SEQUENTIAL AND COHERENT LONG-RANGE ELECTRON-TRANSFER CLOSE TO RESONANCE WITH INTERMEDIATE BRIDGE GROUPS, AND NEW PERSPECTIVES FOR IN-SITU SCANNING-TUNNELING-MICROSCOPY OF ADSORBED METALLOPROTEINS

Three-level electron transfer follows super-exchange patterns when the intermediate electronic level is off-resonance with the donor and acc eptor levels. Close to resonance, new patterns emerge where the interm ediate level is temporarily populated in vibrationally coherent or inc oherent modes, We discuss energy and distance relations associated wit h such electron transfer modes. These appear to accord with fast elect ron transfer in several chemical and biological systems. We also discu ss some recent observations on in situ scanning tunnelling microscopy of metalloproteins and large transition metal complexes which enable, in principle, a distinction between superexchange, coherent, and seque ntial three-level electron transfer.