Multiple Stimuli-responsiveness Research Articles

Fluorescent Metallacage-Core Supramolecular Polymer Gel Formed by Orthogonal Metal Coordination and Host-Guest Interactions.

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host-guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt3)2(OTf)2, tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host-guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host-guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

The preparation and study on drug release of a triply-responsive (redox/thermo/pH) cross-linked polymeric micelle as anti-cancer drug carrier

A multiple-stimuli-responsive drug-conjugated cross-linked micelles was prepared by radical copolymerization. The chemical structure, morphology, and size of the cross-linked micelles were characterized, and the drug loading of the micelle was calculated. The experimental results indicated that the hydrodynamic size of the drug-loaded micelles were about 100 nm, and the as prepared micelles could be degraded and swelled in presence of reducing glutathione (GSH). The low critical solution temperature (LCST) of the micelle was around 39.4℃. According to the experimental results, the micelles will shrink at temperature above the LCST. Subsequently, the accumulative drug release rate was up to 91.78% under acidic (pH 5.0), reductive (GSH 10 mmol/L) and high temperature (42.0℃) conditions mimicking the tumor microenvironment, while a relatively low release rate of 1.12% was observed without stimulation. The drug-conjugated cross-linked micelles showed a strong cell uptake behavior. In the cytotoxicity assay, the micelles exhibited effective anti-cancer activity and excellent biocompatibility. In brief, the experimental results show that the as-prepared drug-conjugated cross-linked micelle exhibits multiple stimuli-responsiveness, which holds great promise for anti-cancer drug delivery.

Self-assemblies of cyclodextrin derivatives modified by ferrocene with multiple stimulus responsiveness.

Two novel cyclodextrin derivatives were synthesized that could self-assemble into a supramolecular polymer and gel in different solvent environments. Importantly, the obtained self-assemblies, including vesicles, micro-fibers and gels, could respond to various external stimuli efficiently.

Hierarchical self-assembly of a fluorescence emission-enhanced organogelator and its multiple stimuli-responsive behaviors.

A discrete hexagonal metallacycle 1 decorated with tetraphenylethylene, amide groups and long hydrophobic alkyl chains was constructed via [3 + 3] coordination-driven self-assembly, from which the fluorescence emission-enhanced organogelator with multiple stimuli-responsiveness was successfully prepared via hierarchical self-assembly.

A pillar[5]arene-based multiple-stimuli responsive metal-organic gel was constructed for facile removal of mercury ions.

A thioacetohydrazide functionalized pillar[5]arene was synthesized, which could further assemble into a linear supramolecular metal-organic polymer upon adding Zn2+. Furthermore, the obtained linear supramolecular metal-organic polymer could self-assemble to form a fluorescent supramolecular metal-organic gel at high concentration. When TBAOH was added to the viscous solution at high temperature, the obtained solution could not form a supramolecular metal-organic gel upon cooling. More importantly, when Hg2+ ions are added to the metal-organic gel, the strong blue fluorescence is clearly quenched, and this metal-organic gel (xerogel) could effectively remove Hg2+ from water. Simultaneously, a thin film based on the metal-organic gel was prepared, which was confirmed to be a convenient test kit for detecting Hg2+.

Monopyrrolotetrathiafulvalene-based supramolecular organogels: Multi-stimuli responsiveness and formation of charge-transfer salt gels

Charge-transfer salts formed by the electron donor tetrathiafulvalene and electron acceptor halogen have been the focus of significant interest in constructing high conductivity supramolecular nano-materials. However, the stable supramolecular gel systems of TTF-X2 combinations with controlled self-assembly pathways cannot be accessed easily in solvents. In this context, a novel representative organogel system was constructed according to the crown ether-monopyrrolotetrathiafulvalene-l- glutamide triad. The formed gel exhibited multiple stimulus responses on various external stimuli, including temperature, sonication, anions and K+. This gel could be transformed into the charge transfer salt gel with I2, which was an important first example of the charge transfer salt gel of TTF with I2 in solvents. The same gel-gel transition was also induced by adding other inorganic oxidants (i.e., Ag+, Fe3+, Cu2+ and TFA) and π-electron acceptors (i.e., TCNQ and C60).

Pure Anisotropic Hydrogel with an Inherent Chiral Internal Structure Based on the Chiral Nematic Liquid Crystal Phase of Rodlike Viruses.

Imparting ordered structures into otherwise amorphous hydrogels is expected to endow these popular materials with novel multiple-stimuli responsiveness that promises many applications. The current contribution reports a method to fabricate pure polymeric hydrogels with an inherent chiral internal structure by templating on the chiral nematic liquid crystal phase of a rodlike virus. A method was developed to form macroscopically homogeneous chiral templates by confinement induced self-assembly in the presence of monomers, cross-linkers and initiators. Polymerization induced gelation was performed without perturbing the elegant 3D chiral organization of the rodlike virus bearing double bonds. Furthermore, a suitable method was found to remove the organic virus template while keeping the desired polymeric replica intact, resulting in a pure polymeric hydrogel with a unique internal chiral feature that originates from the 3D chiral ordering of the cylindrical pores left by the virus. Multiple-stimuli responsiveness has been demonstrated and can be quantified by the change of the pitch of the chiral feature. The chiral structure endows the otherwise featureless hydrogel with a unique material property that might be used as a readout signal for sensing and acts as the basis for responsive, biomimetic nanostructured materials.

Monopyrrolotetrathiafulvalene-succinamide conjugates and their TCNQ charge transfer complex based supramolecular gels with multiple stimulus responsiveness.

A series of monopyrrolotetrathiafulvalene-succinamide conjugates and their 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) charge transfer (CT) complexes have been synthesized and investigated as new low-molecular mass organogelators. The gelation capability of these conjugates is highly dependent on the length of the alkyl chain of the terminal amide. Thus, only the short alkyl chain derivatives and could efficiently gelate cyclohexane and methylcyclohexane (MCH). Surprisingly, these gelators react with TCNQ to form stable CT complex gels in both cyclohexane and MCH. The FE-SEM images of the native gels reveal the characteristic gelation morphologies of microporous or fibrous structures, whereas the morphologies of CT complex gels show the fibrillar and globular aggregates in cyclohexane and MCH, respectively. SAXS study of the native gel and the CT complex gel of in cyclohexane suggests that the molecules maintain rectangular and hexagonal columnar molecular packing models in the gel phase, respectively. The native gels undergo a reversible gel-sol phase transition upon exposure to external stimuli, such as temperature and chemical oxidation/reduction. Alternatively, the corresponding CT complex gels exhibit a complicated response to external stimuli. Chemical oxidation by I2 results in the destruction of the gel state. However, neither Fe(3+) nor Cu(2+) can induce the collapse of the gel phase. Interestingly, all the gels show an irreversible gel-sol transition on successively triggering with trifluoroacetic acid and triethylamine. The reformation of the gel from the sol state is achieved just by the addition of water, showing the phase-selective gelation of the solvents from their mixtures with water.

Nanoporous frameworks exhibiting multiple stimuli responsiveness

Nanoporous frameworks are polymeric materials built from rigid molecules, which give rise to their nanoporous structures with applications in gas sorption and storage, catalysis and others. Conceptually new applications could emerge, should these beneficial properties be manipulated by external stimuli in a reversible manner. One approach to render nanoporous frameworks responsive to external signals would be to immobilize molecular switches within their nanopores. Although the majority of molecular switches require conformational freedom to isomerize, and switching in the solid state is prohibited, the nanopores may provide enough room for the switches to efficiently isomerize. Here we describe two families of nanoporous materials incorporating the spiropyran molecular switch. These materials exhibit a variety of interesting properties, including reversible photochromism and acidochromism under solvent-free conditions, light-controlled capture and release of metal ions, as well reversible chromism induced by solvation/desolvation.

Multistimuli Responsive and Electroactive Supramolecular Gels Based on Ionic Liquid Gemini Guest.

Electroactive supramolecular gels with multistimuli responsiveness were fabricated through host-guest interactions between a host polymer containing β-cyclodextrin (CD) and an ionic liquid (IL) type asymmetric gemini guest, which contains both ferrocene (Fc) and bis(trifluoromethyl-sulfonyl)imide (TFSI-) as the respective α- and ω-guest groups. Owing to the multiple stimuli-responsiveness of the host-guest interactions, reversible sol-gel phase transition could be triggered by various stimuli, including temperature, electrochemical/chemical redox and anion-exchange reactions. Due to the intrinsically conductive properties of the IL gemini guest, the sol-gel transition behavior could be electrochemically controlled by the applied voltage, without using additional supporting electrolyte.

Biodegradable, multiple stimuli-responsive sodium deoxycholate–amino acids–NaCl mixed systems for dye delivery

Multiple stimuli-responsiveness of NaDC–amino acid–NaCl mixed systems.

A pillar[5]arene/imidazolium [2]rotaxane: solvent- and thermo-driven molecular motions and supramolecular gel formation

Based on the pillar[5]arene/imidazolium recognition motif, a [2]rotaxane was effectively prepared. Solvent/temperature triggered molecular motions of the pillar[5]arene ring on the imidazolium axle were successfully realized. By comparison of proton NMR spectra of the [2]rotaxane in different solvents, we found that if we increased the solvent polarity, the pillar[5]arene ring gradually moved away from the imidazolium part. In DMSO, we also could adjust the binding site of the pillar[5]arene ring by changing the temperature. Furthermore, in DMSO, the [2]rotaxane self-assembled to form a supramolecular gel, which showed multiple stimuli-responsiveness.

A Supramolecular Cross-Linked Conjugated Polymer Network for Multiple Fluorescent Sensing

A supramolecular cross-linked network was fabricated and demonstrated to act as a multiple fluorescent sensor. It was constructed from a fluorescent conjugated polymer and a bisammonium salt cross-linker driven by dibenzo[24]crown-8/secondary ammonium salt host-guest interactions. Compared with the conjugated polymer, the network has weak fluorescence due to the aggregation of polymer chains. Thanks to the multiple stimuli-responsiveness of host-guest interactions, the fluorescence intensity of the system can be enhanced by four types of signals, including potassium cation, chloride anion, pH increase, and heating. Hence, the network can serve as a cation sensor, an anion sensor, a pH sensor, and a temperature sensor. It can be used in both solution and thin film. Interestingly, exposure of a film made from this supramolecular cross-linked network to ammonia leads to an increase of fluorescence, making it a good candidate for gas detection.

A Crown Ether Appended Super Gelator with Multiple Stimulus Responsiveness

A crown ether appended super gelator is designed and synthesized. It can gel a variety of organic solvents and shows excellent gelation properties with both low critical gelation concentration and short gelation time. Due to the introduction of the crown ether moiety and a secondary ammonium unit, the supramolecular gels show reversible gel-sol transitions. The supramolecular gels can also be molded into shape-persistent and free-standing objects.

Multiple Stimuli-Responsive Hydrogels for Metal-Based Drug Therapy

A series of homopolymeric and copolymeric hydrogels containing the N-isopropylacrylamide and vinyl monomers with α-amino acid (L-valine and L-phenylalanine) residues have been synthesized and their swelling properties were evaluated under different external stimulations. The hydrogels, obtained with different cross-linking agents (EBA and PEG-DA), have shown unique properties such as biocompatibility in addition to the stimuli-responsive characters. These ‘smart’ hydrogels exhibit single or multiple stimuli-responsiveness which could be used in biomedical applications, including controlled drug delivery. This article focuses on recent developments dealing with the delivery of metal-based drug (cisplatin, lithium) from the stimuli-responsive hydrogels proposed as platforms for cancer and bipolar disorder therapies.

ChemInform Abstract: Noncovalent Water‐Based Materials: Robust yet Adaptive

AbstractReview: 88 refs.

Noncovalent Water‐Based Materials: Robust yet Adaptive

The adaptive properties of noncovalent materials allow easy processing, facile recycling, self-healing, and stimuli responsiveness. However, the poor robustness of noncovalent systems has hampered their use in real-life applications. In this Concept Article we discuss the possibility of creating robust noncovalent arrays by utilizing strong hydrophobic interactions. We describe examples from our work on aqueous assemblies based on aromatic amphiphiles with extended hydrophobic cores. These arrays exhibit fascinating properties, including robustness, multiple stimuli-responsiveness, and pathway-dependent self-assembly. We have shown that this can lead to functional materials (filtration membranes) rivaling covalent systems. We anticipate that water-based noncovalent materials have the potential to replace or complement conventional polymer materials in various fields, and to promote novel applications that require the combination of robustness and adaptivity.

Selective impairment of masked priming in dual-task performance

This study investigated the impact of divided attention on masked priming. In a dual-task setting, two tasks had to be carried out in close temporal succession: a tone discrimination task and a masked priming task. The order of the tasks was varied between experiments, and attention was always allocated to the first task-that is, the first task was prioritized. The priming task was the second (nonprioritized) task in Experiment 1 and the first (prioritized) task in Experiment 2. In both experiments, "novel" prime stimuli associated with semantic processing were essentially ineffective. However, there was intact priming by another type of prime stimuli associated with response priming. Experiment 3 showed that all these prime stimuli can reveal significant priming effects during a task-switching paradigm in which both tasks were performed consecutively. We conclude that dual-task specific interference processes (e.g., the simultaneous coordination of multiple stimulus-response rules) selectively impair priming that is assumed to rely on semantic processing.

Supramolecular Gel Based on a Perylene Diimide Dye: Multiple Stimuli Responsiveness, Robustness, and Photofunction

Design of an extensive supramolecular three-dimensional network that is both robust and adaptive represents a significant challenge. The molecular system PP2b based on a perylene diimide chromophore (PDI) decorated with polyethylene glycol groups self-assembles in aqueous media into extended supramolecular fibers that form a robust three-dimensional network resulting in gelation. The self-assembled systems were characterized by cryo-TEM, cryo-SEM, and rheological measurements. The gel possesses exceptional robustness and multiple stimuli-responsiveness. Reversible charging of PP2b allows for switching between the gel state and fluid solution that is accompanied by switching on and off the material's birefringence. Temperature triggered deswelling of the gel leads to the (reversible) expulsion of a large fraction of the aqueous solvent. The dual sensibility toward chemical reduction and temperature with a distinct and interrelated response to each of these stimuli is pertinent to applications in the area of adaptive functional materials. The gel also shows strong absorption of visible light and good exciton mobility (elucidated using femtosecond transient absorption), representing an advantageous light harvesting system.

Supramolecular Hydrogel Exhibiting Four Basic Logic Gate Functions To Fine-Tune Substance Release

Logic-gate operations displaying macroscopic outputs are promising systems for the development of intelligent soft materials that can perform effective functions in response to various input patterns. A supramolecular hydrogel comprising the phosphate-type hydrogelator 1 exhibits macroscopic gel-sol behavior in response to four distinct input stimuli: temperature, pH, Ca(2+), and light. We characterized this performance through microscopic, spectroscopic, and rheological measurements. On the basis of its multiple-stimulus responsiveness, we constructed gel-based supramolecular logic gates from hydrogelator 1 that demonstrated AND, OR, NAND, and NOR types of stimulus-responsive gel-sol behavior in the presence of various combinations of the four stimuli. Implementation of such logic-gate functions into semiwet soft materials (e.g., supramolecular hydrogels) is an important step toward the design of controlled drug delivery and release systems. Indeed, we demonstrate herein that one of our gel-based supramolecular logic gates is capable of holding and releasing bioactive substances in response to logic triggers. Furthermore, combining our supramolecular gel-based AND logic gate with a photoresponsive supramolecular gel could temporarily modulate the release rate of the bioactive substance.