Ferrocene peptide dendrimers: Synthesis, properties and binding studies

Our first goal was to understand how the dendrimer encapsulation and electron transfer of peptide dendrimers having a ferrocene core were interrelated. The thermodynamics of electron transfer in a dendritic environment are dramatically influenced by the dendrimer sheath. This controls the redox potential in ferrocene-core dendrimers. The larger dendrimer surrounds the core and creates an increasingly hydrophobic microenvironment around the ferrocene and exerts negative shifts on the redox potential of the Fc group. Such negative shifts are due to hydrogen bonding between the dendritic sheath and the proximate amide moieties linked to the ferrocene. The kinetics of the electron transfer in ferrocene peptide dendrimers is also substantially affected. This is indicated by the lack of redox activity of larger dendrimers in solution and on surfaces. These results indicate that the structure of ferrocene core dendrimers exerts a substantial influence on dendrimer conformation and their electrochemical properties.; The second goal was to investigate the effect of metal ion interactions with errocene peptides and dendrimers. Solution studies on smaller ferrocene-peptides showed that metal ions exert positive shifts on the redox potentials of the ferrocene core. These were explained as resulting from through-space electrostatic repulsion from the metal centres and the positively charged oxidized ferrocene. Metal ion coordination in thin films of ferrocene dendrimers showed no changes in redox potential but exhibited extensive decrease in the surface charge of ferrocene in the film. The coordination of alkaline earth and lanthanide ions involved only the carboxylate moiety while the amide NH is unaffected and not involved in coordination.