Cyclodextrins types

It is in the study of this phenomenon where two-dimensional GC offers by far the most superior method of analysis. The use of chiral selector stationary phases, in particular modified cyclodextrin types, allows apolar primary and atropisomer selective secondary separation. Reported two-dimensional methods have been successful... 

A chiral GC column is able to separate enantiomers of epoxy pheromones in the Type II class, but the applications are very limited as follows a custom-made column packed with a p-cyclodextrin derivative as a liquid phase for the stereochemical identification of natural 3,4- and 6,7-epoxydienes [73, 74] and a commercialized column of an a-cyclodextrin type (Chiraldex A-PH) for the 3,4-epoxydiene [71] (See Table 3). The resolution abilities of chiral HPLC columns have been examined in detail, as shown in Table 7 and Fig. 14 [75,76, 179]. The Chiralpak AD column operated under a normal-phase condition separates well two enantiomers of 9,10-epoxydienes, 6,7-epoxymonoenes and 9,10-epoxymonoenes. Another normal-phase column, the Chiralpak AS column, is suitable for the resolution of the 3,4-epoxydienes. The Chiralcel OJ-R column operated under a reversed-phase condition sufficiently accomplishes enantiomeric separation of the 6,7-epoxydienes and 6,7-epoxymonoenes. 

A limited amount of published information on the effect of cyclodextrins on the photostability in the solid state is available. Results similar to those reported for solutions, related to the choice of cyclodextrin type can be expected for the solid state. This was confirmed by Tomono et al.who showed that the remaining content of four different drugs increased or decreased after irradiation, depending on the selected cyclodextrin type (38). 

In an attempt to increase the number of useful components for construction of new catenanes, the Stoddart group recognised that cyclic sugars of the cyclodextrin type were promising candidates. ... 

Another approach is electrochromatography with capillary columns packed with an achiral stationary phase, preferentially a reversed-phase type material. The chiral SO is added to the background electrolyte, and may be adsorbed onto the stationary phase by a secondary equilibration process. Enantioseparations in this additive mode have been reported with cyclodextrin type SOs )504-507) and with a chiral ion-pair agent derived from quinine 1508) as mobile phase additives. 

Drug concentration Crystal modification Cyclodextrins (type)... 

Cyclodextrins are bucketlike or conelike toroid molecules, with a rigid structure and a central cavity, the size of which varies according to the cyclodextrin type see Section 8. The internal surface of the cavity is hydrophobic and the outside of the torus is hydrophilic this is due to the arrangement of hydroxyl groups within the molecule. This arrangement permits the cyclodextrin to accommodate a guest molecule within the cavity, forming an inclusion complex. 

Fig. 2 Influence of cyclodextrin type on the chiral resolution of the basic drug tocainide and related substances using 40 mM sodium phosphate (pH 3.0) containing (a) 20 mM -CD and (b) 50 mM methyl- -CD and 50 mM heptakis (2,6 di-O-methyl-jS-CD. [Adopted with kind permission from D. Beider and G. Schomburg, Chiral separations of basic and acidic compounds in modified capillaries using cyclodextrin-modified capillary zone electrophoresis, J. Chromatogr. A 666 351 (1994).]...

GC on cyclodextrine type CSP of the O-TFA derivative of methyl lactate Analysis of methyl lactate O-TFA form. Good resolution between the two enantiomers Good reproducibility Requires double derivatization with the use of diazomethane 0.1 %... 

GC on cyclodextrine type CSP of a dioxolanone type derivative No racemization of the sample on derivatization Difficult integration of the peaks Derivatization of the sample < 0.5 %... 

Chromatograms corresponding to the separation of the enantiomers of derivatives of methyl and isobutyl esters of lactic acid are presented in Figure 11. The method developed is non racemizing and gives results comparable with those given by GC on cyclodextrine type CSP. 

Popielarski S R, Mishra S, Davis M E (2003). Structural effects of carbohydrate-containing polycations on gene delivery. 3. Cyclodextrin type and functionalization. Bioconjug. Chem. 14 672-678. 

The cyclodextrins can tolerate relatively high buffer concentrations and are stable from pH 3 to pH 14. However, the stability of the silica matrix restricts the pH range from 3. 0 to about 7.0, as silica is significantly soluble at a pH of 8.0 and higher. Cyclodextrin type stationary phases may be operated in the polar or reversed phase mode. As with the other LC stationary phases, mobile phases with high water contents have little dispersive properties and thus the dispersive interactions with the stationary phase can be exploited. Conversely, if strongly dispersive... 

The principal idea behind MIP synthesis is the generation of solution state complexes between the template ligand in hand and appropriate functional monomers, followed by subsequent freezing of these complexes by copolymerization of the above with an excess of a cross-linking monomer. These monomer-template complexes are stabilized by non-covalent interactions, reversible covalent interactions, or metal ion-mediated interactions. The types of interactions that are usually exploited in molecular imprinting are 1) cleavable covalent bonds 2) tt-tt interactions 3) hydrogen bonds 4) hydrophobic van der Waals interactions 5) crown-ether/cyclodextrin type interactions 6) metal-Ugand... 

Chiral separations can be carried out using an amino acid-based or a cyclodextrin-type (Section 3.5.5.2) stationary phase. The latter is most common, and the selectivity is based on surface interactions or inclusion. Usually rather low temperatures are used as enantioselectivity is rare above 200 °C. Because of higher plate numbers, capillary GC columns generally give better enantiomeric separations than HPLC columns. 

FIGURE 6.7 The reduction in headspace volatiles (average of six) above an ethanohwater solution (3.6% alcohol) as inflnenced by temperature and cyclodextrin type (1% cyclodextrin). Y axis is relative to amounts of volatiles in headspace with no cyclodextrin. (From Reineccius, T.A., G.A. Reineccius, T.L. Peppard, J. Food Sci., 68(4), p. 1234, 2003. With permission.)... 

Chankvetadze B, Buijanadze N, Crommen 1, Blaschke G (2001) Enantioseparation of warfarin using cyclodextrin type chiral selectors. Chromatographia 53 S296-S301... 

---