ABSTRACT
This chapter reviews the dynamic control of cation binding using certain stimulus-responsive crown ethers. Redox-switched crown ethers have both a redox-active group and a crown ether ring within a molecule. This class of crown ethers has two opposing functional facets: The ion-binding ability of the crown ether site can be controlled by the redox state of the prosthetic redox-active site; whereas the redox potential of the redox-active site is affected by the prosthetic metal binding site. The concept of the redox switch can be extended to the electrochemical switch. Cations are known to be transported through membranes by synthetic macrocyclic polyethers as well as by antibiotics. Stimuli from the outside world to control cation binding may be substituted with ions, organic molecules. This responsiveness is similar to allosteric enzymes; that is, binding of effectors to the allosteric site induces the changes in enzyme conformation that crucially govern the enzyme activities.
