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  • 1991  (4,027)
  • Polymer and Materials Science  (3,577)
  • Atomic, Molecular and Optical Physics  (238)
  • Industrial Chemistry and Chemical Engineering  (212)
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  • 1990-1994  (4,027)
  • 1945-1949
  • 1935-1939
  • 1890-1899
  • 1860-1869
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Keywords
  • 101
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The introduction of mesogenic groups in main- and sidechains of epoxy thermosets results in an ordered multiphase network with cellular structure, if gelation occurs below the maximal cure temperature Tmax. Tmax is individual for a given combination of monomers. The multiphase network consists of relatively soft anisotropic cell nuclei and hard isotropic cell walls. If gelation occurs above Tmax single phase networks are obtained. The size of the cell nuclei strongly depends on the used monomers and varies up to two orders of magnitude. The multiphase structure was found to have no impact on the tensile elastic modulus.
    Additional Material: 13 Ill.
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  • 102
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 43-50 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The polymerisation of styrene and methylacrylate initiated by hydroperoxides is accelerated in the presence of strong acids such as sulfuric acid, p-toluene-sulfonic acid or perchloric acid. By copolymerising styrene and methylmethacrylate and by phenolic type inhibitors the radical nature of the catalytic effect of the acid was proved. Kinetic experiments demonstrated the acid involvement in the starting reaction.
    Additional Material: 4 Tab.
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  • 103
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 11-21 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: By modification of the resin matrix and by additives unsaturated polyesters result in materials with a large variety of properties. The mechanical values can be tailor-made by chemical modification of the polymer chain or rubber-like additives. Antistatic properties and electrical conductivity can be achieved by addition of carbon black, graphite or metallic fillers. Furthermore the thermal conductivity can be influenced. Other fillers improve the friction and wear behaviour or lead to a significant reduction of weight when microspheres are added. The tailored modification of properties effectively contributes to meet higher security requirements.
    Notes: Ungesättigte Polyester ergeben durch Modifizierung der Harzkomponente oder durch Additive Werkstoffe mit einem breiten Eigenschaftsprofil. Die mechanischen Werte sind durch chemische Modifikation der Polymerkette oder durch kautschukartige Additive gezielt einstellbar. Antistatische Eigenschaften und elektrische Leitfahigkeit lassen sich durch Zugabe von Rußen, Graphit oder metallischen Füllstoffen erreichen. Gleichzeitig kann auch die Wärmeleitfähigkeit beeinflußt werden. Andere Füllstoffe verbessern das Reibungs- und Verschleißverhalten oder können bei Zugabe von Mikrohohlkugeln zu deutlicher Gewichtsverminderung führen. Die gezielte Veränderung der Eigenschaften trägt wesentlich zum Einhalten erhöhter Sicherheitsanforderungen bei.
    Additional Material: 7 Ill.
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  • 104
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 23-32 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Duroplastische Formmassen werden nach konventionellen Verfahren der Kunststofformgebung wie Formpressen und Spritzgießen bzw. deren Varianten Spritzpressen und Spritzprägen verarbeitet. Wie in anderen Industriezweigen hat auch hier der wachsende Kostendruck zu einer steten Weiterentwicklung dieser Verfahren geführt. Über erfolgreiche Verfahrensverbesserungen zur Reduzierung der Herstellkosten wird im folgenden berichtet.Die Einführung der Spritzgießverarbeitung für Duroplaste in den 60er Jahren bedeutete gegenüber der bis dahin ausschließlich betriebenen Preßverarbeitung einen erheblichen Rationalisierungsschritt. Die Zykluszeiten ließen sich durch das Aufschmelzen der Formmasse in der Plastifiziereinheit sowie durch das Einbringen von Friktionswärme beim Einspritzvorgang erheblich reduzieren. Heute erlebt die Preßverarbeitung eine Renaissance insbesondere dann, wenn es gilt, hochpräzise Formteile mit minimaler Schwindung und geringstem Verzug herzustellen. Durch Rundtischautomaten, Vorplastifiziergeräte und Entnahmegeräte ließen sich die wirtschaftlichen Nachteile der klassischen Preßverarbeitung weitgehend kompensieren.
    Additional Material: 8 Ill.
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  • 105
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 51-60 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The crystallization and solidification behaviour of polyamides are influenced by additives such as nucleating agents or fillers. During processing morphological structures are obtained which affect the shrinkage, linear thermal expansion and dimensional changes due to water absorption. By studying the change of volume after water absorption, the dimensional change in length, breadth and thickness are easily understood.
    Notes: Additive in Polyamiden wie Nukleierungsmittel oder Verstärkungsmittel beeinflussen das Kristallisations- und Erstarrungsverhalten. Während der Herstellung von Probekörpern bilden sich morphologische Strukturen, die die Verarbeitungsschwindung, den linearen Ausdehnungskoeffizienten und die Dimensionsänderung während der Wasseraufnahme beeinflussen. Anhand der Volumenänderungen wird der Zusammenhang zwischen der Wasseraufnahme und der Dimensionsänderung in allen drei Raumrichtungen verständlich dargestellt.
    Additional Material: 5 Ill.
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  • 106
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 75-86 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(2,6-dimethyl-1,4-phenylene oxide) with exactly one functional endgroup was synthesized by oxidative polymerization, halogen substitution polymerization, and by phase transfer catalysis. Reaction with 4-vinylbenzoyl chloride resulted in a quantitative conversion to a macromonomer as shown by GPC and endgroup analysis. The macromonomer is a glassy material with a Tg from 150 to 190°C depending on the molecular weight.
    Additional Material: 4 Ill.
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  • 107
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Eigenschaften von Poly[1-(2-hydroxyethyl) aziridin] wurden im Hinblick auf die Komplexbildung für die Metalle Co(II), Zn(II), Ni(II), Cu(II), Cr(III), Fe(III), Cd(II), Pb(II) und Sr(II) in wäßriger Lösung untersucht. Die LPR-Methode beruht auf der Retention von anorganischen Ionen durch lösliche Polymere in einer Membran-Filtrationszelle und nachfolgender Abtrennung der niedermolekularen Anteile vom gebildeten Polymerkomplex. Die Wechselwirkung des hydrophilen Polymeren wurde als Funktion von pH und Filtrationsfaktor bestimmt. Nach dem erhaltenen Wechselwirkungsmuster bildet Cu(II) die stabilsten Komplexe mit dem Polyaziridin innerhalb des pH-Bereiches von 3 bis 7. Bei pH 3 ist es möglich, Cu(II) von allen anderen Metallionen zu trennen. Sr(II) wird im ganzen untersuchten pH-Bereich nur schwach retentiert. Bei pH 7 traten alle Metalle, außer Sr(II), mit dem Polymeren in Wechselwirkung und wurden nahezu quantitativ retentiert.
    Notes: The metal complexing properties of poly[1-(2-hydroxyethyl) aziridine] for the metals Co(II), Zn(II), Ni(II), Cu(II), Cr(III), Fe(III), Cd(II), Pb(II), and Sr(II) in aqueous phase were investigated. The LPR method is based on the retention of inorganic ions by soluble polymers in a membrane filtration cell and subsequent separation of low-molecular species from the polymer complex formed. The metal interaction with the hydrophilic polymer was determined as a function of pH and filtration factor. According to the interaction pattern obtained, Cu(II) forms the most stable complexes with the polyaziridine within the pH range 3 to 7. At pH 3, it is possible to separate Cu(II) from all other metal ions. Sr(II) is only slightly retained at the pH range investigated. At pH 7, all elements, except Sr(II), did interact with the polymer and were almost quantitatively retained.
    Additional Material: 2 Ill.
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  • 108
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 1-10 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Eine neue Klasse von Urethan-Acrylat-Monomeren wurde durch Umsetzung von Diisocyanaten wie Toluylendiisocyanat (TDI) und Hexamethylendiisocyanat (HMDI) mit Hydroxyethylmethacrylat oder Hydroxypropylmethacrylat und gesättigten Alkoholen wie Stearylalkohol oder Decanol hergestellt und durch IR- und NMR-Spektroskopie charakterisiert. Durch radikalische Polymerisation dieser Monomeren wurden Acrylatpolymere mit Urethanseitengruppen erhalten, die IR-spektroskopisch, viskosimetrisch und thermisch charakterisiert wurden.Die thermodynamischen Parameter des Polymerabbaus wurden berechnet; ein möglicher Abbaumechanismus wird vorgeschlagen.
    Notes: A new class of urethane-acrylic monomers was synthesized from diisocyanates such as toluylene diisocyanate (TDI) and hexamethylene diisocyanate (HMDI), unsaturated alcohols like hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), and saturated alcohols such as stearly alcohol and decanol. The monomers were characterized by IR and NMR spectroscopy. Urethane pendent acrylic polymers, obtained by polymerizing these monomers, were characterized by IR, solubility viscosity, and thermal studies. The thermodynamic parameters for the degradation were calculated and a probable degradation mechanism is proposed.
    Additional Material: 2 Ill.
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  • 109
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 33-39 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Umsetzung von Rizinusöl mit Toluylen-2,4-diisocyanat, Hexamethylendiisocyanat, Isophorondiisocyanat oder 4,4′-Diphenylmethandiisocyanat wurden Polyurethan-Präpolymere erhalten, die mit einem Epoxidharz aus Bisphenol-F und mit 1,3-Diaminopropan als Härter in Aceton homogen gemischt wurden. Mit diesen Mischungen getränkte Glasfasermatten wurden in einer Presse ausgehärtet; die Lösungsmittelbeständigkeit, elektrische Eigenschaften, Biegefestigkeit, Izod-Schlagfe-stigkeit und Rockwell-Härte der so erhaltenen Laminate wurde bestimmt. Die Abhängigkeit der elektrischen Leitfähigkeit σ von der Temperatur folgt der empirischen Gleichung σ = σ0, exp(-E/2kT).
    Notes: Prepolyurethanes were obtained by reacting the hydroxyl functionality of castor oil with diisocyanates, namely toluene-2,4-diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, and 4,4′-diphenylmethane diisocyanate, respectively. Homogeneous mixtures of prepolyurethanes and epoxy resin (prepared from bisphenol F in alkaline medium) were prepared in acetone containing 1,3-propanediamine as curring agent. Glass reinforced laminates were prepared by interacting PU/epoxy resin mixtures on glass cloth through compression moulding. The laminates were characterized by chemical resistance to solvents, flexural strength, izod impact strength, and Rockwell hardness. The variation of electrical conductivity σ with temperature was found to confirm with the empirical relation σ = σ0 exp(-E/2kT).
    Additional Material: 3 Tab.
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  • 110
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Menschutkin-Reaktion wurden Polyurethane mit kationischen Viologen-gruppen hergestellt. Die photochromen Eigenschaften dieser Polymeren in einer Poly(vinylalkohol)-Matrix wurden mit UV- und Laserlicht untersucht.
    Notes: The Photochromic properties by UV and laser irradiation of cationic polyurethanes with viologen groups introducted by Menschutkin reaction were studied and poly(vinylalcohol) was used as matrix.
    Additional Material: 7 Ill.
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  • 111
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 87-99 
    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: Im Rahmen dieser Arbeit wurden drei verschiedene Meßmethoden für die Bestim-mung der Kristallinität von Polyethylen angewandt. HDPE, LLDPE und LDPE-Pro-ben wurden  -  nach verschiedener Vorbehandlung  -  durch Dichtebestimmung, DSC und Raman-Spektroskopie untersucht. Die mit verschiedenen Methoden gewonnenen Resultate wurden verglichen, und Korrelationen wurden bestimmt.
    Notes: In this work three different techniques were used to determine the crystallinity of polyethylene. After different pretreatment HDPE, LLDPE, and LPDE samples were investigated by density measurements, differential scanning calorimetry, and Raman spectroscopy. The results were compared and relationships were estabilished between the values measured by the different methods.
    Additional Material: 5 Ill.
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  • 112
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 135-142 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Poly(N-vinylpyrrolidon-co-vinylamin) wurde mit Estern verschiedener Phosphorsäuren (Dimethylphosphit, Methanphosphonsäuredimethylester, Trimethylphosphat und Bis-(2-chlorethyl)-phosphonat methyliert, um physiologisch aktive Polymere zu erhalten. Die alkylierten Produkte wurden mittels IR- und NMR-Spektroskopie sowie Elementaranalyse charakterisiert. Der Alkylierungsumsatz hängt vom verwendeten Alkylierungsmittel ab. Die methylierten phosphorhaltigen Polymeren weisen Herbizidaktivität auf und könnten als Pflanzenwachstumshemmer verwendet werden.
    Notes: Alkylation of amino groups bounded to a polymer chain with esters of phosphorous acids was studied in order to obtain physiologically active polymers. Poly(N-vinyl-pyrrolidone-co-vinylamine) was chosen as a polymer-carrier. The phosphorous acid esters used were dimethyl hydrogen phosphonate, dimethyl methanephosphonate, trimethyl phosphate and bis-(2-chloroethyl)-hydrogen phosphonate. The composition and structure of the isolated final products was proved by IR- and NMR-spectroscopy and elemental analysis. It is established that alkylation takes place to various extents.The obtained alkylated phosphorous-containing polymers exhibit herbicidal activity and could find application as plant growth retardants.
    Additional Material: 4 Tab.
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  • 113
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 153-167 
    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: Um die Weichmacherpermanenz in PVC zu verbessern, wurde Decylmethacrylat (DMA) in Gegenwart eines Bleistabilisators (LS) mittels radikalischer Polymerisation auf PVC gepfropft. Die Molekulargewichte und Glastemperaturen der erhaltenen Produkte bestätigten, daß homogene PVC-g-PDMA-Copolymere entstanden waren.
    Notes: In order to improve the permanence of the plasticizer in a poly(vinylchloride) (PVC) compound we have studied the free radical polymerization and grafting of decyl methacrylate (DMA) onto PVC in the presence of a lead stabilizer. The influence of different parameters has been investigated and homogeneous PVC-g-PDMA copolymers have been obtained. Their molecular weights and the glass transition temperatures were consistent with the grafted nature of the copolymers.
    Additional Material: 8 Ill.
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  • 114
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The crosslinking behaviour of addition-crosslinking Wacker SilGel 600 silicone was investigated in the temperature range of 50 to 90°C with respect to its dependence on heating time. Measurements of the swelling of thin polymer films on special paper (Pecozet Z10) allow the observation of the swelling process which reaches the swelling equilibrium within a few minutes, the selection of a suitable swelling agent, and the rapid determination of the temperature dependence of the degree of swelling Q. Aside from Q, the „solubility parameter“ of the polymer network, the rate constants, and the activation energy of the crosslinking process can be obtained. Measurements of the swelling combined with determination of Huggins' interaction parameter additionally provide the possibility of determining the density of crosslinking of the polymer films.On the basis of these investigations, a rapid method for characterizing the sheathing of optical fibres could be developed. The cylindrical polymer films detach from the glass core during swelling in toluene (25°C). After 5 min the degree of swelling of the sheathing can be measured.
    Notes: Das Vernetzungsverhalten des additionsvernetzenden Silicons Wacker SilGel 600 wurde im Bereich von 50 bis 90°C in Abhängigkeit von der Heizzeit untersucht. Quellungsmessungen an dünnen Polymerfilmen auf Spezialpapier (Pecozet Z10) gestatten eine Verfolgung des in wenigen Minuten bis zum Quellungsgleichgewicht ablaufenden Quellprozesses, die Auswahl eines geeigneten Quellmittels und die schnelle Ermittlung der Temperaturabhängigkeit des Quellungsgrades Q. Neben Q sind der „Löslichkeitsparameter“ des Polymernetzwerkes, die Geschwindigkeitskonstanten und die Aktivierungsenergie des Vernetzungsprozesses zugänglich. Bei der Kombination der Quellungsmessungen mit einer Bestimmung des Hugginsschen Wechselwirkungsparameters kann auch die Vernetzungsdichte der Polymerfilme ermittelt werden.Auf der Basis dieser Untersuchungen konnte eine schnelle Methode zur Charakterisierung der Ummantelung von Lichtleitfasern entwickelt werden. Die zylindrischen Polymerfilme lösen sich während der Quellung in Toluol(25°C) vom Glaskern. Nach 5 min kann der Quellungsgrad der Ummantelung bestimmt werden.
    Additional Material: 11 Ill.
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  • 115
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 187 (1991), S. 207-224 
    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 Synthese und die thermischen Eigenschaften von zwei reaktiven, symmetrischen Azomonomeren und Modellverbindungen wurden untersucht, um thermolabile Mikrokapseln mit thermosensitiven Azogruppen herzustellen. Die Zerfallskinetik dieser thermisch und photochemisch instabilen Verbindungen ist von erster Ordnung, vergleichbar mit AIBN.Durch Grenzflächenpolykondensation der Azomonomeren mit Ethylendiamin, 1,6-Hexamethylendiamin oder Diethylentriamin wurden azogruppenhaltige Polyamide und Polyharnstoffe erhalten, aus denen thermosensitive Mikrokapseln hergestellt wurden. Mit optimierten Herstellungsbedingungen wurden in hohen Ausbeuten Mikrokapseln einheitlicher Größe mit guten Thermo-Transfer-Druckeigenschaften erhalten.
    Notes: In view of applying thermolabile microcapsules with azo groups as thermosensitive sites it was necessary to study the preparation and the thermal behaviour of two reactive, symmetrical azo monomer-compounds and model compounds. They are thermally and photochemically instable and the kinetics of their decomposition is of first order, comparable to that of AIBN.Azo group-containing polyamides and polyureas were prepared by interfacial polycondensation reaction from ethylendiamine, 1,6-hexamethylenediamine, diethylenetriamine and azo monomer-compounds.These polymers were used to prepare thermosensitive microcapsules. Favourable conditions were found to obtain microcapsules of uniform size, in a high yield, and with good properties in thermo-transfer-print.
    Additional Material: 15 Ill.
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  • 116
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 27-40 
    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 Fluorierung von Polyethylen und Polyvinylalkohol wurde mit Dichlordifluormethan CCl2F2 (Freon 12) unter Verwendung von Cobalt-60 γ-Strahlung bzw. elektrischer Lichtbogenentladung durchgeführt und der Einfluß von Reaktionstemperatur und -zeit, Katalysator, Verdünnung etc. untersucht. Dabei wurde bei Polyethylen sowohl die Fluorierung als auch die gleichzeitige Chlorierung beobachtet, wobei der Anteil an Fluorierung bei elektrischer Lichtbogenentladung gewöhnlich höher war als bei Verwendung von γ-Strahlung; in beiden Fällen war dennoch die Chlorierung deutlich bevorzugt. Bei Polyvinylalkohol konnten noch höhere Fluorierungs-bzw. Chlorierungsgrade ermittelt werden.
    Notes: Fluorination of polyethylene and polyvinyl alcohol was carried out by dichloro-difluoromethane under cobalt-60 gamma radiation and under electric spark discharge. The effect of temperature, reaction time, catalyst, inert diluent etc. was studied. Simultaneous chlorination of the polymer samples was observed along with fluorination. The extent of fluorination under electric spark discharge is usually higher than that under gamma radiation. Again, the extent of chlorination is higher than that of fluorination in both the cases. The extent of fluorination as well as chlorination is the highest in case of polyvinyl alcohol.
    Additional Material: 4 Ill.
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  • 117
    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: Celluloseacetatphthalat (CAP) mit einem Acetylgehalt von 19,5 Gew.-% und einem Phthalylgehalt von 21,4 Gew.-% wurde hergestellt und durch fraktionierte Fällung in fünf Fraktionen mit gleichmäßig abnehmendem Molekulargewicht aufgetrennt. Die Werte für das zahlenmittlere Molekulargewicht (M̄n) dieser Fraktionen wurden membranosmometrisch in 0,05 N NaHCO3 gemessen; die Werte für die Grenzviskosität ([η]) wurden ebenfalls von allen fünf Fraktionen bei verschiedenen Temperaturen bestimmt. Die Beziehung zwischen [η] und M̄n wurde nach der Mark-Houwink-Kuhn-Sakurada-Gleichung ausgewertet, und aus den dabei erhaltenen Werten für v zeigte sich, daß CAP offensichtlich ein sehr steifes Polymeres ist. Die Temperaturabhängigkeit der Viskosität verdünnter CAP-Lösungen wurde nach der Methode von Moore durch einen Arrhenius-Ausdruck beschrieben. Die Aktivierungsenergie der Durchflußgeschwindigkeit hängt sowohl von der Konzentration als auch vom Molekulargewicht ab; aus dem dabei erhaltenen empirischen Parameter Ke kann ebenfalls auf ein steifes Polymeres geschlossen werden.
    Notes: Cellulose acetate phthalate (CAP) having an acetyl content of 19.5 wt.-% and a phthalyl content of 21.4 wt.-% was prepared and fractionated into five fractions of regularly decreasing molecular weight. The values of the number average molecular weight (M̄n) of these fractions were measured in 0.05 N NaHCO3 by the help of high-speed membrane osmometer. The intrinsic viscosity [η] values for all the fractions of CAP in 0.05 N NaHCO3 were also determined at different temperatures. The Mark-Houwink-Kuhn-Sakurada equation was applied to the obtained results and the [η]-M̄n relationships for CAP have been established. The results of the values of v suggest that CAP is a stiff polymer. The temperature dependence of the viscosity of dilute CAP solutions has been described by an Arrhenius expression according to Moore's treatment. The activation energy of flow was found to depend on both concentration and molecular weight through an empirical parameter (Ke). The Ke value obtained for CAP also indicates that CAP is a rigid polymer.
    Additional Material: 6 Ill.
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  • 118
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 188 (1991), S. 63-72 
    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: Methylhydro-dimethylsiloxancopolymere wurden aus den Hydrolysaten von Dichlordimethylsilan mit 10, 20, 30, 50 und 70 Vol.-% Dichlormethylsilan hergestellt. Die Copolymeren wurden IR-, 1H-NMR-spectroskopisch und chemisch charakterisiert und als Härter für ein funktionalisiertes RTV-Siliconmaterial eingesetzt. Die Vulkanisateigenschaften wurden geprüft; die Copolymeren mit hohem Hydridgehalt verbesserten die mechanischen Eigenschaften und die thermische Stabilität der Vulkanisate.
    Notes: Synthesis of hydride terminated methylhydro-dimethylsiloxane copolymers from the hydrolyzates of 10, 20, 30, 50 and 70% vol.-% dichloromethylsilane with dichlorodimethylsilane have been carried out. The copolymers were characterized by IR-and 1H-NMR-spectroscopy and standard chemical analysis. They were used as curatives for a standard vinyl functional room temperature vulcanizing (RTV) silicone material based on addition cure, and the vulcanizate properties have been evaluated. The copolymers with high hydride content gave better mechanical properties and thermal stability to the vulcanizates.
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  • 119
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    Angewandte Makromolekulare Chemie 188 (1991), S. 73-84 
    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 thermischen Eigenschaften von Polystyrol and Poly(methylmethacrylat) mit verkapseltem und dispergiertem TiO2 wurden verglichen. Die verkapselnden Polymeren zeigen zwei thermische Relaxationsbereiche, deren nach Wunderlich ermittelte Aktivierungsenergien denen von dynamischen Dispersionen ähnlich sind. Es wird vorgeschlagen, daß die Niedertemperaturrelaxation durch lokale Änderungen der Konformation der Makromoleküle hervorgerufen wird, während die Hochtemperaturrelaxation dem normalen Glasübergang einschließlich der Wechselwirkung mit TiO2 vergleichbar ist. Das thermische Verhalten nahe der Zersetzungstemperatur in verschiedenen Atmosphären deutet darauf hin, daß in den verkapselnden Polymeren spezifische Strukturen vorhanden sind, die eine große Menge Sauerstoff adsorbieren können.
    Notes: Comparing the thermal properties of TiO2 encapsulating polystyrene and poly(methyl methacrylate) with those of TiO2 dispersion polymers it was found that the encapsulating polymers have two thermal relaxation regions. The activation energy of those thermal relaxation regions was determined using the Wunderlich method and it was found that the values are similar to the activation energy for the dynamic dispersion. It is suggested that the low-temperature thermal relaxation is caused by the local change of conformation of molecular chains, while the high-temperature thermal relaxation is similar to that of the normal glass transition temperature including the interaction with TiO2. In addition, the thermal behaviour near the degradation point in different atmospheres indicates that the encapsulating polymer has a specific structure for adsorbing a large amount of oxygen.
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  • 120
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    Angewandte Makromolekulare Chemie 188 (1991), S. 105-111 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Poly(3-dodecylthiophen) (PDDT) wurde auf chemischem Weg synthetisiert und 1H-NMR-, IR- und UV-spektroskopisch charakterisiert. Das bei Raumtemperatur aufgenommene ESR-Spektrum von PDDT zeigt einen g-Wert von 2.0091 und eine Linienbreite von 6.60 Gauss. Aus der Lösung gegossene und mit Iod dotierte PDDT-Filme hatten eine elektrische Leitfähigkeit von 12 S/cm.
    Notes: The chemical synthesis of poly(3-dodecylthiophene) is reported. The polymer was characterized by 1H-NMR, IR and UV absorption spectroscopic techniques. The room temperature electron spin resonance spectrum yielded a g value of 2.0091 and a linewidth of 6.60 Gauss. The solution cast polymer films after doping with iodine exhibited an electrical conductivity of 12 S/cm.
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  • 121
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    Angewandte Makromolekulare Chemie 188 (1991), S. 85-96 
    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: Zwei Methoden zur Herstellung hochmolekularer poröser “Bromamine” (—SO2NBr-Na+) mit Poly (styrol-co-divinylbenzol)-Matrix wurden untersucht, und zwar (a) die Einwirkung von Hypobromiten auf das die entsprechenden Sulfonamidseitengruppen enthaltende Copolymere, und (b) die Einwirkung von Bromiden auf das entsprechende hochmolekulare “Chloramin”. In beiden Fällen wurden Metallsalze des hochmolekularen “Bromamins” erhalten. Das Natriumsalz wurde mit einer 100-proz. Ausbeute an funktionellen Gruppen erhalten; es enthielt 2.1 mmol · g-1 —SO2NBr-Na+ Gruppen, d. h. 4.2 meq · g-1 aktives Brom. Es wurde auch die Stabilität des Harzes getestet, und zwar im Bereich von 20-100°C sowohl im trockenen Zustand als auch in wäßrigen Medien. Darüber hinaus wurden thermoanalytische Messungen bis 1000°C durchgeführt. Es wurden auch Beispiele für die Anwendung des“Bromamins” als polymeres Reagenz für Bromierungen (Iodierungen), Oxidationen, Wasserdesinfektion und Kationenaustausch gegeben. Dieses sehr reaktive polymere Reagenz kann ohne merklichen Verlust seiner Eigenschaften wiederholt debromiert und bromiert werden.
    Notes: Macromolecular pendant group N-monobromosulphonamide metal salts —SO2NBr-M+ having a macroporous styrene-divinylbenzene matrix structure have been obtained by two methods:(a) by the action of aqueous metal hypobromites on the appropriate macromolecular pendant group sulphonamide, and(b) by the action of an aqueous metal bromide on the appropriate macromolecular N-chlorosulphonamide metal salt.In each case the sodium salt product was obtained with a 100% functional yield and it contained 2.1 mmol.g-1 —SO2NBr-Na+ groups, i. e., 4.2 meq · g-1 of active bromine. The stability of the resin was investigated in the range 20-100°C in the dry state as well as in aqueous media.A thermoanalysis (TG, DTG, and DTA curves) was carried out up to 1000°C and its course was interpreted. The resin has brominating, oxidative, microbiocidic, and ionexchanging properties. It reacts in a reversible way: after the loss of the active bromine, it can be reactivated again.
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  • 122
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    Biopolymers 31 (1991), S. 511-518 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ability of tracts of synthetic oligopurine · oligopyrimidines containing both adenosine and guanosine residues to approach the conformation of analogous polypurine · polypyrimidines has been examined as a function of tract length by CD spectroscopy. Tracts of up to 19 contiguous, alternating dA and dG residues yield CD spectra that are distinctly different from that of the analogous alternating polymer. Thus the structural changes reflected in the unusual CD spectrum of poly[d(AG)] · poly [d(CT)] must require even longer tract lengths. Tracts of contiguous adenosines flanked by guanosine residues were seen to approach the CD spectrum of poly[dA] · poly[dT] quite slowly as a function of tract length, requiring more than 24 contiguous adenosines to give CD spectra similar to the homopolymer. These results lead us to the conclusion that oligopurine tracts in vivo are not well modeled by synthetic polypurine · polypyrimidines with one or two base pair repeating units.
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  • 123
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    Biopolymers 31 (1991), S. 537-545 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Oligomers of (-)-epicatechin with 4β → 8 interflavan bonds, and as many as five monomer units, have been studied by conformational analysis and time-resolved fluorescence. The conformational analysis yields 2x-1 conformations for each oligomer with x monomer units. There are two conformations accessible at each interflavan bond. These conformations are denoted by + and -. The dominant conformations for the trimer and higher oligomers have an interaction between the phenolic hydroxyl groups on monomers i and i+2. This interaction involves the hydroxyl group at C(5) on monomer i, and either C(13) or C(8) of monomer i+2, depending on whether the conformation of the two intervening interflavan bonds is + + or + -, respectively. Minor contributions to the ensemble for the tetramer and pentamer are made by conformations that contain the sequence of successive interflavan bonds denoted by -+ or --. In -+ the interaction between monomer units i and i + 2 involves an aliphatic hydroxyl with a phenolic hydroxyl, and there are no hydroxyl-hydroxyl interactions between units iand i + 2 in --. The onset of a different decay law for the fluorescence when x increases from 3 to 4 may be associated with the appearance of the -+ and -- conformations as minor constituents in the ensemble.
    Additional Material: 10 Ill.
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  • 124
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: C-terminal analogues of neuropeptide Y (NPY) of small molecular size have been synthesized. The influence of chain length, single or multiple amino acid substitution, and segment substitutions on receptor binding, pre- and postsynaptic biological activity, and conformational properties have been investigated. Receptor binding and in vivo assays revealed biological activity for NPY Ac-25-36 that increased with increasing α-helicity. In attempts to stabilize the α-helical content, three independent types of modified NPY Ac-25-36 analogues were synthesized. Strong agonistic activities could be detected in a series of discontinuous analogues, which are constructs of N-terminal parts linked via different spacer molecules to C-terminal segments. One of the most active molecules was NPY 1-4-Aca-25-36 (Aca, ε-aminocaproic acid). For the first time conformational properties of a series of small NPY analogues have been investigated by CD, and correlated with biological activity and receptor binding. A C-terminal dodecapeptide segment of NPY with an amount of 50% substitution to the native C-terminal sequence of NPY was found to exhibit significant receptor binding.
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  • 125
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possibility of using molecular dynamics techniques as a tool for simulated annealing is tested in the case of the molecule of biological interest N-acetyl, N′-methyl amides of 3(S)-hydroxy, 4(S)-amino 6-methyl heptanoic acid [(3S, 4S)-statine] and of its (3R,4S) diastereomer. The approach is able to reach global minimum in the conformational space in the case of the mentioned molecule. A description of the method is given. The use of fractional fluctuations of the internal potential energy as an indicator able to point out transition from a given minimum region to a deeper one is investigated. The results about the lowest energy conformation of (3S,4S) diastereomer are in fairly good accordance with the results obtained in the case of search within the whole Conformational hyperspace.
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  • 126
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Automated assignment of proteins is greatly simplified using data from 3D-nmr spectra. A strategy is presented which makes use of 3D-TOCSY-TOCSY and 3D-TOCSY-NOESY; its potential is demonstrated with the example of the spectra of BPTI.The discussion of the potential of 3D-nmr includes the introduction of a simple graph for the description of the information content of multidimensional nmr spectra.
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  • 127
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    Biopolymers 31 (1991), S. 725-733 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,4-Piperazine and 4-hydroxy proline, two small cyclic polyfunctional systems with defined stereochemistry, were introduced as “molecular scaffolds.” We define a “bioactive topology,” which is a derived putative low-energy conformation obtained through theoretical conformational analysis of substance P. Substitution of these molecular scaffolds by pharmacophors characteristic of the bioactive topology of the C-terminal hexapeptide of substance P resulted in active, partially nonpeptidal substance P mimetic agonists. The study discusses the concepts arid tools used to achieve this structural transformation, and points out the need to address flexibility-rigidity issues in an attempt to maintain sufficient molecular plasticity.
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  • 128
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 21-peptide amide antibiotic gallidermin is a potential therapeutic against acne disease. It belongs to the class of polycyclic lanthionine and α,β-clidehydroamino acids containing polypeptides, which were named “lantibiotics.” The structural gene of the recently elucidated lantibiotic gallidermin encodes a precursor peptide containing Ser, Thr, and Cys residues in the Oterminal prolantibiotic part, and an unusually hydrophilic leader peptide. The ribosomally synthesized pregallidermin is posttranslationally modified and processed to a complex peptide antibiotic with four/sulfide rings and two unsaturated residues.The complete solution structure of gallidermin was determined in triffuoroethanol : water (95 : 5) and dimethylsulfoxide by two-dimensional 1H-nmr at 500 MHz, using a combination of double quantum filtered correlated spectroscopy, homonuclear Hartman-Hahn, and nuclear Overhauser enhancement spectroscopy experiments. Using a total number of 152 distance constraints from NOEs and 14 torsional constraints, derived from coupling constants, we obtained a screwlike solution structure of gallidermin. Restrained molecular dynamics simulations yielded a set of five converging structures with an atomic rms difference of 1.7 Å for the backbone atoms, not dependent on the starting structure. The spatial structure model is in excellent agreement with the amphiphilic and channel-forming properties of gallidermin on membranes and its tryptic cleavage at the exposed site between residues 13 and 14.
    Additional Material: 5 Ill.
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  • 129
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have solved the crystal structures of nine pseudo-peptide analogues deriving from the hydrazino analogue of glycine or valine (NβH2-NαH-CαHR-CO2H, R = H or iPr) or proline (NβH2-Nα-CαH-CO2H) and containing the hydrazide (CO-NβH-Nα) or Nβ-Z-aminoamide peptidomimetic link. This study gives access to the average geometry of these two links, to their inter- and intramolecular interaction modes, and to their influence on the conformational properties of the molecules.
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  • 130
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    Biopolymers 31 (1991), S. 1471-1481 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: DNA is generally found within viruses and cells in a tightly packaged state, typically occupying only 10-4-10-6 of the volume of the uncondensed DNA wormlike coil. Condensation can be induced in vitro at low salt by the naturally occurring polyamines spermidine3+ and spermine4+, by hexammine cobalt (III), and even by Mg2+ in methanol-water mixtures. These condensates generally have an orderly, toroidal, or rodlike shape and size similar to that of DNA gently lysed from phage heads. It is also striking that the condensate size distribution is independent of DNA molecular length from 400 to 40,000 base pairs (bp), but that shorter DNA molecules (e.g., 150-bp mononucleosomal DNA) cannot condense in this fashion. We have constructed a successive association equilibrium theory to attempt to explain these results, using an equation devised by Tanford for micelle formation. Most of the obvious attractive and repulsive free energy contributions (mixing, bending, hydration, and other nearest-neighbor interactions) are linear in the amount of DNA incorporated, but the net attractive ΔG° grows nonlinearly because of the increasing average number of nearest neighbors of each duplex as the particle grows. In order that the size distribution have a maximum, a quadratic repulsive free energy is also required, arising from the electrostatic self-energy of the incompletely neutralized particles. The net attractive free energy per base pair interaction is tiny, on the order of 10-3 kT. Despite the apparent generally correct order of magnitude of the various free energy terms, the calculated size distribution is smaller and narrower than observed experimentally. It appears that the size distribution of condensed particles is determined kinetically rather than thermodynamically. Very short DNA molecules cannot nucleate stable aggregates because they cannot develop adequate overlap, either internally or intermolecularly. A substantial fraction of rodlike condensates is observed in aqueous solutions only with a rather inefficient condensing agent, permethylated spermidine. This suggests that slow condensation kinetics may be required to overcome the high activation energy of highly distorted DNA bends or kinks at the turning points of rods. Evidence is reviewed that condensation may be associated with localized helix structure distortion provoked by condensing agents.
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  • 131
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    Biopolymers 31 (1991), S. 1503-1512 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of cyclic retro-inverso dipeptides - 2-[(4-hydroxy)benzyl]-5-benzyl-4,6(1H,2H,3H,5H)-pyrimidinedione (c[mPhe-gTyr]), 2-benzyl-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione (c[mTyr-gPhe]), and 2-benzyl-5-amino-5-[(4-hydroxy)benzyl]-4,6(1H,2H,3H,5H)-pyrimidinedione {c[(α-amino)mTyr-gPhe]} - were synthesized in order to define the minimum structural requirements for binding affinity with opiate receptors and biological activity. Although the first two compounds lack a free amine proposed to be necessary for receptor recognition, the c[mPhe-gTyr] and c[mTyr-gPhe] analogues serve as model molecules in conformational studies of the target analogue, c[(α-amino)mTyr-gPhe]. The cis- and trans-c[(α-amino)mTyr-gPhe] contain all the functional groups such as the amine and phenolic groups in the tyrosine, and the aromatic group in the phenylalanine, necessary for opiate activity. In addition, the c[(α-amino)mTyr-gPhe] analogues possess similar geometries to the Tyr-Pro part of morphiceptin (Tyr-Pro-Phe-Pro-NH2) whose high μ-receptor activity is attributed to conformations with the Tyr-Pro amide bond in a cis conformation because the peptide bonds assume a cis conformation. However, both analogues are inactive in the guinea pig ileum and the mouse vas deferens assays. This may result from wrong orientation of the benzyl group of the gPhe residue with respect to the (α-amino)mTyr residue.Conformational studies of these molecules using 1H-nmr spectroscopy and molecular mechanics calculations will be reported in the following paper. Results of conformational analysis should provide information about backbone-side-chain interactions in the retro-inverso peptide chains since all the fundamental structural elements of the retro-inverso peptides are included in these model systems even though the peptide bonds must assume a cis conformation.
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  • 132
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new model structure is proposed for the silk I form of the crystalline domains of Bombyx mori silk fibroin and the corresponding crystal form of poly(L-Ala-Gly). It was deduced from conformational energy computations on stacked sheet structures of poly(L-Ala-Gly). The novel sheet structure contains interstrand hydrogen bonds but is composed of antiparallel polypeptide chains whose conformation differs from that of the antiparallel β-sheets that constitute the silk II structure. The strands of the new sheet have a two-residue repeat, in which the Ala residues adopt a right-handed and the Gly residues a left-handed sheet-like conformation. The computed unit cell is orthorhombic, with cell dimensions a = 8.94 Å, b = 6.46 Å, and c = 11.26 Å. The model accounts for most spacings in the observed fiber x-ray diffraction patterns of silk I and of the silk-I-like form of poly(L-Ala-Gly), and it is consistent with nmr and ir spectroscopic data. As a test of the computations, the well-established β-sheet structure of silk II and the corresponding form of poly(L-Ala-Gly) have been reproduced. The computed energies for the two forms of poly(L-Ala-Gly) indicate that the silk-II-like form is more stable, by about 1.0 kcal/mol per residue. The main difference between the two structures is the orientation of the Ala side chains of neighboring strands in each sheet. In the Pauling-Corey β-sheet and in the silk II form, referred to as an “in-register” structure, the Ala side chains of every strand point to the same side of a sheet. In the silk I structure, referred to as “out-of-register,” the side chains of Ala residues in adjacent strands point to opposite sides of the sheet.
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  • 133
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational dynamics of α- (1 → 4)- and α- (1 → 6)-glucan homooligomers in the nanosecond time domain have been compared by measuring the 13C-nmr longitudinal relaxation times T1 for carbons of the terminal and interior sugar residues. Measurements are reported on monomeric glucose and on oligomers containing up to ten glucose residues at room temperature in aqueous solution at concentrations of 3 and 20 g/dL. The carbons of terminal residues display longer relaxation times than do those of interior residues, presumably as a consequence of a greater degree of conformational mobility of the chain ends. The T1s of the reducing terminal residues of all oligomers are significantly longer than those of the corresponding nonreducing termini, a phenomenon that we associate tentatively with the anomeric equilibrium at the reducing end. Carbons of the reducing terminal residues in the β-anomeric form relax more slowly than their α-anomeric counterparts. At 20 g/dL the mean T1s for carbons of the terminal and interior residues attain asymptotic behavior with increasing chain length at a chain length of about six residues, and carbons of the α- (1 → 4)-linked maltooligomers relax significantly more slowly than those of the corresponding α-(1 → 6)-linked isomaltooligomers. The T1s of both glucan series increase with decreasing concentration. This concentration dependence disappears below 3 g/dL, where the T1s of the two series of homoligomers are no longer distinguishable. This suggests that in dilute aqueous solution at room temperature viscous damping effects predominate over contributions to the T1-sensitive conformational dynamics from structural differences in the glycosidic linkage region. At 3 g/dL the approach to long chain-length asymptotic behavior is more protracted than at 20 g/dL, and the T1s of carbons of interior oligomeric residues appear to match the corresponding high-polymer behavior at a chain length of eight and greater.
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  • 134
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    Biopolymers 31 (1991) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 135
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We describe statistical mechanical theory that aims to predict protein stabilities as a function of temperature, pH, and salt concentration, from the physical properties of the constituent amino acids: (1) the number of nonpolar groups, (2) the chain length, (3) the temperature-dependent free energy of transfer, (4) the pKa's (including those in the native state) and their temperature dependencies. We calculate here the phase diagrams for apomyoglobin and hypothetical variant proteins. The theory captures essential features of protein stability including myoglobin's Tm vs pH as measured by P. L. Privalov [(1979) Advances in Protein Chemistry, Vol. 33, pp. 167-241] and its ionic strength vs pH phase diagram as measured by Y. Goto and A. L. Fink [(1990) Journal of Molecular Biology, Vol. 214, pp. 803-805].The main predictions here are the following: (1) There are three stable states, corresponding to native (N), compact denatured (C), and highly unfolded (U), with transitions between them. (2) In agreement with experiments, the compact denatured state is predicted to have enthalpy closer to U than N because even though there is considerable hydrophobic “clustering” in C, this nevertheless represents a major loss of hydrophobic contacts relative to configurations (N) that have a hydrophobic “core.” (3) C becomes more prominent in the phase diagram with increasing nonpolar content or decreasing chain length, perhaps thus accounting for (a) why lysozyme and α-lactalbumin differ in their denatured states, and (b) why shortened Staph nuclease molecules are compact. (4) Of major importance for protein calorimetry is Privalov's observation that the enthalpy of folding, ΔH (T, pH) is independent of pH. The theory accounts for this through the prediction that the main electrostatic contribution to stability is not enthalpic; the main contribution is the entropy, mainly due to the different distributions of protons and small ions in the native and denatured states.
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  • 136
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    Biopolymers 31 (1991), S. 1709-1720 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A systematic theoretical study of the CD of double-stranded poly (dG-dC) and its complexes with small molecules is presented. The intrinsic CD of the polymer and the induced CD of a transition belonging to a molecule bound to DNA are calculated using the matrix method. The calculations show considerable differences between pyrimidine-purine and purine-pyrimidine binding sites, and we find that the induced CD of a groove bound molecule is one order of magnitude stronger than that of an intercalated molecule. The results form a sound basis for interpreting the CD of ligand-DNA systems in terms of molecular geometry, interactions, and spectroscopy.
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  • 137
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    Biopolymers 31 (1991), S. 1737-1746 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations without explicit inclusion of solvent molecules have been performed to study the motions of Lewisa and Lewisb blood group oligosaccharides, and two blood group A tetrasaccharides having type I and type II core chains. The blood group H trisaccharide has also been studied and compared with the blood group A type II core chain. The potential energy surface developed by Rasmussen and co-workers was used with the molecular mechanics code CHARMM. The lowest energy minima of the component disaccharide fragments were obtained from conformational energy mapping. The lowest energy minima of these disaccharide fragments were used to build the tri- and tetrasaccharides that were further minimized before the actual heating/equilibration and dynamics simulations. The trajectories of the disaccharide fragments, e.g., Fuc α-(1 → 4) GlcNAc, Gal β-(1 → 4) GlcNAc, etc., show transitions among various minima. However, the oligosaccharides were found to be dynamically stable and no transitions to other minimum energy conformations were observed in the time series of the glycosidic dihedral angles even during trajectories as long as 300 ps. The stable conformations of the glycosidic linkages in the oligosaccharides are not necessarily the same as the minimum energy conformation of the corresponding isolated disaccharides. The average fluctuations of the glycosidic angles in the oligosaccharides were well within the range of ±15°. The results of these trajectory calculations were consistent with the relatively rigid single-conformation models derived for these oligosaccharides from 1H-nmr data.
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  • 138
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The solution conformation of tubulin-β(422-434)-NH2 (YQQYQDATADEQG-NH2) and its Nac-DATADEQG-NH2 fragment has been studied by two-dimensional 1H-nmr spectroscopy in CD3OH/H2O (90/10 v/v) at neutral and low pH. The 13 amino acid peptide is a segment of the C-terminal region of tubulin, and is directly involved in the selective binding site with microtubule-associated proteins MAP-2 and the τ protein. Based on correlated spectroscopy, total correlation spectroscopy, and rotating frame nuclear Over-hauser effect spectroscopy experiments, a complete assignment of all proton resonances was achieved, and the conformation of the backbone could be deduced from coupling constants, NH temperature coefficients, and nuclear Overhauser effects. The spectroscopic evidence indicates that the T8-Q12 section of both molecules forms one complete α-helical turn, stabilized by a NH(Q12)-C=O(T8) hydrogen bond. Furthermore, strong pH-dependent backfolding of the E11 side chain to its own NH proton was found. In addition, close proximity between the aromatic side chains of Y1, Y4, and the α-helical part, resulting in some substantial chemical shift changes when comparing the entire 13-mer with the octamer, could be explained in terms of a nonclassical kink in the DATA section. The conformational space is dominated by extended structures and the nonextended conformers are only a minor, yet spectroscopically clearly discernible entity. The presence of the α-helical region at the C-terminus of the 13-mer is important because binding studies of this peptide with MAP-2 indicate that the D10-E11-Q12-G13 fragment is critical for the binding interaction.
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  • 139
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absorption and CD spectra of the π-π* transition near 200 nm are calculated for helical (Pro)10 forms I and II with a variable proline ring conformation characterized by torsion angle χ2 in the range -60° to 60°. The spectra for poly (Pro) I are not sufficiently sensitive to χ2 to suggest a preferred ring conformation. The spectra for poly (Pro) II are more sensitive to χ2, and suggest preferred ring conformations near either or both of the χ2regions -50 ± 10° and 50 ± 10°.
    Additional Material: 4 Ill.
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  • 140
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    Biopolymers 31 (1991), S. 569-586 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved model for calculating the CD of polypeptides has been developed. Excited state wavefunctions were derived from CNDO/S (complete neglect of differential overlap, spectroscopic) calculations on N-methylacetamide. Four discrete peptide-localized transitions were employed: π0π*(NV1), π+π* (NV2), nπ*, and n′π*. Inclusion of the π+π*transition (λ0 = 140 nm) significantly improves the accuracy of the calculated CD spectra in the 180-250-nm region. Spectra were computed for various helical structures, including right-handed α-, αII-, ω-, π-, 310-, and poly(proline)I-helices, and the left-handed poly(proline)II-helix. Sensitivity to changes in the peptide backbone geometry and chain length are examined. Electronic factors such as ground-state charge distribution, hybridization effects, and basis set deorthogonalization have been investigated. The nonconservative nature of the poly (Pro) I and II CD spectra is reproduced, and the helix band present in earlier exciton calculations on the α-helix has been diminished.
    Additional Material: 13 Ill.
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  • 141
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    Biopolymers 31 (1991), S. 1087-1094 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ultraviolet hyperchromicity experiments indicate that in DNA duplex formation, a C-T mismatch is destabilizing in the center of a duplex, but behaves as a stable base pair at the terminus of a duplex. The C-T base pair is thought to contain two hydrogen bonds, but has thermodynamic parameters (ΔH° and ΔG° of dissociation) that are similar to a G-C base pair. AMBER molecular mechanics calculations were performed to study the possible structural properties of DNA duplexes with central and terminal C-T combinations. These calculations also indicate that a central C-T pair destabilizes a duplex, while terminal C-T forms a stable base pair. Hydrogen bonding between cytosine and thymine occurs only in the energy-minimized structures when the helix diameter decreases and the propeller twist angle between the bases increases. These changes are found to occur only at the end of a duplex in the calculations, which may explain the experimental results.
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  • 142
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    Biopolymers 31 (1991), S. 1115-1134 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An understanding of helix dynamics can aid in interpreting the motions of proteins. The conformational transitions that occur also appear to play a role in protein folding. Structural studies of isolated peptides in solution are just becoming available. However, detailed analysis of the helix-coil transition is still not available and will be difficult to obtain experimentally. For these reasons, we performed a long molecular dynamics simulation of polyalanine at high temperature. Using this approach, we obtain a description of the overall structure and inherent flexibility of the chain as well as a structural picture of the conformational changes that occur. In this way, we can address both equilibrium properties of the peptide and the dynamics and mechanism of the structural transitions. Our results correlate fairly well with the available experimental data and previous simulations aimed at addressing α-helix dynamics. The peptide spends the bulk of its time fluctuating between different conformations with intermediate helix contents. Transitions between highly ordered and highly disordered structures were rare, but they occurred rapidly. Our distribution of conformations favored collapsed states. Hence, our transitions to structures with high helical content were from fluctuating compact structures. The conversion between helix and coil occurred sequentially on a residue-by-residue basis. However, there was local cooperativity; the transition of a residue to the coil state was facilitated after a neighboring group became non-helical. The relevance of our results to protein folding is also discussed.
    Additional Material: 7 Ill.
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  • 143
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    Biopolymers 31 (1991), S. 1171-1180 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complex dielectric response of calf thymus DNA in aqueous saline solutions has been measured from 1 MHz to 1 GHz. The results are presented in terms of the relaxation of the incremental contributions to the permittivity and conductivity from the condensed counterions surrounding the DNA molecules. Measurements of the low-frequency conductivity of the samples also lends support to the condensed counterion interpretation.
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  • 144
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Neurotoxic peptides from venoms of scorpions and honey bees exhibit a consensus pattern in the two disulfide bridgings related to the sequence portions Cys-X-Cys and Cys-X-X-X-Cys. A revised three-dimensional structure of charybdotoxin, as determined by two-dimensional nmr spectroscopy, confirms that the consensus cystine dislocation generates in all these toxins a common structural element, i.e., the cystine-stabilized α-helical (CSH) motif, which may be correlated with their common ion channel blocking activity.
    Additional Material: 5 Ill.
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  • 145
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of valinomycin in a range of organic solvents of varying polarity and in detergent and lipid dispersions has been studied by Fourier transform ir Spectroscopy. In solvents of low polarity such as chloroform, ir spectra of valinomycin are fully consistent with the bracelet structure proposed on the basis of nmr Spectroscopy, showing a single narrow amide I component attributable to the presence of β-turns and a single band arising from nonhydrogen-bonded ester C=O groups. K+ complexation results in a downward shift in the amide I band frequency, indicating an increase in the strength of the amide hydrogen bonds, along with a shift to lower frequencies of the ester C=O absorption due to a reduction in electron density in these bonds upon complexation. Identical results were obtained with NH4+, a finding not previously reported.In solvents of both medium (CHCl3/DMSO 3 : 1) and high (pure DMSO) polarity, we find evidence of significant disruption of the internal hydrogen-bonding network of the peptide and the appearance of a band suggesting the presence of free amide C=O groups. In such solvents, complexation with K+ and NH4+ was not observed.The structure of valinomycin in detergent micelles resembles that in nonpolar organic solvents. However, changes were found in the amide I and ester carbonyl maxima as 2H2O penetrated the micelle which suggest significant interaction between the solvent and peptide. Complexation with K+ was reduced in cationic detergent micelles as a result of a decrease in the effective K+ concentration due to charge repulsion at the micelle surface.In lipid bilayers the structure again appears identical to that found in chloroform. As in detergent micelles, the amide I and ester carbonyl bands exhibit shifts that indicate interactions with solvent. Complexation with both K+ and NH4+ is efficient, producing spectral changes similar to those seen in organic solvents.
    Additional Material: 8 Ill.
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  • 146
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Modified self-consistent phonon theory when applied to the DNA double helix indicates the existence of fairly long-lived states in which single interbase H bonds are disrupted. One can then postulate a number of situations in which particular disrupted H bonds can enhance particular proton exchange. In this paper we postulate a number of such partially open states for a B-conformation GC base pair and calculate the probability of each of these states for a B-conformation poly(dG) · poly(dC). We compare these probabilities to those probabilities needed to explain various observed proton exchange rates. We propose that, for a GC base pair in B conformation, there are two amino proton exchangeable states - a cytosine amino proton exchangeable state and a guanine amino proton exchangeable state; both require the disruption of only the corresponding inter base H bond. The imino proton exchange, however, requires the disruption of all three inter base H bonds and this defines a third open state. Our calculated probabilities for a GC base pair in these three states are in fair agreement with available experimental estimates from measurements of amino and imino proton exchange.
    Additional Material: 1 Ill.
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  • 147
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Individual DNA molecules in the Mb size range were monitored by epifluorescence video microscopy during field inversion gel electrophoresis (FIGE). DNA migrating in an agarose gel gives rise to characteristic V-conformational elements and when doing so exhibits a reduced mobility. When the V-conformational elements per DNA molecule are few, the degree of retardation appears proportional to the number of V's, and since larger DNA species exhibit more V's, to DNA size. For a particular pulse frequency, the proportionality breaks down progressively as the number of V-conformational elements per DNA molecule increases. The loss of proportionality between DNA length and migration rate is being correlated with the macroscopically observed loss of electrophoretic size discrimination known as band compression. For a particular pulsing frequency and size class of DNA, the loss of size discrimination is thought to be due to the different orientations of migration, caused by the asymmetric distribution of V-conformational elements when the number of these elements is moderate. Small and very large DNA by contrast migrate with the direction of the biased field. These events, analyzed by microscopic measurement, are consistent with the known macroscopically observed double-valued mobilities in FIGE.
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  • 148
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    International Journal of Quantum Chemistry 39 (1991), S. 19-29 
    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 procedure for identifying redundancy in the Cartesian force constant matrix is described, and a prescription is given for generating the entire matrix of second derivatives from the minimal set of information. A proof is supplied which demonstrates that the number of nonredundant rows corresponding to a symmetry unique atom is necessarily less than three if the atom is invariant with respect to a symmetry operation of the point group other than the identity or inversion. Furthermore, only one row is required if the atom lies on a threefold or higher-order rotation axis. An application of the procedure to the evaluation of harmonic force constants by numerical differentiation of gradient vectors is briefly described.
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  • 149
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    International Journal of Quantum Chemistry 39 (1991), S. 31-45 
    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: An intermediate neglect of differential overlap (INDO) model for elements of the second transition series is described. Values of exponents for the radial portion of the Slater basis atomic orbitals, the orbital ionization energies, and the beta (or bonding) parameters for these elements are reported. Use of the model to investigate equilibrium geometries, relative energy ordering of geometric isomers, spectroscopic transition energies, energy ordering of state wave functions of different symmetry, trends in dipole moments, and equilibrium stretching frequencies is reported. The results indicate that the INDO method is capable of yielding quality results for species containing atoms of the second transition series.
    Additional Material: 11 Tab.
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  • 150
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    International Journal of Quantum Chemistry 39 (1991), S. 625-645 
    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 numerical properties of a two-dimensional integral representation [J. Grotendorst and E.O. Steinborn, Phys. Rev. A 38, 3857 (1988)] of the three-center nuclear attraction integral with a special class of exponential-type orbitals (ETO'S), the B functions [E. Filter and E.O. Steinborn, Phys. Rev. A 18, 1 (1978)] are examined. B functions span the space of ETO'S. The commonly occurring ETO'S can be expressed in terms of simple finite sums of B functions. Hence, molecular integrals for other ETO'S, like the more common Slater-type orbitals, may be found as finite linear combinations of integrals with B functions. The main advantage of B functions is the simplicity of their Fourier transform that makes the derivation of relatively simple general formulas for molecular integrals with the Fourier transform method possible. The integrand of the integral representation mentioned above shows sharp peaks causing, in the case of highly asymmetric charge distributions, slow convergence of the quadrature method used by Grotendorst and Steinborn. New quadrature schemes are presented that use quadrature rules based on Möbius transformations. These rules are well suited for the numerical quadrature of functions that possess a sharp peak at or near a single boundary of integration [H.H.H. Homeier and E.O. Steinborn, J. Comput. Phys., 87, 61 (1990)]. Numerical results are presented that illustrate the fact that convergence of the new quadrature schemes is about a factor two faster in case of highly asymmetric charge distributions.
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  • 151
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    International Journal of Quantum Chemistry 39 (1991), S. 681-688 
    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: An orbital transformation that minimizes the sum of the squares of the off-diagonal Hamiltonian elements between the singly excited configurations is described. The resulting single-excitations-adapted molecular orbitals (SEAMOS) are found to be very suitable for the description of electronic excited states. The test calculations on the singlet and triplet excited states of the N2, CO, and H2CO molecules are presented.
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  • 152
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    International Journal of Quantum Chemistry 39 (1991), S. 709-727 
    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 theoretical model based on physical, chemical, and biochemical mechanisms has been presented to evaluate the yields of DNA strand breaks (single and double) as a function of linear energy transfer (LET) or -dE/dx. Energetic heavy charged particles are considered explicitly to provide a general theory for low- as well as for high-LET radiation. There are three main features of the calculation: (a) track structure considerations for the energy deposition pattern, (b) three-dimensional structure of DNA molecules to provide information on the exact location of damage, and (c) a Monte-Carlo scheme to simulate the diffusion processes of water radicals. To avoid the complexities of a cellular medium, an aqueous solution of DNA is considered in the calculation. When the results of the calculations are compared with experimental measurements of the yields of strand breaks in mammalian DNA (exposed in a cellular complex), reasonable agreement is obtained. However, only those experimental data have been compared where there were no enzyme repair processes. The method of calculation has also been extended to study breaks in higher-order structures of DNA molecules such as chromatin. Specific limitations of the present model have been pointed out for making further improvements.
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  • 153
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    International Journal of Quantum Chemistry 39 (1991), S. 767-786 
    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: Electronic aspects of the catalytic mechanism of liver alcohol dehydrogenase (LADH) are studied with the help of ab initio analytical gradient SCF MO methods. Three points are considered: (i) role of the catalytic zinc; (ii) geometry and electronic structure of the transition state for the hydride transfer reactions; and (iii) factors affecting the energy gap for the hydride transfer step, namely, substrate binding to zinc, reaction field, and serine 48 effects on the potential energy profile. The coordination sphere of the catalytic zinc has been modeled with an ammonia molecule and two SH- groups; complexes with CH3O-, CH3OH, and CH2O have been studied; a (6, 2, 2, 2, 1/6, 2, 1/3, 2) basis set has been used for Zn++; a (5, 2, 1, 1/3, 2) was used for oxygen, carbon, and sulfur; and a (3, 1) was used for hydrogen atoms. The hydride step was studied with two model systems: pyridinium cation/1,4-dihydropyridine coupled to the CH3O-/CH2O reaction, and cyclopropenyl cation/cyclopropene coupled to the CH3O-/CH2O system. For the latter, the role of Ser48 has been studied at the supermolecule level. The calculation on the hydride transfer step has been done at a 4-31G basis set level. The results obtained shed new light on the sources of catalytic activity of liver alcohol dehydrogenases.
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  • 154
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    International Journal of Quantum Chemistry 39 (1991), S. 839-849 
    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: We present a treatment of chemisorption that uses the Green matrix of the surface and the admolecule, as well as a cluster calculation of a small surface cluster. Since full HF-SCF-band structures with nonlocal exchange are available now for larger systems for a couple of years, it is possible to treat the substrate surface and the admolecule on equal footing. This offers a natural way to solve the embedding problem. We have applied the formalism to the adsorption of H2 on beryllium and show that in contrast to cluster calculations there appears a binding, which is experimentally verified.
    Additional Material: 7 Ill.
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  • 155
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    International Journal of Quantum Chemistry 39 (1991), S. 211-226 
    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 electronic absorption spectra of 2-, 3-, and 4-vinylpyridines and 1,2-(2,3-dipyridyl), 1,2-(2,4-dipyridyl), 1,2-(3,4-dipyridyl), and 1,2-(4,4-dipyridyl) ethylenes have been investigated in polar and nonpolar solvents. A correlation has been made between the geometry of the molecule and the observed spectrum. Molecular orbital calculations have been carried out using the INDO/S—CI procedure and a limited geometry optimization. The solvent effect at the MO level has been calculated. MO calculations predicted the existence of nπ* transitions that were not observed experimentally. The wave functions of the different CI states were calculated. The experimental transition energy as well as oscillator strength corresponded satisfactorily with the calculated ones. The observed transitions were assigned according to the results of MO calculations.
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  • 156
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    International Journal of Quantum Chemistry 39 (1991) 
    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
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  • 157
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    International Journal of Quantum Chemistry 39 (1991), S. 251-267 
    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: From the speculations of G. N. Lewis in 1916, [J. Am. Chem. Soc. 38, 762 (1916)], the spectral predictions of R.S. Mulliken [Nature 122, 505 (1928)], and the quantum mechanical treatment by E. Hückel [Z. Phys. 60, 423 (1930)], the three lowest states of molecular oxygen (3Σg-, 1Δg, and 1Σg+) remained spectroscopic elusives until Gerhard and Lisa Herzberg [G. Herzberg, Nature 133, 759 (1934); L. Herzberg and G. Herzberg, Astrophys. J. 105, 353 (1947); G. Herzberg and L. Herzberg, Astrophys. J. 108, 167 (1948)], precisely defined them by observed infared transitions. The excited singlets remained of interest mainly to atmospheric spectroscopists and astrophysicists, and research on these species was scarce. The discovery in 1963 by A.U. Khan and M. Kasha [J. Chem. Phys. 39, 2105 (1963)] of the simple chemical production of singlet molecular oxygens by the aqueous reaction of hydrogen peroxide and hypochlorite released an explosion of research on the neglected species. Fifteen research symposia and research treatises confirm the broad range of chemical activities of singlet oxygen. The extension to biological systems is now proceeding, with surprising evidence of involvement of natural processes, including the action of singlet oxygen in white blood cell phagocytosis.
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  • 158
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    International Journal of Quantum Chemistry 39 (1991), S. 371-386 
    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: We propose 10 desirable features or criteria for general purpose methods to be applied to the calculation of a range of spectroscopic properties. We discuss the second-order polarization propagator approximation (SOPPA) in light of these criteria by giving the actual computational expression used as well as a few numerical examples taken from the theory of NMR spectra (magnetic shieldings and spin-spin coupling constants). We demonstrate that SOPPA comes close to fulfilling these criteria.
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  • 159
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    International Journal of Quantum Chemistry 39 (1991), S. 423-436 
    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 method for analyzing asymmetric top rovibrational bands displaying both blended and resolved features is described. The two-phase computational procedure uses a modified version of the asymmetric rotor-band contour program FASTPLOT to generate a preliminary set of upperstate spectroscopic constants. The parameters are subsequently refined by employing the assigned line-fitting formalism of the ASYROT program using both resolved and blended features. The technique is detailed in a comprehensive analysis of the ν17 band of pyridine. Inclusion of quartic centrifugal distortion constants was found to satisfactorily model a high-resolution (0.004 cm-1) spectrum of this band, yielding a standard deviation of 0.00137 cm-1. The variation in the rotational parameters with vibrational quantum number is examined in terms of possible weak rovibrational perturbations to the ν17 state. An ab initio calculation of the ν17/ν27 Coriolis coupling constant indicates the observed results are consistent with the interaction of these two vibrational states.
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  • 160
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    International Journal of Quantum Chemistry 39 (1991), S. 521-521 
    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
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  • 161
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    International Journal of Quantum Chemistry 39 (1991), S. 173-181 
    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: An original procedure has been developed to determine the eigenvalues and the eigenfunctions of quantum-mechanical many-body systems with a harmonic oscillator interaction. Exact solutions in the explicit form have been obtained for the case of systems containing three groups of identical particles. For the system containing two groups of identical particles, a solution in the adiabatic approximation has been obtained and compared with the exact one.
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  • 162
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    International Journal of Quantum Chemistry 39 (1991), S. 229-229 
    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
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  • 163
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    International Journal of Quantum Chemistry 39 (1991), S. 233-233 
    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
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  • 164
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    International Journal of Quantum Chemistry 39 (1991), S. 331-344 
    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: 8 Ill.
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  • 165
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    International Journal of Quantum Chemistry 39 (1991), S. 1-2 
    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
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  • 166
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    International Journal of Quantum Chemistry 39 (1991), S. 93-113 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The excitation and ionization spectra of RuO4 and OsO4 are studied theoretically by the symmetry-adapted cluster (SAC) and SAC-CI theories. This is the attempt to assign whole of the spectra by ab initio calculations including electron correlations. In the ground state, electron correlations work to reduce the polarity of the M-O bond overestimated in the Hartree-Fock calculation. The Os-O bond is stronger than is the Ru-O bond, which is reflected in the differences of the excitation and ionization spectra of RuO4 and OsO4. The excitation energies of the experimental spectra are well reproduced by the SAC-CI theory, though the calculated intensities of some peaks are very small in comparison with the experiments. The outer-valence ionization spectra calculated by the SAC-CI theory agree well with the experimental photoelectron spectra. Some shake-up peaks that are accompanied with an electron-transfers from oxygen to metal are also calculated.
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  • 167
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    International Journal of Quantum Chemistry 39 (1991), S. 159-162 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dependence of the rainbow angle on the depth of the potential well, the equilibrium distance, andthe force constant of the potential are discussed for several potential functions.
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  • 168
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    International Journal of Quantum Chemistry 39 (1991), S. 183-196 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An exact, within the Born-Oppenheimer approximation, body-fixed Hamiltonian for the nuclear motions of a triatomic system is presented. This Hamiltonian is expressed in terms of two arbitrarily defined internal distances and the angle between them. The body-fixed axis system is related to these coordinates in a general fashion. Problems with singularities and the domain of the Hamiltonian are discussed using specific examples of axis embedding. A number of commonly used coordinate systems including Jacobi, bond-length-bond-angle, and Radau coordinates are special cases of this Hamiltonian. Sample calculations on the H2S molecule are presented using all these and other coordinate systems. The possibility of using this Hamiltonian for reactive scattering calculations is also discussed.
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  • 169
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    International Journal of Quantum Chemistry 40 (1991), S. 1-2 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 170
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    International Journal of Quantum Chemistry 40 (1991), S. 33-53 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A behavior of a quantum rigid and pointlike dipole in a permanent electric field is under study. A dependence of a number of librational energy levels on the strength of the electric field is investigated on the basis of some rigorous results for the appropriate normal Jacobian matrices.
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  • 171
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    International Journal of Quantum Chemistry 40 (1991), S. 139-148 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A very simple modification of the usual (∼N4) SCF procedure is proposed, permitting the exclusion of basis set superposition errors (BSSE) in problems of intermolecular interactions. No a posteriori corrections are required. The results of this “CHA/F method” are numerically close to those of the Boys-Bernardi correction scheme but are free from the “overcompensation” characteristic of the latter at smaller distances.
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  • 172
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    International Journal of Quantum Chemistry 40 (1991), S. 243-264 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The singly excited functions satisfying Brillouin theorem are expressed as linear combinations of configuration-state functions for any spin and spatial symmetries (atomic or molecular) and for any reference wave function. The generality of the formulation is ensured by the use of the irreducible tensor method that can be adapted to any symmetry point group of interest. The expansion coefficients are simply written as products of fractional parentage coefficients, spin- and orbit-recoupling coefficients, and phase factors. The formalism is illustrated for some atomic (Kh) and molecular (C∞v, C3v, and Td) configurations. Group theoretical techniques are also used to correlate the Brillouin conditions within a chain of groups.
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  • 173
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    International Journal of Quantum Chemistry 40 (1991), S. 299-304 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A model for catecholamine storage in vesicles is analyzed within the SCRF-CNDO/2 approach including continuum solvent effects. The model considers the approach of cationic norepinephrine (NE) to a positively charged guanidinium moiety. Ion-pair formation is found for the whole range of dielectric constants. Even though stable states of H-bonded partners are found for large dielectric constants, this process is ruled out to occur because it involves too high energies. It appears that the medium's polarity is determinant in lowering the energy barrier between the ion-pair complex and the separated partners. Thus, as the medium dielectric constant increases, the equilibrium between the two states is enhanced.
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  • 174
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    International Journal of Quantum Chemistry 39 (1991), S. 519-519 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 175
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    International Journal of Quantum Chemistry 39 (1991), S. 487-517 
    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: We present a general method of implementing the kinetic balance condition within the Dirac-Fock (DF) self-consistent field (SCF) formalism for closed-shell molecular structure. We review the steps leading to the derivation of DF SCF equations for closed-shell molecules, particularly as formulated by Matsuoka et al. In the present approach, the large component of the molecular spinors are expanded in terms of atomic basis spinors of spherical-type Gaussian functions, with the small component related to the large component by the kinetic balance condition. It is shown that imposing the kinetic balance condition on geometric Gaussian-type basis functions allows us to obtain the Fock matrix elements, involving both the large and the small components, form the standard nonrelativistic Cartesian-type matrix elements. By using properties of orthogonal polynomials, the solid spherical harmonics are expressed in Cartesian form, thus providing a general basis for transformation of one- and two-electron-matrix elements, obtained from a Cartesian Gaussian-type basis, to a spherical Gaussian-type basis. The advantages of using kinetically balanced geometric Gaussian-type basis functions in molecular DF calculations including finite-size nucleus effects are emphasized. For the sake of completeness, we have added in an appendix corrections to the nuclear attraction matrix elements for the finite-size nucleus already derived by Matsuoka.
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  • 176
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an “effective” CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment.Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc.Dimethylnitramine is the smallest prototype of the energetic R2N - NO2 nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is initiated in the solid by a breaking of the target bond. Thus, it is crucial to know the difference in energy between breaking a bond in an isolated energetic molecule versus in the molecule in a solid. In the present study, we have carried out MRD-CI calculations for the Me2N - NO2 dissociation of dimethylnitramine in a dimethylnitramine crystal. The cases we investigated were one dimethylnitramine molecule (surrounded by 53 and 685 neighboring dimethylnitramine molecules represented by multipoles), three dimethylnitramine molecules, and three dimethylnitramine molecules (surrounded by 683 neighbors). All multipoles were cumulative atomic multipoles up through quadrupoles. The MRD-CI calculations on dimethylnitramine required large numbers of reference configurations from which were allowed all single and double excitations.
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    International Journal of Quantum Chemistry 39 (1991), S. 667-679 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The frequency-dependent dipole polarizability, α(E), is calculated using the second-order polarization propagator approximation (SOPPA). We have shown how to express α(E) as a function of E2 and thus obtained a form of α(E) that can be used to compute C6-coefficients without invoking complex arithmetic. For He we find that SOPPA recovers a large fraction of the correlation contribution for all frequencies, whereas for H2 where the correlation contributions are much smaller and also basis set-dependent, we find a less definite trend of SOPPA relative to RPA.
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  • 178
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    International Journal of Quantum Chemistry 39 (1991), S. 71-91 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The usefulness of the MS-Xα method for calculating molecular transition properties is investigated in a study of NO2. Two-dimensional potential surfaces are obtained in C2v symmetry for the X̃2A1/Ã2B2 system. Potential curves that approximately follow the asymmetric stretch coordinate are also presented: On investigation, no symmetry-broken solutions were found. At all nuclear geometries investigated, the muffin-tin sphere radii were chosen by an energy-minimization technique. The inclusion of corrections to the muffin-tin form of the Xα total energy is shown to be essential, if the computed surfaces are to be qualitatively correct. The transition dipole moment connecting the two states is evaluated as a function of nuclear coordinates, using the transition-state approximation. Finally, the radiative decay of a single vibronic level in NO2 is modeled and the relevance to experiment is discussed.
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  • 179
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    International Journal of Quantum Chemistry 39 (1991), S. 131-147 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nonempirical quantum chemical method Hartree-Fock-Roothan LCAO SCF MO in a two-exponent Dunning basis with the use of an extended set of Gaussian functions by Huzinaga-Dunning with consideration of electron correlation according to the Meller-Plesset theory of excitations of the second order was used to study monohydrates of Li+, Na+, K+, and HCOO- ions. The indicated basis was supplemented with polarization functions of d-type on the O atom and of p-type on the hydrogen atom as well as with diffusion functions of p-type on the oxygen atom. It has been found that binding energies of the water molecule with Li+, Na+ appeared to be higher and with K+ lower than with HCOO- · H2O. Potential curve shapes of K+ + H2O and HCOO- + H2O reactions are shown to be similar. The molecular mechanism of K+ channel selectivity of an excitable membrane is explained on the basis of the obtained calculations.
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  • 180
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    International Journal of Quantum Chemistry 39 (1991), S. 287-298 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In flow tube studies of the quenching of O2(b1Σg+), broad band emission of O2(b):M collision complexes was found to appear under the discrete rotational lines of the 0-0 band of the b1Σg+ → a1Δg electric quadrupole transition at higher oxygen pressures and on addition of foreign gases. Bimolecular rate constants for the collision-induced emission processes have been derived from the ratio of the intensities of the discrete lines and the continuum as well as from low-resolution measurements of the relative intensities of the b → a and b → X bands as a function of O2 and added gas pressure. They range from ≈10-21 cm3 s-1 for He to ≈4 × 10-19 cm3 s-1 for PCl3 vapor.
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  • 181
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    International Journal of Quantum Chemistry 39 (1991), S. 523-539 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We present a model system for the study of curve-crossing situations in diatomic molecules. All model parameters are determined by the potential energy topology. No coupling functions are fitted. The standard approximation schemes (Born-Oppenheimer approximation, adiabatic approximation, and the generator coordinate approximation) are then applied. The result of these numerical experiments suggest that the generator coordinate approximation is able to remove 80%-90% of the nonadiabatic effect on all levels throughout the crossing region.
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  • 182
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    International Journal of Quantum Chemistry 39 (1991), S. 593-604 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An expression for the product of a single-cycle class [(1)N - P(p)]N and an arbitrary class [(1)l1(2)l … (N)lN]N of the symmetric group has recently been conjectured. This expression involves a sum over a relatively small number of reduced class sums, depending on p indices. A further conjecture is formulated and demonstrated, according to which reduced class coefficients (RCCS) involving cycles whose length is expressed by means of a single index can be related to corresponding coefficients in the product of [(1)N - P+1(p - 1)]N with an arbitrary class sum. Consequently, the problem of evaluating the general class sum product reduces to that of obtaining a relatively small set of fundamental RCCS containing no single-index cycles. The conjectures mentioned can be used to evaluate the product [(1)N - p(p)]N · [(1)N - q(q)]N in terms of fundamental RCCS that can all be obtained from the product [(r)]r · [(r)]r, where r = min(p, q). For the latter product, we use a result due to Boccara.
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  • 183
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  • 184
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    International Journal of Quantum Chemistry 39 (1991), S. 647-647 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 185
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    International Journal of Quantum Chemistry 39 (1991), S. 345-352 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The near-ultraviolet spectrum of a dinaphthonorbornadiene is reported and is interpreted using simple exciton theory that treats this molecule as a dimer of naphthalene. It shows examples of weak, intermediate, and strong coupling for the interaction of the three observed bands of naphthalene.
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  • 186
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    International Journal of Quantum Chemistry 39 (1991), S. 387-397 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Coherent dynamics of multilevel systems is of interest for the elucidation of energy disposal and multiphoton chemistry of polyatomic molecules. We compare the analytical solutions for coherent multiphoton excitation of two sparse multilevel model systems: (1) The spin-J system consisting of N = (2J + 1) equally spaced levels with the radiative coupling being determined by the xth component of the angular momentum. (2) The equally coupled N level system. The transition amplitudes for system (1) are always periodic, which is in contrast to the nonperiodic behavior exhibited by system (2) for N 〉 3.
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    International Journal of Quantum Chemistry 39 (1991), S. 437-447 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A formulation is presented of the effects of van der Waals interaction on infrared intensities. The theory takes account of induction and dispersion interactions (including charge interpenetration) and is applicable to fluids of arbitrary density. The transition moments are developed from generalized van der Waals-induced moments, and expressions are obtained for the adsorption coefficient in terms of generalized charge densities and charge-density (hyper)susceptibilities. Explicit expressions are given also of the integrated absorption coefficient in terms of multipoles, and (hyper)polarizabilities and their derivates, and the usefulness of this formulationin interpreting experimental data is illustrated by several examples. The relevance of the induction and dispersion interactions to allowed and to forbidden transitions made allowed is discussed.
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  • 188
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    International Journal of Quantum Chemistry 39 (1991), S. 455-486 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The interaction between theory and experiment in the field of molecular core electron spectroscopies is reviewed. Those aspects that distinguish the theoretical descriptions of core and valence electron spectra are analyzed in particular. Differences in the theoretical approaches to atomic and molecular spectra in terms of scattering and many-body theories are commented on. The molecular core electron spectroscopies are analyzed from a common point of view with respect to molecular orbital theory, many-body theory, and the role of localization and local selection rules. A brief analysis is presented for the particularities that enter the calculations of core hole spectra. Solutions are described to computational problems posed by the quasi-bound, highly excited nature of core hole states and by the large electronic relaxation following their creation. Two areas where the interaction between theory and experiment is particularly fruitful are briefly reviewed, namely, the theory of vibronic excitations in core electron spectra and the theory of the core photoelectron chemical shift.
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  • 189
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    International Journal of Quantum Chemistry 39 (1991), S. 585-592 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A non-local generalization K(r, r') of the kinetic energy t(r) such that t(r) = ∫K(r, r') dr' is defined using the idempotency property of the Hartree-Fock first-order density matrix. This is, in turn, related by means of an explicit differential equation to the non-local exchange energy density X(r, r'). The relationship is illustrated for a couple of examples: with the Fermi-hole in a uniform electron gas, of importance in the local density version of density functional theory, and with inhomogeneous electron systems.
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  • 190
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    International Journal of Quantum Chemistry 39 (1991), S. 605-613 
    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 total energies, in the Hückel theory, of a large number of polyhex molecules and some containing a four-membered ring have been calculated and analyzed. The results confirm that within a set of isomers the number of Kekulé structures is the dominant variable. It is proposed that this term should be recognized as the aromatic term. The remaining contributions to the energy can be attributed to local features of the molecule. Comparison with the Hess-Schaad analysis of the same energies indicates that this treatment is simpler, more complete, and closer to the original concept of aromaticity.
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  • 192
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    International Journal of Quantum Chemistry 39 (1991), S. 11-17 
    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 common quantum mechanical problem for the total class of saturated hydrocarbons has been stated and solved within the framework of the effective Hamiltonian method. A quantum mechanical substantiation of the transferability of the electronic structure characteristics (bond dipole moments, bond energies, and bond force constants) as well as the investigation of the origin of transferability have been considered for the stated class of chemical compounds.
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    International Journal of Quantum Chemistry 39 (1991), S. 59-70 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simple net sign analysis has been carried out for particle in one- and two-dimensional boxes and harmonic oscillators. The conclusion that no simple rule for the ordering of eigenvalues of two-dimensional systems can be drawn is conjectured. Cyclobutadiene, naphthalene, benz-cyclobutadiene, biphenylene, biphenyl, and p-terphenyl are found to behave topologically as particle in either type of potential. Benzene, anthracene, naphthacene, and pentacene are found to behave topologically as particle in a two-dimensional harmonic oscillator. This analysis provides the physical basis for the net sign approach in the signed graph theory.
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  • 194
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    International Journal of Quantum Chemistry 39 (1991), S. 123-130 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We propose a fomula that directly gives an estimate of the value of a Gaussian integral through only one multiplication. Using this formula, we may neglect about 60%-80% of integrals in quantum chemical ab initio calculations, without any loss in precision theoretically. Such a large molecule as ATP with 183 STOS using the STO-2G method has been calculated utilizing this technique, and only 31 CPU hours of VAX 11/730 were spent on integrals.
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  • 195
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    International Journal of Quantum Chemistry 39 (1991), S. 163-172 
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    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A basis set of evenly spaced S-type Gaussian functions with common exponents is examined. Formulas for common one- and two-electron integrals are derived. Because of thesymmetry of this basis set, a very compact two-electron integral list is produced. The number of two-electron integrals that must be stored is approximately eight times the number of basis functions. Use of this basis set in an SCF calculation is examined. Numerical results show that this approach works well for molecules containing only small atoms such as hydrogen, helium, or lithium, but that the method has problems with the core orbitals of heavier atoms. Procedures for augementing this basis set in calculations involving heavier atoms are examined.
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    International Journal of Quantum Chemistry 39 (1991), S. 227-228 
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    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
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  • 197
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 231-231 
    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
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  • 198
    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 correlated, size-consistent, ab initio effective valence-shell dipole operator (μv) method is used to calculate dipole moments and transition dipole moments of the CH molecule and transition dipole moments of the CH+ ion as a function of internuclear distance. The dipole and transition dipole moments computed here compare well with those of other accurate ab initio methods. The transition dipole moments are then used to calculate oscillator strengths and radiative lifetimes for the A → X and B → A transitions of the CH+ ion and the A → X transition of the CH molecule. Comparisons are made with the best available theoretical and experimental lifetimes. Finally, the CH ground-state dipole moment function is used to evaluate overtone intensities and to examine simple models of the CH overtone intensities in polyatomic molecules.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 199
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 299-308 
    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: Mulliken's model for the intensity of charge-transfer absorption bands in donor/acceptor complexes is extended to transition-metal compounds. Attention is focused on the analysis of systems containing a central metal ion and symmetrically equivalent π-acceptor ligands. The theory is illustrated for a one-donor/two-acceptor complex in D2d point symmetry. Results are stated for symmetries of commonly occurring transition-metal compounds that display well-documented metal-to-ligand charge-transfer transitions.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 200
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 325-330 
    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: Drawing on the results of an analysis of the nature of the pulse that generates complete transfer of population from one to another level in a system with a discrete spectrum, a generalization of the method of stimulated emission pumping is proposed. It is shown that a small subset of the Fourier components of the optimal pulse will, if their relative amplitudes are the same as in the optimal pulse, generate almost as efficient a population transfer, thereby generating the opportunity to prepare a system in a selected state with a selected population.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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