Investigation into the Driving Force Dependence of Excess Electron Transport in Duplex DNA
Campbell, Neil Peter
Rokita, Steven E
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The purpose of this dissertation is to investigate the driving force dependence of excess electron transport in deoxyribonucleic acid (DNA) using napthyl amines as electron donors. The ability of DNA to act as a pathway for the migration of charge was first proposed in 1963 by Elgy and Spivey. Since then, investigation of two complementary processes, hole transport and excess electron transport, have been studied. Of these processes research has focused mostly on hole transport. Hole transport has been studied for several decades. As such, the four fundamental parameters affecting the processes have been elucidated: the distance dependence has been found to be weak, G/C sequences have been found to allow for more efficient hole transport, migration from the 3' to 5' direction is more efficient, and a driving force dependence on the efficiency of hole transport has been found. Only recently has attention turned to the determination of the fundamental parameters affecting excess electron transport. Investigations to date have determined that there is a weak distance dependence on excess electron transport, A/T sequences allow more efficient transport, and excess electron transport is more efficient when migrating from the 5' to 3' end of DNA. The one parameter affecting excess electron transport that has not been investigated is the driving force dependence. To test for driving force dependence, napthyl amines were screened for their ability to initiate charge transfer by reductive electron donation using an assay based on the photoinduced reduction and subsequent scission of duplex DNA containing a 5-bromo-2'-deoxyuridine (BrU) residue and an abasic site. Each compound had varying reducing potentials (driving forces), which allowed investigation into the driving force dependence of excess electron transport. Six compounds (1,5-diaminonapthalene, N1-methyl-1,5-diaminonathalene, N1,N5-dimethyl-1,5-diaminonapthalene, N1,N1-dimethyl-1,5-diaminonapthalene, N1,N1,N5-trimethyl-1,5-diaminonapthalene, N1,N1,N5,N5-tetramethyl-1,5-daiminonapthalene) were screened under both aerobic and anaerobic conditions, and found to initiate charge transfer. No correlation between the reduction potential of the compounds (driving force) and the rate of strand scission was seen. Subsequently, the oligonucleotide conjugates of two of the compounds, 1,5-diaminonapthalene and N1,N1,N5,N5-tetramethyl-1,5-diaminonapthalene, were prepared and studied to determine if a driving force dependence on excess electron transport exists when the compounds are covalently attached to the DNA. 1,5-diaminonapthalene and N1,N1,N5,N5-tetramethyl-1,5-diaminonapthalene were chosen as they showed the greatest difference in their reducing potentials. The conjugates showed no difference in the rate of excess electron transport, thus indicating there is not a driving force dependence on excess electron transport in DNA, at least using these compounds and in this system.