Impedance spectroscopic investigation of the temperature influence on the transfer of tetraphenylborate ions through lipid membranes — Calculation of energy barriers for the ion transfer across lipid membranes

Abstract

Investigating the transfer of tetraphenylborate (TPB) ions through planar lipid membranes we found a strong influence of temperature on the impedance spectrum. The impedance spectrum of TPB modified lipid membranes is governed by two processes, namely, the ion transfer at the membrane surfaces and the ion transfer across the hydrophobic interior of the membrane. The analysis of the measured spectra showed that temperature predominately influences the inner ion transfer and the rate constant for the inner transfer, respectively. We used this temperature dependence to calculate energy barriers for the ion translocation across the membrane interior. Varying the composition of the membrane lipids we found that the inner barrier not only depends on the hydrocarbon part but also on the head group of the lipid. We explain this interesting result with interactions of the permeating TPB ions with the head groups of the membrane. The above-mentioned interactions seem to immobilize the TPB ion at the membrane surface and to enlarge the energy barrier for the ion transfer across the inner part of the lipid membrane. The largest barriers were found for the investigated lecithins whose phosphocholine head group strongly interacts with the TPB ions.