Enantiomeric discrimination of chiral crown ether ionophores containing phenazine subcyclic unit by ion-selective potentiometry

Abstract

In this paper the enatiomeric selectivity of two chiral phenazino-18-crown-6 ether hosts ((R,R)-\textbf1 and (R,R)-\textbf2) is quantified. These hosts were incorporated into plasticized PVC membranes and used as recognition elements of ion-selective electrodes. The potentiometric response towards the two enantiomers of 1-phenylethylammonium ions (PEA⁺) was measured. Potentiometric selectivity coefficients were calculated which reflect the ratio of the stability constants of the diastereomeric complexes. Ligand (R,R)-\textbf1 does not show enantiomeric recognition, while ligand (R,R)-\textbf2 has a slight preference for the (S)-(-) enantiomer over the (R)-(+) enantiomer manifested by a selectivity coefficient of 0.77. The results were compared to enantioselectivity patterns of the ligands towards α -(1-naphthyl)ethyl ammonium perchlorate (NEA⁺ClO₄^-) enantiomers measured by circular dichroism and by ¹H NMR titrations.