A biocleavable polyrotaxane, having a necklace-like structure consisting of many cationic alpha-cyclodextrins (alpha-CDs) and a disulfide-introduced poly(ethylene glycol) (PEG), was synthesized and examined as a nonviral gene carrier. The polyrotaxane formed a stable polyplex having positively charged surface even at low charge ratio. This is likely to be due to structural factors of the polyrotaxane, such as the mobile motion of alpha-CDs in the necklace-like structure. Rapid endosomal escape was observed 90 min after transfection. The positively charged surface and the good buffering capacity are advantageous to show the proton sponge effect. The pDNA decondensation occurred through disulfide cleavage of the polyrotaxane and subsequent supramolecular dissociation of the noncovalent linkages between alpha-CDs and PEG. Transfection of the DMAE-SS-PRX polyplex is independent of the amount of free polycation. Those properties played a key role for delivery of pDNA clusters to the nucleus. Therefore, the polyplex nature and the supramolecular dissociation of the polyrotaxane contributed to the enhanced gene delivery.

A polyrotaxane, in which many β-cyclodextrins (β-CDs) are threaded onto a triblock copolymer of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) capped with fluorescein-4-isothiocyanate (FITC), was synthesized as a model of stimuli-responsive molecular assemblies for nanoscale devices. Coupling of FITC with the terminal amino groups in the polypseudorotaxane was performed in DMF at 5 °C. Under these conditions, a side reaction between the hydroxyl groups of β-CD and FITC was prevented. The interaction of the β-CDs with terminal FITC moieties in the polyrotaxane was significantly observed at low temperature. However, the interaction of the β-CDs with the PPG segment was observed with increasing temperature. On the basis of these results, it is concluded that the majority of the β-CDs move toward the PPG segment with increasing temperature although some β-CDs may reside on the PEG segments.

Supramolecular-structured hydrogels were prepared on basis of the inclusion complexation between poly(ethylene glycol) grafted dextrans and R-cyclodextrins (R-CDs) in aqueous media. The inclusion complexes from the PEG grafted dextrans showed a unique gel-sol phase transition which cannot be obtained from usual polymer inclusion complexes that form crystalline precipitates. The gelsol transition was based on the supramolecular assembly and dissociation, and the transition was reversible with hysteresis. The transition temperature was controllable by variation in the polymer concentration and the PEG content in the graft copolymers as well as the stoichiometric ratio between the guest and host molecules. The properties of the hydrogel were characterized by DSC, X-ray diffraction, and 13 C CP/MAS NMR. The X-ray diffraction data indicated that the gel contains a channel-type crystalline structure, demonstrated by a strong reflection at 2θ ) 20°(d ) 4.44 Å). It was confirmed from the DSC and 13 C CP/MAS NMR measurements that all the PEG grafts participate in the complexation. A phaseseparated structure consisting of hydrophobic and channel-type crystalline PEG inclusion complex domains and hydrated dextran matrices was suggested as the internal structure, which comprises the supramolecular-structured hydrogel.