Photoresponsive Hydrogel System Using Molecular Recognition of α-Cyclodextrin

Using molecular recognition of α-cyclodextrin (α-CD), we have successfully constructed a photoresponsive hydrogel system by combination of simple components, α-CD, dodecyl (C12)-modified poly(acrylic acid) (p(AA/C12)), and a photoresponsive competitive guest, 4,4‘-azodibenzoic acid (ADA). An aqueous solution of p(AA/C12) exhibited a gel-like behavior because polymer chains form a network structure via hydrophobic associations of C12 side chains. When α-CD was added to the gel-like aqueous solution, the gel was converted to a sol mixture because hydrophobic interactions of C12 side chains were dissociated by the formation of inclusion complexes of α-CD with C12 side chains. Upon addition of ADA to a binary sol mixture of p(AA/C12) and α-CD, α-CD interacted predominantly with ADA, and then hydrophobic associations of C12 side chains were restored, resulting in a sol-to-gel transition. When a ternary gel mixture of p(AA/C12), α-CD, and ADA was irradiated with UV light, ADA was isomerized from trans to cis, and the mixture underwent a gel-to-sol transition because α-CD formed inclusion complexes more favorably with C12 side chains than with cis-ADA. When the ternary sol mixture was irradiated with visible light, ADA was isomerized from cis to trans and the mixture underwent a sol-to-gel transition. Furthermore, these gel-to-sol and sol-to-gel transitions occurred repeatedly by repetitive irradiations of UV and visible light

Contrast Viscosity Changes upon Photoirradiation for Mixtures of Poly(acrylic acid)-Based α-Cyclodextrin and Azobenzene Polymers

Polymer−polymer interactions were investigated for mixtures of a poly(acrylic acid) (pAA) carrying azobenzene (pC12Azo) and two kinds of pAA carrying α-cyclodextrin (CD), in which CDs are attached to the main chain through the 3- and 6-positions in CD (p3αCD and p6αCD, respectively), using several techniques, such as viscosity and NMR measurements. Viscosity data exhibited contrast changes upon UV irradiation:  thinning (p3αCD/pC12Azo) and thickening (p6αCD/pC12Azo). NOESY spectra confirmed that the contrast viscosity changes were ascribable to differences in how CD moieties interact with pC12Azo after photoisomerization of azobenzene moieties from trans to cis:  dissociation of inclusion complexes (p3αCD/pC12Azo) and formation of interlocked complexes (p6αCD/pC12Azo)

Nanostructured Materials through Orthogonal Self-Assembly in a Columnar Liquid Crystal

This paper describes a system in which an acid functionalized discotic molecule and poly(propylene-imine) dendrimer self-assemble into a new type of oblique columnar liquid crystalline (LC) phase that displays a well-ordered superlattice. The orthogonal combination of hydrogen bonding in the columnar direction and ionic interaction in the plane perpendicular to the columns gives rise to a structure in which the dendrimer is confined to separate columnar domains. The structure of the mesophases formed in the mixed system has been elucidated by infrared spectroscopy and X-ray diffraction. Investigation by differential scanning calorimetry and polarizing optical microscopy has shown that the LC phase is most stable in an 8:1 molar mixture but remains stable over a wide temperature and composition range. In dendrimer enriched mixtures the lattice swells to take up more dendrimer, while discotic enriched mixtures show the appearance of lamellar phases with a columnar structure that is probably closely related to the oblique superlattice. Additionally, the structure of the oblique superlattice can be covalently stabilized at elevated temperature via amidation of the ionic carboxylic acid−amine complexes. The results show the potential of orthogonal self-assembly in columnar LC phases to obtain nanostructured materials with a periodicity of 2–10 nm

Thermotropic Phase Behavior of Trialkyl Cyclohexanetriamides

The thermotropic phase behavior of symmetric cyclohexanetriamides carrying various linear and branched alkyl chains was investigated using calorimetry, microscopy, solid-state NMR, dielectric relaxation spectroscopy, and X-ray scattering techniques. Cyclohexanetriamides carrying C6 or longer linear alkyl chains formed columnar plastic phases with a pseudocentered rectangular lattice. Those with C8 or longer alkyl chain also showed a nematic liquid crystalline phase. Cyclohexanetriamides carrying branched octyl chains displayed columnar phases with rectangular lattices, except for the triamide with the highly branched tetramethylbutyl group. The occurrence of less symmetrical columnar phases is ascribed to the mode of stacking of cyclohexanetriamides which leads to noncylindrical columns. Dielectric relaxation spectra also featured highly cooperative relaxation processes related to reorientation of the macrodipolar columns in the mesophase, showing the potential of these molecules as building blocks in responsive materials

Shape and Release Control of a Peptide Decorated Vesicle through pH Sensitive Orthogonal Supramolecular Interactions

Shape and Release Control of a Peptide Decorated Vesicle through pH Sensitive Orthogonal Supramolecular Interaction