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Daisy Chain Necklace: Tri [2] rotaxane Containing Cyclodextrins

 



Daisy Chain Necklace: Supramolecular Architecture Toward Molecular Composites and Devices

 

Abstract

Cyclodextrins (CDs: cyclic glucose polymers) have been used as a cyclic building block for the construction of supramolecular architectures. Poly(rotaxane)s, in which many CDs are imprisoned in a polymer chain, have been prepared. When a guest group, a molecule which can be included in a CD cavity, was attached on the cyclic host, the molecule formed intermolecular complexes to give supramolecular polymers, daisy chain. When the supramolecular polymers were treated with bulky stopper groups, they formed cyclic tri[2]rotaxane, daisy chain necklace. A cyclodextrin ring can move in some of their structures. Such compounds have potentials for molecular shuttles, motors, and machines. Design and synthesis of various supramolecular archtectures using cyclodextrins as a cyclic component are described.

Introduction

Recently, much attention has been focused on nano-science and nano-technology, construction of nanometer-scale architectures from bulk materials by top-down engineering. Advances in VLSI(very large-scale integrated systems) production techniques (lithography) have moved processing down from the micrometer to the sub-micrometer level. Even smaller architectures have been required for the construction of new materials and devices. However, there is a limit to top-down approaches for many reasons including the interference of light waves for lithography. Researchers exploit new ways to fabricate smaller architectures. Hence, the bottom-up procedure from a molecule to create new architecture has become an important approach. This approach has already been utilized by nature. Most of the structures of biological systems have been made by self-assembly and self-organization of specific molecules.

Construction of supramolecular structures using specific intermolecular interactions is one of the most important procedures for the construction of nano-scale architectures by bottom-up procedures1. Recently, with the advent of host-guest chemistry and chemistry of molecular recognition, supramolecular science has appeared. Rotaxane (rotor and axle) and Catenanes (chains) are important supramolecular structures2. More recently, supramolecular polymer science has emerged. Although synthetic polymers are now ubiquitous in the world, the rise of supramolecular chemistry has spurred investigations into alternative approaches for polymer synthesis. Whereas molecular polymerization relies upon the formation of covalent bonds between monomeric building blocks, the propagation step in a supramolecular polymerization proceeds via the formation of non-covalent bonds. When a guest part is attached on a cyclic host component, the conjugate may form intramolecular complexes or intermolecular complexes to give supramolecular polymers.

 

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