The study of electron transfer reactions both in solution and at electrode surfaces is currently an area of vigorous research. At the present, however, there exist a number of experimental constraints that hinder the study of many aspects of heterogenous electron transfer. A goal of the project of Dr. Widrig is the development of a general technique for the examination of electrode reactions which will overcome many of these current limitations. In her experimental approach, the technology that recently has been refined in the realization of the scanning tunneling microscope will be applied to the investigation of the redox chemistry of individual molecules. This will be accomplished by using the tip of the scanning tunneling microscope and a planar electrode substrate as the two working electrodes of a bipotentiostat. The substrate electrode will be derivatized with an organized, monomolecular layer containing a reversible redox reagent. As the tip is positioned within Angstroms above the substrate surface, voltages suitable for oxidation and reduction of the immobilized species will be applied to the tip and substrate electrodes, respectively. As the immobilized molecule over which the tip is positioned is continually oxidized and reduced, the magnitude of the resulting current will be dependent on the rate constant for heterogeneous electron transfer to that species. Preliminary calculations indicate that measureable currents will be obtained for redox couples whose standard rate constants are greater than 2 cm/s. Successful implementation of this technique will permit the measurement of formerly indeterminable rate constants for "fast" electrode reactions and allow an unprecedented assessment of the roles of the electrode-reactant separation, orientation, and environment in heterogeneous electron transfer. Preliminary work includes the preparation and characterization of the electroactive monolayer, the development of tip insulation procedures, and modeling of heterogeneous electron transfer through individual molecules. %%% Research Planning Grants enable women who have not had prior independent Federal research support to develop a competitive research project. This project involves the use of technology for the precise placement of electrodes in the scanning tunneling microscope for precision electrolysis of an organized monomolecular layer. This will permit the measurement of the rates of electron transfer previously not measurable.
