pH‐Responsive Host−Guest Complexation between a Water‐soluble Pillar[7]Arene and a 2,7‐Diazapyrenium Salt and Its Application in Controllable Self‐assembly

A novel host−guest recognition motif based on a water‐soluble pillar[7]arene ( WP7 ) and a 2,7‐diazapyrenium salt ( DMDAP ) was prepared. According to the integrated results of ¹H NMR, 2D NOESY, UV–vis spectroscopy and fluorescence titration experiments, we demonstrated that the molecular recognition of WP7 to DMDAP in water not only has high association constant but also has pH‐responsiveness. Subsequently, we took advantage of this molecular recognition motif to fabricate a supra‐amphiphile based on WP7 and an amphiphilic 2,7‐diazapyrenium derivative DAPAC . Its controllable self‐assembly in water was also investigated by means of TEM and DLS techniques.     

A Multiresponsive Amphiphilic Supramolecular Diblock Copolymer Based on Pillar[10]arene/Paraquat Complexation for Rate‐Tunable Controlled Release

Herein, for rate‐tunable controlled release, the authors report a new facile method to prepare multiresponsive amphiphilic supramolecular diblock copolymers via the cooperative complexation between a water‐soluble pillar[10]arene and paraquat‐containing polymers in water. This supramolecular diblock copolymer can self‐assemble into multiresponsive polymeric micelles at room temperature in water. The resultant micelles can be further used in the controlled release of small molecules with tunable release rates depending on the type of single stimulus and the combination of various stimuli.

     

Three‐Component Cucurbit[6]uril Framework with 1:2 Host‐Guest Motif and Dimeric Boric Acid

Three‐component framework of cucurbit[6]uril, 3‐(1‐methylimidazolium‐3‐yl)propane‐1‐sulfonate and boric acid has been constructed. The crystal structure reveals 1:2 host‐guest motif of cucurbit[6]uril and 3‐(1‐methyl‐imidazolium‐3‐yl)propane‐1‐sulfonate, demonstrating both cation binding of imidazolium moiety and anion binding of sulfonate moiety for the first time. Incorporation of dimeric boric acid facilitates the formation of metal‐free three‐dimensional framework.     

Host–Guest Complexation of Perethylated Pillar[5]arene with Alkanes in the Crystal State

Activated perethylated pillar[5]arene crystals show an unexpected alkane‐shape‐ and ‐length‐selective gate‐opening behavior. Activated crystals were obtained upon removing solvents from perethylated pillar[5]arene crystals by heating. The activated crystals could quantitatively take up n‐alkanes with carbon chains containing more than five carbon atoms as a consequence of their gate‐opening pressure. As the chain length of the n‐alkanes increased, the gate pressure decreased. A transformation into a herringbone structure was induced when n‐hexane was used as a guest. By contrast, cyclic and branched alkanes were not taken up and could not induce a crystal transformation because they were too large to fit in the cavities of the pillar[5]arene. Alkane‐shape‐selective molecular recognition of pillar[5]arenes in the solution state was translated into the vapor/crystal state.     

Pillar[10]arene‐Based Size‐Selective Host–Guest Complexation and Its Application in Tuning the LCST Behavior of a Thermoresponsive Polymer

A new molecular recognition motif between a water soluble pillar[10]arene ( WP10 ) and 1,10‐phenanthrolinium guest ( G ) in water is established. Mainly driven by the cooperativity of multiple electrostatic interactions, hydrophobic interactions, and π–π stacking interactions between WP10 and G , this host–guest complex exhibits a high association constant in water, which is about 17 times higher than that between WP10 and paraquat ( PQ ). Furthermore, this size selective host–guest complexation is employed to tune the lower critical solution temperature behavior of a random copolymer with PQ derivative pendants.

     

Tetraphenylethene-Embedded Pillar[5]arene and [15]Paracyclophane: Distorted Cavities and Host–Guest Binding Properties

Two aggregation-induced emission (AIE) macrocycles (DMP[5]-TPE and PCP[5]-TPE) were prepared by embedding Tetraphenylethene (TPE) unit into the skeletons of Dimethoxypillar[5]arene (DMP[5]) and [15]Paracyclophane ([15]PCP) at meso position, respectively. In crystal, the PCP[5]-TPE showed a distorted cavity, and the incubation of hexane inside the DMP[5]-TPE cavity caused a distinct change in the molecular conformation compared to PCP[5]-TPE. There was no complexation between PCP[5]-TPE and 1,4-dicyanobutane (DCB). UV absorption experiments showed the distorted cavity of DMP[5]-TPE hindered association with DCB.     

Stereoselective Synthesis of Pillar[4]arene[1]cis‐diepoxy‐p‐dione and X‐Ray Crystal Structure of Host–Guest System

Herein, we successfully develop a novel route to give rise to polarity for the pillararenes by the introduction of oxygenated functionalities into pillar[5]arene to stereoselectively synthesize the pillar[4]arene[1]cis ‐diepoxy‐p ‐dione. Its host–guest properties with different dinitrile molecules were also investigated and characterized by NMR and X‐ray crystallography.     

A Porphyrin‐Based Discrete Tetragonal Prismatic Cage: Host–Guest Complexation and Its Application in Tuning Liquid‐Crystalline Behavior

The host–guest complexation between a porphyrin‐based 3D tetragonal prism ( H ) and electron‐rich pyrene is investigated. This host–guest molecular recognition is further utilized to suppress the liquid‐crystalline behavior of a nematic molecule ( G ) containing cyanobiphenyl mesogens functionalized with a pyrenyl unit. Furthermore, coronene, with an increased number of π‐electrons, is used as a competitive guest to recover the liquid‐crystalline behavior of G . This supramolecular approach provides a glimpse of the new possibilities to modulate the structures of the mesophases.

     

Host–Guest Chemistry of a Water‐Soluble Pillar[5]arene: Evidence for an Ionic‐Exchange Recognition Process and Different Complexation Modes

The complexation of an anionic guest by a cationic water‐soluble pillararene is reported. Isothermal titration calorimetry (ITC), ¹H NMR, ¹H and ¹⁹F DOSY, and STD NMR experiments were performed to characterize the complex formed under aqueous neutral conditions. The results of ITC and ¹H NMR analyses showed the inclusion of the guest inside the cavity of the pillar[5]arene, with the binding constant and thermodynamic parameters influenced by the counter ion of the macrocycle. NMR diffusion experiments showed that although a fraction of the counter ions are expelled from the host cavity by exchange with the guest, a complex with both counter ions and the guest inside the pillararene is formed. The results also showed that at higher concentrations of guest in solution, in addition to the inclusion of one guest molecule in the cavity, the pillararene can also form an external complex with a second guest molecule.     

Complexation Between (O‐Methyl)6‐2,6‐Helic[6]arene and Tertiary Ammonium Salts: Acid/Base‐ or Chloride‐Ion‐Responsive Host–Guest Systems and Synthesis of [2]Rotaxane

Complexation between (O ‐methyl)₆‐2,6‐helic[6]arene and a series of tertiary ammonium salts was described. It was found that the macrocycle could form stable complexes with the tested aromatic and aliphatic tertiary ammonium salts, which were evidenced by ¹H NMR spectra, ESI mass spectra, and DFT calculations. In particular, the binding and release process of the guests in the complexes could be efficiently controlled by acid/base or chloride ions, which represents the first acid/base‐ and chloride‐ion‐responsive host–guest systems based on macrocyclic arenes and protonated tertiary ammonium salts. Moreover, the first 2,6‐helic[6]arene‐based [2]rotaxane was also synthesized from the condensation between the host–guest complex and isocyanate.     

Photoresponsive Hybrid Raspberry‐Like Colloids Based on Cucurbit[8]uril Host–Guest Interactions

Hybrid raspberry‐like colloids (HRCs) were prepared by employing cucurbit[8]uril (CB[8]) as a supramolecular linker to assemble functional polymeric nanoparticles onto a silica core. The formed HRCs are photoresponsive and can be reversibly disassembled upon light irradiation. This facile supramolecular approach provides a platform for the synthesis of colloids with sophisticated structures and properties.     

Host-Guest Interactions between N,N＇-Bis（ferrocenylmethyl- ene）-Diaminobutane and Benzenetetracarboxylic Dianhydride Bridged Bis（β-cyclodextrin）s

A novel water soluble ditopic guest, the quaternary ammonium salt of N,N＇-bis（ferrocenylmethylene）-diaminobutane （1）, and a known water soluble ditopic host, benzenetetracarboxylic dianhydride bridged bis（β-cyclodextrin）s （2）, have been synthesized and characterized. ^1H NMR spectra and cyclic voltammogram （CV） studies revealed the host-guest interactions between them in aqueous solution. The supramolecular interaction also exists in solid state as confirmed by the studies of the solid samples, which were obtained by frozen-drying the solution sampies, using FTIR spectroscopy and differential scanning calorimetry （DSC） techniques. TEM measurement demonstrated that wire-shaped supramolecular aggregates exist in the aqueous solution of the two compounds. The lengths of the aggregates could reach micrometers.     

A Supramolecular Photosensitizer System Based on Nano-Cu/ZIF-8 Capped with Water-Soluble Pillar[6]arene and Methylene Blue Host–Guest Complexations

Photodynamic therapy (PDT) as a safe, non-invasive modality for cancer therapy, in which the low oxygen and high glutathione in the tumor microenvironment reduces therapeutic efficiency. In order to overcome these problems, we prepared a supramolecular photosensitive system of O₂-Cu/ZIF-8@ZIF-8@WP6–MB (OCZWM), which was loaded with oxygen to increase the oxygen concentration in the tumor microenvironment, and the Cu²⁺ in the system reacted with glutathione (GSH) to reduce the GSH concentration to generate Cu⁺. It is worth noting that the generated Cu⁺ can produce the Fenton reaction, thus realizing the combination therapy of PDT and chemodynamic therapy (CDT) to achieve the purpose of significantly improving the anti-cancer efficiency.     

Ultrastiff Hydrogels Prepared by Schiff's Base Reaction of Bis(p‐Formylphenyl) Sebacate and Pillar[5]arene Appended with Multiple Hydrazides

Herein a facile method is reported to prepare polymer gels based on the formation of acylhydrazone bond under mild conditions. A pillar[5]arene derivative appended with ten hydrazide groups provides multiple sites for the reaction with the aldehyde groups of bis(p‐formylphenyl) sebacate in the presence of a small amount of HCl as the catalyst in dimethyl sulfoxide (DMSO), producing transparent polymer organogels. The mechanical properties of gels can be easily tuned by the molar ratio of the reactant compounds. After solvent exchange from DMSO to water, translucent polymer hydrogels with dramatically enhanced strength and stiffness are obtained. The tensile breaking stress and Young's modulus of hydrogels are 20−60 and 1.2–2.7 MPa, respectively, 100 and 20 times those of the corresponding organogels. These robust hydrogels with ultrahigh stiffness should find applications such as in load‐bearing artificial organs. This work should merit designing functional materials using other macrocycles.