Xueshun Jia

Novel neutral guest recognition and interpenetrated complex formation from pillar[5]arenes

Simple alkyl-substituted pillar[5]arenes can form stable interpenetrated complexes with neutral bis(imidazole) guests utilizing multiple C-H···O(N) hydrogen bond and C-H···π interactions.

Synthesis of pillar[5]arene dimers and their cooperative binding toward some neutral guests.

Three pillar[5]arene dimers, bridged by a flexible aliphatic chain (H1) or a relatively rigid phenylene unit (H2 and H3), were synthesized, with the possible synthetic strategies being discussed. The dimers could significantly enhance the binding affinities toward neutral model substrates in comparison with monomeric 1,4-dimethoxypillar[5]arene (H4) through the cooperative binding of two pillar[5]arene moieties. The molecular binding ability and selectivity are discussed from the viewpoints of the size/shape-fit concept and multiple recognition mechanism.

Complexation of 1,4-bis(pyridinium)butanes by negatively charged carboxylatopillar[5]arene.

The binding behavior of substituted 1,4-bis(pyridinium)butane derivatives (X-Py(CH(2))(4)Py-X, X = H, 2-methyl, 3-methyl, 4-methyl, 2,6-dimethyl, 4-pyridyl, and 4-COOEthyl) 1(2+)-7(2+), with negatively charged carboxylatopillar[5]arene (CP5A) has been comprehensively investigated by (1)H NMR and 2D ROESY and UV absorption and fluorescence spectroscopy in aqueous phosphate buffer solution (pH 7.2). The results indicated that the position of the substituents attached on pyridinium ring dramatically affects the association constants and binding modes. 3- and 4-Substituted guests (1(2+), 3(2+), 4(2+), 6(2+), 7(2+)) form [2]pseudorotaxane geometries with CP5A host, giving very large association constants (>10(5) M(-1)), while 2,6-dimethyl-substituted 5(2+) forms external complex with relatively small K(a) values [(2.4 ± 0.3) × 10(3) M(-1)] because the 2,6-dimethylpyridinium unit is too bulky to thread the host cavity. Both of the binding geometries mentioned above are observed for 2(2+), having one methyl group in the 2-position of pyridinium. Typically, the association constant of [2]pseudorotaxane 1(2+)⊂CP5A exceeds 10(6) M(-1) in water, which is significantly higher than those of previously reported analogues in organic solvents. The remarkably improved complexation of bis(pyridinium) guests by the anionic host was due to electrostatic attraction forces and hydrophobic interactions.

Pillar[5]arene–neutral guest recognition based supramolecular alternating copolymer containing [c2]daisy chain and bis-pillar[5]arene units

A novel supramolecular alternating copolymer with [c2]daisy-chain dimer and macrocycle host dimer as repeating units has been fabricated. A key factor for this new assembly strategy is based on a [c2]daisy-chain pseudorotaxane bearing additional unbound recognition sites at both ends, which was successfully achieved from a careful designed heterotritopic (AB2-type) copillar[5]arene. By utilizing the intermolecular host–guest interactions between the double-threaded dimer and a pillar[5]arene dimer, a linear supramolecular polymer was prepared. These results provided not only a convenient approach for the construction of [c2]daisy chain based supramolecular polymers, but also a novel method for building supramolecular alternating copolymers.

Supramolecular Polymers Based on Efficient Pillar[5]arene—Neutral Guest Motifs

Neutral and efficient: A neutral guest with a cyano site and a triazole site, which can be easily prepared and modified, is demonstrated to strongly bind with pillar[5]arene. Based on this new recognition motif, two neutral supramolecular polymers in organic media, which are currently unfeasible by means of host-guest interactions of crown ethers and calixarenes, were fabricated. One is AA/BB-type, and the other is A2/B3-type.

Complexation of neutral 1,4-dihalobutanes with simple pillar[5]arenes that is dominated by dispersion forces

The complexation of neutral 1,4-dihalobutanes with simple pillar[5]arenes was investigated. The results indicate the formation of interpenetrated complexes, where the dispersive interactions dominate the complex stability. Typically, 1,4-diiodobutane displays the strongest binding strength with ethylpillar[5]arene [K(a) = (1.0 ± 0.1) × 10(4) M(-1)], up to 120 fold as compared with 1,4-difluorobutane.

Selective and effective binding of pillar[5,6]arenes toward secondary ammonium salts with a weakly coordinating counteranion.

The selective and effective binding of secondary ammoniums with a weakly coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF) counteranion by per-ethylated pillar[5,6]arenes is reported. The construction of a first pillararene-based self-sorting system consisting of two wheels and two axles is also described.

Synthesis of a cationic water-soluble pillar[6]arene and its effective complexation towards naphthalenesulfonate guests

A novel positively charged pillar[6]arene derivative bearing twelve pyridinium moieties has been synthesized. Its efficient complexation behavior towards two anionic naphthalenesulfonate substrates in aqueous media is described.

CuCl-catalyzed green oxidative alkyne homocoupling without palladium, ligands and bases

CuCl-catalyzed green oxidative homocoupling of terminal alkynes produces symmetrical 1,4-disubstituted 1,3-diynes in good to excellent yields, using air as an environmentally friendly oxidant and the occurrence of water as exclusive byproduct in the whole process, and eliminating the need for ligands, bases, oxidants and expensive palladium catalysts.

A neutral supramolecular hyperbranched polymer fabricated from an AB2 -type copillar[5]arene.

A heterotritopic copillar[5]arene monomer by introducing effective neutral guest moieties (methylene chains end-capped with cyano and triazole groups) to a pillar[5]arene macrocycle is prepared. This well-designed AB2 -type copillar[5]arene contains strong host-guest recognition motifs that are connected with relatively flexible and long linkers, thus efficiently assembles to form supramole-cular hyperbranched polymer (SHP) in chloroform solution, which is characterized by various techniques including (1) H NMR, DOSY, viscosity, DLS, and TEM. Particularly, this supramolecular polymer can be effectively depolymerized by adding a competitive butanedinitrile guest.