Polymeric membrane ion-selective electrodes based on molecular asterisk ionophores

Abstract

Ion-selective electrodes (ISEs) have been developed that incorporate a novel supramolecular class of ionophores called molecular asterisks. These ionophores are constructed with "arms" of repeating phenylene sulfide units that radiate outward from a core of either benzene or coronene. The flexibility of the arms, as well as the open exterior geometry and multiple soft Lewis base functionalities make these molecules potential candidates as ionophores for ISEs particularly for soft Lewis acids like transition metals. Studies with molecular asterisk-based ISEs show that these ionophores display a high selectivity relative to ion-exchanging ionophores toward Ag+ over a number of other cations. According to theoretical prediction, these ISEs demonstrate a super-Nernstian region of response toward silver from 10-6 to 10-5 M with a Nernstian response above 10-5 M, when primary ion is absent from the internal filling solution. Additionally, it was determined that both the nature of the core entity and the length (or generation) of the arms play a role in governing selectivity of these ionophores.