Cyclodextrin-pillar[n]arene hybridized macrocyclic systems.

Cyclodextrin (CD) and pillar[n]arene are significant macrocyclic host molecules in supramolecular chemistry, and have either similar or contrasting physicochemical properties, for example, both can provide capable cavities available for recognizing various favorite guest molecules, while they usually possess different solubility in aqueous solutions, and exhibit diverse chiral characteristics. To balance their similarity and differences inherited from each chemical structure and incorporate both advantages, the CD-pillar[n]arene hybrid macrocyclic system was recently developed. In this review, we will focus on the preparation and application of CD-pillar[n]arene hybrid macrocyclic systems. Both noncovalent interactions and covalent bonds were employed in the synthesis strategies of building the hybrid macrocyclic system, which was in the form of host-guest inclusion, self-assembly, conjugated molecules, and polymeric structures. Furthermore, the CD-pillar[n]arene hybrid macrocyclic system has been primarily applied for the removal of organic pollutants from water, induced chirality, as well as photocatalysis due to the integration of both cavities from CD and pillar[n]arene as hybrid hosts and chiral characteristics inherited from their chemical structures.

Crown ether-pillararene hybrid macrocyclic systems.

A combination of Nobel macrocycle-crown ether and star macrocycle-pillararenes together in organic synthesis and material science is significant in obtaining hybrid systems, with rigid/flexible structural architecture, induced planar chirality, a negative cooperative effect and multiple fused cyclic hosts. In this review, we will discuss the synthesis/preparation of crown ether-pillararene hybrid macrocyclic systems by covalent bonds, supramolecular interactions and mechanical bonds, leading to hybrid compounds, supramolecular assemblies and mechanically interlocked molecules. The practical applications of crown ether-containing pillararenes will also be discussed in diverse areas, such as molecular recognition via fused multiple macrocycles and ion channels as well as external stimuli-responsive smart materials. We also call the attention of related researchers towards academic and technical issues about topological structures and applied functions in this fresh new fused macrocyclic field.

Pillararene-based self-assembled amphiphiles.

Pillararenes are a unique group of supramolecular macrocycles, presenting important features and potential applications on account of their intrinsic structural properties and functionality. Developing pillararene-based self-assembled amphiphiles (PSAs) is an efficient approach to translate pillararenes into functional systems and materials for facilitating their practical applications. In this review article, we highlight recent significant advancements in PSAs. A new standard according to the number, solubility, and amphiphilicity of building blocks is employed for dividing PSAs into different categories. The fabrication of PSAs based on various building blocks and supramolecular interactions, and the formation of amphiphile-based self-assemblies are then discussed based on this standard. Furthermore, interesting stimulus-responsiveness to various factors, such as pH, redox, temperature, light, ionic effect, and host-guest competition, generated by the functional groups on various building blocks is summarized, and the corresponding supramolecular interactions in PSAs and their self-assemblies are elaborated. In addition, some important applications of PSAs and their assemblies are discussed. This review not only provides fundamental findings on the construction of PSAs, but also foresees future research directions in this rapidly developing area.

Controllable Assemblies of Au NPs/P5A for Enhanced Catalytic Reduction of 4-Nitrophenol.

Efficient catalytic reduction of 4-nitrophenol (4-NP) is one focus of industry and practical engineering, because 4-NP is one of the most important sources of pollution of the ecological environment and human health. Here, coassembled hybrid composites of pillar[5]arene (P5A) and gold nanoparticles (Au NPs) were successfully developed by a one-step synthetic method as a type of water-insoluble catalyst for the reduction of 4-NP. The geometric and topological structures, as well as physiochemical properties of Au NPs/P5A composite catalyst, were fully characterized and analyzed through various tests such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), indicating that Au NPs were well dispersed on the surface of the two-dimensional film of assembled P5A. The influence factors of the catalytic reduction of 4-NP were further investigated and discussed, confirming that the content of Au NPs and the concentration of 4-NP were very significant during the catalysis. The catalytic reaction was carried out at the catalyst concentration of 100 mg·L-1 and an initial 4-NP concentration of 90 mg·L-1 under 30 °C. The calculated reaction rate constant was 0.3959 min-1 and the reduction rate of 4-NP was more than 95% in 20 min. In addition, the as-prepared catalyst can maintain a high catalytic efficiency after five cycles. Thus, the easily recyclable composite catalyst with poor aqueous solution can exhibit prospective application to the treatment of 4-NP in water.

Pillar[n]arene-calix[m]arene hybrid macrocyclic structures.

To reserve planar chirality, enhance molecular recognition, and build advanced self-assemblies, hybrid macrocyclic hosts containing rigid pillar[n]arene and flexible calix[m]arene were designed, prepared and investigated for interesting applications. This review summarizes and discusses different synthetic strategies for constructing hybrid macrocyclic structures. Pillar[n]arene dimer with rigid aromatic double bridges provided the possibility of introducing calix[m]arene cavities, where the planar chirality was reserved in the structure of pillararene. The capacity for molecular recognition was enhanced by hybrid macrocyclic cavities. Interestingly, the obtained pillar[n]arene-calix[m]arene could self-assemble into "channels" and "honeycomb" in both the solid state and solution phase as well as donate the molecular architecture as the wheel for the formation of mechanically interlocked molecules, such as rotaxane. In addition, the pillar[n]arene and calix[m]arene could also be coupled together to produce pillar[n]arene embeded 1,3-alternate and cone conformational calix[m]arene derivatives, which could catalyze the oxidative polymerization of aniline in aqueous solutions. Except for building hybrid cyclophanes by covalent bonds, weak supramolecular interactions were used to prepare pillar[n]arene-calix[m]arene analogous composites with other pillar-like pillar[n]pyridiniums and calix-like calix[m]pyrroles, exhibiting reasonable performances in enhancing molecular recognition and trapping solvent molecules.

Pillar[n]arene-Mimicking/Assisted/Participated Carbon Nanotube Materials.

The recent progress in pillar[n]arene-assisted/participated carbon nanotube hybrid materials were initially summarized and discussed. The molecular structure of pillar[n]arene could serve different roles in the fabrication of attractive carbon nanotube-based materials. Firstly, pillar[n]arene has the ability to provide the structural basis for enlarging the cylindrical pillar-like architecture by forming one-dimensional, rigid, tubular, oligomeric/polymeric structures with aromatic moieties as the linker, or forming spatially "closed", channel-like, flexible structures by perfunctionalizing with peptides and with intramolecular hydrogen bonding. Interestingly, such pillar[n]arene-based carbon nanotube-resembling structures were used as porous materials for the adsorption and separation of gas and toxic pollutants, as well as for artificial water channels and membranes. In addition to the art of organic synthesis, self-assembly based on pillar[n]arene, such as self-assembled amphiphilic molecules, is also used to promote and control the dispersion behavior of carbon nanotubes in solution. Furthermore, functionalized pillar[n]arene derivatives integrated carbon nanotubes to prepare advanced hybrid materials through supramolecular interactions, which could also incorporate various compositions such as Ag and Au nanoparticles for catalysis and sensing.

Hybrid Macrocyclic Polymers: Self-Assembly Containing Cucurbit[m]uril-pillar[n]arene.

Supramolecular self-assembly by hybrid macrocycles containing both cucurbit[m]uril (CB[m]) and pillar[n]arene was discussed and summarized in this review. Due to different solubility, diverse-sized cavities, and various driving forces in recognizing guests, the role of CB[m] and pillar[n]arene in such hybrid macrocyclic systems could switch between competitor in capturing specialized guests, and cooperator for building advanced hybridized macrocycles, by controlling their characteristics in host-guest inclusions. Furthermore, both CB[m] and pillar[n]arene were employed for fabricating advanced supramolecular self-assemblies such as mechanically interlocked molecules and supramolecular polymers. In those self-assemblies, CB[m] and pillar[n]arene played significant roles in, e.g., microreactor for catalyzing particular reactions to bridge different small pieces together, molecular "joint" to connect different monomers into larger assemblies, and "stabilizer" in accommodating the guest molecules to adopt a favorite structure geometry ready for assembling.

Bioapplication of cyclodextrin-containing montmorillonite.

Recent progresses in the integration of CDs and montmorillonite, as well as applications of CD-containing montmorillonite hybrid host systems are summarized in this review. Several efficient synthesis strategies, such as ion exchange, metal coordination, supramolecular strategies, polymerizations and organic synthesis methods, have been discussed during the preparation of CDs/montmorillonite hybrid composites. In particular, diverse instrumental techniques were highly recommended for characterizing the as-obtained hybrid systems, including their chemical composition and structures, crystallinity, surface/self-assembled morphologies, as well as other particular physiochemical properties, providing a direct guide for promoting the desired structures and exploring various applications. It should be noted that the introduction of functional groups, as well as the integration of CDs and montmorillonite granted the thus obtained CD-containing montmorillonite hybrid host systems a lot of unique features, providing great opportunities for expanding the practical applications to a series of biological and environmental areas, such as biosensors, sorption and decontamination of bio/environmental hazardous materials, biostudies about aqueous dispersity, stability and biocompatibility, drug loading and target delivery, controlled and sustained drug release, as well as antibacterial.

Cyclodextrins Modified/Coated Metal-Organic Frameworks.

Recent progress about a novel organic-inorganic hybrid materials, namely cyclodextrins (CDs) modified/coated metal-organic frameworks (MOFs) is summarized by using a special categorization method focusing on the interactions between CDs and MOFs moieties, such as ligand-metal cations interactions, supramolecular interactions including host-guest interactions and hydrogen bonding, as well as covalent bonds. This review mainly focuses on the interactions between CDs and MOFs and the strategy of combining them together, diverse external stimuli responsiveness of CDs-modified/coated MOFs, as well as applications of these hybrid materials to drug delivery and release system, catalysis and detection materials. Additionally, due to the importance of investigating advanced chemical architectures and physiochemical properties of CDs-modified/coated MOFs, a separate section is involved in diverse characterization methods and instruments. Furthermore, this minireview also foresees future research directions in this rapidly developing field.

Pillararenes Trimer for Self-Assembly.

Pillararenes trimer with particularly designed structural geometry and excellent capacity of recognizing guest molecules is a very efficient and attractive building block for the fabrication of advanced self-assembled materials. Pillararenes trimers could be prepared via both covalent and noncovalent bonds. The classic organic synthesis reactions such as click reaction, palladium-catalyzed coupling reaction, amidation, esterification, and aminolysis are employed to build covalent bonds and integrate three pieces of pillararenes subunits together into the "star-shaped" trimers and linear foldamers. Alternatively, pillararenes trimers could also be assembled in the form of host-guest inclusions and mechanically interlocked molecules via noncovalent interactions, and during those procedures, pillararenes units contribute the cavity for recognizing guest molecules and act as a "wheel" subunit, respectively. By fully utilizing the driving forces such as host-guest interactions, charge transfer, hydrophobic, hydrogen bonding, and C-H…π and π-π stacking interactions, pillararenes trimers-based supramolecular self-assemblies provide a possibility in the construction of multi-dimensional materials such as vesicular and tubular aggregates, layered networks, as well as frameworks. Interestingly, those assembled materials exhibit interesting external stimuli responsiveness to e.g., variable concentrations, changed pH values, different temperature, as well as the addition/removal of competition guests and ions. Thus, they could further be used for diverse applications such as detection, sorption, and separation of significant multi-analytes including metal cations, anions, and amino acids.

Photoinduced charge transfer within polyaniline-encapsulated quantum dots decorated on graphene.

A new method to enhance the stability of quantum dots (QDs) in aqueous solution by encapsulating them with conducting polymer polyaniline was reported. The polyaniline-encapsulated QDs were then decorated onto graphene through π-π interactions between graphene and conjugated polymer shell of QDs, forming stable polyaniline/QD/graphene hybrid. A testing electronic device was fabricated using the hybrid in order to investigate the photoinduced charge transfer between graphene and encapsulated QDs within the hybrid. The charge transfer mechanism was explored through cyclic voltammetry and spectroscopic studies. The hybrid shows a clear response to the laser irradiation, presenting a great advantage for further applications in optoelectronic devices.

Successively-responsive drug-carrier vesicles assembled by 'supramolecular amphiphiles'.

Novel vesicles assembled by 'supramolecular amphiphiles' based on the inclusion complexes between 1 and ß-CDs (ß-CD and HP-ß-CD) were found to carry drugs and be successively-responsive to external stimuli for the first time. These vesicles were observed by TEM and SEM and confirmed by DLS. The formation patterns of 'supramolecular amphiphiles' characterized by UV and NMR can be controlled by choosing different hosts. Unlike traditional drug delivery and releasing systems, the 'useless' inclusion complexes 1·ß-CDs in thinking formula can assemble into vesicles to carry both cytotoxic 1 and drugs (piroxicam and ampicillin) at one time, confirmed by TEM, UV, and NMR data. Also the vesicles assembled by 1·ß-CDs can be successively-responsive to acidifying and oxidizing, and release drugs and cytotoxic compounds in order.

Redox-responsive vesicles prepared from supramolecular cyclodextrin amphiphiles.

Redox-responsive vesicles self-assembled by supramolecular cyclodextrin amphiphiles, consisting of the guest (N-1-decyl-ferrocenylmethylamine, 1) and the host (2-O-carboxymethyl-beta-cyclodextrin, CM-beta-CD), were prepared. The morphologies and sizes of these novel vesicles in an aqueous solution were observed by transmission electron microscopy (TEM) and were confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS) measurements. The effects of the host-guest ratio, the concentration and the solvent composition of water and methanol on vesicles were investigated in detail. The interactions between the host and the guest, the complex stoichiometry, the stability constant and conformations of 1.CM-beta-CD in aqueous solution were investigated by cyclic voltammetry (CV), UV and nuclear magnetic resonance (NMR) measurements. According to the complex stoichiometry and 'tadpole-like' spatial conformations, the supramolecular cyclodextrin amphiphiles made from 1.CM-beta-CD were proposed to form the membranes of the vesicles. This kind of vesicle system was responsive to an oxidizing agent, which could pave the way to combine supramolecular host-guest chemistry and membrane chemistry for potentially functional applications.

Controllable vesicles based on unconventional cyclodextrin inclusion complexes.

Vesicles were assembled from an unconventional inclusion complex between beta-cyclodextrin (betaCD), and N,N'-bis(ferrocenylmethylene)diaminohexane (1). The vesicles formed in water and in a mixed solvent (water/methanol) were observed by transmission electron microscopy. The peculiar inclusion effects of 1.betaCD were characterized by UV and cyclic voltammetry. The structure of the complex was characterized by (1)H- and 2D ROESY NMR spectroscopies. The size of the vesicles in water, methanol, and in mixtures of water and methanol was investigated by dynamic light scattering. The vesicles disappeared upon addition of an oxidizing agent. The structures of the inclusion complex and the vesicles formed via the complex are discussed according to the experimental data.