Cyclodextrins arrays

If the cyclodextrins in the rotaxane structure are linked covalently, then the cyclodextrin array is maintained even after the stoppers and the polymer chain have been removed (Fig. 3.19). Reacting the cyclodextrins with epichlorohydrin under weak alkali conditions induces crosslinking between facing hydroxyl groups. The stoppers are then removed under stronger alkali... 

Methods development for chiral analyses has been one of the most challenging separation problems for the analytical chemist in the pharmaceutical industry. Racemic drug substances have a variety of chemical structures and several chiral selectors are available for the analyst to choose in order to obtain the enan-tioselectivity needed for chiral resolution. To alleviate this problem, a fast capillary electrophoresis procedure for the enantiomeric separation of acidic and basic compounds using native and modified cyclodextrins has been described (200). The technique is called cyclodextrin array chiral analysis. A generalized optimi-... 

A Guttman, S Brunet, N Cooke. Capillary electrophoresis separation of enantiomers by cyclodextrin array chiral analysis. LC-GC 14 32-42, 1996. 

T. Furiuke, R. Sadamoto, K. Niikura, K. Monde, N. Sakairi, and S.-I. Nishimura, Chemical and enzymatic synthesis of glycocluster having seven sialyl lewis X arrays using /i-cyclodextrin as a key scaffold material, Tetrahedron, 61 (2005) 1737-1742. 

Numerous CE separations have been published for synthetic colours, sweeteners and preservatives (Frazier et al., 2000a Sadecka and Polonsky, 2000 Frazier et al., 2000b). A rapid CZE separation with diode array detection for six common synthetic food dyes in beverages, jellies and symps was described by Perez-Urquiza and Beltran (2000). Kuo et al. (1998) separated eight colours within 10 minutes using a pH 9.5 borax-NaOH buffer containing 5 mM /3-cyclodextrin. This latter method was suitable for separation of synthetic food colours in ice-cream bars and fmit soda drinks with very limited sample preparation. However the procedure was not validated for quantitative analysis. A review of natural colours and pigments analysis was made by Watanabe and Terabe (2000). Da Costa et al. (2000) reviewed the analysis of anthocyanin colours by CE and HPLC but concluded that the latter technique is more robust and applicable to complex sample types. Caramel type IV in soft drinks was identified and quantified by CE (Royle et al., 1998). 

Scheme 9. Note that /3-cyclodextrin ( 8-CD) contains seven a-l,4-linked D-glucopyranose residues in a cyclic array.

In situ STM has been applied [326] to study the potential-induced self-organi-zation of a-cyclodextrin on Au(lll) surfaces in NaCl04 solutions. The adsorbed molecules formed an ordered array of a cylindrical structure in the potential range 0.20 to —0.15 V (versus SCE), while they were desorbed at potentials lower than -0.40 V. 

In other media like micelles, cyclodextrin, binary solvent mixtures, and proteins (47-55), lifetime distributions are routinely used to model the decay kinetics. In all of these cases the distribution is a result of the (intrinsic or extrinsic) fluorescent probe distributing simultaneously in an ensemble of different local environments. For example, in the case of the cyclodextrin work from our laboratory (53-55), the observed lifetime distribution is a result of an ensemble of 1 1 inclusion complexes forming and coexisting. These complexes are such that the fluorescent probe is located simultaneously in an array of environments (polarities, etc.) in, near, and within the cyclodextrin cavity, which manifest themselves in a distribution of excited-state lifetimes (53-55). In the present study our experimental results argue for a unimodal lifetime distribution for PRODAN in pure CF3H. The question then becomes, how can a lifetime distribution be manifest in a pure solvent ... 

All sensors of the array were exposed simultaneously to the test gases. Dry air was used as a carrier gas. In Fig. 9 the sensor responses of Iipodex E to both enantiomers of halodiether B in a concentration range from 0 to 140 xgl-1 is shown. The interaction between the cyclodextrin-recognition units and the S-enantiomer is stronger than that with the R-enantiomer. 

The first [5] super-cyclodextrin whose nano-sized cyclo-pentameric array is held only by a mechanical bond was synthesized by the pentakis-azo coupling of a new hermaphrodite monomer with 2-naphthol as a stopper, isolated by chromatography, and characterized by MS, 2D NMR, and visible spectral methods with the help of computer simulation [60], Cyclic pentamer (as red film, 15% yield) accompanied with the corresponding monomer (20%) (Figure 22) was obtained. 

For the pattern recognition (PARC) approach, we have coated the piezoresistive cantilevers with different selective layers. Each piezoresistive cantilever had four cantilever elements. Two of these cantilevers were coated with gold, whereas the other two served as reference cantilevers. We have used four separated chips arranged into an array in a single vapor chamber. Each cantilever chip was coated with a different selective agent. The four coatings used in our study include 4-MBA, Au (evaporated), CH3(CH2)n-SH, and a complex of (i-cyclodextrin and alkane. 

In traditional analytical chemistry the determination of enantiomeric purity is sometimes carried out by capillary electrophoresis (CE) in which the electrolyte contains chiral selectors such as cyclodextrin (CD) derivatives [54], Unfortunately the conventional form of this analytical technique allows only a few dozen ee determinations per day. However, as a consequence of the analytical demands arising from the Human Genome Project, CE has been revolutionized in recent years so that efficient techniques for instrumental miniaturization are now available, making ultra-high-through-put analysis of biomolecules possible for the first time [55]. Two different approaches have emerged, namely capillary array electrophoresis (CAE) [55a - e] and CE on microchips (also called CAE on chips) [55f - m[. Both techniques can be used to carry out... 

Solubilisation by surface-active agents is discussed in Chapter 6. Alternatives to micellar solubilisation (or solubilisation in vesicles) include the use of the cyclodextrin family. When the first edition of this book was published in 1981 (and a diagram of a cyclo-dextrin-dmg complex was used to adorn the cover), the use of cyclodextrins was in its infancy. Attention was then focused around a-, P- and yavailable commercially for pharmaceutical use. Ten per cent of this cyclodextrin can enhance the solubility of betamethasone 118 times, of diazepam 21 times and of ibuprofen 55 times. 

Generally speaking, an antenna for light harvesting is an organized multicomponent system in which several chro-mophoric molecular species absorb the incident light and channel the excitation energy to a common acceptor component. Artificial antenna systems based on porphyrin arrays [63], multichromophoric cyclodextrins [64], polynuclear metal complexes [65, 66], dendrimers [66-68], and polymers [69, 70] have been reported. In all these systems, the chromophoric units are connected by means of covalent... 

A simple calixarene built up with four phenol units linked via methylene bridges is shown in Fig. 10 (substitution of the methylene junctions with S atoms gives rise to the class of thiocalixarenes). Cooperative networks of intramolecular hydrogen bonds (circular array of hydrogen bonds, observed also in cyclodextrins) play a capital role in the cavity shape as well as in the conformational features of the macrocyclic skeleton [291-293]. Encapsulation of other molecules in the cavity is also controlled by hydrogen bonds [294]. 

G Luo, Y Wang, AG Ewing, TG Strein. Chiral separation of a novel calcium antagonist using capillary electrophoresis with cyclodextrins and diode array detection. J Capillary Electrophor 1 175-180, 1994. 

Native cyclodextrins are oligosaccharides composed of six or more D-glucopyranose residues attached by a-1,4-linkages in a cyclic array. The most current cyclodextrins contain six, seven, or eight glucose residues and are named a-cyclodextrin (a-CD), /3-cyclodextrin (/3-CD) and y-cyclodextrin (7-CD), respectively (Figure 1). ... 

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