Polyol-responsive pseudopolyrotaxanes based on phenylboronic acid-modified polyethylene glycol and cyclodextrins

Phenylboronic acid (PBA), which reacts with polyols to form cyclic esters, was attached to the amino terminal of polyethylene glycol (PEG) via amide bonds. PBA-PEG was used to prepare pseudopolyrotaxanes (pPRXs) by combining it with cyclodextrins (CyDs). In the case of α-CyD, a single stranded pPRX formed that disintegrated in the presence of catechol (CA), d-fructose (Fru), and d-glucose (Glc). The order of response was CA?>?Fru?>?Glc, which corresponds with the affinities between the PBA moiety and the polyols. In contrast, a pPRX using γ-CyD, which has a double-stranded structure, showed sugar-induced disintegration but did not show a response to CA. We explained these apparently curious responses of the pPRXs using a mechanism based on the penetrability of the polyol-bound PBA toward the cavities of the CyDs. The pPRXs, which are a class of molecular machine, show two selectivities; one is derived from polyol selectivity, and the other is based on the penetrability for CyDs.