Ester-armed cyclens having quadruplicated helical geometry: remarkably stable and selective encapsulation of Na+ ion

A new series of ester-armed cyclens nicely accommodated a Na+ ion in their quadruplicated helical binding spheres and effectively discriminated the cation from Li+ and K+ ions. Crystallographic studies revealed that four ester-functionalized sidearms provided effective coordination with the Na+ ion trapped in the 12-membered cyclen ring. Log K values for their Na+ complexes were estimated as 9-11 in CD3CN or C2D5OD, which were comparable to those of common bicyclic cryptands. FAB-MS, liquid-liquid extraction, and NMR binding experiments demonstrated that the cooperative action of the parent cyclen ring and ester-functionalized sidearms offered stable and selective encapsulation of the Na+ ion based on unique quadruplicated helical geometry.