Bio-catalytic nanoparticle shaping for preparing mesoscopic assemblies of semiconductor quantum dots and organic molecules

We report a unique bio-catalytic nanoparticle shaping (BNS) method for preparing a variety of mesoscopic particles by a facile process. For example, the BNS method affords mesoscopic QD assembly dispersions. Large-size sedimentations (>1 μm) of QDs are first formed using oligo-L-lysine linkers. These then undergo controlled enzymatic cleavage of the linkers using trypsin, which surprisingly leads to mesoscopic particles about 84 nm in size with a narrow size distribution. A detailed mechanism of the BNS method is investigated using tetrakis(4-carboxyphenyl)porphyrin (TCPP), instead of QDs, as a probe molecule. Interestingly, the BNS method can also be applied to other combinations of enzymes and enzymatically degradable linkers, such as hyaluronidase with hyaluronan. As a potential application, the mesoscopic particles of QDs and oligo-lysine exhibit their ability to act as a drug delivery carrier originating from the features of both QDs and oligo-lysine. The BNS method demonstrates the universality and versatility of preparing mesoscopic particles and opens new doors for studying QD assemblies and molecular-based mesoscopic particles.

Recent Applications of Pillar[n]arene-Based Host-Guest Recognition in Chemosensing and Imaging

Pillar[n]arene is a novel kind of synthetic supramolecular macrocyclic host characterized by its particular pillar-shaped structure consisting of an electron-rich cavity and two finely adjustable rims. Benefiting from its rigid structure, facile synthesis, ease of functionalization, and outstanding host-guest chemistry, pillar[n]arene shows great potential for diverse applications. Significantly, the host-guest recognition of pillar[n]arene provides a novel approach for chemosensing and imaging. Herein, this Review critically and comprehensively reviews the applications of pillar[n]arene-based host-guest recognition in chemosensing and imaging. The sensing and imaging mechanisms as well as the unique roles and advantages of pillar[n]arene-based host-guest recognition are summarized. In addition, preparations of hybrid materials based on pillar[n]arene and inorganic materials are also introduced comprehensively in the light of chemosensing and imaging. Finally, current challenges and perspectives on pillar[n]arene-based host-guest recognition in chemosensing and imaging are outlined.

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.

A reversible, switchable pH-driven quaternary ammonium pillar[5]arene nanogate for mesoporous silica nanoparticles

Here we describe the assembly and pH-driven operation of two nanocarriers based on non-functionalized (MCM-41) and carboxylate-functionalized (MCM-41-COOH) containers loaded with the anticancer drug doxorubicin (DOX) and capped by quaternary ammonium pillar[5]arene (P[5]A) nanogates. MCM-41 and MCM-41-COOH containers were synthesized and transmission and scanning electron microscopies showed nanoparticles with spherical morphology and dimensions of 85 ± 13 nm. The nanochannels of MCM-41 loaded with DOX were gated through the electrostatic interactions between P[5]A and the silanolate groups formed at the silica-water interface, yielding the MCM-41-DOX-P[5]A nanocarrier. The second nanocarrier was gated through the electrostatic interactions between the carboxylate groups mounted on the surface of MCM-41 and P[5]A, resulting in the MCM-41-COO-DOX-P[5]A nanocarrier. The DOX release profiles from both nanocarriers were investigated by UV-vis spectroscopy at different pH values (2.0, 5.5 and 7.4) and also in the presence of ions, such as citrate^3- (19 mmol L^-1) and Zn²⁺ (1.2 and 50 mmol L^-1) at 37 °C. MCM-41-COO-DOX-P[5]A can be turned on and off eight times through the formation and breaking of electrostatic interactions. In vitro studies show that MCM-41-COO-DOX-P[5]A can penetrate and release DOX in the nucleus of human breast adenocarcinoma MCF-7 cancer cells leading to a pronounced cytotoxic effect. Therefore, the fabricated nanocarrier based on a water-soluble cationic pillar[5]arene nanogate, which is reversibly opened and closed by electrostatic interactions, can be considered as a promising drug transport and delivery technique for future cancer therapy.

N-doped carbon dots covalently functionalized with pillar[5]arenes for Fe3+ sensing

Fluorescent N-doped carbon dots (CN-dots) covalently functionalized with carboxylatopillar[5]arene (CP[5]), namely CCDs, have been prepared the first time. Compared with CN-dots without pillarene units, the newly constructed fluorescent CCDs could recognize Fe³⁺ with high selectivity. Therefore, such CCDs can potentially serve as a promising chemical sensor for Fe³⁺ ions.

Functionalization of inorganic nanomaterials with pillar[n]arenes

Pillar[n]arenes, which consist of hydroquinone units linked by -CH2- bridges at 2,5-positions, are a relatively new class of synthetic macrocycles since 2008. Their facile preparation and flexible modification properties make them ideal stabilizers for inorganic nanomaterials. Furthermore, their symmetrical and columnar architectures with very rigid and π-rich cavities endow them with rich host-guest properties. This Feature Article provides an overview of the functionalization of inorganic nanomaterials with pillar[n]arenes and their applications. These inorganic nanomaterials are classified into three major classes according to different types of compositions: (1) novel metal nanomaterials; (2) hybrid metal nanomaterials; and (3) porous materials. The applications of these nanomaterials such as catalysis, drug delivery, cancer therapy, and sensing have been comprehensively discussed.

Microphase separation of a quadruple hydrogen bonding supramolecular polymer: effect of the steric hindrance of the ureido-pyrimidone on their viscoelasticity

Supramolecular polymers based on 2-ureido-4[1H]-pyrimidone (UPy) units with extremely high dimerization constants and adjustable properties have received significant attention. In this work, we attempt to discuss the relationship between the micro-phase separation and the viscoelastic properties of the supramolecular polymers. For this reason, polymers with different UPy moieties structures and different UPy moieties contents were prepared and studied. It was found that the UPy moiety with little hindrance at the six-position of the pyrimidone could self-assemble into a nano-fiber structure and the degree of the micro-phase separation increased with the content of the UPy moiety. With the enlargement of the steric hindrance of the six-position of the pyrimidone, the nano-fiber structure gradually disappeared, meaning the degree of the micro-phase separation decreased astonishingly. More importantly, with the degree of the micro-phase separation increased, the storage modulus or the elasticity modulus increased exponentially and the T_m and the loss modulus area increased linearly. These results would lead a new way to study and develop novel polymeric materials.

The supramolecular polymers based on 2-ureido-4[1H]-pyrimidone (UPy) with different structure were prepared and the effects of microtopography on the viscoelasticity were investigated.

Supramolecular Nanosystem Based on Pillararene-Capped CuS Nanoparticles for Targeted Chemo-Photothermal Therapy

A smart supramolecular nanosystem integrating targeting, chemotherapy, and photothermal therapy was constructed based on carboxylatopillar[5]arene (CP[5]A)-functionalized CuS nanoparticles (CuS@CP NPs). CuS@CP NPs with good monodispersibility and strong near-infrared absorption were synthesized in aqueous solution through a facile one-pot supramolecular capping method, followed by surface installation of a liver cancer-targeted galactose derivative through host-guest binding interaction. The resulting smart supramolecular nanosystem, namely, CuS@CPG, exhibited excellent photothermal ablation capability to HepG2 cells upon irradiation with laser at 808 nm. Chemotherapeutic drug, doxorubicin hydrochloride (DOX), was further loaded on CuS@CPG via electrostatic interactions between positively charged DOX and negatively charged CP[5]A to give CuS@CPG-DOX with a high drug-loading capacity up to 48.4%. The weakening of DOX-CP[5]A interactions in an acidic environment promoted the pH-responsive drug release from CuS@CPG-DOX. Significantly, this multifunctional supramolecular nanosystem showed a remarkably enhanced therapeutic effect through the combination of targeted chemotherapy and photothermal therapy upon in vitro cell study. Moreover, preliminary in vivo study demonstrated that CuS@CPG and CuS@CPG-DOX had good biocompatibility and excellent tumor inhibition effects upon near-infrared laser irradiation.

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.

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.

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.

Nanoparticles functionalized with supramolecular host-guest systems for nanomedicine and healthcare

Synthetic macrocyclic host compounds can interact with suitable guest molecules via noncovalent interactions to form functional supramolecular systems. With the synergistic integration of the response of molecules and the unique properties at the nanoscale, nanoparticles functionalized with the host-guest supramolecular systems have shown great potentials for a broad range of applications in the fields of nanoscience and nanotechnology. In this review article, we focus on the applications of the nanoparticles functionalized with supramolecular host-guest systems in nanomedicine and healthcare, including therapeutic delivery, imaging, sensing and removal of harmful substances. A large number of examples are included to elucidate the working mechanisms, advantages, limitations and future developments of the nanoparticle-supramolecule systems in these applications.

Ca2+, pH and thermo triple-responsive mechanized Zr-based MOFs for on-command drug release in bone diseases

A new design opens up the possibility of developing smart biomaterials for bone cancer (lowered pH and hypercalcemia) therapy.

Controlled DNA condensation and targeted cellular imaging by ligand exchange in a polysaccharide–quantum dot conjugate

A polysaccharide–quantum dots hybrid nanosystem was constructed, which could be utilized as a supramolecular nanoplatform in nucleic acid binding and selective cellular imaging.

A pillar[5]arene-containing cross-linked polymer: synthesis, characterization and adsorption of dihaloalkanes and n-alkylene dinitriles

A pillar[5]arene-containing cross-linked polymer was synthesized and utilized to adsorb dihaloalkanes and n-alkylene dinitriles.

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.

Supramolecular assembly-induced yellow emission of 9,10-distyrylanthracene bridged bis(pillar[5]arene)s

Newly synthesized DSA-bridged bis(pillar[5]arene)s with AIE properties form linear supramolecular polymers upon binding to a neutral guest linker, exhibiting supramolecular assembly-induced yellow fluorescence emission.

Porphyrinic supramolecular daisy chains incorporating pillar[5]arene–viologen host–guest interactions

Daisy chains and organogels have been prepared by utilising noncovalent interactions between viologens and pillar[5]arenes together with stacked porphyrins.

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[5]arene-based supramolecular organic frameworks for highly selective CO2-capture at ambient conditions

Low-density, solid-state, porous supramolecular organic frameworks are constructed using pillarenes. The frameworks have a honeycomb-like structure, permanent porosity, high thermal stability, and selective and reversible sorption properties toward CO2. The exceptionally selective CO2-sorption properties (375/1, 339/1) of one framework over N2 and CH4 indicate potential applications in CO2-capture for post-combustion power plants and natural gas sweetening.

Switchable host-guest systems on surfaces

CONSPECTUS: For device miniaturization, nanotechnology follows either the "top-down" approach scaling down existing larger-scale devices or the "bottom-up' approach assembling the smallest possible building blocks to functional nanoscale entities. For synthetic nanodevices, self-assembly on surfaces is a superb method to achieve useful functions and enable their interactions with the surrounding world. Consequently, adaptability and responsiveness to external stimuli are other prerequisites for their successful operation. Mechanically interlocked molecules such as rotaxanes and catenanes, and their precursors, that is, molecular switches and supramolecular switches including pseudorotaxanes, are molecular machines or prototypes of machines capable of mechanical motion induced by chemical signals, biological inputs, light or redox processes as the external stimuli. Switching of these functional host-guest systems on surfaces becomes a fundamental requirement for artificial molecular machines to work, mimicking the molecular machines in nature, such as proteins and their assemblies operating at dynamic interfaces such as the surfaces of cell membranes. Current research endeavors in material science and technology are focused on developing either a new class of materials or materials with novel/multiple functionalities by shifting host-guest chemistry from solution phase to surfaces. In this Account, we present our most recent attempts of building monolayers of rotaxanes/pseudorotaxanes on surfaces, providing stimuli-induced macroscopic effects and further understanding on the switchable host-guest systems at interfaces. Biocompatible versions of molecular machines based on synthetic macrocycles, such as cucurbiturils, pillararenes, calixarenes, and cyclodextrins, have been employed to form self-assembled monolayers of gates on the surfaces of mesoporous silica nanoparticles to regulate the controlled release of cargo/drug molecules under a range of external stimuli, such as light, pH variations, competitive binding, and enzyme. Rotaxanes have also been assembled onto the surfaces of gold nanodisks and microcantilevers to realize active molecular plasmonics and synthetic molecular actuators for device fabrication and function. Pillararenes have been successfully used to control and aid the synthesis of gold nanoparticles, semiconducting quantum dots, and magnetic nanoparticles. The resulting organic-inorganic hydrid nanomaterials have been successfully used for controlled self-assembly, herbicide sensing and detection, pesticide removal, and so forth, taking advantage of the selective binding of pillarenes toward target molecules. Cyclodextrins have also been successfully functionalized onto the surface of gold nanoparticles to serve as recycling extractors for C60. Many interesting prototypes of nanodevices based on synthetic macrocycles and their host-guest chemistry have been constructed and served for different potential applications. This Account will be a summary of the efforts made mainly by us, and others, on the host-guest chemistry of synthetic macrocyclic compounds on the surfaces of different solid supports.

A low pH sensor from an esterified pillar[5]arene

An esterified pillar[5]arene, incorporated into a PVC membrane, displays a non-Nernstian response to changes in pH.