Dual Upconverted and Downconverted Circularly Polarized Luminescence in Donor–Acceptor Assemblies

Through mimicking both the chiral and energy transfer in an artificial self‐assembled system, not only was chiral transfer realized but also a dual upconverted and downconverted energy transfer system was created that emit circularly polarized luminescence. The individual chiral π‐gelator can self‐assemble into a nanofiber exhibiting supramolecular chirality and circularly polarized luminescence (CPL). In the presence of an achiral sensitizer Pd^II octaethylporphyrin derivative, both chirality transfer from chiral gelator to achiral sensitizer and triplet‐triplet energy transfer from excited sensitizer to chiral gelator could be realized. Upconverted CPL could be observed through a triplet–triplet annihilation photon upconversion (TTA‐UC), while downconverted CPL could be obtained from chirality‐transfer‐induced emission of the achiral sensitizer. The interplay between chiral energy acceptor and achiral sensitizer promoted the communication of chiral and excited energy information.     

Fusion‐Induced Structural and Functional Evolution in Binary Emulsion Communities

The biomimetic dynamic behaviours of emulsions are receiving increasing attention from the broad scientific community; however, the spatiotemporal control and functionalization of emulsions based on simple fusion‐induced method is rarely mentioned. A design for protein‐stabilized oil‐in‐water droplets and phospholipid‐stabilized oil‐in‐water droplets is described and a substance‐diffusion‐mediated fusion mechanism proposed within these two different emulsion communities. Significantly, a range of fusion‐induced high‐order behaviours were successfully demonstrated including competitive fusion, fusion‐induced evolution in membrane complexity, and diversified structures with the formation of Janus or various patchy morphologies, fusion‐induced membrane maturation, as well as fusion‐induced multifunctionalization with a directional motility behaviour. These results highlight the fusion‐induced diverse dynamic behaviours in complex emulsions communities and provide a platform for advancing versatile applications of emulsions.     

Versatile supramolecular gelators that can harden water, organic solvents and ionic liquids

We developed novel supramolecular gelators with simple molecular structures that could harden a broad range of solvents: aqueous solutions of a wide pH range, organic solvents, edible oil, biodiesel, and ionic liquids at gelation concentrations of 0.1-2 wt %. The supramolecular gelators were composed of a long hydrophobic tail, amino acids and gluconic acid, which were prepared by liquid-phase synthesis. Among seven types of the gelators synthesized, the gelators containing L-Val, L-Leu, and L-Ile exhibited high gelation ability to various solvents. These gelators were soluble in aqueous and organic solvents, and also in ionic liquids at high temperature. The gelation of these solvents was thermally reversible. The microscopic observations (TEM, SEM, and CLSM) and small-angle X-ray scattering (SAXS) measurements suggested that the gelator molecules self-assembled to form entangled nanofibers in a large variety of solvents, resulting in the gelation of these solvents. Molecular mechanics and density functional theory (DFT) calculations indicated the possible molecular packing of the gelator in the nanofibers. Interestingly, the gelation of an ionic liquid by our gelator did not affect the ionic conductivity of the ionic liquid, which would provide an advantage to electrochemical applications.     

Solvent‐Polarity‐Tuned Morphology and Inversion of Supramolecular Chirality in a Self‐Assembled Pyridylpyrazole‐Linked Glutamide Derivative: Nanofibers,Nanotwists, Nanotubes,and Microtubes

The self‐assembly of a low‐molecular‐weight organogelator into various hierarchical structures has been achieved for a pyridylpyrazole linked L ‐glutamide amphiphile in different solvents. Upon gel formation, supramolecular chirality was observed, which exhibited an obvious dependence on the polarity of the solvent. Positive supramolecular chirality was obtained in nonpolar solvents, whereas it was inverted into negative supramolecular chirality in polar solvents. Moreover, the gelator molecules self‐assembled into a diverse array of nanostructures over a wide scale range, from nanofibers to nanotubes and microtubes, depending on the solvent polarity. Such morphological changes could even occur for the xerogels in the solvent vapors. We found that the interactions between the pyridylpyrazole headgroups and the solvents could subtly change the stacking of the molecules and, hence, their self‐assembled nanostructures. This work exemplifies that organic solvents can significantly involve the gelation, as well as tune the structure and properties, of a gel.     

Chemomechanical and morphological properties with proliferation of keratinocyte cells of electrospun poyhydroxyalkanoate fibers incorporated with essential oil

Delivery systems based on electrospun polymeric nanofibers have shown potential for delivery of bioactive and plant extract formulations. This research focused on the fabrication of polyhydroxyalkanoate (PHA) copolymer nanofibers as a vehicle for loading of the Thai traditional herbal extract of Plai oil (Zingiber cassumunar Roxb). Nanofibers were formed by dissolving PHA and Plai oil together in dichloromethane solvent, with the PHA concentration being varied (5, 8, and 10%), followed by electrospinning for 4 hours. Based on the submicron diameters of the nanofibers, 8% PHA proved to be the optimal concentration. The concentration of Plai oil (10, 20, and 30%) was used, and hence, the solution viscosity influenced the nanofiber synthesis and physical properties of the nanofibers were obtained. Scanning electron microscope results indicated that the average diameters of cylindrical PHA nanofibers loaded with Plai oil (10%, 20%, and 30%) were 1.10, 1.01, and 1.11 μm, respectively, highlighting that fibers composed of 20% Plai oil were classifiable as nanofibers. Tensile testing of 20% Plai oil‐loaded nanofibers indicated that stiffness and elongation at break were within the acceptable range. Fourier transform infrared and differential scanning calorimetry measurements highlighted the presence of terpenen‐4‐ol, a component found in Plai oil, in the nanofiber film samples of PHA/Plai oil, confirming its inclusion in the systems. In addition, cell proliferation was set up to confirm the morphology and toxicity of skin keratinocyte cell line, and the results show that the HaCaT cells were attached on the PHA nanofibers which the nanofibers containing 20% Plai oil may affect cell behavior in spite the fact that it is not toxic to the cells.     

Control of Three‐Dimensional Cell Adhesion by the Chirality of Nanofibers in Hydrogels

In the three‐dimensional (3D) extracellular matrix (ECM), the influence of nanofiber chirality on cell behavior is very important; the helical nanofibrous structure is closely related to the relevant biological events. Herein, we describe the use of the two enantiomers of a 1,4‐benzenedicarboxamide phenylalanine derivative as supramolecular gelators to investigate the influence of the chirality of nanofibers on cell adhesion and proliferation in three dimensions. It was found that left‐handed helical nanofibers can increase cell adhesion and proliferation, whereas right‐handed nanofibers have the opposite effect. These effects are ascribed to the mediation of the stereospecific interaction between chiral nanofibers and fibronectin. The results stress the crucial role of the chirality of nanofibers on cell‐adhesion and cell‐proliferation behavior in 3D environments.     

Fabrication and electrochemical instrumentation of redox‐active nanofiber mat for polyaniline incorporated with poly(imide sulfonate)

In this study, we demonstrate the fabrication of an electrochemically active nanofiber mat that is a composite of high‐performance poly(imide sulfonate) (PIS) and polyaniline (PANI). First, a nonconductive nanofiber mat comprising nanofibers having diameters of ca. 300 nm was fabricated by the electrospinning of ionomeric PIS in N,N‐dimethylformamide (DMF). Then, the nanofibers were modified using PANI, which was synthesized by the oxidative polymerization of aniline, yielding an electrochemically active nanofiber mat having a diameter of ca. 350 nm. It was confirmed that PANI was successfully incorporated onto the PIS nanofiber mats by X‐ray photoelectron spectroscopy. Subsequently, we conducted electrochemical measurements of the PANI‐modified nanofiber mats using a tailor‐made attachment in which the working electrode gently comes in contact with the nanofiber mat surface. This attachment was observed to be widely useful in the cyclic voltammetry measurements related to redox‐active nanofibers. These observations are expected to contribute to the advancements in application development of the electrochemically active nanofiber mats.     

A Library of Multipurpose Supramolecular Supergelators: Fabrication of Structured Silica,Porous Plastics,and Fluorescent Gels

Supramolecular gels find applications in various fields. Usually, a specific gelator is useful only for a specific application. This one‐gelator‐one‐application format is one factor that limits the usefulness of supramolecular gels. We report the synthesis of a library of gelators from a common core by using a click‐chemistry approach. Thus, the click reaction of β‐azido‐4,6‐O‐benzylidene–galactopyranoside ( 1 ) with various alkynes gave 11 different gelators having varying gelation abilities. Whereas gelators having alkyl‐chain substituents congealed alkanes and tetraethylorthosilicate (TEOS), the gelators having aromatic substituents congealed aromatic solvents. We exploited this difference in gelling behavior in the templated synthesis of silica rods and porous plastics. The styrene gel of gelator 2 j was polymerized, and the gelator was removed by washing to obtain porous polystyrene. The TEOS gel of gelator 2 b was polymerized to silica, and the gelator template was removed by calcination to give microstructured silica rods. We also developed fluorescent gelator 2 f by this method, which might find applications by virtue of its fluorescence in the assembled state.     

Reactive Magnetospinning of Nano‐ and Microfibers

Reactive spinning of nano‐ and microfibers that involves very fast chemical reactions and ion exchange is a challenge for the common methods for nanofiber formation. Herein, we introduce the reactive magnetospinning method. This procedure is based on the magnetic‐field‐directed collision of ferrofluid droplets with liquid droplets that contain complementary reactants. The collision, start of the chemical reaction, and the fiber drawing are self‐synchronized. The method is used to synthesize, cross‐link, and chemically modify fiber‐forming polymers in the stage of fiber formation. The method provides new opportunities for the fabrication of nanofibers for biomedical applications.     

Three-dimensional encapsulation of live cells by using a hybrid matrix of nanoparticles in a supramolecular hydrogel

From a library of glyco-lipid mimics with muconic amide as the spacer, we found that 1, a glyco-lipid that has N-acetyl glucosamine and methyl cyclohexyl groups as its hydrophilic head and hydrophobic tails, respectively, formed a stable hydrogel (0.05 wt %) through hierarchical self-assembly of the lipid molecules into supramolecular nanofibers. The formation of the supramolecular hydrogel was verified by rheological measurements, and the supramolecular nanofiber was characterized as the structural element by transmission electron microscopy and atomic force microscopy observations. Absorption and circular dichroism spectroscopic measurements revealed that the muconic amide moieties of 1 are arranged in a helical, stacked fashion in the self-assembled nanofibers. Moreover, we unexpectedly found that the homogeneous distribution of the supramolecular nanofibers of 1 was greatly facilitated by the addition of polystyrene nanobeads (100-500 nm in diameter), as evaluated by confocal laser scanning microscopic observations. It is interesting that the obtained supramolecular hybrid matrix can efficiently encapsulate and distribute live Jurkat cells in three dimensions under physiological conditions. This supramolecular hybrid matrix is intriguing as a unique biomaterial.     

Self‐Assembling Supramolecular Hybrid Hydrogel Beads

With the goal of imposing shape and structure on supramolecular gels, we combine a low‐molecular‐weight gelator (LMWG) with the polymer gelator (PG) calcium alginate in a hybrid hydrogel. By imposing thermal and temporal control of the orthogonal gelation methods, the system either forms an extended interpenetrating network or core–shell‐structured gel beads—a rare example of a supramolecular gel formulated inside discrete gel spheres. The self‐assembled LMWG retains its unique properties within the beads, such as remediating Pd^II and reducing it in situ to yield catalytically active Pd⁰ nanoparticles. A single PdNP‐loaded gel bead can catalyse the Suzuki–Miyaura reaction, constituting a simple and easy‐to‐use reaction‐dosing form. These uniquely shaped and structured LMWG‐filled gel beads are a versatile platform technology with great potential in a range of applications.     

Metallogels from Coordination Complexes,Organometallic, and Coordination Polymers

A supramolecular gel results from the immobilization of solvent molecules on a 3D network of gelator molecules stabilized by various supramolecular interactions that include hydrogen bonding, π–π stacking, van der Waals interactions, and halogen bonding. In a metallogel, a metal is a part of the gel network as a coordinated metal ion (in a discrete coordination complex), as a cross‐linking metal node with a multitopic ligand (in coordination polymer), and as metal nanoparticles adhered to the gel network. Although the field is relatively new, research into metallogels has experienced a considerable upsurge owing to its fundamental importance in supramolecular chemistry and various potential applications. This focus review aims to provide an insight into the development of designing metallogelators. Because of the limited scope, discussions are confined to examples pertaining to metallogelators derived from discrete coordination complexes, organometallic gelators, and coordination polymers. This review is expected to enlighten readers on the current development of designing metallogelators of the abovementioned class of molecules.     

Heat‐Induced Morphological Transformation of Supramolecular Nanostructures by Retro‐Diels–Alder Reaction

Controlling the morphology of supramolecular nanostructures in response to external stimuli is an important challenge in the development of functional soft materials. Here we show that a morphological transformation from 2D nanosheets to a network of 1D nanofibers is triggered by heating, which induces molecular conversion of a bolaamphiphile to a hydrogelator by means of a retro‐Diels–Alder reaction, thereby producing a new heat‐set supramolecular hydrogel. We anticipate that our design will be a starting point for more sophisticated supramolecular systems that integrate the thermodynamics of molecular assembly and the kinetics of chemical reactions to create complex supramolecular nanostructures.     

Vicinal Solvent Effect on Supramolecular Gelation: Alcohol Controlled Topochemical Reaction and the Toruloid Nanostructure

Although solvent is the major component of the gel, it still remains unclear how the solvent molecules take part in the formation of the gel nanostructures in many gels. In this study it was observed that the vicinal effect on gel formation as well as their nanostructures, that is, the vicinal solvent molecules to the gelator, determine the molecular packing and their subsequent structures and properties. A naphthylacryl‐conjugated L ‐glutamide gelator was found to form organogels in various solvents and nanofiber structures. While the nanofibers from other solvents could not show any further reaction, the gel from the alcohol could undergo topochemical [2+2] cycloaddition under photoirradiation and resulted in toruloid nanostructures. Various pure alcohol solvents from methanol to pentanol were found to show a similar property. Interestingly, switching from a single alcohol solvent to mixed solvents of alcohol with miscible or immiscible non‐alcohol solvents could still cause the same change, showing the vicinal effect of alcohol on controlling the molecular packing as well as the structural transformation. More interestingly, when nanofiber xerogel, obtained from non‐alcohol solvents, was exposed to alcohol vapor, the nanofiber was transferred into nanotoruloid. These results provide a new insight into the gelator–solvent interaction in soft gels.     

Dip-pen patterning and surface assembly of peptide amphiphiles

This paper presents results on controlling the surface morphology of evaporation-driven self-assembly of peptide amphiphile (PA) nanofibers by dip-pen nanolithography. These PA nanofibers, which measure only a few nanometers in diameter, can be oriented perpendicularly to the receding edge of a solution. Dragging a meniscus of PA ink with an atomic force microscope (AFM) tip creates reproducibly aligned arrays of isolated and close-packed PA nanofiber patterns on silicon substrates, utilizing surface coating of poly(ethylene glycol) to suppress the self-assembly of nanofibers on AFM tips. We also demonstrate the ability to construct double-layer patterns of differing nanofiber orientations at the same position. This result could be important in producing a complex, multilayer pattern of these peptide-based supramolecular nanostructures.     

Surface morphology and electrical properties of polyurethane nanofiber webs spray‐coated with carbon nanotubes

Multiwalled carbon nanotubes (MWNTs) were spray‐coated on electrospun polyurethane nanofiber webs for electrical conductive application. For the effective coating of MWNTs, hyperbranched polyurethane (HBPU) was used by blending with linear polyurethane, which was synthesized in the A₂ + B₃ approach using poly(ε‐caprolactone)diol, 4,4′‐methylene bis(phenylisocynate), and castor oil. SEM measurements showed that the MWNTs could be coated well along the surface of nanofibers when the HBPU was blended in the linear polyurethane nanofibers. Blending of HBPU in the nanofibers also affected the electrical conductivity of MWNT‐coated nanofiber webs. The low electrical resistance from 20 to 400 Ω/sq was obtained for MWNT‐coated nanofiber webs and their electrical resistance decreased with an increase of spraying frequency. As a potential application of MWNT‐coated nanofiber webs, the electrical heating effect because of applied voltage was demonstrated. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanical and thermal properties of epoxy/silicon carbide nanofiber composites

The silicon carbide (SiC) nanofibers (0.1, 0.25, and 0.5 phr), produced by self‐propagating high‐temperature synthesis (SHS), are used to reinforce the epoxy matrix cured with an anhydride hardener. Morphological studies reveal a better dispersion of SiC nanofibers and a good level of adhesion between nanofiber and the matrix in composites with lower (0.1 and 0.25 phr) nanofiber loading. The flexural studies show that a maximum increase in flexural properties is obtained for composites with 0.25 phr SiC nanofiber. The fracture toughness of epoxy is found to increase with the incorporation of SiC nanofibers, and 0.25 phr SiC nanofiber loading shows maximum fracture toughness value. The possible fracture mechanisms that exist in epoxy/SiC nanofiber composites have been investigated in detail. Thermogravimetric analysis reveals that SiC nanofibers are effective fillers to improve the thermal stability of epoxy matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Glycine Substitution Effects on the Supramolecular Morphology and Rigidity of Cell-Adhesive Amphiphilic Peptides

Self-assembling peptides that are capable of adopting β-sheet structures can generate nanofibers that lead to hydrogel formation. Herein, to tune the supramolecular morphologies, mechanical properties, and stimuli responses of the hydrogels, we investigated glycine substitution in a β-sheet-forming amphiphilic peptide. Glycine substitution generally enhances conformational flexibility. Indeed, glycine substitution in an amphiphilic peptide weakened the hydrogels or even inhibited the gelation. However, unexpectedly, glycine substitution at the center of the peptide molecule significantly enhanced the hydrogel stiffness. The central glycine substitution affected the molecular packing and led to twisted β-sheet structures and to nanofiber bundling, which likely led to the stiffened hydrogel. Importantly, the supramolecular structures were accurately predicted by molecular dynamics simulations, demonstrating the helpfulness of these techniques for the identification of self-assembling peptides. The hydrogel formed by the amphiphilic peptide with the central glycine substitution had cell adhesive function, and showed a reversible thermal gel-to-sol transition. Thus, glycine substitution is effective in modulating self-assembling structures, rheological properties, and dynamics of biofunctional self-assembling peptides.     

Fabrication of Luminescent CdS Nanoparticles on Short‐Peptide‐Based Hydrogel Nanofibers: Tuning of Optoelectronic Properties

The pH‐induced self‐assembly of three synthetic tripeptides in water medium is used to immobilize luminescent CdS nanoparticles. These peptides form a nanofibrillar network structure upon gelation in aqueous medium at basic pH values (pH 11.0–13.0), and the fabrication of CdS nanoparticles on the gel nanofiber confers the luminescent property to these gels. Atomic force microscopy, field‐emission scanning electron microscopy, and high‐resolution transmission electron microscopy clearly reveal the presence of CdS nanoparticles in a well‐defined array on the gel nanofibers. This is a convenient way to make organic nanofiber–inorganic nanoparticle hybrid nanocomposite systems. The size of the CdS nanoparticles remains almost same before and after deposition on the gel nanofiber. Photoluminescence (PL) measurement of the CdS nanoparticles upon deposition on the gel nanofibers shows a significant blue shift in the emission spectrum of the nanoparticles, and there is a considerable change in the PL gap energy of the CdS nanoparticles after immobilization on different gel nanofibrils. This finding suggests that the optoelectronic properties of CdS nanoparticles can be tuned upon deposition on gel nanofibers without changing the size of the nanoparticles.     

Discrete Stimuli‐Responsive Multirotaxanes with Supramolecular Cores Constructed through a Modular Approach

The synthesis of discrete multirotaxanes with well‐defined structures remains a great challenge. Herein, we present the successful construction of diverse discrete multirotaxanes with well‐defined supramolecular metallacycles as cores by a modular approach. Moreover, these novel multirotaxanes featured a stimuli‐responsive property that enabled the introduction and removal of the bromide anion by taking advantage of dynamic nature of the supramolecular metallacycle scaffold. Through the combination of rotaxane‐containing prefunctionalized building blocks with the corresponding different organoplatinum(II) acceptor building blocks (60, 120, or 180°), diverse discrete multirotaxanes with well‐defined metallacycles (rhomboid or hexagon) as cores as well as certain numbers of rotaxane units were successfully obtained quantitatively by means of coordination‐driven self‐assembly. Furthermore, owing to the existence of a dynamic metallacycle as the supramolecular cores, the resultant multirotaxanes showed anion‐induced disassembly and reassembly properties, which allowed for the reversible transformation between multirotaxanes and the corresponding individual rotaxane‐containing building blocks. Therefore, this research not only enriches the family of discrete multirotaxanes, but also provides a novel strategy for the construction of “smart” stimuli‐responsive multirotaxane systems.