Cyclodextrins nanotube complexation

H. Dodziuk, A. Ejchart, W. Anczewski, H. Ueda, E. Krinichnaya, G. Dolgonos, and W. Kutner, Water solubilization, determination of the number of different types of single-wall carbon nanotubes and their partial separation with respect to diameters by complexation with r/-cyclodextrin, Chem. Commun. (2003) 986-987. 

Inclusion properties of molecular nanotubes composed of crosslinked a-cyclodextrin was investigated [47], Induced circular dichroism was used to probe the formation and dissociation of complexes between the nanotubes and azobenzene modified polyethylene glycol), either with or without a hydrophobic alkyl chain. The inclusion complex between the nanotubes and polymers formed at room temperature, and the polymers dissociated from the nanotubes with increasing temperature. 

Yui s group analyzed the thermodynamics on the inclusion complexation between the a-cyclodextrin-based nanotube and sodium alkyl sulfonate [148]. They prepared a supramolecular hydrogel utilizing enthalpy-driven complexation between the molecular tube and an amphiphilic molecule [147]. They carried out the thermodynamic analysis of inclusion complexation between a-cyclodextrin-based molecular tube and poly(ethylene oxide)-Wocfc-poly(tetrahydrofuran)-b/oc/c-poly(ethylene oxide) triblock copolymer in terms of isothermal titration calorimetry [157]. Furthermore, they incorporated the tube into gels that could recognize the length of alkyl chain [158]. 

Noncovalent interactions with belt- or tube-like host molecules might also be suitable to a separation of carbon nanotubes by diameter. Cyclodextrines or beltshaped aromatic compounds could be named as examples here. They may not have proven their applicability as selective complexing agent yet, but considering their geometry reveals favorable dispositions for a discriminative interaction with certain nanotubes. Supramolecular arrangements with carbon nanotubes are also discussed in Section 3.5.7. 

Figure 3.104 Examples of cyclodextrines able to form complexes with carbon nanotubes.

Cyclodextrin complexes are the only group of supramolecular entities that have reached the stage of significant commercialization [1], In the author s opinion, they will only be surpassed in the future by carbon nanotubes when the latter s usage in molecular electronics is realized, allowing the bottom-up approach in computer architecture to be realized. 

Supramolecular chemistry typically involves the complexes based on molecular recognition, which include crown ethers, catenates, rotaxanes, etc. Azobenzene derivatives are often used as structural elements in such supramolecular assembly. Already in 1980 (Shinkai et ah, 1980), azobenzene moiety had been introduced into crown ether. Other recent examples include azobenzene-cyclodextrin complexes (Callari et ah, 2006), azobenzene-attached nanotube-cyclodextrin complexes (Descalzo et al., 2006), and molecular recognition complexes with DNA (Haruta et al., 2008). Numerous examples of photoswitch-able azobenzene supramolecular systems in solutions can be found (Yagai et al., 2005 Balzani et al., 2002). But there are no investigations in these systems concerning photoorientation and mass transport. 

Ning J, Wang Y, Wu Q, Zhang X, Lin X, Zhao H. Novel supramolecular assemblies of repulsive DNA-anionic porphyrin complexes based on covalently modified multi-walled carbon nanotubes and cyclodextrins. RSC Adv 2015 5 21153-60. 

For longer polymers, adsorption and film formation can take place in organic solvents, which are good solvents for the neutral ferrocene-based species but bad solvents for the oxidized species [153, 154, 160-165]. In this case, even diblock copolymers precipitate on the electrode, without indication of the formation of micellar structures upon electrochemical switching [166-168]. Co-precipitation with carbon nanotubes onto electrodes has been achieved [169]. As a matter of fact, common solvents for both redox states are seldom available, unless the hydrophobic ferrocene units are complexed by cyclodextrins (in this case, water is a good solvent) [170, 171]. As another example, dendritic ferrocene-based polymers are sufficiently solubilized, even after oxidation in organic media (probably, the insoluble units are shielded in the interior of the dendrimers) [172]. Star-like... 

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