Electron Transfer Through Organic and Biological Molecules

Author: Leigh, Brian Scott

Year: 2009

Degree: Dissertation (Ph.D.)

Advisor: Gray, Harry B.

Committee Members: Richards, John H.; Gray, Harry B.; Lewis, Nathan Saul; Marcus, Rudolph A.

Option: Chemistry

DOI: 10.7907/EYKS-R134

Abstract

The function of solvent in facilitating long-range coupling in donor/bridge/acceptor complexes is not well understood. There are exceptional challenges inherent to the measurement of the electron transfer coupling properties of solvents. By immobilizing the donor and acceptor in a glass to eliminate the effects of diffusion, statistical methods of analysis can be employed to study electron transfer between randomly dispersed donor and acceptor molecules over long distances. Toluene and 2-methyltetrahydrofuran form glasses that can solubilize donor and acceptor molecules at 77 K. Exponential decay constant of 1.23 per angstrom, for electron tunneling through a frozen toluene glass, and 1.62 per angstrom through 2-methyltetrahydrofuran glass have been found. Identification of the electronic coupling sites on the surfaces of proteins is usually achieved by inspection of a crystal structure. These coupling spots have been experimentally observed by employing mixed self-assembled monolayer electrodes and a variety of mutants. The electron transport protein azurin has a well defined reduction potential on self-assembled monolayer electrodes (0.16 V vs. saturated Ag/AgCl). When a point mutation is made at position 48, electron transfer ceases. This disruption of electron transfer occurs because the mutation forces conformational changes that disrupt a critical hydrogen bond between asparagine-47 and cysteine-112. This hydrogen bond is a key element for electron transfer into and out of the protein.

Files