Synthetic transporters for oxoanions.

This brief review highlights recent advances in the transport of oxoanions using synthetic carriers, focusing on both progress and ongoing challenges in the field. The difficulty of transporting these oxoanions increases with their hydration enthalpies, with less hydrated nitrate and perchlorate being relatively easy to transport. Recent progress has focused on the transport of moderately hydrated anions such as bicarbonate and carboxylates, where studies are influenced by the free diffusion of neutral species obtained by (de)protonation equilibria. Despite significant innovations in the design of synthetic carriers, the transport of the highly hydrated oxoanions sulfate and phosphate remains a major challenge. Progress on sulfate transport has stalled, while the first example of phosphate transport was reported only last year.