Cyclodextrin Chiral Stationary Phases

The cyclodextrins are produced by the partial degradation of starch followed by the enzymatic coupling of the glucose units into crystalline, homogeneous toroidal structures of different molecular size.

Courtesy of ASTEC Inc Figure 44. The Molecular Structure of a, b, and g Cyclodextrins

Three of the most widely characterized cyclodextrins are the alpha-, beta- and gamma-cyclodextrins that have been shown to contain 6 (cyclohexamylose), 7 (cycloheptamylose) and 8 (cyclooctamylose) glucose units respectively. These cyclic, chiral, torus shaped macromolecules contain the D(+)-glucose residues bonded through a-(1-4)glycosidic linkage The arrangement of the glucose units in the three different forms of cyclodextrin are shown in figure 44. The upper aperture of the torus-shaped cyclodextrin molecule has a larger circumference than the base aperture (see figure 45). The primary hydroxyl groups are located at the base of the torus on the C₆ atoms. As these hydroxyl groups are free to rotate they can partially block the base aperture. The size of the cavity increases with increasing number of glucose units (figure 45).