Supramolecular Nanoplatform Based on Mesoporous Silica Nanocarriers and Pillararene Nanogates for Fungus Control

Synthetic fungicides have been widely used to protect crops from fungal diseases. However, excessive use of synthetic fungicides leads to the generation of fungicide resistance in fungal pathogens. Recently, smart cargo delivery systems have been introduced for the construction of a pesticide delivery nanoplatform, benefiting from their controlled release performance. Herein, a fungal pathogen microenvironment-responsive supramolecular fungicide nanoplatform has been designed and constructed, using quaternary ammonium salt (Q)-modified mesoporous silica nanoparticles (MSN-Q NPs) as nanocarriers loaded with berberine hydrochloride (BH) and carboxylatopillar[5]arene (CP[5]A) as nanogates to form BH-loaded CP[5]A@MSN-Q NPs for effective inhibition of Botrytis cinerea. CP[5]A as nanogates can endow the fungicide nanoplatform with pH stimuli-responsive release features for the control of fungicide release. The loaded BH, as a natural plant fungicide, provides an ecofriendly alternative to synthetic fungicides for controlling B. cinerea. Interestingly, we use oxalic acid (OA) secreted by B. cinerea as a trigger so that BH can be released from the fungicide nanoplatform on demand under pathogen microenvironments for controlling B. cinerea. The experimental results indicate that the fabricated fungicide nanoplatform could effectively inhibit the mycelial growth and spore germination, providing a new way for the management of B. cinerea in actual application.

Molecular Recognition in Water Using Macrocyclic Synthetic Receptors

Molecular recognition in water using macrocyclic synthetic receptors constitutes a vibrant and timely research area of supramolecular chemistry. Pioneering examples on the topic date back to the 1980s. The investigated model systems and the results derived from them are key for furthering our understanding of the remarkable properties exhibited by proteins: high binding affinity, superior binding selectivity, and extreme catalytic performance. Dissecting the different effects contributing to the proteins' properties is severely limited owing to its complex nature. Molecular recognition in water is also involved in other appreciated areas such as self-assembly, drug discovery, and supramolecular catalysis. The development of all these research areas entails a deep understanding of the molecular recognition events occurring in aqueous media. In this review, we cover the past three decades of molecular recognition studies of neutral and charged, polar and nonpolar organic substrates and ions using selected artificial receptors soluble in water. We briefly discuss the intermolecular forces involved in the reversible binding of the substrates, as well as the hydrophobic and Hofmeister effects operating in aqueous solution. We examine, from an interdisciplinary perspective, the design and development of effective water-soluble synthetic receptors based on cyclic, oligo-cyclic, and concave-shaped architectures. We also include selected examples of self-assembled water-soluble synthetic receptors. The catalytic performance of some of the presented receptors is also described. The latter process also deals with molecular recognition and energetic stabilization, but instead of binding ground-state species, the targets become elusive counterparts: transition states and other high-energy intermediates.

Pillar[n]arene-Based Supramolecular Switches in Solution and on Surfaces

The design and synthesis of new synthetic macrocycles has driven the rapid development of supramolecular chemistry and materials. Pillar[n]arenes, as a new type of macrocyclic compounds, are used as a promising type of building blocks for switchable supramolecular systems due to their versatile functionalization and the ability of binding toward various guest molecules. A number of guests can form inclusion complexes with pillar[n]arenes and their derivatives in solution, which are sensitive to different external triggers. Interestingly, the pursuit of complex stimuli-responsive functional materials and devices has largely motivated the shift of pillar[n]arene-based switches from solution media to surfaces for controllable macroscopic motions on solid platforms. Facilitated by the facile modification of pillar[n]arenes on various solid supports and the dynamic binding of host-guest complexes, numerous functional hybrid materials with adjustable physical or chemical properties and integrated functionalities have been reported in the last decade. Here, the advance of supramolecular switches in solution and on surfaces based on pillar[n]arenes and derivatives with an emphasis on the efforts and the latest contributions from the field is discussed.

Temperature-Dependent and pH-Responsive Pillar[5]arene-Based Complexes and Hydrogen-Bond-Based Supramolecular Pentagonal Boxes in Water

Supramolecular systems in water are of paramount importance and those based on hydrogen bonds are both intriguing and scarce. Here, after studying the peculiar host-guest complexes formed between per-dimethylamino-pillar[5]arene (1) and the bis-sulfonates 2 a-c, we describe the formation of the first hydrogen-bond-based supramolecular pentagonal boxes (SPBs), which are stable in water. These pH-responsive SPBs are constructed from 1 as a body, benzene polycarboxylic acids 3 a,b as lid compounds, and 2 a-c as guests. We demonstrate that encapsulation of 2 a-c in pillar[5]arene 1 and in the highly stable water-soluble SPBs, that is, 1(3 a)₂ and 1(3 b)₂ , is both temperature and pH dependent and, quite interestingly, depends, on the nature of the lid compounds used for capping the boxes even at high pH. We also highlight the difference in the ¹ H NMR characteristics of 2 b and 2 c in the cavity of 1 and the SPBs.

Supramolecular Vesicles Based on Amphiphilic Pillar[n]arenes for Smart Nano-Drug Delivery

Supramolecular vesicles are the most popular smart nano-drug delivery systems (SDDs) because of their unique cavities, which have high loading carrying capacity and controlled-release action in response to specific stimuli. These vesicles are constructed from amphiphilic molecules via host-guest complexation, typically with targeted stimuli-responsive units, which are particularly important in biotechnology and biomedicine applications. Amphiphilic pillar[n]arenes, which are novel and functional macrocyclic host molecules, have been widely used to construct supramolecular vesicles because of their intrinsic rigid and symmetrical structure, electron-rich cavities and excellent properties. In this review, we first explain the synthesis of three types of amphiphilic pillar[n]arenes: neutral, anionic and cationic pillar[n]arenes. Second, we examine supramolecular vesicles composed of amphiphilic pillar[n]arenes recently used for the construction of SDDs. In addition, we describe the prospects for multifunctional amphiphilic pillar[n]arenes, particularly their potential in novel applications.

Host-guest interaction of nitroxide radicals with water-soluble pillar[6]arenes

The host-guest interaction of nitroxide radicals with water-soluble pillar[n]arenes was studied for the first time by electron paramagnetic resonance spectroscopy and NMR spectroscopy. Our results showed that this interaction strongly depended on the 4-substituents of nitroxides and the cavity size of pillar[n]arenes. The host-guest interaction with water-soluble pillar[6]arene WP6 effectively increased the thermodynamic and kinetic stability of nitroxide radical 4-AT toward ascorbic acid, thus expanding its potential biomedical applications.

Host-Guest Chemistry in Supramolecular Theranostics

Macrocyclic hosts, such as cyclodextrins, calixarenes, cucurbiturils, and pillararenes, exhibit unparalleled advantages in disease diagnosis and therapy over the past years by fully taking advantage of their host-guest molecular recognitions. The dynamic nature of the non-covalent interactions and selective host-guest complexation endow the resultant nanomaterials with intriguing properties, holding promising potentials in theranostic fields. Interestingly, the differences in microenvironment between the abnormal and normal cells/tissues can be employed as the stimuli to modulate the host-guest interactions, realizing the purpose of precise diagnosis and specific delivery of drugs to lesion sites. In this review, we summarize the progress of supramolecular theranostics on the basis of host-guest chemistry benefiting from their fantastic topological structures and outstanding supramolecular chemistry. These state-of-the-art examples provide new methodologies to overcome the obstacles faced by the traditional theranostic systems, promoting their clinical translations.

pH-Responsive Pillar[6]arene-based Water-Soluble Supramolecular Hexagonal Boxes

We describe the preparation of the first water-soluble pH-responsive supramolecular hexagonal boxes (SHBs) based on multiple charge-assisted hydrogen bonds between peramino-pillar[6]arenes 2 with the molecular "lid" mellitic acid (1 a). The interaction between 2 and 1 a, as well as the other "lids" pyromellitic and trimesic acids (1 b and 1 c, respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2, that is, 3, with bis-sulfonate 4 a or 4 b, immediately led to guest escape along with the formation of closed 1 a₂ 2 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH-responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications.

A new amphiphilic pillar[5]arene: synthesis and controllable self-assembly in water and application in white-light-emitting systems

A new amphiphilic pillar[5]arene with excellent surface activity was designed and synthesized successfully for the first time. Interestingly, this pillar[5]arene shows controllable self-assembly behaviour in water and can be applied in white-light-emitting systems.

Investigation of the binding modes of a positively charged pillar[5]arene: internal and external guest complexation

The selective binding behavior of a trimethylammonium-derived pillar[5]arene towards different guests in aqueous media and under neutral conditions is reported. Although it is known that this macrocycle has the capability to form complexes with guests, we anticipate that the intrinsic pillar shape of the macrocycle with two positively charged rims should allow a diversity of binding modes. The three guests were selected based on their charge and size. The inclusion binding modes and the affinity of the macrocycle to form host-guest complexes were determined by ITC and NMR techniques. We reveal the ability of a cationic water soluble pillar[5]arene to effectively complex two guest molecules, one in each rim, evidencing the diversity of binding modes. Two different structures for 1 : 1 and three for 1 : 2 complexes are reported showing the pillararene ability for internal/external binding.

Recent advances in pillar[n]arenes: synthesis and applications based on host-guest interactions

Pillar[n]arenes (n = 5-15) are a novel class of macrocyclic molecules with hydroquinone as the repeating unit linked by methylene bridges at para-positions. Introduced by T. Ogoshi for the first time in 2008, pillararenes have attracted increasing interest and have been widely studied during the last eight years, due to their unique structural advantages as host molecules, such as symmetrical rigid architecture, electron-rich cavities and facile functional modification. In this review, we first describe the syntheses of pillar[n]arenes including cyclooligomerization of pillar[n]arenes and modification of pillar[n]arenes after cyclooligomerization, summarising almost twenty different kinds of guest motifs and dividing them into three types: cationic, neutral and anionic motifs. The main section of this review examines the applications of pillar[n]arenes based on the host-guest interactions in different research fields, including biology, materials science and environmental science. Finally, future research directions and potential for novel applications are discussed.

Determination of dopamine hydrochloride by host-guest interaction based on water-soluble pillar[5]arene

The supramolecular interaction between the water-soluble pillar[5]arene (WP[5]) as host and dopamine hydrochloride (DH) as guest was studied by spectrofluorometry. The fluorescence intensity of DH gradually decreased with increasing WP[5] concentration, and the possible interaction mechanism between WP[5] and DH was confirmed by ¹H NMR, 2D NOESY, and molecular modelling. Based on significant DH fluorescence, a highly sensitive and selective method for DH determination was developed for the first time. The fluorescence intensity was measured at 312nm, with excitation at 285nm. The effects of pH, temperature, and reaction time on the fluorescence spectra of the WP[5]-DH complex were investigated. A linear relationship between fluorescence intensity and DH concentration in the range of 0.07-6.2μgmL^-1 was obtained. The corresponding linear regression equation is ΔF=25.76 C+13.56 (where C denotes the concentration in μgmL^-1), with the limit of detection equal to 0.03μgmL^-1 and the correlation coefficient equal to 0.9996. This method can be used for the determination of dopamine in injection and urine samples. In addition, the WP[5]-DH complex has potential applications in fluorescent sensing and pharmacokinetics studies of DH.

A new synthetic method for non-symmetric pillar[5]arenes with simple isolation and improved yield

We developed a new synthetic method for non-symmetric pillar[n]arenes, which has improved yield and simple isolation.

Synthesis of a water-soluble 2,6-helic[6]arene derivative and its strong binding abilities towards quaternary phosphonium salts: an acid/base controlled switchable complexation process

A water-soluble 2,6-helic[6]arene derivative was synthesized, and it showed strong binding ability and acid/base stimulus-responsive complexation towards quaternary phosphonium salts.

Carboxylatopillar[n]arenes: a versatile class of water soluble synthetic receptors

Carboxylatopillar[n]arenes (CP[n]As, n = 5, 6, 7, 9, 10) constitute a family of water soluble synthetic receptors. These receptors are excellent hosts for a wide range of cationic organic molecules and have shown promising application in the fields of stimuli-responsive supramolecular assemblies, targeted drug delivery vehicles and sensors. Analogous metal-coordinated prismatic structures have shown excellent affinities for analytes.

Cationic pillar[6]arene/ATP host-guest recognition: selectivity, inhibition of ATP hydrolysis, and application in multidrug resistance treatment

Due to the differences in the cavity size of the hosts and the charge and length of the guests, a cationic water-soluble pillar[6]arene (WP6) selectively complexes with ATP to form a stable 1 : 1 inclusion complex WP6⊃ATP. This host-guest complexation was utilized to efficiently inhibit the hydrolysis of ATP, arising from the existence of the hydrophobic cavity of WP6. A folic acid functionalized diblock copolymer (FA-PEG-b-PAA) was employed to PEGylate WP6 to endow the polyion complex (PIC) micelles with specific targeting ability, preferentially delivering WP6 to folate receptor over-expressing KB cell. This host-guest complexation was further used to block the efflux pump to transport anticancer drugs out of cells by cutting off the energy source, which enhanced the efficacy of the cancer chemotherapy of DOX·HCl towards drug resistant MCF-7/ADR cell. This supramolecular method provides an extremely distinct strategy to potentially overcome multidrug resistance (MDR).

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.

A diols-responsive triple-component supra-amphiphile constructed from pillar[5]arene-based recognition

A triple-component supra-amphiphile is constructed from dynamic covalent chemistry and pillar[5]arene-based host–guest recognition. The diol-responsive self-assembly of this ternary supra-amphiphile is investigated in aqueous solution.

Selective precipitation of alkyl dihalides using a newly synthesized water-soluble bisphosphorylpillar[5]arene

Bisphosphorylpillar[5]arene H2 binds strongly to alkyldiammonium ions and alkyl dihalides. The halogen bonds between H2 and alkyl dihalides lead to the rapid precipitation of the complex in water.

Aryl-triazole foldamers incorporating a pyridinium motif for halide anion binding in aqueous media

Aryl-triazole foldamers incorporating a pyridinium motif are shown to be strongly halide anion binding in aqueous solvent mixtures.

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.

Synthesis of the first amphiphilic pillar[6]arene and its enzyme-responsive self-assembly in water

The first amphiphilic pillar[6]arene was successfully synthesized. It can complex with adenosine triphosphate to form vesicles in water. Moreover, these vesicles are efficiently responsive to phosphatase.

Supramolecular hydrophobic guest transport system based on pillar[5]arene

A pillar[5]arene-based bioactive guest loading system was developed, which increased the solubility of norharmane in aqueous medium.

Molecular binding behavior of bipyridium derivatives by water-soluble carboxylato-biphen[3]arene

Complexation of paraquat derivatives and bis(N-mono-substituted bipyridine) cations by a negatively charged carboxylato-biphen[3]arene in water is described.

Host–guest complexation of pillar[6]arenes towards neutral nitrile guests

The binding behavior of a series of nitrile derivatives by ethylated pillar[6]arene is described; this work represents the first example of complexation of neutral guests by pillar[6]arenes.

A dual-responsive supra-amphiphile based on a water-soluble pillar[7]arene and a naphthalene diimide-containing guest

A dual-responsive supra-amphiphile was firstly constructed based on a water-soluble pillar[7]arene and a naphthalene diimide-containing guest with a long alkyl chain and a trimethylammonium group. The morphology of the self-assembly formed from this supra-amphiphile could be adjusted by changing the solution pH or adding α-cyclodextrin.

A Cu2+ specific metallohydrogel: preparation, multi-responsiveness and pillar[5]arene-induced morphology transformation

A Cu²⁺ specific metallohydrogel was constructed from a terpyridine-based low molecular weight ligand. The metallohydrogel showed multi-responsiveness and its morphology could be transformed by pillararene-based host–guest interaction.

Sugar-functionalized water-soluble pillar[5]arene and its host–guest interaction with fullerene

The host–guest interaction between a neutral water-soluble pillar[5]arene containing ten sugar moieties and C₆₀ was investigated.

Solid-state assembly of carboxylic acid substituted pillar[5]arene and its host–guest complex with tetracaine

The first examples of carboxylic acid substituted pillar[5]arene structures in the form of its inclusion complexes with ethanol and the anesthetic drug tetracaine are reported.

Binding of carboxylatopillar[5]arene with alkyl and aryl ammonium salts in aqueous medium

Alkyl ammonium salts exhibited strong binding with carboxylatopillar[5]arene in aqueous medium which resulted in the formation of pseudo[2]rotaxane and pseudo[3]rotaxane species.

Pillar[6]arene-valved mesoporous silica nanovehicles for multiresponsive controlled release

The synthesis and host-guest chemistry of pillararene (PA) derivatives are a hot research topic, and the applications of PAs in relevant research fields are essential to explore. Carboxylate-substituted pillar[6]arene (CPA[6])-valved mesoporous silica nanoparticles (MSNs) functionalized with dimethylbenzimidazolium (DMBI) and bipyridinium (BP) stalks were constructed, respectively, for multiresponsive controlled release. CPA[6] encircled the DMBI or BP stalks to develop supramolecular nanovalves for encapsulation of cargo within the MSN pores. The release of cargo was triggered by acidic pH or competitive binding for the dethreading of CPA[6] and the opening of the nanovalves; moreover, coordination chemistry is the first strategy to activate CPA nanovalves by metal chelating with the carboxylate groups of CPA for cargo release. The controlled release of the CPA[6]-valved MSN delivery systems can meet diverse requirements and has promising biological applications in targeted drug therapy.