Synthesis, Anion Recognition and Transmembrane Anion-Transport Properties of Squaramides and Their Derivatives

Background: It is known that squaramides are able to form up to four hydrogen bonds, in which the remarkably rigid four-membered ring system serves as an ideal hydrogen bond donor/ acceptor unit. Because of the unique physical and chemical properties of squaramides, design and synthesis of squaramide-based functional receptors have become a hot topic in recent years. Objective: This paper reviews the recent advance in the synthesis of squaramide derivatives and their applications in the field of anion recognition and transmembrane transport. In addition, the prospects of squaramide derivatives are also briefly described. Conclusion: Potent anion recognition and high anionophoric activity may be achieved due to the strong hydrogen bonding interactions of anions with pre-organized donor hosts.