An Amylase-Responsive Bolaform Supra-Amphiphile

(1-(4-(5-Phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1H-1,2,3-triazol-4-yl)-methylenyls α,ω-Bisfunctionalized 3- and 4-PEG: Synthesis and Photophysical Studies

Two new azaheterocycle-based bolas, such as (1-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1H-1,2,3-triazol-4-yl)-methylenyls α,ω-bisfunctionalized PEGs, were prepared via Cu-catalyzed click reaction between 2-(4-azidophenyl)-5-(aryl)-oxadiazole-1,3,4 and terminal ethynyls derived from PEG-3 and PEG-4. Due to the presence of two heteroaromatic cores and a PEG linker, these bola molecules are considered as promising fluorescent chemosensors for electron-deficient species. As a result of a well-pronounced "turn-off" fluorescence response towards common nitro-explosive components, such as 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), hard-to-detect pentaerythritol tetranitrate (PETN), as well as Hg²⁺ cation was observed.

Multicharged cyclodextrin supramolecular assemblies

Multicharged cyclodextrin (CD) supramolecular assemblies, including those based on positively/negatively charged modified mono-6-deoxy-CDs, per-6-deoxy-CDs, and random 2,3,6-deoxy-CDs, as well as parent CDs binding positively/negatively charged guests, have been extensively applied in chemistry, materials science, medicine, biological science, catalysis, and other fields. In this review, we primarily focus on summarizing the recent advances in positively/negatively charged CDs and parent CDs encapsulating positively/negatively charged guests, especially the construction process of supramolecular assemblies and their applications. Compared with uncharged CDs, multicharged CDs display remarkably high antiviral and antibacterial activity as well as efficient protein fibrosis inhibition. Meanwhile, charged CDs can interact with oppositely charged dyes, drugs, polymers, and biomacromolecules to achieve effective encapsulation and aggregation. Consequently, multicharged CD supramolecular assemblies show great advantages in improving drug-delivery efficiency, the luminescence properties of materials, molecular recognition and imaging, and the toughness of supramolecular hydrogels, in addition to enabling the construction of multistimuli-responsive assemblies. These features are anticipated to not only promote the development of CD-based supramolecular chemistry but also contribute to the rapid exploitation of these assemblies in diverse interdisciplinary applications.

An Organoplatinum(II) Metallacycle-Based Supramolecular Amphiphile and Its Application in Enzyme-Responsive Controlled Release

Enzyme-responsive nanomaterials are emerging as important candidates for bioanalytical and biomedical applications due to their good biocompatibilities and sensitivities. However, the lack of promising operation platforms compatible with enzyme responsiveness greatly limits the scope and functionality of smart materials. Herein, we report the design and synthesis of a naphthalene-functionalized organoplatinum(II) metallacycle 1 by means of coordination-driven self-assembly, which is subsequently exploited as the organometallic platform to enable enzyme-responsive supramolecular materials. Specifically, a [2 + 2] self-assembled metallacycle 1 first self-assembles into nanosheets in aqueous solution, which can further transform into vesicles with the introduction of β-cyclodextrin (β-CD) because of the formation of a bola-type supramolecular amphiphile β-CD-1. Interestingly, these vesicles show rare α-amylase responsiveness, as demonstrated by structurally transforming back into nanosheets after the addition of α-amylase to their solutions due to the enzyme-induced degradation of cyclodextrins. We also demonstrate the potential application of the self-assembled vesicles in amylase-responsive controlled release.

Stimuli-responsive cyclodextrin-based supramolecular assemblies as drug carriers

Cyclodextrins (CDs) are widely employed in biomedical applications because of their unique structures. Various biomedical applications can be achieved in a spatiotemporally controlled manner by integrating the host-guest chemistry of CDs with stimuli-responsive functions. In this review, we summarize the recent advances in stimuli-responsive supramolecular assemblies based on the host-guest chemistry of CDs. The stimuli considered in this review include endogenous (pH, redox, and enzymes) and exogenous stimuli (light, temperature, and magnetic field). We mainly discuss the mechanisms of the stimuli-responsive ability and present typical designs of the corresponding supramolecular assemblies for drug delivery and other potential biomedical applications. The limitations and perspectives of CD-based stimuli-responsive supramolecular assemblies are discussed to further promote the translation of laboratory products into clinical applications.

Insights into the Formations of Host-Guest Complexes Based on the Benzimidazolium Based Ionic Liquids-β-Cyclodextrin Systems

Inclusion complexation is one of the best strategies for developing a controlled release of a toxic drug without unexpected side effects from the very beginning of the administration to the target site. In this study, three benzimidazolium based ionic liquids (ILs) having bromide anion and cation bearing long alkyl chains, hexyl- ([C₆CFBim]Br), octyl- ([C₈CFBim]Br), and decyl- ([C₁₀CFBim]Br) were designed and synthesized as antibacterial drugs. Inclusion complexes (ICs) of studied ILs have been prepared by the combination of β-cyclodextrin (β-CD), considering these conjugations should enhance the benignity of ILs and make them potential candidates for the controlled drug release. Characterizations and structural analysis of studied ICs have been performed by ¹H NMR, 2D-ROESY NMR, FT-IR, HRMS, TGA, DSC, surface tension, ionic conductivity, dynamic light scattering (DLS), and isothermal titration calorimetry (ITC). Further, the morphology of the ICs has been analyzed by SEM and TEM. Furthermore, neat ILs and ICs have been treated against Escherichia coli and Bacillus subtilis to investigate their antibacterial activity, which confirms the prevention of bacterium growth and the shrinkage of the bacterial cell wall. The findings of this work provide the proof of concept that studied benzimidazolium based ILs-β-CD host-guest complexes should act as a potential candidate in controlled drug delivery and other biomedical applications.

Fluorescence "Turn-On" Enzyme-Responsive Supra-Amphiphile Fabricated by Host-Guest Recognition between γ-Cyclodextrin and a Tetraphenylethylene-Sodium Glycyrrhetinate Conjugate

A novel fluorescence "turn-on" enzyme-responsive supra-amphiphile is developed based on the host-guest recognition between γ-cyclodextrin (γ-CD) and an amphiphilic tetraphenylethene-sodium glycyrrhetinate conjugate (TPE-SGA). The covalent amphiphile TPE-SGA displayed strong fluorescence in aqueous solution owing to the aggregation-induced emission. Upon addition of γ-CD, the fluorescence of TPE-SGA was effectively turned off due to the host-guest recognition with γ-CD prohibiting the aggregation of TPE-SGA in aqueous solution. The as-formed nonfluorescent supra-amphiphile (TPE-SGA/γ-CD) inherited the α-amylase-responsive property of γ-CD. In the presence of α-amylase, the fluorescence of the supra-amphiphile was gradually turned on owing to the hydrolysis of γ-CD, and the fluorescence intensity linearly correlated to the activity of α-amylase. This study enriches the field of supra-amphiphile on the basis of cyclodextrin-based host-guest chemistry and provides a novel strategy to construct fluorescence turn-on functioned self-assemblies. It is anticipated that the fluorescence turn-on supra-amphiphile has potential applications in biological analysis and diagnosis of pancreatic diseases.

Cyclodextrin/surfactant inclusion complexes: An integrated view of their thermodynamic and structural properties

Cyclodextrins (CDs) play an important role in self-assembly systems of amphiphiles. The structure of CDs provides distinguished physicochemical properties, including the ability to form host-guest complexes. The complexation affects the properties of guest molecules and can produce supramolecular aggregates with desirable characteristics for fundamental and practical applications. Surfactants are particularly attractive host molecules due to their wide variety, availability, responsiveness to different stimuli, and high relevance in different fields, e.g. medical, cosmetic, pharmaceutical, and food industries. The tendency of organization in higher-order supramolecular aggregates arises the interest in applying such versatile complexes in the development of novel materials. In this review, we provide a comprehensive overview of the thermodynamics aspects of surfactants and CDs inclusion complexes formation in aqueous environment, emphasizing the assessment of the interactions, thermodynamic driving forces, and structural aspects. Also, the most common analytical techniques used to gather deep insight into the aspects of CDs complexes are discussed and the perspectives for the surfactant-cyclodextrin complexes are pointed out.

Selenium-containing heterodimeric crown ether acting as an unconventional multi-responsive amphiphile in water

A new heterodimeric crown amphiphile was fabricated, wherein the oxacrown and selencrown ethers provided the desired molecular framework for hydrophilicity and hydrophobicity, respectively. From an integrated perspective, the developed amphiphile possesses features of crown ethers, amines, and selenium-containing species, and its assembly in water can be responsive to diverse chemical effectors-H2O2 and CO2 in a switchable ON/OFF mode to achieve controlled release. It is the first case wherein the applications of cyclic polyethers with different solubilities drives the self-assembly in an aqueous medium.

Multiple-responsive supramolecular vesicle based on azobenzene-cyclodextrin host-guest interaction

Multiple-responsive supramolecular vesicles have been successfully fabricated by the complexation between β-cyclodextrin (β-CD) and a pH/photo dual-responsive amphiphile 4-(4-(hexyloxy)phenylazo)benzoate sodium (HPB) with azobenzene and carboxylate groups. When mixing β-CD with HPB to reach a host/guest molar ratio of 1 : 1, the azobenzene group of HPB could be spontaneously included by β-CD molecules. Then, the formed inclusion complexes (HPB@β-CD) could self-assemble into vesicles, which was driven by the hydrophobic interaction of the alkyl chain of HPB and the hydrogen bonds between neighboring β-CDs. The reversible assembly/disassembly of the vesicles could be simply regulated under UV or visible light irradiation. The reversible phase transformation between vesicles and microbelts could also be realized by adjusting the pH values of the sample. Adding both competitive guest molecules (1-adamantane carboxylic acid sodium (ADA)) and α-amylase would result in the phase transformation from vesicles to micelles. Moreover, the vesicles would be destroyed when β-CD was continuously added until the ratio of host/guest reached 2 : 1. Such an interesting quintuple-responsive vesicle system reported here not only has potential applications in various fields such as controlled release or drug delivery, but also provides a reference for the design and construction of multiple responsive systems.

A quintuple-responsive vesicle system was successfully fabricated by simply mixing HPB with an equal amount of β-CD.

Color-tunable single-fluorophore supramolecular system with assembly-encoded emission

Regulating the fluorescent properties of organic small molecules in a controlled and dynamic manner has been a fundamental research goal. Although several strategies have been exploited, realizing multi-color molecular emission from a single fluorophore remains challenging. Herein, we demonstrate an emissive system by combining pyrene fluorophore and acylhydrazone units, which can generate multi-color switchable fluorescent emissions at different assembled states. Two kinds of supramolecular tools, amphiphilic self-assembly and γ-cyclodextrin mediated host-guest recognition, are used to manipulate the intermolecular aromatic stacking distances, resulting in the tunable fluorescent emission ranging from blue to yellow, including a pure white-light emission. Moreover, an external chemical signal, amylase, is introduced to control the assembly states of the system on a time scale, generating a distinct dynamic emission system. The dynamic properties of this multi-color fluorescent system can be also enabled in a hydrogel network, exhibiting a promising potential for intelligent fluorescent materials.

Regulating fluorescent properties of small molecules in a controlled manner has been a fundamental research goal but realizing multi-color emission from a single fluorophore remains challenging. Here the authros demonstrate that combined pyrene fluorophore and acylhydrazone units show multi-color switchable fluorescent at different assembled states.

Cyclodextrin-Based Multistimuli-Responsive Supramolecular Assemblies and Their Biological Functions

Cyclodextrins (CDs), which are a class of cyclic oligosaccharides extracted from the enzymatic degradation of starch, are often utilized in molecular recognition and assembly constructs, primarily via host-guest interactions in water. In this review, recent progress in CD-based supramolecular nanoassemblies that are sensitive to chemical, biological, and physical stimuli is updated and reviewed, and intriguing examples of the biological functions of these nanoassemblies are presented, including pH- and redox-responsive drug and gene delivery, enzyme-activated specific cargo release, photoswitchable morphological interconversion, microtubular aggregation, and cell-cell communication, as well as a geomagnetism-controlled nanosystem for the suppression of tumor invasion and metastasis. Moreover, future perspectives and challenges in the fabrication of intelligent CD-based biofunctional materials are also discussed at the end of this review, which is expected to promote the translational development of these nanomaterials in the biomedical field.

Fluorogenic probes for disease-relevant enzymes

Traditional biochemical methods for enzyme detection are mainly based on antibody-based immunoassays, which lack the ability to monitor the spatiotemporal distribution and, in particular, the in situ activity of enzymes in live cells and in vivo. In this review, we comprehensively summarize recent progress that has been made in the development of small-molecule as well as material-based fluorogenic probes for sensitive detection of the activities of enzymes that are related to a number of human diseases. The principles utilized to design these probes as well as their applications are reviewed. Specific attention is given to fluorogenic probes that have been developed for analysis of the activities of enzymes including oxidases and reductases, those that act on biomacromolecules including DNAs, proteins/peptides/amino acids, carbohydrates and lipids, and those that are responsible for translational modifications. We envision that this review will serve as an ideal reference for practitioners as well as beginners in relevant research fields.

Hierarchical Assembly of l-Phenylalanine-Terminated Bolaamphiphile with Porphyrin Show Tunable Nanostructures and Photocatalytic Properties

Demands related to clean energy and environmental protection promote the development of novel supramolecular assemblies for photocatalysis. Because of the distinctive aggregation behaviors, bolaamphiphiles with two hydrophilic end groups could be theoretically the right candidates for the fabrication of high-performance photocatalysis. However, photocatalytic applications based on bolaamphiphilic assemblies were still rarely investigated. Especially, the relationship between diverse assembled nanostructures and the properties for different applications is urgently needed to be studied. Herein, we demonstrate that using the hierarchical assembly of bolaamphiphiles could correctly induce the porphyrin supramolecular architectures with much better photocatalytic performances than the aggregations containing 450 times of the porphyrin molecules, even though both molecular structures as well as the J-aggregations of porphyrin building blocks are same in two different systems. Thus, the co-assembly of l-phenylalanine terminated bolaamphiphile (Bola-F) and the porphyrin containing four hydroxyl groups (tetrakis-5,10,15,20-(4-hydroxyphenyl)porphyrin) can form microtube in methanol and forms fibers/spheres in methanol/water mixture. For catalyzing the photodegradation of rhodamine B, the small amount of J-aggregated porphyrin within Bola-F microtubes show much better photocatalytic performance comparing with that of huge porphyrin J-aggregations in fibers/spheres. The supramolecular assemblies as well as the photocatalysis were thoroughly characterized by different spectroscopies and electron microscopy. It is demonstrated that the co-assembly with bolaamphiphiles could inhibit the energy transfer of porphyrin aggregation and subsequently benefit the electron transfer and corresponding photocatalysis under photo-irradiation. This work is not only useful for further understanding the hierarchically supramolecular assembly but also provides a new strategy for making novel functional supramolecular architectures based on the assembly of bolaamphiphiles and porphyrins.

Reversible fabrication and self-assembly of a gemini supra-amphiphile driven by dynamic covalent bonds

A smart gemini supra-amphiphile behaving with pH/CO2 dual-sensitive hierarchical self-assembly was fabricated under the effect of dynamic covalent bonds. In the presence of an amino-functionalized cation, water-insoluble terephthalaldehyde, and an amphiphilic anion, the benzoic imine bond can initiate the transformation from a single-tailed supra-amphiphile to a gemini supra-amphiphile with increasing pH, followed by the subsequent evolution from micelles to vesicles. Reversible self-assembly and disassembly of the gemini supra-amphiphile can be realized via CO2/N2 treatment, thus inducing the fission and reversion of vesicles. Interestingly, the flexible nature of supra-amphiphiles allows for the hierarchical assembly of vesicles, leading to the formation of aqueous two-phase systems. Multiple responsive supra-amphiphiles have useful applications in the fabrication of smart supra-molecular materials, including self-healing materials, nanocarriers and chemosensors.

Separately enhanced dual emissions of the amphiphilic derivative of 2-(2'-hydroxylphenyl) benzothiazole by supramolecular complexation

Here, we report separately enhanced dual emissions of the amphiphilic derivative of 2-(2'-hydroxyphenyl)benzothiazole (denoted as HBT-11) by supramolecular complexation with cyclodextrins (CDs). When dispersed in water, HBT-11 shows two relatively weak emission bands, which can be assigned to the emissions of enol- and keto-forms, the two tautomers, owing to excited-state intramolecular proton transfers. Upon the addition of α-CD and β-CD, the keto- and enol-emissions, respectively, are separately enhanced; the enhancement effect is due to the formation of HBT-11/α-CD and HBT-11/β-CD complexes through multiple hydrogen bonding and host-guest interactions, respectively. It is worth to note that the keto-emission caused by the complex of HBT-11/α-CD has a much shorter wavelength compared with that of the aggregates formed by pure HBT-11. To the best of our knowledge, this is the first time that a study on keto-emission of the isolated HBT chromophore has been reported.

Tuning the emission of a water-soluble 3-hydroxyflavone derivative by host-guest complexation

3-Hydroxyflavone derivatives have great potential as fluorescent probes for bio-labeling in aqueous medium. They were extensively studied in various organic solvents for the "excited state intramolecular proton transfer" process, but seldom addressed in aqueous solution due to the poor water solubility. Herein, an amphiphilic molecule bearing 3-hydroxyflavone and oligo(ethylene oxide) (denoted as 3HF-EO) was designed and synthesized. Different from the fluorescence in organic solvents, 3HF-EO in aqueous solution showed a remarkable single fluorescence emission, which is ascribed to the fluorescence of its anionic species. We found that the fluorescence intensity could be efficiently tuned via host-guest complexation. α-CD has little effect on the emission, while β-CD and γ-CD lead to enhanced and reduced emissions of 3HF-EO, respectively. The 1H NMR and 2D NOESY NMR spectra indicate that α-CD barely had any interaction with 3HF-EO, while β-CD and γ-CD formed complexes with one and two 3HF-EO molecules, respectively. These results provide a sound explanation for the modulated fluorescence intensity.

Transformation of H-Aggregates and J-Dimers of Water-Soluble Tetrakis (4-carboxyphenyl) Porphyrin in Polyion Complex Micelles

Tetrakis (4-carboxyphenyl) porphyrin (TCPP) and polyelectrolyte poly(N-methyl-2-vinylpyridinium iodide)-b-poly(ethylene oxide) (PMVP₄₁-b-PEO₂₀₅) can self-aggregate into polyion complex (PIC) micelles in alkaline aqueous solution. UV-vis spectroscopy, fluorescence spectroscopy, transmission electron microscope, and dynamic light scattering were carried out to study PIC micelles. Density functional theory (DFT) calculation method was applied to study the interaction of TCPP and PMVP₄₁-b-PEO₂₀₅. We found that the H-aggregates and J-dimers of anionic TCPP transformed in PIC micelles. H-aggregates of TCPP formed at the charge ratio of TCPP/PMVP₄₁-b-PEO₂₀₅ 1:2 and J-dimer species at the charge ratio above 1:4, respectively. It is worth noting that the transformation from H-aggregates to J-dimer species of TCPP occurred just by adjusting the ratio of polymer and TCPP rather than by changing other factors such as pH, temperature, and ions.

Morphological Evolution of Self-Assembled Structures Induced by the Molecular Architecture of Supra-Amphiphiles

A series of telechelic supramolecular amphiphiles [POSS-Azo₈@(β-CD-PDMAEMA)_1→8] was accomplished by orthogonally coupling the multiarm host polymer β-cyclodextrin-poly(dimethylaminoethyl methacrylate) (β-CD-PDMAEMA) with an octatelechelic guest molecule azobenzene modified-polyhedral oligomeric silsesquioxanes (POSS-Azo₈) under different host-guest ratios. These telechelic supramolecular amphiphiles possess a rigid core and flexible corona. Increasing the multiarm host polymer coupled onto the rigid POSS core made the molecular architecture tend to be symmetrical and spherical. POSS-Azo₈@[β-CD-PDMAEMA]_1→8 could self-assemble into diverse morphologies evolving from spherical micelles, wormlike micelles, and branched aggregates to bowl-shaped vesicles. Distinct from the traditional linear amphiphilic polymers, we discovered that the self-assembly of POSS-Azo₈@[β-CD-PDMAEMA]_1→8 was dominantly regulated by their molecular architectures instead of hydrophilicity, which has also been verified using computer simulation results.

Pillar[7]arene-based host–guest complex in water: dual-responsiveness and application in controllable self-assembly

A dual-responsive supra-amphiphile was constructed based on a water-soluble pillar[7]arene and a pyrene-containing guest. The self-assembly morphology of this supra-amphiphile could be adjusted by changing pH or irradiation by UV light.