Cyclodextrin immobilized

Immobilization. The abiUty of cyclodextrins to form inclusion complexes selectively with a wide variety of guest molecules or ions is well known (1,2) (see INCLUSION COMPOUNDS). Cyclodextrins immobilized on appropriate supports are used in high performance Hquid chromatography (hplc) to separate optical isomers. Immobilization of cyclodextrin on a soHd support offers several advantages over use as a mobile-phase modifier. For example, as a mobile-phase additive, P-cyclodextrin has a relatively low solubiUty. The cost of y- or a-cyclodextrin is high. Furthermore, when employed in thin-layer chromatography (tic) and hplc, cyclodextrin mobile phases usually produce relatively poor efficiencies. 

The well-known reaction between phenol and chloroform in the presence of concentrated sodium hydroxide is amenable to dramatic changes with cyclodextrins. -cyclodextrin, immobilized with epichlorohydrin, seems to give 100 % selectivity for para... 

Not only analytical or preparative separations can be performed on cyclodextrin polymer columns, but also undesired components can be removed from aqueous solutions, bitter tasting substances (narin-gin, limonin) can be removed or at least their concentration can be strongly reduced after treatment of citrus juice with cyclodextrin polymers in batch or column process (65,66). Phenylalanine can be eliminated from dietetic protein hydrolysates (67), water-soluble organic substances (e.g. polychlorinated biphenyls (68), 2-naph-talenecarboxylate or phenol can be removed from aqueous solutions (e.g. from pharmaceutical wastewater) by polystyrene-cyclodextrin derivatives (69), by 8-cyclodextrin immobilized on cellulose (70) or by 6-cyclodextrin-polyurethane polymer (71). 

A simpler and more general alternative relies on the ability of fi -cyclodextrin immobilized on a Sephacryl support to form host/guest complexes with a wide range of organic molecules, including chromophores [105]. On addition of cyclodextrin-functionalized Sephacryl resin 77 to the protein-labeling reactions, the modified protein is bound by the resin while unmodified protein is left in the solution. Following isolation of the resin via filtration, the captured protein... 

Weisz, PB and PA Yardley. Cyclodextrin polymers and cyclodextrins immobilized on a solid surface. US Patent Publication, 5262404. 

Armstrong, D. Tang, Y. Ward, T. Nichols, M. Derivatized cyclodextrins immobilized on fused-silica capillaries for enantiomeric separations via capillary electrophoresis gas chromatography, or supercritical fluid chromatography. Anal. Chem. 1993, (55, 1114-1117. 

ABSTRACT. 3-cyclodextrin immobilized with epichlorohydrin was used... 

A CSP with a smaller (i-cyclodextrin moiety (seven glucose units) immobilized on silica gel (ChiraDex ) is able to separate the dansyl-derivatives [5-(dimethy-lamino)-naphthalin-l-sulfonylchloride] of amino acids [26]. 

Vassileva, A., Burhan, N., Beschkov, V. et al.. Cyclodextrin glucanotransferase production by free and agar gel immobilized cells of Bacillus circulans ATCC 21783, Process Biochem., 38 (2003) 1585-1591. 

One additional advantage of chiral CE over chromatographic techniques is that both the chiral selector and the analyte reside in a free solution in this technique. This makes the investigation of chiral drug-cyclodextrin interactions technically much easier, cheaper, and faster, because unlike chromatographic techniques there is no need to immobilize the receptor (selectors). However, an even more important advantage is that there is no effect of immobilization on the degree of freedom of the selector and the effects of a solid matrix are absent. 

DNA has also been immobilized on Au electrode by its interaction with gem-ini surfactants [216]. Moreover, inclusion complexes of viologen-attached alkanethi-ols and a- and /J-cyclodextrins that spontaneously assemble on Au electrodes have been studied [217, 218]. 

Figure 5. A model of the / -cyclodextrin structure. The hydroxy groups can be (partially) derivatized so as to alter the structure and also to facilitate immobilization chemistry.

Figure 6. Example of resolution of chiral drugs on immobilized /3-cyclodextrin derivatized with (S)-naph-thylethyl isocyanate leaving polar carbamoyl groups. Reprinted with permission from ref 62.

An interesting example of a system whose components become mechanically bound upon surface immobilization is rotaxane trans-21 (Fig. 13.24), consisting of a ferrocene-functionalized /3-cyclodextrin (fi-CD) macrocycle threaded on a molecule containing a photoisomerizable azobenzene unity and a long alkyl chain.33 A monolayer of trans-21 was self-assembled on a gold electrode. Therefore, the ring... 

The separation of enantiomers can be effected either by transforming them into diastereoisomers using a chiral reagent and separating them on conventional phases or by separating the enantiomers on chiral phases. The utilization of chiral phases has not yet become routine, but studies of enantiomeric dipeptides have been carried out (115,116). Pirkle et al. (117) and Hyun et al. (118) separated enantiomeric di- and tripeptides (methyl esters of /V-3-5-dinitrobenzoyl derivatives) on chiral stationary phases (CSPs) derived from (R)-a-arylalkylamines, (S)-N-(2-naphthyl) valine, or (S)-1 -(6,7-dimethyl-1 -naphthyl) isobutylamine. These workers were able to separate four peaks for each dipeptide derivative, corresponding to the two enantiomeric pairs (R,R)/(S,S) and (R,S)/(S,R). Cyclodextrin-bonded stationary phases and chiral stationary immobilized a-chymotrypsin phases were used to separate enantiomeric peptides (118a,b). 

We finish this Section with enzymic conversions that are difficult to classify elsewhere Takasweet, a commercial variety of immobilized glucose-iso-merase, converts 6-O-methyl-D-fructose and 6-deoxy-D-fructose into the gluco isomers in not very satisfactory yield.34 A mixture of catalase (75 U/mmol) and glucose oxidase (80 U/mmol) oxidizes xylitol to L-xylose in 50% yield, on the 100- mol scale.106 The enzyme cyclodextrin a-(l—>4)-glucosyltransferase (1000 U immobilized on silica gel-glutaraldehyde) allows107 preparation of cyclomaltohexaose (0.3 g), cyclomaltoheptaose... 

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