The Design, Synthesis and Redox Properties of Metallated Artificial Oligopeptides
Open Access
- Author:
- Ohr, Kristi
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 11, 2007
- Committee Members:
- Mary Elizabeth Williams, Committee Chair/Co-Chair
Thomas E Mallouk, Committee Member
Mark Maroncelli, Committee Member
Theresa Stellwag Mayer, Committee Member - Keywords:
- self-assembled monolayers
electron transfer
peptide
self-assembly
molecular electronics
multimetallic - Abstract:
- This work details investigations of ligand-substituted artificial oligopeptides that form well-ordered supramolecular structures upon metal complexation. The structures are tailorable based on choice of ligand, metal and sequence, and the arrangement and spacing between the metal centers can be controlled. These unique materials provide a means of controlling and directing charge transport and are important candidates for the assembly of molecular circuits. Chapter two presents the synthesis and characterization of pyridine-substituted artificial oligopeptides of varying length. UV-Visible absorption spectrophotometric titrations of the oligopeptides with Cu(II) and Pt(II) complexes of 2,2’:6’,2”-terpyridine and pyridine 2,6-dicarboxylic acid show stoichiometric binding based on the number of pyridines per peptide strand. Cyclic voltammetry of [Pt(terpyridine)]2+ containing oligopeptides reveal two sequential one-electron reductions at formal potentials independent of oligopeptide length. The diffusion coefficients decrease linearly with increasing oliopeptide length. Chapter three presents the synthesis and characterization of metallated oligopeptide duplex assemblies composed of phenyl-terpyridine ligands cross-linked by Co(II) and Fe(II) ions. Cyclic voltammograms are consistent with one-electron oxidative reactions without strong coupling between the metal complexes. The diffusion coefficients decrease linearly with increasing oligopeptide length, suggesting the primary products are metal-linked oligopeptide duplex assemblies. Larger metallated oligopeptides yield irreversibly adsorbed electroactive films during cyclic voltammetry which are chemically reversible but kinetically quasi-reversible. Chapter four presents the synthesis of metal-crosslinked oligopeptide duplexes containing Co(II) and Fe(II), functionalized with cysteine and adsorbed to Au electrode surfaces. Cyclic voltammetry of mixed monolayers containing metallated oligopeptide and propanethiol reveals facile electron transport in Fe(III/II) and Co(II/I), but a decrease in conductivity of the Co(III/II) reaction, as the length of the oligopeptide increases, suggesting that these structures behave as molecular wires. Chapter five presents electrochemical investigations of the rates of electron transfer in the SAMs described in chapter four. Rates are measured by Laviron analysis of cyclic voltammograms and AC impedance spectroscopy and in all cases are larger than 104 s-1. Values for the transfer coefficients of the films show a dependence on oligopeptide length for the Co (III/II) couple, but not for the Co(II/I) or Fe(III/II).