Design and synthesis of highly ion-selective ionophores for chemical ion-sensors

For developing high performance chemical ion sensors, the optimal design of ionophores, which are used as the ion sensing component for the sensor, is one of the most important areas of investigation. Here I report the general concept and knowledge of ionophore chemistry through a discussion of the design and synthesis of ionophores for alkali metal ions, alkaline earth metal ions and the ammonium ion. There are several important factors when designing ionophores that can be divided into two groups ; one is 'binding nature' which offers the ion binding atoms or groups of the ionophore itself, and the other is the 'stereospecific factor' which concerns the configuration of the ion-ionophore complex. Based on several ionophore molecular models, which are proposed with the consideration of these two factors, highly ion-selective ionophores for Li⁺, Na⁺ (alkali metal ions), Mg²⁺, Ca²⁺ (alkaline earth metal ions) and NH₄⁺ were successfully developed. The stories for developing these ionophores were discussed with the expected and unexpected results on the structural ion-selectivity features of more than 90 kinds of synthesized ionophores.