Polymer-Cyclodextrin Interactions

Besides inclusion complexation, the interaction between polymer and CD or drug-CD molecule is also reported, where water-soluble polymer either partially or totally 

O Drug olubiliz d vid non-indu ion by drug-CO compkx —Polymer 

Drug-CD-polymer complexation can be enhanced by brief heating of complexation media containing drug, CD and water-soluble polymer in an autoclave and cooling to room temperature. Such an effect is observed due to alteration in the hydration of the cyclodextrin molecule, and thus its three-dimensional structme, in aqueous solution [36]. 

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Harada and coworkers reported forming a photoresponsive hydrogel system by combination of a-cyclodextrin, dodecyl-modified poly(acrylic acid), and a photoresponsive competitive guest, 4,4 -azodibenzoic acid. An aqueous solution of dodecyl-modified poly(acrylic acid) exhibits a gel-like behavior, because polymer chains form a network structure via hydrophobic associations of Ci2 side chains. When a-cyclodextrin is added to the gel-like aqueous solution, the gel is converted to a sol mixture because hydrophobic interactions of Ci2 side chains are dissociated by the formation of inclusion complexes of a-cyclodextrin with the C12 side chains. Upon addition of 4,4 -azodibenzoic acid to the binary sol mixture of the modified poly(acrylic acid) and a-cyclodextrin, the cyclodextrin interacts predominantly with 4,4 -azodibenzoic acid ... 

J. Szeman, E. Fenyvesi, and J. Szejtli, Water soluble cyclodextrin polymers their interaction with drugs,/. Inch Phenom. Macrocycl. Chem., 5,427-431,1987. 

Water Soluble Cyclodextrin Polymers Their Interaction with Drugs 427 [319]... 

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. 

In this section an overview of the numerous methods and principles for the discrimination of enantiomers is given. First, the interaction principles of the polymer-based methods adapted from chromatographic procedures are illustrated. The discrimination of enantiomers was achieved some decades ago by using different types of stationary materials, like cyclodextrins or polymer-bonded amide selectors. These stationary-phase materials have successfully been appointed for label-free optical sensing methods like surface plasmon resonance (SPR) or reflectometric interference spectroscopy (RIfS). Furthermore, various successful applications to optical spectroscopy of the well-established method of fluorescence measurements for the discrimination of enantiomers are described. 

The adsorption isotherms of acid azo dyes onto water soluble and insoluble polymers containing cyclodextrin were measured in aqueous solution. The adsorption of dyes on both types of polymers increased with increase in the ratio of hydrophobic components in the dyes [38], Dyes derivative of dialkylaminobenzene were used for the dyeing of nylon 6 and 6,6 in the presence of interacting / -CD [39], / -CD showed good levelling properties in the dyeing of polyamide fibers. The observed effect can be due to the formation of complexes between /Acyclodcxtri n and dyes. 

Summary The analysis of supramolecular structures containing polymers, and the discussion about the effect of polymeric materials with different chemical structures that form inclusion complexes is extensively studied. The effect of the inclusion complexes at the air-water interface is discussed in terms on the nature of the interaction. The entropic or enthalpic nature of the interaction is analyzed. The description of these inclusion complexes with different cyclodextrines with several polymers is an interesting way to understand some non-covalent interaction in these systems. The discussion about the generation and effect of supramolecular structures on molecular assembly and auto-organization processes is also presented in a single form. The use of block copolymers and dendronized polymers at interfaces is a new aspect to be taken into account from both basic and technological interest. The effect of the chemical structure on the self-assembled systems is discussed. 

The importance of non - covalent interactions in biological systems has motivated much of the current interest in supramolecular assemblies [1]. A classical example of a supermolecule has been provided by the rotaxanes [2,3], in which a molecular rotor is threaded by a threaded by a linear axle . Another examples have been previously included as cyclic crown ethers threaded by polymers, paraquat -hydroquinone complexes [4] and cyclodextrin complexes [5,6],... 

Fig. 3 Photoresponsive polymer surface sensitive to pH and light. Adsorption and release of cytochrome c triggered by pH (b, c, and d) release of the polymer layer and cytochrome c by breaking the host-guest interactions between surface-tethered azo dye and cyclodextrin via light irradiation (a and d). The molecular structure on the right represents the host-guest complexa-tion of the azo dye with the cyclodextrin-modified poly(acrylic acid). Reprinted, with permission, from [68]. Copyright (2009) Wiley Interscience...

With "bifunctional" guest, i.e. that interacts with two cyclodextrins the binding is much stronger (57). This is clearly seen in the values of association constants and on the solubility enhancing effect of 8-cyclodextrin and its soluble polymers (Table III). 

Cyclodextrins (CDs) are chiral compounds which interact with enantiomers via diastereomeric interactions. The separation is achieved because of the difference in stabilities of the resulting diastereomeric complexes formed between each enantiomer and the CD. In the first CEC experiments incorporating CDs, di-methylpolysiloxane containing chemically bonded permethylated (3- or y-CD (Chirasil-DEX) was chemically bonded to the inner walls of fused silica capillaries [139,140]. Electoosmotic flow is generated in these capillaries in the same manner as in fused silica capillaries. The Chirasil-DEX does not mask all the silanol groups, so while EOF is decreased, it is not entirely diminished by the coating. Since that time, CDs or CD derivatives have been bonded to silica particles which were then packed into capillaries, and the CD has been incorporated into continuous polymer beds known as monoliths. Table 3 shows some different CSPs, enantiomers separated, resolution, and the number of theoretical plates per meter. 

Szejtli, J., Cserhati,T., and Szogyi, M. (1986), Interactions between cyclodextrins and cell-membrane phospholipids, Carbohydr. Polym., 6, 35 19. 

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