-%. It seemed that there were maximum tensile, bending and compressive strengths when 2 wt.-% EGDMA (in HEMA) was added. Polymerization occurred more rapidly when HEMA and EGDMA were added, whereas the inverse result was found with TCP.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052450105
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  • 8
    Electronic Resource
    Electronic Resource
    The relative physical and thermal properties of polyurethane elastomers. Effect of chain extenders derived from dihydroxynaphthalene (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 89-104 
    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: Polyurethanelastomere wurden in Gegenwart von zwei Dihydroxynaphthalin(DHN)-Verbindungen und deren bromierter Derivate als Kettenverlängerer hergestellt. Als Polyole wurden Polycaprolactondiol und Polytetramethylenglykol und als Diisocyanat-Komponenten Diphenylmethandiisocyanat (MDI) und Dicyclohexylmethan-4,4′-diisocyanat (HMDI) eingesetzt. Der Einfluß der Struktur der Kettenverlängerer auf die physikalischen und thermischen Eigenschaften der Polyurethane wurde untersucht. Wegen der besseren Phasenmischungswirkung der 1,5-DHN-Segmente haben die damit hergestellten Polyurethane höhere Glasübergangstemperaturen und bessere dynamische Eigenschaften als die Polyurethane auf 2,7-DHN-Basis. Der Einbau von bromierten DHN-Einheiten erschwert die Entflammbarkeit. Durch das große freie Volumen der Bromatome wird jedoch die Rotation der DHN-Einheiten eingeschränkt, was zu Polyurethanen mit verringerten Phasenmischungs- und Kristallisationsgraden führt. Die bromhaltigen Polyurethane zeigen zudem eine Verschlechterung der mechanischen und physikalischen Eigenschaften und eine erhöhte Löslichkeit.
    Notes: Polyurethane elastomers were synthesized based on polyols such as poly(caprolactonediol) and poly(tetramethylene glycol), diisocyanates such as diphenylmethane-4,4′-diisocyanate (MDI) and dicyclohexylmethane-4,4′-diisocyanate (HMDI), and two dihydroxynaphthalenes (DHNs) and their brominated derivatives used as chain extenders. The effects of the chemical structures of the chain extenders on the physical and thermal properties of the polyurethanes were investigated. Because of the higher degree of phase mixing of the 1,5-DHN unit, the 1,5-DHN-based polyurethanes have higher Tg values and higher dynamic properties than 2,7-DHN-based polyurethanes. Introduction of bromine atoms increased the flame retardance. However, the large free volume of bromine atoms restricted the rotation of DHNs, thus, directly decreasing the degree of phase-mixing and crystallinity of the polyurethanes. Introducing bromine atoms also decreased the mechanical and dynamic properties and increased the solubility of the polyurethanes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052450108
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of polypyrrolepolyurethane cationomer composites (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 139-147 
    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: Aus Poly(oxytetramethylen), 4,4′-Bibenzyldiisocyanat, N-Methyldiethanolamin als Kettenverlängerer und Acrylsäure/Polyacrylsäure als Quaternisierungsagens wurden Poly(etherurethan)-Kationomere hergestellt. In aus diesen Kationomeren hergestellten Filmen wurde Pyrrol (15 Gew.-%) in Gegenwart von CuCl2 polymerisiert. Die Filme wurden mittels dynamisch-mechanischer Analyse, Thermogravimetrie und Differentialthermoanalyse charakterisiert. Die elektrische Leitfähigkeit beträgt für den Film ohne Polypyrrol 7.5 · 10-12 Ω-1 cm-1 und mit Polypyrrol 4.5 · 10-6 Ω-1 cm-1.
    Notes: Poly(ether urethane) cationomers based on poly(oxytetramethylene), 4,4′-bibenzyldiisocyanate, N-methyldiethanolamine as chain extender, and acrylic acid/poly(acrylic acid) as quaternization agent were synthesized. Pyrrole (15 wt.%%) was polymerized in films of the ionomer containing CuCl2. The films were characterized by dynamic mechanical analysis, thermogravimetry and differential scanning calorimetry. The electric conductivity of the film without polypyrrole is 7.5 · 10-12 Ω-1 cm-1, while incorporation of polypyrrole increases the conductivity to 4.5 · 10-6 Ω-1 cm-1.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052450112
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis, characterization and polymerization of waxy monomers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 155-164 
    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: Wachsartige Monomere und Vernetzer wurden aus kommerziellen Wachsen durch Veresterung mit 2-Hydroxyethylmethacrylat, Glycerindimethacrylat oder Glycidylmethacrylat oder durch Funktionalisierung mit 2-Isocyanatoethylmethacrylat synthetisiert. Die erhaltenen opaken Methacrylate mit Schmelzpunkten zwischen 45 und 80°C wurden in Substanz bzw. Toluollösung in Gegenwart von Radikalinitiatoren polymerisiert. Die Polymeren zeichnen sich durch eine breite Molmassenverteilung aus. Im Gegensatz zur Substanzpolymerisation ist der Doppelbindungsumsatz nach der Lösungspolymerisation nahezu vollständig. Aufgrund der hohen Molmasse der Monomeren ist der beobachtete Polymerisationsschrumpf sehr gering. Polymerisate mit Vernetzermonomeren zeigen eine verbesserte mechanische Stabilität.
    Notes: Waxy monomers and crosslinkers, respectively, were synthesized from commercially available waxes by esterification with 2-hydroxyethyl methacrylate, glycerol dimethacrylate, or glycidyl methacrylate or by functionalization with 2-isocyanatoethyl methacrylate. The resulting opaque methacrylates with melting points between 45 and 80°C were polymerized in bulk and in toluene solution in presence of free radical initiators. The obtained polymers were characterized by a broad molecular weight distribution. Opposite to the bulk polymerization, the double bond conversion in solution polymerization is nearly quantitative. The observed volume shrinkage during polymerization is very low due to the high molecular weight of the monomers. Polymerizates containing crosslinking comonomers exhibit improved mechanical stability.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052450114
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  • 11
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    Zur Kinetik der stabilisierten Fällungs-polymerisation eines Kationischen Monomeren in wäßrigen Natriumchlorid-Lösungen (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 245 (1997), S. 165-181 
    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: The stabilized free-radical precipitation polymerization of the cationic monomer N-(2-methacryloyloxyethyl)-N,N-dimethylbenzylammonium chloride (MADAMBQ) in aqueous solutions of sodium chloride was studied by reaction calorimetry. Poly(ethylene oxide) was used as stabilizer. The rate of polymerization reaches its maximum immediately after initiation and remains nearly constant up to 50 % conversion followed by a decrease that could be described by a first order kinetics. The particles formed are approximately 1 to 30 μm in diameter and are stable over a period of several months.A model based on the theory of homogeneous particle nucleation is suggested to describe the kinetic course of polymerization, taking into account the rate of polymerization in both phases. With the assumption that the concentration of monomer in the phases is determined by a Nernst distribution law, the kinetics of the early stage of polymerization can be modelled reasonably well.The solution polymerization and the unstabilized precipitation polymerization of MADAMBQ was also studied.
    Notes: Die Kinetik der stabilisierten Fällungspolymerisation des kationischen Monomeren N-(2-Methacryloyloxyethyl)-N,N-dimethylbenzylammoniumchlorid (MADAMBQ) in wäßrigen Natriumchlorid-Lösungen wurde mittels Reaktionskalorimetrie untersucht. Polyethylenoxid höherer Molmasse wurde als Stabilisator eingesetzt. Die Reaktionsgeschwindigkeit ist über einen größeren Umsatzbereich nahezu konstant und fällt anschließend mit dem Umsatz annähernd linear ab. Die Teilchengrößenverteilung der gebildeten Dispersion ist bimodal mit Teilchen von etwa 1 bis 30 μm Durchmesser.Zur Beschreibung des Geschwindigkeitsverlaufs der Fällungspolymerisation wird ein Modell vorgeschlagen, das die Polymerisation in der Wasser- sowie in der Polymerphase berücksichtigt. Die Teilchenbildung soll durch homogene Nukleierung erfolgen. Es wird angenommen, daß die Konzentration des Monomeren in den Phasen durch ein Nernstsches Verteilungsgleichgewicht bestimmt wird. Zu Vergleichszwecken wurde auch die Polymerisation von MADAMBQ in Lösung und als nicht stabilisierte Fällungspolymerisation durchgeführt.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052450115
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  • 12
    Electronic Resource
    Electronic Resource
    An investigation of the grafting of cellulose powder with acrylamide under a magnetic field (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 1-9 
    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: Cellulosepulver, hergestellt durch Nitrierung von Eichen-Furfural-Lignocellulose, wurde mit Acrylamid radikalisch gepfropft. Die Pfropfreaktion wurde sowohl in Gegenwart eines äußeren Magnetfeldes (0,15-0,35 T) als auch ohne Magnetfeld durchgeführt. Der Einfluß von Monomerkonzentration, Initiatorkonzentration, Polymerisationszeit und temperatur sowie der magnetischen Feldstärke auf den Polymerisationsverlauf wurde untersucht. Es wurde festgestellt, daß der Pfropfumsatz mit zunehmender Feldstärke signifikant ansteigt.
    Notes: Cellulose powder obtained from oak furfural lignocellulose by nitration reaction was grafted with acrylamide using a radical initiation. The grafting reactions were carried out and compared both in presence and in absence of a continuous external magnetic field with the intensity extended between 0.15-0.35 T. The effect of monomer and initiator concentration, time and temperature of reaction and magnetic field intensity onto the grafting process were examined. It was observed that the presence of a magnetic field leads to a significant increase of the graft conversion.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052460101
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  • 13
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    Radical polymerization of poly(butyl acrylate) in the presence of poly(L-lactic acid), 1. Synthesis, characterization and properties of blends (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 49-63 
    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(L-milchsäure) ist ein biokompatibler, semikristalliner, thermoplastischer Polyester mit ungünstigen mechanischen Eigenschaften. Daher wurde in einem “reactive blending”-Prozeß ein Acrylkautschuk, n-Butylacrylat, mittels einer Suspensionspolymerisation in Wasser auf in einem organischen Lösungsmittel gelöste Poly(L-milchsäure) gepfropft. Die gebildeten Copolymeren konnten isoliert und durch NMR-Spektroskopie und DSC-Messungen charakterisiert werden. Die Untersuchung der mechanischen Eigenschaften ergab keine befriedigenden Ergebnisse, weil die Kautschukphase wahrscheinlich aus viskosen linearen Makromolekülen besteht und daher keine elastischen Eigenschaften besitzt. In weiteren Arbeiten soll der Syntheseweg so modifiziert werden, daß durch den Einbau von Diacrylaten eine zumindest partielle Vernetzung der Kautschukphase erreicht wird.
    Notes: Poly(L-lactic acid) is a biocompatible polyester, semicrystalline, thermoplastic, with low versatility in mechanical properties. To overcome this problem, a reactive blending procedure was performed by grafting an acrylic rubber, n-butyl acrylate, via water suspension polymerization onto poly(L-lactic acid) dissolved in an organic solvent. It was possible to isolate the copolymeric phase formed from the two polymers and characterize it by using NMR and DSC techniques. Mechanical tests on blends gave no satisfactory response, probably because the rubbery phase is composed essentially of viscous linear macromolecules, not able to perform elastic properties. Work is in progress to modify the synthetic pathway to incorporate diacrylates in order to realize a rubbery phase at least partially cross-linked.
    Additional Material: 7 Ill.
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    Tin-coupled styrene-butadiene rubbers (SBRs). Relationship between coupling type and propertiesBased on a paper presented at the 148th Meeting of the Rubber Division, American Chemical Society, Cleveland, Ohio, 17-20 October 1995. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 85-96 
    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: Zur Entwicklung von neuen Styrol-Butadien-Kautschuken (SBRs) für Reifenanwendungen sind mehrere Arten von Zinn-Polymer-Bindungen (Styryl-, Butadienyl-, Isoprenyl- and α-Methylstyryl-Zinn) sowohl in linearen als auch in verzweigten Ketten untersucht worden. Die dynamisch-mechanischen Eigenschaften von Vulkanisaten mit Ruß wurden analysiert, um eine Beziehung zwischen den Strukturparametern der Polymeren und den Materialeigenschaften herzustellen. Der Polymer-Füll-stoff-Wechselwirkungsparameter, der durch das Verhältnis von mechanischen und dynamischen Termen definiert ist, wurde zur Charakterisierung der Verbindungen herangezogen. Der Einbau von verschiedenen Zinn-Polymer-Bindungen in lineare und in verzweigte SBR-Ketten bewirkte eine Verbesserung der Hystereseeigenschaf-ten der Vulkanisate und eine Veranderung des Wechselwirkungsparameters.
    Notes: Following the development of new SBRs for tyre applications, several kinds of tin-polymer bonds (styryl-, butadienyl-, isoprenyl- and α-methylstyryltin) have been studied, in both branched and linear chains.Dynamic-mechanical properties of the carbon black vulcanizates have been analyzed to establish a relationship between structural parameters of polymers and compound properties. The filler-polymer interaction parameter, defined by a ratio of mechanical and dynamic terms, has been used for the evaluation of the compounds. The introduction of different types of tin-polymer bonds, in branched and linear chains of the SBRs, implies an improvement in the hysteresis properties of the vulcanizates as well as a modification of the interaction parameter.
    Additional Material: 1 Ill.
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    A novel spin-finishing method for antistatic modification of polyester fiber. Surface reaction onto amine-containing copoly(amide-ethers) blended with polyester fiber (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 246 (1997), S. 109-123 
    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: Copoly (amid-ether) rnit zwei unteschiedlichen Aminfunktionalitäten wurden als antistatische Modifikatoren für Polyethylenterephthalatfasern (PET) eingesetzt. Die tertiären Aminogruppen schmelzegesponnener Copolymerfilamente wurden rnit drei Alkylierungsmitteln umgesetzt, wobei ein Sulfobetain, ein Carbobetain bzw. Ammoniumionen gebildet wurden. Dadurch wurde der scheinbare spezifische Widerstand der Filamente auf größfienordnungsmäßfiig 106 bis 108 Ω/cm verringert. Da sich die quaternisierten Copolymeren beim Blend-Spinnen rnit PET zersetzen, wurden Blendfasern von PET mit einem Copolymeren nach dem Schmelzespinnen einer Quaternisierung oder Vernetzung rnit Alkylierungsmitteln bzw. Epoxyvernetzern unterzogen, was die antistatischen Eigenschaften der Fasern im Vergleich rnit der unbehandelten Faser verbesserte. Insbesondere die mit Epoxiden vernetzten Fasern wiesen antistatische Eigenschaften auf, wie sie mit dieser Modifizierungsmethode bislang nicht erreicht wurden. Die antistatischen Eigenschaften blieben nach dem Fkben erhalten, da sowohl die hydrophilen als auch die ionischen Gruppen auf der Faseroberflache immobilisiert waren. Da Quaternisierung bzw. Vernetzung in einem Arbeitsgang rnit dem Verspinnen und Verstrecken der Fasern innerhalb einer kurzen Reaktionszeit erfolgen, sollte diese “spin-finishing„ genannte Methode konventio- nellen Verfahren bezuglich Kosten und Produktivitat uberlegen sein.
    Notes: Copoly(amide-ethers) containing two types of tertiary amine units were made as antistatic modifiers for poly(ethylene terephthalate) (PET) fibers. The filaments of the copolymers were melt-spun and reacted with three alkylating agents in order to quaternize the tertiary amine into a sulfo-betaine, a carbobetaine, and an ammonium ion. The apparent electric resistivity of the filaments was greatly reduced by this reaction, being in the range of 106 to 108 Ω/cm. However, because these quaternized copolymers incurred decomposition during blend spinning with PET, a blend PET fiber containing one type of copoly(amide-ether) was melt-spun and subjected to quaternization of the amino groups as well as to surface crosslinking with various alkylating and epoxy agents. The quaternized blend fibers obtained showed improved antistatic properties compared with the original blend fiber. Particularly, the fibers crosslinked with epoxy compounds were found to have the best antistatic properties that had ever been attained with this type of modification. The antistatic properties were retained even after dyeing, because both hydrophilic and ionic groups had been effectively immobilized on the surface. Since this quaternization and crosslinking could be conducted on-line with spinning and drawing within a short reaction time, this modification technique is called “spin-finishing method”, which should be superior to the conventional methods in terms of cost performance and productivity.
    Additional Material: 4 Ill.
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    Etching of a low-density polyethylene film by fuming nitric acid (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 33-46 
    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: Filme aus Polyethylen niedriger Dichte (LDPE) wurden mit rauchender Salpetersäure behandelt. Die Oberflächeneigenschaften sowie die Bildung polarer Gruppen wie auf der geätzten Filmoberfläche wurden mit SEM-, IR- und XPS-Methoden analysiert. Die mechanische Festigkeit eines aus dem geätzten LDPE-Film und einem Epoxidharz hergestellten Laminats sowie die Bedruckbarkeit der geätzten Oberflächen wurden untersucht und mit einer unbehandelten Probe verglichen. Die Oberflächenrauhigkeit und die Gegenwart polarer Gruppen erhöhen die mechanische Festigkeit des Laminats aus dem geätzten Film durch mechanische Verankerung und chemischer Wechselwirkungen. Die Oberfläche des behandelten LDPE-Films ist besser bedruckbar als die des unbehandelten Films.
    Notes: Low-density polyethylene (LDPE) films were treated with fuming nitric acid (FNA). The surface characteristics and also the insertion of polar groups like on the etched LDPE film surface were measured by SEM, IR and XPS analyses, respectively. The mechanical performance of a laminate of the etched film with epoxy resin and also the printability of the etched film surface were tested and compared with the unetched sample. The surface roughening and the presence of polar groups enhance the mechanical strength of the laminate of FNA-treated film due to mechanical interlocking and chemical interaction. The printability of the treated film surface is also superior to that of the untreated LDPE film surface.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052490103
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    Celluloseether als Trennschichten hydrophiler Polymermembranen (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 249 (1997), S. 11-32 
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    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: This paper reports on polymer membranes characterized by a surface layer of hydroxyalkyl derivatives of cellulose. Water compatible polymers like hydroxyalkyl derivatives of cellulose are preferably those exhibiting good chemical stability and desired membrane characteristics. Normally, water-compatible polymers used in the coating solutions must be rendered water-insoluble after coating. By adapting crosslinking conditions on separation problems, the membranes are useful for many processes in the fields of biotechnology, food and chemical industry.The membranes presented here possess the advantage of being highly resistant to chemical and biological degradation and, hence, have long lifetimes under many process conditions.
    Notes: Es wird die Entwicklung hydrophiler Polymermembranen diskutiert, die nach Beschichtung mit Celluloseethern und anschließender Vernetzung auf den asymmetrischen Trägermembranen interessante Permeations- und Trenneigenschaften bei hervorragenden chemischen Stabilitäten, vor allem beim Membrantrennverfahren der Nanofiltration, aufzeigen. Weiterhin werden Aussagen zu den Gastrenneigenschaften der Celluloseetherkompositmembranen getroffen.Erläutert werden die Permeations- und Trenndaten der Kompositmembranen in Korrelation zur Vernetzung der Celluloseether anhand verschiedener Einflußgrößen, was qualitative und gegebenenfalls quantitative Aussagen zum Vernetzungsmechanismus der Celluloseetherderivate erlaubt. Dabei stehen die Vernetzungstemperatur, der Einfluß der katalysierenden Wasserstoffionen und bedingt die Vernetzungszeit im Vordergrund. Abgerundet werden die Arbeiten durch Ermittlungen rheologischer Daten, die in Zusammenhang zu den Vernetzungsreaktionen und damit zu membranspezifischen Größen stehen.Infolge der hervorragenden chemischen Stabilität der Celluloseether werden Einsatzmöglichkeiten der Kompositmembranen zur Nanofiltration niedermolekularer Verbindungen aus organisch hochbelasteten Systemen beschrieben.
    Additional Material: 30 Ill.
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    Products of polycondensation of 4,4′-biphenyldithiol with some hydrocarbon dihalides (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 13-21 
    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: Polysulfide wurden mit hoher Ausbeute durch Hochtemperatur-Lösungspolykondensation von 4,4′-Dimercaptobiphenyl mit ausgewählten aliphatischen und aromatisch-aliphatischen Dihalogenkohlenwasserstoffen hergestellt. Um die optimalen Polykondensationsbedingungen zu bestimmen, wurde der Einfluß folgender Faktoren auf die reduzierte Viskosität und die Ausbeute der Polysulfide ermittelt: Art des organischen Lösungsmittels, Art des Halogenwasserstoff-Akzeptors, Konzentration der organischen Reagenzien, Reaktionstemperatur und -zeit. Die Polykondensation des Dithiols mit Bis(4-chlormethylphenyl)methan wurde als Modellsystem eingehender untersucht. Die Polysulfidstrukturen wurden mittels Elementaranalyse, IR-Spektroskopie und Röntgenstrukturanalyse bestätigt. Aus der thermogravimetrischen Analyse wurden die Zersetzungstemperatur, der Gewichtsverlust bei dieser Temperatur und das Maximum der Zersetzungsgeschwindigkeit erhalten. Weiterhin wurden einige physikalisch-chemische, mechanische und dielektrische Eigenschaften ermittelt. Die beste thermische und chemische Bestandigkeit zeigt das aus dem Dithiol und 4,4′-Bis(chlormethyl)biphenyl hergestellte Polysulfid, was auf dessen vorwiegend aromatische Struktur zuriickgefuhrt werden kann.
    Notes: Polysulfides were synthesized with high yield by high-temperature solution polycondensation of 4,4′-biphenyldithiol with selected aliphatic and aromatic-aliphatic hydrocarbon dihalides. To determine the optimum polycondensation conditions, the influence of the following factors on reduced viscosity and yield was studied: type of organic solvent, type of hydrogen halide acceptor, concentration of reagents, reaction temperature, and reaction time. A thorough examination was carried out only for the polycondensation of dithiol with bis(4-chloromethylphenyl)methane chosen as model system. The structures of the polysulfides were confirmed by elemental analysis, X-ray analysis, and infrared spectroscopy. The temperature of initial decomposition, the percentage of mass loss, and the temperature of the fastest decomposition, process were determined from curves of differential thermal and thermogravimetric analysis. Some physicochemical, mechanical and electrical properties were determined. The highest thermal and chemical resistance has been found for the polysulfide obtained from 4,4′-biphenyldithiol and 4,4′-bis(chloromethyl)biphenyl, probably because of the predominantly aromatic structure.
    Additional Material: 4 Ill.
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    Organic-inorganic hybrid sol-gel materials, 2. Application for dental composites (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 61-72 
    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: Drie organisch-anorganische Hybridmaterialien wurden nach dem Sol-Gel-Verfahren durch kovalenten Einbau von Poly(styrol-co-methylmethacrylat)(Poly(St-co-MMA))-, Polymethylmethacrylat(PMMA)- und Polystyrol(PS)-Struktureinheiten in ein SiO2-Netzwerk hergestellt und als Füllstoffe (bis zu 60 Gew.-%) in Dentalharzen verwendet. Der Einfluß der Füllstoffe auf einige mechanische Eigenschaften der Harze wurde untersucht. Die Härte der gefüllten Dentalharze nahm mit steigendem Füllstoffgehalt zu, wogegen die Biegefestigkeit abnahm. Die Druckfestigkeit der gefüllten Harze war besser als die des ungefüllten Harzes, nahm jedoch mit steigendem Füllstoffgehalt ab.
    Notes: By incorporating poly(methyl methacrylate) (PMMA), polystyrene (PS), and poly(styrene-co-methyl methacrylate) (poly(St-co-MMA)) structure units covalently into the SiO2 glass network via a sol-gel approach, three organic-inorganic hybrid materials (PMMA-SiO2, PS - SiO2, and poly(St-co-MMA) - SiO2) have been prepared. The three hybrid sol-gel materials were used as filler (up to 60 wt.-%) for dental composite resins. The effect of the three filler materials on several mechanical properties of the dental composite resins was investigated. The hardness of the filled dental composites increased with increasing filler content, whereas the bending strength decreased. The compressive strength of the composites was improved, compared with the unfilled resin, but decreased with inreasing filler content.
    Additional Material: 6 Ill.
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    Adsorption of BTX compounds from aqueous solutions by water-insoluble starch (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 107-116 
    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 Adsorption von Benzol, Toluol und p-Xylol (BTX) aus wäßrigen Lösungen mittels hochvernetzter kationischer Stärke mit tertiären Amingruppen wurde untersucht. Der endotherme Adsorptionsvorgang ist vom Anfangs-pH-Wert und der Anfangskonzentration abhängig und kann mit einer Langmuir-Isotherme beschrieben werden.Die Adsorptionswärme (Δ) bei pH 4 beträgt für Benzol, Toluol und Xylol 29,45 kJ mol-1, 34,41 kJ mol-1 bzw. 35,58 kJ mol-1, bei pH 10 30,17 kJ mol-1, 35.56 kJ mol-1 bzw. 39,39 kJ mol-1. Die adsorbierte Menge nimmt in der Reihenfolge Benzol 〉 Toluol 〉 Xylol ab.
    Notes: The removal of benzene, toluene and p-xylene (BTX) compounds from aqueous solutions with highly crosslinked cationic starch containing tertiary amine groups was investigated. The adsorption process has found to be initial pH- and initial concentration-dependent, endothermic, and follows the Langmuir isothermal adsorption.The heats of adsorption (ΔH) at initial pH = 4 of benzene, toluene and p-xylene compounds are 29.45 kJ mol-1, 34.41 kJ mol-1, and 35.58 kJ mol-1, respectively, those at initial pH = 10 are 30.17 kJ mol-1, 35.56 kJ mol-1, and 39.39 kJ mol-1, respectively. The order of the amount of adsorbed BTX compounds on the adsorbent is benzene 〉 toluene 〉 p-xylene.
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    Thermogravimetric and ESR studies of polymer/metal precursors for high-temperature superconductors (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 157-170 
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    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: Bi-Sr-Ca-Cu-Komplexverbindungen von Polymethacrylsäure (PMAA) und Kresolnovolaken, die als Precursoren für Hochtemperatursupraleiter (HTSL) eingesetzt werden, sowie deren Cu-Komplexsalze wurden ESR-spektroskopisch und thermogravimetrisch untersucht. In den PMAA-Proben wurden drei verschiedene Cu2+-Spezies nachgewiesen: i) Cu2+-Paare, ii) isolierte Cu2+-Ionen und iii) Cu2+-Cluster. Bei niedrigem Cu-Gehalt der Proben bilden die Cu2+-Paar-Bindungen den Hauptanteil, bei hohem Cu-Gehalt überwiegen die Clusterbindungen. In den Novolakproben wurden nur isolierte Cu2+-Ionen und Cu2+-Cluster nachgewiesen. Die Einführung der Cu-Ionen erniedrigt die thermische Stabilität der Polymeren, der thermische Abbau erfolgt stufenweise. In den PMAA-Proben wird die erste Abbaustufe bei ≈ 220°C durch die Cu2+-Paar-Komplexe verursacht.
    Notes: Bi-Sr-Ca-Cu complexes of poly(methacrylic acid) (PMAA) and cresol novolac, which are precursors for high-temperature superconductors (HTSC) and Cu complexes of those polymers were investigated by ESR spectroscopy and thermogravimetry. In the PMAA samples three different kinds of Cu2+ species were detected: i) Cu2+ pairs, ii) isolated Cu2+ ions and iii) Cu2+ clusters. While Cu2+ pairs are the main species at low Cu concentrations, clusters become dominant at high Cu contents. In the novolac samples Cu2+ was only detected in isolated sites and clusters. The introduction of Cu ions lowered the thermal stability of the polymers and led to a stepwise decomposition. In the PMAA samples the first decomposition step at ≈ 220°C is caused by the Cu2+ pair complexes.
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    Polymerization of 1,3-butadiene with neodymium chloride/2-ethylhexanolate/triethylaluminium catalyst systemIPCL communication No. 325. (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 193-205 
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    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: Neodymchlorid-2-ethylhexanolate mit der allgemeinen Formel NdCl3 · nL wurden durch eine Liganden-Austauschreaktion zwischen Neodymchloridisopropanolat (I) und 2-Ethylhexanol (EH) hergestellt. Die Hexanolate NdCl3 · 1,5 EH (II) und NdCl3 · 2,5 EH (III) wurden durch Elementaranalyse und Gravimetrie charakterisiert. Die katalytische Aktivität der Hexanolate bei der Homopolymerisation von 1,3-Butadien in Gegenwart von Triethylaluminium wurde untersucht. Die Verbindung III zeigte eine höhere Aktivität als die Verbindung II. Höhere Katalysator- und Cokatalysatorkonzentrationen sowie eine höhere Temperatur steigerten den Umsatz, wogegen die Viskosität der Produkte abnahm. Mit zunehmender Reaktionszeit erhöhten sich sowohl der Umsatz als auch die Viskosität. Die cis-1,4-Konformation wurde durch die Variation von Temperatur und Cokatalysatorkonzentration beeinflußt. Der gesamte Anteil der cis-1,4-Stuktur lag jedoch in allen Fällen über 99%, während die Produkte nur einen sehr geringen Vinyl-Anteil von 〈1% enthielten. Die Zugabe einer elektronenspendenden Verbindung verringerte den cis- 1,4-Gehalt aber auf 87%.
    Notes: Neodymium chloride 2-ethylhexanolates of the general formula NdCl3 · nL were prepared by ligand exchange reaction between neodymium chloride ispropanolate (I) and 2-ethylhexanol (EH). These hexanolates, NdCl3 · 1.5 EH (II) and NdCl3 · 2.5 EH (III), were characterized by elemental analysis and gravimetry. The catalytic activity of these hexanolates in combination with triethyl aluminium in the homopolymerization of 1,3-butadiene was studied, and the activity was found to be higher with III than II. The conversions increased with increasing the catalyst and co-catalyst concentrations and the temperature, whereas the intrinsic viscosity decreased. The conversions and the intrinsic viscosity decreased. The conversions and the intrinsic viscosity increased with reaction time. The cis-1,4 structure was influenced by variation in temperature and co-catalyst concentration, however, the total cis-1,4 structure was always more than 99% with very low vinyl content (〉1%). Addition of an external electron donor decreased the cis-1,4 content to 87%.
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    The effects of desolvation methods of the recrystallized MgCl2-alcohol adduct on catalyst characteristics and the bulk density of polyethylene (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 17-25 
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    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: MgCl2-Träger für einen Ethylenpolymerisationskatalysator wurden mit Hilfe der Rekristallationsmethode hergestellt, wobei Methanol als Lösungsmittel diente. Der Einfluß verschiedener Lösungsmethoden des rekristallisierten MgCl2-Alkohol-Adduktes auf die morphologischen Charakteristika der Katalysatoren wurde untersucht. Die Lösungsmethode beeinflußt die Eigenschaften der Katalysatoren beträchtlich. Die dargestellten Katalysatoren wiesen unterschiedliche Ti/Mg-Verhältnisse auf, sowohl was die Oberfläche als auch die gesamten Katalysator-Partikel betrifft. Betrachtet man die Ti-Verteilung und Aktivitätsprofile, dann erweisen sich nicht nur die Polymerisationsbedingungen, sondern auch die Ti-Verteilung auf dem Katalysator als wichtige Faktoren, welche die Dichte der Polymeren beeinflussen.
    Notes: The MgCl2 supports for an ethylene polymerization catalyst were prepared by the recrystallization method using methanol as a solvent. The effects of different desolvation methods of the recrystallized MgCl2-alcohol adduct on the morphological characteristics of the catalysts were examined. The desolvation method greatly affects the characteristics of the catalyst. The prepared catalysts had different Ti/Mg ratios with respect to both surface content and entire catalyst particles. Considering Ti distribution and activity profiles, not only the polymerization conditions but also the Ti distribution on the catalyst appear to be an important factor which affects the bulk density of the polymers.
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    Synthesis of aromatic poly(ether ketone)s with ferrocene units in the main chain (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 89-97 
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    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: Aromatische Poly(etherketon)e mit Ferrocen-Einheiten in der Hauptkette wurden durch direkte Polykondensation von 1,1′-Ferrocendicarbonsäure mit Diphenylether oder 1,4-Diphenoxybenzol hergestellt. Als Katalysatoren wurden Trifluormethansulfonsäure, Methansulfonsäure/P2O5 (Eatons Reagens) oder Trifluormethansulfonsäure/P2O5 verwendet. Polykondensationen bei Raumtemperatur für 24 h ergaben Poly(arylenetherketon)e mit Grenzviskositäten bis zu 40 mL g-1. Die Monoacylierung von Diphenylether mit Ferrocencarbonsäure wurde im Hinblick auf die Effektivität von Eatons Reagens als Katalysator und Lösungsmittel eingehender untersucht.
    Notes: Aromatic poly(ether ketone)s with ferrocene units in the main chain were prepared by direct polycondensation of 1,1′-ferrocenedicarboxylic acid with diphenyl ether or 1,4-diphenoxybenzene using various catalysts such as trifluoromethanesulfonic acid (triflic acid), a combination of methanesulfonic acid/P2O5 (Eaton's reagent) or a combination of triflic acid/P2O5. Polycondensations at room temperature for 24 h gave poly(arylene ether ketone)s with inherent viscosities up to 40 mL g-1. Monoacylation of diphenyl ether with ferrocenecarboxylic acid was studied in detail in order to show the efficiency of polymer formation employing Eaton's reagent as catalyst and solvent.
    Additional Material: 6 Ill.
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    Mechanical and structural characteristics of phenolphthalein poly(ether sulfone)/ultra-high molecular weight polyethylene blends (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 73-80 
    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 mechanischen und strukturellen Eigenschaften von Blends aus Phenolphthalein-Polyethersulfon und ultrahochmolekularem Polyethylen (UHMWPE) wurden anhand von Zug- und Biegeversuchen, Raster- und Transmissionselektronenmikroskopie untersucht. Die Zugabe einer geringen Menge UHMWPE (2 Gew.-%) führt zu einer Verstärkung der PES-C-Matrix. Höhere UHMWPE-Konzentrationen verschlechtern die mechanischen Eigenschaften. Die Strukturuntersuchungen zeigen, daß die Blends im gesamten Zusammensetzungsbereich mehrphasig sind. Bei geringen UHMWPE-Konzentrationen ist die UHMWPE-Phase gleichmäßig verteilt und entlang der Fließrichtung orientiert, was mit der starken Grenzflächenadhäsion zur Verbesserung des mechanischen Verhaltens beiträgt. Mit steigender UHMWPE-Konzentration nimmt die Domänengröß der UHMWPE-Phase zu.
    Notes: Mechanical and structural properties of blends of phenolphthalein poly(ether sulfone) (PES-C) with ultra-high molecular weight polyethylene (UHMWPE) were investigated using tensile and bending testing, scanning electron microscopy and transition electron microscopy. The incorporation of minor amounts of UHMWPE (2 wt.-%) into PES-C has a reinforcement effect. With higher concentrations of UHMWPE, the mechanical properties decrease gradually. Structural studies demonstrated that the blends are multiphasic in the whole composition range. The minor UHMWPE, dispersed uniformly and oriented along the flow direction, as well as the strong interfacial adhesion contribute to the increase of the mechanical performance of the blends. The domain size of the UHMWPE phase was found to increase with the increase of its concentration.
    Additional Material: 6 Ill.
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    Redox copolymer with N-bromosulfonamide groups for the decomposition of cyanide ions in dilute aqueous solutions (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 117-130 
    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: Ein Redoxcopolymeres, ein makroporöses Poly(Styrol-co-Divinylbenzol) (S/DVB)-Harz mit N-Bromsulfonamidgruppen, wurde angewandt, um Cyanide aus wäßrigen Lösungen zu entfernen. Dieses Harz enthält aktives Brom in den funktionellen Gruppen (1.86 mmol g-1, 3.72 meq g-1) und weist Oxidationseigenschaften auf. Es wurde sowohl in statischen als auch in dynamischen Systemen für die Oxidation von Cyanidionen zu nichttoxischen Verbindungen angewandt. Die Reaktionen wurden in wäßrigen Lösungen mit 26-2600 mg L-1 CN- bei unterschiedlichen pH-Werten durchgeführt. Die Ergebnisse zeigten, daß dieses Harz die Cyanide leicht zu Cyanaten oxidiert, die ca. 1000 mal weniger toxisch sind. Bei Kontakt mit dem Harz fiel die Cyanidkonzentration in den Lösungen unter 0.05 mg L-1 CN-. Die —SO2NBrNa-Gruppen gingen dabei in —SO2NH2-Gruppen über. Diese konnten wiederum mit Natriumhypochlorit- und Natriumbromid-Lösungen reaktiviert werden. Es wurde auch eine Alternative zu der Cyanidionenoxidation mit N-Bromsulfonamid-Harz untersucht, indem ein analoges N-Chlorsulfonamid-Harz in Gengenwart von katalytischen Mengen von Bromiden angewandt wurde.
    Notes: A redox copolymer, macroporous poly(styrene-co-divinylbenzene) (S/DVB) resin having N-bromosulfonamide groups, was used for removal of cyanide ions from aqueous solutions. This resin contains active bromine in functional groups (1.86 mmol g-1, i. e. 3.72 meq g-1) and shows oxidative properties. It was employed in static and flow system for oxidation of cyanide ions to non-toxic compounds. The reactions were carried out in aqueous media containing 26-2600 mg L-1 CN- at different pH values. The data showed that the resin having active bromine easily oxidized cyanides, forming cyanates being 1000-times less toxic than cyanides. In contact with the resin the concentration of cyanides in tested solutions dropped below 0.05 mg L-1 CN-. During the oxidation processes the —SO2NBrNa groups transform to —SO2NH2 groups. They can be reactivated by use of sodium hypochlorite and bromide solutions. As an alternative to oxidation of cyanides by N-bromosulfonamide resin, the oxidation of these ions by N-chlorosulfonamide resin with addition of a small amount of bromides was examined.
    Additional Material: 3 Ill.
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    Mitteilungen/Announcements (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 251 (1997), S. 207-208 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: No Abstract
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    URL: http://dx.doi.org/10.1002/apmc.1997.052510118
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    Hydrolytic and thermal stability of novel polyurethane elastomers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 33-43 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Novel Polyester glycols with alkyl side groups were used for the improvement of thermal stability and hydrolytic stability of polyester urethane elastomers. The novel polyester glycols used are poly( β -methyl- δ -valerolactone)glycol (PMVL), poly(3-methyl pentamethylene adipate) glycol (PMPA), poly(nonamethylene-co-2-methyl octamcthylene carbonate) gycol (PNCO). A mixture of PNCO and poly(dimethyl siloxane)gycol (PNCO/PDMS) was also used. Polyurethane network elastomers were prepared from 4,4′-diphenylmethane diisocyanate (or 2,4-tolylene diisocyanate), and a mixture of 1,4-butane diol and trimethylol propane by a prepolymer method. Mechanical properties, Tg, thermal stability, and hydrolytic stability were measured. Morphology were also measured by means of polarizing microscopy, dynamic viscoelastometer, and ESR. The properties of novel polyurethane elastomers have good mechanical properties comparable to those of the general purpose polyester urethanes, and better thermal and hydrolytic stability than PTMG-based polyurethane. These polyurethane elastomers were exposed in out door during 2 year in Nagasaki, JAPAN. The novel polyurethane clastomers held alomost constant values for gel fraction, swelling ratio, relative modulus during 12 months, while poly(oxytetramethylene oxide)-based polyurethane as a control decreased the these values. Relationship of degradation behaviors with chemical structure and morphology were discussed.
    Additional Material: 9 Ill.
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    Oxidizability of lactams and lactam-based polyamidesDedicated to Dr Jan Šebenda on the occasion of his 70th birthday (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 139-151 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the chain oxidation of N-alkylamides with molecular oxygen, propagation is the ratedetermining step under conditions when the oxidation rate is independent of oxygen pressure. The oxidizability of lactams and lactam-based polyamides correlates with the energy of the formation of N-alkylamide radical by abstraction of hydrogen from the methylene group adjacent to nitrogen. While for lactams this energy depends on the number of carbons in the lactam ring, for N-alkylamides and polylactams such dependence is not observed.
    Additional Material: 1 Tab.
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    Use of EPR to image nitroxyl radicals in hals stabilized polymers (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 179-193 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An X-band EPR-Imaging apparatus which allowed us to determine the distribution of nitroxyl radicals within solid samples of polymeric materials containing hindered amine stabilizers, is described. It is shown that EPR Imaging represents a powerful tool for investigating the growth and decay of nitroxyls formed in polymers irradiated under air for long periods. Since the variations of the radical concentration can be monitored both in time and in the space, this technique provides valuable information not easily attainable by means of other methods.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1997.052520113
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    Photo-oxidation mechanisms of poly(2,6-dimethyl-1,4-phenylene oxide). (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 237-256 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic-type radicals have been detected by spin trapping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo-oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the of photo-oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CH2 Br groups, which has been used for further substitution reactions with alkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accelerated photo-oxidation of a modified copolymer PPO-PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.
    Additional Material: 9 Ill.
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    Zähigkeit und Relaxationsverhalten von Polymethylmethacrylat, Polystyrol und Polycarbonat (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 27-49 
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    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: For innovative applications of plastics, which take advantage of special properties of polymeric materials, comprehensive understanding on strengthening and toughening mechanisms is required. The temperature-dependent mechanical behaviour of PMMA, PS and PC under dynamic loading conditions were investigated by means of an instrumented Charpy impact tester. The elastic-plastic fracture mechanics parameters, the energy-determined J-integral, and the deformation-determined crack opening displacement, δ, enable to do structure-related quantification of micromechanical processes. The J-integral values showed a maximum, resulting from an energy-dissipative process. The maximum values for PMMA occurred at 50°C and for PC at 40°C , which is related to the secondary(β) relaxation as evaluated from the frequency dependence of the mechanical loss factor. The 0-relaxation initiated shear deformation mechanisms, which led to a local increase of toughness. In polycarbonate, toughness is strongly increased due to a stress-induced shear flow process at temperatures higher than -25°C. Correlations between morphology and toughness can be derived with the help of optical investigations of stable crack propagation on fracture surfaces.
    Notes: Innovative Kunststoffanwendungen, die die speziellen Eigenschaften polymerer Werkstoffe gezielt ausnutzen, erfordern vertiefte Kenntnisse über festigkeits- und zähigkeitsbestimmende Mechanismen. Das sich in Abhängigkeit von der Temperatur ändernde Werkstoffverhalten von PMMA, PS und PC wurde bei dynamischer Beanspruchung mittels instrumentierter Kerbschlagbiegeprüfung bestimmt. Mit der verformungsbestimmten Rißöffnungsverschiebung δ und dem energiebestimmten J-Integral stehen Kenngrößen der Fließbruchmechanik zur Verfügung, die eine strukturbezogene Quantifizierung der temperaturabhängigen mikromechanischen Prozesse erlauben. Die J-Integralwerte zeigen für PMMA bei 50°C und für PC bei -60°C ein durch einen energiedissipativen Prozeß verursachtes Maximum. Dieses Maximum steht, wie sich aus der Interpretation der Frequenzabhängigkeit des mechanischen Verlustfaktors ergibt, mit der Neben(β)-Relaxation in Beziehung. Dabei initiiert die β-Relaxation Scherdeformationsmechanismen, die ihrerseits die lokale Zähigkeitserhöhung bewirken. Ab -25°C führt für PC ein spannungsinduzierter Scherfließprozeß zu einer erheblichen Zähigkeitssteigerung. Durch die Einbeziehung lichtmikroskopischer Untersuchungen des stabilen Rißfortschritts auf der Bruchfläche können Morphologie-Zähigkeits-Korrelationen abgeleitet werden.
    Additional Material: 16 Ill.
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    Thermostable block copolymers, 2Part 1 cf. 16.. Preparation and characterization of soluble blockcopolyimides (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 71-88 
    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: Eine Reihe von Polyamidimid-Polyimid-Blockcopolymeren (PAI-PI-BCPs) wurde durch Polykondensation von PAI-Blöcken mit Amino-Endgruppen und PI-Blöcken mit Anhydrid-Endgruppen hergestellt. Zur Synthese der Blöcke mit Molekulargewichten im Bereich von ca. 2000 bis 15000 wurden nur technisch leicht zugängliche Monomere, wie Trimellitsäureanhydridchlorid, Benzophenontetracarbonsäuredianhydrid, 4,4′-Diaminodiphenylmethan, 2,4-Toluylendiamin und 4,4′-Diaminodiphenylsulfon eingesetzt. Dabei zeigte sich, daß durch den blockartigen Aufbau die Löslichkeit-und damit die Verarbeitbarkeit-im Vergleich zu den reinen, unlöslichen Polyimiden wesentlich verbessert werden konnte, bei nahezu gleichbleibender Thermostabilität. So wurden BCPs mit guten mechanischen Eigenschaften, Thermostabilitäten bis ca. 480°C (Thermogravimetrie, 5% Gewichtsverlust) und guten Löslichkeiten in Dimethylacetamid und anderen polaren aprotischen Lösungsmitteln erhalten.
    Notes: New poly(amide-imide)-poly(imide) block copolymers (PAI-PI-BCPs) were prepared by polycondensation of amino-terminated PAI-blocks with anhydride-terminated PI-blocks. For the syntheses of the blocks with molecular weights from 2000 to 15000 only commercially available monomers were used, e.g. trimellitic acid anhydride chloride, benzophenone tetracarboxylic acid dianhydride, 4,4′-diaminodiphenylmethane, 2,4-toluenediamine and 4,4′-diaminodiphenylsulfone. The BCPs were shown to have better solubility compared to the pure, insoluble PIs with only minor decrease of the thermostability. Thus, BCPs with good mechanical properties, thermostabilities up to 480°C (thermogravimetric analysis, 5% weight loss) and good solubility in dimethylacetamide and other polar aprotic solvents were obtained.
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    Block and graft copolymers with polysiloxane and poly(N-acyliminoethylene) sequences (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 139-149 
    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: Eine Reihe von Polysiloxan/Poly(N-acetyliminoethylen)-(PSiO/PNAI)-Block- und -Pfropfcopolymeren wurde durch Polymerisation von 2-Methyl-2-oxazolin (MeOZO) mit funktionellen Polysiloxan-Prepolymeren als Initiatoren synthetisiert. Die Copolymeren wurden mit IR- und 1H NMR-Spektroskopie sowie Elementaranalyse, Differentialkalorimetrie und Thermogravimetrie charakterisiert. Der Einbau sowohl von hydrophoben als auch von hydrophilen Sequenzen verleiht den Polymeren amphiphile Eigenschaften. Ihre Eigenschaften in Lösung und als Feststoffe lassen die Produkte für Anwendungen als nichtionische Emulgatoren, Oberflächenmodifikatoren, Gele, usw. geeignet erscheinen.
    Notes: A series of polysiloxane/poly(N-acetyliminoethylene) (PSiO/PNAI) block and graft copolymers were synthesized by the initiation of 2-methyl-2-oxazoline (Me-OZO) polymerization with functional polysiloxane prepolymers. The copolymerization products were characterized by IR- and 1H NMR spectroscopy, elemental analysis, DSC and thermogravimetry. The insertion of both hydrophobic and hydrophilic sequences in the macromolecular structure induces a behavior characteristic of amphiphilic compounds. Their solution and solid state behavior evidenced peculiarities which make them able to act as nonionic emulsifiers, surface modifiers, gels, etc.
    Additional Material: 4 Ill.
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    The state of water in styrene-grafted and sulfonated poly(vinylidene fluoride) membranes (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 151-167 
    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: Der Zustand von Wasser in Protonenaustausch-Membranen, hergestellt durch Pfropfen von Styrol auf Polyvinylidenfluorid-Filme (PVDF-g-PS) mittels Elektronenstrahlen und anschließendes Sulfonieren (PVDF-g-PSSA), wurde mittels Differentialkalorimetrie (DSC), Raman-Spektroskopie und Rontgen-Diffraktion (SAXS) ermittelt. Die Raman-Untersuchungen zeigten, daß einzelne Wassermolekule durch hydrophobe Wechselwirkungen an die Polymerketten gebunden sind. Die DSC-Untersuchungen zeigten, daß Wasser in den Membranen in drei verschiedenen Umgebungen vorliegt: nicht gefrierendes ionisch gebundenes Wasser, gefrierendes freies Wasser und gefrierendes gebundenes Wasser. Die Menge an nicht gefrierendem Wasser betragt unabhangig vom Pfropfungsgrad etwa 10 H2O/SO3H (mol/mol). Die Menge an gefrierendem Wasser ist stark vom Pfropfungsgrad abhangig. Oberhalb eines Pfropfungsgrades von 50% werden Werte von 40 H20/S03H (mol/mol) erreicht. Die Leitfahigkeit von nur nicht gefrierendes Wasser enthaltenden Membranen ist gering, d. h., das ionisch gebundene Wasser kann nicht allein die fur den Transport von Protonen und Wasser notwendigen Kanale bilden. Die SAXS Untersuchungen zeigten, daß Wasser/Sulfonsaure-Cluster in Membranen aus hydratisiertem PVDF-g-PSSA mit einem Bragg-Abstand von 25 Å gebildet werden. Diese Cluster formen die Kanale fur den Ionentransport und die Leitfähigkeit.
    Notes: The state of water in proton exchange membranes prepared by pre-irradiation (electron beam, 100 kGy) grafting of styrene onto poly(vinylidene fluoride) films (PVDF-g-PS), followed by sulfonation (PVDF-g-PSSA), has been studied with thermal analysis, Raman spectroscopy and small angle X-ray diffraction (SAXS). Raman spectra show that, in addition to free liquid water in the membranes, single water molecules are weakly bound to the polymer backbone. Thermal analysis shows that there are three types of water molecules in the membrane; non-freezable water associated with the ionic sites, freezable free water, and freezable bound water. The amount of non-freezable water is around 10 H2O/SO3H (mol/mol), and is independent of the degree of grafting (d.o.g.). The amount of freezable water is strongly dependent on the d.o.g. as long as the grafting has not penetrated the whole of the film, and reaches a value of around 40 H2O/SO3H (mol/mol) above a d.o.g. of 50%. The conductivity of membranes containing only the non-freezable water is low, i. e. the ionically bound water alone does not form the domains necessary for proton and water transport. SAXS measurements show that water/sulfonic acid clusters in hydrated PVDF-g-PSSA membranes with a Bragg distance of 25 Å are formed; these form the ion conducting channels in the membrane.
    Additional Material: 9 Ill.
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    MITTEILUNGEN/ANNOUNCEMENTS (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 211-211 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    Tensile and flexural behavior of polypropene sheets with different crystallinities of surface layer (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 253 (1997), S. 201-210 
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    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 Zug- und Biegemoduli von preßgeformten Polypropen-Probekörpern mit unterschiedlichen Oberflächenkristallinitäten wurden basierend auf der Annahme eines Schicht-Verbund-Modells untersucht. Es zeigte sich, daß die Spannungs-Dehnungs-Kurven der Zugversuche und die Werte der Biegeablenkung im wesentlichen von der Oberfächenkristallinität abhängen, jedoch erwiesen sich die Bruchspannungen als von der Oberflächenkristallinität unabhängig. Es wird angenommen, daß das beobachtete Zug- und Biegeverhalten der Proben auf der Grundlage eines Schicht-Verbund-Modells, bei dem eine massive, starre Platte zwischen zwei weichen Schichten eingebettet ist, charakterisiert werden kann.
    Notes: The tensile and flexural moduli of the compression-molded sheets of polypropene with different surface layer crystallinity were investigated based on a layered composite model. It was found that the tensile stress-strain curve and flexural deflection depended largely on the surface layer crystallinity, but the ultimate strain-at-break values were independent of the surface layer crystallinity. It is suggested that the tensile and flexural behavior can be characterized using a layered composite model in which a bulk plate was sandwiched between two surface layers.
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    The role of charge transfer complexes in the photodegradation of polyolefins (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 45-54 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Addition of HALS-stabilisers, the cut-off wavelength of the light source, the temperature and the oxygen pressure have an influence on the UV-degradation mechanism of polyolefins. All these parameters influences the conversion of oxygen into polymeric carbonyls. The results are explained assuming that the initiation of the UV-degradation of pololefins is due to substrate-oxygen charge transfer complexes (CTCs).
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    Fracture behavior of exposed HDPE specimens with an embrittled layer due to UV-exposure (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 69-88 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The applicability of fracture mechanics was studied on UV-exposed HDPE Charpy specimens. The failure distribution of the stress at failure measured in three-points bending tests showed a bifurcation in failure processes. At high stresses yielding occurs, resulting in large strain at failures. At lower stresses crack propagation causes low strain at failures. Due to the bifurcation in failure processes the ductile-brittle transition temperature of exposed specimens is hard to determine.Specimens notched after exposure showed a decrease in the critical stress intensity values. The effective notch depth of exposed specimens was found to be larger than the thickness of the oxidized layer measured by FT-IR and density measurements.
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    Deactivation processes of 2-hydroxyphenyl-1,3,5-triazines  -  polymeric and monomeric UV absorbers of the benzotriazole and triazine class (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 252 (1997), S. 119-138 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In the 2-hydroxyphenyl-1,3,5-triazines, the intramolecular hydrogen bond is stronger than in the corresponding 2-hydroxyphenylbenzotriazoles. Compounds with only one aryl group in the 2-hydroxyphenyl-1,3,5-triazine series show proton-transferred fluorescence with large Stokes shift and high quantum yield. No such fluorescence is observed, in contrast, for compunds with three aryi groups bearing no electrondonating groups on the aryl moieties. When the hydrogen atom of the intramolecular hydrogen bond is replaced by CH3, the respective derivative shows fluorescence with a normal Stokes shift.Various copolymers of MA-TIN 1 (2-[2-hydroxy-3-tert.-butyl-5-(O-[2-hydroxy-3-(2-methylpropenoyloxy)propyl]-2-carbonyloxyethyl)phenyl]benzotriazole), and MA-TZ 1 (2,4-Bis(2,4-dimethyl-phenyl)-6-[2-hydroxy-4-(2-hydroxy-3-[2-methylpropenoyloxy])propoxyphenyl]-1,3,5-triazine) with styrene, methyl methacrylate, and methacrylic acid have been synthesized by radical polymerization. The absorption spectra in the longwavelength UV region appear unchanged compared to those of the monomeric UV absorbers indicating that the stabilizer chromophores are conserved intact in the polymer. Both the monomeric and the polymeric stabilizers exhibit a strongly Stokesshifted, temperature-dependent, low-quantum-yield, proton-transferred fluorescence. This may be taken as evidence that the intramolecular hydrogen bond, which is essential for the photostability of this type of UV absorber, remains intact also in the copolymers. Activation energies of the radiationless deactivation process can be evaluated from the temperature dependence of this fluorescence. These energies lie between 4 and 5 kJ/mol for most of the benzotriazole and triazine stabilizers investigated.Fluorescence-decay measurements with crystalline MA-TIN 1 at different temperatures reveal a close correspondence of the temperature dependence between decay times and relative quantum yields. The radiationless process is thence concluded to originate from the proton-transferred level S1'. The decay time at room temperature is estimated at 70 ps, close to the value for crystalline TIN P (2-(2-hydroxy-5-methylphenyl)benzotriazole). The proton-transferred fluorescence of MA-TIN 1 exhibits a biexponential decay profile whereas solid TIN P, in contrast, displays only one single lifetime.
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    Rǒle des electrons π des fonctions amide et ester dans les peptides et depsipeptides (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 169-185 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The IR data for the R1 CO-O-CHR2-CO-NHR3 derivatives are interpreted in terms of a H…π interaction involving the N—H bond and the π orbitals of the ester function and giving rise to a high ν(C=O) frequency and a low ν frequency. The resulting molecular conformation corresponds to the angular values φ # -90°, ψ # 0°. The H…π interaction in MeCO-L-Lac-NHMe is highly destabilized by water and aprotic solvents but is retained in methanol. Considering the high ν(C=O) ester or amide frequency of the middle function in β-folded depsipeptide or peptide sequences, it may be supposed that the residue indexed i + 2 in β turns experiences a H…π interaction which has a stabilizing effect on β turns. Some examples concerning valinomycin and some model compounds are discussed.
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    Masthead (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.1981.360200201
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    Polyelectrolyte contribution to the persistence length of DNA (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 251-268 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The difference between the theories of Manning, on the one hand, and of Odijk and Skolnick and Fixman, on the other, for the polyelectrolyte contribution to the persistence length of DNA is shown to arise entirely from a subtle geometrical error in the theory of Manning. The corrected theory of Manning predicts a negligible polyelectrolyte contribution in 1.0M NaCl and only 33 Å in 0.01M NaCl, thus giving a change in total persistence length by a factor of only 1.07 over that range, in agreement with Odijk. Pertinent data in the literature indicate that the persistence length must change by a factor of ≤ 1.6 between 1.0 and 0.01M NaCl, and very likely by less than a factor of 1.4. Evidently, the intrinsic rigidity of the uncharged double-strand filament dominates the bending rigidity at NaCl concentrations above 0.01M.
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    Conformational studies of peptides: Crystal and molecular structures of L-3,4-dehydroproline and its t-butoxycarbonyl and acetyl amide derivatives (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 283-302 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of L-3,4-dehydroproline, t-butoxycarbonyl-L-3,4-dehydroproline amide, and acetyl-L-3,4-dehydroproline amide have been determined. L-3,4-Dehydroproline is orthorhombic with a = 16.756, b = 5.870, c = 5.275 Å, and Z = 4; t-butoxycarbonyl-L-3,4-dehydroproline amide is orthorhombic with a = 6.448, b = 8.602, c = 21.710 Å, and Z = 4; acetyl-L-3,4-dehydroproline amide is monoclinic with a = 4.788, b = 10.880, c = 7.785 Å, β = 105.25°, and Z = 2. The final R value for the L-3,4-dehydroproline is 0.046 based on 529 reflections; for t-butoxycarbonyl-L-3,4-dehydroproline amide, 0.050 based on 792 reflections; and for acetyl-L-3,4-dehydroproline amide, 0.058 based on 632 reflections. The structures clearly establish that the free amino acid exists in the zwitterionic form in the crystalline state. The molecular conformations of the t-Boc and acetyl derivatives consist of two planes: one involving the primary amide and the other the remaining atoms of the molecule. The acetyl-L-3,4-dehydroproline amide contains a tertiary amide bond in the cis conformation. To the best of our knowledge, this is the first example of a cis bond in an acetyl derivative of an amino acid or peptide. At variance with the previously reported proline amides, which present φ and ψ values corresponding to those of a right-handed α-helical conformation (conformation A), the t-Boc and acetyl derivatives both have φ and ψ values corresponding to a collagenlike conformation (conformation F).
    Additional Material: 6 Ill.
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    Physical properties of type i collagen in solution: Structure of α-Chains and β- and γ-components and two-component mixtures (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 359-371 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of thermally denatured Type I collagen has been studied using laser light scattering. The results indicate that the diffusion coefficients of α-chains and β- and γ-components are 1.550 ± 0.08 × 10-7, 1.000 ± 0.05 × 10-7, and 0.835 ± 0.04 × 10-7 cm2/sec, respectively, at temperatures between 20 and 40°C. It is concluded from diffusion data that these species have hydrodynamic radii of about 13.8 nm (α-chain), 21.5 nm (β-component), and 25.7 nm (γ-component), consistent with previous studies of thermal denaturation by light scattering. It is also concluded, based on volume calculations, that a large volume increase occurs when the triple helix unfolds. Homodyne correlation functions for two component mixtures of α-chains and β-and γ-components appeared to decay exponentially. In all but one case discussed the correlation function could be fitted with a single component having a translational diffusion coefficient which was an intensity weighted average of the diffusion coefficient of each component present.
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    Theoretical π-π* circular dichroic spectra of helical poly(glycine) and poly(L-alanine) as functions of backbone torsion angles (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 387-397 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Circular dichroic spectra and oscillator strengths of the π-π transition near 190 nm are calculated for helical (Gly)6 and (Ala)6 at 30° intervals of the backbone torsion angles (φ,ψ) over the range -180° ≤ φ ≤ -60°, -60° ≤ ψ ≤ 180°, using the partially dispersive normal mode treatment of the dipole interaction model. Polarizabilities of atoms and the NC′O group are those determined semiempirically in previous studies. Calculations for (Ala)6 at (φ,ψ) angles corresponding to the α-helix, the poly(Pro) II helix, a collagen single helix, a poly-(MeAla) helix, and single β-helices are found to agree well with most of the available experimental data.
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    Interaction of the antimalarial drug fluoroquine with DNA, tRNA, and poly(A): 19F-NMR chemical-shift and relaxation, optical absorption, and fluorescence studies (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 435-449 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of the fluorinated antimalarial drug fluoroquine [7-fluoro-4-(diethyl-amino-1-methylbutylamino)quinoline] with DNA, tRNA, and poly(A) has been investigated by optical absorption, fluorescence, and 19F-nmr chemical-shift and relaxation methods. Optical absorption and fluorescence experiments indicate that fluoroquine binds to nucleic acids in a similar manner to that of its well-known analog chloroquine. At low drug-to-base pair ratios, binding of both drugs appears to be random. Fluoroquine and chloroquine also elevate the melting temperature (Tm) of DNA to a comparable extent. Binding of fluoroquine to DNA, tRNA, or poly(A) results in a downfield shift of about 1.5 ppm for the 19F-nmr resonance. The chemical shift of free fluoroquine depends on the isotopic composition of the solvent (D2O vs H2O). The solvent isotope shift is virtually eliminated by fluoroquine binding to any one of the nucleic acids. 19F-nmr relaxation experiments were carried out to measure the spin-lattice relaxation time (T1), 19F{1H} nuclear Overhauser effect (NOE), off-resonance intensity ratio (R), off-resonance rotating-frame spin-lattice relaxation time (T1ρoff), and linewidth for fluoroquine in the nucleic acid complexes. By accounting for intramolecular proton-fluorine dipolar and chemical-shift anisotropy contributions to the fluorine relaxation, all of the relaxation parameters for the fluoroquine-DNA complex can be well described by a motional model incorporating long-range DNA bending on the order of a microsecond and an internal motion of the drug on the order of a nanosecond. Selective NOE experiments indicate that the fluorine in the drug is near the ribose protons in the RNA complexes, but not in the DNA complex. Details of the binding evidently differ for the two types of nucleic acids. This study provides the foundation for an investigation of fluoroquine in intact cells.
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    Hydrodynamic behavior and molecular conformation of poly(L-lysine HBr) in carbonate buffer solution (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 345-357 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In carbonate buffer at pH 10.5, a transparent solution of poly(L-lysine HBr) was obtained up to fairly high concentration of 3 g/dl at room temperature. The hydrodynamic behavior of the solution has been studied by sedimentation analyses and viscosity measurements. A dimer form for high concentrations and a monomer form for low concentrations were inferred. The dimer and monomer forms were assigned to a β-structure and α-helix, respectively, based on the CD and optical rotary dispersion spectra. Using CD spectroscopy, a reversible transition between α-helix and β-structure was observed as a function of either poly(L-lysine HBr) concentration or temperature. An aggregated form which was assigned to the antiparallel pleated sheet appeared at 50°C on the basis of its ir spectrum.
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    Stability and geometry of hydrogen-bonded complexes of peptides (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 707-718 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Observations of induced circular dichroism (CD) bands in chloroform solution demonstrate the formation of specific, asymmetric complexes of the aromatic ligands 2-pyridone and 2,6-dichlorobenzoic acid with cyclic dipeptides of the general formula cyclo(L-Pro-X). The induced CD changes sign with the configuration of X due to subtle influences of the side chain on the geometry of the complex. Computations of interaction energies suggest that a plausible model for the complex of an aromatic ligand with the -CONH- of the cis secondary amide is a nearly planar arrangement of six heavy atoms in a ring containing two hydrogen bonds. The observed CD is matched by that computed for a tilt of the aromatic ligand toward the side chain of X. Binding constants were determined from the induced CD as a function of ligand concentration. For dichlorobenzoic acid these are about 450m-1 for the secondary amide and 50m-1 for the tertiary amide. For pyridone the binding constant is about 45m-1 for either the secondary or tertiary amide. For comparison self-dimerization constants determined by vapor-pressure osmometry in chloroform solution at 25°C are 870, 350, 50, and 20m-1 for pyridone, benzoic acid, dichlorobenzoic acid, and cyclo(L-Pro-Gly), respectively.
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    Proton and phosphorus nmr investigation of the conformational states of acid polyadenylic double helix (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 803-816 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proton and phosphorus nmr have been used to investigate the double-helical structures of polyriboadenylic acid [poly(A)] formed in acidic solutions (pH 〈 6). The results obtained at low pH (∼4.5) are consistent with the model for the acid poly(A) double helix proposed by Rich [Rich, A., Davies, D. R., Crick, F. H. C. & Watson, J. D. (1961) J. Mol. Biol. 3, 71-86]. Other models that have been proposed are inconsistent with the nmr data. The nmr measurements have also been used to examine the conformation of poly(A) helix in the half-protonated state. Although the base-stacking arrangement of this state is similar to that observed in the more extensively protonated low-pH state, the phosphate backbone conformation is different from that found in either the neutral or low-pH structures.
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    Masthead (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981) 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.1981.360200101
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    Effect of some organic cosolvents on the reaction of hemoglobin with oxygen (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 39-51 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We studied the effects of some organic cosolvents (monohydric alcohols and amides) on the reaction of hemoglobin with oxygen. We present evidence showing that our data can be analyzed within the framework of the Monod-Wyman-Changeux model and that the main effect of cosolvents is to alter the T ⇄ R conformational equilibrium of hemoglobin, without significantly affecting the intrinsic oxygen dissociation constants. Following a previously described phenomenological approach, the overall effects have been separated into effects related to the variation of the bulk dielectric constant of the solvent and effects not related to the variation of this constant.
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    XII. Conformational studies of histidine-containing peptides in solution (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 65-88 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectroscopic properties (uv, CD, nmr) of histidine, glycylhistidine, histidylglycine, glycylhistidylglycine have been investigated in water and methanol in the temperature range 200-320 K in order to obtain information about their conformational equilibria. This analysis has been carried out for the different ionic forms of the compounds, in order to evaluate the influence of the ionization state of the carboxyl, histidyl, and amino groups on the rotamer distribution of the histidyl side chain (as evaluated from proton nmr analysis) and on the overall molecule (as judged from CD spectra). On the basis of certain approximations and from the temperature dependence of the proton nmr resonance, the thermodynamic parameters (ΔH° and ΔS°) characterizing the conformational equilibrium of the hystidyl side chain have been evaluated for the different structures and ionization states. Relatively large entropy differences between the rotamers are obtained in some cases. The data of the sidechain rotamer population, as determined by nmr, have been analytically correlated with the CD data, and in the case of hystidine and histidylglycine in basic solution, first-approximation values for the ellipticity of the single conformers have been evaluated. Finally, in the example of glycylhistidine and histidylglycine in basic solution, it is shown how the data obtained from the different experimental approaches (nmr and CD), as well as from theoretical energy calculations, converge to characterize the most stable conformation in solution.
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    Laser light-scattering analysis of the dimerization of transfer ribonucleic acids with complementary anticodons (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 155-168 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photon-correlation spectroscopy is a powerful technique for measuring the translational diffusion coefficient of particles and macromolecules in solution. In the study described here, this technique was used to analyze a specific dimerization process involving the association of two tRNA molecules through complementary anticodons. The tRNAs used in the analysis were E. coli tRNA2Glu and yeast tRNAPhe. The experimental data on the concentration dependence of the observed diffusion constants are shown to agree well with theoretical predictions. From these data, the equilibrium constant of the association reaction was determined for dimers formed over a wide range of temperatures and in several different solution conditions. In solutions of 0.1M ionic strength at 22°C, the equilibrium constants vary from 1 × 105M-1 in the absence of magnesium to 1.5 × 106M-1 in 10 mM Mg+2. The enthalpy and entropy changes for dimer formation in the absence and presence, 5 and 10 mM, of magnesium have been obtained from the temperature dependence of the equilibrium constant. The results show that both ΔH and ΔS contribute to the free energy of binding and that their relative contributions are similar for each solution condition evaluated.
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    Dependence of DNA conformation on the concentration of salt (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 231-235 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.1981.360200116
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    Vibrational circular dichroism of poly(γ-benzyl-L-glutamate) (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 237-240 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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    Low-frequency modes in the raman spectrum of DNA (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 243-247 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.1981.360200119
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    Quantum-mechanical study of model molecules in relation to collagen structure. II. (Gly-Phe-Pro) and (Gly-Pro-Phe) repeating units (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 269-282 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A conformational quantum-mechanical study of (Gly-Phe-Pro) and (Gly-Pro-Phe) repeating tripeptide sequences has been carried out with the PCILO method. Using appropriate molecules as a model, we investigated the conformational possibilities of each in situ residue. Computations have been done taking into account the two typical pyrrolidine ring puckering and the most favorable orientations of the phenylalanyl side chain. Major conclusions drawn from this study are that the phenylalanyl can be accommodated at both second and third positions in the sequence without preventing the formation of triple-helix conformation. However, the analogy observed between the rotational possibilities around the second residue of Gly-Pro-Pro and Gly-Phe-Pro indicates that phenylalanyl in the second position favors the triple-helix formation.
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    Neutron-scattering studies of the structure of chromatin core particles in solution (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 327-343 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the nucleosome core particle in solution has been studied by neutron scattering using the full-contrast variation technique, which reduces the experimental spectra to three fundamental scatter functions holding information on shape and structure. Systematic calculations of the fundamental scatter functions expected from proposed core-particle models have been compared with the observed functions and show that the neutron-scattering criteria severely restrict the number of models which can be valid for the structure in solution. The best model for the core particle in solution has a hydrophobic histone core about which 1.7 ± 0.1 turns of DNA are wrapped at a pitch between 3.0 and 3.5 nm. This core contains most of the histone and has an average thickness of 4 nm and diameter 6.4-7.5 nm. While solution scattering is not able to specify uniquely the actual shape of the core to high resolution, all models which are possible for the shape of the core to a resolution justified by the data have been considered. It is clear that cylindrical or wedge shapes compatible with the above dimensions are valid structures. A hole probably penetrates the histone core, but the data do not allow a diameter greater than 1 nm. Available evidence suggests that about a quarter of the total histone is outside the core.
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    Relationship between proton-proton nmr coupling constants and substituent electronegativities. III. Conformational analysis of proline rings in solution using a generalized Karplus equation (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1211-1245 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The relationship between published vicinal proton-proton coupling constants and the pseudorotation properties of the pyrrolidine ring in L-proline, 4-hydroxy-L-proline, 4-fluoro-L-proline, and several linear and cyclic model proline peptides is investigated. Compared to earlier studies, several important improvements are incorporated: (1) a new empirical generalization of the classical Karplus equation is utilized, which allows a valid correction for the effects of electronegativity and orientation of substitutents on 3JHH; (2) an empirical correlation between proton-proton torsion angles and the pseudorotational parameters P and τm is derived; and (3) the best fit of the conformational parameters to the experimental coupling constants is obtained by means of a computerized iterative least-squares procedure. Two pseudorotation ranges were considered, classified as type N (χ2 positive sign) and type S (χ2 negative sign). The conformational equilibrium is fully described in terms of four geometrical parameters (PN, τN, PS, τS) and the equilibrium constant K. The present results indicate that, in general, the geometrical properties found in x-ray studies of proline and hydroxyproline residues are well preserved in solution. Several novel features are encountered, however. It is demonstrated that the proline ring occurs in a practically 1:1 conformational equilibrium between well-defined N- and S-type forms. Introduction of an amide group at the C-terminal end has no observable effect on this equilibrium, but the formation of a peptide bond at the imino nitrogen site results in a pronounced, but not exclusive, preference for an S-type form which is roughly 1.1 kcal/mol more stable than its N-type counterpart. The hydroxyproline ring system in neutral or acidic medium displays a pure N-type state, but N-acetylation results in the appearance of a minor (S-type) conformation. Cyclic proline dipeptides similarly exist in a biased conformational equilibrium. The major form (77-88%) corresponds to the N-type conformer observed in the solid state; the minor S-form has not been observed before. In contrast, cyclic hydroxyproline dipeptides display complete conformational purity. Ranges of endocyclic torsion angles deduced for the various classes of pyrrolidine derivatives in solution are presented. Each torsion appears confined to a surprisingly narrow range, comprising about 4°-8° in most cases. In all, the proline ring is far less “floppy” than hitherto assumed.
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    Thermodynamics and equilibrium sedimentation analysis of the close approach of DNA molecules and a molecular ordering transition (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1305-1328 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Measurement of the equilibrium distribution of persistence length fragments of DNA in high concentration in the ultracentrifuge shows that the reduced osmotic pressure rises much faster than linearly. From analysis of the data in terms of the Zimm cluster integral we infer that the net interactions between helices are purely repulsive at all distances. A theoretical equation of state derived from scaled particle theory with one adjustable parameter is in excellent agreement with the experimental data so long as the salt concentration is not excessively low. The parameter represents the hard-core radius in a simplified approximation to the potential function for the electrostatic repulsion between helices. Its value depends on the salt concentration, and it shrinks at high salt to a radius in close agreement with direct structural estimates. At a particular value of the osmotic pressure that is only slightly salt dependent, the solution undergoes a reversible transition to a denser, turbid, optically anisotropic phase. The relation between DNA volume fraction, including the electrostatic radius, at the transition point and the effective asymmetry of the molecules as a function of salt is in approximate correspondence with various theoretical treatments. However, the experimental function extrapolates to the correct limit for spherical particles. The work needed to bring DNA to a high concentration is estimated. The results suggest that the phase transition is first order.
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    Quantitative test of Record's theory for proton-induced lowering of DNA melting temperature (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2121-2136 
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    Notes: This report presents a quantitative test of the ability of the counterion condensation theory to describe the proton-induced lowering of DNA melting temperature. From a general approach of Record et al. [Record, M. T., Anderson, C. F. & Lohman, T. H. (1978) Q. Rev. Biophys. 11, 103-178], we have obtained an expression that may be computer-fitted to the experimental data by numerical minimization of χ2. To do this, in addition to the assumptions made by Record et al., it was necessary to suppose that the interchange between protons and sodium is independent of pH and, due to the absence of data, take the enthalpies of protonation as thermally independent over the experimental temperature range. The dependences of the enthalpy of denaturation at neutral pH on sodium concentration and on G + C content were taken from literature. In the fitting process we have used 250 melting temperatures obtained at different pH and sodium concentrations for various natural DNAs. The theoretical expression gives a good quantitative description of the G + C and sodium concentration influences on the phenomenon but is only qualitative with respect to the dependence of dT/d log[Na+] on the pH. The adjusted pK values for the bases in denatured DNA agree with those for isolated deoxynucleosides. Interchange between sodium and protons is found to be less than 1:1. Calculated protonation enthalpies are ill-defined because of their low numerical influence. In short, it appears that the theory gives a good description of most of the aspects of the phenomenon even if it has some shortcomings, perhaps due to the great number of assumptions.
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    Effects of some organic cosolvents on the functional properties of hemoglobin: Kinetics of O2 displacement by CO (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2137-2142 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Notes: We studied the kinetics of replacement of O2 by CO in hemoglobin in the presence and absence of organic cosolvents (methanol, ethanol, iso-propanol, n-propanol, formamide, acetamide, N-methyl-formamide) and at 10 and 25°C. Quantitative analysis of the results indicates that these cosolvents do not affect the intrinsic binding constants of ligands to the heme when hemoglobin is in the R conformation. The present results confirm the previously reported suggestion that the effects of the above cosolvents on the oxygen affinity of hemoglobin are related to effects on the T ⇄ R conformational equilibrium.
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    Influence of the telopeptides on type I collagen fibrillogenesis (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2195-2202 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparations have been made of acid-soluble collagens whose telopeptides have suffered different levels of proteolytic attack. The collagens with more intact telopeptides form fibrils more rapidly than those with degraded telopeptides. In addition, we have shown that a high molecular weight aggregate rich in the carboxyterminal CNBr peptide, α1CB6, can be found in cyanogen bromide digests of fibrils formed from intact collagen. A similar aggregate is found in CNBr digests of native tendons. The aggregate formed in fibrils assembled in vitro can be stabilized by reduction, and its generation is strongly dependent on the presence of intact telopeptides. The latter point is the most objective evidence that to reproduce the characteristics of native fibrils in vitro, the collagen telopeptides must be preserved from proteolysis.
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    Free-sliding ligands: An alternative model of DNA-protein interactions (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2225-2241 
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    Topics: Chemistry and Pharmacology
    Notes: We present an alternative to the common lattice model for nonspecific DNA-protein interactions by using ligands that translate freely along the polynucleotide instead of binding to distinct lattice sites along the polynucleotide chain. The general model we present corresponds to a one-dimensional continuum gas and is referred to as the “continuum model” to distinguish it from the general lattice model. Explicit expressions are obtained for the binding isotherm equation for two version of the continuum model, including the effects of binding-site exclusion and attractions between bound ligands. Theoretical results are compared to those obtained from the McGhee-von Hippel (1974) analysis of the lattice model with cooperative interactions between ligands occupying more than one lattice site. Practical applications of the continuum model are illustrated by analyzing (i) the noncooperative binding to single-stranded DNA by RNase (Jensen and von Hippel, 1976), and (ii) the highly cooperative binding to poly(rA) by a proteolyzed fragment of the gene 32 protein of phage T4 (Lonberg et al., 1981).
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    Simulations of the solvent structure for macromolecules. II. Structure of water solvating Na+-B-DNA at 300 K and a model for conformational transitions induced by solvent variations (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2427-2483 
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    Notes: The structure of water and its interaction energy with a fragment of B-DNA composed of 12 base pairs and of the corresponding 24 sugar and 22 phosphate units and Na+ ions (one at each phosphate group) are analyzed using Monte Carlo simulations. The sample of water molecules, at the simulated temperature of 300 K, is composed of 447 water molecules. The results are discussed either in terms of statistical analyses over the 2,000,000 simulated conformations (after equilibration) or with reference to an “average configuration.” Comparison is made to a simulation previously presented for the same system but without counterions. Isotherm at different relative humidity, hydration, and reactivity scales for different sites, the hydration number at each site, the structure of intraphosphate and interphosphate hydrogen-bonded filaments of water are reported and discussed. The stabilization of the B-conformation induced by the solvent with counterion (“ion-induced compression effect”) is analyzed on the base of the above findings. A preliminary model to predict conformational transition in DNA is presented. The analyses reported are very detailed to allow refined interpretations of spectroscopic (infrared, Raman, and nmr) and scattering (x-ray and neutron beam) data on DNA insolution.
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    Condensed states of nucleic acids. III. Ψ(+) and Ψ(-) Conformational transitions of DNA induced by ethanol and saltPaper II of this series is S.-M. Cheng and S. C. Mohr (1975) Biopolymers 14, 663-674. Portions of this work were presented at the XIth International Congress of Biochemistry, Toronto, Canada, July 1979. (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2533-2552 
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    Notes: The conformational response of calf thymus DNA to solvent conditions altered by varying amounts of ethanol and NaCl has been monitored by circular dichroism (CD). These measurements, which extend over a much greater range of conditions than previously examined, reveal (above critical concentrations of ethanol and salt) a condensed form of the macro-molecule with unusually large positive ellipticity in the 250-300-nm region [the Ψ(+) state]. Mere increase in NaCl concentration at constant 35% (v/v) concentration of ethanol suffices to convert such Ψ(+) samples - via a series of intermediate forms with CD spectra resembling those of A-DNA, then B-DNA - into Ψ(-) states having anomalously large negative ellipticity similar to the well-known Ψ(-) forms produced by above-critical concentrations of poly-(ethylene oxide) and salt. These ethanol/salt-induced transitions are all completely reversible and can occur without formation of any visible precipitates. We suggest that they represent predominantly tertiary structural changes of B-form DNA molecules analogous to the changes which occur in several other systems where Ψ(+) ⇌ Ψ(-) interconversion has been reported. A “skein-of-yarn” model for the condensed tertiary (and quaternary, i.e., aggregated) state of the DNA affords one possible explanation for the inversions of ellipticity in all these cases. Such a model accords well with the accepted description of cholesteric liquid crystals.
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    Nmr studies of the rates of proline cis-trans isomerization in oligopeptides (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2623-2633 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H-Nmr was used to measure the rate of cis-trans interconversion of X-Pro bonds in linear and cyclic oligopeptides. k(cis → trans) = 2.5 × 10-3 s-1 at 25°C was found for the zwitterionic form of H-Ala-Pro-OH, in good agreement with earlier measurements. Replacement of Ala by Phe, Tyr, or Trp resulted in a 10-fold slower interconversion rate, whereas after substitution of Ala by His or Glu, the rate decreased only slightly. Independent of the residues X, the interconversion rate was increased by a factor of ca. 20 when the peptide chain was elongated by addition of Ala to the C-terminal Pro. An additional increase by a factor of 6 was observed when going from the protected linear peptide CF3CO-Gly-Gly-Pro-Ala-OCH3 to the closely related cyclic compound c[-Gly-Gly-Pro-Gly-Ala-]. These data are evaluated with regard to their possible use in future studies on the role of X-Pro cis-trans isomerization in the kinetics of protein folding.
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    Contribution from the chirality of the growing chain to the enantiomer selectivity in activated-NCA polymerization of α-amino acid N-carboxyanhydride (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 507-524 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As a model compound for the growing chain in the activated-NCA type of polymerization of α-amino acid N-carboxyanhydride (NCA), 3-[ω-acetylglycyl-poly(α-amino acid) acyl]-α-amino acid NCA (called the prepolymer) having various degrees of polymerization (DPs) was synthesized by the polymerization of Phe, Val, Glu(OEt), and Asp(OBzl) NCA in the presence of AcGly NCA by the tertiary amine. Activated (S)-Phe, Val, Glu(OEt), and Asp(OBzl) NCA were added to the terminal cyclic group of the corresponding (S)- or (R)- prepolymer, and the enantiomer selectivity in the reaction was investigated. With prepolymers having DPs ranging from 1 to 15, the addition reaction always took place preferentially between species having the same configuration, and the degree of the enantiomer selection increased with increasing DP of the prepolymer. With prepolymers having DP = 1 and 2, we found contributions from the chiral terminal unit and the chiral penultimate unit to the enantiomer selection, respectively. Prepolymer having DP = 5 was shown to take a β-type conformation, which led to higher enantiomer selection; and prepolymers having DP = 10 and 15 were shown to take an α-helix conformation, which led to much higher enantiomer selection than did the β-type conformation. In the present investigation the mechanisms of terminal-unit control, penultimate-unit control and conformational control of the enantiomer selection in the activated-NCA type of polymerization were clearly observed.
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    Spectroscopic studies on the structure of poly(8-bromoadenylic acid): Effect of glycosidic torsion angle on the conformation and flexibility in polyribonucleotides (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 573-603 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The helix-coil transition and conformational structure of poly(8-bromoadenylic acid) [poly(8BrA)] have been investigated using 1H- and 13C-nmr, CD, and ir spectroscopy. The results have been compared with the structure of the related 5′-mono- and polynucleotides. The chemical shifts of H(2′), H(3′), C(2′), and C(3′) nmr signals show an interesting correlation with both the puckering of ribose ring and glycosidic bond torsion angle. Poly(8BrA) shows an upfield shift of the C(3′) signal and a downfield shift of the H(3′) signal compared to the chemical shifts in poly(A). These shifts are consistent with a C(3′) endo-syn conformation for poly(8BrA). A similar effect has been reported previously and is also observed here on the C(2′) and H(2′) signals when the preferred conformation is C(2′)endo-syn (e.g., in 5′-8BrAMP). The chemical-shift parameters thus act as a probe for studying syn ⇄ anti and N ⇄ S equilibria in solutions. The three-bond 1H-′13C coupling constants between H(1′) and C(8) and C(4) have been measured in poly(8BrA) and 5′-8BrAMP and their structural implications have been discussed. The observed preference of a C(3′)endo-syn conformation for poly(8BrA), coupled with other evidence, throws doubt on the validity of a correlation previously reported whereby a syn conformation is associated with a C(2′)endo ribose pucker. The backbone conformation of randomly coiled poly(8BrA) is very similar to the structures found in polyribonucleotides: poly(A) and poly(U). All three polymers show strong preferences for the backbone angles found in RNA helices. The CD spectrum of poly(8BrA) has a striking relationship to that of poly(A). The signs of all extrema are inverted, and the magnitudes are related by a constant factor. We suggest that these differences result from a change in the angle between coupled transition moment vectors in the two polymers. Infrared spectra of poly(8BrA) in H2O and D2O solution are reported for the frequency range below 1400 cm-1. The antisymmetric 〉PO2- stretching vibration is observed at an unusually low frequency in the helix (1214 cm-1). The symmetric 〉PO2- stretch occurs at ∼1095 cm-1 but is not resolved from a ring vibration near this frequency. A conformationally sensitive band, characteristic of helical RNA structures, is observed at 817 cm-1 and disappears when the helix is melted. This observation confirms the conclusion that ordered poly(8BrA) has a regular helical structure with an RNA backbone conformation. A stereochemical explanation is provided for the failure of poly(8BrA) (or other syn polymers) to form double helices with anti-polyribonucleotides.
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    Kinetics of chemical modification of arginine and lysine residues in calf thymus histone H1 (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1103-1112 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The arginine and lysine residues of calf thymus histone H1 were modified with large molar excesses of 2,3-butanedione and O-methylisourea, respectively. Kinetic study of the modification reaction of the arginine residue revealed that the reaction is divided into the two pseudo-first-order processes. About a third (1 Arg) of the total arginine residues of the H1 molecule was rapidly modified without causing any detectable structural change of the molecule, and the slow modification of the remaining arginine residues (2 Arg) led to a loss of the folded structure of H1. In the case of lysine residue modification, 93% (56 Lys) of the total lysine residues of the H1 was modified with the same rate constant, while 7% (4 Lys) of lysine residue remained unmodified. When the reaction was performed in the presence of 6M guanidine-HCl, all of lysine residues were modified. It is concluded that the 2 arginine and 4 lysine residues resistant to modification are buried in interior regions of the H1 molecule and play an important role in the formation of the H1 globular structure, while the other 1 arginine and 56 lysine residues are exposed to solvent.
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    Optical anisotropies of amides and peptides in dioxane (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1191-1209 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The molar Kerr constants mK, molar refractions mR, and dipole moments μ are reported for the N-methylacetamides CX3CONHCH3 (X = H, CH3, F. CI, Br) and acetamides CX3CONH2 (X = H, F, Cl, Br). The components of the polarizability tensor α are deduced for N-methylacetamide and acetamide on the basis of the bond additivity approximation. This α is found to be considerably more anisotropic than was indicated in previous determinations by other methods. The data for N-methylacetamide were used to calculate mK, μ, and γ2 (anisotropy squared) of N-acetyl-N′-methylglycine amide and N-acetyl-N′-methyl-alanine amide as functions of the torsional angles (φ,Ψ). The statistical mechanical averages of mK, μ, and γ2 were calculated from conformational energies obtained by the methods of Scheraga.
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    Elastin as a random-network elastomer: A mechanical and optical analysis of single elastin fibers (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1247-1260 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The physical properties of single, 5-8-μm diameter, water-swollen elastin fibers have been investigated on a microtest apparatus attached to a polarizing microscope. Analysis of the mechanical and optical properties at extensions below 100% indicate that the elastic modulus (G) has a value of 4.1 × 105 N m-2, the average molecular weight of chains between crosslinks is in the range of 6000-7100, and the stress optical coefficient (C′) is 1 × 10-9 m2 N-1 at 24°C. Analysis of the temperature dependence of the stress optical coefficient indicates that the polarizability of the random link decreases with increasing temperature, with an apparent activation energy for this process of the order of 1.6 kcal/mol. Analysis of the non-Gaussian mechanical and optical properties at extensions above about 100% suggest that the chains between crosslinks contain approximately 10 “effective” random links, with each link consisting of 7-8 amino acid residues. These parameters for the random chains in the elastin network have been used to predict the dimensions of other random proteins. The close correlation of these predictions with published values for the dimensions of a series of proteins in solution in 6M guanidinium hydrochloride provides an independent test of the appropriateness of our analysis.
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    Novel cell for light scattering from solutions (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1333-1335 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    n-Mer binding on a one-dimensional lattice of two-state m-site cells: Heavy meromyosin on regulated actin as an example (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1399-1411 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Notes: Heavy meromyosin binding to F-actin saturated with tropomyosin is studied theoretically. The problem is formulated as a special case of n-mer adsorption to a one-dimensional Ising lattice which is divided into m-site-long blocks.
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    Monte Carlo approach to the analysis of the rotational diffusion of wormlike chains (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1481-1502 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Monte Carlo analysis is presented which establishes a relationship between the rotational diffusion coefficients and the flexibility (persistence length, P) of short, wormlike chains. The results of this analysis are presented in terms of experimentally observable quantities; namely, the rotational relaxation times for the field-free decay of optical anisotropy. The pertinent theoretical quantity is R, defined as the ratio of the longest rotational relaxation time of a wormlike chain to the transverse rotational relaxation time of a rigid cylinder having the same axial length (L) and segmental volume. R, so defined, is essentially independent of the axial ratio of the cylinder for any value of L/P within the range of validity of the present analysis (axial ratio 〉 20; 0.1 〈 L/P 〈 5). It is pointed out that P can be determined with reasonable accuracy even in the absence of a precise knowledge of the local hydrodynamic radius of the chain.
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    One hundred-fold acceleration of DNA renaturation rates in solution (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1537-1547 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvents which accelerate DNA renaturation rates have been investigated. Addition of NaCl or LiCl to DNA in 2.4M Et4NCl initially increases renaturation rates at 45°C and then leads to a loss of second-order behavior. The greatest accelerations are seen with LiCl and dilute DNA. Volume exclusion by dextran sulfate is the most effective method of accelerating DNA renaturation with concentrated DNA. Addition of dextran sulfate beyond 10-12% in 2.4M Et4NCl fails to increase the acceleration beyond approximately 10-fold. Accelerations of 100-fold may be achieved with 35-40% dextran sulfate in 1M NaCl at 70°C. No other mixed solvent system was found to be more effective, although acceleration may be achieved in solvents containing formamide or other denaturants. The acceleration in 2M NaCl occurs without loss of the normal concentration and temperature dependence of DNA renaturation and is also independent of dextran sulfate concentration if sufficient dextran sulfate is used. Dextran sulfate may be selectively precipitated by use of 1M CsCl.
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    Investigation of the flexibility of DNA using transient electric birefringence (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1503-1535 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the preceding article, a Monte Carlo analysis was presented which provides a quantitative numerical relationship between the rotational diffusion coefficients, as measured by the decay of optical anisotropy following an electric field pulse, and the flexibility (persistence length) of short, wormlike chains. In the present article, the results of the foregoing analysis are applied to the observed rates of decay of birefringence for a series of sequenced DNA fragments ranging in size from 104 to 910 base pairs. Under the conditions used in this study, the DNA fragments exist as native, duplex molecules. Furthermore, conditions are defined in which the observed relaxation times are not dependent on DNA concentration, field strength, or the duration of the pulse. It is pointed out that the ionic atmosphere associated with a wormlike polyion does not exert any significant (direct) influence on the rotational diffusion of the polyion and, therefore, that the rotational relaxation times are a true measure of the configurations of the DNA molecules in solution. Moreover, excluded-volume effects are shown not to be significant for the moderately short molecules employed in this study. The major conclusion of this study is that there is no strong ionic strength dependence of the persistence length for ionic strengths above 1 mM and that the persistence length, under conditions where electrostatic contributions are negligible, is approximately 500 Å. For ionic strengths significantly lower than 1 mM, electrostatic contributions to the stiffness of DNA become significant.
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    Structure of amphotericin B aggregates as revealed by UV and CD spectroscopies (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1575-1588 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aqueous and hydroalcoholic solutions of the heptenic macrolide amphotericin B display strong and variable signals in CD and absorption spectroscopies in the range of the π* ← π transition. An interpretation of the spectroscopic changes is proposed based on the equilibrium between two forms of the intermolecular organization: the aggregated one (A) with strong excitonic interaction and the nonaggregative one (B) whose spectra are like those of linear conjugated polyenes in true solution with a well-developed vibrational structure. The intermediate spectra are fitted by linear combination of the A- and B-form spectra. A two-level organization of the aggregates is proposed for the A-form: (1) a close packing of few molecules, which is the origin of the absorption maxima hypsochromic shift; and (2) interaction between the preceding small units inside the aggregates, which is spectroscopically expressed by the intense CD couplet.
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    Use of potentiometric titration for determination of α- and ω-peptide bonds in poly(aspartic acid) and poly(glutamic acid) (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1625-1633 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polypeptides of dicarboxylic amino acids having the monomer units linked in α- and ω-peptide bonds contain two kinds of carboxyls of different acidity. How well potentiometric titration can distinguish these two carboxyls and so characterize the nature of the peptide bonds is evaluated critically. An analysis of the equation describing the dependence of pH on the degree of neutralization based on neglecting the polymer effect and a discussion of the dissociation behavior of polyanions show that the method of evaluating experimental data found in the literature is incorrect. Nevertheless, if a conformational transition does not interfere, some useful and reliable information may be gained by this method; namely, an indication of the presence of two different peptide bonds, their mole ratio, and an approximate pK value for the carboxyl of the amino acid linked in the ω-peptide bond. The presence of two types of carboxyls complicates the evaluation of the titration curves in the conformation studies.
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    Conformational and structural constraints in double-helical polynucleotides (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1707-1725 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational analysis of antiparallel double-helical polynucleotides with Watson-Crick base pairing was reduced to a four-dimensional problem using original mathematical methods. In the four-dimensional conformational space the family of structures, characterized by the base-pair stacking with the most stable conformations in water solution as well as in the solid state, was localized. For the C′2-endo sugar pucker, both right-handed and left-handed structures were found; right-handed structures only, however, seem to be allowed for the C′3-endo pucker, the only possible one for ribonucleotides with base stacking.
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    Conformation and activity in angiotensin II peptides (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1971-1983 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Angiotensin II and its competitive inhibitor [Sar1, Ile8]-angiotensin II, as well as several analogs of these two compounds specifically chosen for their well-defined pharmacological properties, were studied by circular dichroism and nuclear magnetic resonance methods at various pH values in aqueous solution and in d6-dimethylsulfoxide. The results were compared with their biological activities. This allowed us to establish relationships between conformation and pressor activity, explaining most of the properties of angiotensin II, its inhibitor, and the analogs successively substituted in positions 3 and 5.
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    Tobacco mosaic virus as a carrier for small molecules: Artificial receptor antibodies and superhormones (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2011-2020 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Peptide agonists covalently attached to tobacco mosaic virus exhibit such unusual properties as superpotency, superaffinity, enhanced resistance towards enzymic degradation, and prolonged action at the target cell. These properties can be exploited for the isolation by density-gradient centrifugation of membrane vesicles bearing specific receptors for the peptides and for radioactive and fluorescent labeling of cell-surface receptors. Our observations can be explained by cooperative-affinity phenomena caused by the deployment in space of the agonist molecules.
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    Early stages of fibrinogen to fibrin conversion studied by static and dynamic light scattering (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2035-2049 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The early steps of fibrin aggregation induced by low Reptilase concentrations were studied by means of static and dynamic light scattering. In order to obtain information on the size and shape of the first oligomers, the angular dependence of the scattered intensity and the mean Rayleigh line width were measured. Under physiological pH and ionic strength, oligomer formation was detectable immediately after enzymatic activation. Comparison of the calculated data for different models with experimental results shows that the early fibrin polymerization proceeds as an end-to-end aggregation of elongated and possibly flexible molecules approximately 75 nm long.
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    The equivalent conductivity of aqueous salt-free solutions of DNA: Influence of univalent counterions (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2083-2091 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The equivalent conductivity of salt-free solutions of deoxyribonucleates of alkali metals and ammonium obtained by filtering an isoionic DNA solution through a cation exchanger in the corresponding form has been investigated in the concentrations range of 1 × 10-4 to 4 × 10-3M. For all counterions investigated there is a linear dependence of the equivalent conductivity on \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {C_p} $\end{document}, where Cp is the nucleic phosphorus concentration. The limiting equivalent conductivity of deoxyribonucleates increases linearly with the limiting mobility of a counterion. By extrapolation to the zero mobility of the counterion, we have obtained the limiting mobility of a macroion, which is equal to 19 × 10-4 Sm m2 equiv.-1, which is in good agreement with the literature data for denatured DNA obtained by the method of a moving boundary. It is shown that the degree of binding of counterions calculated from the conductometric data in diluted DTA solutions in independent of the nature of the univalent counterion. The degree of dissociation of H+-DNA in the isoionic solution calculated with allowance for the fraction of unprotonated bases practically coincides with this value for salts of DNA. The parameter of Manning's theory calculated from the experimental data corresponds to the distance between phosphates along the chain of the macroion, which is equal to 6.7 Å. We attribute the smaller value of this distance as compared with the theoretical one for denatured DNA to the aggregation of macroions.
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    Structure of cellulose II hydrate (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2165-2179 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A hydrate of cellulose II can be formed by swelling Fortisan fibers in hydrazine and then washing in water. The hydrate is stable at 93% relative humidity and has a monoclinic unit cell with dimensions a = 9.02 Å, b = 9.63 Å, c = 10.34 Å, and γ = 116.0°; the space group is P21. The unit cell contains disaccharide sections of two chains and approximately four water molecules. The structure was refined using the LALS method, based on 10 observed and 10 unobserved reflections. An antiparallel arrangement of adjacent chains was assumed, since this occurs in cellulose II (the starting material), and the hydrate also reverts to cellulose II on dehydration. Refinement of the positions and side-chain conformations of the chains shows that the chains are stacked in the same way as in cellulose II, and the hydrate is formed by insertion of water molecules between the stacks. However, all efforts to arrange the water molecules in crystallographically regular positions led to unsatisfactory agreement between the observed and calculated intensities. These results suggest an irregular arrangement of the water molecules, which was modeled using water-weighted atomic scattering factors. The analysis resulted in two refined models with relative chain staggers of ∼ +c/4 and ∼ -c/4, which are indistinguishable in terms of the x-ray agreement. Our preference is for the +c/4 model, for which the stacks of chains are analogous to those in cellulose II.
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    Interaction of calcium ions with α-elastin: An equilibrium dialysis, circular dichroism, and microcalorimetric study (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 2213-2223 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of calcium ions with α-elastin has been investigated by equilibrium dialysis, CD, and microcalorimetric techniques. Consistent with literature data, it was found that the interaction in water is very poor. In trifluoroethanol (TFE), equilibrium dialysis experiments showed that calcium ions bind to ∼-elastin with an association constant of ∼250 L × mol-1. Such a figure is not consistent with highly specific, highly selective binding. It was also found that the CD response is not directly proportional to the amount of bound calcium but depends on the protein concentration. From microcalorimetric experiments it was found that the heat effect relative to the binding process is of the order of 1.9 kcal/g ion. From this figure and from the binding constant, a positive ΔS value of about 17 e.u. was evaluated, leading to the conclusion that the binding process is entropy driven. From microcalorimetric measurements a ΔH of 1.5 kcal/residue was found for the calcium-induced conformational transition of the protein.
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    Buckling transitions in superhelical DNA: Dependence on the elastic constants and DNA size (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 5-25 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Buckling transitions in superhelical DNA are sudden changes in shape that accompany a smooth variation in a key parameter, such as superhelical density. Here we explore the dependence of these transitions on the elastic constants for bending and twisting, A and C, important characteristics to DNA's bending and twisting persistence lengths. The large range we explore extends to other elastic materials with self-contact interactions, modeled here by a Debye-Hückel electrostatic potential.Our collective description of DNA shapes and energies over a wide range of ρ = A/C reveals a dramatic dependence of DNA shape and associated configurational transitions on ρ: transitions are sharp for large ρ but masked for small ρ. In particular, at small ρ, a nonplanar circular family emerges, in agreement with Jülicher's recent analytical predictions; a continuum of forms (and associated writhing numbers) is also observed.The relevance of these buckling transitions to DNA in solution is examined through studies of size dependence and thermal effects. Buckling transitions smooth considerably as size increases, and this can be explained in part by the lower curvature in larger plasmids. This trend suggests that buckling transitions should not be detectable for isolated (i.e., unbound) DNA plasmids of biological interest, except possibly for very large ρ. Buckling phenomena would nonetheless be relevant for small DNA loops, particularly for higher values of ρ, and might have a role in regulatory mechanisms: a small change in superhelical stress could lead to a large configurational change.Writhe distributions as a function of ρ, generated by Langevin dynamics simulations, reveal the importance of thermal fluctuations. Each distribution range (and multipeaked shape) can be interpreted by our buckling profiles. Significantly, the distributions for moderate to high superhelical densities are most sensitive to ρ, isolating different distribution patterns. If this effect could be captured experimentally for small plasmids by currently available imaging techniques, such results suggest a slightly different experimental procedure for estimating the torsional stiffness of supercoiled DNA than considered to date. © 1997 John Wiley & Sons, Inc.
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    Conformational analysis and molecular dynamics simulation of α-(1 → 2) and α-(1 → 3) linked rhamnose oligosaccharides: Reconciliation with optical rotation and NMR experiments (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 83-96 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular mechanics and dynamics calculations were carried out on the disaccharides α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → OMe) (1) and α-L-Rhap-(1 → 3)-α-L-Rhap-(1 OMe) (2), and the trisaccharide α-L-Rhap-(1 → 2)-α-L-Rhap-(1 → 3)-α-L-Rhap-(1 → OMe) (3). The semiflexible conformational behavior of these molecules was characterized by the occupation of a combination of different glycosidic linkage and side-chain conformational positions whose relative occupations were sensitive to dielectric screening. Molecular dynamics simulations of the trisaccharide 3 showed little difference between the linkage conformations in the trisaccharide and the component disaccharides 1 and 2.Experimental optical rotation data of 1 and 2 were obtained as a function of temperature in varying solvents. The molecular models were combined with the semiempirical theory of Stevens and Sathyanarayana to yield calculated optical rotations. Interpretation of the data of both 1 and 2 implied that a combination of conformations, both in glycosidic and side-chain positions, could explain the experimental data. Solvents effects were important in influencing the conformational mix and averaged optical rotation.Three-bond heteronuclear coupling constants 3JC, H were obtained for the glycosidic linkages of 1 and 2 in D2O and DMSO. Analysis of the coupling constants with a Karplus curve showed that small reductions in the glycosidic torsion angles of the conformations of the models used here of ca. 10°-15° in φ and 5°-10° in ψ were required to give better agreement with experiment; a combination of conformations for both 1 and 2 was consistent with the data. There was a negligible influence on the coupling constants of 1 on changing the solvent from D2O to DMSO. © 1997 John Wiley & Sons, Inc.
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    Protein folding: Optimized sequences obtained by simulated breeding in a minimalist model (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 165-180 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: For a minimalist model of protein folding, which we introduced recently, we investigate various methods to obtain folding sequences. A detailed study of random sequences shows that, for this model, such sequences usually do not fold to their ground states during simulations. Straightforward techniques for the construction of folding sequences, based solely on the target structure, fail. We describe in detail an optimization algorithm, based on genetic algorithms, for the “simulated breeding” of folding sequences in this model. We find that, for any target structure studied, there is not only a single folding sequence but a patch of sequences in sequence space that fold to this structure. In addition, we show that, much as in real proteins, nonhomologous sequences may fold to the same target structure. © 1997 John Wiley & Sons, Inc.
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    Fourier transform IR studies of the self-association of N-tert-butoxycarbonyl-α-amino acids (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 205-212 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The self-association of several N-urethanyl-L-amino acids (N-t-Boc-glycine, N-t-Boc-L-alanine, N-t-Boc-L-methionine, and N-t-Boc-O-Bz-L-tyrosine has been investigated in carbon tetrachloride by Fourier transform (FTIR) spectrometry. The fractions of nonbonded OH and NH groups have been determined from the intensities of the free OH and NH-stretching vibrations. The FTIR spectra have been examined in the carbonyl stretching regions by using Fourier self-deconvolution techniques. The results show that intermolecular hydrogen bonds are formed between the carboxylic acid group of one molecule and the urethane group of another molecule, suggesting that the leading factor for the self-association of N-t-Boc amino acids is the acidity of the OH groups. In N-t-Boc glycine, more heterodimers are formed than in the other amino acids. In N-t-Boc-O-Bz-L-tyrosine where the steric hindrance of the substituent implanted on the Cα atom is higher, the concentration of homodimers and heterodimers is lower than in N-t-Boc-L-alanine or N-t-Boc-L methionine. © 1997 John Wiley & Sons, Inc.
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    A heteropolymer model study for the mechanism of protein folding (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 239-250 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A heteropolymer model of randomly self-interacting chains in two dimensions is studied with numerical simulations in order to elucidate the folding mechanism of protein. We find that the model occasionally shows folding propensity depending on the sequence of random numbers given to the chain. We study the thermodynamic and kinematic roles in the folding mechanism by grouping the local energy minima found in the simulations into clusters according to the similarity of their conformations. It is suggested that the local minima to which some heteropolymers show a folding tendency are always the lowest energy states of the energy spectrum within a cluster, though which cluster is selected depends on the sequence. For the eight random sequences we study, we find that the energy gap between the ground state and excited states is little correlated with folding or nonfolding. We rather find that folding propensities are correlated with the global structure of the average energy surface, implying a dominant kinetic role in the folding mechanism, although thermal factors cannot be ignored as the mechanism of choosing the ground state within a cluster of states connected by small deformations. We suggest that a hierarchical cluster structure plays an important role in selecting a unique folded state out of the huge number of local minima of heteropolymers. © 1997 John Wiley & Sons, Inc.
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    Ordered aggregation of ribonucleic acids by the human immunodeficiency virus type 1 nucleocapsid protein (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 301-312 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleocapsid protein NCp7, which is the major genomic RNA binding protein of human immunodeficiency virus type 1, plays an important role in several key steps of the viral life cycle. Many of the NCp7 activities, notably the nucleic acid annealing and the genomic RNA wrapping ones, are thought to be linked to a nonspecific binding of NCp7 to its nucleic acid targets. The mechanism of these activities is still debated but several clues are in favor of an intermediate aggregation of nucleic acids by NCp7. To check and characterize the nucleic acid aggregating properties of NCp7, we investigated the interaction of NCp7 with the model RNA homopolymer, polyA, by quasielastic light scattering and optical density measurements. The ordered growth of monodisperse large particles independently of the nucleic acid size and the almost complete covering of polyA by NCp7 strongly suggested an ordered aggregation mechanism. The aggregate kinetics of growth in the optimum protein concentration range (≥2 μM) were governed by a so-called Ostwald ripening mechanism limited by transfer of NCp7-covered polyA complexes from small to large aggregates. The aggregation process was strongly dependent on both Na+ and Mg2+ concentrations, the optimum concentrations being in the physiological range. Similar conclusions held true when polyA was replaced by 16S + 23S ribosomal RNA, suggesting that the NCp7 aggregating properties were only poorly dependent on the nucleic acid sequence and structure. Finally, as in the NCp7 annealing activities, the basic regions of NCp7, but not the zinc fingers, were found critical in nucleic acid aggregation. Taken together, our data indicate that NCp7 is a highly efficient nucleic acid aggregating agent and strengthen the hypothesis that aggregation may constitute a transient step in various NCp7 functions. © 1997 John Wiley & Sons, Inc.
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    NMR three-dimensional solution structure of the serine protease inhibitor cyclotheonamide A (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 349-358 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nmr solution conformation of cyclotheonamide A (CtA) was determined in aqueous media. The data produced 15 distance and 10 torsional constraints which were used to generate conformations using restrained simulated annealing (SA) and distance geometry/simulated annealing (DG/SA) calculations. Two different calculation protocols were performed to ensure proper sampling of conformational space and even though the torsional restraints were input differently, both calculation methods yielded the same conformation of CtA. In the structure calculations, all solutions of the Karplus equation were sampled simultaneously using the restrained SA protocol and large ranges were used for the dihedral restraints in the DG/SA protocol because all solutions to the Karplus equation could not be sampled simultaneously. The solution conformation was also compared to the solid state x-ray conformations of CtA bound to thrombin and trypsin. The conformation of the residues important for active site binding (d-Phe, h-Arg, and Pro) are nearly identical in aqueous solution and solid state with largest differences at the a-Ala and v-Tyr residues. CtA appears to be preordered in structure and does not undergo a significant conformational change upon binding to the enzyme active site. © 1997 John Wiley & Sons, Inc.
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    The reconstruction of a protein backbone from Cα coordinates (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 381-389 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Monte Carlo Protein Building method to construct the backbone and Cβ atomic coordinates from known Cα coordinates is reported. The method selects values of dihedral angles from ranges established from a statistical analysis of the relationship between dihedral angles of the backbone and Cα coordinates for a protein data base. The averaged coordinates from ten backbone models of a protein were used to define a mean structure that was refined by energy minimization using the AMBER force field (GB/SA). By the latter method the average atomic deviation and rmsd of the backbone and Cβ atoms for 24 proteins is between 0.14 and 0.32 Å (average 0.22 Å) and 0.22 and 0.61 Å (average 0.43 Å), respectively. A comparison with other methods is made. © 1997 John Wiley & Sons, Inc.
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    The reconstruction of side-chain conformations from protein Cα coordinates (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 391-405 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model of nine proteins including side-chain atoms have been built from the known Cα coordinates and amino acid sequences using a Monte Carlo Protein Building Annealing method. The Cartesian coordinates for the side-chain atoms were established with bond lengths and angles selected randomly from within previously determined ranges. A simulated annealing technique is used to generate some 300 structures with differing side-chain conformations. The atomic coordinates of the backbone atoms are fixed during the simulated annealing process. The coordinates of the side-chain atoms of 300 low energy conformations are averaged to obtain a mean structure that is minimized with the Cα atoms constrained to their position in the x-ray structure using the OPLS/AMBER force field with the GB/SA water model. The rms deviation of the main-chain atoms (without Cβ) compared with the corresponding crystal structures is in the range 0.20-0.64 Å. The rms deviation of the side-chain atoms is between 1.72 and 2.71 Å and for all atoms is between 1.19 and 1.99 Å. The method is insensitive to random errors in the Cα positions and the computational requirement is modest. © 1997 John Wiley & Sons, Inc.
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    Simulation of electrostatic and hydrodynamic properties of Serratia endonuclease (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 443-450 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We analyze the electrostatic and hydrodynamic properties of a nuclease from the pathogenic gram-negative bacterium Serratia marcescens using finite-difference Poisson-Boltzmann methods for electrostatic calculations and a bead-model approach for diffusion coefficient calculations.Electrostatic properties are analyzed for the enzyme in monomeric and dimeric forms and also in the context of DNA binding by the nuclease. Our preliminary results show that binding of a double-stranded DNA dodecamer by nuclease causes an overall shift in the charge of the protein by approximately three units of elementary charge per monomer, resulting in a positively charged protein at physiologic pH. In these calculations, the free enzyme was found to have a negative (-1 e) charge per monomer at pH 7. The most dramatic shift in pKa involves His 89 whose pKa increases by three pH units upon DNA binding. This shift leads to a protonated residue at pH 7, in contrast to the unprotonated form in the free enzyme. DNA binding also leads to a decrease in the energetic distances between the most stable protonation states of the enzyme. Dimerization has no significant effect on the electrostatic properties of each of the monomers for both free enzyme and that bound to DNA.Results of hydrodynamic calculations are consistent with the dimeric form of the enzyme in solution. The computed translational diffusion coefficient for the dimer model of the enzyme is in very good agreement with measurements from light scattering experiments. Preliminary electrooptical calculations indicate that the dimer should possess a large dipole moment (approximately 600 Debye units) as well as substantial optical anisotropy (limiting reduced linear electric dichroism of about 0.3). Therefore, this system may serve as a good model for investigation of electric and hydrodynamic properties by relaxation electrooptical experiments. © 1997 John Wiley & Sons, Inc.
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    Structural characterization (shape and dimensions) and stability of polysaccharide/lipid nanoparticles (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 511-520 
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    ISSN: 0006-3525
    Keywords: biovector ; light scattering ; lipid ; microgel ; polysaccharide ; soft sphere ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of a new supramolecular drug carrier (named Biovectors - BV) was studied using light scattering and scanning electronic microscopy techniques. This system consists of a polysaccharide core of chemically cross-linked maltodextrins to which phospholipids (and, in some cases, cholesterol) are added. Both polysaccharide cores and BV cross-linked with phosphate (negatively charged) and epichlorhydrin (no net charge) are spherical particles. The increase in the ionic strength of the medium increases the density of the charged polysaccharide cores. The lipid strongly interacts with neutral and negatively charged cores, decreasing both intra- and interparticle interactions. The results (mainly, ρ = Rg/Rh 〈 0.775 in some cases) suggest that BV are gel-like particles of variable density, referred to as microgels or soft spheres. Neutral polysaccharides have a strong tendency to self-aggregate. This self-aggregation of polysaccharide neutral cores is prevented by the addition of lipid or dimethylsulfoxide. © 1997 John Wiley & Sons, Inc. Biopoly 41: 511-520, 1997
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    Protein hinge bending as seen in molecular dynamics simulations of native and M61 mutant T4 lysozymes (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 533-544 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dynamical model of interdomain “hinge bending” of T4 lysozyme in aqueous solution has been developed on the basis of molecular dynamics (MD) simulation. The MD model study provides a description of the conformational reorganization expected to occur for the protein in aqueous solution as compared to the crystalline environment. Three different 500 ps molecular dynamics simulations were calculated, each using a distinctly different crystal conformation of T4 lysozyme as the starting points of the MD simulations. Crystal structures of wild-type lysozyme and “open” and “closed” forms of M6I variant structures were analyzed in this study. Large-scale, molecular-conformational rearrangements were observed in all three simulations, and the largest structural change was found for the open form of the M6I allomorph. All three simulated proteins had closed relative to the wild-type crystal structure, and the closure of the “jaws” of the active site cleft occurred gradually over the time course of the trajectories. The time average MD structures, calculated over the final 50 ps of each trajectory, had all adapted to conformations more similar to each other than to their incipient crystal forms. Using a similar MD protocol on cytochrome P450BM-3 [M. D. Paulsen and R. L. Ornstein (1995) Proteins: Structure Function and Genetics, Vol. 27, pp. 237-243] we have found that the opposite type of motion relative to the starting crystal structure, that is, the open form of the crystal structure, had opened to a greater degree relative to the incipient crystal structure form. Therefore we do not believe that either result is merely a simulation artifact, but rather the protein dynamics are due to protein relaxation in the absence of crystal packing forces in the simulated solution environments. © 1997 John Wiley & Sons, Inc. Biopoly 41: 533-544, 1997
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    Structural comparison between retro-inverso and parent peptides: Molecular basis for the biological activity of a retro-inverso analogue of the immunodominant fragment of VP1 coat protein from foot-and-mouth disease virus (1997)
    New York : Wiley-Blackwell
    Biopolymers 41 (1997), S. 569-590 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Antibodies induced against intact foot-and-mouth disease Virus (FMDV) particles bind to the retro-inverso analogue of fragment 141-159 of the viral coat protein VP1 of FMDV, variant A, equally well as to the parent peptide. A conformational investigation of this retro-inverso peptide was carried out by nmr spectroscopy and restrained molecular modeling in order to identify the structural basis for the antigenic mimicry between these retro-inverso and parent peptides. In 100% trifluoroethanol a well-defined left-handed α-helical region exists from residue 150 to residue 159, which is consistently present in all conformational families obtained from restrained modelling. A less-defined left-handed helical region is present in the tract 144-148, which is also consistent for all structures. Conformational flexibility exists about Gly149, which leads to two types of structures, either bent or linear. In the bent structures, a three-residue inverse tight turn is found, which can be classified as an inverse γ-turn centered at Gly149. The overall structural features of the retro-inverso peptide are shown to be similar to those of the parent L-peptide. The two molecules, however, are roughly mirror images because they share inherently chiral secondary structure elements. By comparing these conformational conclusions with the x-ray structure of the Fab complex of a corresponding VP1 antigenic fragment, a rationale is proposed to account for the topological requirements of specific recognition that are implied by the equivalent antigenic activity of the natural and retro-inverso compounds. © 1997 John Wiley & Sons, Inc. Biopoly 41: 569-590, 1997.
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