A D2 symmetric tetraamide macrocycle based on 1,1′,4,4′-tetrahydro[3,3′(2H,2′H)-spirobiquinoline]-2,2′-dione:: synthesis and selectivity for lithium over sodium and alkaline earth ions

Macrocyclic ionophores d,l-3 and d,l-4 with four amide carbonyl ligands were synthesized and investigated in lithium ion-selective electrodes. In solvent PVC membranes, ion selectivity of d,l-3 and d,l-4 for lithium relative to sodium was observed as log K-Li,Na(pot) = -1.4 and - 1.23, respectively. Spiromacrocycle d,1-3 and analogue dibenzospiromacrocycle d,1-4 have similar ion selectivity patterns for alkali metal ions, but d,l-4.could discriminate against alkaline earth metal ions better than d,l-3. It is an example of an endopolarophilic/exolipophilic macrocyclic ionophore whose selectivity for monovalent cations over divalent cations is enhanced by thick lipophilic shells. (c) 2006 Elsevier Ltd. All rights reserved.