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  • 1985-1989  (5,460)
  • 1988  (5,460)
  • Polymer and Materials Science  (3,199)
  • Analytical Chemistry and Spectroscopy  (1,301)
  • Engineering  (598)
  • Engineering General  (570)
  • Atomic, Molecular and Optical Physics  (222)
  • Life Sciences (general)  (140)
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  • 1985-1989  (5,460)
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  • 101
    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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  • 102
    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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  • 103
    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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  • 104
    Electronic Resource
    Electronic Resource
    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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  • 105
    Electronic Resource
    Electronic Resource
    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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  • 106
    Electronic Resource
    Electronic Resource
    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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  • 107
    Electronic Resource
    Electronic Resource
    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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  • 108
    Electronic Resource
    Electronic Resource
    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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  • 109
    Electronic Resource
    Electronic Resource
    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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  • 110
    Electronic Resource
    Electronic Resource
    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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  • 111
    Electronic Resource
    Electronic Resource
    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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  • 112
    Electronic Resource
    Electronic Resource
    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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  • 113
    Electronic Resource
    Electronic Resource
    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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  • 114
    Electronic Resource
    Electronic Resource
    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.
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    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.
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    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.
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    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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    URL: http://dx.doi.org/10.1002/bip.360270109
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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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270112
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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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    URL: http://dx.doi.org/10.1002/bip.360270111
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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 
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    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Using 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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    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.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270208
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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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    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360270214
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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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    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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    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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    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.
    Additional Material: 8 Ill.
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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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    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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    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.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270607
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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 
    Details
    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.
    Additional Material: 8 Ill.
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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 
    Details
    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.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/bip.360270510
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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 
    Details
    ISSN: 0006-3525
    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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  • 135
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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 
    Details
    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.
    Additional Material: 8 Ill.
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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 
    Details
    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.
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    URL: http://dx.doi.org/10.1002/bip.360270605
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  • 137
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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.
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    URL: http://dx.doi.org/10.1002/bip.360270611
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  • 138
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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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  • 139
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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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  • 140
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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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  • 141
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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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  • 142
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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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    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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  • 144
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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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  • 145
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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.
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    URL: http://dx.doi.org/10.1002/bip.360271111
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  • 146
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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.
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  • 147
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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.
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    URL: http://dx.doi.org/10.1002/bip.360271108
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  • 148
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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.
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    URL: http://dx.doi.org/10.1002/bip.360271110
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  • 149
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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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  • 150
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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.
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    URL: http://dx.doi.org/10.1002/bip.360271203
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    Erratum (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 585-585 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330614
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  • 152
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    Theoretical studies on conformational preferences of model modified nucleic acid base N6-(N-alanylcarbonyl) adenineNCL Communication No. 4069. (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 37-46 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Conformational preferences of model modified nucleic acid base N6-(N-alanylcarbonyl) adenine, ac6Ade, have been investigated using the quantum chemical PCILO (perturbative configuration interaction using localized orbitals) method. The multidimensional conformational space has been searched using selected grid points formed by combining the various torsion angles that take favored values derived from energy variation with respect to each torsion angle individually.The preferred molecular structure is stabilized by an intramolecular hydrogen bond from N(11)H of the amino acid to N(1) of the adenine. The observed crystal structure conformations for the naturally occurring, anticodon adjacent, threonyl analogs, tc6Ade, correspond to the predicted most stable conformation for the model modified base ac6Ade. Three stable, low energy conformations differing in the orientations of the carboxyl group and the amino acid side chain are predicted within 1 kcal/mol of the most stable structure. The possible bifurcated hydrogen bonding of N(11)H with N(1) and either of the carboxyl oxygens is of minor significance.The indicated orientational flexibility for the carboxyl group and the amino acid side chain may enable convenient probing of the molecular environment, in the vicinity of the anticodon in tRNA, by the amino acid substituent, with only modest changes in energy stabilization.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340106
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    Erratum (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 89-90 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340111
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  • 154
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    A regular periodic table of the elements and its quantum mechanical requirement (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 107-119 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By using the n + (1/2)l filling rule of the atomic Aufbau principle, where n is the principal quantum number and l is the azimuthal quantum number, a new periodic table is presented, its periods having, in order, 8, 18, 18, 32, 42, 50, … elements. The mentioned rule is proposed instead of the n + l rule (or Madelung's rule) which constitutes the quantum mechanical basis of the current periodic table and predicts periods having, in order, 2, 8, 8, 18, 18, 32, 32, 50, … elements. The new periodic table is called “regular” because its groups are formed according to a single rule (namely, the first elements of each period are placed in the same order as the elements of the preceding period), in contrast with the current periodic table, where no simple rule can be applied for the same purpose. The most characteristic feature of the regular periodic table is the fact that its groups are also related in a periodic manner.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340204
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  • 155
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    Control over theoretical descriptions of atoms and molecules. An information theoretic approach to the automatic classification and systematic improvement of approximate wave functions (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 185-190 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A rigorous approach to the study of the quality of theoretical descriptions of atoms and molecules is proposed. Theoretical descriptions, i.e., collections of atomic or molecular properties obtained via quantum chemical methods, are associated with information quantities defined with respect to reference theoretical or experimental data. In this way the comparison of two theoretical descriptions is reduced to the comparison of the respective information quantities. An increase in information is interpreted as improvement of the theoretical description. The aforementioned approach should be useful in problems related to classifications and systematic improvements of approximate wave functions and consequently for comparing the performance of quantum chemical methods in calculations of atomic and molecular properties. This approach should also constitute a powerful tool for the construction of suitable basis sets for use in calculations of atomic and molecular properties.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340209
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  • 156
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    Spin and charge densities from Hiller-Sucher-Feinberg identities. Test calculations for He, B, C, N, O, and F atoms and H2O, N2, and CH3 molecules (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 195-197 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340212
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  • 157
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    Fifth-order constant denominator perturbation therory within a localized bond model: Contributions from single and double excitations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 497-527 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Fifth-order constant denominator perturbation treatment of all single and double excitations occuring in the third-order perturbation wave function is presented for the perturbation configuration interaction using localized orbitals (PCILO) method. Contributions from triple and quadruple excitations which decay back to singles and doubles at third order are automatically included in this theory. This method is computationally very fast, with an execution speed proportional to N3, Where N is the number of orbitals present. A [2,1] Padé approximate involving only singles and doubles contributions through to fifth order is shown to be remarkably accurate.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330604
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  • 158
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    Hall transformation of exp( - r): Correction of the results (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 563-566 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Owing to an error in his determination of the repulsion integral and the kinetic energy. Hall's results [1] for the ground state of atomic two-electron systems are wrong. Here these results have been corrected. For Z ≤ 5, the results have been obtained by determining the pertinent integrals numerically: but for Z ≥ 5, these can be found sufficiently accurately from Z expansions.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330608
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  • 159
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    Ab-initio calculation of resonance states of H2O (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 567-576 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a dissociation attachment experiment of water, three peaks were observed at 7,9, and 12 eV. The origin of the third peak has been believed to be 2B2. However, the calculated energy of this state is 0.6 eV higher than the experimental value. This discrepancy is quite large compared with the case of the lower two peaks. In this study we propose new candidates for resonant states responsible for the third peak. The configurations considered are (3a1)-1(3pa1)2, (3a1)-1(3pb1)2, (3a1)-1(3pb2)2, (3a1)-1(3pa1)1(3pb1)1, (3a1)-1(3pb2)1(3pa1)1, and (3a1)-1(3pb2)1(3pb1)1 which have the parent state (3a1)-1(3pa1)1, (3a1)-1(3pb1)1, or (3a1)-1(3pb2)1. The energy levels arising from these configurations are calculated by a method of configuration interaction. A Few resonance states, which could be responsible for the third peak, are found. New decay process of these states are proposed.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330609
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  • 160
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    The sequential product of geminals and the ground states of some atoms (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 9-14 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By means of the SPG function which is associated with an extreme point of the set of N-representable second-order reduced density matrices, an attempt is made to perform the calculations of the ground states of some atoms with four electrons such as Be. The results show that the SPG function is as suitable as the well-known AGP function for approximating the ground states of atoms and molecules.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340103
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  • 161
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    A sequential product of geminals and its applications (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 15-23 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper, an SPG function, which is associated with an extreme point of the set of N-representable second-order reduced density matrices, is used to perform the calculation of the ground state energy of LiH with the variation of internuclear separation. The result of our calculation essentially is in accordance with that of AGP function.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340104
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  • 162
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    The concept of the topological atom within the MO-LCAO approach. II. On the nature of the nephelauxetic effect (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 1-8 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new MO-LCAO description of the nephelauxetic effect is proposed based on the concept of the topological atom and on the method of reduced density matrices. This approach allows one to overcome some conceptual difficulties of ligand-field theory and to derive effective parameters of d-d electron repulsion of a bound transition-metal in a proper way. The two ligand-field mechanisms of the nephelauxetic effect - the central field covalency and the symmetry-restricted covalency - are clarified and generalized. In addition, a new factor, important for the nephelauxetic effect is found: its size-dependence on the region of the topological atom.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340102
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  • 163
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    A Crystal Orbital approach for two- and three-dimensional solids on the basis of CNDO/INDO Hamiltonians. Basis equations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 47-71 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Hartree-Fock (HF) self-consistent field (SCF) crystal orbital (CO) formalism for two- and three-dimensional (2D/3D) solids on the basis of semiempirical CNDO/INDO (complete neglect of differential overlap; intermediate neglect of differential overlap) Hamiltonians is presented. The employed SCF variants allow for the treatment of atomic species up to bromine under the inclusion of the first (i.e., 3d) transition metal series. Band structure investigations of 2D and 3D materials containing more than 30 atoms per unit cell are feasible by the present SCF HF CO formalism. The theoretical background of the computational scheme is given in this contribution. Special emphasis is placed on physically reliable truncation criteria for the lattice sums, the adaptation of the crystal symmetry in k space, as well as the suitable choice of domains in Brillouin zone (BZ) integrations required in the determination of charge-density matrices. The capability and limitations of the semiempirical SCF HF CO approach is demonstrated for some simpler solids by comparing the present computational results with those of ab initio CO schemes as well as conventional numerical methods in soid-state theory. The employed model solids are graphite and BN (2D and 3D networks for both solids) as well as diamond, silicon, germanium, and TiS2.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340107
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  • 164
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    Long distance electron transfer (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 1-22 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantum mechanical models to treat long distance electron transfer are being developed. The model is based on the theory of R.A. Marcus. Our contribution is in the calculation of the electron coupling factor k. Estimations of the latter number, as well as the bond and solvent relaxation energies, λi and λo, respectively, are necessary to be able to calculate the rate constant for a reaction of the conductivity in an electric field. k may be approximately calculated from orbital energy differences at avoided crossings between orbitals localized in different parts of the system. A novel spectroscopic NDO method is suggested in which one may include any atom of the periodic table. Another problem discussed is the inclusion of electronic relaxation effects of the solvent or protein in the calculation. Applications are made to systems where metal ions are connected by organic bridges of different kinds such as dipyridine with coplanar and perpendicular pyridyl groups. As expected the electronic factor depends strongly on the conformation of the bridge. A strong conformational dependence is also obtained for a saturated bridge of the type NH2 · (CH2)n · NH2. In another study we use an α helix as a bridge between two metal ions. If one glycine in this α-helix is substituted by phenylalanine the electronic factor increases by factors of 1.5-10. It is suggested, however, that larger enhancement factors are possible if an aromatic group is positioned in a favorable way. The CNDO/S method is used to study the charge separation process in a bichromophoric molecule and in the reaction center (RC) of Rhodopseudomonas viridis. In those cases where the electronic coupling is large enough for the charge transfer states to be seen in the spectrum, the calculated results agree well with the experimental ones, but suggest a novel assignment. The CNDO/S results verify that electron transfer is possible through saturated spacers. In the special pair of RC the S1 state is calculated at approximately the correct position. Like the ground state, it has a delocalized character.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340704
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  • 165
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    Electrostatic interactions and conformation of some thromboxane antagonists (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 67-84 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A class of thromboxane antagonists exists where the prostaglandin side chain containing the C16 hydroxyl moiety is replaced by a phenyl ring, and the bridged six-membered pyranose moiety by cyclohexane, pyranose and dioxane ring systems. Analysis of antagonist potency data in terms of a binding constant model previously used for membrane bound receptor-drug interactions shows that the major patterns of antagonist potency are governed as much by axial/equatorial conformer preference of the phenyl moiety and its orientation as by electrostatic effects of the aliphatic ring oxygen atoms. The conformational restriction of the two substituted side chains of the σ-bonded 6-membered ring is shown to be a primary requirement for binding to thromboxane receptors, and a quantitative separation of electrostatic and conformational components in the potency data is attempted.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340708
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    An ab initio molecular orbital study of hydrogen bonding and ion-molecule association in model systems for DNA bases (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 119-135 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ab initio calculations have been performed to investigate hydrogen bonding and ion-molecule association in complexes of H2O with the neutral, protonated, and Li+ complexes of N-formylformaldehyde and N-formylformamidine. In the complexes with the neutral bases, H2O assumes an in-plane bridging position in the amide and amidine regions. The most stable complex is the bridging N-formylformamidine-H2O complex in the amidine region, which has an MP2/6-31 + G(d,p) binding energy of -9 kcal/mol. Hydrogen bonded complexes of H2O with the oxygen-protonated bases have open structures with the protonated bases as proton donors, and binding energies ranging from -16 to -24 kcal/mol. Nitrogen protonation of N-formylformamidine leads to an equilibrium chelated hydrogen bonded structure with a stabilization energy of -21 kcal/mol. When Li+ associates with these bases at a carbonyl oxygen, hydrogen-bonded bridging structures with H2O reappear, and wobble complexes exist in the amide and amidine regions of N-formylformaldehyde and N-formylformamidine. These complexes have binding energies of -13 to -14 kcal/mol. However, the most stable comples has H2O directly bonded to Li+, with an MP2 binding energy of -30 kcal/mol. No hydrogen bonded structures of H2O with N-formylformamidine exist in the amide region when Li+ associates with this base at the C=N group. Hydrogen bond energies computed at the single-determinant Hartree-Fock level with the 6-31G(d) basis set approximate correlated MP2/6-31 + G(d, p) energies to within 1 kcal/mol for all of the neutral and charged complexes. However, when H2O is bonded to Li+, HF6-31G(d) association energies overestimate MP2/6-31 + G(d, p) energies by 3 kcal/mol.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340712
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    Dependence of MO shapes on a continuous measure of delocalization (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 1-13 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Whereas localization of orbitals has long been a tool for a semiclassical interpretation of chemical properties, it is in fact electron delocalization that is a fundamental property of quantum mechanical molecules. A mathematically well-defined measure is suggested for the degree of delocalization of molecular orbitals. It is shown that an orbital set of maximum delocalization exists for which the degree of delocalization depends on the charge distribution of the molecule. Hartree-Fock canonical orbitals are definitely more localized than the most uniformaly distributed MO's giving an equivalent description of the molecule. The changes in the geometrical shape of molecular orbitals are studied passing (quasi-) continuously from the strongly localized description towards the most delocalized picture. In the case of charge-inhomogeneities even the most delocalized orbitals remain rather compact. The degree of maximum delocalization may be correlated with chemical properties such as reactivity. The shape distortion of MO's under the perturbing effect of other ions and small molecules is investigated in several examples.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340804
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  • 168
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    Density and density matrix from optimized linearly independent product basis functions for Be (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 43-49 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The density matrix was computed from the density using basis orbitals which form linearly independent products (LIP). Calculations were performed on the Be atom using LIP bases containing several of the natural spin orbitals from an accurate nonrelativistic 650-term configuration interaction (CI) wavefunction. Calculations were also performed using a basis set of 6 s-type orbitals optimized so that the lowest eigenvalue, d1, of the overlap matrix of products is maximized and the energy of a small CI wavefunction is minimized. The value of d1 in the optimized basis is 1 × 10-7. The density and the potential energy obtained from the 650-term CI wavefunction were accurately reproduced by the density matrix expressed in the optimized LIP basis, but the kinetic energy was somewhat less accurate.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340809
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  • 169
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    Geometry optimization using local-density functional methods: Numerical aspects (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 77-84 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The need to perform a numerical integration of the exchange-correlation functional because of its non-analyticity severely complicates the accurate application of local-density functional methods to molecules and clusters. The optimal choice of grid points for this integration and the estimation of the error made by the choice are subtle considerations. In particular, because the position and/or weighting of each grid point must change when the nuclear positions change, these errors are most noticeable when different geometries are compared. We have determined a method of grid point selection and weighting that reduces these errors. We have also determined a simple method of estimating the extent of the error made in the particular density of points used for the grid. These results are illustrated for a selection of small molecules.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340813
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    Topological electronic rules for polycyclic hydrocarbons - quantum chemical deductions directly from structural formulas (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 143-147 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All bicyclo[p.q.0] conjugated hydrocarbons are found to fall into ten homolog classes each characterized by the numbers of nonbonding, bonding, and antibonding molecular-orbitals of its first prototype and by the prototype itself. The energy level patterns are obtained by the new “structural covariance” pictorial rules directly from structural formulas. The HOMO-LUMO types, aromaticity or three types of nonaromatic behavior, and reactivities towards nucleophiles or electrophiles thereby also result.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340818
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  • 171
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    Calculation of harmonic frequencies and harmonic force fields by the hartree-fock-slater method (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 173-181 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Results are presented from Hartree-Fock-Slater (HFS) calculations on harmonic frequencies and force constants of H2O, H2S, NH3, PH3, CH4, SiH4, and C2H4. Both frequencies and force constants were calculated by a numerical (finite difference) differentiation of analytical energy gradients. It is shown by a comparison with experimental data and results from ab initio Hartree-Fock (HF) calculations that the HFS-method provides harmonic frequencies and force constants in at least as good agreement with experiment as the HF-scheme.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340821
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    A progress report on the status of the COLUMBUS MRCI program system (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 149-165 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The COLUMBUS program system is a collection of Fortran programs for performing general multireference single- and double-excitation configuration interaction (MRSDCI) wave function optimization based on the graphical unitary group approach. The program system also includes integral generation, SCF and MCSCF orbital optimization, integral transformation, and wave function analysis programs. The original program system was written in 1980 to 1981. Since that time, it has evolved into one of the most popular MRSDCI program systems used in the computational chemistry community. The discussion of this evolution will include the exploitation of efficient matrix-matrix and matrix-vector product computational kernels, the use of generally contracted symmetry-adapted orbital basis sets, general Hamiltonian diagonalization procedures, energy-based internal walk selection, flexible DRT specification, improved coupling-coefficient evaluation methods, coupled-pair functional and multireference CPF capabilities, and density matrix construction. The numerous versions of the program system that are maintained at different sites and on different computers are now in the process of being merged. The source code for this combined version will be made available to the computational chemistry community. The source code for a specific computer may be generated from the source code for another computer by a single pass through a simple filter utility that is included with the program system. The directly supported computers will initially include various models of VAX, Cray, FPS, IBM, CDC, and ETA machines with the addition of other machines shortly thereafter. The ongoing developments of the COLUMBUS system that are discussed include a new method for computing analytic energy gradients for MRSDCI wave functions. This effective-density-matrix based method avoids the “coupled perturbed MCSCF” solutions for each coordinate direction, avoids the transformation of any derivative-integral quantities from the AO to the MO basis, avoids the transformation of the coupling coefficients from the MO to the AO basis, allows a subset of the MCSCF doubly occupied orbitals to be frozen in the CI wave function, and allows the MRSDCI wave function to be generated from general reference CSFs that are not necessarily related to the MCSCF expansion CSFs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340819
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  • 173
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    Theoretical study of the geometry of Mn5 (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 231-236 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The geometry of Mn5 in rare gas matrices has been proposed to be a planar pentagon with 25 unpaired electrons. Simple unrestricted Hartree-Fock (UHF) calculations have been carried out using a basis of STO-6G for 1s, 2s, and 2p orbitals with STO-4G for 3s, 3p, 3d, 4s, and 4p in the HONDO5 program. The structure is optimized at the UHF level using the analytic gradient formalism for a planar pentagon. Binding energies and spinmixing are given for the optimized structure.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340827
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  • 174
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    Molecular hardness and softness parameters and their use in chemistry (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 349-366 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The semiempirical Atoms-in-a-Molecule (AIM) hardness matrix, η, is defined, using the usual finite difference formula, ηii = Ii - Ai, for the diagonal AIM hardness and the Ohno formula, ηij = 1/(a2 + R2ij)1/2, for the off-diagonal AIM hardness. The Ohno formula is shown to exhibit the correct asymptotic behavior and satisfies the relevant stability criterion. The normal displacements in the AIM electron populations are examined for pyrrole and N-methyl pyrrole, and their relation to the polarization channels is briefly discussed. The new AIM hardness matrix is also tested by comparing the predicted global hardnesses with the corresponding experimental finite difference data for selected diatomics and triatomics. Finally implications of the hardness combination rules are examined and the corresponding softness combination rules are used to calculate the regional and global softnesses of selected molecules. We examine how the regional softnesses reflect known trends in selectivity of protonation of five membered heterocycles, and comment on the signs of the AIM fukui function and the Hard-Soft-Acids-and-Bases principle.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340840
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  • 175
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    Electronic Resource
    Modified breit-pauli hamiltonian suitable for variational calculations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 425-430 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Breit-Pauli type Hamiltonian with an effective positive term in substitution of the Darwin term is proposed for variational calculations. The Hamiltonian is bounded from below and does not exhibit variational collapse. Calculations on one electron atoms for the ground state, 2pl/2 and 2p3/2 states are presented. The results essentially coincide with those obtained from first order perturbation theory.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340845
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  • 176
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    Electronic Resource
    Titanium in large silicon clusters (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 297-308 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The application of molecular ab initio methods to investigate the electronic structure of localized impurities in semiconductors requires the study of the convergence of the results with increasing cluster size. Here we compare results for interstitial Ti in silicon, obtained with clusters of increasing size: TiSi10H16, TiSi30H40, and TiSi66H64. These clusters contain one, two, or three shells of silicon atoms, respectively, centered around Ti at a Td interstitial site. The hydrogen atoms serve as saturators of the dangling bonds. The Si core electrons are replaced by an effective potential. The calculations are based on open shell RHF theory and limited CI extensions. The charge distribution in the central part of the three clusters is very similar. In the clusters the partially occupied orbitals are much more delocalized than the 3d orbitals in the free ions. The total impurity-induced electronic charge, however, is quite localized, due to the compensating response of the Si closed shell density. Ionization of the impurity also causes a compensating response of the Si closed shells: only about 10% of the density difference is in the impurity region and the major part is behind the outermost shell of Si atoms. Transition metal associated (3d-like) excitation energies are not very dependent on the cluster size, and the relative ordering of the lowest lying states remains unchanged. Impurity associated ionization energies decrease considerably due to the extra relaxation offered by the additional shells of Si atoms. Our results indicate that a reliable description of interstitial transition metals in silicon can be provided by calculations on reasonably small clusters: Si30H40 is sufficiently large.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340834
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  • 177
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    Theoretical kinetic and thermodynamic study on the disilene-silylsilylene isomerization (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 343-347 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The titled isomerization has been studied at the HF/3-21G level. The changes in thermodynamic functions, equilibrium constant K(T), conversion efficiency C(T), and the rate constant k(T) for the isomerization have been calculated using our energies of the reactant (R), transition state (TS), and product (P), their harmonic vibrational frequencies, and the classical and corrected barrier (by vibrational zero-point energies). In the range of temperature, 300-1200K, ΔH 〈 0, ΔS 〉 0 and ΔG 〈 0; i.e., it is exothermic, increasing in the entropy, and spontaneous reaction. ΔS≠ 〈 0, log A is about 12.0 ±0.15 (s-1), but the k(T) is from 2.627 × 10(-33) to 6.933 × 10(8) (5-1); i.e., it passes through a tight TS, the A factor changes little, but the rate constant varies rapidly with the temperature. These results agree with the fact that the isomerization occurs readily at high temperature. Furthermore, Newman's mechanism, 2SiH2 → (H2SiSiH2)* → (HSiSiH3)* → Si2H2 + H2, is supported. Similarly, the isomerization, HDSiSiH2 → HSiSiDH2, is also studied.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340839
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  • 178
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    Iteration of the many-particle schrödinger equation in momentum space (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 437-444 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A generalization of the Fourier convolution theorem is used to iterate the many-particle Schrödinger equation in momentum space. The method is applied using hyperspherical coordinates, with many-dimensional hydrogenlike wave functions as the starting point for iteration. The problem of angular integration is converted into a problem of differentiation by means of the theory of harmonic polynomials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340847
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  • 179
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    Relativistic CASSCF/CI calculations: Applications to transition metal dihydrides (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 465-476 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete active space MCSCF (multi-configuration self-consistent field) scheme (CASSCF) using relativistic effective potentials followed by configuration interaction and relativistic CI calculations provides a very good description of the electronic states and potential energy surfaces of transition metal dihydrides. Such calculations are of considerable value not only in our understanding of the transition metal-hydrogen bonding but also in the prediction of the barrier to insert the metal atom into the H2 bond. All-electron CASSCF/CI calculations are carried out on twelve electronic states of CoH2. Comparable RECP-CASSCF/CI calculations are also carried out to show that the RECP-CASSCF/CI calculations provide an accurate method for the investigation of transition metal compounds. The general method of RECP-CASSCF/CI calculations for molecules containing heavy atoms is described. The calculations on CoH2 are compared with similar calculations on ScH2, YH2, PtH2, and PdH2. A critical comparison of all these transition metal hydrides reveals that in general the low-spin excited metal atom inserts into H2 spontaneously while the high spin ground state atom has to surmount a large barrier.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340850
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  • 180
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    The nonabelian two-dimensional algebra and the franck-condon integral (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 503-505 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two mapping operators are used to relate the eigenstates of two distorted and displaced oscillators. It is found that these operators satisfy a nonabelian two-dimensional algebra. We exemplify the method by calculating the Franck-Condon integral for the case of two harmonic oscillator wells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340855
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  • 181
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    Use of quantum mechanical models in studies of reaction mechanisms (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 557-566 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problems involved in determining the mechanisms of reactions by quantum mechanical calculations are discussed. Various precautions must be taken if the results of any calculation are to be chemically meaningful. Ab initio studies of reactions must also be carried out at a high level, using large basis sets and allowing for electron correlation. Such calculations are usually restricted to the simplest example of a reaction, which is often untypical. More information can usually be obtained at far less cost through AM1 calculations for a number of examples of a reaction for which experimental data are available. These points are illustrated by recent studies of the Cope rearrangement.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340860
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  • 182
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    Symbolic computation in quantum mechanics. Several simple examples (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 537-548 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this article is to illustrate the use of symbolic computation in solving some problems in quantum theory. Emphasis will be given to the possibility of manipulating expressions symbolically and to the interface of numerical and algebraic languages. The illustrate the use of the scientific computation language Maple as a research tool, we present our work on lower energy bounds for anharmonic oscillators and on the spherical Zeeman effect. Another example consists in the perturbation calculations of the N-dimensional hydrogen atom, keeping the quantum labels in general form. Further, we describe the interface of Maple, Fortran, and the typesetting language, Troff. The basic feature is illustrated on the application of the inner projection technique and of the method of intermediate Hamiltonians on the benzene molecule as well as on the geminal approach to the butadiene molecule; the main calculations were first done in Maple and then transferred into Fortran's notation so that Fortran subroutines could be used. Finally, the results either in Maple or in Fortran can be transferred to a Troff file.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340858
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  • 183
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    Simple models for describing the fragmentation behavior of multiply charged cations (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 567-573 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The potential energy curve describing the fragmentation of a diatomic dication AB2+ is considered as arising from an avoided crossing between an attractive diabatic curve (correlating with A2+ + B) and a repulsive diabatic curve (correlating with A+ + B+). The simplest avoided-crossing (AC) model neglects diabatic coupling and polarization and leads to useful predictions of the transition structure bond length (rTS) and the kinetic energy released (T) in fragmentations of dicationic systems in which the difference (Δ1) between the ionization energies of A+ and B is small. When Δ1 is not small, it is necessary to include diabatic coupling and polarization in the treatment. The resultant ACDCP (avoided crossing with diabatic coupling and polarization) model provides very satisfactory estimates of rTS and T for both small and large Δ1. Its implementation requires only atomic ionization energy and polarizability data and comes at virtually no computational cost. Both the AC and ACDCP models are readily generalized to fragmentations of more highly charged cations.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340861
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  • 184
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    Electronic Resource
    Spatial correlation of electrons in metals (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 655-664 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of electron-electron repulsions is assessed, primarily in the expanded fluid alkali metals, by confronting experimental data on these systems with the predictions of theory. This is usefully divided into two types of approach: (i)full inclusion of the long-range Coulomb interaction e2/rij between electrons i and j, but perturbative treatment of electron-ion interaction and(ii)the simplified on-site interaction described by the Hubbard U.The main conclusion is that both electron-ion and electron-electron correlations are of major importance in the expanded fluid alkali metals, and especially in Cs. The momentum distribution of the conduction electrons is changed in a very important quantitative way from the predictions of the jellium model at the same density by the electron-ion interaction. This leads to a metal-insulator transition at a much higher electron density than the jellium prediction. The relevance of this conclusion to crystalline alkalis is finally referred to.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340867
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  • 185
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    Electronic Resource
    Electrostatic potential maps of flavone acetic acids: A new class of antitumor drugs (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 697-705 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complete geometry optimizations have been carried out with the AM1 method on flavone acetic acid and several of its derivatives. Molecular electrostatic potential maps have been used to predict new com.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340870
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  • 186
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    Electronic Resource
    Erratum (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 741-741 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340876
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  • 187
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    Masthead (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340101
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  • 188
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    Electronic Resource
    A spin-free form of valence bond theory (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 25-36 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Classical valence bond theory is recast in a spin-free form which provides a practicable route to ab initio calculations of molecular electronic structure. The approach is simple and direct and requires only efficient algorithms for the generation and processing of permutations and the handling of Rumer diagrams: it makes modest demands on computing power and pilot calculations have indeed been performed entirely within the fast memory of a personal computer, which should be sufficient for dealing with systems possessing up to 10 electrons outside a closed shell. Simple applications confirm the conclusion of Cooper et al. [1] that, by using strongly overlapping orbitals, a small number of classical (nonpolar) structures can give results close to those obtained in a “full CI” calculation.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340105
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  • 189
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    The role of hydrophobicity in the Ames test. The correlation of the mutagenicity of nitropolycyclic hydrocarbons with partition coefficients and molecular orbital indices (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 91-101 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A set of 20 nitropolycyclic aromatic hydrocarbons, whose mutagenicity has been determined in the Ames test, has been studied using octanol-water partition coefficients (P) as a measure of relative hydrophobicity and molecular orbital energies to account for variation in their electronic characteristics. A good structure-activity relationship was found using log P and ∊LUMO. The latter were taken from the results of ab initio calculations performed by Maynard, Pedersen, Posner, and McKinney [7] and were also calculated by the MNDO method. The dependence of mutagenicity on hydrophobicity was found to be similar to that observed for triazenes [2]. ∊LUMO values calculated by MNDO and STO-3G were found to be strongly correlated, and the role of hydrophobicity in correlating mutagenicity was not significantly affected by the molecular orbital model employed.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340202
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  • 190
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    Electronic Resource
    Molecular conformations and molecular shape: A discrete characterization of continua of van der Waals surfaces (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 517-526 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A characterization of molecular model surfaces is proposed. It is based on a graph associated with the van der Waals surface, defined by the detailed information on the interpenetration of van der Waals spheres of the constituent atoms. This “van der Waals graph” describes the three-dimensional body of the molecule, and it does not coincide in general with the less informative bond graph obtainable from the molecular skeleton.The description in terms of the graph reveals clearly the changes in molecular shape induced by conformational rearrangements. The nuclear configurations can be classified by the graph associated with the molecular surface, and the graph-theoretical analysis provides a rigorous partitioning of the configurational space based on shape properties.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340605
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  • 191
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    The use of symmetry in reciprocal space integrations. Asymmetric units and weighting factors for numerical integration procedures in any crystal symmetry (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 571-594 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic collection of spatial domains for reciprocal space integrations is derived for all possible crystal symmetries. This set can be used as a simpler alternative to the conventional Brillouin zones. The analysis is restricted to integrations where the function in the integrand satisfies inversion symmetry in k space. In this case only 24 different spatial domains have to be defined in order to allow for k space integrations in the 230 different crystal symmetries. A graphic representation of the asymmetric unit for each of the 24 integration domains is given. Special positions and the associated weighting factors required for numerical integrations in theoretical solid-state approaches are tabulated.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340609
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  • 192
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    Thermodynamic calculations on biological molecules (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 221-234 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Application of free-energy simulation methods to the calculation of thermodynamic properties for biologically relevant processes will be presented. Attention will be given to the usefulness of thermodynamic methods to explore the accuracy of empirical energy functions. Calculations of aqueous hydration and binding thermodynamics for drug molecules (trimethoprim and other related compounds) to biological targets (the enzyme dihydrofolate reductase) will be presented. In these applications we will discuss differences in “binding modes” for different drugs and the ability of thermodynamic methods to predict these changes. Finally, comments will be made regarding the free energy derivative methods and coordinate-coupled free energy calculations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340720
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  • 193
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    A rational selection of graph-theoretical indices in the QSAR (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 34 (1988), S. 267-285 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we have addressed an important problem: how to develop a strategy for identification of the topological indices which are most important in establishing a model for structure-activity analysis. In particular we consider a rational selection of graph theoretical (topological) indices in QSAR. The approach is illustrated by the study of the toxicity of ethers on mice. The indices examined include the connectivity indices based on adjacency matrix, the conceptually related graph distance indices, and an information theoretic index based on partitioning of electrons in various domains. We have outlined the similarities and differences and discuss advantages and limitations among different approaches. Our emphasis is on the problem how to select in a rational way appropriate graph-theoretical descriptors and how to introduce higher “corrections” in order to improve derived correlation.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560340724
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  • 194
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    Vibrational frequencies and assignments for some isotopomers of urcail using a scaled ab initio force field (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 1-17 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Vibrational frequencies and IR band intensities for 18 isotopomers of uracil, including deuterated 15N and 18O species, have been calculated using the scaled ab initio force field of Ref. 1. The results obtained are compared with available experimental data, and a number of refinements in former assignments are proposed. The good agreement between the calculated and experimental frequencies confirms the reliability of the scaled quantum mechanical-force field.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330102
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  • 195
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    The complexes of phenyl acetylene with HF, H2O, and NH3: An ab initio study (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 69-76 
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    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Phenyl acetylene complexes with HF, H2O, and NH3 are investigated with ab initio molecular orbital calculations using the 6-31G Gaussian basis set. HF is found to form a π complex, whereas H2O and NH3 form σ complexes. Observations of experimental spectroscopic shifts are rationalized.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330202
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  • 196
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    Announcement (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 169-169 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330208
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  • 197
    Electronic Resource
    Electronic Resource
    Masthead (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330301
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  • 198
    Electronic Resource
    Electronic Resource
    Masthead (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988) 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330401
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  • 199
    Electronic Resource
    Electronic Resource
    Self-consistent reaction field calculations on the proton transfer in ammonia-formic acid systems as a model for hydrogen bonding in amino acids in solution (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 41-52 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction field (RF) model of solvent effects, implemented within the SCF-CNDO/2 scheme of calculation, has been applied to analyze the proton transfer in the NH3…HCOOH system in the presence of several polarizable media. The aim of such a study was to characterize the tatutomeric equilibrium between the neutral and zwiterionic forms of H-bonded amino acids in aprotic solvents. Qualitative results concerning the energetics of this equilbrium show the stabilization of two different H-bonded complexes, corresponding to two separate minima in the free energy surface. These well known double minima potentials are found to be dependent on both the intermolecular N—O distance and the strength of the reaction field. The behavior of this model is qualitatively consistent with experimental observations of nitrogen-substituted amino acids in solution: both show, for low values of the dielectric constant, tautomeric equilibria where the H-bonded complexes appear to be more stable than the corresponding monomeric forms. The charge transfer process associated with the proton migration along the H-bond is also discussed. It is found that the amount of charge transferred increases with the N—O distance and with the RF strength, In order to test the general approach and compare it with previous work, calculations on the real monomeric systems glycine, β-alanine, and γ-amino butyric acid was also performed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330105
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  • 200
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    Electronic Resource
    Analytical potential from ab initio calculations for the Fe+-H2O and Feo-H2O systems (1988)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 77-85 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Analytical intermolecular potentials for the Fe+-H2O and Feo-H2O systems have been determined from ab initio calculations. Interaction energies for a lot of points along the two potential energy surfaces were calculated using Huzinga's MINI-2 basis set. The results obtained were fitted to an analytical function containing 11 adjustable parameters that we have already used with success for the Fe2+-H2O system. The goodness of the generated intermolecular potentials is discussed.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560330203
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