Ion transport across bilayer lipid membranes between two aqueous phases in the presence of iodide and triiodide ions

Abstract

I⁻ and I₃⁻ usually coexist in nature, and it is well-known that I₃⁻ is much more hydrophobic than I⁻. Both I⁻ and I₃⁻ play a crucial role in human physiological activities and can be applied to various medical applications, such as synthesis of medicine, antibiotics, etc. During the measurement of the ion-transport current of KI aqueous solution, I₃⁻ is spontaneously generated and causes an increase in ion permeation. However, the mechanism of facilitated ion transport remains unclear. In this study, the influence of I₃⁻ on the ion transport across bilayer lipid membranes (BLMs) was elucidated. Physically stabilized BLMs were formed using the track-etched membrane (TM), and the ion-transport current was measured by applying a membrane potential across BLMs. Under asymmetric ionic concentration conditions, the permeability of K⁺, I⁻, and I₃⁻ was evaluated. The permeability of I⁻ across BLMs was about 8 times higher than that of K⁺. In the presence of I₃⁻, the permeability of K⁺ across BLMs drastically increased. The permeability of K⁺ became 9 times higher than that of I⁻ in the presence of 50 µM I₃⁻. It is considered that I₃⁻ facilitated the transport of K⁺ across BLMs by serving as a carrier of K⁺ within BLMs.