Pillar[5]arenes are [1(5)]paracyclophane derivatives consisting of 1,4-disubstituted hydroquinones linked by methylene bridges in the 2,5-positions. The first report of these novel macrocycles was in 2008, when 1,4-dimethoxypillar[5]arene was prepared in 22% yield, and subsequent improvements in synthetic methods have allowed the number of derivatives to expand significantly. In addition to D(5) symmetric pillar[5]arenes, asymmetric pillar[5]arenes with two different substituents in the 1- and 4-positions and copillar[5]arenes consisting of two different repeat units in a 4 : 1 ratio have been synthesised. Crystallographic, computational and spectroscopic studies are starting to shed light on the compounds' unusual inclusion phenomena, from gelation and transportation of water through nanotubes to the formation of chromogenic rotaxanes. Applications as molecular sensors are starting to appear with a focus on guest detection by fluorescence quenching. This tutorial review will provide a summary of research into the pillar[5]arenes since their recent discovery.

A series of podands based on two or three hydrogen bonding ''arms'' situated in mutually ortho, meta, or para relationships about an aryl core have been prepared, and their affinities for simple inorganic anions were measured. Of the two-arm hosts the meta compound and to a lesser extent the ortho host exhibit a cooperative anion binding effect. The two arms function essentially independently in the para derivative. The mutually meta three-arm host shows dramatically enhanced cooperative binding. Conformational changes within the meta two-arm host result in significantly enhanced electrochemical anion sensing compared with the more conformationally rigid three-arm host.

Macrocyclic chemistry has provided chemists with a wealth of molecular 'hosts'. Ever since resurgence in the field during the 1970s and 1980s these hosts' similarities to natural structures, such the active sites of enzymes, have been noted. Latterly there has been great interest in the recently reported pillar[n]arenes. As if to underline the importance of these compounds, exciting applications are starting to emerge, from electrochemical sensors to antimicrobial agents. Novel uses appear destined to have an impact on clinical conditions from Alzheimer's disease to cancer treatment. In order to demonstrate the impact of pillar[n]arenes across the chemistry-biology interface this review will cover the current state of the art from biomimicry and analyte-specific detection to emerging clinical applications. Examples include pillar[n]arene-based ion channels, enzyme-responsive compounds, imaging agents, biofilm inhibiting derivatives, drug complexing and drug releasing systems.

A series of podands based on three hydrogen bonding 'arms' have been prepared and their affinities for simple inorganic anions measured.

SummaryHexahomotrioxacalix[3]arenes, commonly called oxacalix[3]arenes, were first reported in 1962. Since then, their chemistry has been expanded to include numerous derivatives and complexes. This review describes the syntheses of the parent compounds, their derivatives, and their complexation behaviour towards cations. Extraction data are presented, as are crystal structures of the macrocycles and their complexes with guest species. Applications in fields as diverse as ion selective electrode modifiers, fluorescence sensors, fullerene separations and biomimetic chemistry are described.