DESIGN AND SYNTHESIS OF HIGHLY SELECTIVE IONOPHORES FOR LITHIUM ION BASED ON 14-CROWN-4 DERIVATIVES FOR AN ION-SELECTIVE ELECTRODE

Highly Li+-selective ionophores based on 14-crown-4 derivatives were d esigned and synthesized, and the relationship of their molecular struc tures and ion selectivities was investigated in order to obtain a high ly Li+-selective electrode. The ion selectivities were examined with 1 1 kinds of 14-crown-4 derivatives, which were prepared according to th e proposed two types of Li+ ionophore models. Excellent Li+-selective ionophores were obtained by introducing a bulky ''block'' subunit into the ethano-bridge section of the base crown ring, which effectively p revents the formation of a 2:1 or 3:1 sandwich-type complex consisting of the crown ether and cations larger than Li+. The best Li+/Na+ sele ctivity (more than 1000) was obtained for the electrode using the 14-c rown-4 derivative with a bulky decalin subunit. These results offer th e general ion selectivity features of 14-crown-4-based compounds.