Cyclodextrin-solute complexation

The pH, temperature, and ionic strength of the mobile phase also affect the cyclodextrin-solute complexation and retention properties. Many enantioseparations using cyclodextrin-modified systems involve solutes with an aromatic ring substituent or similar cyclic structure at the chiral center. A variety of chiral barbiturates, hydantoins, and related compounds have been resolved by using (3-cyclodextrin and alkylated B-cyclodextrin-modified systems. 

Several intermolecular interactions have been proposed and discussed as being responsible for the formation of cyclodextrin inclusion complexes in an aqueous solution 6-10). They are... 

Cyclodextrin solution for extraction studies was prepared at a concentration of 1.00 x 10" iif by dissolving solid y-CDx in deionized water (Continental Water Systems, Atlanta, Georgia). Fresh solution was prepared daily to prevent bacterial growth and CDx decomposition from interfering with complexation and extraction. Cyclodextrin was purchased from Advanced Separation Technologies, Inc. (Whippany, New Jersey) and was used as received. Solid CDx from one lot number was used for all extractions. 

Lopez-Nicolas JM, Bru R, Sanchez-Ferrer A and Garcia-Carmona F. 1995. Use of soluble lipids for biochemical processes linoleic acid cyclodextrin inclusion complexes in aqueous solutions. Biochem J 308 151-154. 

Complexes of metal cations with carbohydrates in solution, 47, 1 -43 Courtois, Jean Emile, obituary of, 49,11 -18 Cyclomalto-oligosaccharides(cyclodextrins), inclusion complexes of, 46, 205-249 addendum to, 46, 333-335... 

Of particular interest in the application of cyclodextrins is the enhancement of luminescence from molecules when they are present in a cyclodextrin cavity. Polynuclear aromatic hydrocarbons show virtually no phosphorescence in solution. If, however, these compounds in solution are encapsulated with 1,2-dibromoethane (enhances intersystem crossing by increasing spin-orbit coupling external heavy atom effect) in the cavities of P-cyclodextrin and nitrogen gas passed, intense phosphorescence emission occurs at room temperature. Cyclodextrins form complexes with guest molecules, which fit into the cavity so that the microenvironment around the guest molecule is different from that in... 

The majority of reported studies of formation of cyclodextrin inclusion complexes in solution have been mainly concerned with determination of the stability constants by using equilibrium spectroscopic techniques, and the measurement of the enthalpy and entropy changes characterizing the complexation reaction. The aim of much of this work has been to determine the driving force of complex-formation. Despite the amount of research in this area, however, no general agreement has been reached, and... 

Rao et al. observed that photoirradiation of tran.v-stilbene in crystalline y-cyclodextrin inclusion complexes yields a single isomer of. svn-tctraphenylcy-clobutane (119) [109] stereoselectively in high yield (70%). In contrast, the photodimerization of stilbene in solution is very inefficient, and no photodimer was observed even after prolonged irradiation of pure stilbene crystals. 

Cyclodextrins form complexes with diazonium salts. Rates and product distribution for spontaneous dediazoniation of isomeric methylbenzenediazonium salts in the presence of a-, / -, and y-CD in aqueous acidic solution were found to be independent on acidity and CDs concentration [8], cf. [9],... 

It was found that formation of the 6-cyclodextrin inclusion complex improved the compound solubility from less than 0.5 mg/mL to 160 mg/mL, eliminating the formulation problems associated with solubility concerns [65]. Although retinoic acid does exhibit intrinsic CD when dissolved in dimethyl sulfoxide, the CD spectrum is drastically upon formation of the cyclodextrin inclusion complex (see Figure 10). That CD can be measured in the absorption bands located at 350 and 400 nm can be taken as evidence that it is the conjugated sidechain of the retinoic acid solute which becomes included in the cavity of the cyclodextrin host system. 

Cholesterol may be removed selectively by cyclodextrins. Melted milk fat is mixed with a cyclodextrin solutions and the complex is removed by washing. The ability of cyclodextrin to form an inclusion complex with cholesterol has been applied to reduce the cholesterol content of milk fat, cream or milk (Courregelongue and Maffrand, 1989 Oakenfull et al., 1991). However, the high cost of cyclodextrin prevents its use on an industrial scale. 

Aqueous a-cyclodextrin solutions seem to be generally applicable for TLC separation of a wide variety of substituted aromatics on polyamide thin-layer stationary sheet (13-14). In most cases, the compounds moved as distinct spots and their R, values were dependent on the concentration of the cyclodextrin in tne mobile phase. In a given family of compounds, (o-, m-, and p-nitrophenols, for example) the isomer with the largest stability constant for a-cyclodextrin complex formation had the larger value. In general, the para-substituted isomers have larger R values than the meta-isomers, which in turn have larger R values than the ortho substituted ones. 

Least-Squares Iterations Nonlinear Evaluation of Cyclodextrin Multiple Complex Formation with Static and Ionizable Solutes... 

Studies by Rundle et al., which were reviewed by Szejtli and Augustat,382 point to the helical structure of amylose in aqueous solutions. The dimensions of the amylose helix are well recognized, and therefore the structural similarity of the turns of the helix to cyclomaltohexaose (a-cyclodextrin) is sound. The a-cyclodextrin-water complex contains two guest molecules of water inside the cavity.383 Therefore, it may be accepted that part of the constitutional water of starch is included inside the amylose helix. Indeed,... 

The cyclodextrin-solute inclusion complexation is a reversible reaction with an equilibrium constant similar... 

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