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  • 1
    Electronic Resource
    Electronic Resource
    Conversion of .alpha.-Keto Esters into .beta.,.beta.-Difluoro-.alpha.-keto Esters and Corresponding Acids: A Simple Route to a Novel Class of Serine Protease Inhibitors (1995)
    s.l. : American Chemical Society
    The @journal of organic chemistry 60 (1995), S. 5174-5179 
    Details
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jo00121a040
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular belts. 2. Substrate-directed syntheses of belt-type and cage-type structures (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 5422-5429 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00066a010
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  • 3
    Electronic Resource
    Electronic Resource
    Second-Sphere Coordination (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 981-990 
    Details
    ISSN: 0009-2940
    Keywords: Molecular recognition ; Second-sphere coordination ; Transition metals ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The design and synthesis of artifical receptors, able to recognize and bind transition metal complexes, is an area of growing interest in supramolecular chemistry. Macrocyclic hosts such as crown ethers, cyclodextrins, and cyclophanes have been employed to generate second-sphere adducts with numerous transition metal complexes as a result of nonconvalent bonding interactions, such as hydrogen bonding, π-π stacking, and hydrophobic interactions. The effect of second-sphere coordination on the chemical, electrochemical, and photochemical properties of the adducts, as well as on their geometries in solution and in the solid state, has been investigated; these investigations have demonstrated the potential of second-sphere coordination in modulating the behavior of transition metal complexes by designed external intervention.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961290902
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  • 4
    Electronic Resource
    Electronic Resource
    Template-Directed Synthesis of a Rotacatenane (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1295-1302 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Mechanically interlocked molecules ; Molecular recognition ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A [2]catenane, able to bind π-electron-rich guests inside the cavity of one of its two macrocyclic components has been designed and synthesized using supramolecular assistance. This recognition motif has been exploited to template the formation of a so-called rotacatenane - i.e., a molecule composed of a dumbbell-shaped component threaded through the cavity of one of the two mechanically interlocked macrocyclic components of a [2]catenane. The structure of this [2]catenane, as well as that of a model [2]catenane, have been characterized unequivocally by single-crystal X-ray analyses. Furthermore, some of the co-conformational changes associated with these mechanically interlocked molecules in solution have been probed by variable-temperature 1H-NMR spectroscopy.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Anthracene-Containing [2]Rotaxanes: Synthesis, Spectroscopic, and Electrochemical Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 591-602 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Molecular recognition ; Molecular shuttles ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two dumbbell-shaped compounds (8 and 11), each composed of two polyether chains intercepted by a 1,4-dioxybenzene recognition site, terminated by tetraarylmethane-based stoppers, and emanating from a central 9,10- or a 2,6-dioxyanthracene unit, have been synthesized. Two [2]rotaxanes (9 · 4 PF6 and 12 · 4 PF6) have been prepared by interlocking these dumbbell-shaped compounds (8 and 11) with a bipyridinium-based tetracationic cyclophane (15 · 4 PF6) - namely, cyclobis(paraquat-p-phenylene). A [3]rotaxane (10 · 8 PF6) incorporating two cyclophane components (15 · 4 PF6) was also obtained when the 9,10-dioxyanthracene-containing dumbbell-shaped compound (8) incorporating two 1,4-dioxybenzene recognition sites was employed. The 1H-NMR spectroscopic investigation of the [2]rotaxanes (9 · 4 PF6 and 12 · 4PF6) revealed that the cyclophane component encircles one of the two 1,4-dioxybenzene recognition sites in the 9,10-dioxyanthracene-containing [2]rotaxane (9 · 4 PF6) and the 2,6-dioxyanthracene unit in the other [2]rotaxane (12 · 4 PF6). These structures have been confirmed by UV/Vis and electrochemical experiments. Comparison with the spectroscopic properties of simple model compounds shows the presence of electronic interactions which lead to (i) the occurrence of very efficient energy transfer processes in the dumbbell-shaped components and (ii) perturbations in the absorption spectra with appearance of two charge-transfer absorption bands and complete luminescence quenching in the [2]rotaxanes. For the 2,6-dioxyanthracene-containing [2]rotaxane (12 · 4 PF6), it has been demonstrated that the cyclophane can be displaced from the dioxyanthracene to the 1,4-dioxybenzene station upon electrochemical oxidation.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Template-Directed Syntheses, Spectroscopic Properties, and Electrochemical Behavior of [n]Catenanes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1121-1130 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Cyclophanes ; Electrochemistry ; Electronic spectroscopy ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Catenanes composed of two, three, five, or seven interlocked macrocycles have been synthesized in yields ranging from 1 to 30%. Their template-directed syntheses rely on a series of cooperative noncovalent bonding interactions between π-electron rich 1,5-dioxynaphthalene ring systems and π-electron deficient bipyridinium units which are incorporated within the macrocyclic components. The interlocked structure associated with one of the [3]catenanes was demonstrated unequivocally by single crystal X-ray analysis which also revealed the formation of polar stacks stabilized by intermolecular [π···π] interactions. The number of interlocked components of each catenane was determined by liquid secondary ion, matrix-assisted laser desorption ionization/time-of-flight, and/or electrospray mass spectrometries. The absorption spectra, emission spectra, and electrochemical properties of the macrocyclic components and of the catenanes have been investigated. Two kinds of charge-transfer absorption bands (intramolecular in the cyclophanes containing electron-donor and electron-acceptor units, intercomponent in the catenanes) have been found. Such charge-transfer excited states are responsible for the quenching of the potentially fluorescence units of the cyclophanes, and of the crown ethers in the catenanes. Charge-transfer electronic interactions are also evidenced by the electrochemical behavior. Correlations among the redox potentials of the various compounds are reported and discussed.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Cyclobis(paraquat-4,4′-biphenylene)-an organic molecular square(Molecular Meccano), Part 8: for Part 7, see P. R. Ashton, P. T. Glink, J. F. Stoddart, P. A. Tasker, A. J. P. White, D. J. Williams, Chem. Eur. J. 1996, 2, 729-736. (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 877-893 
    Details
    ISSN: 0947-6539
    Keywords: catenanes ; second-sphere coordination ; self-assembly ; template syntheses ; topological stereoisomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Template-directed syntheses of cyclobis(paraquat-4,4′-biphenylene) (1)- a Molecular square-have been achieved by use of π-electron-rich macrocyclic hydroquinone-based and acyclic ferrocene-based templates. In particular, the use of a polyether-disubstituted ferrocene derivative as a template permits synthesis of 1 (which is accessible only in very low yields without templates) on a preparative scale. Furthermore, the use of a macrocyclic hydroquinone-based polyether template in corporating an ester function in one polyether chain-an (oriented) macrocycle-affords a 1 : 1 mixture of two topologically stereoisomeric [3]catenanes. Ester hydrolysis of the π-electron-rich macrocyclic components mechanically interlocked with 1 within the catenated structures releases the tetracationic cyclophane in quantitative yield as a result of the degradation of the [3]catenanes. The molecular square has been characterized by X-ray crystallography, FAB mass spectrometry, 1H NMR and 13C NMR spectroscopies, and elemental analysis. The binding properties of 1 and of the smaller cyclophane cyclobis(paraquat-p-phenylene) toward a series of π-electronrich guests have also been investigated with the above techniques and UV/VIS spectroscopy. The self-assembly of the resulting supramolecular complexes in solution and in the solid state is driven mainly by π-π stacking interactions and hydrogen-bonding interactions, as well as by edge-to-face T-type interactions. In particular, the complexation of ferrocene or a ferrocene-based derivative within the cavity of 1 suggests the possibility of constructing functioning ferrocene-based molecular and supramolecular devices that can be controlled electrochemically in the form of catenanes, rotaxanes, and pseudorotaxanes.
    Additional Material: 20 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020718
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  • 9
    Electronic Resource
    Electronic Resource
    Main-Chain and Pendant Poly([2]catenane)s Incorporating Complementary π-Electron-Rich and -Deficient Components (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2109-2117 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Molecular recognition ; Polycatenanes ; Self-assembly ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A main-chain poly([2]catenane), incorporating an average of 25 repeating [2]catenane units and having an Mn value of 35 kg mol-1, was synthesized by the polyesterification of a [2]catenane monomer composed of a bipyridinium-based tetracationic cyclophane mechanically interlocked with a 1,5-dioxynaphthalene-based macrocyclic polyether. Similarly, two main-chain poly(bis[2]catenane)s, both incorporating an average of 15 repeating bis[2]catenane units and both having Mn values of 45 kg mol-1, were prepared by the copolymerizations of a bis[2]catenane monomer, possessing two hydroxymethyl functions with an appropriate bis(isocyanate). The same copolymerization was employed in order to produce a pendant poly([2]catenane), incorporating an average of 20 repeating [2]catenane units and having an Mn value of 27 kg mol-1, from a [2]catenane monomer possessing two hydroxymethyl groups on its macrocyclic polyether component.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Molecular Meccano, 48Probing Co-Conformational Changes in Chiral [2]Rotaxanes by 1H-NMR Spectroscopy (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 899-908 
    Details
    ISSN: 1434-193X
    Keywords: Co-conformation ; Molecular recognition ; Planar chirality ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The template-directed syntheses of three [2]rotaxanes possessing either chiral centers or elements of planar chirality, in one of their two mechanically interlocked components, have been realized and their solid-state structures have been analyzed by X-ray crystallography. In one instance, an enantiomerically pure dumbbell-shaped component incorporating a 1,5-dioxynaphthalene recognition site and two (1R,2S,5R)-menthyl stoppers was employed to template the formation of the achiral tetracationic cyclophane, cyclobis(paraquat-p-phenylene). The resulting enantiomerically pure [2]rotaxane was isolated in a yield of 55%. In the other two instances, an achiral 1,5-dioxynaphthalene-based dumbbell-shaped component was employed to template the formation of bipyridinium-based cyclophanes possessing either one or two elements of planar chirality. The resulting [2]rotaxane, possessing one element of planar chirality, was isolated as a racemate in a yield of 24%. The related [2]rotaxane, possessing two elements of planar chirality, was isolated as a mixture of a meso form and an enantiomeric pair in an overall yield of 28%. The 1H-NMR-spectroscopic analysis of this mixture revealed a diastereoisomeric ratio of 4:1. A degenerate co-conformational change was identified by variable-temperature 1H-NMR spectroscopy in all [2]rotaxanes. The symmetry loss arising from the introduction of one or two elements of planar chirality enabled the elucidation of the mechanism of this dynamic process in two instances.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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