Hydrogels having tubular α-cyclodextrin structure: effect of nano-tube structure on long alkyl chain partitions

Abstract

New hydrogels having the tubular structure of a-cyclodextrins (a-CDs) crosslinked by poly(ethylene glycol) (PEG) (MT-PEG hydrogels) were prepared by using a hydrolyzable polyrotaxane. The hydrolyzable polyrotaxane, in which many a-CDs are threaded onto a PEG chain capped by a hydrolyzable ester moiety, was used to form a tubular structure in the hydrogel. After crosslinking with another PEG chain, the ester linkage in the polyrotaxane was hydrolyzed in 1N NaOH. This led to exposing hydrophobic cavity of a-CDs. The tubular-structured hydrogel incorporated sodium dodecyl sulfate (SDS) much faster than normally crosslinked a-CDs hydrogel (a-CD-PEG hydrogel). Furthermore, partition coefficient (K) of SDS to the MT-PEG hydrogel was two times larger than the a-CD-PEG hydrogel. These results suggest that the tubular structure of a-CDs, made from a template of the polyrotaxane, is much more attractive to include SDS in the a-CD cavities. Unsaturated fatty acids (palmitoleic acid (C16:1) and oleic acid (C18:1)) were also effectively incorporated into the tubular-structured hydrogel during 6 days. The K value of C16:1 was as the same order in magnitude as C18:1. Thus, the tubular structure of a-CDs was advantageous to incorporate long alkyl chains into the hydrophobic cavity of a-CDs in aqueous conditions.

Key Words:

• Cyclodextrin
• Tubular structure
• Hydrogels
• Partition
• Polyrotaxane
• Supramolecular structure
• Fatty acids
• Crosslinking
• Poly(ethylene glycol)