Valinomycin as a Classical Anionophore: Mechanism and Ion Selectivity

In the present study, we use theory and modeling to investigate K+ carrier valinomycin (Vln) as a classical anionophore. We discuss formation of the ion pair VlnK(+), Cl- versus encapsulation of the anion into VlnCl(-) complex as two alternative mechanisms that could account for surprisingly high anionophoretic activity of the cyclic peptide (Riddell and Zhou in J Inorg Biochem 55:55-279, 1994), meanwhile constructing kinetic models to help distinguish between the two. The study is guided by the idea to create valinomycin for anions and in this respect the selectivity problem is at the heart, as synthetic anionophores are expected to have the same issues with the counterion translocation as Vln has. The study helps to understand what Vln really is and so what valinomycin for anions has to be. Furthermore, using recent examples, we explore how Vln has been utilized as a tool for research in the two different fields, with an aim to illustrate advantages and potential of basic scientific methods over supramolecular way, celebrating victory of science over commonsense.