Voltammetrically Controlled Electron Transfer Reactions from Alkanethiol Modified Gold Electrode Surfaces to Low Molecular Weight Molecules Deposited within Lipid (Lecithin) Bilayers

A procedure was developed for initiating electron transfer from a gold electrode to a low molecular weight electron acceptor present inside supported lipid (lecithin) bilayers, followed by further electron transfer to an electron acceptor present in an aqueous solution. The electron acceptors present in the lecithin bilayers and aqueous phase were 7,7,8,8-tetracyanoquinodimethane (TCNQ) and [Fe-III(CN)(6)](3-), respectively. A polished planar gold disk electrode was first coated via self-assembly procedures with an alkanethiol monolayer. A phospholipid layer consisting of multiple bilayers of lecithin containing TCNQ was subsequently deposited onto the alkanethiol monolayer. The Au/alkanetbiol/lecithin-TCNQ electrode was placed in an aqueous solution containing various amounts of [Fe-III(CN)(6)](3-) and [Fe-III(CN)(6)](4-), with 0.5 M KCl as the supporting electrolyte. In the absence of TCNQ inside the alkanethiol/lecithin layers, only a small background current was observed. When TCNQ was included in the alkanethiol/lecithin layers, the voltammetry showed features typical of a catalytic process, due to the TCNQ being reduced to TCNQ-within the lecithin bilayers and then undergoing oxidation back to TCNQ via interaction with [Fe-III(CN)(6)](3-) at the lecithin-aqueous solution interface. The procedures for preparing the alkanethiol/lecithin-TCNQ coatings were optimized in order to obtain the most reproducible voltammetric response. Experiments were also performed using tetrathiafulvalene (TTF) as an electron donor in the lipid bilayer phase.