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  • 1
    Electronic Resource
    Electronic Resource
    Molecular Meccano, 27.Part 26: R. E. Gillard, F. M. Raymo, J. F. Stoddart, Chem. Eur. J., in press. A Template-directed Synthesis of a Molecular Trefoil Knot (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2485-2494 
    Details
    ISSN: 0947-3440
    Keywords: Crown compounds ; Molecular knots ; Self-assembly ; Supramolecular chemistry ; Template-directed synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A design logic for the self-assembly of a molecular trefoil knot and of its isomeric trivial knot is described. The approach relies on the formation of a double-stranded supramolecular complex between an acyclic π-electron rich 1,5-di-oxynaphthalene-based polyether and an acyclic π-electron deficient bipyridinium-based tetracation. The reversible complexation of the two acyclic complementary components in solution is followed by the irreversible formation of covalent bonds connecting the termini of these two precursors within the supramolecular complex, affording both a trefoil knot and a trivial knot, though only in extremely low yields. The isomers were separated by preparative high-performance liquid chromatography and characterized by liquid secondary ion mass spectrometry which revealed the binding of up to two ammonium ions in the case of only one of the two isomers - namely, the trivial knot. In addition, we have performed binding studies between some model acyclic and macrocyclic 1,5-dioxynaphthalene-based polyethers and the bipyridinium based precursor of the knots. One of the complexes was also characterized in the solid state by X-ray crystallography which revealed the formation of a [2]pseudorotaxane in the solid state.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971210
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  • 2
    Electronic Resource
    Electronic Resource
    Electrochemically Induced Molecular Motions in Pseudorotaxanes: A Case of Dual-Mode (Oxidative and Reductive) Dethreading (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1992-1996 
    Details
    ISSN: 0947-6539
    Keywords: cyclic voltammetry ; logic gates ; molecular devices ; pseudorotaxanes ; spectroelectrochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The electrochemical and spectroscopic properties of a pseudorotaxane formed in acetonitrile solution by self-assembly of a wire-type electron donor based on the tetrathiafulvalene unit and the cyclobis(paraquat-p-phenylene) tetracationic electron acceptor have been investigated. We show that a) reversible dethreading/rethreading cycles of the pseudorotaxane can be performed by either oxidation and successive reduction of the electron-donor wire or reduction and successive oxidation of the electron-accepting tetracationic cyclophane, and b) because of this special behavior, the input (electrochemical)/output (absorption spectrum) characteristics of this molecular-level system correspond to those of an XNOR logic gate.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031214
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  • 3
    Electronic Resource
    Electronic Resource
    Starch-Filled PHB and PHB/HV copolymer (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 39 (1996), S. 175-181 
    Details
    ISSN: 0959-8103
    Keywords: starch ; poly-3-hydroxybutyrate ; biodegradable polymers ; mechanical properties ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The structure and mechanical properties of melt-pressed sheets of bacterially produced poly-3-hydroxybutyrate (PHB) and poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHB/HV) filled with various amounts of particulate maize starch granules have been investigated. The experimental methods included stress-strain measurements, differential thermal analysis to determine heats of fusion and melting temperatures, scanning electron microscopy, and optical microscopy to obtain information on crystallization behaviour and spherulite growth.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Some properties of poly(3-hydroxybutyrate)-poly(3-hydroxyvalerate) blends (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Polymer International 39 (1996), S. 215-219 
    Details
    ISSN: 0959-8103
    Keywords: poly-3-hydroxybutyrate (PHB) ; poly-3-hydroxyvalerate (PHV) ; biodegradable polymers ; polymer blends ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The melting, crystallization and dynamic mechanical behaviour of blends of bacterially produced poly[D(-)-3-hydroxybutyrate] (PHB) and poly[D(-)-3-hydroxyvalerate] (PHV) have been investigated. Results showed that melt-pressed PHB-PHV blends contained phase-separated domains in the melt which subsequently crystallized as PHB and PHV type spherulites respectively. The two melting regions detected by DTA related to separate melting of PHB and PHV crystallites, which were almost unaffected by the blend composition. The mechanical behaviour of a random copolymer of PHB/HV was compared with that of a blend of almost the same composition, and found to be markedly different.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Solvent dependence of the one-electron reduction of substituted benzo- and naphthoquinones (1997)
    Weinheim : Wiley-Blackwell
    Electroanalysis 9 (1997), S. 629-632 
    Details
    ISSN: 1040-0397
    Keywords: Benzoquinone ; Naphthoquinone ; Cyclic voltammetry ; Hammett equation ; Solvent dependence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Potentials for the one-electron reduction of a series of substituted benzo- and naphthoquinones were measured in 10 aprotic solvents by cyclic voltammetry and used to construct Hammett plots. Hammett reaction constants, ρ, were determined in each solvent and used as indicators of the solvent-mediated stabilization of the charged radical-anion product of the reduction reaction. Correlations of Hammett ρ values with solvent parameters suggest that the Lewis acidity of the solvent, in particular the solvent's ability to donate a partially positive proton, is a consistent predictor of the degree of charge stabilization of the quinone radical anion. Other mechanisms of charge stabilization, including solvent-solute charge transfer complexes and dipole-dipole interactions involving the molecular dipole moment (or an induced dipole moment) of the solvent, were found to be inconsistent predictors of the effect of solvent on one-electron quinone reduction in aprotic media.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elan.1140090810
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  • 6
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    A revision of Ordovician series and stages from the historical type area (1995)
    Cambridge University Press
    Details
    Publication Date: 1995-01-01
    Description: This paper is a revision of the standard chronostratigraphy of the Ordovician of the historical type area in England and Wales. The revision is a response to the need for more precise definitions of series and stages, especially for practical international correlation. In some cases this has entailed moving horizons for Series bases away from those in the classical sections. The scheme will be used as the standard for a forthcoming revision of the Correlation Chart of the British Ordovician System. The Ordovician is divided into five series: Tremadoc, Arenig, Llanvirn, Caradoc and Ashgill. The Llanvirn is extended to include part of the classical Llandeilo Series, which is included within it as a stage. Where stage subdivisions of standard series have not yet been defined, as in the Tremadoc, they are proposed in this paper. However, Bancroft’s fine stadial divisions of the Caradoc, which have been criticized for their brevity and local utility, are combined into four new stages, which will have wider application. The former Caradoc subdivisions are retained as substages for the purposes of regional correlation.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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  • 7
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    Late Caradoc graptolitic faunal gradients across the Iapetus Ocean (1995)
    Cambridge University Press
    Details
    Publication Date: 1995-09-01
    Description: Late Caradoc graptolite assemblages across the Iapetus Ocean in Wales and Scotland became progressively more disparate despite the narrowing of the ocean. We compare faunal distributions in continuous sections from opposite sides of Iapetus, at Whitland in South Wales and Hartfell Score in the Southern Uplands of Scotland. A comprehensive graptolite range-chart is given for each. The graptolite assemblages from the clingani Biozone are subdivided into a lower Ensigraptus caudatus Subzone and upper Dicellograptus morrisi Subzone at both localities, though the faunas differ in detail. Higher in the sequence, the distinctive Scottish linearis Biozone fauna is not recognizable at Whitland, its presumed equivalent being a fauna dominated by variable morphotypes of the genus Normalograptus. This suggests that environmental gradients (depth and/or temperature) were changing more rapidly than the geography. Significantly, the subsequent inception of limestone deposition at Whitland was approximately contemporaneous with widespread replacement of black mudstones by oxic, bioturbated sediments elsewhere in the Welsh Basin and in Scotland. This was possibly a response to an early phase of cooling prior to the end-Ordovician glaciation. In Wales the claimed hiatus at the Caradoc-Ashgill boundary may rather reflect biofacies variation.
    Print ISSN: 0016-7568
    Electronic ISSN: 1469-5081
    Topics: Geosciences
    Published by Cambridge University Press
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