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  • 1
    Electronic Resource
    Electronic Resource
    Spektrographische Bestimmung von Eisen, Nickel und Chrom in Platin-Netzen (1966)
    Springer
    Microchimica acta 54 (1966), S. 1162-1166 
    Details
    ISSN: 1436-5073
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Summary A method is described for the spectrographic determination of iron, nickel and chromium in platinum-rhodium nettings that are employed as catalysts in the hydrocyanic synthesis. The method is based on the dilution, with aluminium nitrate solution, of the samples dissolved in aqua regia; the diluted solution is then taken to dryness and converted to oxide. Aluminium serves as reference element.
    Abstract: Résumé On a décrit une méthode de dosage spectrographique du fer, du nickel et du chrome dans les grilles platine-rhodium utilisées comme catalyseurs dans la synthèse de l'acide cyanhydrique. Elle repose sur la dilution par une solution de nitrate d'aluminium des échantillons dissous dans l'eau régale. Ils sont ensuite séchés et utilisés sous forme d'oxydes. On prend l'aluminium comme élément de référence.
    Notes: Zusammenfassung Eine Methode zur spektrographischen Bestimmung von Eisen, Nickel und Chrom in Platin-Rhodium-Netzen, die als Katalysatoren bei der Cyanwasserstoffsynthese gebraucht werden, wurde beschrieben. Sie beruht auf der Verdünnung der in Königswasser gelösten Probe mit Aluminiumnitratlösung, die dann getrocknet und in Oxid verwandelt wird. Als Bezugselement dient Aluminium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01217723
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular orbital computations of the conformational energy of ethyl methyl phosphate (1981)
    Springer
    Theoretical chemistry accounts 60 (1981), S. 41-51 
    Details
    ISSN: 1432-2234
    Keywords: Ethyl methyl phosphate, conformational analysis of ∼ ; Intramolecular energy, decomposition of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract As part of a research aimed at an improvement of the description of conformations of polynucleotide chains, we carried outab initio SCF-MO computations on 24 conformations of ethyl methyl phosphate (EMP), a molecule which can be taken as a model for the ω′-rotation of polynucleotides. Quantum-mechanical energies were then reproduced, with good accuracy (standard deviation of fitted fromab initio values 0.12 kcal mole−1), through a classical potential function consisting of a “6–12” Lennard-Jones plus a Coulomb term, and a contribution with twofold periodicity accounting for the anomeric effects in the phosphate group. The binding energies were analyzed using dementi's concept of Bond Energy Analysis. It was found that the variation of the binding energy as a function of conformation depends on pair atom-atom interactions distributed all over the molecule. This trend in the conformational energy is absent in the classic representation, where changes in binding energy only depend on interactions between non-bonded atom pairs alone. The dependence on interatomic distance of the quantum-mechanical energies, however, is remarkably similar to the one described by classical functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00554385
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  • 3
    Electronic Resource
    Electronic Resource
    Conformational analysis of dimethylphosphate with quantum-mechanical and classical methods (1978)
    Springer
    Theoretical chemistry accounts 50 (1978), S. 169-179 
    Details
    ISSN: 1432-2234
    Keywords: Dimethylphosphate, conformational analysis of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In order to shed light on the conformational behavior of polynucleotide chains, and in particular to clarify the origins of the barriers to internal rotation in the phosphodiester linkage, we computed, with a quantum-mechanical ab initio procedure, the energies associated to 86 combinations of the two torsion angles in the dimethylphosphate anion (CH3O)2PO2 −, and then we sought for an analytical expression apt to reproduce these energies with the highest possible accuracy. An excellent agreement (standard deviation of the fitted energies from the ab initio energies 0.28 kcal/mole) with the quantum-mechanical calculations was reached with a potential consisting of four terms: 1) a 6–12 Lennard-Jones contribution, in which different parameters are used to describe the interactions of methyls with the ester oxygens and with the anionic oxygens; 2) a contribution with twofold periodicity, accounting for the anomeric effects connected to the interactions between the lone pair electrons and the polar bonds of phosphorus with the anionic oxygens; 3) a contribution with threefold periodicity, representing the usual bond-staggering term; and 4) a Coulombic contribution, arising from electrostatic interactions between partially charged atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00550189
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum calculation of the intrinsic torsional barrier of C-C and C-O bonds (1982)
    Springer
    Theoretical chemistry accounts 62 (1982), S. 29-38 
    Details
    ISSN: 1432-2234
    Keywords: n-butane ; Internal rotation in ∼ ; Methyl ethyl ether ; Internal rotation in ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract PCILO and ab initio calculations have been performed to investigate the energies associated to rotation about the central bond in n-butane and methyl ethyl ether. Quantum mechanical energies have been fit to a classical intramolecular force field, containing torsional and nonbonded (Lennard-Jones 6–12 plus Coulomb) contributions, with a standard deviation comprised between 0.03 and 0.09 kcal mol−1. Two conditions have proved indispensable to reach such level of accuracy: (a) the use of a torsional potential with threefold periodicity, which corrects for the part of the rotation barrier not covered by van der Waals repulsions and may be interpreted as bond-bond repulsion; (b) the introduction in the force field for ethers of terms accounting for orbital interaction effects of different nature than the normal molecular mechanics nonbonded interactions; these terms are represented either by low order rotational potential functions or preferably by interactions of atoms simulating lone-pair orbitals and bonded to oxygen in such a way as to render it sp 3-hybridized. According to ab initio, the height of the threefold torsional potential about C-C and C-O bonds is comparable and is of the order of 3 kcal mol−1. According to PCILO, it is larger for C-C (ca. 1.5 kcal mol−1) than for C-O (ca. 0.5 kcal mol−1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00551051
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  • 5
    Electronic Resource
    Electronic Resource
    The shape of calibration curves in the IR analysis of copolymer composition (1973)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 170 (1973), S. 231-234 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1973.021700118
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  • 6
    Electronic Resource
    Electronic Resource
    Kinetics of chain growth in binary copolymerization (1973)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 171 (1973), S. 105-112 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Wachstumsschritt von binären Copolymerisationen wurde untersucht. Die Zusammensetzung der Copolymeren von beliebigem Polymerisationsgrad wurde mit dem stationären Grenzwert verglichen, der aus der Differentialform der Copolymerisationsgleichung gewonnen wurde und nur durch die Übergangswahrscheinlichkeiten bestimmt ist. Es wurde gezeigt, daß die Zusammensetzung der n-meren sich dem für das Copolymere charakteristischen Wert in einer Weise nähert, die sich, je nach dem Produkt der Copolymerisationsparameter, nicht nur quantitativ, sondern auch qualitativ unterscheidet. Die drei Fälle von physikalischer Bedeutung, d. h. Block- (r1r2 〉 1), statistische (r1r2 = 1) und alternierende (r1r2 〈 1) Copolymere, werden ausführlich diskutiert.
    Notes: The chain propagation step in binary copolymerizations was studied. The composition of copolymers with any arbitrary degree of polymerization was compared with the stationary limit, obtained from the differential form of the copolymerization equation and determined by the transition probabilities alone. It was shown that the n-mer composition approaches the value characteristic of the copolymer in a manner which differs not only quantitatively but also qualitatively, depending on the product of the reactivity ratios. The three cases of physical significance, viz. block (r1r2 〉 1), random (r1r2 = 1) and alternating (r1r2 〈 1) copolymers, are thoroughly discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1973.021710111
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  • 7
    Electronic Resource
    Electronic Resource
    On the chain growth in three-component copolymerizations (1975)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 176 (1975), S. 177-183 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Der Kettenwachstumsschritt bei einer Drei-Komponenten-Copolymerisation wurde untersucht durch Vergleich der Zusammensetzung der wachsenden Ketten mit dem Grenzwert, wie ihn die Terpolymerisationsgleichungen liefern. Wenn man die Terpolymere nach den Produkten der Copolymerisationsparameter für die drei binären Copolymerisationen klassifiziert, zeigt sich die große Ähnlichkeit der Kurven von Terpolymeren und von binären Copolymeren.
    Notes: The chain propagation step in three-component copolymerizations was studied by comparing the composition of the growing chains with the limiting value obtained from the terpolymerization equations. On the basis of a classification of terpolymers according to the products of reactivity ratios for the three binary copolymerizations, the close similarity of the curves regarding terpolymers and binary copolymers was shown.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1975.021760112
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  • 8
    Electronic Resource
    Electronic Resource
    Derivation of the copolymerization equation from a variational principle (1975)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 176 (1975), S. 453-457 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Copolymerisationsgleichung wurde sowohl für das „terminal“- als auch für das „penultimate“-Modell unter Anwendung eines Variationsprinzips auf die Informations-entropie des Copolymeren abgeleitet.
    Notes: The copolymer composition equation for both terminal and penultimate models, was derived by applying a variational principle to the informational entropy of the copolymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1975.021760216
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  • 9
    Electronic Resource
    Electronic Resource
    The randomness in copolymers with penultimate mechanism of copolymerization (1971)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 150 (1971), S. 199-208 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Vorstellung der „Informations-Entropie“ wird auf solche Copolymeren ausgedehnt, deren Wachstum durch den Einfluß charakterisiert ist, den die vortetzte Einheit des Polymeren auf dessen radikalische Reaktionsfähigkeit den Monomeren gegenüber ausübt. Berechnungen werden sowohl unter Anwendung der Methoden der Statistik als auch der der Informationstheorie durchgeführt. Der Wert für die „Informations-Entropie“ solcher Copolymeren, die einen Penultimate-Effekt aufweisen, ist nur geringfügig kleiner als der für Copolymere mit reinem Endgruppen-Effekt. Als Beispiele werden die Methacrylsäuremethylester/Acrylsäurenitril- und α-Methylstyrol/Acrylsäurenitril-Copolymeren angeführt.
    Notes: The notion of informational entropy has been extended to copolymers whose growth is characterized by influence of the penultimate units on the radical reactivity with monomers. Calculations have been performed by procedures both of combinatorial analysis and of information theory. The value for informational entropy of copolymers with penultimate effects is slightly smaller than that of copolymers with terminal effects only. The copolymer systems methyl methacrylate/acrylonitrile and α-methyl styrene/acrylonitrile are shown as examples.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1971.021500116
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  • 10
    Electronic Resource
    Electronic Resource
    Conformational studies on polynucleotide chains. V. A comparison between the quantum-mechanical and the consistent force field approachPart IV of this series; see Ref. 6. (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1059-1088 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Consistent force field (CFF) calculations were performed for the sugar-phosphate-sugar fragment, taken as a model of the polynucleotide backbone. The potential-energy-function is the sum of four contributions, accounting for bond and angle deformation, torsional motions, and nonbonded interactions. Both deoxyribose and ribose systems, with either C(2′)-endo or C(3′)-endo puckering in the starting geometry of ribose rings, were considered. A fair number of minima of the conformational-energy hypersurface were found. Although the numerical method employed in the CFF context cannot solve the problem of finding the global minimum in a definite way, one of the final conformations has a total energy much more attractive than the others, and may be regarded as the most stable conformation attainable with our potential-energy function. The energy-minimization affects the puckering of the first ribose ring differently from that of the second: in general, for the C(2′)-endo system the second ring retains its starting conformation (Ψ′ = 152°), while in the first the Ψ′ is modified by up to 70°; the opposite occurs for the C(3′)-endo system. This is explained by the different positions of the two rings relative to the phosphate group.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1981.360200515
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