Measurements of DNA dynamics are typically limited to the nanosecond (ns) timescale because of the ns decay times of commonly used fluorescence such as ethidium bromide and acridine derivatives. At the suggestion of Dr. Lakowicz of the Center for Fluorescence Spectroscopy in Baltimore we synthesize a metal-ligand DNA probe which displays a long decay time. We shoed that the time-resolved anisotropy measurements could be extended to the microsecond timescale using metal-ligand complexes. The ruthenium complex [Ru(2, 2', -bipyridine)2 (dipyrido [3, 2-a~, 2', 3', -c] phenazine]2+, was found to display high anisotropy near 0.2 when excited in its long wavelength absorption bands. The decay time of (Ru(bpy)2 (dppz)]2+ when bound to DNA is near 200 ns, allowing anisotropy to be measured to be 600 ns. Other Ru complexes display still longer lifetimes to be measured to 600 ns. Other Ru complexes display still longer lifetimes to 2 fsec when bound to DNA. This class of fluorophores enables measurements of DNA dynamics over a wide range of time, 1 ns to several fs, which was previously inaccessible using time-resolved fluorescence.
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