Structural investigation on ion-selective ionophoric properties of armed 12-oxacrown-3 derivatives

We designed and synthesized new armed 12-oxacrown-3s bearing oxygen donor arms and forming encapsulated complexes with metal ions. The ISEs based on the single armed 12-oxacrown-3s exhibited Na+ ion selectivity, while the ISE based on the double armed 12-oxacrown-3 exhibited Li+ ion selectivity. The conformational analysis was performed on the free armed 12-oxaciown-3s and the non-encapsulated and the encapsulated armed 12-oxacrown-3 complexes using a semi-empirical method. The conformational analysis indicated that all armed 12-oxacrown-3s structurally prefer the Na+ ion rather than the Li+ ion. Further, it became apparent that the single armed 12-oxacrown-3s without a guest cation have the C3v 12-oxaciown-3 ring and the double armed 12-oxacrown-3 without a guest cation has the bent 12-oxacrown-3 ring. The oxygens except carbonyl oxygens were directed toward the cation center in the structures of the complexes. It was clear that the ether and ester oxygens participate in the sidearm coordination.