Cyclodextrins using

Fig. 7. A tethered cyclodextrin and the structure of P-cyclodextrin, the most common cyclodextrin used as a bonded ligand in Hquid chromatography.

Cyclodextrins can solubilize hydrophobic molecules in aqueous media through complex formation (5-8). A nonpolar species prefers the protective environment of the CDx cavity to the hulk aqueous solvent. In addition, cyclodextrins create a degree of structural rigidity and molecular organization for the included species. As a result of these characteristics, these macrocycles are used in studies of fluorescence and phosphorescence enhancement (9-11), stereoselective catalysis (.12,13), and reverse-phase chromatographic separations of structurally similar molecules (14,15). These same complexing abilities make cyclodextrins useful in solvent extraction. 

An interesting equilibrium study was performed by Kasatani and coworkers on the interaction of a series of cyanine dyes with beta and gamma cyclodextrin, using u.v.-visible spectrophotometric measurements. The results were consistent with the enhancement of dimer formation by inclusion of the dye molecules within the cyclodextrin. As expected from the work of others, such geometrical factors " as the size of the aromatic groups and the lengths of the central methine chains strongly influence the occurrence of dimer formation within the cyclodextrin cavity. 

As a third example, consider a passage from the cyclodextrin article (P16). The authors provide useful background information on two types of cyclodextrins used in bioremediation HPBCD and RAMEB. The two cyclodextrins are compared, and the authors explain why RAMEB was chosen over HPBCD, thereby leading up to the current work. 

Substance Cyclodextrin used Analysis Reference comments... 

P Cescutti, D Carozzo, R Rizzo. Study of the inclusion complexes of aromatic molecules with cyclodextrins using ionspray mass spectrometry. Carbohydr Res 290 105-115, 1996. 

Attempted asymmetric halogenation of fraws-2-butenoic acid in a crystalline a-cyclodextrin using gaseous Br2 or CI2 at 45-50 °C was unsuccessful, giving very poor enantioselectivity162. Exposure of chiral crystals of dibenzobarrelene (90) to bromine vapour results in formation of the rearranged addition product 91 in up to 8% e.e.163. 

Adsorption chromatography on cellulose was examined for azo dyes that form complexes with CDs using aqueous solutions of a-CD as eluents. The cyclodextrin substantially increases the RF values [61], Commercial a-, [>-. and y-CD polymers were used for the same purpose, however changes of RF were observed only for some azo dyes [62], 2-Hydroxypropyl-P-cyclodextrin used in 10-20% concentration causes complete elution of many compounds [63],... 

Girardeau et al. [53] have described the chain dynamics of PEO within nanotubes of a-cyclodextrin using dueterated PEO (d-PEO) and 2H solid - state NMR spectroscopy. The chain dynamics were explored and compared with the respective unthreaded d-PEO. As these materials are continually proposed for applications in molecular-level devices [54,55] characterization of their molecular dynamics is important since they play a key role in governing bulk physical properties. 

Calculate the area(s) under the peak for each volatile organic compound, and convert it to milligrams per kilograms of gamma-Cyclodextrin using the response factor for 8-cyclo-hexadecen-l-one. The response factor is determined from a calibration curve using 8-cyclohexadecen-l-one concentrations of 0.1 to 6 mg/100 mL of hexane. 

Aktas et al. [141] showed an increased permeation of pilocarpine nitrate com-plexed with hydroxy-propyl-P-cyclodextrin using isolated rabbit cornea. They found a significant reduction in the pupil diameter compared to a simple aqueous solution... 

Photolysis of chlorpromazine (1). The photolysis of 1 results mainly in oxidation to the corresponding sulfoxide. Irradiation in the presence of a cyclodextrin (CD), however, results mainly in dechlorination to promazine (2), which is also converted into a sulfoxide, (3), on photolysis. The rate of conversion of 1 to 2 depends on the cyclodextrin used, the rates following the order /3-cyclodextrin >y-cyck)dextrin> a-cyclodextrin. Since these cyclodextrins differ in the size of the cavity, it appears that the conversion of 1 to 2 takes place within the inclusion complex. ... 

Cyclodextrins can form inclusion complexes with some drugs, modifying their physical and chemical properties. Because cyclodextrins are mainly used to increase the solubility of poorly soluble drugs, most investigations in this field focus on photostability of drugs in solution. Here, the positive effect of cyclodextrins on the photostability of colchicine (36), emetine and cephaeline (37) could be shown. However, these results show that the photoprotective effect depends on the particular cyclodextrin used. For some forms of cyclodextrin, an increase of the photodegradation rate can be obtained, as the example of molsidomine shows (13). 

Suzuki, M. Ito, K. Fushimi, C. Kondo, T. Application of freezing point depression to drug interaction studies. I. A study of 1 1 Plus 1 2 complexes between barbiturate and a-cyclodextrin using the freezing point depression method. Chem. Pharm. Bull. 1993, 41 (8), 1444—1447. 

Sulfobutylether P-cyclodextrin is prepared by alkylation of P-cyclodextrin using 1,4-butane sultone under basic conditions. The degree of substitution in P-cyclodextrin is controlled by the stoichiometric ratio of P-cyclodextrin to sultone used in the process. 

Blaschke, G. Separation of brompheniramine enantiomers by capillary electrophoresis and study of chiral recognition mechanisms of cyclodextrins using NMR spectroscopy, UV spectrometry, electrospray ionization mass spectrometry and X-ray crystallography. J. Chromatogr., A 2000, 875, 471-484. 

Fig. 20 a The polyrotaxane formed by a-CD and PEO with 2,4-dinitro-phenyl end caps, b The figure-of-eight cross-link covalently cross-linked cyclodextrins. c Schematic diagram of the polyrotaxane gel prepared from the sparse polyrotaxane by covalently cross-linking cyclodextrins using cyanuric chloride as crosslinking agent [89]... 

---