Current Organic Chemistry - Volume 19, Issue 23, 2015

This review describes two families of ion transporters: the lariat ethers and the hydraphiles. The lariat ethers transport ions as carriers and hydraphiles of appropriate length form pores in bilayer membranes. Hydraphiles insert into liposomes and into the bilayers of bacteria and yeast causing toxicity at micromolar concentrations. Toxicity corresponds to channel length and ion transport efficacy. Toxicity of lariat ethers to bacteria has also been found. At lower concentrations, the presence of hydraphiles enhances antibiotic potency of erythromycin, kanamycin, rifampicin, and tetracycline against both Gram negative and Gram positive bacteria. When hydraphiles are added to the growth medium, the model plant Arabidopsis thaliana undergoes significant alterations in growth and root architecture.

Due to their easy functionalization and their unique conformational and recognition properties, calixarenes are attracting molecular platforms for the elaboration of separation systems. Thus, in the last decades, these macrocyclic compounds have been subject to extensive research in analytical chemistry. This review is focused on the use of calixarenes as selectors in the chromatographic separation field. The structures of calixarene derivatives and their applications as stationary phases for gas chromatography as well as high-performance liquid chromatography are described.

The biological activities of the calix[n]arenes have been extensively reported on, with regard to various forms of life ranging from self-replicating systems, such as, viruses, through bacteria, fungi and mammalian cells to human beings. This article reviews more than one hundred different calix[n]arenes classified according to their biological effects directly observed on living species. These macrocyclic molecules have been reported as detoxifying agents, as having antibacterial, antiviral, anticoagulant, anticancer, antifungal activities, as membrane protein modulators / extracters, drug transporters and fluorescent probes. Special in vivo sections, have been inserted when possible for each biological effect showing the impact of the calix[n]arenes on whole living system such as animals or humans.

Research on supramolecular polymers is in full bloom: the seed was planted 25 years ago, with the first report on the hydrogen bond-directed self-assembly of liquid crystalline polymers, and it has now branched out in several directions, each characterized by different recognition motifs and non-covalent interactions underlying the most diverse families of supramolecular polymers devised so far. Among these, calixarene-based polymers have been intensively studied, even though calix[5]arenes have enjoyed much less attention than the smaller homologous calix[4]arenes. Three strategies have emerged so far for the construction of AABB- and/or ABtype polymers, namely, C60 encapsulation, primary alkylammonium complexation, and organic cations recognition. This review article aims at organizing the results obtained (and knowledge gained) to date on the self-assembly of calix[5]arene-derived building blocks.

Molecular capsules are containers endowed with isolated nanometer-sized cavities. In particular, supramolecular capsules -generated by exploiting hydrogen bonds, metal-coordination bonds and/or hydrophobic effects- represent an intriguing version of these fascinating molecules, and an impressive challenge for synthetic chemists. Resorcin[4]arene-based cavitands and conformationally preorganized calixarenes are two classes of receptors largely used as building blocks for the construction of these assemblies. This review focuses on the capsular self-assembly of suitably functionalized building blocks, analyzing from time to time the main driving force(s) involved for their formation.

Besides cyclodextrins and crown ethers, calixarenes are the most commonly studied macrocyclic compounds. Although their chemistry is well documented, sub-categorizing of azacrown conjugates of calixarenes still stands as a mystery. This review, mustered with 104 references, offers the readers of various disciplines an overview of the up to date knowledge of calixazacrowns apropos to their recognition behavior in solution and at the surface, and assesses the state of the art achievements in their self-assembly and application in nanomaterial chemistry, sensing, light-emitting, electronics and biology. The progress of calixazacrowns in the nanoworld is anticipated to emerge as a rich research area in near future.