Self-assembly of a double calix[6]arene pseudorotaxane in oriented channels |
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Authors: | Arduini Arturo Credi Alberto Faimani Giovanni Massera Chiara Pochini Andrea Secchi Andrea Semeraro Monica Silvi Serena Ugozzoli Franco |
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Institution: | Dipartimento di Chimica Organica e Industriale, Università di Parma via G.P. Usberti 17/a, 43100 Parma, Italy. arturo.arduini@unipr.it |
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Abstract: | A synthetic study to disclose the more appropriate manner by which two calix6]arene units could be connected for the construction of an extended tubular structure was undertaken. As a result, a head-to-tail double calix6]arene having the structure of an oriented nanotube that is about 2.6 nm long and 1.6 nm wide was prepared and characterized. This molecule is able to act as a wheel-type host and forms a supramolecular complex with an axle-type molecule, derived from 4,4'-bipyridinium (viologen), through very efficient self-assembly in solution. The properties of such a pseudorotaxane-type complex, which is stabilized by a combination of noncovalent interactions, were investigated in solution by UV/Vis absorption spectroscopy and voltammetric methods. These observations provide a clue about the location of the bipyridinium unit along the nanotube. In the solid state, the complex undergoes a further stage of self-assembly, thereby initiating extended oriented tubular structures. Crystallographic studies revealed that the positioning of the viologen dication in this asymmetric wheel is addressed by a complicated pattern of cooperative noncovalent intermolecular interactions that involve only one half of the host, whereas the remaining (more polar) half of the host is exploited to create long-range structural order that leads to a "secondary" structure of extended supramolecular channels that, in turn, self-assemble in the lattice, thus giving rise to a "tertiary" structure of parallel sandwiches of nanotubes. |
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Keywords: | calixarenes electrochemistry ion channels nanotubes self‐assembly X‐ray diffraction |
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