Part 1: Controlling barriers to charge transfer in DNA Part 2: DNA-directed assembly of conducting oligomers
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A series of anthraquinone-linked DNA oligonucleotides was prepared and the efficiency of long-distance radical cation migration was measured. In one set of oligonucleotides, two GG steps are separated by either a TATA or an ATAT bridge. In these two compounds, the efficiency of radical cation migration from GG to GG differs by more than an order of magnitude. Replacement of the thymines in the TATA or ATAT bridges with 3-methyl-2-pyridone (t, a thymine analog) results in the much more efficient radical cation migration across the bridge in both cases. This is attributed to a decrease in the oxidation potential of t to a value below that of A. In contrast, replacement of the thymines in the TATA or ATAT bridges with difluorotoluene (f, a thymine analog with high oxidation potential) does not measurably affect radical cation migration. These findings are readily accommodated by the phonon-assisted polaron-hopping mechanism for long-distance charge transfer in duplex DNA and indicate that DNA in solution behaves as a polaronic semiconductor. Oligomers containing thiophene-pyrrole-thiphene (SNS) monomers were covalently linked to the nucleobases of DNA. Treatment of these oligomers with horseradish peroxidase and hydrogen peroxide lead to the formation of conducting oligomers conjoined to the DNA. The DNA template aligns the oligomers along one strand of the duplex and limits the intermolecular reaction of monomers. This method enables utilization of the unique self-recognizing properties and programmability of DNA to create tailored oligomers.