Binding and transport of alkali metal ions by synthetic analogues of nactins

Abstract

Our new synthesis of 32-linked macrocycles, models of nactin ionophores, has been extended to more complex structures. The complexation properties of these macrocycles were determined using the method of extraction of alkali metals from an aqueous phase. Extraction constants of some compounds are much higher than those measured for nonactin and for dibenzo-18-crown-6, whereas the association constants measured for the same alkali metals are very weak. There is no complexation selectivity towards the cations, only a slight preference for lithium is observed. These synthetic ionophores are able to transport alkali metal ions through a non-polar barrier, but without clear selectivity. The measured rates are lower than those obtained for nonactin and dibenzo-18-crown-6, the decomplexation being the rate-determining step.