Controlled Supramolecular Assembly of Helical Silica Nanotube–Graphene Hybrids for Chiral Transcription and Separation

Chiral templating and enantioselective separations are demonstrated on graphene surfaces as directed by encapsulated silica nanotubes. Electrostatic assembly of helical silica nanotubes within graphene sheets results in a hybrid material with the electrochemical properties of graphene and the capability for chiral recognition. Control of the silica nanotube helicity within the graphene hybrid provides a means for directed chiral templating of guest molecules on the outer graphene surface as revealed in the chiral transcription of <i>N</i>¹,<i>N</i>³,<i>N</i>⁵-tri(4-pyridinyl)cyclohexane-1,3,5-tricarboxamide as well as polyallylamine into supramolecular templated assemblies. Changing the helicity of the internal nanotube also provides control over enantiomer selectivity as demonstrated by the chiral separation of racemic mixtures of phenylalanine, tryptophan, and alanine derivatives

Luminescent Calix[4]arene-Based Metallogel Formed at Different Solvent Composition

We have synthesized a calix[4]­arene derivative (<b>1</b>) containing terpyridine and showed that gelation occurred in the presence of Pt²⁺ in DMSO/H₂O of varying compositions. Gelation was presumably mediated by the Pt–Pt and π–π stacking interactions. The scanning electron microscopy image of the xerogel showed a spherical structure with diameter of 1.8–2.1 μm. Interestingly, the metallogel showed strong luminescence enhancement, which was dependent on the DMSO/H₂O ratio of the solvent. We examined the effects of concentration, temperature, and time resolution on the luminescence emission of both the gel <b>1</b>-Pt²⁺ and the sol <b>1</b>-Pt²⁺. The luminescence lifetimes of the metallogel were particularly long, on the order of several microseconds. The luminescence lifetimes were also strongly dependent on the solvent composition. We also determined the thermodynamic parameters for the self-assembly of the gel by the Birks kinetic scheme. Furthermore, the rheological properties of the metallogels in the presence of more than 4.0 equiv of Pt²⁺ were independent of the concentration of Pt²⁺ applied

Conformation Control of a Conjugated Polymer through Complexation with Bile Acids Generates Its Novel Spectral and Morphological Properties

Control of higher-order polymer structures attracts a great deal of interest for many researchers when they lead to the development of materials having various advanced functions. Among them, conjugated polymers that are useful as starting materials in the design of molecular wires are particularly attractive. However, an equilibrium existing between isolated chains and bundled aggregates is inevitable and has made their physical properties very complicated. As an attempt to simplify this situation, we previously reported that a polymer chain of a water-soluble polythiophene could be isolated through complexation with a helix-forming polysaccharide. More recently, a covalently self-threading polythiophene was reported, the main chain of which was physically protected from self-folding and chain–chain π-stacking. In this report, we wish to report a new strategy to isolate a water-soluble polythiophene and to control its higher-order structure by a supramolecular approach: that is, among a few bile acids, lithocholate can form stoichiometric complexes with cationic polythiophene to isolate the polymer chain, and the higher-order structure is changeable by the molar ratio. The optical and morphological studies have been thoroughly performed, and the resultant complex has been applied to the selective recognition of two AMP structural isomers

Geometric Change of a Thiacalix[4]arene Supramolecular Gel with Volatile Gases and Its Chromogenic Detection for Rapid Analysis

A coordination polymer gel that is self-assembled to form a network structure between a thiacalix[4]­arene derivative (<b>L</b>) and Co²⁺ has been prepared. This gel is capable of selectively changing color in the presence of gases that yield hydrogen chloride upon hydrolysis. The UV–vis absorption spectrum of a coordination polymer gel derived from Co­(NO₃)₂ exhibits an absorption band at 527 nm and is colored red, indicating the formation of an octahedral Co²⁺ complex. Treatment with a small amount of volatile gases containing a chlorine atom (VGCl) causes a red shift of ∼150 nm, resulting in a new strong band with a maximum at 670 nm and a color change to blue. In addition, the red color of the filter paper coated with a Co­(NO₃)₂ coordination polymer gel changed to blue upon exposure to VGCl, reflecting a change in the coordination geometry. Red and blue colors of single crystals of Co²⁺ complexes were obtained from a basic solution. From X-ray crystallographic analysis, the red Co²⁺ complex corresponds to an octahedral structure, while the blue Co²⁺ complex reflects the presence of a tetrahedral structure. Thus, the induced color change of Co²⁺ gel from red to blue upon exposure to VGCl is due to the coordination geometry. The quantitative concentration of VGCl was calculated by employing the RGB histogram available in a smartphone application

Cohelical Crossover Network by Supramolecular Polymerization of a 4,6-Acetalized β‑1,3-Glucan Macromer

Natural polysaccharides represent a renewable resource whose effective utilization is of increasing importance. Chemical modification is a powerful tool to transform them into processable materials but usually sacrifices the original structures and properties of value. Here we introduce a chemical modification of Curdlan, a β-1,3-glucan, via 4,6-acetalization. This modification has successfully combined a helix-forming ability of Curdlan with new solubility in organic media. Furthermore, it has operationalized efficient cohelical crossovers (CCs) among the helices to demonstrate the formation of an extensive supramolecular network that goes well beyond the nanoscopic regime, allowing for preparation of flexible self-supporting films with macroscopic dimensions. This protocol, which is now viewed as supramolecular polymerization of a helical polysaccharide macromer, can add a new dimension to “polysaccharide nanotechnology”, opening a door for the creation of unconventional polymer materials based on the cohelical crossover network (CCN)