Novel Amphi-Ionophores

Abstract

The interactions of cyclic peptides containing glycines with cations (Li+, Na+, Be2+, Mg2+) and anions (F- and Cl-) have been investigated using ab initio calculations. The cyclic peptides are found to be exciting novel amphi-ionophores which show strong affinities for both cations and anions. In the presence of a cation, the CO groups orient toward the center, whereas in the presence of an anion, the N−H groups do so. To our knowledge, we believe that these cyclic peptides are the first amphi-ionophores reported in the literature. Since there are few ionophores for anions, the cyclic peptides would be important anionophores in that they have large anion affinities. Although the individual amide group is rigid, the entire cyclic structures are very flexible, resulting in amphi-ionophores. If glycines are substituted by other residues, it could be utilized to design cyclic peptide ionophores to show different selectivities for cations and anions with varying flexibilities.