Lariat ethers: from cation complexation to supramolecular assemblies

Lariat ethers are now well-known as macrocycles having one or more sidearms that contain donor groups and can interact with ring bound cations. Variations in structure and donor group arrangements lead to variation in cation binding strengths and selectivities. Such systems exhibit enhanced cation complexation and generally high complexation dynamics. The binding dynamics and strength may readily be altered by reductive switching. This process has been accomplished using both reducing metals and electrochemical techniques. Cyclic voltammetry and EPR techniques confirm the redox switching and the formation of intramolecular ion pairs. Redox-switched lariats have been utilized in cation transport through bulk liquid membranes. When the sidearms are highly lipophilic systems such as cholesteryl, they readily form completely synthetic lipid bilayers or micelles and can assemble into vesicle systems of considerable size and stability.