Anion recognition in water

Anion recognition by synthetic receptors in water is not a new field, indeed the first receptors that were shown to interact with anionic species exhibited high affinity in aqueous solutions. Anion recognition in aqueous solution was, however, for a long time the domain of receptors containing multiple positive charges and/or metal ions while interactions of neutral receptors with anions were believed to be too weak to be efficient in water. Independent work in several groups has recently shown that this assumption is not necessarily correct. As a consequence, a much wider range of receptors is now available with which anion recognition in competitive aqueous media can be achieved. This tutorial review presents selected examples of synthetic anion receptors active in aqueous solutions and guidelines to achieve anion recognition in water.