Electrochemistry of calixarene and its analytical applications

The electrochemistry of calixarene as a redox-dependent ionophore and its s tructural dependence are described. One or more redox-centers such as quino ne, ferrocene, cobaltocenium and ruthenium bipyridine moieties have been in troduced into the calixarene frame of the lower or upper rim. Although the electrochemical behavior depends mainly on the inherent redox property of t hese electrochemically active groups, the structural effect and solvent als o play important roles, especially, in the presence of charged guests. When cationic species such as metal ions and ammonium ion are added to a quinon e-functionalized calixarene solution, electron transfer to quinone is enhan ced by the electrostatic effect or the formation of hydrogen bonds. In addi tion to redox-active hosts for voltammetric use, a number of calixarenes wi th novel structures have been developed as ionophores for potentiometric an alysis and found to be successful for some target ions. In terms of Na+, Cs + and Ca2+ selective ionophores for ion-selective electrodes, calixarenes a re found to be excellent compared to crown ether derivatives or cryptands. Calixarenes can be also utilized to construct chemically modified electrode s, which are sensitive to gas species and biologically important compounds. The sophisticated design and synthesis of calixarenes are essential to spe cific potential applications to diverse fields.