DESIGN AND SYNTHESIS OF SODIUM ION-SELECTIVE IONOPHORES BASED ON 16-CROWN-5 DERIVATIVES FOR AN ION-SELECTIVE ELECTRODE

To develop an ionophore that is highly selective for sodium for use in an ion-selective electrode, we propose a model based on 16-crown-5 wh ich has a cavity just the size of Na+ and has a ''block'' submit to pr event complex formation with ions larger than Na+, Based on this molec ular model, eight kinds of 16-crown-5 derivatives have been synthesize d, and their structural ion selectivity has been evaluated in detail, The 16-crown-5 derivatives having two bulky ''block'' subunits showed high Na+ selectivity relative to Kt, In particular, the derivative wit h two decalino subunits (DD16C5) exhibited the highest Nat selectivity of all the ionophores examined, When a phosphate ester-type membrane plasticizer, tris(ethyl-hexyl) phosphate, was used as the membrane sol vent for the ion-sensing membrane based on poly(vinyl chloride), the e lectrode using DD16C5 exhibited a Na+ selectivity of over 1000 times r elative to alkali metal and alkaline earth metal ions, including K+, w hich is the most serious interferant. The evaluation of the relationsh ip between the ionophore chemical structures and the ion-selective fea tures contributes to the host-guest chemistry to give a highly selecti ve ionophore for an alkali metal ion.