Luminescence
of [Ru(bpy)<sub>2</sub>(dppz)]<sup>2+</sup> Bound to RNA Mismatches
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Abstract
The
luminescence of <i>rac</i>-[Ru(bpy)<sub>2</sub>(dppz)]<sup>2+</sup> (bpy = 2,2′-bipyridine and dppz = dipyrido[3,2-<i>a</i>:2′,3′-<i>c</i>]phenazine) was
explored in the presence of RNA oligonucleotides containing a single
RNA mismatch (CA and GG) in order to develop a probe for RNA mismatches.
While there is minimal luminescence of [Ru(bpy)<sub>2</sub>(dppz)]<sup>2+</sup> in the presence of matched RNA due to weak binding, the
luminescence is significantly enhanced in the presence of a single
CA mismatch. The luminescence differential between CA mismatched and
matched RNA is substantially higher compared to the DNA analogue,
and therefore, [Ru(bpy)<sub>2</sub>(dppz)]<sup>2+</sup> appears to be also a sensitive light switch probe
for a CA mismatch in duplex RNA. Although the luminescence intensity
is lower in the presence of RNA than DNA, Förster resonance
energy transfer (FRET) between the donor ruthenium complex and FRET
acceptor SYTO 61 is successfully exploited to amplify the luminescence
in the presence of the mismatch. Luminescence and quenching studies
with sodium iodide suggest that [Ru(bpy)<sub>2</sub>(dppz)]<sup>2+</sup> binds to these mismatches via metalloinsertion from the minor groove.
This work provides further evidence that metalloinsertion is a general
binding mode of octahedral metal complexes to thermodynamically destabilized
mismatches not only in DNA but also in RNA