The Mechanism of Chromatographic Retention - Chiral Chromatography > Chiral Polysiloxane Stationary Phases > Page 69
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. Three of the most widely characterized are the alpha-, beta- and gamma-cyclodextrins and 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 linkages. The arrangement of the glucose units in the three different forms of cyclodextrin are shown in figure 33.
The mouth of the torus-shaped cyclodextrin molecule has a larger circumference than at the base and is linked to secondary hydroxyl groups of the C2 and C3 atoms of each glucose unit (see figure 34).
Figure 33 The Structure of a, b, and g Cyclodextrins