[Ru(bpy)2(dppz)]2+ (bpy = 2,2 -bipyridine, dppz = dipyrido[3,2-a:2 ,3 -c]phenazine) (RuBD), a long-lifetime metal-ligand complex displays favorable photophysical properties including long lifetime, polarized emission, and very little background fluorescence.
To further show the usefulness of this luminophore (RuBD) for probing nucleic acid dynamics, its intensity and anisotropy decays when bound to tRNAval were examined using frequency-domain fluorometry with a blue light-emitting diode (LED) as the modulated light source.
Unexpectedly much longer mean lifetime was obtained at 4℃ (<τ> = 178.3 ns) as compared to at 25℃ (<τ> = 117.0 ns), suggesting more favorable conformation of tRNAval for RuBD when intercalated at 4℃.
The anisotropy decay data showed longer rotational correlation times at 4℃ (52.7 and 13.0 ns) than at 25℃ (32.9 and 10.3 ns).
The presence of two rotational correlation times suggests that RuBD reveals both local and overall rotational motion of tRNAval.
Due to long lifetime of RuBD and small size of tRNAval, very low steadystate anisotropy values were observed, 0.048 and 0.036 at 4 and 25℃, respectively.
However, a clear difference in the modulated anisotropy values was seen between 4 and 25℃.
These results indicate that RuBD can be useful for studying hydrodynamics of small nucleic acids such as tRNAval.