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  • 1
    ISSN: 0947-6539
    Keywords: molecular devices ; nanostructures ; rotaxanes ; self-assembly ; translational isomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A number of nanometer-scale molecular assemblies, based on rotaxane-type structures, have been synthesized by means of a template-directed strategy from simple building blocks that, on account of the molecular recognition arising from the noncovalent interactions between them, are able to self-assemble into potential molecular abacuses. In all the cases investigated, the π-electron-deficient tetracationic cyclophane cyclobis(paraquat-p-phenylene) is constrained mechanically around a dumbbell-shaped component consisting of a linear polyether chain intercepted by at least two, if not three, π-electron-rich units and terminated at each end by blocking groups or stoppers. The development of an approach toward constructing these molecular abacuses, in which the tetracationic cyclophane is able to shuttle back and forth with respect to the dumbbell-shaped component, begins with the self-assembly of a [2]rotaxane consisting of two hydroquinone rings symmetrically positioned within a polyether chain terminated by triisopropylsilyl ether blocking groups. In this first so-called molecular shuttle, the tetracationic cyclophane oscillates in a degenerate fashion between the two π-electron-rich hydroquinone rings. Replacement of one of the hydroquinone rings - or the insertion of another π-electron-rich ring system between the two hydroquinine rings - introduces the possibility of translational isomerism, a phenomenon that arises because of the different relative positions and populations of the tetracationic cyclophane with respect to the π-donor sites on the dumbbell-shaped component. In two subsequent [2]rotaxanes, one of the hydroquinone rings in the dumbbell-shaped component is replaced, first by a p-xylyl and then by an indole unit. Finally, a tetrathiafulvalene (TTF) unit is positioned between two hydroquinone rings in the dumbbell-shaped component. Spectroscopic and electrochemical investigations carried out on these first-generation molecular shuttles show that they could be developed as molecular switches.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 108 (1996), S. 1242-1286 
    ISSN: 0044-8249
    Keywords: Molekulare Erkennung ; Nanochemie ; Nanostrukturen ; Nichtkovalente Wechselwirkungen ; Supramolekulare Chemie ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Zwar steht der Entwicklung von nanometergroßen Strukturen prinzipiell nichts im Wege, doch setzt sich immer mehr die Auffassung durch, daß sich Strukturminiaturisierungen unter die gegenwärtig durch lithographische Techniken erreichbare 1-μ-Grenze als nicht mehr praktikabel erweisen werden. Es wurde daher deutlich, daß nur durch ein grundlegendes Verständnis der Selbstorganisation von funktionellen makroskopischen biologischen Strukturen mit Abmessungen im Nanometerbereich und sogar darunter (Verkleinerungsansatz) und durch die Erweiterung unseres Wissens über die chemische Synthese von mikroskopischen Strukturen (Vergrößerungsansatz) die Brücke zwischen Anspruch und Wirklichkeit bei Nanosystemen geschlagen werden kann. Die Konstruktion von Nanostrukturen und -systemen aus kleinen Molekülbausteinen ist das „engineering-up“ zum Aufbau von molekularen Funktionseinheiten. Bedeutende Fortschritte können auf dem Gebiet der Nanowissenschaften erzielt werden, wenn die Konzepte, die in der Biologie gefunden wurden, auf die Chemie übertragen werden. Im Zentrum dieser Aufgabe steht die Entwicklung von einfachen chemischen Systemen, die sich selbst durch gegenseitige Erkennung zu größeren Molekülaggregaten organisieren können. Die genaue Programmierung derartiger Erkennungsprozesse und somit auch der korrekte Aufbau der Überstrukturen setzen ein fundamentales Verständnis und die Nutzung inter- sowie intramolekularer nichtkovalenter bindender Wechselwirkungen voraus. Die supramolekulare Chemie - eine Chemie, die in jeder Hinsicht über die Chemie der Moleküle hinausgeht - hat begonnen, den großen Graben zwischen molekularen und makromolekularen Strukturen zu schließen. Durch Nutzung von so unterschiedlichen Wechselwirkungen wie aromatischen π-Stapel- und Metall-Ligand-Koordinationswechselwirkungen als Informationsquellen der Aufbauprozesse haben Chemiker in den letzten zehn Jahren biologische Konzepte wie die Selbstorganisation zur Konstruktion von Nanostrukturen und Überstrukturen mit einer Vielzahl von Formen und Funktionen herangezogen. Wir wollen hier einen Eindruck davon vermitteln, wie die Selbstorganisation in natürlichen Systemen funktioniert und wie diese Prinzipien nutzbringend auf nichtnatürliche Systeme angewendet werden können.
    Additional Material: 88 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 35 (1996), S. 1154-1196 
    ISSN: 0570-0833
    Keywords: molecular recognition ; nanochemistry ; nanostructures ; non-covalent interactions ; supramolecular chemistry ; Molecular recognition ; Nanostructures ; Noncovalent interactions ; Supramolecular chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Although there are no fundamental factors hindering the development of nanoscale structures, there is a growing realization that “engineering down” approaches, in other words a reduction in the size of structures generated by lithographic techniques below the present lower limit of roughly 1 μm, may become impractical. It has, therefore, become increasingly clear that only by the development of a fundamental understanding of the self-assembly of large-scale biological structures, which exist and function at and beyond the nanoscale, downwards, and the extension of our knowledge regarding the chemical syntheses of small-scale structures upwards, can the gap between the promise and the reality of nanosystems be closed. This kind of construction of nanoscale structures and nanosystems represents the so-called “bottom up” or “engineering up” approach to device fabrication. Significant progress can be made in the development of nanoscience by transferring concepts found in the biological world into the chemical arena. Central to this mission is the development of simple chemical systems capable of instructing their own organization into large aggregates of molecules through their mutual recognition properties. The precise programming of these recognition events, and hence the correct assembly of the growing superstructure, relies on a fundamental understanding and the practical exploitation of non-covalent bonding interactions between and within molecules. The science of supramolecular chemistry - chemistry beyond the molecule in its very broadest sense - has started to bridge the yawning gap between molecular and macro-molecular structures. By utilizing inter-actions as diverse as aromatic π-π stacking and metal-ligand coordination for the information source for assembly processes, chemists have, in the last decade, begun to use biological concepts such as self-assembly to construct nanoscale structures and superstructures with a variety of forms and functions. Here, we provide a flavor of how self-assembly operates in natural systems and can be harnessed in unnatural ones.
    Additional Material: 88 Ill.
    Type of Medium: Electronic Resource
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