Host-guest properties water soluble

Cyclodextrins (CDs) are macrocyclic oligosaccharides consisting of p-glucopyranose units. In particular, six-, seven-, and eight-membered macrocycles are, respectively, called a-cyclodextrin (a-CD), P-cyclodextrin (p-CD), and y-cyclodextrin (y-CD). They all exhibit different cavity diameters and chemical natures such as water solubilities and host-guest properties (Figure 5.3). 

Combining the supramolecular host-guest properties of calixarenes, the optical properties of calixarene-modified CdSe/ZnS semiconductor QDs were controlled for the optical detection of neurotransmitter (acetylcholine), Ceo and mercury ions [65-70]. SC[4,6]A was selected to prepare highly fluorescent, stable and water-soluble CdSe QDs by simple, rapid ligand exchange route [71]. Then, this kind of QDs were used to construct Au electrode with enhanced photocurrents systems. [72] CdTe QDs in silica spheres coated with calix[4]arene were also synthesized as luminescent probes for pesticides and PAHs [64]. 

CDs are cyclic oligosaccharides comprised of a-l,4-linked glucopyr-anose units (37- 0). The following properties make CDs attractive components in organic chemistry and supramolecular catalysis/ enzyme mimics in particular (i) CDs are water soluble (ii) their hydrophobic cavity can host a variety of lipophilic guest molecules ... 

In addition to the light-harvesting property, this host-guest complex also exhibits a high photocytotoxicity. Its IC50 value, defined as the dye concentration required to kill 50% of the cells, for HT29 human colon adenocarcinoma cells is only 0.09 p,M, which is comparable with that of 113 itself formulated with Cremophor EL (0.15 p,M). The complexation with 93 (M = 2H) enhances the water solubility of 113 and therefore can prevent the use of Cremophor EL, which may cause serious hypersensitivity reactions. 

Recently, we are also able to perform liquid-liquid extractions of water-soluble dyes from water to organic solvents like toluene using the unimolecular dendritic micelles as extractants. These guest-host properties of the modified poly(propylene imine) dendrimers make use of the basic nature of the interior of the dendrimer. Therefore, it is possible to transfer dyes like Bengal Rose into toluene. Although simple tri-octylamines are capable of transferring these dyes as well, it is evident from the experiments that unimolecular dendritic inverted micelles are much more selective, probably due to the shielding effect of the apolar shell [70]. 

For binding to occur, a host must possess suitable binding sites with favourable electronic properties such as polarity and hydrogen bond donor/acceptor abilities that complement those of the guest. Cyclophanes such as I, calixarenes II, homocalixarenes IH, and resor-cinarenes FV fulfil these requirements (Scheme 12.1). Cucurbiturils V are water soluble container molecules without aromatic subunits. Therefore, both electrostatic interaction other than cation- r interaction and hydrophobic interaction play a dominant role. 

As a result of the host-guest complexes formed by CDs with a variety of lumophores, characteristic luminescence properties of the included lumophore, sensitive to viscosity/polarity or dielectric, may change. In fact, the inclusion of a lumophore in a CD cavity has proved to provide a means of triplet-state stabilization, luminescence intensity enhancement, optical activity induction, improved solubility of poorly soluble analytes in water, etc. 

This paper describes our studies on the design, synthesis, and properties of water-soluble cyclophanes as hosts having hydrophobic cavities of definite shape and size for forming inclusion complexes with various organic guests in aqueous solution. 

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