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  • Wiley-Blackwell  (19,421)
  • American Meteorological Society
  • 2015-2019
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  • 1
    Electronic Resource
    Electronic Resource
    Properties of a single chain embedded into a polymer matrix of varied thermodynamic quality and densityDedicated to Prof. Dr. D. Braun on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 189-202 
    Details
    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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850118
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  • 2
    Electronic Resource
    Electronic Resource
    MATERIAUX TRIPHASIQUES ALVEOLAIRES POLYMERE / CHARGE / LIQUIDE OU GAZ. Préparation de Matériaux triphasiques Polystyrène / billes de Verre / Eau ou AirDédié au Prof. Dr. D. Braun à l'occasion de son 60ème anniversaire (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 227-237 
    Details
    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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850121
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  • 3
    Electronic Resource
    Electronic Resource
    Gas sorption in poly(butylene terephthalate). A critical test of the influence of molecular gas dataDedicated to Prof. Dr. D. Braun on the occasion of his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 265-274 
    Details
    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.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850125
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  • 4
    Electronic Resource
    Electronic Resource
    RINGÖFFNENDE METATHETISCHE POLYMERISATION (ROMP) VON 5-CYANO-2-NORBORNENHerrn Prof. Dr. D. Braun zum 60. Geburtstag gewidmet (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 283-292 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The 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%).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850127
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetics of radical polymerization, LIII. The absolute rate constants in the radical polymerization of ethyl acrylateDedicated to Prof. Dr. D. Braun on the occasion on his 60th birthday (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 303-310 
    Details
    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.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850129
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  • 6
    Electronic Resource
    Electronic Resource
    Organische Gläser mit hohen Glasumwandlungstemperaturen auf Basis niedermolekularer Verbindungen.Herrn Prof. Dr. D. Braun zum 60. Geburtstag Gewidmet (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 329-334 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051850132
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  • 7
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    Electronic Resource
    Soluble maleimide prepolymers containing 1,3,5-triazine groups as composite resin matrices. Synthesis, characterization, and evaluation (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 1-14 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051900101
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  • 8
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    Electronic Resource
    Synthesis and properties of cationic resins derived from aniline/benzylamine-modified epoxy resins and diethylamines (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 15-32 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein 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.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051900102
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  • 9
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    Electronic Resource
    Studies on new non-shrinking, thermally stable araldite-type photopolymers with pendent arylacryloyl-groups. I. Photoreaction of some aryl acrylic-acid methyl esters in solution (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 33-52 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051900103
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  • 10
    Electronic Resource
    Electronic Resource
    Matériaux composites à base de bois rétifié, IIIPartie 2 cf. lit.7.. Etude de l'influence de la granulométrie des charges lignocellulosiques (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 190 (1991), S. 67-80 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051900105
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  • 11
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    Electronic Resource
    Pervaporation separation of water-ethanol through modified chitosan membranes, IIPart I: cf.1.. Carboxymethyl, carboxyethyl, cyanoethyl, and amidoxime chitosan membranesPresented at The 1990 International Congress on Membranes and Membrane Processes (ICOM ′90), Chicago 20 to 24 August 1990. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 169-181 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920114
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  • 12
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    Zusammenhänge zwischen mechanischem Verhalten und Morphologie von eigenfaserverstärkten Poly(propylen)/Poly(1-buten)-Blends, kristallisiert aus der hochorientierten Schmelze (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 183-197 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The 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.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920115
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  • 13
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    Cationic polyelectrolytes, XIPart X cf.7.. Polymers with quaternary N-atoms in the main chain obtained by condensation polymerization of epichlorohydrin with amines (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 199-211 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920116
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  • 14
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    MITTEILUNGEN (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 213-213 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051920117
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  • 15
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    Studies on rubber bound antioxidants (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 1-11 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 7 Ill.
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    Study of the conduction mechanisms in polycarbonate (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 13-20 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die 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.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051930102
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  • 17
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    Porous terpolymers: Poly(acrylonitrile-co-vinyl acetate-co-divinylbenzene) (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 21-28 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 2 Ill.
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  • 18
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    Studies on PE-HD/PE-LLD blends (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 193 (1991), S. 39-49 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die 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.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051930105
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  • 19
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    Copolymerization reactivity ratios of N,N-dimethyl acrylamide and isopropyl methacrylate determined by 1H-NMR spectroscopy (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 51-55 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920104
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  • 20
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    Polymer molecular properties and hydrodynamic lubrication (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 69-79 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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*.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920106
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    Tensile properties and morphology of injection-molded poly(1-butene) (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 57-67 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die 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.
    Additional Material: 7 Ill.
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    Synthesis and biological activity of chlorinated polyketone resins (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 103-111 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920109
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  • 23
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    The reaction of pyromellitic dianhydride with 4,4′-diaminodiphenylmethane (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 145-153 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920112
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  • 24
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    Miscibility of polyarylate/phenoxy/poly(butyleneterephthalate) ternary blends (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 133-144 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920111
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  • 25
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    Solid-state polycondensation of poly(ethylene terephthalate) films (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 155-168 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die 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.
    Additional Material: 10 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051920113
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    Preparation and properties of porous particles from trimethylolpropane trimethacrylateSystematic UIPAC name: 2,2-bis(methacryloyloxymethyl)butyl methacrylate. (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 192 (1991), S. 113-132 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 11 Ill.
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    Interfacial adhesion in short-fibre composites (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 31-38 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Eine 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.
    Additional Material: 5 Ill.
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    URL: http://dx.doi.org/10.1002/apmc.1991.051910103
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    Functionalization of polyethylene and ethylene propylene diene terpolymer in the bulk through dibutyl maleate grafting (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 15-30 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 7 Ill.
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    Effect of surface structure of porous silica microballoons on dynamic mechanical properties of amine cured epoxy resin composites (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 71-80 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die 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.
    Additional Material: 5 Ill.
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    Pervaporation separation of pentane-alcohol mixtures through ionically crosslinked blended membranes. I. Thermal measurements, electron microscopy and tensile studies (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 39-69 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.%.
    Additional Material: 11 Ill.
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    Mehrphasensysteme auf basis von fluorpolymeren, 1. Modifizierung von füllstoffoberflächen (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 81-107 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 17 Ill.
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    Mehrphasensysteme auf basis von fluorpolymeren, 2Teil 1 siehe1.. Modifizierung der polymermatrix (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 109-126 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 8 Ill.
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    Zur reaktionstechnischen und fluiddynamischen stabilität von multirohrreaktoren für die massepolymerisation (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 127-144 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: 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.
    Additional Material: 9 Ill.
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    Nucleophilic substitution reaction of ethanolamine onto poly(phenyl acrylate) and substituted poly(phenyl acrylate)s (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 191 (1991), S. 171-176 
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    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die 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.
    Additional Material: 4 Tab.
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    The analysis of circular dichroism spectra of natural DNAs using spectral components from synthetic DNAs (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 85-106 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have tested 21 different basis sets of synthetic DNA circular dichroism spectra and have slected one for use in spectral analyses of natural DNAs. This “standard” set consists of spectra of eight polymers: poly[d(A-A-T)·d(A-T-T)], poly[d(A-G-G)·d(C-C-T)], poly[d(A-T)·d(A-T)], poly[d(G-C)·d(G-C)], poly[d(A-G)·d(C-T)], poly[d(A-C)·d(G-T)], poly[d(A-T-C)·d(G-A-T)], and poly[d(A-G-C)·d(G-C-T)]. This basis set, applied according to the first-neighbor polymer procedure of Gray and Tinoco, allows a more uniformly accurate spectral analysis of six natural complex DNAs and eight (A+T)-rich satellite DNAs for base composition and first-neighbor frequencies than was previously possible. We find that spectra of poly[d(A)·d(T)] and/or poly[d(A-C-T-)·d(A-G-T)] are not generally required for good analysis results but we show in this and the following paper that these spectra are needed for the most accurate analyses of some satellite DNAs.
    Additional Material: 4 Ill.
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    A semiempirical extension of polyelectrolyte theory to the treatment of oligoelectrolytes: Application to oligonucleotide helix-coil transitions (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 159-166 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction of counterions with a suitably long, charged oligomer appears susceptible to treatment in the context of polyelectrolyte theory by the introduction of an end-effect parameter that reflects the reduced association of counterions with the terminal regions of the oligo-ion. Use of a physically reasonable value for the end-effect parameter provides excellent agreement between theory and the experimental data of Elson, Scheffler, and Baldwin [J. Mol. Biol. 54, 401-415 (1970)] on the dependences of melting temperature on salt concentration and chain length for a series of hairpin helices formed by d(TA) oligomers. The differences in behavior expected for hairpin, dimer, and oligomer-polymer helices are discussed. The salt dependence of the end-joining equilibrium investigated for λ DNA by Wang and Davidson [Cold Spring Harbor Symp. Quant. Biol. 33, 409-415 (1968)] is treated as an oligomer-polymer interconversion. The dependence of equilibrium constant for this reaction on counterion concentration is in good agreement with that predicted by theory for an end-region totalling 24 nucleotides, the known length of the λ ends.
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    Solvent denaturationThis paper is an expanded version of a paper dedicated to J. Sturtevant at the symposium held on March 25, 1977 in honor of his achievement of emeritus status at Yale University. (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1305-1322 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent denaturation is developed along thermodynamic lines rather than from multiple-binding theory. Almost all the relations derivable from site-binding theory have their counterparts in the thermodynamic formulation showing that the details of binding models may be sufficient but are not necessary for the general description of solvent denaturation. Equations are derived for the effect of denaturant concentration on stability at constant temperature and on tm. It is recommended that the thermodynamic treatment be used instead of binding models unless stoichiometric interactions are demonstrable experimentally.
    Additional Material: 4 Ill.
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    Base stacking in A fluorescent dinucleoside monophosphate: εApεA (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1361-1372 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optical properties of the 1,N6 - etheno derivative of ApA (εApεA) have been studied. Absorbance and CD measurements suggest that (1) neutral salts tend to unstack this molecule and (2) the stacking interaction is weaker than in ApA. εApεA is found to be quenched strongly with respect to the monomer. (εAMP); this quenching is solvent dependent (1M NaCl 〉 5M NaClo4〉40%glycerol) and increases with the ratio of temperature to viscosity (T/η) in each case. Fluorescence lifetime measurements also reveal a temperature- and solvent-dependent decay which is nonlinear on a semilog plot. In the presence of 95% glycerol, this decay return to linearity. These data have been considered from two points of view: (1) two-state pictures which are based on thermodynamic least-squares fit to quatum yield and CD curves, together with two exponential fits to the decay curves and (2) a dynamical model in which relatives fluorophore motion leads to deexcitation via intramolecular collision. A simple model of type (2) gives qualitative agreement with the observed behavior.
    Additional Material: 7 Ill.
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    Characterization of receptor affinity heterogeneity by scatchard plots (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1385-1386 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.1978.360170522
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    Masthead (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978) 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.1978.360170601
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    Competition between native and monoacetylated polymyxin for charged adsorption sites (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1513-1521 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The native antibiotic polymyxin B, carrying five positive charges, displaces the monoacetylated on from its adsorbed state at the interface between negatively charged lipid layers ans water. A simulation model for asdorption, governed by electrostatic forces, is presented. The model adequently representes the competitive adsorption kinetics and equilibria.
    Additional Material: 6 Ill.
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    Comparison of conformation and antimicrobial activity of synthetic analogs of gramicidin S: Stereochemical consideration of the role of D-phenylalanine in the antibiotic (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1549-1565 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to study the role of D-amino acid residues in keeping the stable β-sheet conformation and in the antimicrobial activity of gramicidin S (GS), the four analogs of GS containing D-Ala, L-Ala, Gly, and Aib (α-aminoisobutyric acid) in place of D-Phe were synthesized. D-Ala-and Gly-containing analogs showed antimicrobial activity, while those containing L-Ala and Aib showed no activity. Conformation of these analogs and their derivatives were studied by comparison of ORD and CD spectra and by slective methylation method. It is concluded that the biologically active analogs have β-sheet conformation while inactive analogs have a much different conformation from that of GS. This indicates that D-Ala-Pro and Gly-Pro sequences favor taking a β-bend form but L-Ala-Pro and Aib-Pro sequences do not because the presence of L-side methyl group on the α-carbon atom of LAla and Aib residues destabilizes the β-bend form. This would explain why the inactive analogs which take a different conformation from that of the active ones result in the loss of activity.
    Additional Material: 7 Ill.
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    Dipole-dipole interaction and the relative stability of different types of aggregates of helical polypeptides (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 811-814 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bip.1978.360170321
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    Collagen fibrils and elastic fibers in rat-tail tendon: An electron microscopic investigation (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 843-855 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Earlier studies by the authors showed that the collagen fibrils in rat-tail tendon have a bi-modal distribution of fibril diameters from a time shortly after birth through to the onset of maturity at about 3-4 months. Present work has extended those observations for rats up to the age of 2 years. Histograms of the fibril diameter distributions for mature tail tendon and direct electron microscope observations show that the fibrils break down as the tendon ages. Further work on the constant diameter subfibrils of diameter 140 Å described previously, has confirmed that these are part of the elastic fibers present in tendon at all ages. It has been shown that there is relatively little variation in the collagen fibril diameter distribution as a function of the position of the specimen in the tail, and as the measured percentage of the area taken by the collagen fibrils present at any particular point. Estimation of the fibrillar collagen content of rat-tail tendon as a function of age indicates that it increases steadily from birth and reaches a maximum at the onset of maturity, beyond which the fibrillar collagen content appears to remain constant.
    Additional Material: 6 Ill.
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    Packaging of DNA in bacteriophage Heads: Some considerations on energetics (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 785-794 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have made quantitative estimates of some of the energetic factors to be considered in packaging of double-stranded DNA in virus particles. Numerical calculations were made using parameters appropriate for T4 bacteriophage. The unfavorable factors, and the Gibbs free energies per mole virus at 20°C associated with them, are bending, 1.5 × 103 kcal/mol; conformational restriction upon condensation, 5.1 × 102 kcal/mol; polyelectrolyte repulsion, 2.1 × 105kcal/mol; and melting or kinking, 6.9 × 103 kcal/mol. These must be counterbalanced in the assembled phage by noncovalent bonding interactions between protein subunits in the phage-head shell; by interactions between the DNA and polyvalent cations, especially putrescine and spermidine; nad perhaps by repulsive excluded volume and electrostatic interaction between the DNA and acidic polypeptides. Indeed, a rough estimate of the standard free energey of interaction between T4 DNA and the putrescine and spermidine contained in the head is --2.1 × 105 kcal/mol. In the absence of the other two sources of stabilization, each head protein subunit must contribute about 210 kcal/mol of binding energy.
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    Extrinsic cotton effect and helix-coil transition in a DNA-polycation complex (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 815-815 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1978.360170322
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    Application of thin film dialysis to the determination of equilibrium constants (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 837-842 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theoretical basis for thin-film dialysis involving binding between a ligand and nondialyzing species is presented. A general differential equation that applies to the case of equivalent, noninteracting sites is derived relating [A]F, [A]T, [P]T, and K. Numerical solutions to this equation are used to develop a series of escape curves corresponding to specific values of the parameters [P]T, [A]i, K, and k0. A general method for determining an equilibrium binding constant from thin-film dialysis data is given. A comparison of thin-film dialysis results predicted by this theory with literature data shows essential agreement.
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    The electronic structure of cytosine, 5-azacytosine, and 6-azacytosine (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 887-896 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The normal and vacuum uv spectra of cytosine, 5-azacytosine, and 6-azacytosine thin layers were determined. The spectra were resolved into a series of Gaussian bands and the experimental band positions and oscillator strengths were compared with the calculated values. The calculations were carried out with the PPP-SCF-CI method. The agreement of the calculations with those of others and with the experiment is discussed.
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    Solvent accessibilities in the dimeric subunits of RNA and DNA (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2503-2518 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To obtain information on the solvent-solute interactions in the dinucleoside monophosphates pertaining to the dimeric subunits of RNA and DNA, we have computed the accessibility of a water molecule to the oxygen atoms of the subunits following the method of Lee and Richards [J. Mol. Biol. 55, 379-400 (1971)]. The solute molecules (dimeric unit) is represented by a set of interlocking spheres of appropriate van der Waals radii assigned to each atom, a solvent (water) molecule is rolled along the envelope of the van der Waals surface, and the total surface accessible to the solvent molecule - and hence the solvent accessibility of various atoms of the solute molecule for different conformations - are computed. From the calculated atomic accessibilities, solvation maps in the (ω′,ω) space have been constructed, keeping ψ at 60°, 180°, and -60°. The C(3′)-endo sugar system in the case of DNA subunit have been considered. The solvation maps describing the solvatability of single and groups of atoms give significant information on the backbone conformational domains that are preferred for solvent interaction, thus adding knowledge to the relative stability of the various possible conformations. The B-DNA-type conformer exposes three polar atoms - namely, PO1, O(3′), and O(1′) - to external solvent, whereas the A-DNA- and C-DNA-type conformers expose only one polar atom - O(3′) and O(1′), respectively - to the solvent. The O(2′) atom of the furanose ring system in the RNA subunit could give added stability via solvent association or interunit hydrogen bonding with or without a bridging water. The superposition solvation maps describing the accessibility of a group of polar atoms help to interpret a good number of phosphodiester conformations observed in a energetically less favored conformational domains in the tRNAPhe crystal. Another intresting fact that results from this study is the prediction that the trans oriented of ω is the most favorable conformations of random-coil polynucleotides in solution.
    Additional Material: 4 Ill.
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    Conformational properties of the N-terminal residues of S-peptide. II. The guanidine hydrochloride-water-trifluoroethanol system (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2545-2559 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Conformational properties of synthetic S-peptide analogs, in which the residues in the N-terminal sequence 1-6 were progressively deleted or replaced with amino acids of lower helical propensity, were studied by CD. Increasing the concentration of guanidine hydrochloride and decreasing the temperature were found to produce progressive destruction of ordered conformations, in the parallel with the increasing solubility of the peptide unit, while increasing the concentration of trifluoroethanol and decreasing the temperature produced the opposite effect. The maximum helicity determined in the these sets of experiments is found equal to or greater than that determined in the formation of the ribonuclease S′ complexes. With some peptides the maximum value of predicted helical conformation is reached, and the tendency of tertiary structure to reduce the maximum possible helicity is evident. We discuss the validity of the procedure by which conformational information, drawn from measurements in helicogenic solvents, is related to the state in native protein.
    Additional Material: 7 Ill.
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    Thermal perturbation techniques in characterizing ligand-macromolecule interactions: Theory and application to the proflavin-α-chymotryspin system (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1773-1792 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A thermal perturbation curve (TPC) is defined to be the derivative of the fractional degree of saturation, f, with respect to temperature, considered as a function of the natural logarithm of free ligand concentration, y. The theoretical framework for the use of such curves in the thermodynamic analysis of ligand binding to macromolecules is presented. The thermal perturbation curve either provides or complements the information obtained from the derivative binding isotherm ∂f/∂y. For a single set of identical and independent sites the TPC is identical to the derivative binding isotherm. Analysis of such a curve directly yield ΔH0 and ΔG0 for the binding reaction. In actual experimental work, however, the TPC can only be approximated because of “self-buffering” effects relations between the parameter of the approximate curve and the thermodynamic quantities have been developed. This technique is applied to the proflavin-α-chymotryspin system to demonstrate its usefulness. The general features of thermal perturbation curves for cases of multiple sets of independent sites and cooperatively interacting sites have also been developed. The analysis of thermal perturbation curves in combination with other methods should provide a more powerful approach to the characterization of ligand-macromolecule interactions.
    Additional Material: 8 Ill.
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    Conformational studies of sequential polypeptides containing lysine and tyrosine (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1837-1848 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of three sequential copolypeptides, poly(L-tyrosyl-L-lysine), poly(L-tyrosyl-L-lysyl-L-lysine), and poly[L-tyrosyl-(L-lysyl)2-L-lysine] have been studied by a variety of techniques, including CD, ir spectroscopy, analytical ultracentrifugation, and x-ray diffraction. Depending upon the pH and sovent composition, poly(L-tyrosyl-Llysyl-L-lysine) and poly [L-tyrosyl-(Llysyl)2-L-lysine] can adopt either the α-helical or random-coil conformation, while poly(L-tyrosyl-L-lysine) forms either inter- or intramolecular β-structures.
    Additional Material: 6 Ill.
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    Proton magnetic relaxation in solid poly(L-alanine), poly(L-leucine), poly(L-valine), and polyglycine (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1913-1925 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular motion in solid poly(L-alanine), Poly(L-leucine), poly(L-valine), and polyglycine has been investigated through measurement of the portion spin-lattice relaxation time at 30 and 60 MHz between 110 and 350°K. Rapid random reoriention of sied-chain methyl groups provides the dominent source of relaxation in the first three; activation energies are 10.5 ± 1 1, 8.5 ± 1 kJ/mol, respectively, significantly lower than in the monomeric crystals. Relaxation times in poyglycine are two orders of magnitude longer than in the monomeric crystals. Relaxation times in polyglycine, significantly lower than in the monomeric crystals. Relaxation times in polyglycine are two orders of magnitude longer and are attributed mainly to segmental motions of the polymer chains. Evidence of nonexponential recovery of nuclear magnetization was encountered in the first three homopolyamino acids but not in polylycine, and was attributed to the correlated time to characterize these motions gave quite good agreement with the data; some improvement was obtained for two polymers using a Cole-Davidson distribution of correlation times. For biopolymers using a Cole-Davidson distribution of correlation times. For biopolymers generally it is concluded that rapid methyl group reorientation is a common dynamical feature and an important source of nuclear magnetic relaxation.
    Additional Material: 7 Ill.
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    Measurement of the strongly held water of myoglobin by drying (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 1957-1972 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The karl Fischer reagent method has been used to study the drying of whale skeletal muscle myoglobin. Drying curves for metmyglobin were obtained by mechanical pumping (moderate vacuum) and diffusion pumping (high vacum) at 20, 10, 0, -10, and -20°C. Strongly held water is present in about the same amounts as were previously observed with lysozyme. Nearly all of this strongly held water is still present during the drying of acid denatured metmyoglobin. This suggest that a core structure containing strongly held water is still present at pH 4.0. Comparison of the drying of metmyoglobin, deoxymyoglobin, and oxymyoglobin indicates that the iron-coordinated water of methyoglobin is the second most strongly held water of the molocule.
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    Some global β-sheet characterstics (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2033-2037 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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    Tail-fiber attachement in bacteriophage T4D studied by quasielastic light scattering-band electrophoresis (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2015-2028 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mixtures of bacteriophage T4D particles with up to six tail fibres attached were seprated and analyzed in a quasielastic light scattering-band electrophoresis apparatus. The electrophoretic mobilities and diffusion coefficients of the seprated bands were determined during the same experiment. Species differing in mobility by 0.05 × 10-4 cm2/V sec were resolved. Henry's electropheresis theory for spheres indicates that each tail fiber contributes about 140 effective positive charges to the phage structure. Estimate of the charge using the permanent dipole moment and the electrophorectic mobility (Bontje et. al. (1977) Biopolymers 16, 551-572) gives an effective charge of + 230 to -250 per tail fiber. The charge distribution on the fiberless particles was estimated to be -3380 on the head and -290 on the tail if the dipole moment was assumed positive and -1400 on the head and -1000 on the tail for a negative dipole. Tail-fiber attachement does not proceed to completion in our invitro system, as substantial distributions as a function of tail-fiber input indicates the reaction is a random, noncooperative process.
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    Conformational properties of the N-terminal residues of S-peptide. I. The ribonuclease S′ system (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2525-2543 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The contribution of the 1-6 N-terminal sequence to the conformational properties of the S-peptide (the 1-20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn10]-S-peptide analogs, in which lysine1, glutamic2 and threonine3 were progressively deleted, alanine4 and alanine5were alternatively replaced by serine, and alanine6 was substituted by serine or proline. Both the deletion of the three N-terminal residues and the alanine6/proline replacement produces the loss of the helical structure up to lysine7. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N-terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x-ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region.
    Additional Material: 10 Ill.
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    Solvent effect in the stereoselective polymerization of α-amino acid N-carboxyanhydride and some considerations on the mechanism of stereoregulation (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2561-2572 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the Polymerization of phenylalanine N-carboxyanhydride (NCA) in No2Oh initiated by MeNHBzl, L-,D-, and DL-NCA As were polymerized at the same rate, and no stereoselectivity was observed. When the same experiment was carried out in HCONEt2, however, L- and D-NCA were both polymerized at a rate which was about twice as large as that of DL-NCA. In this case, the polymerization is stereoselective, ascribable to a preferable reaction between the optical enantiomorphs of the terminal residue of the growing chain and the NCA of the same chirality. On the other hand, the polymerization initiated by SarNMe2 and MeNH(CH2)2CONMe2 were stereoselective in NO2Ph and HCONEt2, but they were not stereoselective in m-(MeO)2Ph. These findings indicate that the polymerizations initiated by a strong base in highly dipolar solvents are stereoselective. Apparently, the reaction between a chiral, cyclic terminal of growing chain and a chiral, cyclic activated NCA in the activated-NCA mechanism is highly stereoselective. In addition, from a kinetic investigation on on the copolymerization between L- and D-NCAs, the penultimate chiral centers were also suggested to contribute to the stereoselection. Stereoselection by the α-helical conformation of the growing chain and by a chiral, linear terminal amine have been considered so far, and the contribution from the present type of stereoselection must have been overlooked.
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    Transient electric birefringence of T-even bacteriophages. IV. T2L0 and T6 with extended tail fibers (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2689-2702 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Transient electric birefringence measurements of the bacteriophages T2L0 and T6 were performed under such conditions that the tail fibers are extended. The data obtained are compared to previously reported data for T4B. For all T-even phages the degree of extension of the tail fibers is a function of pH, ionic strength, and temperature. For T4B, much higher ionic strengths are needed than for T2L0 and T6 to accomplish complete tail-fiber extension. The rotational diffusion coefficients of the phages with fully extended fibers are equal to 120 ± 3 sec-1, 132 ± 5 sec-1, 157 ± 4 sec-1 for T2L0, T4B, and T6, respectively. The respective optical anistropies are - (2.66 ± 0.05) × 10-4, and - (3.07 ± 0.15) × 10-4. The differences in the rotational diffusion coefficient and optical anisotropy arise because the conformation of the fully extended tail fibers is different for the three phages. The tail fibers of T2L0 project further into the solution (away from the head) than do those of T4B and T6. The apparent permanent dipole moments of T2L0 and T6 decrease with increasing ionic strength. This decrease is caused by the screening of the surface charges on the phage body by the counter-ions in the solution. The biological relevance of this decrease is illustrated by the fact that the adsorption rate of T6 phages to E. coli B bacteria shows a similar dependence of ionic strength. Evidence is pressented that the tail fibers may move more or less independently of the phage body when an electric field is applied to the suspension.
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.360310101
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    Heteronuclear two-dimensional 15N- and 13C-nmr studies of DNA oligomers and their netropsin complexes using indirect proton detection (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 45-55 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Heteronuclear multispin coherence proton-detected two-dimensional nmr spectroscopic experiments were used to obtain information on protonated carbons and nitrogens of the self-complementary d (G-G-T-A-T-A-C-C) and d (G-G-A-A-T-T-C-C) duplexes, with and without the drug netropsin dissolved in aqueous solution. Many correlations of protons coupled to 13C nuclei on the base and sugar rings of the octanucleotides were detected, allowing the carbon resonances to be assigned based on previous homonuclear proton two-dimensional nmr studies. Imino nitrogen assignments can also be made using the proton assignments from previous one-dimensional nuclear overhauser effect experiments. Imino nitrogen shifts may be useful indicators of changes in local hydrogen-bonding interactions to base-pair edges.
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    Polyelectrolyte properties of biopolymers: Conductivity and secondary structure of polyriboadenylic acid and its salts in solutions (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 65-76 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polyriboadenylates of alkali metals were obtained from (1) K+-poly(A) (salts I) and (2) H+-poly( A) (salts II) by the ion-exchange method. The conductivity of these salts as well as of H+-poly(A) were studied. Salts I and II of the same counterion were shown to have significantly different conductivity coefficients (f) and polyion conductances (λp0). The charge density parameter (ζ) was 1.3 and 2.5, respectively, with λp0 equal to 44 and 83 ohm-1 cm2 mole-1 for poly(A)-I and poly (A)-II salts, respectively. This is credited to the difference in the conformations of corresponding polyions. The linear dependence of equivalent conductivity on the square root of polymer concentration (Kohlrausch coordinates), earlier obtained for DNA, is also satisfied for the studied polynucleotides. A comparison of the slopes of straight lines in Kohlrausch coordinates for poly(A), simple electrolytes, and for earlier studied polyribouridylic acid salts lends credence to the concepts, developed by a number of authors, that DNA can act as a “buffer” against the ion-ion interaction in concentrated electrolyte solutions. Using the approximation that the polyion conductance is independent of the counterion nature, parameter f (agreeing in this case with Eisenberg parameter φ) has been shown to decrease as the polynucleotide concentration is increased; the decrease is caused by the relaxation effect. The transference numbers of counterions, which have negative values in poly (A)-II solutions, grow with the increase in polymer concentration; the higher the ζ, the more apparent is this increase. This is explained by the increase in the fraction of conductivity along the polyion chains (“surface” conductivity) with the growth of polyelectrolyte concentration.
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    Study of the “molten globule” intermediate state in protein folding by a hydrophobic fluorescent probe (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 119-128 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of the hydrophobia fluorescent probe, 1-anilino-naphthalene-8-sulfonate (ANS), to synthetic polypeptides and proteins with a different structural organization has been studied. It has been shown that ANS has a much stronger affinity to the protein “molten globule” state, with a pronounced secondary structure and compactness, but without a tightly packed tertiary structure as compared with its affinity to the native and coil-like proteins, or to coil-like, α-helical, or β-structural hydrophilic homopolypeptides.The possibility of using ANS for the study of equilibrium and kinetic molten globule intermediates is demonstrated, with carbonic anhydrase, β-lactamase, and α-lactalbumin as examples.
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    Premelting thermal fluctuational base pair opening probability of poly(dA) · poly(dT) as predicted by the modified self-consistent phonon theory (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 139-148 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We employ a mean field, modified, self-consistent phonon theory to evaluate the single base-pair opening rate and the probability of a base pair in the amino proton exchangeable state for the homopolymer poly(dA) · poly(dT) at temperatures below the helix-coil transition region. Our calculated premelting single base-pair opening probabilities are in general agreement with several available experimental estimates from imino proton exchange and formaldehyde-induced DNA melting measurements. These calculated opening probabilities, however, are in disagreement with the prediction of the helix-coil transition theory. Possible reasons for the differences are discussed, especially the possible different definition of a meaningful open state in the premelting region. The premelting open state of the modified self-consistent phonon approximation theory seems to be appropriate to describe a solvent-accessible open configuration that is sufficient to facilitate important chemical reactions such as imino proton exchange and formaldehyde reaction with the bases. This can be compared with the completely unstacked open state of the helix-coil transition theory originally defined in the helix-coil transition region. We propose that the amino proton exchangeable state is different from the open state associated with melting and only involves the breaking of the amino interbase H bond. The agreement between the calculated and experimentally estimated probability of a base pair in the amino proton exchangeable state seems to support this hypothesis.
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    Shielding effects of small ions in gel electrophoresis of DNA (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 169-176 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results of free electrophoresis and free sedimentation of charged rods are introduced to allow for electrical double-layer effects in the gel electrophoresis of DNA, modeled as a Random flight sequence of rodlike Kuhn chain elements. The kinetics of DNA is shown to depend strongly on the orientation of the chain elements with respect to the external field and with respect to the direction of their velocity. The new theory gives approximate agreement between the DNA charge derived from electrophoresis of free and tethered DNA (close to 1.0e per DNA phosphate in both cases), compared with the earlier discrepancy of a factor 10 or 20 for the theory without shielding by salt. As part of a realistic force field for macromolecular dynamics simulation, the small ion effects are included in an expression for the gel forces restraining the DNA in gel electrophoresis from moving as in free electrophoresis.
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    A molecular dynamics study of the effect of G · T mispairs on the conformation of DNA in solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 211-232 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of G · T mispair incorporation into a double-helical environment was examined by molecular dynamics simulation. The 60-ps simulations performed on the two hexanucleotide duplexes d (G3C3)2 and d (G3TC2)2 included 10 Na+ counterions and first hydration shell waters. The resulting backbone torsional angle trajectories were analyzed to select time spans representative of conformational domains. The average backbone angles and helical parameters of the last time span for both duplexes are reported. During the simulation the hexamers retained B-type DNA structures that differed from typical A- or B-DNA forms. The overall helical structures for the two duplexes are vary similar. The presence of G · T mispairs did not alter the overall helical structure of the oligonucleotide duplex. Large propeller twist and buckle angles were obtained for both duplexes. The purine/pyrimidine crossover step showed a large decrease in propeller twist in the normal duplex but not in the mismatch duplex. Upon the formation of wobble mispairs in the mismatched duplex, the guanines moved into the minor groove and the thymines moved into the major groove. This helped prevent purine/purine clash and created a deformation in the relative orientation of the glycosidic bonds. It also exposed the free O4 of the thymines in the major groove and N2 of the guanines in the minor groove to interactions with solvent and counterions. These factors seemed to contribute to the apparently higher rigidity of the mismatched duplex during the simulation.
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    Biased sinusoidal field gel electrophoresis for size-dependent DNA separation (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 253-254 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Evidential study of correlated events in biochemistry: Physicochemical mechanisms of nucleic acid hydration as revealed by factor analysis (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 255-273 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using a factor analysis technique, the experimental physicochemical data on the hydration of mononucleotides, several polynucleotides, their double-helical complexes and natural DNAs were studied. The information about the factors determining the changes in physicochemical parameters vs the hydration was obtained. This work discusses a possible physical sense of the factors obtained and the expedience of using factor analysis to interpret the molecular-biophysical experiments.
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    The Electrostatically Driven Monte Carlo method: Application to conformational analysis of decaglycine (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 319-330 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Electrostatically Driven Monte Carlo (EDMC)method was applied in a study of a decamer of glycine whose conformational behavior is described by the Empirical Conformational Energy Program for Peptides (ECEPP/2) potential energy model. When free neutral end groups were used, it was found that conformations that were not α-helical had significantly lower potential energies than fully α-helical ones. However, when the N- and C-termini were blocked by acetyl and methyl amide groups, respectively, the number of unsatisfied hydrogen-bond donors and acceptors at the helix termini was diminished from 8 to 6; in this case, the possibility of forming two additional α-helical hydrogen bonds was an important enough factor in making the α-helical conformation the one with the lowest energy. The EDMC method was used as a global energy optimizer since it does not often become trapped in high-energy local minima.
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    1H- and 31P-nmr studies of ditercalinium binding to a d(GCGC)2 and d(CCTATAGG)2 minihelices: A sequence specificity study (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 331-353 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of the complexes formed in aqueous solution between ditercalinium, a bisintercalating drug, and both the self-complementary tetranucleotide d(GCGC)2 and octanucleotided(CCTATAGG)2, have been investigated by 400-MHz 1H-nmr and 162-MHz 31P-nmr. All the nonexchangeable protons, as well as the exchangeable imino protons and the phosphorus signals, have been assigned. Both oligonucleotides have been shown to adopt a right-handed B-DNA type structure. The addition of ditercalinium to the oligo-nucleotides lead to the formation of complexes in slow exchange at the nmr time scale with the free helices. At all drug-to-helix ratios studied, the ditercalinium was found in the bound form, whereas free and complexed oligonucleotides were in slow exchange, allowing resonance assignments through two-dimensional chemical exchange experiments.For d(GCGC)2 the strong upfield shifts induced on all aromatic protons of both the bases and the drug by complexation with ditercalinium suggest an interaction by intercalation of the two rings. However, the loss of twofold symmetry upon binding, as well as the chemical shift variation of the drug proton signals of one of the chromophores with temperature and concentration, favor a model in which the drug-nucleotide complexes have one ring of the drug intercalated and the other stacked on top of the external base pair. The intermolecular contacts between drug protons and nucleotide protons give a defined geometry for complexation that is consistent with the proposed model.In contrast, with d(CCTATAGG)2 several drug-nucleotide complexes were formed and a large increase in line broadening was observed at high drug-to-DNA ratios, precluding a detailed analysis of these complexes. However, the large upfield shift in the imino proton resonances together with the shielding of the ditercalinium ring protons favor a model with bis-intercalation of ditercalinium. This model is supported by the downfield shift of at least 4 out of 14 phosphorus signals. The results are compared with those obtained on ditercalinium binding to the homologous sequences d(CGCG)2 and d(TTCGCGAA)2, and discussed in terms of sequence specificity.
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    A sequence preference for nucleation of α-helix - crystal structure of Gly-L-Ala-L-Val and Gly-L-Ala-L-Leu: Some comments on the geometry of leucine zippers (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 397-407 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthetic peptide Gly-L-Ala-L-Val (C10H19N3O4·3H2O; GAV) crystallizes in the monoclinic space group P21, with a = 8.052(2), b = 6.032(2), c = 15.779(7) Å, β = 98.520(1)°, V = 757.8 Å3, Dx = 1.312 g cm-3, and Z = 2. The peptide Gly-L-Ala-L-Leu (C11H21N3O4·3H2O; GAL) crystallizes in the orthorhombic space group P212121, with a = 6.024(1), b = 8.171(1), c = 32.791(1) Å, V = 1614 Å3, Dx = 1.289 g cm-3, and Z = 4. Their crystal structures were solved by direct methods using the program SHELXS-86, and refined to an R index of 0.05 for 1489 reflections for GAV and to an R index of 0.05 for 1563 reflections for GAL. The tripeptides exist as a zwitterion in the crystal and assume a near α-helical backbone conformation with the following torsion angles: ψ1 = -150.7°; φ2, ψ2 = -68.7°, -38.1°; φ3, ψ31, ψ32, = -74.8°, -44.9°, 135.9° for GAV; ψ1 = -150.3°; φ2, ψ2 = -67.7°, -38.9°; φ3, ψ31, ψ32 = -72.2°, -45.3°, 137.5°, for GAL. Both the peptide units in both of the tripeptides show significant deviation from planarity [ω1 = -171.3(6)° and ω2 = -172.0(6)° for GAV; ω1 = -171.9(5)° and ω2 = -173.2(6)° for GAL]. The sidechain conformational angles χ21 and χ22 are -61.7(5)° and 175.7(5)°, respectively, for valine, and the side-chain conformations χ12 and χ23's are -68.5(5)° and (-78.4(6)°, 159.1(5)°) respectively, for leucine. Each of the tripeptide molecule is held in a near helical conformation by a water molecule that bridges the NH3+ and COO- groups, and acts as the fourth residue needed to complete the turn by forming two hydrogen bonds. Two other water molecules form intermolecular hydrogen bonds in stabilizing the helical structure so that the end result is a column of molecules that looks like an α-helix.
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    Mobility models for stiff and flexible macromolecules in dilute gels (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 435-447 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effective sphere approximation for modeling electrophoretic transport of macromolecules in highly porous gels (the “Ogston model”) is examined, and contrasted with similar mobility models for stiff and flexible solutes. Calculation of segmental depletion near gel obstacles of various shapes demonstrates the limited applicability of the effective sphere approach. For highly flexible chains, both theory and experiment reveal a nonunique mapping between mobility and molecular size when the molecular radius is comparable to that of gel fibers. Turning to mobility behavior in more concentrated gels, neither flexible or stiff macromolecules behave as spheres; for the particular case of flexible chains, the presence of entropic barriers in concentrated gels can be understood in terms of a simple random planes model for the gel structure.
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    Differential scanning calorimetry studies of NaCl effect on the inverse temperature transition of some elastin-based polytetra-, polypenta-, and polynonapeptides (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 465-475 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Differential scanning calorimetry studies of the effect of NaCl on protein-based polymer self-assembly has been carried out on six elastin-based synthetic sequential polypeptides- i.e., the polypentapeptide (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-L-Ala3-L-Val4-Gly5)n; the polytetrapeptide (L-Val1-L-Pro2-Gly3-Gly4)n and its more hydrophobic analogue (L-IIe1-L-Pro2-Gly3-Gly4)n; and the polynonapeptide (a pentatetra hybrid), (L-Val1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6-L-Pro7-Gly8-Gly9)n.Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations.In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature ΔTm/[N], is about 14°C/[N], with the dependence on peptide hydrophobicity being fairly small. Interestingly, however, the δΔQ/ [N] does depend on the hydrophobicity of a polypeptide.
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    A molecular dynamics study of thermodynamic and structural aspects of the hydration of cavities in proteins (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 919-931 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and activity of a protein molecule are strongly influenced by the extent of hydration of its cavities. This is, in turn, related to the free energy change on transfer of a water molecule from bulk solvent into a cavity. Such free energy changes have been calculated for two cavities in a sulfate-binding protein. One of these cavities contains a crystallo graphically observed water molecule while the other does not. Thermodynamic integration and perturbation methods were used to calculate free energies of hydration for each of the cavities from molecular dynamics simulations of two separate events: the removal of a water molecule from pure water, and the introduction of a water molecule into each protein cavity. From the simulations for the pure water system, the excess chemical potential of water was computed to be -6.4 ± 0.4 kcal/mol, in accord with experiment and with other recent theoretical calculations. For the protein cavity containing an experimentally observed water molecule, the free energy change on hydrating it with one water molecule was calculated as -10.0 ± 1.3 kcal/mol, indicating the high probability that this cavity is occupied by a water molecule. By contrast, for the cavity in which no water molecules were experimentally observed, the free energy change on hydrating it with one water molecule was calculated as 0.2 ± 1.5 kcal/mol, indicating its low occupancy by water. The agreement of these results with experiment suggests that thermodynamic simulation methods may become useful for the prediction and analysis of internal hydration in proteins.
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    Topographical requirements for δ-selective opioid peptidesAbbreviations: All amino acids are of the L variety unless otherwise stated. Abbreviations for amino acid residues follow those recommended by the IUPAC. Other abbreviations include the following: DPDPE. enkephalin, H-Tyr-D- Pen, penicillamine or β,β-dimethylcysteine; DCFPE, DRE, dermen kephalin, H-Tyr-D-Met-Phe-His-Leu-Met-Asp-NHg; DPLPE, DSLET, H-Tyr-D-Ser-Gly-Phe-Leu-Thr-OH; DSTBULET, H-Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr-OH; BUBU, H-Tyr-D-Ser(OtBu)-Gly-Phe-Leu-Thr(OtBu)-OH; DAGO, [D -ala2, N-MePhe4, Gly5]enkephalin-OL. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 941-955 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational possibilities of three different δ-selective opioid peptides, which are DPDPE , and DRE (Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, dermenkephalin), were explored using energy calculations. Sets of low-energy conformers were obtained for each of these peptides. The sets consisted of 61 structures for DPDPE, 32 for DCFPE, and 38 for DRE, including various types of rotamers of the Tyr and Phe side-chain groups. Comparison of the geometrical shapes of the conformers was performed for these sets using topographical considerations, i.e., examination of the mutual spatial arrangement of the N-terminal α-amino group, and of the Tyr and Phe side-chain groups. The results obtained suggest a model for the δ-receptor-bound conformer(s) for opioid peptides. The model suggests the placement of the Phe side chain in a definite position in space corresponding to the g- rotamer of Phe for peptides containing Phe4 and to the t rotamer for peptides containing Phe.3 The position of the Tyr1 side chain cannot be specified so precisely. The proposed model is in a good agreement with the results of biological testing of β-Me-Phe4-substituted DPDPE analogues that were not considered in the process of model construction.
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    Conformational analysis of two cyclic disulfide peptides (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 835-843 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complete nmr and CD studies of two cyclic tetrapeptides with disulfide bonds, 1 and 2 bonds have been carried out in different solvents to investigate the formation and stabilization of β-turn structures and to determine the stereochemistry of the disulfide linkage. Both peptides have three-dimensional structures with a type II β-turn, as derived from quantitative nuclear Overhauser effect data. The combined use of CD and nmr indicates that the dihedral angle of the disulfide bridge is different in the two peptides, although the chirality is maintained.
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    Time-Resolved study of network self-organization from a biopolymeric solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 859-868 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Time-resolved studies of network self-organization from homogeneous solutions of the representative biostructural polymer agarose are presented. Solutions are temperature quenched and observed by several techniques. Consistent with previous suggestions by the authors, experiments at concentrations up to about 1.75% w/v provide direct kinetic evidence for the occurrence of at least two distinct processes, leading, in sequence, to self-assembly. These are as follows: (a) a liquid-liquid phase separation of the solution occurring via spinodal demixing and resulting in two sets of regions that have, respectively, higher and lower than average concentrations of random-coiled polymers; and (b) the subsequent 2 coils → double helix transition and accompanying cross-linking and gelation (due to branching of double helices), occurring in the high-concentration regions. The size of the high-concentration regions depends upon agarose concentration and quenching temperature, and is in the range from a fraction of micrometers to a few micrometers, in agreement with earlier experiments. Bundling of the double-helical segments is known to follow self-assembly and can be considered as a third step (gel curing). This follows from the thermo-dynamic instability of the helical segments in the solvent, behaving as a system of rod-like particles connected by more or less flexible joints.The two processes leading in succession to self-assembly are discussed in terms of a phase diagram consistent with available data. Their time scales differ remarkably. At the end of the first process, all polymers remain random coiled and freely drifting. Much later coil-helix transition is observed, always in coincidence with polymer cross-linking and gelation. The enhancement of concentration of random-coiled polymers in specific regions of the sol caused by spinodal demixing is thus a prerequisite for self-assembly of these biostructural gels in the concentration interval studied. Conceptually, concentration enhancements of this type can provide a new pathway for promotion of functional biomolecular interactions even at very low average concentrations. The mechanism will work identically if the region of instability is reached by varying the polymer concentration (e.g., by biosynthesis), rather than by temperature quenching.
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    Molecular and crystal structures of Aib-containing oligopeptides Boc-Leu4-Aib-Leu4-OBzl and Boc-(Leu4-Aib)2-OBzl (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 975-985 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sample peptides Boc-Leu4-Aib-Leu4-OBzl and Boc-(Leu4-Aib)2-OBzl, were crystallized by the solvent-evaporation method. Both crystals are monoclinic, with space group of P21 and Z = 2. The cell parameters are a = 16.580(7), b = 21.105(7), c = 11.583(4) Å, and β = 104.90(3)° (Boc-Leu4-Aib-Leu4-OBzl), and a = 15.247(9), b = 19.04(l), c = 16.311(9) Å, and β = 117.10(1)° [Boc-(Leu4-Aib)2-OBzl]. Crystal structures were solved by the direct method and refined to R values of 0.096 (the former peptide) and 0.112 (the latter). Peptide backbones fold into a right-handed α-helix, except for the C-terminal Aib residue in Boc-(Leu4-Aib)2-OBzl. Both peptide molecules are stabilized by six (the former) or seven (the latter) intramolecular (5 → 1) hydrogen bonds, and arranged in the head-to-tail fashion, which makes an infinite column. In this column, one (the former) or two (the latter) intermolecular hydrogen bonds link the neighboring molecules. In the case of Boc-Leu4-Aib-Leu4-OBzl, the solvent molecule N, N-dimethylformamide was found in the difference Fourier map. There was a hydrogen bond between peptide and solvent molecule. Along the lateral direction, only hydrophobic contacts were observed between adjacent peptide molecules.
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.360310901
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    Ionization of clusters. IV. Cooperativity and allosterism derived from shared clusters in macromolecules (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1037-1047 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Clusters of ionizable groups are examined for conditions that develop cooperativity (1) on the binding of protons, and (2) on the binding of an associated ligand when the clusters are shared between domains or subunits in macromolecules. Cooperative binding isotherms for protons have long been observed (but not emphasized as cooperative binding) when studies have been done on clusters for the evaluation of metal ion complexation [A. E. Martell & M. Calvin (1952) Chemistry of the Metal Chelate Compounds, Prentice-Hall, Englewood Cliffs, New Jersey]. Reactions are formulated in this paper to show that anions, chelating to positively charged clusters, are also capable of developing the cooperative binding of protons. Extension of these simple reactions to those where clusters of ionizable groups are shared between domains of macromolecules provides models for cooperative binding, which include the allosteric, Bohr, anion, and cation effects in proteins.
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    Mass-weighted molecular dynamics simulation of cyclic polypeptides (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1077-1086 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A modified molecular dynamics (MD) method in which atomic masses are weighted was developed previously for studying the conformational flexibility of neuroregulating tetra-peptide Phe-Met-Arg-Phe-amide (FMRF-amide). The method has now been applied to longer and constrained molecules, namely a disulfide-linked cyclic hexapeptide, c [CYFQNC], and its linear and [pseudo-cyclic] analogues. The sampling of dihedral conformational space of the linear hexapeptide in mass-weighted MD simulations was found to be improved significantly over conventional MD simulations, as in the case of the shorter FMRF-amide molecule studied previously. In the cyclic hexapeptide, the internal constraint of the molecule due to the intramolecular disulfide bond (hence the absence of free terminals in the molecule) does not adversely affect the significant improvement of conformational sampling in mass-weighted MD simulations over normal MD simulations. The pseudo-cyclic polypeptide is identical to the linear CYFQNC molecule in amino acid sequence (i.e., side chains of the cysteine residues are reduced), but the positions of its two terminal heavy atoms were held fixed in space such that the molecule has a nearly cyclic conformation. For this molecule, the mass-weighted MD simulation generated a wide range of polypeptide backbone conformations covering the internal dihedral degrees of freedom; moreover, the physical space of the pseudo-cyclic structure was also sampled in a complete revolution of the entire molecular fragment about the two fixed termini during the simulation. These characteristics suggest that mass-weighted MD can also be an extremely useful method for conformational analyses of constrained molecules and, in particular, for modeling loops on protein surfaces.
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    Intercalation binding of 6-substituted naphthothiopheneamides to DNA: Enthalpy and entropy components (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1105-1114 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-(3-dimethylaminopropyl) naphtho [2, 1-b] thiophene-4-carboxamide and the 6-substituted methoxy, methyl, fluoro, chloro, bromo, trifluoromethyl, and cyano derivatives have been shown to bind to DNA via intercalation with binding constants in the 35-900 × 103 range at 25°C, pH 7, and [Na+] = 0.019M . Both electron-donating and -withdrawing substituents enhance intercalation binding, but the binding affinity is most enhanced by the cyano substituent. Calorimetric titrations for calf thymus DNA differ dramatically from those reported for ethidium [Hopkins et al. (1990) Biopolymers Vol. 29, pp. 449-459]. Apparent enthalpy parameters (ΔHB) for intercalation are constant only at low coverage of sites and become much more positive as saturation is approached. In the plateau region, ΔHB values for the parent and the cyano-, fluoro-, chloro-, and bromo-substituted compounds are nearly the same (∼ -5.9 kcal/mol). For the methyl- (-6.8 kcal/mol) and methoxy- (-7.5 kcal/mol) substituted compounds, the ΔHB values are more exothermic than that for the un-substituted compound, whereas ΔHB for the trifluoromethyl compound is approximately 1 kcal/mol less exothermic. The corresponding ΔSB values, corrected for mixing effects, are in the 7-15-cal/deg/mol range and are approximately linearly related to ΔHB if the cyano derivative is excluded.
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    Differential behavior of the two free sulfhydryl groups of human plasma fibronectin: Effects of environmental factors (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1159-1170 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report here a novel approach to label specifically one of the two cryptic, free sulfhydryl groups per subunit of human plasma fibronectin with either an 15N, 2H-maleimide spin label or a coumarinylphenyl maleimide fluorescent label. This permits the use of electron spin resonance (ESR) or fluorescence techniques to study molecular dynamics of fibronectin with the label attached to a single site per chain on the protein molecule. The method is based on our observation that upon adsorption of fibronectin to a gelatin-coated surface, the SH1 site, located between the DNA-binding and the cell-binding domains, is partially exposed, while the SH2 site, located within the carboxyl-terminal fibrin-binding domain, remains buried and unreactive. The procedures for the preparation of the selectively labeled fibronectins are described in detail. The physicochemical properties of these single-site labeled fibronectins, particularly as affected by high salt, heparin, surface binding, and temperature, were characterized by ESR spin-label and steady-state fluorescence techniques. The steady-state fluorescence measurement indicates that both local environments of SH1 and SH2 sites are relatively hydrophobic, and that the SH2 site is more hydrophobic than the SH1 site. The ESR results show that heparin or high salt induces an increase in the domainal flexibility in both SH1 and SH2 regions, perhaps through the disruption of domain-domain interactions in the fibronectin molecule, and that the former is more effective than the latter in producing such an effect. The observed heparin effect is reversible by addition of calcium ions in the SH2 regions but not in the SH1 regions. In addition, at temperatures above 44°C, both type III homologous regions containing the free sulfhydryl groups are shown to undergo denaturation and aggregation processes. The data presented here suggest that the newly developed method for differential labeling of the free sulfhydryl groups in fibronectin should be useful for mapping the spatial arrangement of structural domains in the protein molecule using spin-label-spin-probe and fluorescence energy transfer techniques.
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    Experimental and theoretical studies of DNA separations by capillary electrophoresis in entangled polymer solutions (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1221-1228 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Studies of electrophoretic separations of DNA restriction fragments by capillary electrophoresis in solutions of (hydroxyethyl) cellulose (HEC) were performed. Rheological studies were used to confirm that the entanglement threshold (Φ*) for the HEC solutions used is approximately 0.004 g/mL, in good agreement with theoretical predictions. A mesh size an order of magnitude smaller than that found in agarose gels (on a per weight basis) was calculated using polymer-entanglement theory and was confirmed by electrophoretic measurements. Electrophoretic migration was shown to follow the Ogston regime under most conditions. An approach for obtaining smaller mesh sizes is presented.
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    Masthead (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991) 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.360311101
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    Probe diffusion in solutions of filamentous actin formed in the presence of gelsolin (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1265-1271 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dynamic light scattering was used to characterize the diffusion of monodisperse polystyrene latex spheres (PLS) of different sizes (55-, 105-, and 265-nm radii) in column-purified 0.65 mg/mL actin solutions polymerized with 100 mM KCl in the absence and presence of various amounts of the actin-binding protein gelsolin. The gelsolin and its interaction with actin was initially studied to ensure that the gelsolin could be used to produce filament populations with well-defined mean lengths. Measurements with PLS diffusion probes present showed, in the absence of gelsolin, that the effective local microviscosity in the actin solutions was 5-20 times that of water and that a large fraction of the PLS are trapped within the pores of the actin filament network, as found previously [J. Newman, K. L. Schick, & K. S. Zaner, (1989) Biopolymers 28, 1969-1980]. As the molar ratio of gelsolin to actin was increased, the diffusion coefficients of the PLS approached those in pure water while the degree of PLS trapping went to zero. Measurements of the dependence of the PLS diffusion coefficients on the ratio of actin concentration to the semidilute overlap concentration showed, for the smaller PLS, a transition occurring near the mean global overlap concentration. These results reflect the dissolution of the actin network as the gelsolin concentration is increased and illustrate the role of gelsolin/actin interactions in the control of macromolecular transport within the periphery of cells.
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    A reexamination of 25Mg2+ nmr in DNA solution: Site heterogeneity and cation competition effects (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1343-1346 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Drug-DNA interactions: Spectroscopic and footprinting studies of site and sequence specificity of elliptinium (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1325-1341 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The binding of the antitumoral ellipticine derivative 2-methyl-9-hydroxyellipticinium acetate (elliptinium; NMHE) to DNA was analyzed by the combined use of DNase I foot-printing and spectroscopic methods. Using two fragments of pBR322 DNA, five discrete NMHE binding sites of 5-7 protected base pairs (bp) were detected by footprinting at 4°C on the analyzed regions. These corresponded to alternating pyrimidines and purines. The inactive derivative 2-methyl ellipticinium acetate L(NME) lacking a hydroxy group failed to demonstrate DNA protection even at low temperature. Ultraviolet-absorption and 1H-nmr analysis was performed using two autocomplementary octanucleotides d(TGACGTCA) (I) and d(ACTGCAGT) (II). The uv-absorption titrations resulted in an intercalative binding mode for NMHE in the oligomers. Analysis of the derived biphasic Scatchard plots yielded two binding sites corresponding to ∼6-bp and 2-bp sizes and characterized by apparent association constants K1 ∼ 108M-1 and K2 ∼ 106M-1, respectively. The 1H-nmr analysis of exchangeable (imino) protons and nonexchangeable protons performed in the one- and two-dimensional modes confirmed the intercalation of NMHE, and further revealed the existence of multiple sites on DNA. Assuming that imino resonance line width concerned the sole kinetic effects, 10-ms order lifetimes were estimated for the drug-oligonucleotide complexes at 7°C, pH 7, and 0.1 ionic strength. Finally examination of every drug-DNA spectra in the light of the footprinting results indicated that there was a preference for binding of NMHE to the CpG (octamer I) and TpG (octamers I and II) steps.
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    Resolution of end-to-end diffusion coefficients and distance distributions of flexible molecules using fluorescent donor-acceptor and donor-quencher pairsDedicated to Professor Robert F. Steiner on the occasion of his 65th birthday. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1363-1378 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We used time-dependent fluorescence energy transfer, time-dependent collisional quenching, and global analysis of the data resulting from these through-space and contact interactions to recover the end-to-end distance distributions and diffusion coefficients of flexible fluorescent molecules. The fluorescence decays of covalently linked tryptamine-acceptor and tryptamine-quencher pairs were measured by the frequency-domain method. These data were fit using numerical solutions of the differential equation, which predicts the time-and distance-dependent population of the excited state donors in the presence of energy transfer or collisional quenching, followed by transformation to the frequency domain for nonlinear least-squares comparison with the experimental data. We found that the energy transfer data for the donor-acceptor pair alone were adequate to recover the starting distribution and the end-to-end diffusion coefficient; however, the resolution is dramatically improved by the use of both the through-space and contact interactions.
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    Photodegradation of hyaluronic acid: EPR and size exclusion chromatography study (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1429-1435 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Photochemically induced radical reactions involving the lateral sequences and the end macromolecular chain groups of hyaluronic acid in aqueous solutions at 293K were studied by EPR spin trapping technique with DMPO (5,5-dimethylpyrroline-1-oxide). In the first 1-10 minutes of irradiation EPR indicates spin adducts of two carbon centered radicals with the splitting constants of aN = 1.60 mT, aH = 2.51 mT and aN = 1.56 mT, aH = 2.28 mT. After longer irradiation time (over 10 minutes) dominate two further DMPO adducts of radicals centered on hetero-atoms with splitting constants of aN = 1.44 mT, an = 1.60 mT and of aN = 1-49 mT, aH = 1.49 mT. Simultaneously, molecular weight followed by SEC decreases, suggesting that UV irradiation leads to the breaking of interglycosidic bonds of hyaluronic acid main macromolecular chain.
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    Photograph of Bruno Zimm (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1459-1459 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/bip.360311302
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    The Hodgkin-Huxley Na+ channel model versus the five-state Markovian model (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1483-1502 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In describing the Na+ channel-gating kinetics, it is generally believed the Hodgkin-Huxley model is inadequate and other types of Markovian models are more appropriate. In this paper, we perform detailed kinetic analyses to find out whether the Hodgkin-Huxley model is really unacceptable. Specifically, we consider two models for the analyses: A five-state Markovian model that allows inactivation to take place before opening and a Hodgkin-Huxley eight-state model. The criteria used to check the goodness of the two models are (a) Akaike's information criterion; (b) χ2 tests on the waiting-time, open-time, and closed-time distributions, and the number of openings per record; and (c) comparison between all latency distributions and the probability of the open state predicted from the two models. In order to do this, we first develop a method of constructing probability density histograms of a specified event (e.g., waiting time, closed time, open time, number of openings per patch) from the multichannel patch-clamp recordings. The goodness of our method is checked by simulating multichannel patch recordings using a multinomial random number generator. Our kinetic analysis on the single Na+ channel recordings from the cardiac cells revealed that (a) on the basis of Akaike's information criterion, the Hodgkin-Huxley model is definitely a better model than the five-state model, but (b) on the basis of χ2 tests on the probability density functions, the latter model is slightly better than the former. We find no evidence that the Hodgkin-Huxley model is inferior to the five-state model for this cell type.
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    The elastic resilience of DNA can induce all-or-none structural transitions in the nucleosome core particle (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1543-1557 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA on the surface of the histone octamer in the native nucleosome core particle is modeled as a circumferentially wound elastic line on the surface of a cylinder. In a model for the radial transition, the line is allowed to straighten, and thus lose energy, by swinging off the surface, but it is impeded in such an excursion by a radial force field representing the attractive interaction between DNA and histone octamer. In a model for the axial transition, the line may straighten by becoming more parallel to a generator of the cylinder while remaining on the surface. In this mode of straightening, dimer-tetramer or tetramer-tetramer interfaces are disrupted, and the resulting energy gain impedes the transition. Both radial and axial transitions are predicted to occur in all-or-none fashion. We propose that these models are related to the abrupt transitions actually observed in the nucleosome core particle.
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    A probabilistic model for genetic recombination of nonreplicating λ-phage DNA, stimulated by “mismatch repair” of UV photoproducts (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1565-1579 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Genetic recombination of nonreplicating phage λ-DNA, during infection of homoimmune lysogenic bacteria, was previously observed to be dramatically stimulated by prior uv irradiation of the phages, even when the Escherichia coli hosts lacked the major uv-photo-product excision-repair system (UvrABC). UvrABC-independent recombination of circular phage molecules depends on host MutHLS functions and on undermethylation of adenines at GATC sites in the phage DNA, and thus appears to be the result of “mismatch repair” of uv photoproducts. Recombinant frequencies pass through a relatively sharp maximum at 20 J/m2 and decrease at higher doses, whereas most plausible models for the process predict monotonic increases with dose, or a plateau at high uv doses. A uv-dose-dependent loss of biological activity (restriction) of all intracellular phage DNA was also observed previously. In order to provide a framework for testing possible explanations for the unusual recombinant-frequency vs uv-dose curve, a statistical model was constructed. This model includes probability terms for all possible one-exchange and two-exchange recombination processes, and incorporates the assumption that dimer recombinants are more susceptible to restriction than monomer parents (or recombinants), because of their larger target size. By adjustment of model parameters, particularly ∊, the efficiency per photoproduct of initiation of a recombinational exchange, a theoretical dose-response curve that agreed well with experiment was obtained. The best fit corresponded to ∊ = 0.035, close to the previously observed restriction efficiency of 0.053. In the calculations, the value for h0, the average length of heteroduplex DNA, was taken to be 0.5 λ units, i.e., about 25 kilobase pairs. This estimate for h0 was obtained here by analysis of the density distributions of the progeny of crosses between nonreplicating density-labeled λ-phage chromosomes, published by others [M. S. Fox, C. S. Dudney and E. J. Sodergren (1979) Cold Spring Harbor Symposium on Quantitative Biology, Vol. 43, pp. 999-1007].
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    Importance of oligoelectrolyte end effects for the thermodynamics of conformational transitions of nucleic acid oligomers: A grand canonical Monte Carlo analysisDedicated to Emeritus Professor Bruno H. Zimm, in whose laboratory one of us (MTR) began his study of the thermodynamic behavior of nucleic acid polyelectrolytes. (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1593-1604 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Effects of salt concentration on the stabilities of oligonucleotide helices are analyzed directly in terms of ΔΓN→yN ≡ ΓyNden - ΓNnat, the difference in the salt-nucleotide phosphate preferential interaction coefficients for the denatured state, having yN phosphate charges, and for the native state, having N phosphate charges (y = 1 for hairpin denaturation and y = 0.5 for dimer denaturation). Previous experimental studies of the denaturation of hairpin oligo-nucleotides (having 18 〈 N 〈 44) indicate significant differences between ΔΓN→N and ΔΓ∞, the value determined for the denaturation of the corresponding polynucleotide. These differences are thermodynamic manifestations of the oligoelectrolyte end effect. In contrast, the available data on the denaturation of oligonucleotide dimer helices (N ≤ 22) imply that differences between ΔΓ∞ and ΔΓN→0.5N, and hence oligoelectrolyte end effects, are small or negligible. To determine the origin of these apparently conflicting implications concerning the importance of oligoelectrolyte end effects, we have calculated the N dependence of ΓN from grand canonical Monte Carlo simulations for an idealized model of the structure and charge distribution of each oligomer conformation. Our calculations are in quantitative agreement with the experimental finding for d(TA) hairpin oligomers that - ΔΓN→N decreases linearly as N-1 increases, and with the extant experimental determinations of ΔΓN→0.5N. These results provide an illustration of how the large electrostatic end effects exhibited by the hairpin denaturation data are masked when ΔΓ∞ is compared with values of ΔΓN→0.5N for short dimer helices (N ≤ 22). For 0.5N 〉 24, - ΔΓN→0.5N is predicted to be a linear function of N-1 whose slope has the opposite sign from, and is more salt-concentration dependent than, the corresponding slope of - ΔΓN→N as a function of N-1. Our calculations also yield predictions about the N dependences of the individual values of ΓN that can be tested by determining Donnan coefficients from membrane dialysis equilibrium experiments. For long enough hairpin and dimer oligonucleotides (yN ≥ 24), in either native or denatured forms, we predict that the (positive) difference Γ∞ - ΓN increases linearly with increasing N-1. For smaller values of N the difference Γ∞ - ΓN continues to increase with increasing N-1.
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    Transient electric birefringence of two small DNA restriction fragments of the same molecular weight (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1651-1667 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The transient electric birefringence of two small DNA restriction fragments of the same molecular weight, one of which migrates anomalously slowly on polyacrylamide gels, has been investigated. Both fragments exhibit negative birefringence. The decay of the birefringence of the anomalously slowly migrating fragment is 8-9% faster than that of the normally migrating fragment. The faster birefringence decay of the anomalous fragment 12A persists under a variety of buffer conditions, suggesting that it is due primarily to static bending and/or curvature of fragment 12A. In reversing electric fields the absolute amplitude of the birefringence of fragments 12A and 12B decreased about 26% before returning to the steady state value. The minimum in the birefringence occurred faster than expected from the birefringence decay times and decreased with increasing electric field strength, suggesting that the minimum is due to a slow polarization of the ion atmosphere. For both fragments, the rise of the birefringence in the Kerr region is about 10% slower than the field-free decay. The buildup of the negative birefringence is preceded either by an interval when no birefringence is observed or by a small positively birefringent transient, suggesting that a small transverse ionic polarizability is also present. Both DNA fragments exhibit Kerr law behavior over most of the range of electric field strengths investigated. Analysis of the shapes of the saturation curves suggests that differences may exist in the polarization mechanisms of the two fragments.
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    On the flexibility of myosin in solution (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1677-1687 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rabbit skeletal muscle myosin from the same rabbit was prepared by two different methods, and then purified by either Sephadex or hydroxylapatite chromatography. The resulting myosin samples were analyzed in 2-10 mM sodium pyrophosphate solutions at pH 9 using transient electric birefringence. The birefringence decay signals were fitted using a Fortran program called DISCRETE and two relaxation times, 49.7 ± 5.6 and 11.2 ± 2.5 μs, were determined. These relaxation times were independent of the method of myosin preparation, the method of myosin purification, the concentration of sodium pyrophosphate between 2 and 10 mM, the concentration of myosin between 0.08 and 1.59 mg/mL, and the temperature between 4.0 and 20.0°C, after correction to 20.0°C. The longer relaxation time is consistent with a rigid, linear myosin molecule. The shorter relaxation time is consistent with myosin that has a completely flexible hinge region in the myosin tail. Both relaxation times are inconsistent with the previously reported single relaxation time of myosin obtained by fitting the birefringence decay data to only 90% of the decay signal. By forcing some of the birefringence decay data in the present work to fit 90% of the decay signal with a single relaxation time, approximately the same relaxation time as previously reported was obtained.
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    Heterogeneous molecular aggregation and fractal structure in chitosan/acetic acid systems (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1721-1726 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of deacetylation degree on heterogeneous molecular aggregation has been investigated for chitosan solution in 2 wt % acetic acid aqueous solution using rheological and small-angle x-ray scattering (SAXS) methods. Three samples of chitosan, which were designated CS62, CS79, and CS96, were used, and the deacetylation degrees of these samples were 0.62, 0.79 and 0.96, respectively.Rheological properties show that the systems of CS62 and CS96 are homogeneous, and the system of CS79 has a certain heterogeneous structure with a long-time relaxation mechanism. According to the SAXS measurement, the heterogeneous system has a fractal structure and the fractal dimension is about 1.3.
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    Salt dependence and ion specificity of the coil-helix transition of furcellaran (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1727-1736 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational transition and the cation-binding properties of aqueous furcellaran (a gel-forming, low-sulfated polysaccharide of the carrageenan family) in various salts and salt mixtures was studied by optical rotation and by 133Cs-nmr. The results were compared with theoretical predictions based on the Poisson-Boltzmann cell model (PBCM). The conformational transition of furcellaran occurs in a single step, which implies a nonblocklike distribution of sulfate groups along the polymer chain. The chloride salts of sodium, lithium, and tetramethylammonium are equally potent in inducing helix formation of furcellaran, indicating that these ions act by nonspecific electrostatic interactions. In contrast, the potassium and cesium ions specifically promote helix formation and aggregation (gelation) of furcellaran. The divalent calcium and magnesium ions are nonspecific, but more potent than the nonspecific monovalent ions in inducing helices. Anions differ in their capacity to stabilize the furcellaran helix in the sequence Cl- 〈 NO3- 〈 Br- 〈 SCN- 〈 I-. The iodide and thiocyanate anions impede aggregation and gel formation. 133Cs-nmr chemical shifts indicate specific binding of cesium ions to the furcellaran helix. Thus, with respect to its ion specificity and ion-binding properties, furcellaran, with 0.6 sulfate group per repeating disaccharide, resembles κ-carrageenan (1 sulfate/disaccharide) but differs from ι-carrageenan (2 sulfates/disaccharide). The conformational transition temperatures of furcellaran are, however, generally higher than those of κ-carrageenan under comparable conditions, and in mixtures of the two polysaccharides, separate transitions still occur, indicating that no mixed helices are formed. The observed ion sensitivity and cation-binding properties of furcellaran agree with predictions, by the PBCM, for a K-carrageenan with a reduced charge density.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311407
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