Cyclodextrins Work in Oils

Abstract

Cyclodextrins (CDs), which are produced from starch, are a class of cyclic oligosaccharides consisting of several α-(1,4)-linked D-glucose units. They have a cavity of sub-nanometer size, into which a guest molecule of the appropriate size and shape can be selectively incorporated. The ability of CDs to form inclusion complexes with guest molecules has been studied academically, and applications in various industrial fields including food, cosmetics, and pharmaceuticals have been developed. However, in most cases, inclusion complex formation with CDs has been limited to aqueous media and several kinds of polar organic media. On the other hand, the effective guest inclusion by CD hosts in nonpolar media has not been achieved yet, because the enormous amounts of nonpolar solvents and oils become a strong competitor for inclusion within the CD cavity. Recently, we found that 6-O-modified β-CDs, such as heptakis(6-O-tert-butyldimethylsilyl)-β-CD and heptakis(6-O-triisopropylsilyl)-β-CD, effectively formed inclusion complexes with polychlorinated aromatic compounds and pyrene in nonpolar solvents. In this review, I describe the inclusion complex formation between 6-O-modified β-CDs and various guest molecules in nonpolar media and the removal and recovery of polychlorinated biphenyls (PCBs) in oil using various CD hosts.