Synthetic anion receptors based on sigma-hole interactions are increasingly used to transport anions across membranes. This article discusses the progress in the field and prospects for biological applications.

A calix[6]arene with three preorganised halogen bond donating groups gives >100-fold selectivity for Cl ⁻ uniport over HCl symport, in contrast to analogous compounds with strong hydrogen bond donating groups.

Azines provide an attractive balance in dynamic covalent chemistry, with rapid exchange in acidic conditions and good stability in the presence of water.