A facile procedure for incorporating a Ru(diimine)(3)(2+) complex at the nucleobase in an oligonucleotide is reported that combines the advantages of Pd(0) cross-coupling and solid-phase DNA chemistries. These ruthenium-modified oligonucleotides form stable duplexes, and the favorable photophysical properties associated with the Ru(diimine)(3)(2+) complex are retained after site-specific covalent attachment.
A facile procedure for the incorporation of Ru(bpy)3
2+ in an oligonucleotide is reported. A Ru(bpy)3
2+
phosphoramidite is synthesized, and then attached to the 5‘-terminus of DNA using a standard protocol on an
automated DNA solid-phase synthesizer. Photophysical studies of the Ru(II) tris-diimine complex as well as the
corresponding labeled oligonucleotides demonstrate that the excited-state electron is localized on one specific
bipyridine with the dipole directed toward the linkage to DNA, and that the Ru(II) excited state is long-lived
when attached to the DNA.
The synthesis and photophysical properties of a novel ruthenium-modified nucleoside are reported. The key synthetic
step to 5-[Ru(bpy)2(4-m-4‘-pa-bpy)]2+-2‘-deoxyuridine involves the Pd(0)-catalyzed cross-coupling of a propargylamine-derivatized Ru(bpy)3
2+ and 3‘,5‘-dibenzoyloxy-2‘-deoxy-5-iodouridine. The long-lived 3MLCT excited
state (1300 ns) of 5-[Ru(bpy)2(4-m-4‘-pa-bpy)]2+-2‘-deoxyuridine has an emission maximum centered at 640 nm.
Step-scan Fourier transform infrared (S2FTIR) time-resolved spectroscopy reveals the excited-state electron to be
localized on the modified bipyridine with the excited-state dipole oriented toward the 2‘-deoxyuridine.
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