Cyclodextrins molecular devices

Cyclodextrin Rotaxanes and Catenanes 7 Cyclodextrin Molecular Devices and 15... 

Synthetic peptides containing side-chain modification have also been used as molecular scaffolds for the preparation of multiple receptors and molecular devices. 5 These include the use of crown ethers, cyclodextrins, porphyrins, and peptides with metal-binding sites (including ferrocenyl and EDTA side chains) (Section 9.4). Cyclization procedures have been developed to prepare biologically active cycloisodityrosine peptides which contain 14-or 17-membered rings (Section 9.5). The use of tryptathionine, a cross-linking dipeptide consisting of side-chain-to-side-chain linked L-Trp-L-Cys that is present in phallotoxins, 6 a family of cyclic heptapeptides, is also described (Section 9.6). 

Since caroviologens are rather fragile compounds, they can be protected from the environment by inclusion into polyanionic derivatives of (J-cyclodextrin in a rotaxane fashion 102 [8.156]. Also, in the design of molecular devices, it may be desirable to introduce some extent of redundancy in order to reduce the risk of device failure. This is the case in the tris-carotenoid macrobicycle 103 that represents a sort of triple-threated molecular cable whose crystal structure 104 has been determined. It forms a dinuclear Cu(i) complex 105 in which the bound ions introduce a positive charge at each of the species, a feature of potential interest for transmembrane inclusion [8.157]. 

Rotaxanes are considered to be one typical prototype of molecular devices machines, because they have a rooter and an axle in the molecule. a-Cyclodextrin was first used as a rotor of rotaxane by Ogino et al. in 1978. ° They used metal complexes as stoppers. Since then some rotaxanes containing cyclodextrins have been reported (Fig. 1.20). Most of them used metal complexes as stopper groups. However, the metal coordination bonds are so weak that cyclodextrin rings may escape from the bond. All the rotaxanes reported are ionic so as to solubilize the rotaxanes in water, except one example in which all the components are non-ionic and soluble in organic solvents." In this case there are some inter-... 

Several physical studies have been carried out on cyclodextrin derivatives. Thus the X-ray structure of per-(6-bromo-6-deoxy-2,3-di-0-methyl)P-cyclodextrin has been examined by single crystal X-ray diffraction analysis. The conformation deviates significantly from C symmetry. Likewise the X-ray structure of heptakis-2,3,6-tri-C>-methyl-P-cyclodextrin shows that one of the seven rings is inverted. Conformational analysis of an extensive set of per-O-substituted p-cyclodextrins reveals that several show conformational isomerism. The relevance of this to the use of cyclodextrins in molecular device design is examined. Related work undertook n.m.r. and molecular modeling studies on a-cyclodextrin in vriiich one of the units is in the 3,6-anhydro from. The work included the examination of two model disaccharide imits. ... 

Any electrochemical device using a low molecular weight redox couple to shuttle electrons from the redox center of an enzyme to the surface of an indicator electrode, thereby increasing the effectiveness of amperometry in the detection of a substrate for the particular enzyme. The internal cavities of six-, seven-, and eight-membered cyclodextrins are trapezoids of revolution with larger open mouths dimensions (/. c., respective diameters of... 

Girardeau et al. [53] have described the chain dynamics of PEO within nanotubes of a-cyclodextrin using dueterated PEO (d-PEO) and 2H solid - state NMR spectroscopy. The chain dynamics were explored and compared with the respective unthreaded d-PEO. As these materials are continually proposed for applications in molecular-level devices [54,55] characterization of their molecular dynamics is important since they play a key role in governing bulk physical properties. 

As illustrated in Figure 5.23, Willner et al. [49] have developed a light-driven molecular shuttle. This device consists of a ferrocene-functionalized /3-cyclodextrin... 

Switching devices that are reversible and work on the molecular level are essential features of nanomachinery. Control of the access to capsules, the transport of molecules in and out of the cavities, is desirable and we examined a well-established system that uses light as a switching device the cis-trans photoisomerization of azobenzenes [58, 59]. The azobenzenes have been applied in the supramolecular chemistry of crown ethers [60-62], cyclodextrins [63,64], and even proteins [65, 66]. The photoisomerization changes the shape in a predictable way and we used azobenzene photoisomerization in an indirect sense to control reversible encapsulation. 

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