Chiral Arrangement of Achiral Au Nanoparticles by Supramolecular Assembly of Helical Nanofiber Templates

Chiral materials composed of organized nanoparticle superstructures have promising applications to photonics and sensing. Reliable customization of the chiroptical properties of these materials remains an important goal; hence, we report a customizable scheme making use of modular gelator components for controlling the helicity and formation of nanofibers over long length scales resulting in hydrogel templates. Controlled growth of gold nanoparticles at spatially arranged locations along the nanofiber is achieved by UV reduction of Au­(I) ions on the supramolecular templates. The resulting materials were found to have significant interparticle interactions and well-defined helicity to provide high quality, chiroptically active materials. With this novel approach, the tailored assembly of nanoparticle superstructures with predictable chiroptical properties can be realized in high yield, which we expect to allow rapid advancement of chiral nanomaterials research

Calix[4]arene-based fluorescent probe and the adsorption capacity of its electrospun nanofibrous film for the cesium cation as an adsorbent

<p>Calix[4]arene-based cation receptor 1 has been synthesised by following a multi-step synthetic procedure. The fluorescence properties of 1 upon the addition of various metal ions were investigated by fluorescence spectroscopy. As a result, it was revealed that 1 displayed dramatic quenching effect upon the exposure to Cs⁺. In contrast, no significant quenching effects were observed upon the addition of other metal ions such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ag⁺, Zn²⁺ and Ni²⁺. Compound 1 was also found by Job plot to form a 1:1 complex with Cs⁺. In addition, we also prepared 1-embedded electrospun nanofibrous film (NF-1) as an adsorbent for Cs⁺. NF-1 is proved to adsorb Cs⁺ effectively from an aqueous solution, indicating that it would be usefully utilised as an adsorbent to remove Cs⁺.</p

A benzothiazole-based receptor-immobilised silica nanoparticle as chemosensor for Hg²⁺

<div><p>Fluorogenic benzothiazole-based receptor has been easily immobilised onto filter paper and silica nanoparticle by sol-gel reaction. The sensing ability of the benzothiazole-immobilised thin layer filter paper chromatography (<b>TLC-1</b>) was evaluated on the basis of fluorescent changes caused by metal ions that were dropped onto the TLC plate. The <b>TLC-1</b> exhibited a high affinity and selectivity for Hg²⁺ over other competing metal ions. Therefore, the <b>TLC-1</b> holds promise as a portable sensor for the detection of Hg²⁺ in aqueous solution. Furthermore, the adsorption capacity of a column packed with <b>SiO</b>_<b>2</b><b>-1</b> was evaluated by the application of metal ions under various experimental conditions, such as pH, flow rate and concentration. The <b>SiO2-1</b> column removed 98% of Hg²⁺ from drinking water containing 10 ppb of Hg²⁺. The adsorption capacity of the <b>SiO</b>_<b>2</b><b>-1</b> column was not strongly affected by pH and flow rates.</p></div

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

Reinforcement of a Sugar-Based Bolaamphiphile/Functionalized Graphene Oxide Composite Gel: Rheological and Electrochemical Properties

A sugar-based bolaamphiphile/graphene oxide composite hydrogel has been prepared using simple mixing. Unlike the corresponding sugar-based native gel, the composite gel exhibits a fibrillar structure with a 10–20 nm fiber diameter. The composite gel forms an interdigitated bilayer structure incorporating intermolecular hydrogen-bonding interactions. The composite gel formation did not change the beneficial electrical properties of graphene offering the potential for integration of this new material into electronic systems. Interestingly, the mechanical and electrochemical properties of the composite gel are both dramatically enhanced when compared to the native gel, thereby reflecting that the functionalized graphene oxide layers are efficiently intercalated within the composite gel structure

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

Bis(naphthol)-based fluorescent chemoprobe for cesium cation and its immobilisation on silica nanoparticle as a high selective adsorbent

<p>A bis(naphthol)-based cation receptor <b>1</b> has been synthesised by three steps of synthetic procedure. The spectroscopic properties of <b>1</b> upon addition of various metal ions were investigated by UV–vis absorption and fluorescence spectroscopy. As a result, the absorption of <b>1</b> was linearly decreased as a function of concentration of added Cs⁺. Also, <b>1</b> exhibited dramatic fluorescence quenching effect upon exposure to caesium cation. Contrastively, no significant quenching effect was observed upon addition of other metal ions such as Na⁺, K⁺, Rb⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Ni²⁺ and Zn²⁺. It was found that <b>1</b> formed a 1:1 complex with Cs⁺ by Job’s plot. Furthermore, we also prepared <b>1</b>-functionalised silica nanoparticle (<b>SiO</b>_<b>2</b><b>-1</b>) as an adsorbent for Cs⁺. <b>SiO</b>_<b>2</b><b>-1</b> showed a great capacity for selective removal of caesium ion from aqueous solution as well as from tap water. Thus, it is potentially useful for the detection and removal of caesium cation from environmental and biological fluids polluted by nuclear radiation and nuclear waste.</p

Formation of Calix[4]arene-Based Supramolecular Gels Triggered by K⁺ and Rb⁺: Exemplification of a Structure–Property Relationship

Supramolecular gels based on calix[4]­arene tetraacetate were prepared in the presence of K⁺ and Rb⁺. The Rb gel shows higher mechanical stability than the K gel: crystals derived from the K gel have an H-bonded framework, while those obtained using the Rb gel have a framework stabilized by H bonds and coordination bonds

Different Origins of Strain-Induced Chirality Inversion of Co²⁺-Triggered Supramolecular Peptide Polymers

We report a distinctly different dynamic helix inversion pathway of self-assembled terpyridine-based ligands composed of different numbers of peptide moieties with Co²⁺ and its amplification of strain-induced chirality from an achiral terpyridine moiety. The helical chirality of the metal centers, coordinated by terpyridine ligands, is controlled by strain-induced chirality with complex ligand-to-Co²⁺ ratios. We also show that the distinct helical inversion mechanism is significantly dependent on the number of peptides attached to ligands. The helical inversion pathway of the self-assembled ligand (<b>R-1</b> and <b>S-1</b>) complexes composed of one alanine analogue (<i>R</i>- or <i>S</i>-2-amino-1-propyl moiety) and one long saturated alkyl chain relies on two steps of chirality with different complex geometries, first from strain-induced chirality originating from an octahedral structure to octahedral structure with different helical direction and then on to helical chirality in a square-pyramidal structure. In contrast, the helix inversion of the self-assembled <b>R-2</b> and <b>S-2</b> complexes containing an alanine analogue and two glycine moieties with Co²⁺ was followed by one step to form two distinct coexisting complex geometries having the same helical direction. In particular, the circular dichroism (CD) intensities of the self-assembled <b>R-1</b> and <b>R-2</b> complexes with Co²⁺ were 900–1500-fold amplified compared to those of free <b>R-1</b> and <b>R-2</b>. The Gibbs free energies of the self-assembled complexes with different geometries were also calculated by temperature-dependent CD observation; the square-pyramidal structure of the self-assembled <b>R-1</b> complex with Co²⁺ was more stable than the self-assembled <b>R-2</b> complex with Co²⁺. Furthermore, the self-assembled <b>R-1</b> and <b>S-1</b> complexes with 1.0 equiv of Co²⁺ could classify amino acids by their chirality

Determining Chiral Configuration of Diamines via Contact Angle Measurements on Enantioselective Alanine-Appended Benzene-Tricarboxamide Gelators

Spectroscopic techniques exist that may discern between enantiomers and assess chiral purity. A nonspectroscopic approach that may be directly observed could provide numerous benefits. Using chiral alanine-appended benzene-tricarboxamide gelators, we reveal a methanol gel system that is capable of providing visual discrimination between enantiomers of various diamines. Specifically, gelation is induced by supramolecular nanofiber assembly resulting from interaction between a chiral gelator and a diamine of opposing chirality (i.e., a heterochiral system). Upon further implementing the chiral gelator in electrospun fibers as solid state films, we revealed enantioselective surface wetting properties that allowed for determining chirality through contact angle measurements. While these two approaches of observable gelation and surface wetting offer nonspectroscopic approaches, we also find that the supramolecular nanofiber assembly was able to enhance the induced circular dichroism signal resulting from addition of chiral diamines, allowing precise quantification of their enantiomeric purity