Synthesis and Electrochemistry of Anthraquinone−Oligodeoxynucleotide Conjugates

Electroactive oligodeoxynucleotides (ODNs) with specific base sequences have a potential application as electrical sensors for DNA molecules. To this end, a phosphoramidite that bears a 9,10-anthraquinone (AQ) group tethered to the 2‘-O of the uridine via a hexylamino linker, 2‘-O-[6-[2-oxo(9,10-anthraquinon-2-yl)amino]hexyl]-5‘-O-(4,4‘-dimethoxytrityl)uridine 3‘-[2-(cyanoethyl)bis(1-methylethyl)phosphoramidite] (3), has been synthesized and used to prepare three ODNs with tethered AQs using standard phosphoramidite chemistry. The synthetic methodology thus allows the synthesis of ODNs with electroactive tags attached to given locations in the base sequence. Cyclic voltammetric behavior of these AQ−ODN conjugates was examined in aqueous buffer solutions at a hanging mercury drop electrode. At slow sweep rates, nearly reversible two-electron waves characteristic of an adsorbed anthraquinone/hydroquinone redox couple was observed for all of the AQ−ODN conjugates. Approximate Langmuirian isotherms were found for the AQ−ODNs with molecular footprints, calculated from the saturation coverages, that scaled with molecular size. The cyclic voltammetric response of the duplexes formed from the AQ−ODNs and their complementary ODN was complicated by the competitive adsorption of the individual ODNs and possibly the duplex species as well.