Free radical formation in reactions of lecithin with tetracyanoquinodimethane and tetracyanoethylene: Relating the behavior of membrane-partitioned electrochemical cells to charge carrier using electron spin resonance

Electron spin resonance spectra of solutions used to make conductive bilayer lipid membranes reveal that free radical formation is a precursor to membrane conductivity. Tetracyanoquinodimethane (TCNQ) forms a stable radical that self-aggregates in nonaqueous media, yet will diffuse into the aqueous phase as a monomer, potentially allowing interfacial exchange. Tetracyanoethylene (TCNE) will undergo hydrolysis via a radical intermediate, and the decomposition product is ESR silent. The electrochemical response of an electrochemical cell partitioned by a membrane modified by these dopants is ionic for TCNE. Although the mechanism is less clear for TCNQ, the role of a stable radical is clearly implicated. (C) 1997 Academic Press.