Speed control for cyclodextrin rings on polymer chains

Molecular Recognition of Fluorescent Probe Molecules with a Pseudopolyrotaxane Nanosheet

Pseudopolyrotaxane nanosheets (PPRNS) are ultrathin two-dimensional (2D) materials fabricated via supramolecular self-assembly of β-cyclodextrin (β-CD) and poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymers. In this study, the molecular loading of various fluorescent probe molecules onto PPRNS was systematically investigated. ¹H NMR study for R6G absorption to PPRNS indicated that the small hydrophobic groups, such as the methyl group, of R6G were absorbed by PPRNS. Consistently, the fluorescent probes without methyl groups were not absorbed. These results indicate that PPRNS has a molecular recognition absorption property based on the host-guest interaction of the functional groups on probe molecules and molecular-sized spaces of PPRNS surfaces, which may be vacant β-CDs and voids between β-CD columns. The absorbed amount of the molecular probes onto PPRNS was investigated by UV-vis spectra, and the absorption behavior could be described well by the Langmuir absorption isotherm. This is consistent with the suggested model that the probes are absorbed onto the PPRNS surfaces. This study demonstrates that PPRNSs can be applied as adsorbents for toxic compounds, drug delivery systems, and 2D sensors.

Towards Cyclodextrin-Based Supramolecular Materials

Inclusion complexation between cyclodextrins (CDs) and various guests has been extensively investigated in supramolecular chemistry. Besides CDs, there are several important macrocyclic host families, such as crown ethers and cucurbiturils. Until now, the contribution of these other families to macromolecular self-assembly has been small compared to CDs. This chapter will focus on CDs as hosts for interaction with guest monomers to form hydrogels. CD interactions with other monomers were made possible depending on proper molecular recognition. Macroscopic molecular recognition can be categorized by three types of interactions: main chain (polyrotaxane), side chain, and sequential complexes. Utilizing CD as host molecule, polymers such as polyethers, cationic polymers, polyamines, polyesters, π-conjugated polymers, polyolefins, polyamides, polyurethanes, and inorganic polymers could interact to form inclusion complexes. This chapter will attempt to discuss these studies. Depending on the functional groups attached to the polymeric component, supramolecular formation can be altered based on the stimuli response. Introducing polymer side chains or groups that respond selectively towards external stimuli could affect the hydrogel formation. This chapter also discusses the stimuli response of such systems.

Recent advances in the preparation of cyclodextrin-based polyrotaxanes and their applications to soft materials

The present review article deals with recent novel studies on the preparation and application of polyrotaxanes comprised of cyclodextrins (CDs) and various linear polymers, especially poly(ethylene glycol) (PEG). First, a brief introduction of the historical background of the pioneering work on the preparation of an inclusion complex and polyrotaxane is provided. Subsequently, the authors have focused on the recently developed solvent systems for the polyrotaxane. These new solvents are interesting from two fundamental viewpoints: (1) from the perspective of the clarification of the hydrogen-bonding-based dissolution mechanism of polyrotaxanes; and (2) from the practical viewpoint of the preparation of modified polyrotaxanes or slide-ring gels containing ionic liquids. A wide variety of polyrotaxane derivatives, whose cyclodextrin moiety was modified to carry various functional groups, and their intriguing characteristics are introduced in this article. Finally, many instances of the application of the PEG-CD polyrotaxane to soft materials, such as gels, molecular tubes and multivalent ligand systems, are summarized.