Cyclodextrins and water solubility

Matsumoto, M., Matsuzawa, Y., Noguchi, S., Sakai, H., and Abe, M. (2004), Structure of Langmuir-Blodgett films of amphiphilic cyclodextrin and water-soluble benzophenone, Mol. Cryst. Liq. Cryst., 425,197-204. 

Although the understanding of IPTC is still limited in comparison to that of normal PTC, it is clear that this method is apt to effect organic reactions in water. As discussed in the introduction simple pyridine derivatives were introduced mainly in connection to kinetic and mechanism studies, but more recently, it was shown that the use of host compounds such as cyclodextrins and water-soluble calix[n]arenas,offers the opportunity to combine IPTC, molecular recognition, and transition metal catalysis, with additional economic and environ-metal advantages deriving from the use of water as a bulk solvent. 

L.N.C. Rodrigues, M.G. Issa, A.C.C. Asbahr, M.A.C. Silva, and H.G. Ferraz, Multicomponent complex formation between pyrimethamine, cyclodextrins and water- soluble polymers,... 

B. Cappello, C. Carmignani, M. lervohno, M.L La Rotonda, and M.F. Saettone, Solubilization of tropicamide by hydroxypropyl-beta-cyclodextrin and water-soluble polymers In vitro/in vivo studies, Int. J. Pharm., 213 (1-2), 75-81,2001. 

Reduction via inclusion complexes has received considerable attention because it allows both the diastereo- and enantioselectivity of the reaction to be controlled. Cyclodextrins and water-soluble cyclophanes are the most frequently used hosts in aqueous medium. P-CD/ketone (1 1) complexes suspended in NaBH4 aqueous alkaline solution give the corresponding alcohols quantitatively but with modest ee [75]. An improvement is obtained by using crystalline a-, P- and y-CD inclusion complexes of achiral amine-boranes at 0°C in heterogeneous aqueous medium [76]. Under these conditions, 1-phenylethanone and 4-phenyl-2-butanone give the (5) and (R) alcohol with 91% and 89% ee, respectively. 

Addition of an aqueous solution of PEG to a saturated aqueous solution of a-CD at room temperature did not lead to complex formation unless the average molecular weight of PEG exceeded 200 [46]. Moreover, carbohydrate polymers such as dextran and pullulan failed to precipitate complexes with PEG, and the same was true for amylose, glucose, methyl glucose, maltose, maltotriose, cyclodextrin derivatives, such as glucosyl-a-CD and maltosyl-a-CD, and water-soluble polymers of a-CD crosslinked by epichlorohydrin. These facts suggested to Harada et al. the direction for further research. 

T. Andersson, K. Nilsson, M. Sundahl, G. Westman, and 0. Wenner-strom, C6o embedded in 7-cyclodextrin A water-soluble fullerene. J. Chem. Soc. Chem. Commun. 604-606 (1994). 

Cyclodextrins are water-soluble materials and provide a hydrophobic microenvironment in water. On this basis, CDs can accommodate various organic compounds, and unique reactions may proceed in the constrained media. In this chapter, we have described mainly modified CDs with one, two, or more chro-... 

Cyclodextrins are water-soluble cyclic oligosaccharides with hydrophilic cavities of different sizes. For incorporation of Ceo, thereby facilitating its dissolution in aqueous media, y-CD is the most promising candidate. Molecular modeling (i.e., balancing of cavity radius and fullerene size) suggests that a full inclusion in the... 

In eye drop formulations, cyclodextrins form water-soluble complexes with lipophilic drugs such as corticosteroids. They have been shown to increase the water solubility of the drug to enhance drug absorption into the eye to improve aqueous stability and to reduce local irritation. ... 

Cyclodextrins are water-soluble hosts for hydrophobic guests. The formation of inclusion complexes is controlled by the dimensional compatibility of the guest and host cavity. Commercially available dextrins are, in fact, inclusion complexes of cyclodextrins with two water molecules closing the entrance to the cavity. The formation of cyclodextrin inclusion complexes is reversible and, therefore, is governed by concentration of guests competing for a place inside the cavity. 

Stability constants (equilibrium constants for complex formation, Kc) for many steroids in a-, P and y-cyclodextrin have been reported (IX) for hydrocortisone and simple substitutions, they typically have magnitudes of Kc = 2000 to 4000 M 1 for P and f- CD s, and Kc = 50 to 200 for O- CD. They are hydrophilic and water soluble. We tested them for angiogenic activity in combination with hydrocortisone, with negative success. 

Andersson T, Nilsson K, Sundahl M, Westman G and Wennerstrom O 1992 Cgg embedded in y-cyclodextrin a water-soluble fullerene J. Chem. Soc., Chem. Common. 604-6... 

It is known from crystal structure and spectroscopic analyses that the cyclodextrins in the solid state as well as in solution exist in an approx, round, conical shape (4) with a height of the wall of approx. 8 A and an inner cavity diameter varying between 5 (GC-) and 7.5 A (y-CyD). The cyclodextrins are water-soluble due to their high number of hydroxylic groups they contain and which all lie on the outside of the molecule. In contrast to that, the cavity of the cyclodextrins is surrounded by CH- and glycosidic C—O bonds and therefore is hydrophobic inside. 

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]. 

Cyclodextrins are water-soluble cyclic oligomers of glucose, the most common of which are a-, / - and y-cyclodextrin with six, seven or eight glucose moieties, respectively. Owing to their conical shape with a hydrophobic interior and a hydrophilic exterior, they form water-soluble complexes with inorganic or organic compounds. Comparison of the VCD spectra of the a- and /3-cyclodextrins with hydroxyl-... 

The water-soluble complexes with fullerenes have been achieved by using y-cyclodextrin (y-CD), water-soluble cal-ixarene, miscelle, and water-soluble polymers. 

Amiel, C. Sandier, A. Sebille, B. Valat, P. Wintgens, V. Associations between end-capped polyethylene oxide and water-soluble b-cyclodextrin polymers,J. polymer Analysis Characterisation 1995. 1, 289-300. 

To circumvent these difficulties, a preparation of water-soluble coelenterazine has been developed (Teranishi and Shimomura, 1997a). The preparation contains coelenterazine and 50-times (by weight) of hydroxypropyl-P-cyclodextrin. To prepare this material, 0.1 ml of 3.0 mM coelenterazine in methanol and 0.2 ml of 45 mM solution of the cyclodextrin are mixed and dried under reduced pressure. The dried residue is extracted with 1.0 ml of lOmM phosphate buffer, pH 7.0, containing 2 mM EDTA (if needed), and the extract (after centrifugation) is again dried under reduced pressure. With this preparation, an aqueous solution containing up to 3 mM coelenterazine can be made. 

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

Dendritic hosts can be used in aqueous solution to encapsulate water-soluble fluorescent probes. Changes in the photophysical properties of these encapsulated probes are useful to understand the properties of the microenvironment created by the dendritic interior. For example, adamantyl-terminated poly(pro-pylene amine) dendrimers from the first to the fifth generation (36 represents the third generation) can be dissolved in water at pH<7 in the presence of -cyclodextrin because of encapsulation of the hydrophobic adamantyl residue inside the /1-cyclodextrin cavity and the presence of protonated tertiary amine units inside the dendrimer [72]. Under these experimental conditions, 8-anifi-... 

As described above, the enzymatic polymerization of phenols was often carried out in a mixture of a water-miscible organic solvent and a buffer. By adding 2,6-di-0-methyl-(3-cyclodextrin (DM-(3-CD), the enzymatic polymerization of water-insoluble m-substituted phenols proceeded in buffer. The water-soluble complex of the monomer and DM-(3-CD was formed and was polymerized by HRP to give a soluble polymer. In the case of phenol, the polymerization took place in the presence of 2,6-di-O-methyl-a-cyclodextrin (DM-a-CD) in a buffer. Only a catalytic amount of DM-a-CD was necessary to induce the polymerization efficiently. Coniferyl alcohol was oxidatively polymerized in the presence of a-CD in an aqueous solution. ... 

A variety of new water-soluble ligands are being developed and the role of additives, particularly for enhancing solubility of sparingly soluble solutes in water, has been assessed even the use of (3-cyclodextrin to increase solubility has been studied. 

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