Supramolecular dissociation of biodegradable polyrotaxanes by enzymatic terminal hydrolysis

Abstract

Supramolecular dissociation of biodegradable polyrotaxanes via terminal hydrolysis by an enzyme (papain) in vitro was investigated in relation to their solution properties. The polyrotaxanes were synthesized by the introduction of L-phenylalanine (L-Phe) at both ends of an inclusion complex consisting of α-cyclodextrins (α-CDs) and amino-terminated poly(ethylene glycol) (PEG) via peptide linkages, followed by the hydroxypropylation of α-CDs. From static and dynamic light scattering studies, it was clarified that the polyrotaxanes form a loosely packed association but L-Phe-terminated PEGs form a tightly packed association. Further, the polyrotaxanes were found to maintain their rod-like structures in physiological conditions. In vitro degradation experiments using papain revealed that the terminal hydrolysis of the polyrotaxanes is completed and accompanied by the release of hydroxypropylated α-CDs, and this behavior is not affected by the association number of the polyrotaxanes. On the other hand, the terminal hydrolysis of L-Phe-terminated PEG is limited under similar conditions. From these results, the complete dissociation of the polyrotaxanes by hydrolysis is considered to be due to the loosely packed association, presumably related to the rod-like structure.