The hydroxyl groups on the surface of the beta-cyclodextrin are reacted with either "S" or "R,S" propylene oxide. This has the effect of extending hydrogen-bonding capabilities to accommodate greater distances of the chiral center from an aromatic ring structure. The "S" version (Astec® CYCLOBOND I 2000 SP) sometimes shows enhanced selectivity and efficiency for some separations, e.g., methadone.
