| The work presented in this thesis was directed towards the understanding of the electron transfer (ET) mediation properties of molecules containing amides and peptides. Our specific interest is to examine molecules in which the rate constant and an intervalence charge transfer (IVCT) absorption band are both observable. Establishing a defined correspondence between the measured rates and optical measurements of intervalence bands could become an important method for determining ET rates that are not easily measurable. A series of mononuclear and binuclear ruthenium (II/III) and osmium (II/III) pentaammine complexes bridged 4-pyridylisonicotinamide (iso-apy) and 4-methylpyridylisonicotinamide (iso-mapy) were synthesized and studied. The IVCT bands (nm) and extinction coefficients (M−1 cm−1) of the mixed-valence ruthenium derivatives were observed at 809 (50) and 743 (20), respectively. Enhanced absorption bands were expected for the osmium derivatives, however, the more intense MLCT bands overlap the weaker IV bands and complicated the analysis. Spectral simulations however showed the IVCT bands are at 840 nm and 794 nm, respectively.; A more direct approach to the ET measurement is to produce the kinetic intermediate by adding an electron to the fully oxidized binuclear ruthenium (III/III) species using pulse radiolysis. Results from these experiments showed that for the iso-mapy derivative, intramolecular ET rate constant of 3 × 106 s−1 was observed. The more planar derivative, iso-apy, was found to have faster kinetics, with a rate constant ≥7 × 107 s−1 . The measured values are in close agreement with calculated values using Hush's model, 1 × 107 s−1 and 3 × 108 s−1, respectively. Extension to peptide bridges was carried out by separating the amide bond with proline or glycine residues. The binuclear complexes were synthesized, however, no intramolecular ET was observed. Based on earlier results, the rates are expected to fall in the microsecond time range. Similar experiments were done using fulleropyrrolidine derivatives of the form (acac)2RuIII -bpy-pron-fulleropyrrolidine. These compounds were synthesized and characterized, but again, no intramolecular ET rates between the ruthenium center and the fullerene were observed. Finally, the results obtained for the iso-apy and iso-mapy ligands and their respective donor acceptor complexes will serve as a guide for the type of changes necessary to induce faster ET reactions and more intense intervalence bands in extended peptide assemblies. |
