Conformationally constrained peptides as new nanomaterials for electrons and energy transfer

In this thesis the electron mediating properties of 310 helical peptides have been investigated, both in solution and on gold surfaces, by means of photochemical, electrochemical and photoelectrochemical methods. The directional character of the electron transfer process along helical oligopeptides as a result of the electrostatic field associated to the helix macrodipole is demostrated. It is shown that this effect is smaller for a 310 helix than that in a alpha-helix, because of the carbonyl dipole distortion with respect to the helical axis. For very short peptides the helix macrodipole does not affect very much the redox potential of the probe and of the gold surfaces, but it affects the electron transfer rate toward the gold substrate. The ability of short helical peptides to generate photocurrent is also demonstrated, together with the possibility of constructing a molecular photodiode able to switch the current direction. It is also shown that the gold substrate on which the a peptide SAM is built up strongly influences the photocurrent efficiency, showing the maximum value for interdigitated gold microelectrodes, in which the substrate is Si3N4. Furthemore, a new approach is utilized for the construction of a mixed SAM , making use of the helix-helix macrodipoles interaction. By these favourable interactions, a peptide has been intercalated into a covalently linked peptide SAM. Both peptides have been functionalized by a photoactive group, so that it could be possible to switch the direction of the generated current by selective excitation of the two peptides. All these results confirm the very good electron mediating properties of helical peptides, and make them very promising materials for the development of molecular devices based on peptide molecular wires.