Guest complexes dyes with

There are three main types of CDs a-cyclodextrin (a-CD), -cyclodexlrin (p-CD), and y-cyclodextrin (y-CD), which are macrocycles formed by six, seven, and eight sugar ring molecules, respectively. The spatial structure of p-CD is shown on Fig. 3. Review [19] generalizes data on the synthesis, modification, physicochemical and theoretical investigations of CDs, and certain applications particularly for enantio-separation and pharmaceutical applications. CDs are able to form host-guest complexes (pseudorotaxanes) with hydrophobic molecules such as aza-dyes... 

This chapter describes the synthesis, properties, and biomedical applications of cyanine and squaraine dyes encapsulated in CDs, CBs, Leigh-type tetralactam macrocycles, aptamers, and micro- or nano-particles. The optical and photochemical properties of supramolecular guest-host nanostructures that are based on intra-and intermolecular complexes of crown-containing styryl dyes with metal cations, and aggregates of carbocyanine dyes are discussed in a separate review [18]. 

Analysis of the available literature data on host-guest complexes based on cyanine and styryl dyes with CDs shows that rotaxane formation in general... 

However, if the dye is of an appropriate size to form a one host-two guests complex with beta or gamma cyclodextrin, it was found that, on addition of the cyclodextrin, dye solutions often show spectral changes... 

Hirai, H., Toshima, N., and Uenoyama, S. (1985) Inclusion Complex Formation of y-Cyclodextrin. One Host-Two Guest Complexation with Water-soluble Dyes in Ground State, Bull. Chem. Soc. Jpn. 58, 1156-1164. 

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. 

QDs-based aptamer sensors were further developed by applying aptamer subunits that would self-assemble into supramolecular aptamer subunits-guest complexes in the presence of the analyte. CdSe/ZnS QDs were modifled with a subunit of the anti-cocaine aptamer (23), while the second aptamer subunit was functionalized with an acceptor dye (24). In the presence of a cocaine analyte, supramolecular complex formation occurred between the aptamer subunits and cocaine, which led to the FRET process between the QDs and the dye acceptor (Figure 6.21). 

Similar to other triptycene-derived macrocyclic arenes, triptycene-derived tetralactam macrocycles also had fixed conformations with large electron-rich cavities, which made them promising candidates as the host for some electron-deficient guests with comparatively large sizes. Squaraines [26] were a family of fluorescent dyes with specific near-IR photophysical properties, which had wide potential applications. However, their instability limited the utilization of them, and thus improving their chemical stability and the photophysical properties were the key to applications of squaraines [27]. Consequently, we [25, 28] found that macrocycles 35a-b could form a new kind of stable pseudorotaxane-type complexes with the squaraine in both solution and solid state. We further studied the chemical stability of squaraine in these complexes, and found that free guest 35b underwent hydrolytic decomposition to turn colorless in polar THF-water solvent in 4 days, but for squaraine 36b (Fig. 18.15) in complexation with 35a-b, its blue colors could be retained for several weeks. This observation revealed that the formation of complexes could efficiently protect the squaraine dyes from polar solvents. 

With further studied on the complexation of the macrocycles and the squaraine dyes with different terminal groups (Fig. 18.15), we found that these complex exhibited the complexation-induced asymmetry of the guest, which might result... 

Ohashi and coworkers [12] have reported that MMP2 [20] calculations on the interactions of cyanine dyes with P- and y-cyclodextrin correctly reproduced the relative stability of the inclusion complexes, as well as predicting that in most cases a dye dimer would be preferentially bound within the cavity of the cyclodextrin. Electrostatic interactions between the dye molecules and the cyclodextrin played an important role, in addition to the VDW interactions, in stabilizing the complex. Menger and Sherrod [6,21], enroute to an exploration of the interactions of ferrocenylacrylate esters with P-cyclodextrin, have reported the calculated host-guest complexes between ferrocene and a-, p-, and y- cyclodextrin which are consistent with X-ray structures and spectroscopic data Ferrocene was found to bind in an equatorial manner with y-cyclodextrin, in an axial manner with P-cyclodextrin, and the predicted structure for the 2 1 complex between a-cyclodextrin and ferrocene was found to be precisely correct when the X-ray structure of the complex was published over one year later by Harada [22]. 

Eor complexation studies with a guest that exhibits intermolecular self-association, the association should also be considered in the analysis. An example for this is the complexation of phenothiazine dyes with CDs. The dyes form non-fluorescent dimers. The monomers form 1 1 complexes with /i-CD, while the dimers form 1 1 complexes with y-CD. Evaluation of equilibrium constants... 

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