The role of the anion on the ionophore properties of valinomycin was studied in a model floating bilayer lipid membrane (fBLM) using supporting electrolytes containing K + with four different counter anions (ClO4 -, H2PO4 -, Cland F -). The electrochemical impedance spectra indicate that the membrane resistance of the bilayer decreases with the decrease of Gibbs free energy of anion solvation. The IR spectra demonstrate that valinomycin does not readily bind to K + in the KH2PO4, KCl and KF

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... trolyte solutions, but in the presence of KClO4, valiomycin readily binds to K + forming a vailinomycin-K + complex. The results in the present paper reveal the role of the counter anion on the transport of cations by valinomycin across the lipid bilayer. The valinomycin-cation complex creates an ion pair with the anion and this ion pair could enter the hydrophobic region of the bilayer and transport cation across the bilayer. Anions with low solvation energies facilitate the formation of the ion pair. This paper sheds new light on the transport