How valinomycin transports water across the bilayer: effect of the cation in the electrolyte

Surface-enhanced infrared absorption spectroscopy (SEIRAS) was employed to investigate the structure of the interfacial water in the 1,2-diphytanoyl- sn-glycero-3-phosphocholine (DPhPC)/valinomycin floating bilayer on the gold surface in two electrolytes with different cations, KClO 4 and NaClO 4 . The SEIRAS studies indicate that interfacial water adopts different structures in the bilayer with different cations. The structure of interfacial water in the DPhPC/valinomycin bilayer in the NaClO 4 solution is similar to water in the DPhPC bilayer (without valinomycin), while the structure of water in the bilayer in the KClO 4 solution has a high amount of disordered hydrogen bond network. The results of the present study confirm that valinomycin selectively transports K + across the lipid bilayer as an ion pair and that the ion pair is bonded to residual water that is released into the submembrane region.