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  • 1985-1989  (8,591)
  • 1965-1969
  • 1830-1839
  • 1988  (8,591)
  • Chemistry  (8,591)
  • 101
    Electronic Resource
    Electronic Resource
    Transformation products of antioxidants: The role in stabilization mechanismsPaper presented at the 18th Colloquium of Danubian Countries for “Natural and artificial ageing of plastics” in Villach, Austria, June 24-26, 1987. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 158 (1988), S. 209-219 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Antioxidants acting in polymers by chain-breaking and hydroperoxide decomposing mechanisms are chemically transformed during the stabilization process as a consequence of trapping radicals R•, RO• or RO•2 and/or reactivity with hydroperoxides. New chemical compounds with typical structures characteristic of the starting stabilizer are formed stepwise in the polymer mass. Most of these transformation products participate actively in consecutive steps of polymer degradation. Finally observed phenomena depend on the concentration of individual transformation products. Generally, autocooperative effects with starting stabilizers take place. Important data regarding properties of transformation products have been summarized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051580111
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  • 102
    Electronic Resource
    Electronic Resource
    Measurement of thermooxidative stability of polyolefins by isothermal differential thermal analysisVortrag anläßlich des 18. Donauländergesprächs über “Natürliche und künstliche Alterung von Kunststoffen” in Villach (Österreich) vom 24. bis 26. Juni 1987. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 158 (1988), S. 187-207 
    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 isotherme Differentialthermoanalyse ist als Methode zur Abschätzung der thermooxidativen Beständigkeit von Polyolefinen seit längerem bekannt. In der vorliegenden Arbeit wird über isotherme DTA-Messungen an Proben aus Polybuten-1 im Temperaturbereich von 260°C bis 130°C berichtet, wobei Oxidationsinduktionszeiten bis 7000 Stunden gemessen wurden. Die Auftragung der Oxidationsinduktionszeiten in Arrhenius-Diagrammen zeigte für Polybuten-1 keine für Extrapolationszwecke geeignete Linearität des Logarithmus der Oxidationsinduktionszeiten über der reziproken absoluten Temperatur über weitere Bereiche der Meßzeiten bzw. Prüftemperaturen. Die thermoanalytisch bestimmten Oxidationsinduktionszeiten stimmten mit dem Steilabfall der Reißdehnung und der molaren Masse in Ofenalterungsversuchen überein. Damit können aufwendige Ofenalterungsversuche durch experimentell einfache isotherme DTA-Versuche ersetzt werden. Die Messung der thermooxidative Restbeständigkeit im isothermen DTA-Versuch bei erhöhter Prüftemperatur ermöglicht einen wesentlich deutlicheren Einblick in den thermooxidativen Schädigunqszustand eines Polyolefins während der Induktionsperiode des thermooxidativen Abbaus als die Messungen der molaren Masse oder der Reißdehnung. Bei hohen Ofenlagerungstemperaturen erfolgte die Abnahme der thermooxidativen Restbestandigkeit linear uber der Alterungszeit, bei Alterungstemperaturen unterhalb von 160°C nahm die thermooxidative Restbeständiqkeit degressiv in Abhängigkeit von der Ofenalterungszeit ab. Schließlich konnte mit Hilfe der isothermen Differentialthermoanalyse die Extraktion von Stabilisatoren aus Polybuten-1 in einfacher Weise beobachtet werden.
    Notes: Isothermal differential thermal analysis (DTA) is a well known method of testing thermooxidative stabilities of polyolefins. Oxidation induction times, measured up to 7000 hours and over a temperature range from 260°C to 130°C has been used to study the stability of polybutene-1 in the melt state.The Arrhenius plots of DTA results show that straight line extrapolation from high to low temperatures is not possible. Thermoanalytically measured oxidation induction times and mechanical failure in oven ageing experiments agree well for polybutene-1. Measurements of molecular weight and of mechanical properties of polybutene-1 during the induction period of oven ageing experiments revealed that molecular weight and tensile properties are not sensitive indicators for the beginning of ageing. The state of deterioration can be estimated easier by measurement of residual lifetime in the isothermal DTA experiment. At high ageing temperatures the residual lifetime decreased linearly during the induction period, at ageing temperatures below 160°C the decrease of residual lifetime was found degressive.Finally the extraction of stabilizer by not water could be measured by isothermal DTA.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051580110
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  • 103
    Electronic Resource
    Electronic Resource
    Gemeinsame Kondensation von Harnstoff, Melamin und Formaldehyd. II. ModellreaktionenTeil I s. Lit.1. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 156 (1988), S. 1-20 
    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: By model reactions of partially substituted melamine- and urea-compounds with formaldehyde the cocondensation of melamine and urea with formaldehyde was studied. Investigations on the model systems urea/benzoguanamine/formaldehyde and dimethylurea/2-amino-4,6-di-(N-methylanilino)-1,3,5-triazine/formaldehyde with gelchromatography, IR-spectroscopy, and thermogravimetry showed bridges between urea- and melamine-compounds.Also in urea-melamine-formaldehyde-resins it was possible to prove the occurrance of cocondensates by precipitation the melamine derivates with picric acid and analysis of the precipitates by urease-decomposition.
    Notes: Anhand von Modellreaktionen von teilweise blockierten Melamin- und Harnstoff-derivaten mit Formaldehyd wurde die gemeinsame Kondensation von Harnstoff, Melamin und Formaldehyd studiert. An den Modellsystemem Harnstoff/Benzoguanamin/Formaldehyd und Dimethylharnstoff/2-Amino-4,6-di-(N-methylanilin)-1,3,5-triazin/Formaldehyd konnten mit Hilfe der Gelchromatographie, IR-Spektroskopie und Thermogravimetrie chemische Brücken zwischen den Triazin- und Harnstoffkomponenten, also Cokondensate, festgestellt werden.Auch beim System Harnstoff/Melamin/Formaldehyd konnten durch Pikratfällung der Triazinkomponenten und Urease-Spaltung dieses Niederschlages Cokondensate nachgewiesen werden.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051560101
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  • 104
    Electronic Resource
    Electronic Resource
    Studies on chemical resistance of polyesters (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 156 (1988), S. 21-27 
    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 wurden Polyester basierend auf 1,4,5,6,7,7-Hexachlor-5-norbornen-2,3-dicarbonällureanhydrid (I), Tetrachlorphthalsäureanhydrid (II), Dibromneopentylglykol (II), ein Polyesterblend (V) bestehend aus dem Polyester (III) und einem Polyester (IV) für allgemeine Zwecke, ein Polyester (VI) basierend auf 1,4,5,6,7,7-Hexachlor-5-norbornen-2,3-dicarbonsäureanhydrid und dem Polyester III und ein Polyesterblend (VII) bestehend aus den Polyestern I und III hergestellt. Ihre chemische Resistenz und ihre Feuchtigkeitsaufnahme bei Temperaturen von 25 und 65°C wurden in Säuren, 20% NaOH und Wasser untersucht. Hierbei wurde gefunden, daß der Polyester (III) von den Säuren am wenigsten angegriffen wird. Verglichen mit unbehandelten Poly meren fand bei beiden Temperaturen in 20% NaOH eine Gewichtsabnahme bei allen Polyestern statt, mit Ausnahme des Polyesters VII. Erne Gewichtszunahme aller Polyester wurde beobachtet durch Feuchtigkeitsaufnahme sowohl bei 25 als auch bei 65°C, wobei die Zunahme bei der höheren Temperatur größer war. Der Polyester III zeigte die geringste Feuchtigkeitsaufnahme.
    Notes: Chlorendic anhydride based polyester (I,) tetrachlorophthalic anhydride based polyester (II), dibromoneopentyl glycol based polyester (III,) general purpose polyester (IV,) blend of dibromoneopentyl glycol based polyester with general purpose polyester (V,) chlorendic anhydride and dibromoneopentyl glycol based polyester (VI), and a blend of chlorendic anhydride based polyester and dibromoneopentyl glycol based polyester (VII) were prepared and their chemical resistance and moisture absorption studied in various reagents, acid, alkali, and water, at 25 and 65°C. It is found that the polyester (III) is the least affected in the presence of the acids. In 20% NaOH, there was a decrease in weight for all polyesters at both the temperatures compared to the control except the polyester (VII). Increase in weight of all the polyesters was observed during the absorption of moisture both at 25 and 65°C. The increase was higher at higher temperature. Polyester (III) thus shows the least absorption of moisture.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051560102
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  • 105
    Electronic Resource
    Electronic Resource
    Synthesis and characterization of some polyurethanes (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 156 (1988), S. 29-35 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Polymere mit Urethaneinheiten wurden durch Lösungspolymerisation der Bisphenole A, C und F mit Diisocyanaten wie Toluol-2,4-diisocyanat, Hexamethylendiisocyanat, Isophorondiisocyanat bzw. Diphenylmethandiisocyanat hergestellt. Die erhaltenen Polymeren waren blaßgelbe Pulver. Diese Polymeren wurden durch IR-Spektroskopie und Bestimmung des Stickstoffgehalts charakterisiert. Die zahlenmittleren Molekulargewichte (M̄n) wurden durch Leitfähigkeitstitration und Bestimmung der Grenzviskositätszahl in Dimethylformamid ermittelt. Mittels Thermogravimetrie wurde das thermische Verhalten untersucht. Die kinetischen Parameter des Abbaus wurden berechnet.
    Notes: Polymers containing urethane units were synthesized by solution polymerization of bisphenols A, C, and F with diisocyanates viz. toluene-2,4-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate, respectively. Thus obtained polymers were pale yellow amorphous powders. These polymers were characterized by infrared spectral studies and nitrogen content. The number-average molecular weights (M̄n) were estimated from conductometric titration and limiting viscosity number [η] in dimethyl formamide. From thermogravimetric analyses, the thermal behaviour was studied. Kinetic parameters for their degradation were computed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051560103
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  • 106
    Electronic Resource
    Electronic Resource
    Synthesis of asymmetric diglycidyl ester compounds. Reaction with aromatic diamines (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 156 (1988), S. 37-48 
    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: Neue Diglycidylester wurden in Gegenwart von quaternären Ammoniumsalzen als Katalysator aus ihren entsprechenden Dicarbonsäuren und Epichlorhydrin hergestellt. Die neuen unsymmetrischen Produkte wurden durch spektroskopische Methoden identifiziert und als Monomere in einer Aushärtungsreaktion eingesetzt. Der Reaktionsverlauf wurde mittels IR-Spektroskopie verfolgt. Die Struktur einiger 1öslicher Zwischenprodukte wurde durch 13C-NMR-Spektroskopie ermittelt. Das thermische Verhalten dieser ausgehärteten Epoxidharze wurde ebenfalls untersucht.
    Notes: New diglycidyl esters coming from the corresponding diacids and epichlorohydrin were synthetized using a quaternary ammonium salt as a catalyst. The new asymmetric compounds were characterized by spectroscopic methods and employed as starting monomers in a crosslinking process. The course of the reactions was followed by IR spectroscopy. Some intermediate species were identified in the onset of the reactions by recording 13C-NMR spectra until the products became insoluble in the usual deuterated solvents. The thermal behaviour of these cured epoxy resins was also studied.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051560104
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  • 107
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    Electronic Resource
    Synthesis and applications of reactive carbohydrates. III. Preparation and methylolation of polyacrylamide-carboxymethyl cellulose graft copolymersPart II: cf. ref.9. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 156 (1988), S. 79-89 
    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: Carboxymethylcellulose (CMC) wurde bei 80°C unterschiedlich lange (15 - 60 min) mit HCl behandelt. Sowohl die hydrolysierten CMC-Proben als auch die ursprüngliche Probe wurden mit Acrylamid unter Verwendung von K2S2O8 als Initiator gepfropft. Es zeigte sich, daß mit zunehmender Hydrolysezeit die Kupferzahl der CMC anstieg, während der Carboxylgehalt dagegen abnahm. Die saure Hydrolyse erhöhte die Empfindlichkeit der CMC gegenüber Pfropfung bedeutend. Die Pfropfung reduziert die Kupferzahl der hydrolisierten CMC-Proben, höchst wahrscheinlich durch Umwandlung der aldehydischen in carboxylische Gruppen unter Mitwirkung von K2S2O8, wiährend der Pfropfung. Pfropfen reduziert ebenfalls den Carboxylgehalt der ursprünglichen CMC-Probe, aber es erhöht dagegen die Carboxylgehalte der hydrolysierten CMC-Proben. Durch Methylolierung der Polyacrylamid-CMC-Pfropfcopolymeren erhält man ein Appreturmittel für Textilien. Die Anwendung dieser Pfropfcopolymeren auf Baumwollgewebe gemäü der herkömmlichen „pad-dry-cure“- Methode lieferte folgende Ergebnisse: 86% der Appretur blieben auf dem Gewebe haften, wenn man CMC-Copolymere benutzte, 92% dagegen bei Verwendung von Copolymeren der hydrolysierten CMC.
    Notes: Carboxymethyl cellulose (CMC) was treated with HCl at 80°C for different time periods (15 - 60 min). The hydrolyzed CMC samples as well as the original sample were graft copolymerized with acrylamide using K2S2O8 as initiator. It was disclosed that the increasing duration of acid hydrolysis is accompanied by a progressive increment in the copper number of CMC, meanwhile its carboxyl content decreases. Acid hydrolysis enhances significantly the susceptibility of the CMC toward grafting. The latter reduces the copper number of the hydrolyzed CMC samples most probably via conversion of the aldehydic to carboxylic groups under the action of K2S2O8 during grafting. Grafting also reduces the carboxyl content of the original CMC sample while increasing those of the hydrolyzed CMC samples. Methylolation of the polyacrylamide-CMC graft copolymers results in reactive finishes. When the latter were applied to cotton fabric according to the conventional pad-dry-cure method followed by a thorough washing, the fabric retained ca. 86% of the finish derived from the copolymer of CMC and 92% of finishes derived from the copolymers of hydrolyzed CMC.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051560108
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  • 108
    Electronic Resource
    Electronic Resource
    Shape-memory pore structure in porous crosslinked polystyrenes (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 157 (1988), S. 123-136 
    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 Porengröße von porösen, vernetzten Polystyrolen wurde mit einer Intrusionsmethode untersucht. Hierbei wurde der Druck gemessen, der nötig war, um das Quecksilber in die Poren zu pressen. Die verschiedenen Nachbehandlungen dieser Polymeren lieferten interessante Ergebnisse über das Verhalten der mit der oben genannten Methode untersuchbaren „stationären Poren“, im allgemeinen Makroporen genannt. Es wurde gefunden, daß die Makroporen sich verkleinern oder ganz verschwinden, wenn man die porösen, vernetzten Polystyrole entweder in dem guten Lösungsmittel Ethylendiclorid (EDC) quellen läßt oder über ihre Glastemperauren (Tg) erhitzt. Weiterhin wurde beobachtet, daß diese wieder erscheinen, wenn man die so behandelten Polymeren wieder quellen läßt, und zwar zuerst in EDC und anschließend in dem schlecten Lösungsmittel Methanol. Diese Ergebnisse legen nahe, daß die Struktur der Makroporen memoriert wurde ähnlich den Legierungen mit Strukturerinnerungsvermögen.
    Notes: Porosity of porous crosslinked polystyrenes was examined by the pressurized-mercury intrusion method. Various aftertreatments of those polymers revealed interesting results of behaviors of “fixed pores”, whichS indicates pores measurable by this method: (1) fixed pores were found to diminish or vanish by swelling them with ethylene dichloride (EDC) as a good solvent or by heating them above the glass transition temperature (Tg), but (2) those pores were observed to reappear after the polymers treated above were swollen again with EDC, followed by replacing EDC with methanol as a poor solvent. This implies that the fixed-pore structure has been memorized like a shape-memory alloy.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051570110
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  • 109
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    Electronic Resource
    Solvent/nonsolvent solubility and polarity parameters in fractional separation of oligomers 2. Styrene-acrylic acid copolymersPart 1 cf. lit.4. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 157 (1988), S. 137-151 
    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: Styrol-Acrylsäure (St-AA)-Copolymere mit niedrigen Molekulargewichten (M̄w 〈 15000) wurden bei hohen Temperaturen (230 - 300°C) in einem kontinuierlichen Rührkesselreaktor hergestellt. Diese wurden dann in Lösungsmittel/Nichtlösungsmittel-Systemen fraktioniert ausgefällt. Um Monomerreste und Oligomere mit niedrigsten Molekulargewichten zu entfernen, wurden die Fraktionierungsexperimente mit dem Methanol-Dichlormethan/Hexan-System ausgeführt (1. Schritt). Im zweiten Fällungsschritt wurden unter Benutzung des gleichen Lösungsmittel/Nichtlösungsmittel-Systems die Ldslichkeitsgrenzen der St-AA-Copolymeren als Funktion der Copolymerzusammensetzung (mit Hilfe der Triibungspunktmethode) bestimmt. Zur Charakterisierung der Copolymeren wurden die Gelchromatographie (mit Styragelsaulen), die Kleinwinkellaserlichtstreuung (LALLS) und die volumetrische Titration der Carboxygruppen angewendet. Zur Bestimmung des Ldslichkeitsdiagramms der niedermolekularen St-AA-Copolymeren wurden die beiden Ldsungsmittelparameter S, und Polaritatsindex P′ benutzt.
    Notes: Styrene-acrylic acid (St-AA) low molecular weight copolymers (M̄w 〈 15,000) synthesized at high temperatures (230 - 300°C) in a continuous stirred tank reactor were fractionally precipitated in solvent/nonsolvent systems. Fractional precipitation experiments were done in the system methanol-dichloromethane/hexane to remove residual monomers and the lowest molecular weight oligomers (1st step). Solubility limits of St-AA copolymers as a function of copolymer composition were determined using the same solvent/nonsolvent system in the 2nd step of precipitation tests (cloud point base). GPC on Styragel-type columns, low-angle laser light scattering (LALLS), and volumetric titration of carboxylic groups were applied for copolymer characterization. Two solvent-derived parameters the total solubility parameter δT and the polarity index P′ are used to determine the solubility diagrams of St-AA low molecular weight copolymers.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051570111
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  • 110
    Electronic Resource
    Electronic Resource
    Saponification kinetic study of mica-acrylonitrile graft copolymers (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 157 (1988), S. 177-187 
    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 Kinetik der alkalischen Hydrolyse von Glimmer-Acrylnitril-Pfropfcopolymeren wurde untersucht. Die Abhängigkeit des Verseifungsgrades von der Alkalikonzentration und der Hydrolysezeit wurde bestimmt. Chemische und spektroskopische Techniken wurden zur Bestimmung des Hydrolysemechanismus herangezogen.
    Notes: Kinetics of alkaline hydrolysis of mica-acrylonitrile graft copolymers was studied. The dependence of alkali concentration and the time of hydrolysis on the degree of saponification was determined. Chemical and spectroscopical techniques were used to determine the mechanism of hydrolysis.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051570114
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  • 111
    Electronic Resource
    Electronic Resource
    A novel method for vinyl grafting onto cotton fabric using ceric-cellulose thiocarbonate redox system (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 157 (1988), S. 153-163 
    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 Behandeln von Baumwollgewebe mit Schwefelkohlenstoff in Gegenwart von NaOH ergibt Cellulosethiocarbonat, welches mit Cerammoniumnitrat (CAN) einen Komplex bildt. Nach ausgiebigem Waschen war das CeIV-Cellulosethiocarbonat fähig, die vinylische Pfropfpolymerisation auf Baumwollgewebe ohne Homopolymerbildung zu initiieren. Die Pfropfausbeute wuchs im Falle von Methylmethacrylat mit wachsenden CAN-Gehalt (0 - 50 mmol/l) und steigender Temperatur (60 - 80°C). Bei pH 2 war die Pfropfung besonders begünstigt. Dagegen wurde die Pfropfung im alkalischen Bereich gestoppt. Die Zugabe von bis zu 7% Methanol, Ethanol oder Isopropanol zum wäßrigen Polymerisationsmedium erhöhte die Pfropfausbeute bedeutend; hierbei wurde mit Isopropanol die hdchste Steigerung erhalten. Hdhere Alkoholmengen dagegen erniedrigten die Ausbeute. Die Pfropfgeschwindigkeit ist anfangs hoch, spater wird die Pfropfungsreaktion langsamer. Unabhingig von den verwendeten Reaktionsbedingungen war eine Reaktionszeit von 60 Minuten ausreichend. Es wurde die Fahigkeit des Cdv-Cellulosethiocarbonats untersucht, die Pfropfung mit Methylmethacrylat, Acrylnitril und Acrylamid zu initiieren. Dabei ergab sich fur die Pfropfgeschwindigkeit folgende Reihenfolge: Methylmethacrylat 〉 Acrylnitril 〉 Acr ylamid.
    Notes: Treatment of cotton fabric with carbon disulphide in presence of NaOH resulted in cellulose thiocarbonate. The latter formed a complex when treated with ceric ammonium nitrate (CAN). After being thoroughly washed, the CeIV cellulose thiocarbonate was capable of initiating vinyl graft polymerization onto cotton fabric without homopolymer formation. The graft yield obtained with methyl methacrylate was found to increase by increasing CAN from zero to 50 mmol/l at temperatures from 60 to 80°C. Grafting was greatly favoured at pH 2; alkaline pH offset grafting. Incorporation of up to 7% of methanol, ethanol, or isopropanol in the aqueous polymerization medium enhanced grafting significantly with the certainty that the highest graft yield was obtained with isopropanol; using higher alcohol percentages decreased grafting. The rate of grafting showed an initial fast rate followed by a slower rate; 60 minutes reaction time proved appropriate for grafting irrespective of the condition used. In addition to methyl methacrylate the ability of CeIV-cellulose thiocarbonate to induce grafting of acrylonitrile and acrylamide was also examined. The rate of grafting followed the order methyl methacrylate 〉 acrylonitrile 〉 acrylamide.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051570112
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  • 112
    Electronic Resource
    Electronic Resource
    Interface distribution functions of diluted polymer systems containing core fibrils (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 157 (1988), S. 165-176 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Aus der Röntgenkleinwinkelstreuung von aus der orientierten Schmelze kristallisierten Legierungen aus isotaktischem Polypropylen und Poly(1-buten) wurden Grenzflächenverteilungsfunktionen berechnet. Die Proben enthalten Nadelkristalle, die in Bezug auf ihre Abstandsverteilung ein „verdünntes System“ darstellen. Es wird gezeigt, daß die Berechnung von Grenzflächenverteilungsfunktionen aus jeweils nur zwei Grenzflächen möglich ist. Der Vergleich der erhaltenen Nadeldicken mit Ergebnissen aus anderen Auswertemethoden ergibt eine gute Übereinstimmung.
    Notes: Interface distribution functions have been evaluated from the equatorial small angle x-ray scattering of blends of isotactic polypropylene and poly(1-butene) crystallized in the shear field of the oriented melt. The samples contain core fibrils which represent a diluted system with respect to their distance statistics. It is shown, that interface distribution functions can be calculated from only two interfaces (diffuse phase boundaries between fibrils and amourphous phase). The calculated thicknesses agree well with values determined from other methods.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051570113
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    Mitteilungen (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 157 (1988), S. 199-199 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: No Abrstract.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051570116
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  • 114
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    Kinetics and mechanism of inhibited oxidationPaper presented at the 18th Colloquium of Danubian countries for “Natural and artificial ageing of plastics” in Villach, Austria, June 24-26, 1987 (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 158 (1988), S. 15-69 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: This paper accumulates the mechanism and kinetics of oxidation and the inhibition mechanism of oxidation processes using preventive antioxidants, chain-breaking antioxidants and deviations from the simple inhibition mechanism.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051580102
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  • 115
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    Reaction of some polymers containing carbonyl groups with phenol in the presence of mineral acids (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 160 (1988), S. 83-90 
    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 Reaktion von Poly(methylvinylketon) und acetyliertem Polystyrol mit Phenol in Gegenwart von HCl oder H2SO4 wurde untersucht, um Polymere mit Strukturen ähnlich dem Bisphenol A zu erhalten. Die Reaktion an Poly(methylvinylketon) führt zu intramolekularer Aldol-Kondensation, während acetyliertes Polystyrol die gewünschte Bisphenol A-Struktur liefert.
    Notes: The reaction of polymers containing carbonyl groups such as poly(methyl vinylketone), poly(methyl vinyl ketone-co-styrene) and acetylated polystyrene with phenol in the presence of HCI or H2SO4 has been studied in order to produce bisphenol A type structure on the polymer chain. Poly(methyl vinyl ketone) shows intramolecular aldol condensation and acetylated polystyrene results in bisphenol A type structure.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051600106
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  • 116
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    Viscoelastic properties of short fiber filled SBR composites (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 160 (1988), S. 29-39 
    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 vorliegenden Arbeit wird der Einfluß der Verformungsamplitude, der Temperatur und der Frequenz auf die dynamischen Eigenschaften von SBR-Faserverbundstoffen untersucht. Der Einbau von Kurzfasern erhöht den Speichermodul bei beliebiger Verformungsamplitude. Je nach Fasertyp verringert sich die lineare Reaktionszone des Moduls auf die Verformung oder verschwindet vollkommen. Der Verlustfaktor tan δ ist größer bei Faserverbundstoffen, obwol die Signale größenmäßig sich nicht verändern, lediglich die entsprechende Verformung.Bei Temperaturanstieg verringert sich der Modulwert, jedoch ist dieser Abfall weniger stark ausgeprägt im Faser-SBR-Verbund. Die Relaxationsspektren zeigen eine maximale Dämpfung, die der Hauptrelaxation in der Elastomermatrix entspricht. Die Temperatur,bei der dieses Maximum auftritt, verlagert sich zu höheren Werten mitsteigender Anregungsfrequenz. Dadurch wird die Ermittlung der scheinbaren Relaxationsaktivierungsenergie möglich, die im Verbund Faser-Haftmittel-SBR höher ist (225-275 kJ/mol) als in dem faserfreien Stoff (194.6 kJ/mol) als Folge einer stärkeren Faser-Matrix-Wechselwirkung.
    Notes: This paper examines the effects of deformation amplitude, temperature and frequency on the dynamic properties of SBR-short fiber composites. The presence of the fiber increases the storage modulus at any deformation amplitude. Depending on the nature of the fiber, the linear response zone of the modulus versus deformation either diminishes or disappears. The loss factor tan δ is higher in fiber composites. Although the peaks do not vary in magnitude, they occur at different deformation amplitudes.Temperature increase causes the moduli to decrease, the gradient, however, being less pronounced for fiber composites. The relaxation spectra show a damping peak which correlates to the principal relaxation process in the elastomeric matrix. The temperature at which this peak appears is displaced towards higher values with increasing excitation frequency. This allows the determination of the apparent relaxation activation energy, which is higher in fiber plus adhesive composites (225 - 275 kJ/mol), as compared to the fiber-free composite (194 kJ/mol), as a consequence of stronger fiber-matrix interaction.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051600103
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  • 117
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    Preparation and properties of UV-curable polydimethylsiloxane urethane acrylate (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 160 (1988), S. 41-66 
    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 wurde ein neuer Typ eines UV-härtbaren Polyurethanacrylatharzes synthetisiert, das auf hydroxyterminierten Polydimethylsiloxan (PDMS)-Weichsegmenten mit einem Molekulargewicht von 1800 und 2,4-Toluoldiisocyanat (TDI)/2-Hydroxyethylmethacrylat (HEMA) Hartsegmenten basiert. Die Reaktivität von 2,4-TDI mit den Hydroxygruppen von Silanol und HEMA wurde anhand von IR-Messungen diskutiert. Die charakteristischen Absorptionspeaks der NCO-Gruppen von 2,4-TDI in para- und ortho-Stellung sollten mit zunehmender Reaktionszeit abnehmen.Die Meßmethodik der wesentlichen physikalischen Eigenschaften dieser Art von UV-härtbaren Materialien wurde ebenso wie auch der Einfluß verschiedener reaktiver Verdünnungsmittel und einiger Pigmente untersucht. Dieses Harz mit guten optischen, elektrischisolierenden und Hafteigenschaften an verschiedenen Matrizes konnte in den chemischen Eigenschaften verbessert und die Viskosität reduziert werden, während die Beschichtungsverarbeitbarkeit durch Mischen mit verschiedenen reaktiven Verdünnern gefördert wurde. Die hervorragenden Hafteigenschaften auf Glasplatten wurden der ähnlichen Struktur zwischen den PDMS Weichsegmenten und Glas zugeschrieben, was eine breite Anwendung in der Beschichtungsindustrie erschließt.
    Notes: A new type of a UV-curable polyurethane acrylate resin based on hydroxyterminated polydimethylsiloxane (PDMS) soft segments with molecular weight 1800 and 2,4-toluene diisocyanate (TDI)/2-hydroxyethyl methacrylate (HEMA) hard segments were synthesized. The reactivity of 2,4-TDI with the hydroxy groups of silanol and HEMA was discussed by means of IR measurements. The characteristic absorption peaks of the  - NCO groups of 2,4-TDI in the para- and ortho-position should decline with increasing the reaction time. The measurements of fundamental physical properties of this type of UV-curable materials had been widely studied in addition to the effects of using various reactive diluents and some pigments. This kind of resin with good optical, electrical insulating, and adhesive properties on various matrices, could be improved in chemical properties and reduced in viscosity while promoting the coating processability by mixing with various reactive diluents. The excellent adhesive properties on glass plates can be attributed to the similar structure between the PDMS soft segments and glass which makes the application in the coating industry possible.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051600104
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  • 118
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    Photooxidative behaviour of polypropylene fire retarded with instumescent additiveResults presented at the “VIII Convegno Italiano di Scienza delle Macromolecole”, 18-22 October 1987, Milano, Italy. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 160 (1988), S. 203-209 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A typical intumescent fire retardant additive for polypropylene, which is a mixture of ammonium polyphosphate and pentaerythritol, does not sensibly modify the photooxidative behaviour of unstabilized polypropylene whereas it modifies that of polypropylene stabilized with a substituted o-hydroxybenzophenone and a sterically hindered amine. The photostabilizing effectiveness of the amine is probably decreased owing to protonation by polyphosphoric acid. On the contrary, the photo-protection effectiveness of the o-hydroxybenzophenone is increased in the presence of the intumescent fire retardant. This might be due to a photoinhibition effect of pentaerythritol.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051600117
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    Einfluß der chemischen Struktur auf die mechanischen Eigenschaften von modifizierten PolycarbonatenHerrn Prof. Dr. G. Kämpf zum 60. Geburtstag gewidmet (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 162 (1988), S. 109-121 
    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: Beginning with the current theories concerning the solid state structure of bisphenol-A-polycarbonate, the effect of chemical substitution of the bisphenol upon the thermal, mechanical, and dynamic mechanical properties will be discussed in detail. The observed mechanical properties of the various polycarbonates is considerably influenced by their chemical structure. Among all of the polycarbonates, bisphenol-A-polycarbonate is unique, particularly with respect to its low temperature properties. The ductile-to-brittle transition as a function of temperature correlates to the high temperature region of Gamma relaxation (G′′). Any theoretical approach to completely characterize and describe the experimentally observed phenomena must take into consideration as a fundamental parameter the conformational flexibility of the polycarbonate chain.
    Notes: Ausgehend von den bisher erarbeiteten Vorstellungen über die Festkörperstruktur des Bisphenol-A-Polycarbonats wird die Auswirkung einer chemischen Substitution des Bisphenols auf die thermischen, mechanischen und mechanisch-dynamischen Eigenschaften diskutiert. Innerhalb der Substanzklasse der Polycarbonate zeigt sich dabei hinsichtlich der beobachteten mechanischen Phänomene ein erheblicher Einfluß der chemischen Struktur. Vor allen Polycarbonaten ist das Bisphenol-A-Polycarbonat besonders hinsichtlich seiner Tieftemperatur-Eigenschaften ausgezeichnet. Der Spröd/Zäh-Übergang als Funktion der Temperatur korreliert mit der Hochtemperaturflanke des mechanischen Nebenrelaxationsgebietes. Eine die experimentell beobachteten Phänomene vollständig charakterisierende Theorie muß als wesentlichen Parameter die konformative Beweglichkeit der Polycarbonat-Ketten berücksichtigen.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051620107
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    Effect of vulcanization temperature on the cure characteristics and vulcanizate properties of natural rubber and styrene-butadiene rubberPresented at the International Symposium on Polymer Materials, Aug. 31 - Sep. 4, 1987, San Sebastian, Spain. (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 162 (1988), S. 123-134 
    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: Mischungen von Elastomeren wie Naturkautschuk und Styrol-Butadien-Kautschuk werden bei verschiedenen Temperaturen vulkanisiert und die Behandlungscharakteristika und Vulkanisateigenschaften verglichen. Die optimale Behandlungszeit bei einer bestimmten Vulkanisationstemperatur konnte empirisch durch eine Exponentialbeziehung dieser Temperatur ausgedrückt werden. Die Vernetzungsdichte der Vulkanisate nimmt mit steigender Vulkanisationstemperatur ab. Für eine vorgegebene Mischung gibt es eine bestimmte Vulkanisationstemperatur, bei der die Materialien die besten Eigenschaften für spezifische Anwendungen besitzen.
    Notes: Gum compounds of natural rubber (NR) and styrene-butadiene rubber (SBR) are vulcanized at different temperatures and the cure characteristics and vulcanizate properties are compared. The optimum cure time at a particular vulcanization temperature could be expressed empirically in terms of that temperature using an exponential relation. The crosslink density of the vulcanizates is found to decrease with an increase in the vulcanization temperature. For a given compound there is a particular vulcanization temperature which gives the best compromise of properties for specific applications.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051620108
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  • 121
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    GPC estimation of molecular mass distribution of addition polymers from bisphenol-a-diglycidyl ether and amines (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 162 (1988), S. 149-162 
    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: Thermisch polymerisierte Proben von linearen Additionspolymeren des Bisphenol-A-Diglycidylethers (DGEBA) mit den drei unterschiedlichen Aminen, (A) Benzylamin (BA), p-Chloranilin (PCA) und Cyclohexylamin (CHA), wurden mittels Gelpermeationschromatographie (GPC) unter Verwendung von THF als Elutionsmittel untersucht.Bei der Eichung des Systems und der Interpretation der Chromatogramme wurde der Solvatationseffekt der Hydroxylgruppen durch THF berücksichtigt. Der Vergleich der Chromatogramme weist darauf hin, daß das Polymere mit CHA schon im Bereich kleiner Molmassen (einschließlich der Dimeren) und in einem frühen Reaktionsstadium cyclisiert. Der Vergleich der mittleren Molmassen der Proben, die nach zwei unabhiingigen Methoden  -  Dampfdruckosmometrie (VPO) und GPC  -  gemessen wurden, zeigt, daß die Cyclisierung der Polymeren mit BA und PCA in einem geringeren Umfang stattfindet. Die beiden letztgenannten Polymeren neigen also weniger zur Cyclisierung.
    Notes: Thermally polymerized samples of linear addition polymers of bisphenol-A-diglycidyl ether (DGEBA) and the following three different amines (A): benzylamine (BA), p-chloroaniline (PCA), and cyclohexylamine (CHA) were chromatographed by gelpermeation chromatography (GPC) using THF as eluent. The solvation effect of hydroxyl groups by THF has been taken into consideration when calibrating the system and interpreting the chromatograms. The comparison of the chromatograms suggests that the polymer with CHA is cyclized already in the range of small molecular masses (including dimers) and in an early stage of reaction. The comparison of average molecular masses of the samples as measured with independent methods - vapour pressure osmometry (VPO) and GPC - shows that the cyclization of the polymers with BA and PCA takes place to a lower extent, the latter polymer being less capable of cyclization.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051620110
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    Synthèse de Copolymères Greffés Poly(ethylène-g-Méthacrylate de méthyle) et leur Influence sur les Propriétés Mécaniques des Alliages de Polyéthylène avec le Polychlorure de Vinyle (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 162 (1988), S. 175-191 
    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: Graft copolymers P(E-g-MMA) were prepared by ozonisation of low density polyethylene (LDPE) and grafting of methyl methacrylate (MMA) in bulk onto the peroxides and hydroperoxides thus obtained (Mn graft PMMA = 7700 and 21400). The emulsifying effect of P(E-g-MMA) copolymers on PE-PVC mixtures was examined. With added quantities of 5.0% copolymers the braking strength value σB for the mixture PE-PVC 50-50 is varying between 0.60 to 1.10 kg/mm2; the variation of the elongation at break point εB is more difficult to explain. The alloy fractographs were also examined under the scanning electron microscope. We observed PE modules of 20 to 30 in average diameter, without copolymer, and 1 to 2 after adding 5% of copolymers. This underlines the emulsifying role played by the copolymer. These results are compared with those of other teams. The P(E-g-MMA) that we prepared, can be considered as a suitable emulsifier for LDPE-PVC mixtures and presents the advantage of being more accessible for industrial synthesis of new alloys PE-PVC.
    Notes: Les copolymères greffés P(E-g-MMA) sont préparés par réaction du méthacrylate de méthyle (MMA) en masse sur le polyéthylène basse densité ozonisé. La masse moyenne des greffons de PMMA variable suivant la température et le temps de réaction est de 7700 et 21400. Ces copolymères sont testés comme émulsifiants de mélanges de PE et de PVC dont les propriétés mécaniques, la contrainte à la rupture σR, l'allongement à la rupture εR% et le module d'élasticité E sont mesurées avant et après l'addition de 5% en poids de copolymère. Pour le mélange PE-PVC 50-50 σR passe de 0,60 à 1,10 kg/mm2, la variation de εR est plus complexe. La visualisation, au microscope électronique à balayage, des fractographies de ces divers mélanges, montre une diminution d'au moins un facteur 10 de la taille des phases après addition de copolymère et confirme bien le rôle d'émulsifiant d'émulsifiant de ceux-ci permettant d'obtenir ainsi de nouveaux alliages PE-PVC dont les propriétés sont comparées avec celles d'alliages préparés par d'autres auteurs avec d'autres émulsifiants.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051620112
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    Estimation of polymer fractionation efficiency by comparison of theoretical models and experimental molecular mass distribution (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 162 (1988), S. 163-173 
    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 dieser Arbeit wird die Effizienz einer neuen modifizierten Säulenfraktionierungsmethode durch Vergleich von theoretischen Modellen und experimentell erhaltenen Molmassenverteilungen vorgestellt. Fünf theoretische Funktionen wurden zur Anpassung der experimentellen Daten benutzt: die Log-normal-, Tung-, Schulz-, Polynomial- und Flory-Verteilungsfunktion. Die Kurvenanpassung wurde durch die mittlere quadratische Abweichung abgeschätzt. Die mittlere quadratische Abweichung war in allen theoretischen Modellen von der gleichen Größenordnung. Mit der Polynomial- und Flory-Funktion wurden die kleinsten Werte für die mittlere quadratische Abweichung und somit die beste Anpassung der aus der Gelpermeationschromatographie erhaltenen Verteilungskurven erreicht. Diese Kurven geben die wahre Verteilung der benutzten Polymeren wieder. Diese theoretischen Modelle dienten auch als Referenzverteilungsfunktionen. Die experimentell mit zwei verschiedenen LCIsungsmittelpaaren bestimmten Fraktionswerte wurden dann den ausgewlhlten Referenzmodellen angepdt. Die Fraktionswerte der beiden benutzten Lösungsmittelpaare stimmten gut mit dem Polynomial- und Flory-Modell überein. Dies bestätigt die hohe Effizienz der vorgeschlagenen Fraktionierungsmethode.
    Notes: In this paper the efficiency of a new modified column fractionation method was presented through the comparison of theoretical models and experimentally obtained molecular mass distribution. Five theoretical functions were used for fitting the experimental data: log-normal, Tung, Schulz, polynomial, and Flory distribution function. The curve fittings were estimated by the mean square deviation. The mean square deviations in all the theoretical models were of the same order. The least values of mean square deviation and consequentely the best fitting of the gel permeation chromatography (GPC) distribution curve, which deals as a true distribution of the applied polymer sample, were achieved with polynomial and Flory model. These theoretical models were further chosen as a reference distribution function. The experimental fractionation data in two quite different solvent pairs were afterwards fitted to the chosen referent models. Fractionation data of the both applied solvent pairs have been in close agreement with Flory and polynomial model. This confirms the high efficiency of the proposed fractionation method.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051620111
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    Thermal chlorination of atactic polypropylene (1988)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 163 (1988), S. 23-35 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Chlorierung von ataktischem Polypropylen (APP) wurde thermisch gestartet und in Tetrachlorkohlenstoff durchgeführt. Es wurde gefunden, daß mit zunehmender Verdünnung der Chlorierungsgrad steigt, was in % Gewichtszunahme gemessen wurde. Grund für dieses Verhalten ist eine größere Aufweitung und Beweglichkeit der APP-Ketten, wodurch die durch Chlor zu ersetzenden Stellen besser zugänglich werden. Die Reaktionsordnung in Abhängigkeit von der APP-Konzentration beträgt 0,84 und die Aktivierungsenergie (Er) 5,29 kcal/mol. Die Erhöhung der Strömungsrate führt zu einem höheren Chlorierungsgrad. Dieser steigt bis zu einer Strömungsrate von 1 l/h linear an, um dann ein konstantes Nivoau anzustreben. IR-Spektroskopie und 13C-NMR-Untersuchungen weisen darauf hin, daß die Chlorierung an allen drei ersetzbaren H-Atomtypen vorkommt. Der Startschritt des Mechanismus ist wahrscheinlich die Substitution des tertiären H-Atoms durch freie Chlorradikale und nachfolgendem Austausch der sekundären und primären H-Atome durch entweder fortschreitende Substitution oder den Eliminierungs-Additions-Mechanismus.
    Notes: Chlorination of atactic polypropylene (APP) was thermally initiated and carried out in carbon tetrachloride (CCl4) solution. It was found that with the increase in dilution, there is an increase in the extent of chlorination, as measured in terms of % weight-gain. The reason for this behaviour has been ascribed to a greater degree of opening up and mobility of APP chains thus increasing the accessibility of the replaceable sites to chlorine. The order of the reaction with respect to APP concentration was found to be 0.84, the overall activation energy (Er) being 5.29 kcal/mol. Increase in flow rate leads to an increase in the extent of chlorination and was found to be increasing linearly with a flow rate up to 1 l/h beyond which it levels off. IR spectroscopy and 13C-NMR studies indicate the chlorination occurring in all the three types of replaceable H-atoms in APP. The mechanism appears to be initial substitution of tertiary H-atom by free chlorine radical followed subsequently by replacement of secondary and primary H-atoms via either progressive substitution or elimination-addition mechanism.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1988.051630103
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    Masthead (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988) 
    Details
    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.360270101
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    Translational friction of a particle inside a vesicle studied by an extended shell method (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 97-111 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The translational friction of a particle inside a rigid hollow sphere is determined in this work. This should be important in model studies of solute diffusion in cells or vesicles. An extended shell algorithm is developed and used in which the cell or vesicle is modeled as a large number of beads. In the extended algorithm, the shell is divided into groups of beads and the assumption is made that the force exerted by each bead on the solvent is constant within a group. The algorithm is tested by using it to determine the translational friction constants of spheres and prolate ellipsoids modeled as shells of beads.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270108
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    An analysis of the 225-230-nm CD band of elapid toxins (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 113-122 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Spectroscopic measurements of three representative elapid toxins are presented. An analysis of the data leads to the conclusion that the 228-nm CD band in this class of proteins originates largely in the disulfide chromophore. The intensity of this CD band is sensitive to conformational change associated with the disulfide group.
    Additional Material: 5 Ill.
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    A synthetic model of collagen: An experimental investigation of the triple-helix stability (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 157-163 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Variations I-XVIII of a trimerlike cross-linked collagen model peptide were synthesized and used to investigate the cooperation of different neighboring Gly-X-Y tripeptides. The carboxy-terminal decapentapeptide of the tripe-helical part of collagen type I was chosen as the starting point of sequentially modified elongations. The transition temperatures determined by CD measurements show that the incorporation of the imino acid free tripeptides Gly-Ala-Ala and Gly-Ile-Ala results in a weakening of the triple-helical structure. It is demonstrated that the desired thermal stability of the collagen triple helix requires the “clustered” arrangement of helix-promoting tripeptides, especially of Gly-Pro-Hyp.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270112
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  • 129
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    Anion effects on equilibria and kinetics of the disorder-order transition of κ-carrageenan (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 139-155 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of a number of tetramethylammonium salts on the equilibria and kinetics of the disorder to order transition in the polysaccharide κ-carrageenan have been investigated. Data from the temperature dependence of optical rotation show that anion stabilization of the ordered form follows the lyotropic series I- 〉 Br- 〉 NO-3 〉 Cl- 〉 F-. Stopped-flow polarimetry was used to study the kinetics of conformational ordering following a rapid increase in salt concentration. The transition to the new equilibrium position was shown to be biphasic for all of the tetramethylammonium salts studied. The rate equation for the fast phase and the temperature dependence of the observed forward rate constant accord with a cooperative dimerization process. Activation parameters for helix nucleation, ΔH* and ΔS*, vary with both salt concentration and (at constant ionic strength) the anion type, increasing through the lyotropic series from I- to F-. The slow phase shows second-order kinetics, and is interpreted as further stabilization of the ordered form either through limited aggregation or annealing. The rate constant for the slow phase also follows the lyotropic series. Thus we have shown that both the growth and nucleation processes are anion dependent.
    Additional Material: 9 Ill.
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  • 130
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    Effect of discrete distribution of ions on B- and Z-DNA: A theoretical investigation (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 187-200 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using an iterative approach, we have placed monovalent (“solvated”) and divalent (both solvated and “unsolvated”) ions around a 20 base pair sequence, (dC-dG)10, in standard B and ZI conformations. The molecule with its attendant ions in the various conformations is subjected to to energy minimization using the program AMBER. In the presence of solvated cations (both monovalent as well as divalent) the B form is more stable than the Z form. However, direct binding with the unsolvated divalent cations makes the Z form more stable. Groove-binding provides some insight into the facility with which the B to Z transition occurs with higher charged cations. In the presence of unsolvated divalent cations, the Z form binds more charges at the groove through more ligands, compared to the B form. The orientation around the CpG phosphates in the minor groove of the Z form is found ideal for ion binding. Detailed molecular models for the ion binding have been developed. In general, phosphate groups dominate the ion binding. Large perturbations are seen mostly in the angles that control the phosphate orientation.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270203
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  • 131
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    Determination of thermodynamic functions from scanning calorimetry data. II. For the system that includes self-dissociation / association process (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 271-297 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The basic relations between the molar fractions and the scanning calorimetry data for the system that includes self-dissociation/association process such as \documentclass{article}\pagestyle{empty}\begin{document}$$ m_0 {\rm A}_{\rm 0} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} m_1 {\rm A}_{\rm 1} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} m_2 {\rm A}_{\rm 2} \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} ... \mathbin{\lower.3ex\hbox{$\buildrel\textstyle\rightarrow\over {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}}$}} m_n {\rm A}_n $$\end{document} are presented, where mi is the stoichiometric coefficient of the ith state Ai. The relations are described for each state j as \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{d}{{dT}}\left[{- m_j \log f_j (T) + \sum\limits_i {m_i f_i (T)}} \right] = \Delta H_j (T)/RT^2 $$\end{document} where fj(T) is the molar fraction function of state j and ΔHj(T) is the difference enthalpy function of the system referred to the state j, which can be obtained by scanning calorimetry; R is the gas constant; and T is the absolute temperature. By these relations, scanning calorimetry data can be deconvoluted in order to determine the thermodynamic functions by means of single and double deconvolution. The concentration dependence of the data is analyzed by a method presented in this paper. The nonlinear least squares fitting method for the determination of the functions is discussed. For an example of the application of this method to the actual scanning calorimetry data, thermodynamic data of multistate thermal transition of Vibrio parahaemolyticus hemolysin are analyzed.
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  • 132
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    The role of hydroxyproline in collagen folding: Conformational energy calculations on oligopeptides containing proline and hydroxyproline (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 299-312 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have observed that the rate of folding of the enzymatically hydroxylated form of poly(Gly-Pro-Pro) into the triple-helical conformation is considerably higher than that of the unhydroxylated polypeptide [R. K. Chopra and V. S. Ananthanarayanan (1982) Proc. Natl. Acad. Sci. USA 79, 7180-7184]. In this study, we examine a plausible kinetic pathway for triple-helix formation by selecting peptide models for the unhydroxylated collagen molecule, and computing their conformational energies before and after proline hydroxylation. Starting with the available data on the preferred conformations of proline- and hydroxyproline-containing peptide sequences, energy minimization was carried out on the following pairs of peptides: Gly-Ala-Pro-Gly-Ala and Gly-Ala-Hyp-Gly-Ala; Gly-Pro-Pro-Gly-Ala and Gly-Pro-Hyp-Gly-Ala; Gly-Ala-Pro-Gly-Ala-Pro and Gly-Ala-Hyp-Gly-Ala-Hyp. It was found that, with each pair of peptides, the energetically most favorable conformation (I) has an extended structure at the Gly-Ala or Gly-Pro segment and a β-bend at the Pro-Gly or Hyp-Gly segment. In the Hyp-containing peptides, this conformation is further stabilized by a (Hypi + 2)OH…OC(Glyi) hydrogen bond. Conformation I is lower in energy by about 6-13 kcal/mol of the peptide than the fully extended conformations that resemble the single collagen polypeptide chain and contain no intramolecular hydrogen bond. In contrast to the proline counterpart, the hydroxyproline-containing peptides are found capable of adopting a partially extended conformation that does not contain the β-bend but retains the (Hyp)OH…OC(Gly) hydrogen bond. The energy of this conformation is intermediate between conformation I and the fully extended conformation. The continuation of the β-bend along the chain is restricted by stereochemical constraints that are more severe in the latter two pairs of peptides than in the first pair. Such a restriction may be considered to trigger the “unbending” of the minimum energy conformation leading to its straightening into the fully extended conformation; the latter, in turn, would lead to triple-helix formation through favorable interchain interactions. We propose that the partially extended conformation in the Hyp-containing peptides could serve as a kinetic intermediate on the way to forming the fully extended conformation. Because of the (Hypi + 2)OH…OC(Glyi) hydrogen bond, this conformation would also serve to lock the trans geometry at the Gly-Ala(Pro) and Ala(Pro)-Hyp peptide bonds, thereby enhancing the rate of their helix formation. A scheme for collagen folding in proposed on the basis of these results.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270209
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  • 133
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    Salt-induced isomerization of a synthetic RNA poly[r(A-U)] (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 351-354 
    Details
    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.360270214
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  • 134
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    Structural versatility of peptides from Cα,α-dialkylated glycines. II. An IR absorption and 1H-nmr study of homo-oligopeptides from Cα,α-diethylglycine (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 373-379 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational preferences of the N-trifluoroacetylated homo-peptides of Cα,α-diethylglycine from monomer to pentamer in chloroform solution were determined by using ir absorption and 1H-nmr. Intramolecular hydrogen bonding was found to be the dominant factor for all NH groups. The likely absence of a conformational transition upon increasing main-chain length, and the remarkable stability to dilution, heating, and addition of perturbing agents, are additional relevant findings of this study. These results are in agreement with those of the fully extended, C5-conformation-forming homo-peptides from the higher homolog Cα,α-di-n-propylglycine, but contrast dramatically to those of the homo-peptides from the lower homolog Cα,α-dimethylglycine, which have been shown to adopt the 310-helical structure.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270303
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  • 135
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    Helical formation of a 13-residue C-peptide analogue of ribonuclease a in sodium dodecyl sulfate solution (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 423-430 
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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 conformation of a 13-residue C-peptide analogue of ribonuclease A -  - in surfactant solutions was studied by CD. The CD spectrum of the peptide in excess NaDodSO4 solution was typical for a helical conformation; the spectrum appeared to be virtually independent of pH (2.5-6) and temperature (3-25°C). Analysis of the CD data indicated a helicity of about 65-70% with no α-sheet and β-turn; this corresponded to 8 or 9 residues in the helical form or slightly more than two turns of α-helix. This compares with an average of about one turn of α-helix for the C-peptide analogue in water at pH 4.7 and 7°C. The conformation of the peptide in cationic surfactant, dodecyl ammonium chloride, and nonionic surfactant, dodecyl heptaoxyethylene ether, solution resembled that in water. We concluded that the C-peptide analogue can develop a maximum helicity close to the corresponding segment in ribonuclease A in hydrophobic environment provided by the clustering of NaDodSO4 molecules to the cationic side groups of the peptide, except that the end effects may destabilize two or three residues each at both ends of the helix. Thus, in the interior of a protein molecule this hydrophobic effect may overshadow the charged-group effect than can be explained by the helix dipole model for the helical segments on the exterior of the protein molecule.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270306
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  • 136
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    Masthead (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988) 
    Details
    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.360270401
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  • 137
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    Base sequence effects in double-helical DNA. II. Configurational statistics of rodlike chains (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 561-584 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Matrix generator techniques have been adapted to account for precise structural features of the nucleotide repeating unit and to translate the primary sequence of DNA base pairs into three-dimensional structures. Chains have been constructed to reflect the local sequence-dependent differences of bending and twisting of adjacent residues and various overall chain properties, including the average unperturbed moments of the end-to-end vector r and the mean angular orientation (〈γ〉 between base pair normals, 〈φ1〉 between long axes, and 〈φ2〉 between short axes) of terminal chain residues, have been computed. The chain backbone is treated implicitly in terms of the spatial fluctuations of successive base pairs. Motions are limited to low-energy perturbations of the standard B-DNA helix. Approximate potential energy schemes are used to represent the rules governing the patterns of local base-base morphology and flexibility. Theoretical predictions are compared with experimental observations at both the local and the macro-molecular level. Initial applications are limited to the rodlike poly(dA) · poly(dT) and poly(dG) · poly(dC) helices. The former duplex is found to be more compressed and the latter more extended than random-sequence DNA of the same chain length. The flexibility of the duplexes as a whole is described in terms of the average higher moments of the displacement vector ρ = r - 〈r〉 and the likelihood of chain cyclization is estimated from the three-dimensional Hermite series expansions of the displacement tensors. Emphasis is placed on theoretical methodology and the practical relevance of the calculated chain moments to observed physical properties.
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    URL: http://dx.doi.org/10.1002/bip.360270403
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    Base sequence effects in double-helical DNA. III. Average properties of curved dna (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 585-603 
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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 matrix-generator methods set forth in the preceding paper for treating rodlike DNA are adapted here to the calculation of average chain extension, macroscopic flexibility, and terminal residue orientation in curved duplexes. The different characteristics of curved vs rodlike chains are illustrated with the hypothetical poly[d(A5G5)] · poly[d(T5C5)] duplex. The curved helix is both more compact and macroscopically stiffer than either the poly(dA) · poly(dT) or the poly(dG) · poly(dC) chain. The calculations have also been extended to simple repetitive DNA sequences generated by synthetic ligation studies and the computed average chain properties compared with observed gel mobilities. The predicted chain extension is also checked against the measured persistence lengths of the rodlike poly[d(GC)] and poly[d(AT)] alternating copolymers, and the known cyclization tendencies of selected repeating sequences. Chains are generated from local potential energy maps describing the morphology and flexibility of adjacent base pairs. The energy maps, while approximate, are more accurate descriptors of local structure than many of the intuitive models of DNA curvature offered to date. According to the energy surfaces, the intrinsic bending of curved DNA can be traced to asymmetry in the bending of the Gs and Cs that join half-helical turn stretches of adenines in these chains. The oligo A stretches are analogous to residues of a perfectly elastic DNA that bend with equal likelihood in opposing directions. In other models of DNA curvature, the (G · C) base pairs are presumed to adopt the classical B-DNA structure, while the (A · T) base pairs are thought to be in some perturbed conformation.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270404
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  • 139
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    Masthead (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988) 
    Details
    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.360270601
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  • 140
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    Conformational studies of N-acetyl-N′-methylamide derivatives of α-aminobutyric acid, norvaline, and valine. I. Preferred conformations in solution as studied by 1H-nmr spectroscopy (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 969-984 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H-nmr studies were extensively carried out to elucidate preferred conformations of dipeptides CH3C*O - X - NHCH3, with X = Abu, nVal, and Val in various solvents. The vicinal 1H - 1H coupling constants for the NH - CαH moiety and those around the Cα - Cβ bond in the articulated side chain provided the information regarding the average conformation of these molecules. The results indicate that transformation of skeletal conformations takes place in solution among conformers having similar dihedral angles, θHN - CαH, in the Karplus expression.
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    URL: http://dx.doi.org/10.1002/bip.360270607
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  • 141
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    1H-nmr studies of the 20-31 fragment of calmodulin and of its cyclic analogue (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 789-803 
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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: High-resolution 1H-nmr spectroscopy at 500 MHz has been used to study the Ca2+ binding domain I of bovine brain calmodulin in aqueous solution. All the resonances of the linear dodecapeptide Asp-Lys-Asp-Gly-Asn-Gly-Thr-Ile-Thr-Thr-Lys-Glu and of its cyclic analogue, synthesized by classical solution methods, have been completely assigned using a combination of several one- and two-dimensional nmr experiments, including the zero quantum correlation. Chemical shift values and 3JCHNH coupling constants indicate that, on the nmr time scale, both peptides are flexible and assume multiple conformations in rapid equilibrium, with no relevant contribution of structured features. Addition of Ca2+ causes only minor spectral changes in aqueous solution of both peptides, while larger effects are observed in more hydrophobic mixtures such as water/trifluoroethanol. The linear analogue shows nonspecific interactions, while only Asp3 and Asn5 are significantly perturbed in the cyclic peptide. This evidence, together with identical findings in La3+ titration studies of the cyclic analogue in pure water, suggest that loop I of calmodulin is endowed with an intrinsic binding ability.
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    URL: http://dx.doi.org/10.1002/bip.360270507
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  • 142
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    On the interaction of chromomycin A3 with calf thymus DNA in the presence of metal cations at different pH values (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 831-842 
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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: The interactions of the antitumor antibiotics, chromomycin A3, with a variety of metal cations in the pH range of 3.0-8.5 were systematically studied by CD, absorption, and 1H-nmr spectroscopies. Results were compared with those obtained in the presence of increasing amounts of calf thymus DNA. The negatively charged chromomycin A3, pKa 6.3, forms aggregates that become ordered and smaller in size, in the presence of variety of metal cations. Spectrophotometric titrations have shown that binding of the neutral drug to DNA at pH 4.5 does not require divalent cations, although the strength of the binding is greatly enhanced in their presence. At higher pH values (〉 7.0) and low DNA/drug ratio ( 〉 20), the metal cations are necessary to induce the binding between chromomycin A3 and DNA. At higher DNA/drug ratios (〉 100: 1), an appreciable proportion of the drug is bound even in the absence of divalent cations. Its binding affinity to the DNA is enhanced in the presence of these cations and at low pH values. Therefore, we conclude that chromomycin A3 binds in two related modes, in the presence and in the absence of divalent cations. The spectral data accumulated indicate the metal cation is involved in the binding of the drug to the DNA by forming a drug-metal-DNA ternary complex.
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    URL: http://dx.doi.org/10.1002/bip.360270510
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  • 143
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    Vibrational spectroscopy of L-valyl-glycyl-glycine, a parallel-chain β-structureThis is paper number 38 in a series on “Vibrational Analysis of Peptides, Polypeptides, and Proteins,” of which paper number 37 is Ref. 27. (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 885-908 
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bands in the ir and Raman spectra of L-valyl-glycyl-glycine (VGG) and VGG-ND have been assigned on the basis of a normal mode analysis of the known parallel-chain β-structure of this tripeptide. Amide I, II, III, and V mode shifts are obtained by the interactions of dipole derivatives in symmetry coordinates, referred to as dipole derivative coupling. These derivatives, obtained from ab initio studies, are also used to calculate ir intensities of amide I, II, and V modes. The agreement between predicted and observed frequencies and intensities is very good, providing confidence in the application of our force fields to the calculation of the vibrational modes of the general parallel-chain β-sheet structure (following paper).
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    URL: http://dx.doi.org/10.1002/bip.360270602
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  • 144
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    Interaction of the fibrinogen-binding tetrapeptide gly-pro-arg-pro with fine clots and oligomers of α-fibrin; comparison with αβ-fibrin (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 775-788 
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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 tetrapeptide Gly-Pro-Arg-Pro(GPRP) was introduced by diffusion into fine unligated clots formed from human fibrinogen at pH 8.5 and ionic strength 0.45 by batroxobin (αβ-fibrin) and by thrombin (α-fibrin). The α-fibrin clots were essentially liquefied at GPRP concentrations above 1 mM and αβ-fibrin clots above 15 mM, and the degree of polymerization of the resulting oligomers decreased progressively with increasing GPRP concentration as shown by γ-γ ligation with factor XIIIa and subsequent gel electrophoresis. Much smaller concentrations of GPRP, when introduced into unligated clots by diffusion, were sufficient to modify their mechanical properties profoundly. The shear modulus of elasticity G25 measured 25 s after imposition of stress fell, for example, by a factor of 0.4 at 0.1 mM GPRP in α-fibrin and at 1.1 mM in αβ-fibrin. The rate of shear creep under constant stress and the proportion of irrecoverable deformation also increased enormously. This behavior, and the corresponding decrease in steady flow viscosity, may be interpreted in terms of competition of GPRP with A sites on the E domains of fibrin monomers for bidning to “a” sites on the D domains, resulting in a moderate increase with increasing GPRP concentration of the average proportion of severed network strands and an enormous increase in the rate at which all strands dissociate and reassociate. Reassociation of severed strands in new configurations is a necessary corollary since the differential modulus or compliance remains constant during creep and creep recovery. The greater susceptibility of α-fibrin clots to interaction with GPRP is attributed to stabilization of contacts between monomer units by Bb associations in αβ-fibrin. Ligated clots, with or without GPRP, exhibited essentially no time-dependent creep and no irrecoverable deformation, corresponding to an absence of any severance of network strands.
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    URL: http://dx.doi.org/10.1002/bip.360270506
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    Vasopressin conformational fluctuations: A molecular dynamics study (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 939-956 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations have been used to study the conformational fluctuations of the oligopeptide hormone vasopressin. Starting coordinates for these simulations were built upon the crystal structure of pressinoic acid, the cyclic ring moiety of vasopressin, recently determined by x-ray diffraction. Coordinates for the additional tripeptide “tail” of vasopressin were selected by arbitrary positioning of this segment using interactive computer graphics. Two such starting configurations were minimized to relax strains, and long dynamics simulations (20 and 40 ps) in vacuo were then conducted following extensive heating and equilibration sequences (36 ps). In these studies, vasopressin was found to undergo few substantial conformational changes at 300 K on the time scale simulated, in contrast to the results of a shorter previous simulation, but comparable structural transitions were observed during the equilibration periods. The pressinoic acid structure was found to be a reasonably stable possible conformation for vasopressin in vacuum on this time scale.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270605
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  • 146
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    Equilibrium dialysis study of binding of hexammine cobalt(III) to DNA (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1045-1051 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270611
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  • 147
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    On the multiple-minima problem in the conformational analysis of polypeptides. II. An electrostatically driven Monte Carlo method - tests on poly(L-alanine) (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1283-1303 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new approach to the multiple-minima problem in protein folding is presented. It is assumed that the molecule is driven toward the native structure by three types of mechanism. The first one involves an optimization of the electrostatic interactions, whereby the molecule evolves toward conformations in which the charge distribution becomes energetically more favorable. The second mechanism involves a Monte Carlo-energy minimization approach, and the third one is a backtrack mechanism that acts in the opposite direction, increasing the energy - the third type of movement provides a means to perturb the molecule when it is trapped in a stable but energetically unfavorable local energy minimum. This paper describes the implementation of a model based on these mechanisms, and illustrates its effectiveness by computations on different arbitrary starting conformations of a terminally blocked 19-residue chain of poly(L-alanine) for which the global minimum apparently corresponds to the right-handed α-helix. In all cases, the global minimum was attained, even when the starting conformation was a left-handed α-helix. In the latter case, the trajectory of conformations passed through partially melted forms of the left-handed α-helix (because of electrostatic defects at the ends), and then through the formation of structures leading to the more stable right-handed α-helix.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270808
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  • 148
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    Order-Disorder conformation change of xanthan in 0.01M aqueous sodium chloride: Dimensional behavior (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1641-1654 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Weight-average molecular weights Mw, second virial coefficients, and z-average radii of gyration 〈S2〉1/2z were determined by light scattering as a function of temperature T for four sodium salt samples of xanthan in 0.01M aqueous NaCl, in which the polysaccharide undergoes an order-disorder conformation change with increasing T. The data for 〈S2〉1/2z and Mw at 25 and 80°C, the lowest and highest temperatures studied, confirmed the previous conclusion that the predominant conformation at the former T, i.e., in the ordered state, is a double helix, while that at the latter T, i.e., in the disordered state, is a dimerized coil expanded by electrostatic repulsions between charged groups of the polymer. As T was increased from 25 to 80°C, 〈S2〉1/2z sigmoidally decreased or increased depending on the dimer's molecular weight. This temperature dependence of 〈S2〉1/2z and that determined elsewhere for a high molecular weight sample were found to be described almost quantitatively by a simple dimer model in which the double helix melts from both ends, when the double-helical fraction in the dimer at a given T estimated previously from optical rotation data was used.
    Additional Material: 7 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271009
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  • 149
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    Reversal of the Mg++-induced B-to-Z transition of poly[d(G-C)] with hydrostatic pressure (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1687-1690 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271012
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  • 150
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    Masthead (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988) 
    Details
    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.360271101
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  • 151
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    Binding of nogalamycin to model tetranucleotides (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1491-1517 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Intercalated complexes of the antitumor antibiotic nogalamycin (NGM) with the double-stranded oligonucleotides d(GCGC)2, d(ATAT)2, and d(ACAC) · d(GTGT) are investigated with the theoretical method SIBFA. The amino sugar part of the drug locates preferentially in the minor groove. An intrinsic preference for the d(ATAT)2 sequence over the d(ACAC) · d(GTGT) and d(GCGC)2 sequences is obtained, corresponding to relative energies 0, 11, and 15 kcal/mole, respectively. A mixed sugar-puckering pattern is preferred in the d(ATAT)2 complex while a uniform sugar-puckering pattern is preferred for the other sequences. No direct specific interaction involves the N+ - H part of protonated NGM. The location of the amino sugar as well as the sequence selectivity is due to the global electrostatic interaction of the dimethylammonium group with the given groove. The two hydroxyl groups of the amino sugar and the carbonyl of the carbomethoxy group encounter partners for hydrogen bonding at the intercalation site, but these interactions do not appear to govern the base sequence selectivity. The nogalose part is not found to be directly involved in the binding or in the selectivity. The conformations of isolated and intercalated NGM are discussed.
    Additional Material: 11 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270913
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  • 152
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    Chromatography and electron microscopy of cross-linked fibrin polymers - a new model describing the cross-linking at the DD-trans contact of the fibrin moleculesa part of this work was presented at the xth international congress of thrombosis and haemostasis, san diego, usa, july 14-19, 1985, and was published in abstract form (1985) [thromb. haemostas. 54, 937]. (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1733-1748 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polymerization of fibrin molecules results in the formation of a double-stranded protofibril. Although convincing data have not been presented, it is classically believed that γ-chain cross-linking of fibrin molecules occurs between the longitudinal end-to-end contacts (DD-long contacts) of the molecules within each of the two strands of a protofibril (intrastrand cross-linking). In this investigation the question addressed was whether γ-chain cross-linking takes place across the two strands (interstrand cross-linking) between the transversal half-staggered contacts of the molecules. Demonstration of double-stranded protofibrils in the presence of urea would indicate an interstrand cross-linking, whereas in the case of intrastrand cross-linking, the chaotropic agent urea would dissociate the double-stranded structure to form single-stranded fibrils. Protofibrils were obtained by generating soluble cross-linked fibrin polymers (sXLFbP): After incubation of souble fibrin polymers with Factor XIIIa at 37°C, the polymerization and cross-linking reaction was stopped by the addition of 6M urea and EDTA. Gel filtration of the reaction mixture in the presence of 3M urea was effect in separating sXLFbP from monomeric molecules. The sXLFbP-containing fractions were adsorbed onto mica in the presence of different concentrations of urea and investigated by electron microscopy after rotary shadowing. In the presence of 3M urea the sXLFbP appeared as double-stranded protofibrils. In the presence of 4M urea some parts of the double-stranded structure were found to be unfolded whereas in the presence of 6M urea multiple-bended single-stranded fibrils were observed. SDS-polyacrylamide gel electrophoresis of the sXLFbP demonstrated no γ-chain cross-linking within the protofibrils. Ultracentrifugation of the sXLFbP showed that in the presence of 3M urea noncross-linked fibrin polymers dissociated to monomeric molecules. When sXLFbP was centrifuged into 6M urea on sucrose density gradients, no reduction of the polymer size could be observed. The data indicate that γ-chain cross-linking occurs between the transversal contacts of the fibrin molecules within a protofibril, thus generating interstrand cross-linking. A model of the cross-linking of polymerized fibrin molecules is developed and the term DD-trans contact is proposed for this specific alignment of the D-domains.
    Additional Material: 9 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271104
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  • 153
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    Diffusion coefficients of segmentally flexible macromolecules with two subunits: A study of broken rods (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1771-1786 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A general treatment for the solution dynamics of segmentally flexible macromolecules having two subunits is presented. Bead modeling allows for a complete inclusion of hydrodynamic interactions in this treatment. The finite size of the beads is also considered, so that it is therefore possible to account properly for torsional motions of the subunits. Expressions for the components of the resistance matrix are derived. From them, the translational and rotational diffusion coefficients can be calculated. Distinction is made between hinged macromolecules, whose only internal motion is bending, and swivel-jointed macromolecules, for which torsions of the subunits are also allowed. Numerical results are presented for broken rods with the two types of flexibility. The effects of hydrodynamic interaction between arms of broken rods are about 25% for translation and under 10% for rotation. These findings give support to the treatments of Harvey, Wegener, and co-workers in which interactions were neglected. The rotational dynamics of hinged and swivel-jointed rods are compared. Although there are differences in the short-time behavior, the longest relaxation time is the same for the two cases. Finally, the validity of Wegener's rotational diffusion constants is discussed.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271107
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  • 154
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    Cluster analysis of protein fourier transform infrared spectra (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1831-1838 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cluster analysis techniques were used to examine a set of Fourier transform infrared (FT-IR) spectra of bovine serum albumin (BSA) in the adsorbed and nonadsorbed states. The region from 1480 to 1600 cm-1, comprising the amide II band, was used. Spectra were preprocessed to compensate for linear baseline variation, and the single linkage method of cluster analysis was applied. As expected, the spectra of adsorbed and nonadsorbed BSA fell into two distinct clusters. However, no further clustering was observed among the adsorbed BSA spectra on the basis of surface type, suggesting that surface specificity of the spectral changes induced in BSA by adsorption is not detectable above experimental variation. This work illustrates the value of using cluster analysis in the FT-IR study of proteins as a complement to other data analysis methods.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271111
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  • 155
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    Fourier transform ir spectroscopy of collagen and gelatin solutions: Deconvolution of the amide I band for conformational studies (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1749-1760 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ir spectra of lathyritic rat skin collagen and calf skin gelatin solutions at a variety of temperatures were obtained using Fourier transform ir spectroscopy and a 9-reflection, 2-pass ZnSe prism sample cell. The spectra were then deconvolved (based on Kauppinnen's method) and the behavior of the amide I band at ∼ 1650 cm-1 observed in detail. Throughout the temperature range studied (4-50°C), three component absorption peaks within the amide I band (at 1633, 1643, and 1660 cm-1) are common to the spectra irrespective of the degree of triple helix content of the sample. Changes in the relative intensities of these component peaks are, however, conformationally dependent. During denaturation of the triple helix, the dominant 1660-cm-1 component in the native collagen spectrum diminishes and the 1633-cm-1 peak becomes relatively intensified. The inherently strong basicity of the carbonyl group of the proline residues together with the frequent occurrence of this imino acid in the X position of the Gly-X-Y triplet of collagen largely accounts for the -30-cm-1 shift of the amide I band during denaturation. Temperature and conformationally dependent changes in the fine structure of the amide I band from dilute solutions of collagen can be monitored in a reproducible and quantitative fashion.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271105
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  • 156
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    Dielectric relaxation studies on bovine ligamentum nuchae (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1787-1793 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Dielectric relaxation studies of bovine ligamentum nuchae are reported over the frequency range of 1 MHz to 1 GHz and over the temperature range of 23-48°C. A temperature-dependent relaxation process was observed at low megahertz-frequency with the correlation time of around 40 ns. The result is quite similar to that of a synthetic polypentapeptide (VPGVG) and of α-elastin. The relaxation is proposed to arise in part from the peptide libration within the polypentapeptide of bovine ligamentum nuchae.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360271108
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  • 157
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    Study of furanose ring flexibility in polynucleotide chains using raman spectra analysis (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1817-1829 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bands within the range of 800-850 cm-1 of Raman spectra of polynucleotides sensitive to the change in conformation of sugar-phosphate backbone are analyzed theoretically. The bands are interpreted as the appearance of a quasi-local deoxyribose vibrational mode whose frequency is dependent on the ring puckering. The localization region of the vibrational mode is pointed out. The theory establishes a relationship between the observed spectral intensity and the population of deoxyribose conformational states described in the framework of the pseudorotation concept. The approach developed allowed one to describe the band shapes and their temperature behavior, and to determine the pseudorotation potential of deoxyribose in the helix B-form of A · T containing polynucleotides. Using the analysis of Raman spectra of DNA fibers in water-ethanol mixture the deoxyribose flexibility during the B-A transition is investigated in terms of the population of conformers and effective potential. It is shown that N- and S-type deoxyribose conformers are populated in the DNA B-form (those of the S-type are preferable), whereas N-type conformers are primarily populated in the DNA A-form.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360271110
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  • 158
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    Masthead (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988) 
    Details
    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.360271201
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  • 159
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    Molecular structure of L-lysyl-L-alanyl-L-alanine: A tripeptide found in histone H1 (1988)
    New York : Wiley-Blackwell
    Biopolymers 27 (1988), S. 1887-1896 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structure of L-lysyl-L-alanyl-L-alanine hydrochloride has been determined by x-ray diffraction. The peptide is in zwitterionic form with the carboxylic group deprotonated, and with positive charges both in the amino terminal and ∊-amino groups of lysine. Crystals are monoclinic, space group P21 and Z = 4, with two peptide molecules in the asymmetric unit, which show different conformations. While one molecule has torsional angles for the Lys-Ala peptide bond (ϕ2, ϕ2) in the β-pleated sheet region, the values for the other molecule are close to those for the α-helix. This molecular flexibility is of interest for the study of H1 histone, which contains this sequence repeated several times. The two lysine residues show fully extended side chains. Two methanol molecules and two acetonitrile molecules are also present in the unit cell. An extensive network of hydrogen bonds and ionic interactions stabilize the crystal structure.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360271203
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  • 160
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    100 Jahre Metallcarbonyle. Eine Zufallsentdeckung macht Geschichte (1988)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 22 (1988), S. 113-122 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In den meisten Bereichen der chemischen Forschung dürfen metallorganische Verbindungen unterschiedlichster Prägung heutzutage eine Schlüsselfunktion beanspruchen, zumindest aber wertvolle Hilfsdienste anbieten. Ob man sich für Grundfragen der chemischen Bindung interessiert oder für den gezielten Aufbau organischer Moleküle, komplizierte Naturstoffe eingeschlossen, ob über stöchiometrische Bindungsknüpfungen hinaus katalytisch verlaufende Prozesse gefragt sind, ob Oberflächeneffekte von Metallen und Metalloxiden auf kohlenstoffhaltige Verbindungen studiert und modellhaft verstanden werden sollen, ob endlich auch die differenzierten Wirkungen von Metallen, leichten wie schweren, auf körpereigene Stoffe zu erforschen sind - für alles das muß man eine Menge metallorganische Chemie verstehen. Gerade das hochbrisante Thema der Lebensbedrohung durch Schwermetalle sollte uns daran erinnern, daß wir den Inhalt der „Büchse der Pandora“ nur begreifen, wenn wir sie öffnen, den gefährlichen Stoff mit Umsicht charakterisieren und daraus unsere Schlüsse ziehen. 100 Jahre Metallcarbonyle [1] sind dazu angetan, auch darüber nachzudenken.
    Additional Material: 19 Ill.
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    URL: http://dx.doi.org/10.1002/ciuz.19880220402
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  • 161
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    Gene. Lehrbuch der molekularen Genetik. Von Benjamin Lewin. VCH Verlagsgesellschaft, Weinheim 1988. 725 S., 616 Abb., 83 Tab., DM 98,-. ISBN 3-527-26745-X (1988)
    Weinheim : Wiley-Blackwell
    Chemie in unserer Zeit 22 (1988), S. 183-184 
    Details
    ISSN: 0009-2851
    Keywords: Chemistry ; Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ciuz.19880220506
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  • 162
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    Die stereoisomeren Sinensiaxanthine und Sinensiachrome: Trennung und Bestimmung ihrer absoluten Konfiguration. 7. Mitteilung über Rosenfarbstoffe6. Mitteilung, s. [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 24-30 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoisomeric Sinensiaxanthins and Sinensiachromes: Separation and Absolute ConfigurationThe so-called sinensiaxanthins and sinensiachromes, important apocarotenols from various fruits, have been separated into 2 and 4 stereoisomers, respectively, and their absolute configurations have been determined: (3S,5R,6S)-5,6-epoxy-5,6-dihydro-10′-apo-β-carotene-3,10′-diol (2), its (9Z)-stereoisomer 7, the (8R)- and (8S)-epimers of (3S, 5R)-5,8-epoxy-5,8-dihydro- 10′ -apo-β-carotene-3, 10′-diol (4 and 5), and their (9Z)-stereoisomers 3 and probably 6. Thus, sinensiaxanthins are cleavage products from (Z/E)-isomeric antheraxanthins or violaxanthins (scission at C(9′)-C(10′)) and sinensiachromes analogously from mutatoxanthins or auroxanthins.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710103
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  • 163
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    Enantioselektive Verseifung der Diacetate von 2-Nitro-1,3-diolen mit Schweineleber-Esterase und Herstellung enantiomerenreiner Derivate von 2-Nitro-allylalkoholen (chirale Verknüpfungsreagenzien)Kurzmitteilung mit ausführlicher Beschreibung der Isolierung und Anwendung von Schweineleber-Esterase Rohpräparaten, s. [1].Teilweise erwähnt in einem Übersichtsartikel über EPC-Synthesen unter C,C-Verknüpfung mit Hilfe von Enamine, s. [2]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1-23 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantioselective Saponification of Diacetates of 2-Nitro-1,3-propanediols by Pig-Liver Esterase and Preparation of Enantiomerically Pure Derivatives of 2-Nitro-allylic Alcohols (Chiral Multiple-Coupling Reagents)The reproducible enantioselective saponification of open-chain and cyclic diacetates of meso-2-nitro-1,3-propanediols (see 4b-13b) with pig-liver esterase (PLE) gives monoacetates (see 4c-l3c) of 〉 95% enantiomeric excess. The Re enantiotopic acetate group appears to be saponified preferentially, as proved by the X-ray crystal structure analysis of three camphanoates 4d, 6d, and 7d. Elimination of H2O or AcOH from the hydroxy acetates thus available gives derivatives of nitro-allylic alcohols (see 20-24, 27, and 29) which are subjected to diastereoselective Michael additions or SN2′ substitutions.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710102
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  • 164
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    New Pterocarpinoids from Dolichos marginata ssp. erecta (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 72-76 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four new pterocarpinoids, sphenostylin A, B, C, and D (1-4), have been isolated from the CHCl3 extract of the root bark of Dolichos marginata ssp. erecta (Leguminosae) by preparative liquid chromatography. The structures have been established by spectroscopic methods (UV, 1H-NMR, 13C-NMR, EI-MS, DCI-MS, CD) and chemical transformations. The isolated compounds showed weak antifungal activity against Cladosporium cucumerinum.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710109
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  • 165
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    Condensed Heterotricycles. Synthesis and Reactions of b-Fused 1(2H)-Isoquinolinones with unusual enaminic propertiesContribution No. 822 from Hindustan Ciba-Geigy Ltd., Research Centre. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 77-92 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homophthalic acid (1) undergoes reaction with 1,2-, 1,3-, and 1,4-diamines to give condensed 1(2H)-isoquinolinones like 2, 4, 13, and 25, which exhibit marked enamine character. These are attacked by electrophiles at the N or C terminus. Some notable reactions of imidazoisoquinolone 2 are those with maleic and acrylic acids to form the tetracycles 48 and 51, respectively. With propiolic acid, 5 underwent an interesting reaction to form the benzimidazonaphthyridine 53. An equally interesting behaviour was elicited from 2 in its reaction with formaldehyde, when in addition to the expected methylene-bridged molecule 59, the novel spiro derivative 60 was formed by the dimerisation of a presumed azadiene intermediate 63.
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    URL: http://dx.doi.org/10.1002/hlca.19880710110
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  • 166
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    The dimeric and polymeric anhydride of 2,3-O-isopropylidene-β-D-ribofuranose. An NMR study (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 120-123 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H- and 13C-NMR data of the dimeric anhydride 1 of 2,3-O-isopropylidene-β-D-ribofuranose are reported together with the 1H-NOE values. The data show that the products of the polymerization of 1,5-anhydro-2,3-O-isopropylidene-β-D-ribofuranose are α- and β-D-ribofuranans and not an α-D-ribofuranan and a β-D-ribofuranan and a β D ribo-pyranan as claimed before [2] [3].
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710114
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  • 167
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    Complexes with a Pincers. 2,6-Diphenylpyridine as Twofold-Deprotonated (C ∧ N ∧ C) terdentate ligand in C,C-trans-, and as mono-deprotonated (C ∧ N) chelate ligand in chiral C,C-cis-complexes of platinum(II) and palladium(II). Preliminary communication (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 130-133 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,6-Diphenylpyridine forms, as twofold-deprotonated, terdentate ligand, complexes with Pt(II) and Pd(II), having two adjacent five-membered metallocycles. As mono-deprotonated, bidentate ligand, it forms cis-bis-complexes having a chirality axis. Pt(II) complexes undergo thermal and photochemical oxidative addition reactions, yielding stable Pt(IV) compounds. Pd(II) complexes yield substitued 2,6-diphenylpyridine in photochemical reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710116
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  • 168
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    Silicon-Directed Nazarov Cyclizations. Part V. Substituent and heteroatom effects on the reaction (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 168-194 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ability to incorporate alkyl, alkenyl, aryl, and heteroatomic groups into substrates for the silicon-directed Nazarov cyclization and their subsequent reactions has been investigated. In general, most of the groups are compatible with the conditions for the cyclization and do not interfere even when directly attached to the divinyl ketone. The influence of substituents on the rate of the cyclization has been addressed and is consistent with a simple mechanistic picture. O- and N-Containing functions are tolerated except when attached to the α-vinyl C-atom of the divinyl ketone. The diastereoface-directing effect of a fused cyclobutane is discussed.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710120
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  • 169
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    Synthesis of Aristotelia-Type Alkaloids. Part III.Part II: [1]. (3R,4R)- and (3R,4S)-1-p-menthene-3,8-diol and the corresponding racemates: Preparation and assignment of configuration (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 209-217 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A 1:1 mixture of the racemic trans- and cis-1-p-menthene-3,8-diols ((±)-3 and (±)-4, resp.) was readily prepared in 3 steps starting from 3-methyl-2-cyclohexen-1-one. The relative configuration of the diols, purified via the corresponding cyclocarbonates, was assigned by 1H-NMR spectroscopy and found to be at variance with tentative claims in the literature. Optically active samples of 3 and 4 were prepared by resolution of the racemates with (R)-1-phenylethylamine. The absolute configuration of the resulting diols was determined by chemical correlation with standards of known absolute configuration.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710122
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  • 170
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    Herstellung enantiomerenreiner, α-alkylierter Lysin-, Ornithin- und Tryptophan-Derivate (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 224-236 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Enantiomerically Pure, α-Alkylated Lysine, Ornithine, and Tryptophan DerivativesThe imidazolidinones 9 and 10 as well as the oxazolidinone 18a were prepared in several steps by known methods from lysine and ornithine with an overall yield of ca. 20%. After double deprotonation with LDA, the corresponding dianionic derivatives could be diastereoselectively alkylated with electrophiles (MeI, C6H5CH2Br, C6H5CHO, CH3CHO). Acid hydrolysis led to the two enantiomeric 2-methyl- and 2-benzyllysines and to the enzyme inhibitor (S)-2-methylornithine. Several α-alkylated tryptophan derivatives were obtained through alkylation of the heterocycles derived from various amino acids with 1-(tert-butyloxycarbonyl)-3-(bromomethyl)indole (26). Alkaline hydrolysis of the five-membered auxiliary ring of 30b followed by treatment with HCl afforded (S)-2-methyltryptophan (31).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710124
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  • 171
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    Hydrogénation de sels de flavylium: formation de composés heptacycliques; structure radiocristallographique du [tétrahydro-10b,10c,16,16a-diméthyl-16,16a-méthylène-10b,16-5aH-di(benzo[1]pyranno)[4,3-b:3′,4′,-c;2,3:2′,3′]-benz[1]oxépinyl-5a]-2-phénol (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 254-257 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrogenation of Flavylium Salts: Formation of Heptacyclic compounds; X-Ray Crystal Structure of 2-[10b,10c,16,16a-Tetrahydro-16,16a-dimethyl-10b,16-methylene-5aH-di[1]benzopyrano[4,3-b:3′,4′ -c; 2,3:2′,3′][1]benzoxepin-5a-yl]phenolThe hydrogenation of flavylium salts 1 either by catalytic reduction or by chemical reduction afforded the unexpected heptacyclic compound 2, the structure of which was determined by X-ray analysis. The latter was confirmed by 1H-NMR and mass spectra.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710128
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  • 172
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    Konformationsanalysen von Modell-Tripeptiden: Der Einfluss von α,α-disubstituierten α-Aminosäuren auf die Sekundärstruktur. Teil II. Röntgenstrukturanalyse und Konformationsenergie-Berechnungen (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 268-273 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational Analysis of Tripeptide Models: The Influence of α,α-disubstituted α-Amino Acids on the Secondary Structure. X-Ray Analysis and Conformational Energy CalculationsThe X-ray analysis of tripeptide Z-Ile-Val(2-Me)-benzocaine (1f) reveals the presence of a type-III β-turn. Moreover, MMP2 calculations on tripeptides, e.g. Z-Ile-Aib-benzocaine (1c), Z-Ile-D-Val(2-Me)-benzocaine (1g), Z-Ile-Gly(2,2-Pr2)-benzocaine (1h), Z-Ile-Gly-benzocaine (1a), and 1f, fit well into the frame of NMR and CD investigations. They allow considerations on the relative stability of different types of β-turns depending on the peptide sequence, e.g. the kind of α,α-disubstituted amino-acid moieties.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710130
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  • 173
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    Synthese von (-)-(R)-Nephthenol und (-)-(R)-Cembren A (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 292-297 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of (-)-(R)-Nephthenol and (-)-(R)-Cembren AStarting for L-serine,(-)-(R)-nephthenol((-)-2) and (-)-(R)-cembren A((-)-3) were synthesized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710133
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  • 174
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    Low-Temperature X-ray Crystal-Structure Analysis of the Thermally Unstable Lithiated 2-Butenyl tert-Butyl Sulfide: A comparison with model ab initio MO calculationsPart of the projected Dissertation of Th. M., ETH Zürich. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 299-311 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Single crystals of the N,N,N′,N′-tetramethylethylenediamine (TMEDA) complex 6 of the title compound have been isolated. Compound 6 decomposes in the crystalline state above -20°. From the bond lengths and angles obtained by X-ray crystal-structure analysis (data collected at -70°), compound 6 is best described as a (E)-1-(tert-butylthio)-1-lithio-2-butene with the double bond acting as an additional ligand on lithium (unsymmetrical allylic group). The S-atom is in a cisoid arrangement in a common plane with the four C-atoms of the butenyl system. The t-Bu group and the Li-atom are located above and below this plane. The structure is discussed with respect to the reactivity of 6 (α/γ reactivity). The gross structure is reproduced surprisingly well by an ab initio SCF MO calculation of the model lithiopropene-1-thiol 7(HS instead of t-BuS, CH2 instead of CHCH3, no solvation of Li). The prominent difference is the symmetry of the allyllic moiety in the calculated structure.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710202
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  • 175
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    Notiz zur Synthese Eines Optisch Aktiven Ace-Hemmers mit Amino-oxo-benzazepin-1-alkansäure-Struktur mittels enantiokonvergierender kristallisationsinduzierter Racemat-Trennung (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 337-343 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Note on the Synthesis of an Optically Active ACE Inhibitor with Amino-oxo-benzazepine-1-alkanoic-Acid Structure by Means of an Enantioconvergent Crystallization-Based ResolutionAn enantioselective synthesis of the potent angiotensin-converting enzyme inhibitor (1′S,3S)-3-[(1′-(ethoxy-carbonyl)-3′-phenylpropyl)amino]-2,3,4,5-tetrahydro-2-oxo-1H-1-benzazepine-1-acetic acid hydrochloride (3) is described which user a crystallization-based resolution of a racemic amino intermediate with concomitant racemization of the unwanted enantiomer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710205
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  • 176
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    Polycyclopentane Als Steroid-Analoga (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 363-368 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Polycyclopentanes as Steroid AnalogaThe synthesis of linearly annellated pentaquinanes from a readily available triquinane is reported.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710209
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  • 177
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    Synthese Eines Optisch Aktiven Penem-Zwischenprodukts Mittels Asymmetrischer Amidoalkylierung (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 395-403 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of an Optically Active Penem Intermediate by Asymmetric AmidoalkylationThe amidoalkylation of an optically active, cationic glycine derivative with methyl acetoacetate furnishes an intermediate 10a (Scheme 2) that is transformed in six steps to the optically active, silyl-protected 4-acetoxy-3-(1-hydroxyenthyl)-2-azetidinon 18a, a well known intermediate in penem synthesis.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710213
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  • 178
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    Circular Dichroism of Planar, Exocyclic S-cis-Butadienes Remotely PerturbedInteraction between non-conjugated chromophores, Part 29. Part 28, see [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 419-428 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically pure 5,6-dimethylidenebicyclo[2.2.1]hept-2-yl derivatives have been prepared. The sign of the Cotton effects associated with lowest-energy transition of 2-(dicyanomethylidene)-((-)-(1S,4S)-15), (E)-2-(methoxyimino)-((+)-(1S,4S)-16), (Z)-2-(methoxyimino)-5,6-dimethylidenebicyclo[2.2.1]heptane ((-)(1S,4S)-17), and 2,3,5-trimethylidenebicyclo[2.2.1]heptane ((-)-(1R,4S)-18) is opposite to the chirality constituted by the coupling of the electric transition moments of the two homoconjugated π-chromophores (Kuhn-Kirkwood dipole-coupling mechanism). When the substituents at C(2) are not π-functions, no general rule can be retained for the chiroptical properties of the 5,6-dimethylidenebicyclo[2.2.1]hept-2-yl systems as shown for dimethyl acetal (-)-(1S,4S)-19, ethylene acetal (+)-(1R,4R)-20, exo and endo methyl ethers (+)-(1R,2S,4R)-21 and (+)-(1R,2R,4R)-22, and for spirol[5,6-dimethylidenebicyclo[2.2.1]heptane-2.2'-oxiranes](-)-(1S,2S,4S)-23 and (-)-(1S,2S,4S)-24.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710215
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  • 179
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    Ferroelectric Liquid Crystals. Part 2.‘Ferroelectric Liquid Crystals’, Part 1: [1]. Chiral phenyl benzoates incorporating a trans-1,4-disubstituted cyclohexane ring (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 451-460 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: About forty novel phenyl benzoates also incorporating a trans-1,4-disubstituted cyclohexane ring and a chiral centre have been prepared. The dependence of the liquid-crystal transition temperatures of this new class of compounds on lateral substituents, diverse central linkages, chain lengths, and position of the chiral centre has been studied systematically. The synthesis and liquid-crystal transition temperatures of these new compounds are described in detail.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710218
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  • 180
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    [4 + 2]-Cycloadditionen von α,β-ungesättigten Hydrazonen. Teil 1. Pyridin-2,3-dicarboximide aus 1-(Dimethylamino)-1,4-dihydropyridin-Derivaten (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 486-492 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: [4 + 2] Cycloadditions of α,β-Unsaturated Hydrazones to Pyridine-2,3-dicarboximides via 1-(Dimethylamino)-1,4-dihydropyridine DerivativesThe [4 + 2] Cycloaddition of α,β-unsaturated hydrazones of type 1 (1-aza-1,3-butadienes) with 2-halogenomaleimides 4 affords 1,4-dihydropyridines 6 which, after treatment with an acid, yield highly substituted pyridine-2,3-dicarboximide derivatives 7 (Scheme 1).
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710222
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  • 181
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    Photochemistry of 2,2-Dimethyl-2H-Furo[3,4-b]Pyran-4,7(3H, 5H)-Dione (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 498-501 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation (λ 〉 340 nm) of the title compound 2a in t-BuOH affords 3,3,10,10-tetramethyl-2,8-dioxatricyclo-[4.3.2.01,6]undecane-5,9-dione (3) via photoextrusion of 2-methylpropene and subsequent photocycloaddition of 2a to the alkene. The same regioisomer 3 is formed selectively and in much higher yields on irradiating 2a in the presence of excess 2-methylpropene. Irradiation of 3 (λ = 300 nm) in t-BuOH in the presence of the same alkene gives a 6:1 mixture of spirooxetanes 7a and 7b but not α-cleavage products. In 2-propanol, 2a is photoreduced to a 2:1 mixture of diastereoisomeric hydrodimers 9.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710224
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  • 182
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    Masthead (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710301
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  • 183
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    Une synthèse générale des tétraazamacrocycles mono-C-fonctionnalisés (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 602-608 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A General Synthesis for Mono-C-Functionalized TetrazamacrocyclesA new synthesis, under usual conditions of concentration, medium, and temperature, of a series of mono-C-functionalized tetraazamacrocycles is given. The method may easily be generalized. The new procedure allows the modification of the length of the side-chain or the size of the cavity by choosing fitted staring materials. The key intermediate has a tosylated linear side-chain susceptible to be transformed into a large variety of functional groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710313
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  • 184
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    Enantiomerically pure 7-oxabicylo[2.2.1]hept-5-en-zyl derivatives as synthetic intermediates. Part IIIPart I, see [1]; Part II, see [2].. Total synthesis of D- and L-ribose derivativesFor a preliminary communication, see Y. Auberson, R. Bimwala, J. Wagner, P. Vogel, Société Suisse de Chimie, Berne, 16 Oct. 1987, Abstract p. 29. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 624-630 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomerically pure methyl 5-bromo-5-deoxy-2,3-O- isopropylidene-β-D- (D-5b) and -β-l-ribofuranoside (l-5b) have been derived from (-)-(1R,2S,4R)-2-exo-cyano-7-oxabicylo[2.2.1]hept-5-en-endo,-yl (1′S)-camphanate (1) and (+)-(1S,2R,4S)-2-exo-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl(1′R)-camphanate (2), respectively, in 5 synthetic steps and 28% overall yield. Hydrolysis of D-5b and L-5b afforded methyl 2,3-O isopropylidene-β-D-ribofuranoside (D-5a) and methyl 2,3-O-isopropylidene β-L-ribofuranoside (L-5a), respectively. The intermediate (+)-(1R,4R,5R,6R) 5-exo,6-exo-(isopropylidenedioxy)-7-oxabicyclo[2.2.1]heptan-2-one ((+)-7) and its enantiomer(-)-7 were also obtained enantiomerically pure by resolution of (=)-7 by the Johnson-Zeller method. In bothe approaches, the chiral auxiliaries ((-)- and (+)-camphanic acids, or (+)-(S)-N,S-dimethyl-S-phenylsulfoximide) were recovered at an early stage of the synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710316
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    Mécanisme de solvolyse des cis- et trans-(p-toluènesulfonates) d'aryl-2-cyclopentyle I. Etude de la première étape de la solvolyse: effets isotopiques de l' atone de deutérium en position 2, effets de sel basique et effet spécial de sel (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 648-657 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Solvolysis Mechanism of cis - and trans-2-Arylcylopentyl p-Toluenesulfonates. The Step: 1-Deuterium Isotope Effects, Basic Salt Effects, and Special Salt EffectWe have studied the first step of the solvolysis of cis and trans-2-arylcyclopentyl p-toluenesulfonates in HCOOH, AcOH, and EtOh. All substrates show a high kinetic 1-deuterium isotope effect (kH/kD(1) 〉1.15). This fact indicates that first step leads to classical intimate ion-pair Which dissociates to a solvet-separated ion-pair, without participation either of solvent, the 2-aryl group, or a H-atom at C(2). The slight influence of added basic ions on reaction rate allows us to exclude any direct solvent attack on the covalent substrate even in the most favorable case, i.e. ethanolysis of 2-(p-nitrophenyl)cylopentyl-p-toluenesulfonates. Furthermore, solvent-separated ion pair formation is indicated by the special salt effect induced by LiClO4.
    Notes: No abstract.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710319
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  • 186
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    Masthead (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988) 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710401
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  • 187
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    Anion-receptor molecules: Synthesis of a chiral and functionalized binding subunit, a bicyclic guanidinium group derived from L- or D- asparaginePresented in part at the 11th International Congress of Heterocyclic Chemistry, Heidelberg, Federal Republic of Germany, August, 1987. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 685-693 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The optically active (4S,8S)-4, 8-bis(hydroxymethyl)-1,5,7-triazabicyclo[4.4.0]dec-5-ene ((S,S)-1) has been synthesized in nine steps from L-asparagine with a total yield of 5.1%. Similarly, the enantiomer (R,R)-1 has been prepared from D-asparagine. (S,S)- and (S,S)-1 are representative examples of rigid and functionalized bicyclic guanidine systems and constitute useful intermediates in the construction of chiral selective anion-receptor molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710402
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  • 188
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    Studies on Antifungal Agents. Part 22. 3-aryl-5-[(aryloxy)alkyl]-3-[(1H-imidazol-1-yl)methyl]-2-methylisoxazolidines and related derivatives (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 718-732 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis and antifungal activity of a novel series of 3-aryl-5-[(aryloxy)alkyl]-3-[(1H-imidazol-1-yl)-methyl]-2-methylisoxazolidines and related compounds, are discussed. The synthesis of the title compounds was accomplished via a 1,3-dipolar cycloaddition of α-substituted ketonitrones with l-alkenyl phenyl ethers (Scheme 2 and 3). The compounds were evaluated for in vitro antifungal activity in solid agar cultures against a broad variety of yeast and systemic mycoses and dermatophytes. While antifungal activity was evident throughout the series, in general, derivatives having halogen atom(s) in either or both aryl rings demonstrated the highest potency, especially against Trichophyton rubrum and Candida albicans. The dichloro analog 20 (PR 967-248) was found to possess the most useful activity. Its minimum inhibitory concentration (MIC) values ranged between 0.2 and 2.0 μg/ml, as compared to 0.2-20.0 μg/ml for the standard drug ketoconazole (4).
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710406
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  • 189
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    Captodative olefins in normal and inverse Diels-Alder ReactionsPart 3 of Thermal Reactions of Donor-Acceptor Systems. Part 2: [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 742-748 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Olefins with captodative substitution are reactive dienophiles in Diels-Alder reactions with normal and inverse electron demand. This is shown for reactions of 2-(tert-butylthio)acrylonitrile (1) with various dienes and heterodienes, e.g. 1,3-cyclohexadiene, hexachloro-1, 3-cyclopentadiene, acrolein, methacrolein, and methyl vinyl ketone (Schemes 2 and 3). In case of the hetrodienes, 3,4-dihydro-2H-pyrans are formed beside small amounts of tetrahydrothiophenes; however, with methyl vinyl ketone, both reaction pathways are equally followed. The high reactivity of captodative olefins in Diels-Alder reactions are rationalized on the basis of Sustmann's FMO model under consideration of Viehe's concept of captodative substitution of alkenes.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710408
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  • 190
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    A novel rearrangement of 2(5H)-furanones (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 783-787 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel rearrangement of 2(5H)-furanones is described. When refluxed in aq. Ethanolic solution in the presence of excess KOH, the 2,5-dihydro-2-oxofuran-3-carboxamides 6 underwent a novel rearrangement to the corresponding 4,5-dihydro-4-oxo-2-(phenylamino)-3-furancarboxylic acids 1 in moderate-to-excellent yields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710413
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  • 191
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    Kurze Totalsynthesen von (±)-Sativen und (±)-cis-Sativendiol (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 788-807 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Short Total Syntheses of (±)-Sativene and (±)-cis-SativenediolOur approach to (±)-sativene (7) and (±)-cis-sdtivenediol (9) involves: (a) reaction of 3-methylbutanoyl chloride with Et3N/cyclopentadiene to give the endo-isopropyl-ketone 1 (here improved to 71%), (b) NBS bromination of 1 to a 5:1 mixture (87%) of the bromo-ketones 2 and 3, (c) NFD-reaction sequence initiated by the attack of 1,2-butadienyl titanate (complex of 15, obtained from 2-butine) on 2/3 to afford 52% of the brexenone derivative 4 (along with 8% of its epimer 16), (d) addition of dibromomethane to 4 forming 63% of the diene-alcohol 5 (along with 13% of the diene-carbaldehyde 38), and (e) carbenoid ring-expansion with MeLi applied to 5 resulting in 41% the diene-ketone 6 (along with 15% of a 1:3 mixture of the diene-ketones 32 and 33). Wolff-Kishner reduction of 6 led to 81% of (±)-sativene (7), when enough O2 was present, but to 97% of the diene 8 in the strict absence of O2. (±)-cis-Sativenediol (9) was obrained (86%) by OsO4 hydroxylation of 8. The brexenone derivatives 4 and 16 (6:1, 50%) were also produced when the NFD-reaction sequence was applied to the isomeric bromo-ketone mixture 13/13 (1:3). The latter was obtained by NBS bromination of 10, which in turn was available by base epimerization of 1, followed by destructive removal of unreacted 1 by repeated gas-flow thermolysis. An analogous (less convenient) route to (±)-sativene (7) passed through a series of dihydro compounds (the ene series) it started with the methylidene-ketone 36, which was the product (97%) of a partial hydrogenation of 4. Addition of dibromomethane to 36 led t 62% of the methylidene-alcohol 39 (along with a little tetracyclic ether 40). Carbenoid ring expansion of 39 with MeLi afforded ca. 42% of the methylidene-ketone 41 (along with 7% of the methylidene-ketone 43 or, under slightly different condition, along with 9% of the methylidene-ketone 42 and 10% of the methylidene-carabaldehyde 44). The methylidene-alcohol 39 and the methylidene-ketone 43 were also obtained by partial hydrogenation of 5 and 33, respectively. Wolff-Kisher reduction converted 41 into (±)-sativene (7 99%); the same conditons applied to 42 afforded only ca. 8% 7 (along with three other hydrocarbons, one of them (ca. 21%) probably being (±)-copacamphene (45)). In the diene series, the two succeeding reactions (4→5 and 5→6) competed with the same side reaction, a rearrangement leading to the brendene-aldehyde 38. In the ene series, the corresponding dihydro-by-product 44 was found in the reacton 39→41, but not during 36→39. These side reactons could largely be suppressed by keeping the reaction temperature low. An explanation is proposed.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710414
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  • 192
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    Reactions of Haloarenes with Thiolate Anions in Tetraglyme: Competition between electron transfer and SNAr mechanisms (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 859-866 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the bromo-substituted naphthalene 1 with the alkanethiolate anions 2a-b and arenethiolate 2c in tetraglyme gave the corresponding 1-naphythyl thio-ethers 3a-c. Thio-ethers 3a-c were oxidized to the corresponding sulfones 4a-c with m- chloroperoxybenzoic acid. The reaction of the dichloro-substituted anthracene 5a with 2b gave the disubstutution product 6a. The reaction of 9-bromoanthracene 5c with the alkanethiolate 2b gave 6b, whereas the reaction of 5c with the arenethiolate 2c gave a mixture of substitution product 6c and anthracene 7. The observation of the formation of both 6c and 7 is explained by the competition between substitution (SnAr) and electron-transfer (ET) mechanisms. Consistent with this interpretation, the reaction of the monochloro-substituted 5b, which has a higher-energy σ* orbital, with 2c gave 6c without the formation of 7. Zn/KOH in tetraglyme was shown to reduce the aryl halides 5b-c and thio-ether 6c to 7.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710421
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  • 193
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    Synthèse de l'acide décarboxythamnolique (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 876-880 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Decarboxythamnolic AcidThe total synthesis of the meta-depside decarboxythamnolic ( = 3-[(3-formyl-2-4-dihydroxy-6-methyl-phenyl)oxy]-2-hydroxy-6-methoxy-4-methylbenzoic acid; 25) by the biomimetic condensation of the substituted β-orcinol units 9 and 22 is described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710424
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  • 194
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    Metabolism of Carotenoids in Salmonids. Part 3Part 1: [4]; Part 2:[1].. Metabolites of astaxanthin and canthaxanthin in the skin of atlantic salmon (salmo salar, L.) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 887-896 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diets supplemented with astaxanthin and canthaxanthin, respectively, and a control diet without carotenoid additions, were fed to 1½-year-old Atlantic salmon (Salmo salar, L.) for one year. The integuments were investigated as to their quantitative and qualitative carotenoid composition. Astaxanthin and canthaxanthin deposited in the skin amounted to 20 and 14% of the total carotenoids only. Seventy % must be considered as metabolites of astaxanthin and canthaxanthin and 10% as basic xanthophylls also present in the control groups. Astaxanthin apparently underwent the following metabolic pathway: astaxanthin→idoxanthin→adonixanthin→zeaxanthin→zeaxanthin 5,6-epoxides. Reduction of the 4′-carbonyl group was stereospecific leading to the (4′R)-idoxanthin. Canthaxanthin was obviously converted to β,β-carotene via 4′-hydroxyechinenone, echinenone, and 4-hydroxy-β,β-carotene.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710426
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  • 195
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    Antifungal Polyphenols from Cordia goetzeiGürke (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1210-1219 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Four highly oxygenated polyphenols 1-4, have been isolated from the stem bark of Cordia goetzei Gürke (Boraginaceae) and their structures elucidated by a combination of one- and two-dimensional (including COLOC) NMR spectroscopic techniques, mass spectroscopy, and chemical methods. The first new compound, cordigone (1), is a tetrahydrofuran derivative and the second one, cordigol (2), a furobenzopyran derivative. The benzofurans 3 and 4 are orange pigments, responsible for the coloration of the stem bark of the tree. All four polyphenols are fungicidal against cladosporium cucumerinum.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710532
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  • 196
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    8-Aza-7-deaza-2′-deoxyguanosine: Phosphoramidite synthesis and properties of octanucleotides (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1191-1198 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Base-modified octanucleotides derived from d(G1-G2-A-A-T-T-C-C-) (11) but containing 8-aza-7-deaza-2′-deoxyguanosine (2) instead of 2′-deoxyguanosine (1) have been prepared by solid-phase synthesis employing P(III) chemistry. Isobutyrylation of 2, followed by 4, 4′-dimethoxytritylation and subsequent phosphitylation yielded the methyl or the cyanoethyl phosphoramidites 6a or 6b, respectively. They were used as building blocks in automated DNA synthesis. The resulting octanucleotides 12-14 containing 2 showed increased Tm values compared to the parent oligomer 11. The oligomers 11-14 were employed as sequence-specific probes in endo-deoxyribonuclease Eco RI oligonucleotide recognition. Whereas displacement of dG-2 (enzymic cleavage site of 11) abolished phosphodiester hydrolysis, replacement of dG-1 enhanced the cleavage rate compared to 11.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710530
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  • 197
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    Synthesis of Optically Pure Tricarbonyliron Complexes of 5,6-Dimethylidenebicyclo[2.2.2.]oct-2-yl derivatives. Crystal structure and absolute configuration of (+)-tricarbonyl(1S,2S,4R,5R,6S)-C,5,6,C,-η-(5,6-dimethylidenebicyclo[2.2.2]oct-2-yl p-bromobenzoate)iron (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1349-1353 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The title complexes have been derived from tricarbonyl [(1R,4S,5S,6R,)-C,5,6,C-η-(5,6-dimethylidenebicyclo[2.2.2]oct-2-ene)]iron (1.). The crystal structure and absoulte configuration of (+)-tricarbonyl (1S,2S,4R,5R,6S)-C,5,6,C,-η-(5,6-dimethylidenebicyclo[2.2.2]oct-2-yl p,-bromobenzoate)]iron ((+)-6) determined by X-ray diffrac-tion studies proved earlier attribution of the relative configuration (endo us. exo,) of the tricarbonyliron moieties in complexes 1 and 2 of 5,6-dimethylidenebicyclo[oct-2-ene. The structure of (+)-6 confirms the absolute configuration derived earlier from circular-dichroism spectra of 5,6-dimethylidenebicyclo[2.2.2]oct-2-yl esters and 5,6-dimethylidenebicyclo[2.2.2]octan-2-one.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710546
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  • 198
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    Photocycloadditions of 2-(trimethylsilyloxy)-1,3-butadiene to 2-cycloalkenones. Access to the basic pentalenolactone skeletonPreliminary communication: [1]. (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1392-1398 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [2 + 2] Photocycloaddition of 2-(trimethylsilyloxy)-1,3-butadiene to a number of 2-cycloalkenones proved to be quite a general reaction leading to good yields of the cycloadducts (Table). This finding is surprising since dienes, in general, are better known as quenchers of enone triplets rather than as photochemical reactants. Both the high substrate concentrations, which can be employed in these cycloadditions, and the remarkable regio and stereoselectivity of the processes qualify them as valuable for syntheses. In a first application, the photoproducts 1a, b were transformed in three steps into a viable precursor 4 of the pentalenolactone-G and -H antibiotics.
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/hlca.19880710603
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  • 199
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    Transition-Metal Complexes with Bidentate Ligands Spanning trans-Positions. Part XVIIPart XVI: see [1].. Some platinum(II) complexes with anionic ligands such as methoxide, formate, carboxylate, hydride, and borohydride, and the X-ray crystal structure of [PtHCl()] (PP = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene) (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1442-1457 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complexes trans-[PtXY(2] (X = H or Me; Y = OMe, OCHO, CO2H, and BH4; 2 = 2,11-bis{bis[3-(trifluoromethyl)phenyl]phosphinomethyl}benzo[c]phenanthrene) were prepared, and their decompositions to trans[PtHX(2)] were studied. Some binuclear hydrido-bridged complexes, e.g.[(2)HPt(μ-H)PtH(2)]+, were also obtained. The preparation of complexes trans-[PtHX(28)2] (X = H or Me, 28 = bis[3-(trifluoromethyl)phenyl]benzylphosphine) is also reported. The X-ray crystal structure of trans-[PtHCl1)] (1 = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene) was carried out.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710608
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  • 200
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    Singlet-Oxygen Quenching by Carotenoids: Steady-state luminescence experiments (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1005-1010 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The near-infrared luminescence of singlet oxygen (1O2) has been measured in order to determine the efficiency of 1O2 quenching by two carotenoid compounds, β-carotene and canthaxanthin. 1H-Phenalen-1-one and rose bengal have been used as photosensitizers in those steady-state luminescence experiments. Stern-Volmer analysis of the 1O2 luminescence in solutions of CCl4 and CD3OD, containing different concentrations of the carotenoids, has shown a very efficient quenching by canthaxanthin. The rate constants are about a factor of 2 below the diffusion limited values for the given solvents, confirming earlier results in benzene. In comparison, the efficiency of 1O2 quenching by β-carotene is slightly lower than that by canthaxanthin in non-polar solvents and is reduced by an order of magnitude in CD3OD, due to the aggregation of this quencher.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/hlca.19880710510
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