Binding of methyl orange and its homologs by powdered nylon 66

Powdered Nylon 66 was prepared as a model of amorphous polymers. The resultant powder polyamide was composed of only amorphous regions. The extent of uptake of the acid azo dyes, a homologous series of methyl orange derivatives, by the polymer was measured in an aqueous solution. The first binding constants and the thermodynamic parameters in the course of the binding were evaluated. The thermodynamic behaviors obtained are very similar to those of crosslinked polyvinylpyrrolidone. The favorable free energy of the binding is accompanied by an entropy gain and an exothermic enthalpy change. The shorter the alkyl chain of the dyes, the more negative is the enthalpy change and, hence, the smaller is the entropy change. The thermodynamic data for butyl orange showed that the binding process is athermal and is wholly an entropic effect. The binding of the dyes to the matrix is entropically favorable as a result of the operation of the hydrophobic effect. In addition, an electrostatic force is operative between the sulfonate group on the dyes and the terminal amino groups on the polyamide.     

1H NMR titration study of stimuli-responsive supramolecular assemblies: inclusion complexes between PEG–b-PEI copolymer-grafted dextran and naphthalene-appended γ-cyclodextrin via double-strand inclusion

We have previously prepared a stimuli-responsive inclusion complex between PEG–b-PEI–g-dextran graft copolymer (PEG–PEI–dex) and γ-cyclodextrin (γ-CD) in order to investigate unique inclusion phenomena, double-axle inclusion. For further study, a γ-CD derivative, mono-6-O-(2-sulfonato-6-naphthyl)-γ-CD (SN-γ-CD) was additionally synthesized for ¹H NMR titration study, which is expected to induce the competition of pendant naphthyl group with external polymer guests. Consequently, ¹H NMR titration results of the inclusion complex of PEG–PEI–dex with SN-γ-CD showed stoichiometric changes, temperature-dependence, and reversibly pH-responsive properties of the inclusion complexes in terms of chemical shift variation.     

Using ruthenium-catalysed propargylic substitutions for the efficient syntheses of rotaxanes

This Letter describes an efficient method—one that takes advantage of hydrogen bond-guided self-assembly and ruthenium-catalysed propargylic substitution—for the preparation of rotaxanes. The substitution reactions of a pseudorotaxane with a diverse range of heteroatom- and carbon-atom-centred nucleophiles were catalysed by the [(Cp^∗)RuCl(SMe)]₂ complex to furnish rotaxanes in good yields.     

Dextran Hydrogels Containing Poly(N‐isopropylacrylamide) as Grafts and Cross‐Linkers Exhibiting Enzymatic Regulation in a Specific Temperature Range

Summary: Specific temperature‐responsive biodegradable hydrogels were synthesized and characterized in terms of their regulation of enzymatic accessibility based on the physical properties of the temperature‐responsive polymers. The hydrogels consist of glycidyl methacrylate‐modified dextran grafted with the poly(N‐isopropylacrylamide) (PNIPAAm) homopolymer, and cross‐linked by co‐polymerization with NIPAAm and N,N‐dimethylacrylamide (DMAAm). The coil‐globule change in the grafted poly(NIPAAm) chains and only a slight dehydration of the poly(NIPAAm‐co‐DMAAm) cross‐linkers are effective in controlling the enzymatic degradation over a specific temperature range.

The thermo‐responses of the graft chains (steric hindrance) and the crosslinkers (slight deswelling of the hydrogel networks) control the enzymatic degradation of the hydrogel.     

Supramolecular hydrogel formation based on inclusion complexation between poly(ethylene glycol)-modified chitosan and alpha-cyclodextrin

Supramolecular hydrogels have been prepared on the basis of polymer inclusion complex (PIC) formation between poly(ethylene glycol) (PEG)-modified chitosans and alpha-cyclodextrin (alpha-CD). A series of PEG-modified chitosans were synthesized by coupling reactions between chitosan and monocarboxylated PEG using water-soluble carbodiimide (EDC) as coupling agent. With simple mixing, the resultant supramolecular assembly of the polymers and alpha-CD molecules led to hydrogel formation in aqueous media. The supramolecular structure of the PIC hydrogels was confirmed by differential scanning calorimetry (DSC), X-ray diffraction, and (13)C cross-polarized/magic-angle spinning (CP/MAS) NMR characterization. The PEG side-chains on the chitosan backbones were found to form inclusion complexes (ICs) with alpha-CD molecules, resulting in the formation of channel-type crystalline micro-domains. The IC domains play an important role in holding together hydrated chitosan chains as physical junctions. The gelation property was affected by several factors including the PEG content in the polymers, the solution concentration, the mixing ratio of host and guest molecules, temperature, pH, etc. All the hydrogels in acidic conditions exhibited thermo-reversible gel-sol transitions under appropriate conditions of mixing ratio and PEG content in the mixing process. The transitions were induced by supramolecular association and dissociation. These supramolecular hydrogels were found to have phase-separated structures that consist of hydrophobic crystalline PIC domains, which were formed by the host-guest interaction between alpha-CD and PEG, and hydrated chitosan matrices below the pK(a).The formation of inclusion complexes between alpha-cyclodextrin and PEG-modified chitosan leads to the formation of hydrogels that can undergo thermo-reversible supramolecular dissociation.     

Ligand accessibility to receptor binding sites enhanced by movable polyrotaxanes

Functionalized polyrotaxanes are utilized to investigate the relation to multivalent interactions between the mannose moiety and Con A immobilized surfaces. According to the results of SPR spectroscopy, the mannose-conjugated polyrotaxanes show a higher response than any other mannose conjugate on both surfaces of high- and low-density Con A. Moreover, the results of the FRET analysis suggest that the mobility of α-cyclodextrins in the polyrotaxane more efficiently contributes to their binding interactions in a multivalent manner. This well-defined polyrotaxane system provides control over ligand density, ligand mobility, and gives an efficient response to the biological interaction receptor, which has not been easy to achieve in covalently bound polymeric systems.