Synthesis and properties of metal-labeled oligodeoxynucleotides

In this work, ruthenium and ferrocene labels for ODNs are discussed. Two methods have been used to prepare ODNs labeled with these compounds. The phosphoramidite approach is a popular method for automated DNA synthesis, which has been adapted to incorporate metallo-nucleosides during a solid-phase synthesis scheme. Alternatively, metal-labeled ODNs have been prepared using an on-column derivatization method, in which a halogenated nucleoside is incorporated into an ODN and a propynyl-terminated metal complex is coupled to the ODN while still on solid support.; Using these methods, ruthenium- and ferrocene-labeled ODNs have been synthesized. These ODNs have been characterized by mass spectrometry, circular dichroism spectroscopy, UV-Vis and emission spectroscopy and thermal denaturation studies. The labeled strands form stable duplexes of B-form DNA with melting temperatures decreasing slightly from unlabeled duplexes (ΔT _m = 0–9°C). Photophysical studies of the ruthenium-labeled nucleoside, single strand, and double strand, indicate that these complexes retain the favorable emission and lifetime properties of Ru(bpy)₃ 2+. Lifetime studies indicate that the ruthenium excited state is not quenched by the single- or double-stranded ODNs. However, when the duplex is labeled with ruthenium and phenothiazine, partial quenching is observed.; Electrochemical interrogation of the ferrocene and ruthenium labels reveals that the derivatives posses redox potentials similar to unmodified Ru(bpy) ₃2+ and ferrocene. Likewise, UV-Vis absorption spectra of the labels compare favorably with that of the parent compounds.; Derivatization of a gold-ball electrode with self-assembled monolayers of redox-labeled ODNs is investigated using AC voltammetry. The redox-labeled ODNs are designed such that the redox probe is close to the electrode surface when no complement is present, but is forced away from the surface upon addition of a complementary strand. Hybridization of a complementary ODN to the hairpin probe results in a decrease of the current response.