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  • Polymer and Materials Science  (6,707)
  • AERODYNAMICS  (1,253)
  • Humans
  • 1990-1994  (4,696)
  • 1985-1989  (4,052)
  • 1991  (4,696)
  • 1985  (4,052)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 33 (1991), S. 442-449 
    ISSN: 1432-1432
    Keywords: Humans ; Mouse ; Rat ; Codon usage ; Mutation bias ; Selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A new statistical test has been developed to detect selection on silent sites. This test compares the codon usage within a gene and thus does not require knowledge of which genes are under the greatest selection, that there exist common trends in codon usage across genes, or that genes have the same mutation pattern. It also controls for mutational biases that might be introduced by the adjacent bases. The test was applied to 62 mammalian sequences, the significant codon usage biases were detected in all three species examined (humans, rats, and mice). However, these biases appear not to be the consequence of selection, but of the first base pair in the codon influencing the mutation pattern at the third position.
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  • 2
    ISSN: 1432-0878
    Keywords: Skeletal muscles ; Ultrastructure ; Exercise ; Glycogen ; Humans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Distribution of glycogen particles in semithin and ultrathin sections of biopsy samples from human muscles subjected to either short- or long-term running were investigated using PAS and Periodic Acid-ThioSemiCarbazide-Silver Proteinate (PA-TSC-SP) staining methods. Glycogen particles were predominantly found immediately under the sarcolemma or aligned along the myofibrillar Iband. After long-term exhaustive exercise type-1 fibers with a few or no glycogen particles in the core of the fibers were frequently observed. The subsarcolemmal glycogen stores of these “depleted” type-1 fibers were about three times as large as after exhaustive short-time exercise. Another indication of utilization of subsarcolemmal glycogen stores during anaerobic exercise was that many particles displayed a pale, rudimentary shape. This observation suggests fragmental metabolization of glycogen. Thus, depending on type of exercise and type of fiber differential and sequential glycogen utilization patterns can be observed.
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  • 3
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The properties (squared dimensions, anisotropy, numbers of intra- and intermolecular contacts) of a single five-way cubic lattice chain embedded into an environment (matrix) of chains of the same length n = 50 were evaluated as a function of matrix volume fraction (matrix density) v and intermolecular interaction between the matrix polymer and the minority chain segments, characterized by a parameter φ. No convincing evidence was found for the occurrence of a coil-globule transition in the range of matrix densities (v ≤ 0.7) and repulsive interactions between matrix and minority chain (φ ≤ 0.2) investigated. For moderate attractive interaction (φ ≈ -0.17) a compensation of the chaincompressing action of the matrix and the chain-expanding interaction with the matrix was observed resulting in a zero-dependence of the size and shape of the minority chain on matrix density. It further turned out that there are fixed relations among the various size and shape data irrespective of the specific combination of matrix density and thermodynamic interaction by which a particular polymer dimension is produced. These interrelations are fairly the same as those evaluated for isolated chains the size of which is varied by an intramolecular energy parameter φi.
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  • 4
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New three phases composite materials made of glassbeads as filler, water as liquid dispersed phase and polystyrene as matrix were obtained by polymerization of a water in oil emulsion formed by water dispersed in styrene in which glass beads are added. For this purpose glass beads have to be modified by silanization by a coupling agent 3-(Trimethoxysilyl)propylmethacrylate (TPM) or a silane Octadecyltrichlorosilane (ODMS), in order to prevent the wetting of the glass by water. Only low coverage of the glass surface by the coupling agent (0,05% of TPM) are convenient for the preparation cellular materials having good mechanical properties. At higher coverage ratio, strong hydrophobic glass beads are obtained which destabilize the water / styrene emulsion and lead to macroporous products. Study of the rheology of the filled emulsion appears to be the more simple and more sensitive method to determine the level of wettability of the glass bead by the emulsion which is the most significant parameter for the preparation of such three phases composite materials. Composite materials made of glass beads, air and polystyrene are simply obtained by evaporation of water under vacuum.
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  • 5
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: To test the molecular parameters concerning gas sorption in polymers, the concentration of CO2, N2O, CO, N2, CH4 and the noble gases Ne, He in glassy poly(butylene terephthalate) films (PBTP) has been studied gravimetrically with a recording microbalance at 25°C. The sorption isotherms exhibit downward curvature to the pressure axis. As neither solubility nor adsorption can explain the experimental results, analysis was carried out based on the dual-sorption model: gas dissolution and microvoid filling are considered as independent sorption mechanisms. The parameters of the dual-sorption model for the mentioned penetrants are determined. The results indicate that for parameter correlation the Lennard-Jones potential parameters give a rough idea, but size exclusion of gases in small diameter microvoids is proposed and special chemical interactions must be considered.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 283-292 
    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 ring opening metathesis polymerisation (ROMP) of 5-cyano-2-norbornene with tungsten hexachloride, tungesten oxytetrachloride, bis(dichloralkoxo)tungsten tetrachloride and bis(dichloralkoxo)tungsten oxydichloride as transition metal component was studied. Methylaluminoxan, diethylaluminium ethoxide, tetraisobutyldialuminoxan and tetrabutyltin served as cocatalyst. Toluene, Chlorobenzene and dichloromethane were used as solvents. The concentration of the tungsten components was in the range from 5 × 10-4 to 5 × 10-3 mol/l. Among the catalyst studied, tungsten hexachloride with diethylaluminium ethoxide proved to be the best. The polymerisation was highly selective with this system even at high monomer/tungsten ratios (e.q. 10200:1) and let to high conversions (≥82%).
    Notes: Die ringöffnende metathetische Polymerisation (ROMP) von 5-Cyano-2-norbornen wurde unter Einsatz von Wolframhexachlorid, Wolframoxidterachlorid, Bis(dichloralkoxo)wolframtetrachlorid und Bis(dichloralkoxo)wolframoxiddichlorid als Übergangsmetallkomponente untersucht. Als Cokatalysatoren dienten Methylaluminoxan, Diethylaluminiumethoxid, Tetraisobutyldialuminoxan und Tetrabutylzinn. Als Lösungsmittel wurden Toluol, Chlorbenzol und Dichlormethan verwendet. Die Konzentration der Wolframkomponente lag im Bereich 5 × 10-4 - 5 × 10-3 mol/l. Unter den geprüften Katalysatoren erwies sich Wolframhexachlorid in Verbindung mit Diethylalumiumethoxid als der geeignetste. Mit diesem System verlief die Polymerisation auch bei großen Monomer/Wolfram-Verhältnissen (10200 :1) hochselektiv und führte zu großen Umsätzen (≥82%).
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  • 7
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dependence of dilution on the chain propagation and termination rate constants was investigated in the polymerization of ethyl acrylate in benzene solution at 50°C, with the rotating sector method. The errors of the above rate constants were determined and, by our method applied to decrease these errors, the errors of the propagation rate constant was reduced to its half value. By the application of our earlier results in polymerization kinetics, we found that in this system the chain propagation step is exclusively responsible for the solvent effects observed. Our experimental results can be quantitatively described in terms of the hot redical theory.
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  • 8
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 329-334 
    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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  • 9
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 1-14 
    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: Durch gemeinsame Reaktion von Benzophenontetracarbonsäuredianhydrid, Maleinsäureanhydrid und Diaminen mit 1,3,5-Triazingruppen wurden niedermolekulare Prepolymere mit Amin-Endgruppen erhalten, die sowohl 1,3,5-Triazingruppen als auch Etherbindungen enthalten. Diese reaktiven Prepolymeren sind in niedrigsiedenden Lösemitteln wie z. B. Chloroform und Tetrahydrofuran löslich. Sie wurden durch Elementaranalyse, IR- und NMR-Spektroskopie, Dampfdruckosmometrie und Viskosimetrie charakterisiert. Beim Erhitzen der Prepolymeren auf Temperaturen zwischen 180 und 190°C tritt Kettenverlängerung durch Michael-Addition auf; gleichzeitig vernetzen sie durch Reaktion der Amin- mit den Maleimid-Endgruppen. Die vernetzten Polymeren sind thermisch stabil; ihr thermisches Verhalten wurde durch TGA, DTA und isotherme Alterung untersucht. Die Biegefestigkeit und interlaminare Scherfestigkeit von aus den Prepolymeren und Carbonfasergeweben hergestellten Laminaten wurden gemessen.
    Notes: Low molecular weight amine-terminated monomaleimide prepolymers containing 1,3,5-triazine groups as well as ether linkages were synthesized by reacting benzophenone tetracarboxylic dianhydride, diamines having 1,3,5-triazine group and maleic anhydride. These reactive prepolymers are soluble in low boiling solvents such as chloroform, tetrahydrofuran etc. They were characterized by elemental analyses, IR and NMR spectroscopy, vapour pressure osmometry, and viscosity. On heating at 180-190°C these prepolymers undergo simultaneous chain extension by Michael addition reaction and crosslinking by mutual reaction between their amine-terminated and maleimide-terminated ends. The cured polymers are thermostable and the thermal behaviour was studied by TGA, DTA, and isothermal aging. Laminates fabricated using these prepolymers and carbon fiber as reinforcing agent were evaluated by their flexural strength and interlaminar shear strength.
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  • 10
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 15-32 
    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 Epoxidharz wurde durch Reaktion mit Anilin bzw. Benzylamin in unterschiedlichen molaren Verhältnissen modifiziert. Die modifizierten Harze wurden dann mit Diethylamin und anschließend mit teilblockiertem Toluylendiisocyanat umgesetzt, wobei thermisch vernetzbare Harze mit tertiären Aminen in und am Ende der Polymerkette erhalten wurden. Die partielle Ansäuerung mit Essigsäure lieferte thermisch vernetzbare kationische Harze, aus denen durch Lösen in geeigneten Lösungsmitteln und Zugabe von entionisiertem Wasser Emulsionen hergestellt wurden. Diese wurden hinsichtlich ihrer Eignung zur elektrolytischen Abscheidung untersucht und verglichen. Die Ergebnisse zeigen, daß die Abscheidungsausbeute und das Streuvermögen der Emulsionen aus Benzylamin-modifizierten Epoxidharzen besser sind als die der Anilin-modifizierten Epoxidemulsionen. Ein hohes, vom pH-Wert der Emulsion abhängiges Streuvermögen ist für diese kationischen Harze charakteristisch.
    Notes: Aniline/benzylamine-modified epoxy resins with different molecular weights, which contain tertiary amines in the middle of the polymer chain, were synthesized by the reaction of aniline/benzylamine with epoxy resin at various molar ratios. The resulting aniline/benzylamine-modified epoxy resins were reacted with diethylamine and subsequently reacted with 2-ethylhexanol-blocked toluene diisocyanate to obtain thermally crosslinkable resins which contain tertiary amines at the end and in the middle of the polymer chain. These resins were partially neutralixed with acetic acid to give thermally crosslinkable cationic resins. The resulting cationic resins were dissolved in suitable solvents and mixed with deionized water to form various emulsions. The emulsion and electrodeposition properties of these resins were studied in some detail to compare the properties of these cationic resins. The results show that the deposition yields and throwing power of the emulsions prepared from benzylaminemodified epoxy resins are higher than those of the emulsions prepared from anilinemodified epoxy resins. The emulsion having proper pH values can give a high throwing power. High throwing power is the characteristic property of these modified cationic resins. Factors determining the throwing power and deposition yield of the emulsions were also investigated.
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  • 11
    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: Arylacrylsäuren, wie Furylacrylsäure und Thienylacrylsäure können durch Knoevenagel-Reaktion der Arylcarbaldehyde mit Malonsäure in Pyridin dargestellt werden. Durch einfache Veresterung der Arylacrylsäuren in Methanol/Schwefelsäure werden die entsprechenden Arylacrylsäuremethylester mit guten Ausbeuten erhalten. Diese isomerisieren bei Bestrahlung mit UV-Licht (λ ≥ 280 nm) in methanolischer Lösung. Bei der Photoreaktion in Lösung wurde keine Photodimerisierung beobachtet. Die Reaktionskinetik der Photoreaktionen wurde untersucht.
    Notes: Aryl acrylic acids, e. g. furyl acrylic acid or thienyl acrylic acid are readily formed by the Knoevenagel condensation reaction of arylcarbaldehydes and malonic acid in pyridine. Esterification of these acids with methanol/sulfuric acid gives the corresponding aryl acrylic acid methyl esters in good yields. In methanolic solution these methyl esters isomerize upon irradiation (λ 280 nm). No photodimerization was observed. Kinetic data are given.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 67-80 
    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: Different composite materials, with retified or natural poplar and polyester resin were prepared by molding. The influence of the filler granulometry on certain physicochemical (density, humidity, hardness) or mechanical properties of the materials was studied. The density and the increase of mass in humid atmosphere were always found to be less when the wood was thermally treated. On the other hand, the hardness of the composites made from natural poplar was much higher. The mechanical properties were found to be weak when the wood was retified.When the wood was thermally treated, it was possible to optimise the three parameters, namely, density, water retention capacity and mechanical properties. The optimal granulometry of poplar was determined between 0.75 and 1.5 mm.The results obtained are discussed considering the physico-chemical properties of the different varieties of wood studied and the interactions which exist between the polar resin and the wood.
    Notes: Divers matériaux composites à base de peuplier rétifié ou naturel et de résine polyester insaturée ont été préparés par moulage. L'influence de la granulométrie de la charge a été étudiée sur quelques propriétés physico-chimiques (densité, reprise d'humidité, dureté) ou mécaniques des matériaux obtenus. La densité et la reprise de masse en milieu humide sont toujours plus faibles si la charge est traitée thermiquement sous atmosphère inerte. Par contre, la dureté des composites issus du peuplier naturel est plus importante. Les propriétés mécaniques sont inférieures si la charge est rétifitée.Si la charge lignocellulosique est traitée thermiquement, il est possible d'optimiser les trois paramètres: densité, reprise d'eau et propriétés mécaniques; la granulométrie optimale du peuplier est ainsi comprise entre 0,75 et 1,5 mm.Les résultats obtenus sont expliqués en tenant compte des propriétés physico-chimiques des charges et des interactions existant entre la résine polaire et le bois.
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  • 13
    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 vorliegende Arbeit untersucht das Wasserdurchlässigkeitsverhalten von vier Arten verschieden modifizierter Chitosanmembranen zur Abtrennung von Wasser aus wäßrigen Ethanolmischungen. Chitosan wurde aus Chitin von Krebstierschalen durch Verseifung (Deacetylierung) gewonnen. Die in dieser Arbeit untersuchten modifizierten Chitosanmembranen enthielten Carboxymethyl-, Carboxyethyl-, Cyanethyl- und Amidoxim-Chitosan. Die Einführung hydrophiler funktioneller Gruppen in der 6-O Position des Chitosans erhöht die Selektivität der modifizierten Membranen im Vergleich zu den mit Essigsäure komplexierten Chitosanmembranen. Die Untersuchungen zeigen, daß Chitosanmembranen, die Carboxygruppen enthalten, die höchste Wasserdampfdurchlässigkeit aufweisen. Carboxymethyl-Chitosanmembranen zeigen eine maximale Quellung und den höchsten Ethanoldurchfluß bei einer Ethanolkonzentration von ca. 15 Gew.-% im Zulauf aufgrund von Bindungs- und Weichmachereffekten.
    Notes: The present study investigates the pervaporation performance of four kinds of modified chitosan membranes to separate water from aqueous ethanol solution. Chitosan was prepared from chitin abstracted from the crab shell and subsequently deacetylated with aqueous NaOH solution. Modified chitosan membranes examined in this study include carboxymethyl chitosan, carboxyethyl chitosan, cyanoethyl chitosan, and amidoxime chitosan. The incorporation of hydrophilic functional groups into the 6-O position of chitosan enhances the selectivity of modified chitosan membrane compared to the previously reported chitosan-acetic acid complex membrane. Among the modified chitosan membranes, membranes containing carboxy groups show the best pervaporation performance. Carboxymethyl chitosan membranes show the maximum swelling and ethanol flux at approx. 15 wt.-% feed ethanol concentration due to the coupling and plasticizing effect.
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  • 14
    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 tensile properties of self reinforced poly(propylene)/poly(1-butene) composites, obtained by rapid extension of the melt, have been measured and correlated to morphological parameters derived from x-ray experiments. Critical fiber lengths as a function of sample composition and the elastic modulus and yield stress of the fibers could be determined. It is shown, that, applying a load to the system, the forces are fully taken up by the fibers and the system breaks by fail of the fibers. The longitudinal structure of the fibers is found to be independent of sample composition.
    Notes: Mechanische Parameter wie Elastizitätsmodul, Fliß- und Bruchspannung von aus der hochorientierten Schmelze hergestellten nadelkristallinen Mischungen aus Poly(propylen) und Poly(1-bute) wurden mit morphologischen Parametern, die aus Röntgenmessungen abgeleitet wurden, korreliert. Es wird gezeigt, daß der Elastizitätsmodul des Verbundes aus den E-Moduln der Fasern und der Matrix berechnet werden kann (Mischungsregel). Die an der Probe angreifenden Kräfte werden voll auf die Fasern übertragen; der Verbund kann daher als eigenfaserverstärktes System angesehen werden. Die Abschätzung der kritischen Faserlänge ergibt, daß die Festigkeit der FAsern voll ausgenutzt wird; der Bruch des Systems bei Belastung ist daher auf das Versagen der Fasern zurückzuführen. Das mechanische Verhalten des Verbundes wird stark beeinflußt durch die Komponentenzusammensetzung. Die longitudinale Struktur der Nadeln beider Komponenten bleibt unbeeinflußt von der jeweiligen Co-Komponente.
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  • 15
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    Angewandte Makromolekulare Chemie 192 (1991), S. 199-211 
    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: Lösliche kationische Polyelektrolyte mit quartären Stickstoffatomen in der Hauptkette wurden durch Polykondensation von Epichlorhydrin (ECH) mit Dimethylamin (DMA) und N,N-Dialkylaminoakylaminen erhalten. Die Reaktionsparameter, die die Polymereigenschaften hauptsächlich beeinflussen, sind: Molverhältnis DMA/asymmetrische Diamine, Ausgangskonzentration der Aminlösung, Molverhältnis ECH/Amine und die Struktur der asymmetrischen Diamine. Das viskosimetrische Verhalten verdünnter wäßriger Lösungen mit oder ohne Zugabe neutraler Salze veranschaulicht die flexible Natur der Polyelektrolyten.
    Notes: Water soluble cationic polyelectrolytes containing quaternary nitrogen atoms within the main chain were prepared via condensation polymerization of epichlorohydrin (ECH) with dimethylamine (DMA) and N,N-dialkylaminoalkylamines. The main parameters of the reaction that influence the polymer properties are: DMA/asymmetrical diamine molar ratio, the initial concentration of amine solution, NaOH/amine molar ratio, ECH/amine molar ratio, and asymmetrical diamine structure. The feature of flexible polyelectrolyte own to the investigated polymers was emphasized by the viscosimetric behaviour in dilute aqueous solutions with and without salt presence.
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  • 16
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    Angewandte Makromolekulare Chemie 192 (1991), S. 213-213 
    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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  • 17
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    Angewandte Makromolekulare Chemie 193 (1991), S. 1-11 
    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: Antioxidantien wurden in einer modifizierten Friedel-Crafts-Reaktion mit wasserfreiem Zinkchlorid als Katalysator an Flüssig-Naturkautschuk mit Hydroxy-Endgruppen gebunden. Die immobilisierten Antioxidantien waren weniger flüchtig und extrahierbar als konventionelle Antioxidantien. Sie wurden sowohl einem Latex als auch trockenem Kautschuk zugesetzt; die daraus hergestellten Vulkanisate zeigten eine bessere Alterungsbeständigkeit als Vulkanisate mit konventionellen Antioxidantien.
    Notes: Antioxidants were attached to hydroxy-terminated liquid natural rubber by modified Friedel-Crafts alkylation reaction using anhydrous zinc chloride as catalyst. The rubber bound antioxidants were found to be less volatile and less extractable compared to conventional antioxidants. The bound antioxidants were tried both in latex compounds and dry rubber compounds. The vulcanizates showed improved ageing resistance compared to vulcanizates based on conventional antioxidants.
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  • 18
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    Angewandte Makromolekulare Chemie 193 (1991), S. 13-20 
    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 Strom-Spannungs-Charakteristik eines Bisphenol-A-Polycarbonats im Span-nungsbereich 50-1000 V und der Einfluß von UV-Bestrahlung (λ = 225 und 300 nm) und Tempern auf die elektrische Leitfähigkeit (σ) des Polycarbonats wurden untersucht. Die Abhängigkeit von σ gegen 1/T deutet auf zwei verschiedene Leitfähigkeits-mechanismen hin. Aus den Ergebnissen wurden die Aktivierungsenergien der Leitfähigkeit und die Sprungdistanzen berechnet.
    Notes: Current-voltage characteristics of polycarbonate samples (PC) have been studied in the voltage range 50-1000 V. The effect of UV-irradiation at λ = 225 and 300 nm, and thermal annealing on the electrical conductivity (σ) of PC was studied. The σ vs. 1/T relationship shows two slopes, i.e. two possible conduction mechanisms. The obtained results made it possible to determine a complete set of conduction parameters including activation energy and jump distance.
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  • 19
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    Angewandte Makromolekulare Chemie 193 (1991), S. 21-28 
    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: Durch Suspensionspolymerisation wurden Terpolymere aus Acrylnitril (AN), Vinylacetat (VA) (7,5-30 mol-%, bezogen auf AN) und Divinylbenzol (DVB) (10 Gew.-%) hergestellt. Als Verdünner wurden Mischungen von Toluol oder Cyclohexanol (90 Vo1.-%) mit Hexadecan, Octan, Dodecan, 2-Ethylhexanol oder Benzylalkohol (jeweils 10 Vo1.-%) verwendet.Die Porosität der AN-VA-DVB-Terpolymeren ist mit 0,61-0,68 größer als die der entsprechenden AN-DVB-Copolymeren. Die übermolekulare Struktur der Terpolymeren hängt vom verwendeten Verdünner ab, obwohl sich die Porositäten nicht sehr voneinander unterscheiden. Die beim Erhitzen der Terpolymeren auf Temperaturen über 200°C auftretenden thermischen Effekte sind signifikant größer als die bei der Cyclisierung von AN-Polymeren gemessenen.
    Notes: Terpolymers of acrylonitrile (AN), vinyl acetate (VA) (7.5-30 mol-%, related to AN), and divinylbenzene (DVB) (10 wt.-%) were prepared by suspension polymerization. The diluents used were mixtures of toluene or cyclohexanol (90 vol.-%) with solvents (10 vol.-%) such as hexadecane (HD), octane (O), dodecane (D), 2-ethylhexanol (E) or benzyl alcohol (B).It has been found that AN-VA-DVB terpolymers have a higher porosity, about 0.61-0.68, than corresponding AN-DVB copolymers. The terpolymers obtained with mixtures of various diluents differ in their supermolecular structure although they had similar porosity characteristics.The thermal effects accompanying heating of the terpolymers above 200°C significantly exceed that of nitrile groups cyclization observed of the other AN polymers.
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  • 20
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    Angewandte Makromolekulare Chemie 193 (1991), S. 39-49 
    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 rheologischen und mechanischen Eigenschaften von Blends aus PE-HD und zwei verschiedenen PE-LLD-Typen wurden im gesamten Mischungsbereich gemessen. Die Polymeren sind im festen Zustand und in der Schmelze ausreichend verträglich, so daß ihre vorteilhaften Eigenschaften genutzt werden können.
    Notes: A high density polyethylene grade is blended with two selected grades of linear low density polyethylene and the mechanical and rheological properties of the blends are evaluated over the entire composition range. The blends show sufficient compatibility in the solid phase and in the melt and hence they can be advantageously used to capitalize on their useful properties.
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  • 21
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    Angewandte Makromolekulare Chemie 192 (1991), S. 51-55 
    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: N,N-Dimethylacrylamid (DMA) und Isopropylmethacrylat (IPM) wurden in Dimethylformamid mit Azoisobutyronitril als Initiator copolymerisiert. Die Copolymerzusammensetzung wurde 1H-NMR-spektroskopisch ermittelt. Die Copolymerisationsparameter (rDMA = 0,58, rIPM = 2,76) wurden nach Kelen-Tüdős berechnet.
    Notes: Copolymers of N,N-dimethyl acrylamide (DMA) and isopropylmethacrylate (IPM) were prepared in dimethyl formamide using azoisobutyronitrile as initiator. The composition of copolymers was determined by 1H-NMR analysis. Reactivity ratios (rDMA = 0.58, rIPM = 2.76) were calculated from these values by using the Kelen-Tüdős differential linear equation.
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  • 22
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    Angewandte Makromolekulare Chemie 192 (1991), S. 69-79 
    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: Es wird ein allgemeines numerisches Verfahren vorgestellt, um die Modifikation der Grundgleichung für hydrodynamische Schmierung, die von mit Polymeren versetzten Schmierölen mit scherabhängiger Viskosität erbracht wird, zu berechnen.Das Verfahren basiert auf dem verallgemeinerten Newtonschen Fileßmodell und erlaubt, alle Fileßregionen zwischen dem rein Newtonschen und dem Exponentialgesetzverhalten kontinuierlich zu behandeln. Die Ergebnisse zeigen, daß der Einfluß der scherspannungsabhängigen Viskosität durch eine dimensionslose Zahl vollkommen charakterisiert wird, nämlich U · τ*/h*, wobei U die relative Gleitgeschwindigkeit, h* die charakteristische Filmdicke und τ* die Relaxationszeit des Schmieröles darstellen.Als praktisches Beispiel wird die Anwendung des Verfahrens aufgezeigt, um den Einfluß des Molekulargewichts und der Konzentration der Polymerkomponente des Schmieröls auf die hydrodynamische Schmierung zu bestimmen. Dieser Einfluß ist durch die starke Beziehung zwischen Polymereigenschaften und τ* verursacht.
    Notes: A general numerical procedure is presented to calculate the modification of the basic equation for hydrodynamic lubrication brought about by the use of polymeric fluids with shear depending viscosity. The procedure is based on the generalized Newtonian fluid model and allows to treat continuously all the flow regions between the pure Newtonian and the power law behavior. The results show that the influence of the viscosity depending on shear stress is completely characterized by one dimensionless number, namely U.·τ*/h*, where U is the relative sliding velocity, h* is the characteristic film thickness, and τ* is a characteristic time of the lubricant. The procedure is exemplified by applying it for the determination of the influence of the molecular weight and concentration of the polymeric component of the lubricant on the hydrodynamic lubrication. This influence is brought about by the strong relation between the polymer properties and τ*.
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  • 23
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    Angewandte Makromolekulare Chemie 192 (1991), S. 57-67 
    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 Morphologien von spritzgegossenem und formgepreßtem Poly(1-buten) (PB-1) wurden im Polarisationsmikroskop und im Transmissionselektronenmikroskop untersucht. Eine dünne Oberflächenhaut und bis in den Kern der Probekörper reichende abgeplattet-sphärolithische Strukturen werden bei spritzgegossenem PB-1 beobachtet, während in formgepreßtem PB-1 typische Sphärolithe vorliegen. Das Bruchbild des spritzgegossenen PB-1 zeigt unter der Oberflächenhaut viele aufgereihte streifenartige Hohlräume, die senkrecht zur Spritzrichtung zur Mitte des Probekörpers wachsen. Aus diesen Beobachtungen kann geschlossen werden, daß eine beim Spritzgießen durch den Schmelzefluß induzierte Scherspannung nicht nur die Entstehung der Oberflächenhaut verursacht, sondern auch bis in die Mitte des Probekörpers hinein die Bildung abgeplatteter Sphärolithe bewirkt. Diese abgeplattet-sphärolithischen Strukturen sind für die beim Dehnen des spritzgegossenen PB-1 entstehenden, streifenartigen Hohlräume verantwortlich, während die Oberflächenhaut und die abgeplatteten Sphärolithe im Kern die Sprödigkeit und die im Vergleich zu formgepreßtem PB-1 geringere Bruchdehnung bewirken. Diese kann durch Tempern oberhalb des Schmelzpunktes erhöht werden.
    Notes: The injection-molded poly(1-butene) (PB-1) is found to be more brittle than the compression-molded PB-1. The morphologies of these specimens are examined by use of polarized optical microscopy and scanning electron microscopy (SEM). A skin layer and an oblate spherulitic structure extended to the core region are observed in the injection-molded PB-1, while typical spherulites exist in the compression-molded PB-1. Below the skin layer of the injection-molded PB-1, the fracture surface is found to consist of many aligned strip-like voids with ribbon edges propagating to the center of the specimen and perpendicular to the flow direction of injection-molding. Based on these observations, it can be inferred that shear stress induced by the melt flow during the injection-molding does not only cause the formation of skin layer, but also penetrates deeply into the central region of the injection-molded specimen causing the formation of oblate spherulites. The oblate spherulitic structure is responsible for the aligned voids during elongation of PB-1, while the existence of the skin layer and the oblate spherulites in core region is responsible for the brittleness of the injection-molded PB-1. The elongation of the injection-molded PB-1 is found to be lower than that of the compression-molded. This can be attributed not only to the presence of the skin layer but also to the oblate spherulites in the core region. The elongation can be improved by annealing at a temperature above the melting point of PB-1.
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  • 24
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    Angewandte Makromolekulare Chemie 192 (1991), S. 103-111 
    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: Durch Kondensation von p-Xylol mit Chloracetylchloride, 1,2-Dichlorethan und Dichlormethan mit Aluminiumtrichlorid in Schwefelkohlenstoff wurden Polyketone hergestellt und IR-spektroskopisch sowie bezuglich des Molekulargewichtes charakterisiert. Die thermischen Eigenschaften wurden thermogravimetrisch und mittels DSC untersucht. Die Prüfung der Harze auf ihre biologische Aktivität gegen Pseudomonas fluorescens, Bacillus subtilis and Aspergillus niger ergab, daß deren Wachstum durch die Polyketonharze kontrolliert werden kann.
    Notes: Some polyketones were prepared from p-xylene, chloroacetylchloride, 1,2-dichloroethane and dichloromethane using anhydrous aluminiumtrichloride and carbon disulfide as solvent. The resins thus obtained have been characterized by IR spectra and number average molecular weight. The thermal properties have been studied by thermogravimetry and differential scanning calorimetry. All the resins were tested for their biological activity against Pseudomonas fluorescens, Bacillus subtilis and Aspergillus niger. The results show that the growth of the tested organisms can be controlled by the polyketone resins.
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  • 25
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    Angewandte Makromolekulare Chemie 192 (1991), S. 145-153 
    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: In der Arbeit wurde die homogene Polyaddition von Pyromellitsäuredianhydrid und 4,4′-Diaminodiphenylmethan untersucht. Die Abhängigkeit des zahlenmittleren Molekulargewichts (M̄n) von der Zeit weist ein Maximum auf. Die Ursache der niedrigen Gleichgewichtswerte von M̄n beruht auf einer durch Wasserspuren im Lösungsmittel verursachten Dianhydridhydrolyse und damit einer gestörten Äquimolarität der funktionellen Gruppen. Im Laufe der Stabilisierung des M̄n-Gleichgewichtswertes entsteht auch die wahrscheinlichste Molmassenverteilung.
    Notes: The homogeneous polyaddition reaction of pyromellitic dianhydride with 4,4′-diaminodiphenylmethane was investigated. The dependence of the number average molecular weights on time has a maximum; low equilibrium values of M̄n are caused by a disturbed equimolarity of functional groups due to the hydrolysis of dianhydride with water present in the solvent. In the course of establishment of the equilibrium M̄n value, the molecular weight distribution changes to the most probable value.
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  • 26
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    Angewandte Makromolekulare Chemie 192 (1991), S. 133-144 
    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: Das Phasen- und Mischbarkeitsverhalten der binären und ternären Polymermischungen von Polyarylat (PAR), Phenoxid und Poly(butylenterephthalat) (PBT) wurde untersucht. Die Mischungen wurden durch Ausfällen aus gemeinsamen Lösungen hergestellt, und die Mischbarkeit wurde durch DSC-Messungen und Transparenz der Schmelze beurteilt. Im Falle der binären Blends zeigten PAR/PBT und Phenoxid/PBT Mischbarkeit, während sich PAR/Phenoxid nicht mischen ließ. Die Mischbarkeitstendenz der unmischbaren PAR/Phenoxid-Mischungen konnte jedoch durch Zugabe von PBT erhöht werden; eine ausreichende Menge PBT machte die ternären Mischungen mischbar, so daß diese eine einzige Tg in der DSC-Kurve zeigten. Im ternären Phasendiagramm war das Maximum der Mischbarkeitsgrenze in Richtung auf die Phenoxidseite hin verschoben, was auf die bessere Mischbarkeit von PAR/PBT im Vergleich zu Phenoxid/PBT zurückgeführt wird.
    Notes: The phase and miscibility behavior of binary and ternary blends containing polyarylate (PAR), polyhydroxyether of bisphenol AIUPAC: poly[oxy(2-hydroxytrimethylene)oxy-1,4-phenylene-isopropylidene-1,4-phenylene]. (Phenoxy), and poly(butylene terephthalate) (PBT) were studied. The blends were prepared by solution-precipitation method and miscibility was examined by DSC and melt transparency. In binary blends, PAR/PBT and Phenoxy/PBT blends show miscibility, while PAR/Phenoxy appeared to be immiscible. However, the miscibility of incompatible PAR/Phenoxy blend was enhanced by addition of PBT. The addition of sufficient amount of PBT caused the ternary blend to have a single glass transition temperature. The shape of miscibility boundary of ternary blend was skewed to the apex of Phenoxy, which was attributed to the better miscibility of PAR/PBT than that of Phenoxy/PBT.
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  • 27
    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 Festphasen-Polykondensation von amorphen, unorientierten Poly(ethylenterephthalat)-Folien (PET) (Vorstufe der Du Pont Mylar® -Polyesterfilme), die mit einem speziellen Katalysator-und Monomer-System hergestellt wurden, war Gegenstand dieser Arbeit. Der Einfluß verschiedener Reaktionsparameter, wie Reaktionstemperatur und -zeit, auf die inhärente Viskosität (ηinh) und auf die Anzahl der Carboxy-und Hydroxy-Endgruppen wurde untersucht. Aus den Messungen von ηinh wurde eine empirische Gleichung erstellt, die die Berechnung von M̄n der PET-Folien nach der Festphasen-Polykondensation bei gegebener Zeit und Temperatur erlaubt. Das Schmelzverhalten verschiedener Festphasen-Polykondensate wurde ebenfalls untersucht.
    Notes: The solid-state polycondensation of poly(ethylene terephthalate) (PET) amorphous and unoriented films from Du Pont (precursor for their Mylar® Du Pont's registered trade mark for the polyester film. polyester film) prepared from a specified catalyst and monomer system has been studied. The effect of various reaction parameters such as reaction temperature and time on inherent viscosity (ηinh) and number of carboxy and hydroxy end-groups has been investigated. From ηinh measurements an empirical equation was taken which allows the calculation of (M̄n) of PET film after solid-state polycondensation at a certain temperature and time. The melting behaviour of the solid-state polycondensated samples was also studied.
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  • 28
    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: Sphärische makroporöse Partikel, die als Trägermaterialen für verschiedene Säulen-Operationen eingesetzt werden sollen, wurden mittels Suspensions- und Mikrosuspensionspolymerisation von Trimethylolpropan-trimethacrylat (TRIM) in Gegenwart verschiedener Mengen porogener Reagenzien (Toluol bzw. Mischungen von Toluol und Isooktan) hergestellt. Textur und Eigenschaften der Partikel variierten deutlich mit dem Anteil und der Zusammensetzung des porogenen Reagens und wurden zusätzlich durch die Wahl des Suspensionstabilisators beeinflußt. Die makroporösen Partikel wiesen ein Gesamtporenvolumen von 0,4 bis 3,6 cm3/g und eine spezifische Oberfläche von 7 bis 〉 450 m2/g auf. Alle Partikel enthielten Makroporen und, außer den Teilchen mit sehr niedriger spezifischer Oberfläche, einen gewissen Anteil an Mikroporen (Durchmesser 〈 60 Å). Durch Erniedrigung der Monomerkonzentration und Erhöhung des Isooktan-Gehaltes im porogenen Reagens auf 50 Gew.-% konnte das Auftreten von Mikroporen vollständig unterdrückt werden. Das Erhöhen des Isooktan-Gehaltes führte zu einem vergrößerten Gesamtporenvolumen und zu einem verringerten Quellvermögen der Polymermatrix in Toluol. Der Einfluß einer Hitzebehandlung bei 130°C und eines Aufpfropfens von Polymethylmethacrylat auf die Partikeleigenschaften wurde ebenfalls untersucht.Die Menge an nicht umgesetzten Doppelbindungen in den Partikeln konnte durch Variation der Polymerisationstemperatur verändert werden. Das Vorhandensein leicht zugänglicher Doppelbindungen ist wichtig, da sie zur Funktionalisierung der festen makroporösen Partikel verwendet werden können.
    Notes: Spherical macroporous particles, intended for use as carrier particles in various types of column operations, were prepared by suspension and microsuspension polymerization of trimethylolpropane trimethacrylate (TRIM), in the presence of various amounts of porogenic agents (toluene or mixtures of toluene and isooctane). The texture and properties of the particles varied markedly with the amount and composition of the porogenic agent, and were also affected by the choice of suspension stabilizer. Macroporous particles were prepared, ranging in total pore volume from 0.4 to 3.6 cm3/g, and in specific surface area from 7 to 〉450 m2/g. All of the particles contained macropores, and except for those with very low specific surface area, contained a certain fraction of micropores (diameter 〈60 Å). The presence of micropores could be eliminated completely by decreasing the monomer concentration and increasing the isooctane content of the porogenic agent to 50 wt.-%. Increasing the isooctane content also resulted in an increase in the total pore volume and a decrease in the tendency of the polymer matrix to swell in toluene. The effect on properties of particles by heat treatment at 130°C and by grafting poly(methyl methacrylate) onto the particles was also studied.The amount of unreacted double bonds of the particles could be varied by varying the polymerization temperature. The presence of easily accessible double bonds is important as they can be utilized for functionalization of the rigid macroporous particles.
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  • 29
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    Angewandte Makromolekulare Chemie 191 (1991), S. 31-38 
    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 einfache Methode für die Bestimmung der Grenzflächenhaftung in kurzfaserverstärkten Polymeren, beruhend auf der Längenverteilung von aus der Bruchfläche herausgezogenen Faserteilen, wurde entwickelt. Die Messungen mit Faserverbundwerkstoffen von isotaktischem Polypropylen mit 32 Gew.-% Kurzglasfasern bestätigen die Brauchbarkeit dieser Methode für eine empfindliche Beurteilung von Unterschieden in der Grenzflächenhaftung. Die Einflüsse von Temperatur, Polymer- und Glasfasermodifizierung sowie Faserorientierung auf die Grenzflächenhaftung wurden untersucht.
    Notes: For the evaluation of the interfacial adhesion in short-fibre composites, a simple method based on fibre pull-out length distribution was proposed. The experiments with three composites of isotactic polypropylene with 32 wt.-% of short-glass fibres confirm the potentials of the method for a sensitive determination of differences in the interfacial adhesion. The effects of temperature, crystallinity and fibre orientation angle on the interfacial adhesion were investigated.
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  • 30
    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: PE und EPDM-Kautschuk wurden durch Aufpfropfen von Dibutylmaleat (DBM) mit Dicumylperoxid (DCP) als Initiator in Substanz im Temperaturbereich von 140-220°C funktionalisiert. Der Pfropfungsgrad wurde IR-spektroskopisch und durch DSC-Messungen ermittelt. Die für die Pfropfung optimalen DBM- und DCP-Konzentrationen betragen 0,5 bzw. 0,2 Gew.-%. Die Kinetik der Pfropfreaktion ist für PE und EPDM vergleichbar; die Aktivierungsenergien betragen ca. 145 bzw. 130 kJ/mol. Die Pfropfungsgrade sind für PE höher als für EPDM; bei PE/EPDM-Blends steigt der Pfropfungsgrad mit zunehmendem PE-Anteil. Ein Pfropfungsmechanismus, der Nebenreaktionen berucksichtigt, wird vorgeschlagen.
    Notes: Functionalization of polyethylene (PE) and ethylene propylene diene terpolymer (EPDM) in the bulk through dicumyl peroxide (DCP) initiated grafting of dibutyl maleate (DBM) has been studied in the temperature range from 140 to 200°C. The degree of grafting has been determined by infrared spectrophotometry and DSC. The concentration of DBM and DCP has been optimized. 0.5 wt.-% and 0.2 wt.-% DCP for PE and EPDM, respectively, and 10% DBM for both have been found to be the optimum. The kinetics of the grafting reaction is comparable for PE and EPDM. The activation energy of grafting is ca. 145 kJ/mol for PE and ca. 130 kJ/mol for EPDM. The influence of structure of polyolefins on the degree of grafting has also been studied. A higher degree of grafting is obtained for PE than for EPDM. For PE/EPDM blends, the degree of grafting increases with increasing PE content in the blends. A through discussion and proposed mechanism for grafting and other competitive secondary reactions has been provided.
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  • 31
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    Angewandte Makromolekulare Chemie 191 (1991), S. 71-80 
    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 dynamisch-mechanischen Eigenschaften von gehärteten Epoxidharzen, gefüllt mit porösen Siliciumdioxid-Mikrokugeln mit unterschiedlichen spezifischen Oberflächen, Porenradien, Porenvolumina und adsorbierter Wassermenge, wurde untersucht. Die Glasubergangstemperaturten (Tg) der Composite sind 12-14°C niedriger als die des ungefullten Harzes, was auf die bevorzugte Adsorption von Härter an den porösen Mikrokugeln zurückgeführt wird. Mit zunehmender adsorbierter Wassermenge steigt die Tg der Composite an. Der Speichermodul ist mit der mit Quecksilber bestimmten spezifischen Oberfläche (Hg-Oberfläche) der Mikrokugeln, die der Summe der Oberfläche von Poren mit einem Durchmesser größer als 4 nm entspricht, korreliert.Das Verbältnis tan δc/tan δm nimmt mit zunehmender Hg-Oberfläche ab.
    Notes: Dynamic mechanical properties were studied for epoxy resin filled with porous silica microballoons with varying surface area, pore radius, pore volume and adsorbed water. The glass transition temperature (Tg) of the composites is 12-14°C lower than the Tg of the unfilled epoxy resin. This Tg depression is attributed to the preferential adsorption of curing agents on the porous silica microballoons. Tg of the composite increases with increase in the adsorbed water on fillers. The storage modulus has a distinct correlation with the Hg-surface area of silica microballoons, which corresponds to the sum of the surface area of pores with radii larger than about 4 nm.Tan δc tan δm decreases with increasing Hg-surface area.
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  • 32
    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: Membranen aus Blends von Nylon 6 mit Poly(acrylsäure) (PAA) mit PAA-Gehalten zwischen 25 und 45 Gew.-% wurden durch Filmgießen hergestellt und anschließend durch Eintauchen in eine Aluminiumsalzlösung ionisch vernetzt. Die Glasübergangstemperaturen (Tg) der Membranen wurden mit der DSC-Methode bestimmt. Alle Proben zeigen eine einzige Tg oberhalb der Tg der Homopolymeren, die sich mit zunehmender Scanzeit verschiebt; dies wird auf die Eliminierung von Wasser und die Bildung von Anhydriden im nicht vernetzten PAA-Anteil zurückgeführt.Die Morphologie wurde rasterelektronenmikroskopisch untersucht; die Membranen zeigen eine dichte, porenfreie Struktur ohne Phasenseparation, was auf eine völlige Mischbarkeit der beiden Homopolymeren im untersuchten Zusammensensetzungsbereich schließen läßt. Die Festigkeit der Membranen liegt je nach PAA-Gehalt zwischen 5 und 26 MPa; Membranen mit hohem PAA-Anteil zeigen trotz höherer Vernetzungsdichte eine geringere Zugfestigkeit, was mit der geringen Festigkeit von PAA und der mit größerem PAA-Anteil zunehmenden Quellung zusammenhängt. Letztere wurde durch Messen der Wasseraufnahme trockener Membranen bestimmt; sie steigt von 23,6 Gew.-% bei einem PAA-Gehalt von 25 auf 76,3 Gew.-% bei einem PAA-Gehalt von 45 Gew.-%.
    Notes: Ionically crosslinked blended membranes were prepared from blends of nylon 6 and poly(acrylic acid) (PAA) with the proportion of PAA ranging from 25 to 45 wt.-%. The technique consists of casting a film of the blend, followed by drying and immersion in an aluminum salt crosslinking solution for a predetermined time. The glass transition temperature (Tg) of the membranes was determined by differential scanning calorimetry (DSC). All the samples exhibited a single Tg, which is higher than that of either polymer. There is also a shift in the Tg with increasing scanning time. This phenomenon is attributed to the elimination of water molecules and the formation of anhydrides in the non-crosslinked PAA portion of the membrane. The membrane morphology was studied using scanning electron microscopy (SEM) and shows a dense structure without any pores. No phase separation is observed by scanning cross-sections of the samples, indicating that nylon 6 and PAA are completely miscible in the ranges studied. The membrane material strength lies in the range of 5 to 26 MPa and varies with the amount of PAA in the membrane. Samples with higher PAA content show lower tensile strength in spite of increased crosslinking density. This is due to the inherent low strength of PAA, coupled with increasing swelling of the membrane with increasing PAA content. The latter is confirmed by the measurement of water uptake into a dry membrane which increases from 23.6% to 76.3% with the membrane PAA content increasing from 25 to 45 wt.%.
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  • 33
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    Angewandte Makromolekulare Chemie 191 (1991), S. 81-107 
    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: Practically no adhesion is observed at the interface poly(tetrafluoroethylene)/glass fiber. We have investigated methods to improve adhesion between these interfaces. We have also discussed the question of possible reinforcement, i.e. increase of tensile strength and a simultaneous decrease of elongation.In this first part we present some calculations demonstrating the prerequisites for reinforcement using existing theoretical models. We describe the influence of modification of the glass fiber surface by dispersion coating or by plasma polymerization.In a second part the influence of polymer surface modification and of additives will be dealt with.
    Notes: In Mehrphasensystemen aus Poly(tetrafluorethylen) (PTFE) und Glasfasern besteht praktisch keine Haftung zwischen Matrix und Füllstoff. Es wurde der Frage nachgegangen, ob es Wege zur Verbesserung der Grenzflächenhaftfestigkeit gibt und ob diese Verbesserungen ausreichen, eine Verstärkung, d. h. Anhebung der Reißfestigkeit bei gleichzeitigem Rückgang der Dehnung des Gesamtsystems zu erzielen.In diesem ersten Teil wird den theoretischen Voraussetzungen und der Modifizierung der Füllstoffoberflächen mittels Dispersionsbeschichtungen sowie Plasmaätzen und Plasmapolymerisation nachgegangen.In einem zweiten Teil werden Möglichkeiten zur Verbesserung der Grenzflächenhaftung durch Modifizierung der Polymer-Oberfläche und durch Additive untersucht.
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  • 34
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    Angewandte Makromolekulare Chemie 191 (1991), S. 109-126 
    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: Practically no adhesion is observed at the interphase of poly(tetrafluoroethylene)/glass fiber. We have investigated methods to improve this adhesion and discuss the influence of this improved adhesion on the mechancial properties of the multiphase system.In this paper the influence of a modified polymer surface and of additives is described.
    Notes: In Mehrphasensystemen aus Poly(tetrafluorethylen) (PTFE) und Glasfasern besteht praktisch keine Haftung zwischen Matrix und Füllstoff.Es wurde die Frage untersucht, ob es Methoden gibt, diese Grenzflächenhaftung zu erhöhen und welchen Einfluß diese Erhöhung auf die Eigenschaften des Verbundsystems hat.In dem hier vorliegenden Teil 2 wird speziell auf den Einfluß der Modifizierung der Polymeroberfläche und des Zusatzes von Additiven eingegangen.
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  • 35
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    Angewandte Makromolekulare Chemie 191 (1991), S. 127-144 
    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: Due to the very strong variation of the viscosity of the reaction mass with increasing monomer conversion, three stationary states for the tubes of a multitubular system with cooling vessel can be found. As a consequence, a maldistribution of the fluid arises, so that the reactor stability and the polymer quality are negatively influenced. The recycling of the reaction mass is a helpful method to increase the reactor stability. In this paper some fundamental aspects of the use of multitubular reactors for the polymerization of styrene are studied.
    Notes: Infolge der sich mit steigendem Monomerumsatz stark verändernden Viskosität der Reaktionsmasse existieren im Multirohrreaktor mit Kühlung mindestens drei stationaäre Punkte bezüglich des Einzelrohrmassenstromes gleichzeitig. Als Konsequenz ergibt sich eine Ungleichverteilung der Rohrbelastung, die sowohl die Reaktorstabilität als auch die Polymerqualität negativ beeinflußt. Das Betreiben einer Rückführung kann das Reaktorverhalten stabilisieren. In der vorgelegten Arbeit werden einige fundamentale Aspekte der Anwendung von Multirohrreaktoren für die Massepolymerisation von Styrol untersucht.
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  • 36
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    Angewandte Makromolekulare Chemie 191 (1991), S. 171-176 
    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 nucleophile Substitution von verschieden substituierten Phenoxygruppen in Polyphenylacrylaten durch Ethanolamin in Dioxan wurde bei 60, 80 und 100°C untersucht. Der Umsatz wurde IR- und 1H-NMR-spektroskopisch und elementaranalytisch bestimmt; er hängt sowohl von der Temperatur als auch von der Art der Substituenten am Phenylring ab.
    Notes: The nucleophilic substitution reaction of differently substituted phenoxy groups with ethanolamine in various poly(phenyl acrylate)s was investigated in dioxane at 60, 80, and 100°C. The conversion, as determined from IR- and 1H-NMR spectroscopy and elemental analysis, depends on the temperature and the kind of substituents at the phenyl ring.
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  • 37
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    Biopolymers 24 (1985), S. vi 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
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  • 38
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    Biopolymers 24 (1985), S. 49-63 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A molecular model for the complex formed between the jack bean lectin concanavalin A (Con A) and glycopeptides of the complex biantennary class is described. The model was derived using coordinates for Con A determined by x-ray crystalographic refinement techniques, with 1.75-Å resolution data, and coordinates for the glycopeptides obtained from 1H-nmr measurements, using the nuclear Overhauser effect. Previous solution and crystallographic studies provided several constraints on the possible mode of interaction of the lectin and the glycopeptide. Examination of the model suggests that the glycopeptide binding site is defined by four loops on the protein surface made up by amino acid residues: 12-18, 98-102, 205-208, and 226-229. Within these loops, it favorable interactions with high-affinity ligands and tose responsible for the unfavourable interactions with poor ligands.
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  • 39
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    Topics: Chemistry and Pharmacology
    Notes: Peptide hormones and neurotransmitters are functional amphiphilic substances that deploy their chared and nonpolar substituents as required for traversing aqueous phases en rout to their ultimate transfer into the lipid-rich environment of their membrane-embedded receptors. As a means of determining the role(s)that cellular membrane lipids may play in mediating these events, we describe an experimental approach, using high-resolution 1H-and 13C-nmr spectroscopy, for delineation of the structures of complexes between the (neurotransmitter pentapeptide) enkephalins and micellar and vesicular phospholipid particles. Residue-specific enkephalin interactions with lipid are identified; affinity constants for the hydrophobic component(s) of peptide/lipid association are calculated for enkephalin and several of its analogs; and comparisons with morphine are presented. Finally, based on molecular details obtained from nmr experiments, a model is proposed for the encoutner of a peptide hormone with a phospholipid membrane surface.
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  • 40
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    Biopolymers 24 (1985) 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 41
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Both (dC-dG)4 and d(CGCATGCG) crystallize in hexagonal lattices and their three-dimensional structure has been solved by x-ray diffraction analysis. Both molecules are found to form Z-DNA, although the fine details of the structure cannot be visualized due to the statistical disordering of the molecules along the c-axis, which is brought about by the symmetry constraints of the space group. This represents the first time in which the unmodified dinucleotide sequences CpAp and TpGp have been found to form Z-DNA in a crystalline lattice.
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  • 42
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    Biopolymers 24 (1985), S. 359-377 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential melting curves (DMCs) of DNAs pA03 and pBR322 in solutions of different ionic strength (0.02 and 0.2M Na+) were obtained. A previously developed procedure of glyxal fixation of partially denatured DNA molecules at temperatures within the melting range was used to construct electron-microscopic melting maps for pBR322 and pAO3 plasmid DNA and for the replicative form of bacteriophage φX174 DNA, allowing the melting of these DNA molecules to be followed in solutions of low (0.1 × SSC) and high (1 × SSC) ionic strength. In spite of the fact that the melting was at nonequilibrium at the low ionic strength, the melting maps for the two kinds of solutions practically coincided. Experimental data are compared with theoretical calculations based on the Fixman-Freire algorithm. The conclusion is that the melting pattern of these DNAs is, on the whole, correctly described by the theory, although there are appreciable differences between the theoretical and experimental differential melting curves. We have also determined the relation between the melting temperature of a region and its GC content, with allowances made for the boundary conditions of melting in 0.1 × SSC and 1 × SSC solutions, and have analyzed the theoretical shape of peaks of the DMCs.
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    Biopolymers 24 (1985), S. 421-423 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 24 (1985) 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 45
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    Biopolymers 24 (1985), S. 427-439 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrostatic effects are believed to determine the molecular structure and function of macromolecules in many ways. In metallo-based enzymes and in metal-macromolecule interactions in solution, these effects may predominate. In order to tackle metal ion-nucleic acid interactions theoretically, we propose a modification of Debye's distance-dependent dielectric function first proposed more than 50 years ago. This function more closely approximates physical reality at small interatomic separations. Our theory yields a dielectric function that gives reasonable agreement with experimental data in preliminary calculations.
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  • 46
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    Topics: Chemistry and Pharmacology
    Notes: It is suggested that the three-dimensional structure of globular proteins is partly determined by a framework of strengthened hydrogen bonds that involves both ionic side chains and water molecules in addition to the polypeptide backbone. This conclusion follows from a combination of the results of ab initio molecular-orbital computations on small model molecules and high-accuracy x-ray data on the rubredoxin molecule. The computations yield the idea of hydrogen-bonded bridges that are built from tens of atoms, and the experimental information yields the idea that the bridges are assembled into clusters, each of which is built from hundreds of atoms. Some 10 such clusters then form a globular protein.
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    Biopolymers 24 (1985), S. 581-581 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 48
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    Biopolymers 24 (1985), S. 581-581 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 49
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    Biopolymers 24 (1985), S. 157-166 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Monoclonal antibodies to different parts of bacteriorhodopsin were raised to define its topography in the membrane. It is shown that the amino acid residue Glu 194 is a part of an antigenic determinant and should be located on the membrane surface. We found that the removal of the C-terminal 17 amino acid sequence does not affect the efficiency of the proton transport in bacteriorhodopsin. From a combination of proteolysis and secondary structure prediction methods an experimentally testable structural model for bovine rhodopsin is presented. The complete amino acid sequence of the transducin γ-subunit consisting of 69 residues was determined.
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    Biopolymers 24 (1985), S. 403-419 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fluorescence and absorbance methods were used to study the interaction of daunomycin with calf-thymus DNA over a wide range of temperatures and NaCl concentrations. van't Hoff analysis provided estimates for the enthalpy of the binding reaction over the NaCl range of 0.05-1.0 M. Daunomycin binding is exothermic over this entire range, and the favorable binding free energy arises primarily from the large, negative enthalpy. Both the enthalpy change and entropy change are strong functions of ionic strength. Possible molecular contributions to the enthalpy and entropy are discussed, leading to the tentative conclusion that hydrogen-bonding interactions at the interacalation site are the primary contributors to the observed thermodynamic parameters. The dependence of the enthalpy on the ionic strength is well beyond the predictions of current polyelectrolyte theory and cannot be fully accounted for. The enthalpy and entropy changes observed compensate one another to produce relatively small free-energy changes over the range of solution conditions studied.
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  • 51
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    Topics: Chemistry and Pharmacology
    Notes: Mechanical creep and creep recovery in small shearing deformations have been studied in unligated clots formed with both thrombin and ancrod. In thrombin clots, both A binding sites (which interact with “a” sites to link monomer units within a protofibril) and B sites (which interact with “b” sites to form links between protofibrils) are exposed to enable formation of linkages; in ancrod clots, only the A sites are exposed. Fine clots (with minimal lateral aggregation of protofibrils), coarse clots (with substantial aggregation of fibril bundles), and clots of intermediate coarseness were compared. Fine thrombin clots showed less creep at short times but more creep at long times than coarse or intermediate clots and had more irrecoverable deformation relative to the initial elastic deformation. Ancrod clots had greater irrecoverable deformation than the corresponding thrombin clots, both fine and coarse. The permanent deformation in fine ancrod clots was enormous, corresponding almost to fluid character; the rate of permanent deformation was larger than that in fine thrombin clots by more than two orders of magnitude. For all types of clots, differential measurements of compliance (or its reciprocal, elastic modulus), as well as the applicability of the Boltzmann superposition principle to calculation of creep recovery, showed that the overall density of structure remained constant throughout the mechanical history; i.e., if structural elements were breaking, they were reforming at the same rate in different configurations. The possibility that the weakness of ancrod clots is attributable to partial degradation of α-chains rather than absence of Bb linkages was eliminated by comparisons of clots made with thrombin, ancrod, and ancrod plus thrombin; the last two showed identical partial degradation of α-chains (by gel electrophoresis), but the first and third had essentially identical initial elastic moduli and creep behavior. Two alternative mechanisms for irrecoverable deformation in fine clots are discussed, involving rupture of protofibrils and slippage of twisted segments, respectively.
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    Biopolymers 24 (1985), S. 735-745 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently, it was suggested that parallel β-sheets have a significant dipole moment, in contrast to antiparallel sheets. Ab initio molecular-orbital (MO) calculations on parallel and antiparallel β-strands of tetra(Gly) show that they have very similar charge distributions. Interaction energies between two and three strands of tetra(Gly), obtained using the direct reaction field Hamiltonian, show that a particular choice of point charges is probably not crucial for calculating interactions within β-sheets, but that it might be for calculating interactions between these sheets and other parts of a protein, in particular, α-helices. The point-charge representation of our MO-SCF results will probably reduce the hazard of introducing artefacts in electrostatic calculations of protein conformational energies, provided the short-range interactions are treated in a more realistic way, i.e., such that intra- and interchain induction effects are included.
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  • 53
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: The pH and ionic strength dependence of conformation of the COOH-terminal fragment 206-316 (fragment FII) of thermolysin was monitored by far-uv CD and difference absorption measurements. This fragment was shown previously to possess the properties of a protein domain, i.e., able to refold into a stable nativelike structure [Fontana, A., Vita, C. & Chaiken, I. M. (1983) Biopolymers 22, 69-78]. Analysis of the CD spectra in the pH range of 1-12 indicated that near pH 1, the conformation of fragment FII appears to be in an intermediate state (H) between the fully unfolded one (U) [the guanidine hydrochloride (Gdn · HCl)-induced unfolded state] and the nativelike state (N - that attained at neutral pH). Quantitative analysis of secondary structure from CD spectra revealed that state H at 4°C is characterized by some 30% α-helical structure, compared to 47% for state N. The heat- and Gdn · HCl-mediated unfolding transitions of state H were fully reversible and characterized by little cooperativity, which is taken as an indication that state H corresponds to several species possessing different, and low, conformational stabilities. The midpoint transition from state H to N occurs near pH 2.5, implying that the acid transition results from the titration of carboxyl groups of the fragment with anomalously low pK, as would be expected for groups involved in specific salt bridges. Fragment FII at pH 1 (state H) may be induced to exhibit nearly the same degree of helicity of state N simply by increasing the ionic strength of the solution, thus reducing the repulsive interactions between positive charges within the highly charged fragment at pH 1. The results obtained emphasize the role of electrostatic interactions in the folding and stability of fragment FII and suggest a mechanism of folding of the fragment from U to N involving an intermediate state characterized by an assembly of fluctuating α-helices.
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  • 54
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    Biopolymers 24 (1985), S. 867-882 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA supercoiling is both an interesting problem from the theoretical point of view and an important phenomenon affecting DNA functions in vivo. Experimentally, however, hardly more than the overall hydrodynamic shape, superhelical density, and enzymic or chemical reactivity of the parameters that are in some way related to DNA secondary and tertiary structure in the superhelical state can be determined. Consequently, it is highly desirable to build up models of DNA supercoiling that, on the one hand, match the above type of global data and, on the other, take advantage of the knowledge about DNA structure at lower levels of complexity, i.e., with linear DNA molecules and its synthetic models. One possible approach, presented here, deals with an extension of Fuller's and Benham's general ideas concerning an elastomechanical model of DNA supercoiling. We extend their model with an algorithm suitable for numerical calculations and construct a fast computer program, ROPASE, that displays the rod shapes as dependent on its elastic properties and applied stress. Development of this program made inevitable a detailed analysis of the input parameters found to be degenerate in the sense that not all of them should be considered variable to generate the whole set of possible solutions of the model. Many calculations were performed using ROPASE to test its properties and the properties of the elastomechanical model. Representative DNA shapes are presented.
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    Biopolymers 24 (1985), S. 905-910 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 24 (1985), S. 883-895 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermotropic behavior of lipid vesicles prepared from dimyristoylphosphatidylcholine in the presence of cytochrome c oxidase has been studied by highly sensitive differential scanning microcalorimetry. This protein has a remarkable effect on the gel-liquid crystalline transition of dimyristoylphosphatidylcholine. In the presence of cytochrome c oxidase, the thermogram of the lipid vesicles exhibits a second endothermic peak, which is adjacent to the main lipid phase-transition peak and appears at a higher temperature. As the concentration of added protein increases, the two endothermic peaks become further separated, and the transition temperatures and the heats of transition corresponding to both endothermic peaks decrease. A greater decrease in the transition temperature at the lower-temperature peak with added protein suggests that the lower-temperature peak is more perturbed than the higher-temperature peak. The higher-temperature peak is not thermally reversible. Treatment of sample well above the transition temperature results in a reduction of the magnitude of the higher-temperature peak. The lipid-protein interaction contributing to the higher-temperature peak is discussed.
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  • 57
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    Topics: Chemistry and Pharmacology
    Notes: An intercalation model of a complex between DNA and a bleomycin fragment (BLMF), consisting of the bithiazole core and an amide and a protonated amino substituent, is presented. The model, which shows a preference for BLMF with the protonated amine in the minor groove and the acetyl terminal inserted into either the minor and major grooves, respectively, agrees with recently obtained nmr data. The selection of sites I and II, which have the smallest unwinding of the three theoretical intercalation sites, is consistent with the experimental unwinding angle of 12°. The bithiazole moiety stacks between two base pairs of the double helix, while the protonated substituent interacts ionically with the negatively charged regions of the backbone in the minor groove of the DNA. The protonated amine also forms an intramolecular hydrogen bond with the carbonyl oxygen of the amide group on the same substituent. Analysis of drug complexes with different base-pair sequences reveal four energetically defined groups. The relative energy of the dimer duplex complexes of BLMF correlates with bleomycin's observed base-sequence specificity upon cleavage. The most stable intercalation complexes form adjacent to the bases cleaved most readily. This correlation suggests a primary connection between intercalation and cleavage. A model cleavage site based on these preliminary theoretical calculations and the experimental observations is proposed. It consists of an intercalation site in a trimer duplex. Pyrimidine(p)purine sequences are the predominant sites for intercalation, and the base adjacent to the site at the (3′) end is cleaved.
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    Topics: Chemistry and Pharmacology
    Notes: Boc-L-Leu-Aib-Pro-Val-Aib-Aib-Glu(OBzl)-Gln-Phl (Boc = t-butyloxycarbonyl, Aib = α-aminoisobutyric acid, Bzl = benzyl, Phl = phenylalaninol), C59H90N10O14, the protected C-terminal nonapeptide with the sequence 12-20 of alamethicin, crystallizes in the orthorhombic space group P212121 with a = 15.666, b = 16.192, c = 26.876 Å, and Z = 4. The molecular conformation is right-handed helical with three α-(5 → 1 hydrogen bonds) and three β-turns (4 → 1 hydrogen bonds). All but two of the hydrogen bonds are significantly longer than the usual value and show bifurcation to some extent. The α/310r-helical nonapeptide molecules are arranged head-to-tail along the a direction. The resulting linear antiparallel chains are linked by a weak intermolecular hydrogen bridge, thus forming a two-dimensional layer structure in the ab plane. The conformation of this nonapeptide is almost identical with that of the corresponding C-terminal part found by x-ray crystallography of the eicosapeptide alamethicin.
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  • 59
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: A newly designed host-guest approach is introduced as a experimental tool to explore the relationship between the sequence of peptides and their secondary structure. From the CD spectra of the host-guest peptides studied, a tentative scale for the α-helix potential in 2,2,2-trifluorethanol of guest amino acids is delineated. The conformational preferences are also examined in β-structure supporting media (solid state, CH2Cl2, CH3OH, H2O) using ir-absorption and CD techniques. Scales for the β-forming tendency of guest amino acid residues in the different media are delineated. It is shown that the preferred conformation of the host-guest peptides is a function of the medium, the chain length, and the protecting groups. Given the fact that conformational effects are important in peptide synthesis, the tentative scales may serve as a guideline to predict secondary structures of side-chain-protected or -deprotected peptides in a given solvent, complementing the well-known empirical conformational prediction parameters.
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    Biopolymers 24 (1985), S. 1107-1111 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 24 (1985) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
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    Notes: The interaction of CuCl2 with poly(S-carboxymethyl-L-cysteine) (poly[Cys(CH2COOH)]) and poly(S-carboxyethyl-L-cysteine) (poly[Cys(C2H4COOH)]) were studied by absorption spectra and circular dichroism (CD). On mixing CuCl2 with polypeptide solutions, absorption bands appeared at 320-325 nm in both polypeptides, and at 255-260 nm in the case of poly[Cys(CH2COOH)]. A stable bound species was formed in the case of poly[Cys(CH2COOH)], since the apparent molar absorption coefficient of the bound species did not depend on the mixing ratio. From the absorption data, it was inferred that Cu2+ ions were complexed with the side chains, most probably with sulfur atoms and carboxyl groups. Induced optical activities were observed for the two polypeptides. The CD spectra of poly[Cys(CH2COOH)] + CuCl2 gave simpler aspects than those of poly[Cys(C2H4COOH)] + CuCl2.
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    Notes: The atomic motions from a molecular-dynamics simulation of yeast tRNAPhe are analyzed and compared with those observed in protein simulations. In general, the tRNA motions are of larger amplitude, they are more anisotropic, and they arise from potentials of mean force that are more anharmonic than in the protein case. In both cases, the amplitudes are largest for atoms on the surface of the molecules. On the other hand, the most anisotropic and anharmonic atomic motions are generally found in the interior of the tRNA, while they are found on the surface of the protein. These differences are discussed in terms of the differences in structure between nucleic acids and proteins.
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  • 64
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    Biopolymers 24 (1985) 
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  • 65
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    Biopolymers 24 (1985), S. 947-960 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The purpose of this work was to improve our understanding of quasielastic light scattering from long rigid rods (QL 〉〉 1). For these scatterers, only small angular displacements are required to produce dephasing of the scattering light. This plus the fact that only rods lying perpendicular to Q contribute to the scattered light allow one to simplify the intermediate scattering function to an analytic form. This form is shown to be nonexponential, exhibiting (t)-½ behavior at long delay times. This new scattering function can then be fit to experimental functions using standard methods.
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  • 66
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    Biopolymers 24 (1985), S. 1001-1008 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report high-resolution Raman spectra obtained from the circularly closed double stranded DNA (Form I) of the plasmid pBR322 and from its corresponding linear form (Form III). Comparison of the Raman spectra of the two forms demonstrates that, at a superhelical density (σ) of -0.069, which is of the same order as those found for most naturally occurring circularly closed DNAs, no major structural transitions occur under the influence of supercoiling. It is shown that at least 98% of all bases are fully basepaired, and that the conformation of the sugar-phosphate backbone is essentially identical to that of linear DNA. Thus, the structural influence of supercoiling, under these conditions, is confined to minor stretches of the plasmid DNA.
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  • 67
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    Biopolymers 24 (1985), S. 1075-1087 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The force field established for guanine is applied here to guanine-containing biopolymers by considering the model compound 9-methylguanine, in which the methyl group is taken as a dynamic unit whose mass is concentrated on the carbon. In-plane normal-mode frequencies for this model compound and its N-deuterated analog are calculated. Band frequencies observed for guanine residue in Raman biopolymer spectra, such as those for DNA, RNA, or poly(G), are associated with calculated modes having similar wavelengths. They are discussed by taking into account observed and calculated D, 15N, and 18O isotopic shifts. The atomic displacements for the normal modes corresponding to the principal bands are illustrated and a number of assignments proposed.
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    Biopolymers 24 (1985), S. 935-945 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A comparative study has been made using molecular mechanics of the ring entity of the active enkephalin analogs, Tyr-cyclo(-Nω-D-XXX-Gly-Phe-Leu-), where XXX is variously A2pr, A2bu, and Orn. Several conformations are favored for all three, and the lower-energy models are compatible with a Gly3-Phe4 bend in the active form of enkephalin. Some difficulties in assuming standard geometries in conformational surveys are illustrated.
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    Biopolymers 24 (1985), S. 961-978 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The x-ray structure of Boc-L-Ala-Aib-Ala-Aib-Ala-Glu(OBzl)-Ala-Aib-Ala-Aib-Ala-OMe(I) represents the first α-helix determined by direct methods. This undecapeptide is a model of the N-terminus of alamethicin, and it exhibits voltage-dependent pores in bilayer membranes at a higher voltage and concentration than alamethicin. The molecule crystallizes in the monoclinic space group P21 with a = 10.602(1), b = 23.884(3), c = 13.622(1) Å, β = 95.61(6)°, and Z = 2. It adopts a right-handed α-helical conformation in the solid state with intramolecular 5 → 1 hydrogen bonds. An additional intramolecular hydrogen bond is bifurcated, forming a stronger 4 → 1 interaction (i.e., a β-turn III) and a weaker 5 → 1 interaction, thus prolonging the α-helical part up to 9 residues. The α-helix radius of 2.1 Å, the height per residue (distance Ni … Ni + 4) of 1.53 Å, the resulting length of the α-helical part of 13.8 Å (9 residues) resp. 15.3 Å (10 residues), the van der Waals radius (4.7 Å), and the minimal diameter of pores formed by aggregation of 3-10 α-helices were calculated omitting the Glu(OBzl) side chain. In the crystal, the α-helices are linked head to tail via two hydrogen bridges forming continuous chains. Adjacent helices are oriented in antiparallel with their helix axes and have only van der Waals contacts.
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    Biopolymers 24 (1985), S. 1009-1022 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Time-resolved fluorescence polarization anisotropy measurements were performed on two fractionated samples of duplex poly(dGdC) containing 230 (+40, -30) base pairs (bp) and 590 ± 40 bp. Deconvolution using the intermediate zone formula for the twisting correlation functions (which is not valid for such short DNAs) yields apparent torsion constants for these two samples that are disparate and, in any case, too low. By similarly deconvoluting simulated data constructed from the correct twisting correlation functions, it can be inferred that these two samples actually exhibit the same torsion constant, α = (4.0 ± 0.4) × 10-12 dyn cm. Within the experimental uncertainties, this value is the same as that reported previously from this laboratory for linear φ29 and linearized M13mp7 DNAs. The 590-bp sample exhibited a peculiar evolution of its apparent torsional rigidity from a very high initial value, \documentclass{article}\pagestyle{empty}\begin{document}$ \hat \alpha $\end{document} = (11 ± 1) × 10-12 dyn cm, to a normal value over a period of several months, during which time many very small fragments appeared to be dissociated from, or annealed out, of the predominant high-molecular-weight species. Possible interpretations of these observations are discussed.
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  • 71
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    Notes: The conformation and internal dynamics of supercoiled pUC 8 DNA (2717 bp) are examined by dynamic light scattering, and the magnitude and uniformity of its torsional rigidity are determined using time-resolved fluorescence polarization anisotropy of intercalated ethidium dye. Neither measurement gives any indication of an appreciably reduced bending or twisting rigidity, or anomalously rapid internal motions. For 31P, in supercoiled pUC 8, we measure T2 = (2.0 ± 0.5) × 10-3 s. This lies within the range of present theoretical estimates obtained using normal rigidities. The proton linewidths observed for pUC 8 and pBR322 (4363 bp) DNAs are within a factor of 2-3 of those similarly estimated assuming ordinary rigidities.According to Bendel, Laub and James [(1982) J. Am. Chem. Soc. 104, 6748-6754], supercoiled pIns36 DNA (7200 bp) exhibits an astonishingly long T2 = 1.17 s for 31P, a slowest rotational relaxation time, τ = 5 × 10-9 s, and an enormously reduced bending rigidity. Serious questions raised by these findings are examined here. The 5 × 10-9 s slowest rotational relaxation time is shown to be physically inadmissible.The nmr relaxation theory developed previously by Allison, Shibata, Wilcoxon, and Schurr [(1982) Biopolymers 21, 729-762], is modified to incorporate new results for deformable filaments, which directly introduce the highly nonexponential tumbling correlation function for reorientation of the local helix axis. Essential requirements for a complete calculation of R2, including estimation of the tumbling correlation function and evaluation of the still unknown DIP/CSA cross-term, are described in detail. Slow coil-deformation modes analogous to the Rouse-Zimm modes of linear DNAs are shown to make an important, if not dominant, contribution to the R2 relaxation rate. Geometrical parameters in the theory are chosen to provide good agreement with literature data for 600-bp linear DNA. Using this theory and an informed guess for the tumbling correlation function, we find that the 31P-nmr relaxation data of Bendel et al., if correct, necessarily impose on their DNA one or more extreme properties, such as enormously reduced bending or twisting rigidities. In contrast, the same theory yields reasonable agreement with the T2 reported here for 31P in supercoiled pUC 8 DNA when its rigidities are assumed to be quite ordinary.
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    Biopolymers 24 (1985), S. 1131-1146 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aggregation behavior of the chemotactic peptide analogs, Formyl-Met-Leu-Phe-OMe (1) and Formyl-Met-Aib-Phe-OMe (2), has been studied in chloroform and dimethylsulfoxide over the concentration range of 0.2-110 mM by 1H-nmr spectroscopy. Both peptides associate in CDCl3 at concentrations ≥ 2 mM, while there is no evidence for aggregation in (CD3)2SO. Analog 1 adopts an extended conformation in both solvents favoring association to form β-sheet structures. A folded, γ-turn conformation involving a 3 → 1 hydrogen bond between Met CO and Phe NH is supported by 1H-, 13C-nmr, and ir studies of analog 2. The influence of backbone conformation on the ease of peptide aggregation is demonstrated by ir studies in CHCl3 and CD studies in dioxane.
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    Biopolymers 24 (1985), S. 1169-1188 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A 24-ps molecular-dynamics simulation of motions in yeast tRNAPhe has been completed. The overall structure of the molecule is well preserved, for the motions represent fluctuations about an average structure that is very much like the crystallographic structure. The four helical stems remain intact, the structures of the loop regions do not deteriorate, and even the base stacking in the single-stranded amino acid acceptor terminus is maintained. With two exceptions, none of the sugar puckers is significantly changed. The unconstrained floppy motions of base A76 are responsible for the repuckering of ribose 76. The other sugar that repuckers is ribose, 46, and this is the result of a very small structural change in the center of the molecule that is also responsible for the breakage of one tertiary hydrogen bond. This change in local structure does not seriously distort the base-stacking and intercalation patterns where the variable loop and the D-stem interact.
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    Biopolymers 24 (1985), S. 1233-1246 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The persistence length and effective long-range bending rigidity are derived for a discrete model of an anisotropically bending filament and shown to be independent of the torsional rigidity. The twisting persistence length is found to be independent of the anisotropic bending rigidity. Other statistical properties are briefly discussed, including the dependence of tangent vector projections on contour length. The dependence of a tensor contraction on contour length is derived for an isotropically bending filament with no equilibrium twist.
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  • 75
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    Biopolymers 24 (1985), S. 1257-1263 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vibrational CD (VCD) and ir absorption data are reported for a series of films of Boc-(L-Ala)n-OMe homo-oligopeptides (n = 3-7) in the amide I and A regions. The data evidenced a sharp change between n = 3 and n = 4, which parallels the onset of β-structure formation, and another between n = 5 and n = 6, which parallels the full development of β-structure. This represents the first report of the application of VCD to oligopeptide conformation. The data resembled earlier reported film VCD studies of higher-molecular-weight polypeptides of known β-structure.
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    Biopolymers 24 (1985), S. 1271-1291 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational-energy calculations have been carried out in order to determine favorable packing arrangements within a group of α-helices. The influence of side chains and of the number of interacting α-helices on the mode of packing was analyzed. In this work, our earlier methods for computing the packing energy of a pair of α-helices [Chou, K.-C., Némethy, G. & Scheraga, H. A. (1984) J. Am. Chem. Soc. 106, 3161-3170] have been extended to treat the interactions among several helices. Also, new algorithms allow the matching of standard peptide geometry to x-ray coordinates of helical complexes and the analysis of interrelations between several helices. As a specific test case, the packing of three neighboring α-helices, viz., the A, G, and H helices of sperm whale myoglobin, was considered. Minimum-energy arrangements were computed for the separate A-H and the G-H α-helix pairs as well as for the A-G-H three-helix complex. For the packing of the nearly antiparallel G and H α-helices, the same optimal structure was obtained in two- and three-helix complexes, indicating that a single packing arrangement is specifically favored by interhelix interactions. For the pair of nearly perpendicular A and H α-helices, interactions are less specific, so that there is no unique optimal structure in the two-helix complex; in the three-helix complex, however, a specific mode of packing is favored even for the A-H pair. This result indicates that the presence of other nearby α-helices can influence the packing of a given α-helix pair. The computed arrangement of the A-G-H complex is very close to that of the crystallographically determined structure. These results can be used to make deductions about the likely sequence of events in protein folding, where, in this particular case, it appears that the G-H helix pair may form first and then induce proper orientation of the A helix.
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  • 77
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    Notes: Quantum-mechanical equations are derived that are particularly well suited to actual computations of the CD for helical polymers. They make use of cyclic boundary conditions and helical symmetry, so that only two matrices with a size equal to the number of transitions considered need be diagonalized. The final equations are expressed directly in terms of monomer properties and helical parameters to invite the same input as earlier calculations, and are given as a rotational strength times a shape function for ease of comparison with the earlier work. The shape of the helix term is expressed as a derivative with respect to ω and depends on the distance between monomers along the helix axis. Other terms involving two electric transition dipoles depend on the distance from the helix axis to the transition center. These equations are directly comparable to the classical equations derived for cyclic boundary conditions and helical symmetry. We present an outline of the derivation and enough intermediate steps to clarify how the equations arise.
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    Biopolymers 24 (1985), S. 1385-1385 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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    Biopolymers 24 (1985), S. 1479-1491 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Raman and ir spectra of α-helical poly(L-glutamic acid) have been assigned on the basis of a normal mode calculation for this structure. The force field was based on our previously refined main-chain force constants for α-poly(L-alanine) and side-chain force constants for β-calcium-poly(L-glutamate). Despite the identical backbone α-helical structures, significantly different frequencies are calculated, and observed, in the amide III and backbone stretch regions of α-poly(L-glutamic acid), as compared with α-poly(L-alanine). This clearly demonstrates the influence of side-chain structure on mainchain vibrational modes.
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    Biopolymers 24 (1985), S. 1501-1514 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The quasielastic light scattering method was used to study the ionic strength dependence of the mutual diffusion coefficient of sodium polystyrene sulfonate (NaPSS) as a function of NaCl and CaCl2 concentrations. The results indicate a splitting in the relaxation times that depends on the ratio Cp/Cs, where Cp and Cs are the polyion and added salt concentrations. A universal relationship taking into account Manning's theory of condensation and the Debye screening due to the added salt is proposed to characterize the fast-slow relaxation time transition.
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    Biopolymers 24 (1985), S. 1573-1593 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
    Notes: A theory of the electrophoresis of DNA through gels with large interfiber spacing, such as dilute agarose, is presented. We assume that the DNA molecule moves along its axis through a “tube” in a neutral gel under the influence of the electric field. The tube is random except for possible bias due to the effects of the field. When the field is small, we easily recover the inverse-length dependence of the mobility found previously by de Gennes and by Doi and Edwards. At higher fields, a new effect appears; the tube becomes oriented because the field biases the direction of the leading end of the chain as it moves to form an extension of the tube. This leads to an increase of the mobility with increasing field by adding a field-dependent but length-independent term to the mobility expression. In agreement with experiment, we find that the field effect can be important at fields as low as 1 V/cm and that the effect can seriously decrease the sensitivity of the mobility to chain length. We also examine the fluctuation of the migration distance, the degree of orientation induced by the field, and the transient effects occurring when the feld direction is rotated by a right angle.
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    Biopolymers 24 (1985) 
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    Keywords: Chemistry ; Polymer and Materials Science
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  • 84
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    Topics: Chemistry and Pharmacology
    Notes: The confortmational behavior of the cholecystokinin-related fragments CCK4, CCK5, and CCK6 as determined by 1H-nmr spectroscopy in DMSO-d6 and water and fluorescence-transfer measurements in aqueous medium are greatly dependent on the ionization states of these peptides. Under netral conditions, the backbones of CCK5 and CCK6 preferentially adopted folded forms with a β-turn including the four residues Gly-Trp-Met-Asp, probably stabilized by a hydrogen bond between the CO of Gly and the NH of Phe. In these structures, possible induced by an ionic interaction between the carboxylic group of Asp32 and the NH3+ group of the N-terminal amino acid, the lateral chains of the various residues are quite distant from each other (15-16 Å). Under acidic conditions, extended structures without interactions between side chains predominate for CCK5 and CCK6, while for CCK4, a conformational change drawing the Trp and Phe side chains in close proximity was shown by fluorescence. The conformations observed in aqueous medium at physiological pH are discussed in relation to the biological activity of these peptides.
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    Biopolymers 24 (1985), S. 1647-1662 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermally induced helix-coil transitions of myosin rod, light meromyosin, and tropomyosin were studied by optical rotatory dispersion (ORD). Fractional helicity was calculated from both the Moffitt-Yang parameter, b0, and the corrected mean residue rotation [m′] at 231.4 nm. Between 3 and 30°C, [m′] increases linearly with a slope of 59/°C, whereas b0 is virtually constant, indicating apparently different thermal melting behavior. Poly(L-lysine) and poly(L-glutamic acid) in their helical forms and myoglobin also show a nearly linear temperature dependence of [m′]231.4. Muscle proteins in 6M guanidine hydrochloride and the random-coil forms of the homopolymers exhibit temperature-dependent values of [m′]231.4 and b0. We conclude from these observations that ORD properties of both α-helices and random-coil polypeptides have significant intrinsic temperature dependencies. A new method of estimating fractional helicity as a function of temperature is proposed.
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    Biopolymers 24 (1985), S. 2035-2040 
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology
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  • 88
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    Topics: Chemistry and Pharmacology
    Notes: The conformation of phenylacetyl-D-alanyl-D-alanine in the crystalline state was characterized by Fourier-transform ir and Raman spectroscopy and was unambiguously solved by x-ray single-crystal determination. In the crystalline state, the molecule adopts a partially folded conformation quite similar to that of another cell wall peptide, acetyl-D-alanyl-D-alanine [Benedetti et al. (1981) J. Biol. Chem. 256, 9229-9234], although the crystal structure is stabilized by a quite different intermolecular hydrogen-bond pattern. No significant deviation from the usual trans-planar peptide group geometry was detected. The conformations accessible in the noncrystalline state were investigated by ir measurements in solution and conformational energy calculations. The theoretical study revealed that the peptide is a highly flexible molecule, since 55 minima were detected, within 3 kcal/mol, including the conformation found in the single crystal. The ir data for phenylacetyl-D-alanyl-D-alanine in different solvents were in accordance with virtually extended conformations, with some indication for weak, intramolecularly hydrogen-bonded C5-rings. These conformational data obtained for the cell wall peptide analog are compared with those known for penicillin G in the crystalline state.
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    Biopolymers 24 (1985), S. 1863-1879 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular mechanical calculations were done on complexes of ethidium cation with various base-paired deoxydinucleoside monophosphates [(ApT)2, (TpA)2, (A2 · T2), (GpC)2, (CpG)2, and (G2 · C2)] and deoxyhexanucleoside pentaphosphates [(ATATAT)2, (TATATA)2, (A6 · T6), (GCGCGC)2, (CGCGCG)2, and G6 · C6]. Relative binding energies, sequence preferences, and conformational aspects of the intercalation complexes were studied. The most detailed models used (an all-atom force field) gave results in good agreement with previous calculations and experimental work. Less-sophisticated models did not perform as well.
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    Biopolymers 24 (1985), S. 1931-1940 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transient photodichroism (TPD) data of Wang, Hogan and Austin [(1982) Proc. Natl. Acad. Sci. USA 79, 5896-5900] for methylene blue intercalated in nucleosomal DNA are reanalyzed using correct expressions for the twisting correlation functions of short DNAs. The data are found to rule out several models, including one in which the helix axis is constrained to girdle the equator of the sphere (representing a core particle) but the DNA is everywhere able to undergo twisting deformations and/or spinning around its local helix axis. However, when the ends of the DNA are rigidly clamped (against twisting/spinning) to the sphere, the same model gives an excellent fit to the data with suitable choices of parameters. From these and other observations, it is concluded that nucleosomal DNA must be rigidly clamped to the core particle at one or more points, although it is free to twist at most sites of binding of the dye. Moreover, if the dye is actually bound between two clamped points, then the torsional rigidity of DNA in the nucleosome is at least 2.5 times smaller than that of an ordinary linear DNA.
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  • 91
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 92
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    Biopolymers 24 (1985), S. 1881-1897 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The configurational properties of an isotropically bendable wormlike chain have been investigated using a Monte Carlo approach. In particular, radial distributions for end-to-end separation, ring closure probabilities, and the angular correlation of the two ends of the chain have all been determined as a function of the contour length of the chain. The results of this analysis, when applied to the data of Shore et al. [(1981) Proc. Natl. Acad. Sci. USA 78, 4833-4837] for the length dependence of ring closure for doublehelical DNA, yields a value for the persistence length of DNA in remarkable agreement with earlier hydrodynamic studies.
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  • 93
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    Biopolymers 24 (1985), S. 1909-1930 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optical anisotropy data spanning a very wide time range are analyzed using a recently developed theory for filamentous macromolecules that can bend, twist, and also admit overdamped local libration (or wobble) of the chromophore. A rapid relaxation in the fluorescence polarization anisotropy (FPA) near 10-10 s is fitted well by superimposing isotropic wobble of the chromophore (7° rms polar and azimuthal amplitude) on the long-wavelength twisting and bending motions that characterize the relaxation at longer times but not by the latter alone. Moreover, the decay of the FPA from 0.5 to 150 ns cannot be satisfactorily fitted by chromophore wobble in an otherwise rigid DNA and must be assigned primarily to twisting, as noted previously.Data from 26 ns to 20 μs for 600 base-pair DNA are accurately fitted with only a single adjustable scaling factor when the tumbling correlation function is taken to be the empirical electric birefringence decay function of Elias and Eden. The Barkley-Zimm (BZ) tumbling correlation for very long filaments appears to decay too rapidly and results in significant overestimation of the depolarization for t ≤ 300 ns. In the range of the FPA experiments (t ≥ 150 ns), equally good fits with equally uniform torsion constants are obtained for long DNAs, whether one assumes the BZ tumbling correlation function or neglects tumbling entirely, but the best-fit torsion constant (actually the product of the torsion constant and friction factor) is increased by the factor 1.9 when the BZ result is used with a persistence length of a = 500 Å. The BZ bending theory is compared with other experimental data, and also with a simulation at very short times with mixed results. Present uncertainties regarding the tumbling dynamics and the friction factor for azimuthal rotation allow the torsion constant to be as much as 3.8 times larger than the initial estimate of Thomas et al. Apparent torsion constants obtained from relative ligase kinetics measurements are also briefly discussed.
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  • 94
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    Biopolymers 24 (1985), S. 1981-1993 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electric-field pulses of e.g. 20 kV/cm and 100 μs induce a strong decrease in the scattered light intensity of DNA condensed by spermine. Analysis of this effect demonstrates that the decrease of the scattered light intensity results from decondensation of DNA. The decondensation reaction requires an electric-field strength exceeding a threshold value. Complete decondensation can be achieved at field strength that are only slightly higher than the threshold value. The decondensation process is strongly accelerated at high electric-field strengths. At 30 kV/cm, the decondensation time constant is ∼8 μs, corresponding to an acceleation factor of 105 relative to the field-free decondensation reaction. The dependence of the time constants on the electric-field strength suggests that the field-induced decondensation is due to a dissociation field effect. The condensation process observed after electric-field pulses at low concentrations of DNA and spermine shows a characteristic induction period, which strongly depends on the spermine concentration. This induction period reflects the time required for the binding of spermine to DNA, until the degree of binding is sufficiently high for the condensation reaction. The fast dissociation of condensed DNA by electric-field pulses together with a relatively long lifetime of the free DNA results in a reaction cycle resembling a hysteresis loop.
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  • 95
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    Biopolymers 24 (1985) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 96
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    Biopolymers 24 (1985), S. 2041-2043 
    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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  • 97
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    Biopolymers 24 (1985), S. 2057-2085 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theory of adsorption of a polypetide chain capable of undergoing the coil-β-structure transition on a solid planar surface has been developed. The mutual influence of two order-disorder phase transitions, a conformational and an adsorption transition, was investigated. Various types of adsorption transitions are possible, depending on the initial conformational state (partly or completely β-structured) and the selectivity of adsorption: (a) the second-order phase transition, in which the chain is partly structured, both in adsorbed and desorbed states; and (b) the first-order phase transition, in which the chain exhibits a regular β-structure, at least on one side of the adsorption transition boundary. The chain bonding to the surface alters the degree of β-structure, both in the case of selective and nonselective adsorption (similar to the adsorption of the chains with other types of secondary structure). We show that the slope of the adsorption curves for partly β-structural chains increases as a result of an increase in the degree of β-structuring, and this effect is even stronger than the analogous effect of β-structuring.
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  • 98
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various copolypeptides were prepared by benzylamine or tertiary amine-initiated copolymerizations of alanine-N-carboxyanhydride (Ala-NCA) and valine-N-carboxyanhydride (Val-NCA). The number-average molecular weights of these copolypeptides were detemined by 1H-nmr spectroscopic end-group analyses and viscosity measurements. The sequences were characterized by 15N-nmr spectra in solution, and the average lengths of the homogeneous blocks were determined from the signal intensities. The 50.3-and 75.4-MHz 13C-nmr CP/MAS spectra of the solid copolypeptides are not sensitive to sequence effects, but allow qualitative and quantitative analyses of the secondary structures. In contrast to other methods, the 13C-nmr spectra allow determination of the extent to which individual amino acids are incorporated into β-sheet or α-helix phases. Depending on primary structure and molecular weight, the secondary structure of (Ala/Val) copolypeptides may vary significantly. Both monomer units may be predominantly helical or predominantly β-sheet structure, or the Val units may prefer the β-sheet structure with most Ala-units forming β-helices. However, these secondary structures are more or less thermodynamically unstable and revert to the stable conformations on reprecipitation from trifluoroacetic acid/water.
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  • 99
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    Biopolymers 24 (1985), S. 2231-2242 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The intramolecular formation of multiple clusters of interacting helices has been characterized in a homopolymer. The configuration partition function permits the formation of clusters in which the number of interacting helices may be as large as the greatest integer in n/2, where n denotes the number of amino acid residues in the chain. The theoretical formulation has its origin in a recent [Mattice, W. L. & Scheraga, H. A. (1984) Biopolymers 23, 1701-1724], tractable matrix expression for the configuration partition function for intramolecular antiparallel β-sheet formation. Reassignment of the expression for one of the n(n+3)/2 elements in the sparse statistical weight matrix, along with a simple change in notation, converts that treatment into a matrix formulation of the configuration partition function for a chain containing multiple clusters of interacting antiparallel helices. The five statistical weights used are δ, fl, w, and the Zimm-Bragg σ and s. Each tight bend that connects two interacting helices contributes a factor of δ, fl is used in the weight for larger loops between interacting helices, and w arises from helix-helix interaction. The influence of the helix-helix interaction is well illustrated by two helix-coil transitions in a chain with n = 156 and σ = 0.001. In the absence of helix-helix interaction, the transition occurs by the nucleation and subsequent elongation of a small number of helices. When helix-helix interaction is attractive, the transition can occur by a different mechanism. Formation of a single pair of interacting helices is followed by addition of new helices to the initial cluster. In the latter process, individual helices experience relatively little growth after they are formed.
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  • 100
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    Biopolymers 24 (1985), S. 2279-2299 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The low-energy conformations accessible to dCpdG modified at guanine N2 via trans epoxide opening by (+) and (-) 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (anti-BPDE) have been delineated by minimized semiempirical potential-energy calculations with all torsion angles flexible. Nearly 4000 trials were made, representing a fairly thorough investigation of the conformation space of the adducts. Carcinogen-base stacked states and base-base stacked conformers were found in the low-energy regions of both enantiomers. Many ω′, ω, ψ domains accommodate the two types of conformations, with B-like backbones among the most preferred states in each case. The conformational differences between the two enantiomers on the dimer level reside in subtle distinctions in orientation of the carcinogen-base linkage.
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