A potentiostatic study of hydrophobic ion transfer across lipid bilayer membranes: Part II. Transport of tetraphenylborate ions at high concentration in the aqueous solution

Abstract

The transfer of tetraphenylborate (TPB −) ions across black lipid membranes in aqueous solutions ranging from 10 −5 M to 10 −3 M, has been studied under potentiostatic conditions. A theoretical treatment of the problem accounts for the two time constants given and for the diffusion current for prolonged periods of time if one assumes that the adsorption-desorption transfer currents are large. This is tantamount to considering that these two processes are highly reversible and that the dipolar nature of the drop in potential between the closest approach and adsorption planes determines the adsorption. The resistances corresponding to the translocation and adsorption-desorption processes have thus also been evaluated. Using these results and those given by surface potential measurements on monolayers of glycerylmono-oleate, the number of adsorbed ions has been calculated. This has led to an explanation of the well known conductance maximum encountered when the concentration of the tetraphenylborate ions varies.