Crown ethers as sensory materials in chemical measurements: Interfaces for chemical signal transformation

Transformation of chemical signals into electric signals is one of the essential processes in modern chemical measurements. Compounds designed on host-guest consideration can be used as key material in developing an interface or a transducer for such signal transformation devices. The concept of chemical transducer or interface is presented with examples which use crown ether derivatives as sensory host compounds. Crown ether derivatives equipped with ion-recognition part (crown ether) and signal transformation part (chromophore) are developed for extraction photometry of mono- and di-valent metal ions. Synthetic, chiral molecular bilayer membranes which show peculiar circular dichroism are used as a transducer of ion-recognition signals which are produced by crown ether ionophores doped in the membranes. Crown ether polymer-coated electrodes give an interface which interacts with alkali metal ions and produces a change in its dielectric property, which can then be picked up as an electrical signal by impedance measurement in an alternating current circuit.