Photo-Controlled Reversible Uptake and Release of a Modified Sulfamethoxazole Antibiotic Drug from a Pillar[5]arene Cross-Linked Gelatin Hydrogel

Pillararene cross-linked gelatin hydrogels were designed and synthesized to control the uptake and release of antibiotics using light. A suite of characterization techniques ranging from spectroscopy (FT-IR, 1H and 13C NMR, and MAS NMR), X-ray crystallographic analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) was employed to investigate the physicochemical properties of hydrogels. The azobenzene-modified sulfamethoxazole (Azo-SMX) antibiotic was noncovalently incorporated into the hydrogel via supramolecular host-guest interactions to afford the A-hydrogel. While in its ground state, the Azo-SMX guest has a trans configuration structure and forms a thermodynamically stable inclusion complex with the pillar[5]arene motif in the hydrogel matrix. When the A-hydrogel was exposed to 365 nm UV light, Azo-SMX underwent a photoisomerization reaction. This changed the structure of Azo-SMX from trans to cis, and the material was released into the environment. The Azo-SMX released from the hydrogel was effective against both Gram-positive and Gram-negative bacteria. Importantly, the A-hydrogel exhibited a striking difference in antibacterial activity when applied to bacterial colonies in the presence and absence of UV light, highlighting the switchable antibacterial activity of A-hydrogel aided by light. In addition, all hydrogels containing pillar[5]arenes have demonstrated biocompatibility and effectiveness as scaffolds for biological and medical purposes.

Copillar[5]arene Chemistry: Synthesis and Applications

Research on pillar[n]arenes has witnessed a very quick expansion. This emerging class of functionalized macrocyclic oligoarenes not only offers host–guest properties due to the presence of the central cavity, but also presents a wide variety of covalent functionalization possibilities. This short review focuses on copillararenes, a subfamily of pillar[n]arenes. In copillararenes, at least one of the hydroquinone units bears different functional groups compared to the others. After having defined the particular features of copillararenes, this short review compares the different synthetic strategies allowing their construction. Some key applications and future perspectives are also described.

1 Introduction

2 General Features of Pillar[5]arenes

3 Synthesis of Functionalized Copillar[4+1]arenes

4 Concluding Remarks

Grafting Dendrons onto Pillar[5]Arene Scaffolds

With their ten peripheral substituents, pillar[5]arenes are attractive compact scaffolds for the construction of nanomaterials with a controlled number of functional groups distributed around the macrocyclic core. This review paper is focused on the functionalization of pillar[5]arene derivatives with small dendrons to generate dendrimer-like nanomaterials and bioactive compounds. Examples include non-viral gene vectors, bioactive glycoclusters, and liquid-crystalline materials.

The synthesis and applications of porphyrin-containing pillararenes

Recent progress regarding the combination of porphyrins and pillararenes into hybrid compounds and supramolecular systems is summarized in this review.

Insights into the synthesis of pillar[5]arene and its conversion into pillar[6]arene

The synthesis of pillar[5]arenes from p-dialkoxybenzene and formaldehyde in the presence of iron(iii) chloride and tetramethylammonium chloride under mild reaction conditions was investigated in detail.

Stimuli-responsive supramolecular nano-systems based on pillar[n]arenes and their related applications

Stimuli-responsive supramolecular nano-systems (SRNS) have been a trending interdisciplinary research area due to the responsiveness upon appropriate stimuli, which makes SRNS very attractive in multiple fields where precise control is vital.

Restricting shuttling in bis(imidazolium)…pillar[5]arene rotaxanes using metal coordination

Metal coordination to a series of bis (imidazolium)…pillar[5]arene [2]rotaxanes through the formation of metal-carbene bonds facilitates a new strategy to restrict the shuttling motion in [2]rotaxanes. Whereas the pillar[5]arene macrocycle rapidly shuttles along the full length of the bis (imidazolium) rod for the parent [2]rotaxane, Ag(i) coordination to the imidazolium groups through the formation of N-heterocyclic carbenes leads to restricted motion, effectively confining the shuttling motion of the [2]rotaxane. The Ag(i) coordinated [2]rotaxanes can be reacted further, either removing the Ag-carbene species to recreate the parent [2]rotaxane, or reaction with more bulky Pd(ii) species to further restrict the shuttling motion through steric inhibition.

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.

Synthesis of diamido-bridged bis-pillar[5]arenes and tris-pillar[5]arenes for construction of unique [1]rotaxanes and bis-[1]rotaxanes

The pillar[5]arene mono- and di(oxyalkoxy)benzoic acids were successfully prepared in high yields by sequential alkylation of ω-bromoalkoxy-substituted pillar[5]arenes with methyl or ethyl p-hydroxybenzoate followed by a hydrolytic reaction under basic conditions. Under catalysis of HOBt/EDCl, the amidation reaction of pillar[5]arene mono(oxybutoxy)benzoic acid with monoamido-functionalized pillar[5]arenes afforded diamido-bridged bis-pillar[5]arenes. 1H NMR and 2D NOESY spectra clearly indicated that [1]rotaxanes were formed by insertion of longer diaminoalkylene unit into the cavity of one pillar[5]arene with another pillar[5]arene acting as a stopper. The similar catalysed amidation reaction of pillar[5]arene di(oxybutoxy)benzoic acid with monoamido-functionalized pillar[5]arenes resulted in the diamido-bridged tris-pillar[5]arenes, which successfully form the unique bis-[1]rotaxanes bearing longer than diaminopropylene diamido bridges.

Supramolecular chemistry of pillar[n]arenes functionalised by a copper(i)-catalysed alkyne-azide cycloaddition "click" reaction

Since we discovered pillar[n]arenes in 2008, many chemists have developed a strong interest in pillar[n]arene chemistry because of the many advantages associated with these materials, including their facile and high yielding synthesis, versatile functionality, planar chirality and unique host-guest properties. In this feature article, we discuss recent advances in the field of supramolecular chemistry based on the use of pillar[n]arenes as substrates for copper(i)-catalysed alkyne-azide cycloaddition (CuAAC) "click" chemistry. The CuAAC reaction provides facile access to 1,4-disubstituted triazoles by a reaction between alkyne and azido substrates in the presence of a Cu(i) catalyst. Pillar[n]arenes bearing alkyne or azido groups can therefore be used as substrates for this reaction. Herein, we discuss not only the synthesis of pillar[n]arenes bearing alkyne or azido groups but also the application of these functionalised systems to the CuAAC reaction to construct supramolecular assemblies. We also discuss the rational molecular design and synthesis of guest compounds using the CuAAC reaction because linear alkanes sandwiched between 1,2,3-triazole moieties are good guests for cyclic pentamer pillar[5]arenes.

Bis- and mono(m-benzoic acid)-functionalized pillar[5]arenes

Installation of m-benzoic acid functionalities on pillar[5]arene rims resulted in bis- and mono(m-benzoic acid)-functionalized pillar[5]arenes 1 and 2. Bis(m-benzoic acid)-functionalized pillar[5]arene 1 was able to self-assemble to form one-dimensional channels with DMF molecules residing in pillar[5]arene cavities. Esterification of two carboxylic acids in 1 with decane-1,10-diol did not afford a [1]catenane, but a bicyclic compound. Although 1-decanol esterification of mono(m-benzoic acid)-functionalized pillar[5]arene 2 did not form a self-included [1]pseudorotaxane-like structure, a mono(decyl m-benzoate)-functionalized pillar[5]arene bearing an ethyl acetate chain was found to form a self-included complex with the ethyl acetate moiety residing inside the pillar[5]arene cavity.

Light-driven nanofiber and nanoring morphological transformations in organogels based on an azobenzene-bridged biscalix[4]arene

The morphologies of an azobenzene-bridged biscalix[4]arene organogel (1) in different organic solvents can be photo-reversibly switched between nanofibers and nanorings as well as between closed and open-form vesicles.

Surveying macrocyclic chemistry: from flexible crown ethers to rigid cyclophanes

This review features the progress made in the development of macrocycles since Pedersen's ground-breaking discovery of the crown ethers in 1967.

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as "pillar[n]arenes". Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host-guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host-guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in the field and inspire discoveries concerning pillar[n]arene chemistry.

Redox-responsive supramolecular amphiphiles based on a pillar[5]arene for enhanced photodynamic therapy

Supramolecular amphiphiles based on a pillar[5]arene with enhanced photodynamic therapy have been fabricated.

Pillar[5,6]arene-functionalized silicon dioxide: synthesis, characterization, and adsorption of herbicide

A layer of synthetic supramolecular macrocycles, that is, perhydroxyl-pillar[5]arene and perhydroxyl-pillar[6]arene, has been covalently attached to hydrophilic silica supports through Si-O-Si linkages with a coverage of up to 250 μmol pillar[5,6]arenes/g to form novel absorbent hybrid materials. Their adsorption toward a typical herbicide, namely, paraquat, from its aqueous solution has been investigated. Kinetic studies disclosed that paraquat adsorption fits a first-order kinetic model. Equilibrium adsorption data could be explained very well by the Langmuir equation. The pillar[6]arene-modified materials showed more obvious adsorption as compared with pillar[5]arene-modified ones and the saturation adsorption quantity reached about 0.20 mmol of paraquat per gram of materials. The entire process of adsorption was endothermic, and significantly an elevated temperature led to an increase in the adsorption quantity. This new type of pillarene-based adsorbent materials can be considered as a potential adsorbent for harmful substances removal from wastewaters.

A [2]rota[2]catenane, constructed from a pillar[5]arene-crown ether fused double-cavity macrocycle: synthesis and structural characterization

A [2]rota[2]catenane, based on a pillar[5]arene-crown ether fused bicycle, was constructed and its structure was determined crystallographically.

Magnetic-responsive supramolecular vesicles from self-organization of amphiphilic pillar[5]arene and application in controlled release

A new amphiphilic pillar[5]arene (AP5-glycol) with five oligomeric glycol groups and five alkyl chains was prepared. AP5-glycol spontaneously formed bilayer vesicles in water, and these vesicles were still stable after several weeks. Additionally, when they were exposed to external physical stimuli, these vesicles also showed reversible thermal and dynamic properties. Interestingly, oleic-acid-stabilized magnetic iron oxide nanoparticles could be incorporated into the bilayer of the AP5-glycol vesicles to form hybrid magnetic-responsive supramolecular vesicles.

Functionalizing pillar[n]arenes

Macrocyclic chemistry has relied on the dominance of some key cavitands, including cyclodextrins, calixarenes, cyclophanes, and cucurbiturils, to advance the field of host-guest science. Very few of the many other cavitands introduced by chemists during these past few decades have been developed to near the extent of these four key players. A relatively new family of macrocycles that are becoming increasingly dominant in the field of macrocyclic chemistry are the pillar[n]arenes composed of n hydroquinone rings connected in their 2- and 5-positions by methylene bridges. This substitution pattern creates a cylindrical or pillar-like structure that has identical upper and lower rims. The preparation of pillar[n]arenes is facile, with pillar[5]- through pillar[7]arene being readily accessible and the larger macrocycles (n = 8-14) being accessible in diminishing yields. The rigid pillar[n]arene cavities are highly π-electron-rich on account of the n activated aromatic faces pointing toward their centers, allowing the cavities to interact strongly with a range of π-electron-deficient guests including pyridiniums, alkylammoniums, and imidazoliums. The substitution pattern of pillar[n]arenes bestows chirality onto the macrocycle in the form of n chiral planes. The absolute configuration of the chiral planes in pillar[n]arenes can be either fixed or rapidly undergoing inversion. The future of pillar[n]arenes is going to be dependent on their ability to fulfill specific applications. Chemical modification of the parent pillar[n]arenes lets us create functionalized hosts with anticipated chemical or physical properties. The featured potential applications of pillar[n]arenes to date are far reaching and include novel hosts with relevance to nanotechnology, materials science, and medicine. Pillar[n]arenes have an overwhelming advantage over other hosts since the number of ways available to incorporate handles into their structures are diverse and easy to implement. In this Account, we describe the routes to chemically modified pillar[n]arenes by discussing the chemistry of their functionalization: monofunctionalization, difunctionalization, rim differentiation, perfunctionalization, and phenylene substitution. We assess the synthetic complications of employing these functionalization procedures and survey the potential applications and novel properties that arise with these functionalized pillar[n]arenes. We also highlight the challenges and the synthetic approaches that have yet to be fully explored for the selective chemical modification of these hosts. Finally, we examine a related class of macrocycles and consider their future applications. We trust that this Account will stimulate the development of new methods for functionalizing these novel hosts to realize pillar[n]arene-containing compounds capable of finding applications.

A pillar[5]arene and crown ether fused bicyclic host: synthesis, guest discrimination and simultaneous binding of two guests with different shapes, sizes and electronic constitutions

A pillar[5]arene- and crown ether-based bicyclic host molecule binds two guest species selectively by its two independent cyclic host subunits.

Photoresponsive supramolecular self-assembly of monofunctionalized pillar[5]arene based on stiff stilbene

We reported a photoresponsive monofunctionalized pillar[5]arene based on stiff stilbene.Z-1tends to form self-complexing [1]pseudorotaxanes and [c2] daisy chains, whereasE-1forms supramolecular polymers.