## Dissertations from ProQuest

#### Title

The influence of side-chains on electronic coupling between metal centers in simple model systems

1995

Article

#### Degree Name

Doctor of Philosophy (Ph.D.)

Chemistry

#### First Committee Member

Nita A. Lewis, Committee Chair

#### Abstract

Electron transfer reactions are key steps in photosynthesis, respiration and numerous other biochemical processes. Electron transfer reactions generally occur between protein-bound cofactors that are separated by distances that are large on a molecular scale, often between 10 and 25 A. An important current question is how the protein matrix between redox centers provides pathways to facilitate electron transfer. Studies on both small and large molecules, especially proteins, have been reported in which the electron transfer pathways are better described by through bond than by direct metal-to-metal distances. The role of the intervening medium in the biochemical redox process is found to be difficult to quantify due to the size and complexity of proteins. Therefore, small synthetic model systems are often used as a powerful tool to probe details of the electron transfer pathway. In the present study, we designed and synthesized a series of dinuclear complexes in which the through-bond distance and driving force between the donor and acceptor are constant. Only the side chains along the electron transfer pathway are changed in a systematic manner. The dinuclear compounds and their mononuclear derivatives are characterized by UV-vis spectroscopy. The structures are characterized by $\sp1$H and $\sp{13}$C NMR spectrometry and X-ray crystallography. Correlations are observed between functions of E$\rm\sb{op}$ and $\varepsilon\rm\sb{max}$ of the transition bands and $\Delta{\rm E}\sb{1/2}$ measured electrochemically, the sum of the Taft $\sigma$I parameters for the substituents, the dihedral angle between the two pseudoaromatic rings in the system, and the HOMO bond energies of the complexes calculated by ZINDO.

#### Keywords

Chemistry, Analytical; Chemistry, Inorganic