Chengyou Han

Pillar[6]arene-Based Photoresponsive Host–Guest Complexation

The trans form of an azobenzene-containing guest can complex with a pillar[6]arene, while it cannot complex with pillar[5]arenes due to the different cavity sizes of the pillar[6]arene and the pillar[5]arenes. The spontaneous aggregation of its host-guest complex with the pillar[6]arene can be reversibly photocontrolled by irradiation with UV and visible light, leading to a switch between irregular aggregates and vesicle-like aggregates. This new pillar[6]arene-based photoresponsive host-guest recognition motif can work in organic solvents and is a good supplement to the existing widely used cyclodextrin/azobenzene recognition motif.

Pillar[6]arene/Paraquat Molecular Recognition in Water: High Binding Strength, pH-Responsiveness, and Application in Controllable Self-Assembly, Controlled Release, and Treatment of Paraquat Poisoning

The complexation between a water-soluble pillar[6]arene (WP6) and paraquat (G1) in water was investigated. They could form a stable 1:1 [2]pseudorotaxane with an extremely high association constant of (1.02 ± 0.10) × 10(8) M(-1) mainly driven by electrostatic interactions, hydrophobic interactions, and π-π stacking interactions. This molecular recognition has not only high binding strength but also pH-responsiveness. The threading and dethreading processes of this [2]pseudorotaxane could be reversibly controlled by changing the solution pH. This novel recognition motif was further used to control the aggregation of a complex between WP6 and an amphiphilic paraquat derivative (G2) in water. The reversible transformations between micelles based on G2 and vesicles based on WP6⊃G2 were realized by adjusting the solution pH due to the pH-responsiveness of WP6. The controlled release of water-soluble dye molecules from the vesicles could be achieved by the collapse of the vesicles into the micelles upon changing the solution pH to acidity. Additionally, the high binding affinity between WP6 and paraquat could be utilized to efficiently reduce the toxicity of paraquat. After the formation of a stable host-guest complex between WP6 and paraquat, less opportunity was available for paraquat to interact with the reducing agents in the cell, which made the generation of its radical cation more difficult, resulting in the efficient reduction of paraquat toxicity.

A Water-Soluble Pillar[6]arene: Synthesis, Host–Guest Chemistry, and Its Application in Dispersion of Multiwalled Carbon Nanotubes in Water

The first water-soluble pillar[6]arene was synthesized. Its water solubility can be reversibly controlled by changing the pH. This solubility control was used in reversible transformations between nanotubes and vesicles and dispersion of multiwalled carbon nanotubes in water.

Syntheses of copillar[5]arenes by co-oligomerization of different monomers.

Three copillar[5]arenes, pillar[5]arenes containing different repeating units, were successfully prepared by co-oligomerization of different monomers. It was demonstrated that the yields of pillararenes could be improved by using hydroquinone diethers with appropriate aliphatic chain lengths. Pseudorotaxane-type threaded structures were obtained in the solid state by the inclusion of an n-hexane molecule into the cavity of either a homopillar[5]arene, a pillar[5]arene containing only one repeating unit, or a copillar[5]arene.

A Sugar-Functionalized Amphiphilic Pillar[5]arene: Synthesis, Self-Assembly in Water, and Application in Bacterial Cell Agglutination

A novel sugar-functionalized amphiphilic pillar[5]arene containing galactose groups as the hydrophlic part and alkyl chains as the hydrophobic part was designed and synthesized. It self-assembles in water to produce nanotubes as confirmed by TEM, SEM, and fluorescence microscopy. These nanotubes, showing low toxicity to both cancer and normal cells, can be utilized as excellent cell glues to agglutinate E. coli. The existence of galactoses on these nanotubes provides multivalent ligands that have high affinity for carbohydrate receptors on E. coli.

DIBPillar[n]arenes (n = 5, 6): Syntheses, X-ray Crystal Structures, and Complexation with n-Octyltriethyl Ammonium Hexafluorophosphate

DIBPillar[n]arenes (n = 5, 6) were synthesized. They showed different host-guest properties with n-octyltriethyl ammonium hexafluorophosphate G due to their different cavity sizes. DIBpillar[5]arene showed no complexation with G, while DIBpillar[6]arene formed a 1:1 complex with G with an association constant of 334 (±24) M(-1) in chloroform. In this letter, the first pillar[6]arene crystal structure and the first investigation of the host-guest chemistry of pillar[6]arenes are reported.

A solvent-driven molecular spring

A solvent-driven doubly threaded rotaxane dimer based on an amino-modified copillar[5]arene was prepared using bis(trifluoromethyl)phenyl isocyanate as stoppers. By comparison of proton NMR spectra of the rotaxane dimer and the control compound, the inclusion-induced shielding effects of the decyl protons of the dumbbell compound were estimated. From the crystal structures of previously reported analogous pillar[5]arene/alkane pseudorotaxanes, we know that four methylenes can be totally encapsulated in the pillar[5]arene cavity. When a pillar[5]arene is swaying along a guest with a long linear alkyl chain (more than four methylenes), its cavity statistically locates on the four methylenes whose protons showed relatively larger upfield shifts. Based on this, the length of the rotaxane dimer can be estimated. In CDCl3, it was in a contracted state with a length of 31 A. In DMSO-d6, it was in a extended state with a length of 37 A. Moreover, as the polarity of the solvent is changing, the length of the rotaxane dimer can change continuously as the contraction/stretching systems work in living organisms. Therefore, we can control the length of this molecular spring as needed.

A non-symmetric pillar[5]arene-based selective anion receptor for fluoride

A novel non-symmetric pillar[5]arene-based anion receptor containing multiple triazole anion-binding sites was designed and synthesized. It has high affinity and selectivity for the fluoride anion.

Formation of a Cyclic Dimer Containing Two Mirror Image Monomers in the Solid State Controlled by van der Waals Forces

Two new copillar[5]arenes were prepared. They are arranged in two completely different motifs, a cyclic dimer containing two monomers with two different conformations that are mirror images of each other and linear supramolecular polymers in the solid state. Not only has it been shown that to form this kind of dimer is a unique feature associated with pillar[5]arene macrocycles but also it was demonstrated that weak van der Waals forces can be used to control the self-organization of monomers during their supramolecular polymerization process.

Complexation between Pillar[5]arenes and a Secondary Ammonium Salt

We demonstrate that n-octylethyl ammonium hexafluorophosphate (G) can thread through the cavity of 1,4-dimethoxypillar[5]arene to form a [2]pseudorotaxane with a binding constant of 1.09 (±0.31) × 10(3) M(-1) in chloroform. The formation of this threaded structure has been confirmed by proton NMR spectroscopy, electrospray ionization mass spectrometry, and X-ray single crystal analysis. The complexation between 1,4-dimethoxypillar[5]arene and G in chloroform can be switched off by adding Cl(-). For comparison, the complexation between 1,4-bis(n-propoxy)pillar[5]arene and G has also been investigated.