Undesirable reaction of aqueous cyclodextrin solutions with polypropylene

Cyclodextrins are cyclic sugars that have extensive applications in the pharmaceutical, food, biomedical, and other industries. Although cyclodextrins are water-soluble sugars, they have hydrophobic central cavities that are capable of accommodating nonpolar molecules of the right dimensions. This inclusion complexation property, which is key to its utilization in solubilization and stabilization of nonpolar guest molecules, can also lead to undesirable reactions. The present investigation demonstrates the ability of aqueous cyclodextrin solutions to extract plastic additives when stored in polypropylene tubes that are commonly used in biological research. Storage of α- and γ-cyclodextrin solutions in polypropylene microcentrifuge tubes led to the extraction of 2,6-di-tertbutyl-p-cresol, or BHT, a common additive used as an antioxidant and for polymer stabilization. γ-Cyclodextrin solutions also formed an insoluble complex with an unidentified substance. These results suggest the potential of cyclodextrin solutions stored in plastic containers to be contaminated with additives. In many cases, the additives added by plastic manufacturers may be trade secrets and difficult to identify. One should be cautious in using aqueous cyclodextrin solutions stored in plastic containers for biological or biomedical research and applications.