Highly selective binding of basic amino acids, i.e. lysine, arginine, and histidine, by a negatively charged carboxylatopillar[5]arene (CP5A) is reported. And the complexation behavior of the CP5A host towards lysine metabolites including cadaverine (Cad), acetyl-l-lysine (AcLys) and trimethyl-l-lysine (TMLys) is also described.

Highly effective binding of neutral dinitriles by simple alkyl-substituted pillar[5]arenes and the formation of interpenetrated geometries are reported. The resulting host-guest complexes represent one of the most efficient recognition motifs based on pillararenes.

We describe the one-pot synthesis, unique geometries and intriguing host–guest properties of a new class of supramolecular macrocycles – biphen[n]arenes (n = 3, 4).

A simple bis(imidazolium) dication, 1,4-bis[N-(N'-hydroimidazolium)]butane, can act as a new template for formation of [2]pseudorotaxane with pillar[5]arene, in which the dethreading/rethreading process can be controlled by addition of base and acid. The effect on the association constant of both the solvent and counterion is also described.

The complexation behavior of a series of paraquats (G1.2PF(6)-G5.2PF(6)) and bis(pyridinium) derivatives (G6.2PF(6)-G14.2PF(6)) with pillar[5]arene (P5A) host has been comprehensively investigated by (1)H NMR, ESI mass and UV-vis absorption spectroscopy. It is found that P5A forms 2 : 1 external complexes with N,N'-dialkyl-4,4'-bipyridiniums (G1-G4.2PF(6)); while it forms 1 : 1 pseudorotaxane-type inclusion complexes with methylene [-(CH(2))(n)-] linked bis(pyridinium) derivatives possessing appropriate chain lengths (n = 3-6, G7-G10.2PF(6)). Host-guest association constants in dimethyl sulfoxide (DMSO) were determined, indicating G7-G10.2PF(6) axles form stable [2]pseudorotaxanes with P5A wheel in this very high polarity solvent and 1,4-bis(pyridinium)butane (G8.2PF(6)) was the most suitable axle unit. Meanwhile, the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior. The introduction of pyridyls (G13.2PF(6)) increases not only the K(a) value (4.5 x 10(2) --> 7.4 x 10(2) M(-1)), but also the charge transfer (CT) absorption (colorless --> yellow). Furthermore, the solvent effects have also been investigated, showing they significantly influence the association strength during the course of host-guest complexation. Particularly, the K(a) value of P5A-G13.2PF(6) in 1 : 1 (v:v) acetone-d(6)/DMSO-d(6) is enhanced by a factor of 7.3 compared with pure DMSO-d6 (7.4 x 10(2) --> 5.4 x 10(3) M(-1)).