Using Cyclodextrins to Achieve Chiral and Non-chiral Separations in Capillary Electrophoresis

Cyclodextrins (CDs) are cyclic oligosaccharides composed of D-glucose units that are linked by α(1,4)-glucosidic bonds. The practically important, industrially produced CDs are α-CD, β-CD and γ-CD which differ in the number of glucose units involved [i.e., α-CD contains 6 glucose units, β-CD has 7 glucose units (Figure 1) and γ-CD has 8 glucose units]. CDs are generally produced through enzymatic conversion of starch. CDs have the shape of a torus with a hydrophobic interior cavity and a hydrophilic outside. The narrow rim is occupied by the primary hydroxyl groups at C6 while the wider rim contains the secondary hydroxyl groups at C2 and C3. The hydroxyl groups can be chemically modified resulting in a number of derivatives. With regard to their use as chiral selectors in CE the most important difference is the cavity size which is the smallest for α-CD and the largest for γ-CD.