Cyclodextrin host-guest complexes

Auletta T, de Jong MR, Mulder A, van Veggel FCJM, Huskens J, Reinhoudt DN, Zou S, Zapotoczny S, Schonherr H, Vancso GJ, Kuipers L. 3-Cyclodextrin host-guest complexes prohed under thermodynamic equilibrium thermodynamics and AFM force spectroscopy. J Am Chem Soc 2004 126 1577-1584. 

Example 3.14b Oxidative Poiymerization of a Cyclodextrin Host-Guest Complex of Pyrrole from Homogeneous Aqueous Solution (Conducting Polymer)... 

Fig. 2.3. Probable structure of dinuclear iron-cyclodextrin host guest complexes.

The geometric (size and shape) complementarity between the cyclodextrin host and the organometallic guest determines a well manifested selectivity in the formation of inclusion complexes and can be used for the separation of ferrocene from dime-thylferrocene (only the latter forms a complex with y5-CD) [471], and of (benzene)-chromium tricarbonyl, (7 -C6H6)Cr(CO)3 from (hexamethylbenzene)-chromium tricarbonyl, ( y -C6Me6)Cr(CO)3 (only the latter forms a complex with y-CD) [471], Cyclodextrin host-guest complexation also affords the resolution of hydroxyethylferrocene enantiomers [489]. 

Fig. 2. Scheme of formation of styrene-cyclodextrin host-guest complex... 

Dyck ASM, Kisiel U, Bohne C. Dynamics for the assembly of pyrene-y-cyclodextrin host-guest complexes. J Phys Chem B 2003 107 11652-9. 

B.V.K.J. Schmidt, M. Hetzer, H. Ritter, and C. Barner-Kowollik, Complex macromolecular architecture design via cyclodextrin host/guest complexes. Prog. Pol ScL, 39 (1), 235-249, 2014. 

Bortolus, P., Grabner, G., Kohler, G., and Monti, S., Photochemistry of cyclodextrin host-guest complexes. Coord. Chem. Rev., 123, 261, 1993. 

P-Cyclodextrin is assumed to form host-guest complexes with diazonium ions (Fukunishi et al., 1982, 1985), but if so, complexation increases the extent of thermal dediazoniation, i. e., it has the contrary effect to that usually seen. 

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... 

R Kuhn, F Stoeklin, F Emi. Chiral separations by host—guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis. Chromatographia 33 32—36, 1992. 

Very recently a new method was developed that opens the possibility to polymerize even hydrophobic monomers in aqueous solution. This method is based on the finding that hydrophobic monomers can be made water-soluble by incorporation in the cavities of cyclodextrins. It has to be mentioned that no covalent bonds are formed by the interaction of the cyclodextrin host and the water-insoluble guest molecule. Obviously only hydrogen bonds or hydrophobic interactions are responsible for the spontaneous formation and the stability of these host-guest complexes. X-ray diffraction pattern support this hypothesis. Radical polymerization then occurs via these host-guest complexes using water-soluble initiators. Only after a few percent conversion the homogeneous solution becomes turbid and the polymer precipitates. 

Variations of this method are possible in several ways. First of all, cyclodextrin which is available on a large scale by enzymatically catalyzed modification of starch can be tailored by chemical reactions. Furthermore, copolymerizations between different host-guest complexes are possible whereby in some cases the reactivity ratios differ from those reported in literature. 

However, for the positional isomers of phthalate (56-58), the response selectivity was different for the two types of membranes. Whereas membranes 1 and 2 showed responses in the order of 56 (ortho) > 57 (meta) > 58 (para), membrane 53 interestingly showed a different response order, i.e., 57 (meta) > 58 (para) > 56 (ortho), a selectivity which is quite different from that expected on the basis of simple electrostatic effects. Such a difference in the selectivity is possibly due to host-guest complexation involving not only electrostatic interactions but also inclusion into the P-cyclodextrin cavity, which is capable of recognizing differences in the steric structures of the guests. 

Zhang, X., Gramlich, G., Wang, X. and Nau, W.M. (2002) A joint structural, kinetic, and thermodynamic investigation of substituent effects on host-guest complexation of bicyclic azoalkanes by -cyclodextrin./. Am. Chem. Soc., 124 (2), 254-263. 

Time-resolved fluorescence of coumarin C522 was determined in water and in host-guest complex with p-cyclodextrin, representing free aqueous and cavity restricted environments, respectively. Experimental fluorescence clearly showed faster dynamics in a case of water. The time parameters of monoexponential fit for water and p-cyclodextrin at 500 nm and 520 nm were determined to be 1.37 ps and 2.02 ps, and 2.97 ps and 7.14 ps, respectively. Multi-mode Brownian oscillator model, as an attempt to simulate the solvation dynamics, supported these fluorescence dynamics results. 

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