Proposal for direct measurement of reorganization energies in electron-transfer proteins by the V-I characteristics of photoinduced STM currents via large adsorbates with a redox active center

When an electron-transfer protein with a redox active center is adsorbed on the substrate, the STM current rises steplike at a threshold bias at low t emperatures. This threshold is determined not only by the redox potential o f the active center, but also by the energy lambda of reorganization in the protein matrix upon the redox change. Under photoirradiation raising the a ctive center to its excited state, the current will rise also at a smaller threshold bias. Being proportional to A, the threshold difference enables u s to directly obtain lambda, which plays important roles in electron-transf er rates to or from the protein. (C) 2001 Elsevier Science B.V. All rights reserved.