A Comparison of Electron-Transfer Rates of Ferrocenoyl-Linked DNA

Abstract

Electron transfer (ET) through two configurations of double-stranded (ds)-DNA was investigated by the attachment of a ferrocenoyl (Fc)-labeled and thiol-labeled DNA to Au electrodes. The first configuration positions the Fc moiety on the same strand as the thiolate, whereas the second configuration positions the Fc group on the complementary strand. The subtle difference in structure leads to a difference in E0' values (29 mV) and in ET rate constants (25 vs 115 s-1). The results have led to a further understanding of electron transfer in ds-DNA, and several models of ET are proposed.

Electrochemical switching of the flavoprotein dodecin at gold surfaces modified by flavin-DNA hybrid linkers

“…This synthetic procedure was expected to be more controlled than, e.g., the attachment of redox centers after hybridization or adsorption ͑the hybridized DNA is in equilibrium with its single stranded form, in which additional reactive groups are accessible͒. It is difficult to compare the results of this work directly with those of other groups who have reported about ET through ds-DNA monolayers on gold [14][15][16][17][18][19][20][21][22] because important parameters can be varied. ͑i͒ The employed thiol tether can vary in length and composition and can be attached to the 3Ј or 5Ј end of DNA.…”

“…For instance, one or two electrons can be transferred, and additional protonation steps can be involved in ET. Covalent attachment of redox centers is possible at the end of one of the DNA strands ͑either at the same strand bearing the thiol modification or the opposite͒ 18 or as intercalator within the ds-DNA when daunomycin is used. 16,48,49 In contrast to covalently attached redox centers, intercalators have been used quite frequently.…”

“…40 ͑iv͒ ET through DNA monolayers, labeled with covalently attached redox centers, was often studied with the ds-DNA adsorbed directly after hybridization. [15][16][17][18] In some cases the adsorption was carried out in the presence of mercaptoalcohol ͑or disulfide͒ or a separate mercaptoalcohol incubation step was added. 14,39 The more complicated Tarlov procedure was not applied when ET through DNA monolayers of DNA equipped with covalently linked redox centers has been investigated.…”

“…The HO͑CH 2 ͒ 6 S-S͑CH 2 ͒ 6 tether was applied in its disulfide form without previous conversion into the free thiol. 14,18,34 Following the work of Barton and co-workers, 16,17 CofC4-O20 and RS-O20 were first hybridized in solution and thereafter adsorbed on gold. This straightforward approach, which will be termed direct adsorption procedure, resulted in the additional adsorption of the protecting group R. The SPR kinetics, i.e., the changes in reflectivity at a fixed angle ͑within the linear scan range͒ during the individual steps, is depicted in Fig.…”

“…[29][30][31] Furthermore, different groups have independently shown that ET through monolayers of short double stranded DNA ͑ds-DNA͒ adsorbed on gold is possible. [14][15][16][17][18][19][20][21][22] Here, a first approach using ds-DNA of 20 base pairs as potential molecular wire system is presented.…”