Supramolecular hosts polymers

Electrocatalytic groups such as porphyrins and phthalocyanines that act as supramolecular hosts for different metals and mimic the active sites of various proteins are commonly used in amperometric sensors [66,67]. A biomimetic sensor based on an artificial enzyme or synzyme has been demonstrated [68]. The artificial enzyme used in this study was a synthetic polymer (quaternised polyethyleneimine containing 10% primary amines) which decarboxylated oxaloacetate. The product carbon dioxide was detected potentiometrically via a gas membrane electrode. 

Finally, the application of new extractants such as hyperbranched polymers [53] and the use of ionic liquids [54] are developments which tend to aid and promote supramolecular host-guest complexation and will undoubtedly further stimulate the development of more efficient and selective extraction systems. 

Supramolecular hyperbranched polymers have been developed that utilize molecular recognition to facilitate selective binding of a guest molecule or molecules by a (dendritic) host or self-assembly that involves numerous weak noncovalent interactions to generate large functional assemblies. Examples of both these classes of supramolecular hyperbranched polymers are examined in the following sections. 

Figure 1 Schematic illustration of single-molecule force-distance measurement of a supramolecular host-guest pair exploiting a surface-attached single-polymer chain. The conversion of the recorded cantilever deflection-piezo displacement signal (a) into a force-extension curve of the single-polymer chain (b) is shown. (Redrawn from Ref. 21. Wiley-VCH, 2006.)...

Figure30 Supramolecular functional guest-host polymer 41.

A similar host-guest interaction was exploited to prepare photo-responsive, supramolecular, hyperbranched polymer 44 using an azobenzene dimer and a ji-CD trimer. Light-induced trans-to-cis transition of azobenzene results in a bent conformation of the guest and disfavoured host-guest interaction with j3-CD. 

Finally, the complementary molecular affinity between a [60]fullerene component and a complementary host in organic solution has been used to construct supramolecular polymeric nano-arrays of [60]fullerene. Haino and coworkers have developed a supramolecular fullerene polymer through the iterative com-plexation of ditopic calix[5]arene 30 and dumbbell-shaped [60]fullerene 31 (Figure 9.33) [110]. Although pulsed-field gradient NMR studies indicate that the... 

The network structures to be discussed will all involved hydrogen bonding as the supramolecular synthon. It should be noted however that other interactions such as coordinate bonds and host-guest interactions may also organise host molecules into network structures. Coordination polymers constructed from molecular hosts may involve functionalised calixarenes [8-11], cyclotriveratrylene [12], or cucurbituril [13]. Calixarenes have also been used to build up network structures via host-guest interactions [14,15]. It is also notable that volatile species may be trapped within the solid state lattice of calix[4] arene with a structure entirely composed of van der Waals interactions [16]. 

In principle, there are four basic strategies to compensate for the repulsive effects between the hydrophobic fullerene surface and water (a) encapsulation in the internal hydrophobic moiety of water-soluble hosts like cyclodextrins (Andersson et al., 1992 Murthy and Geckeler, 2001), calixarenes (Kunsagi-Mate et al., 2004) or cyclotriveratrylenes (Rio and Nierengarten, 2002) (b) supramolecular or covalent incorporation of fullerenes or derivatives into water-soluble polymers (Giacalone and Martin, 2006) or biomolecules like proteins (Pellarini et al., 2001 Yang et al., 2007) (c) suspension with the aid of appropriate surfactants and (d) direct exohe-dral functionalization in order to introduce hydrophilic moieties. 

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