Origins of the voltammetric response of bilayer membranes modified with strong electron acceptors

Abstract The electrical properties of bilayer lipid membranes modified with strong electron acceptors are examined by the voltammetric method. Diffusion-limited current-potential curves are obtained in the absence of exogenous redox agents in the aqueous phase when the membrane is modified with tetracyanoethylene (TCNE) or tetracyanoquinodimethane (TCNQ). Other substituted 1,4-benzoquinone modifiers yield either no response (chloranil) or a current-voltage response indicative of a membrane limiting charge transfer step. In all cases that demonstrate an eletrical response, material can be detected leaching into the aqueous phase by spectroscopic means. Free radicals are detected subsequent to the mixing of modifier with an organic phase containing lipid; however, the material detected in the aqueous phase is not a radical. Voltammetric experiments on BLMs modified with charge transfer complexes of these electron acceptors elicits kinetic changes that suggest the membrane is behaving as a barrier to ion transport. Nernst plots at pH 5.5 and 7.5 demonstrate that the charge on the carrier varies with pH and thus these data indicate that the charge carrier responsible for these voltammograms is an ion traversing the membrane interface.