Bis(2,2′-bipyridine)ruthenium(II)
complexes with
imidazo[4,5-f ][1,10]-phenanthroline or
2-phenylimidazo[4,5-f
][1,10]phenanthroline
Abstract
Imidazo[4,5-f]1,10-phenanthroline (ip),
2-phenylimidazo[4,5-f][1,10]phenanthroline (pip) and
their (bipy)
2
Ru
2+
complexes
(bipy = 2,2′-bipyridine) have been synthesized and
characterized. The oxidation potentials of
[Ru(bipy)
2
(ip)]
2+
and
[Ru(bipy)
2
(pip)]
2+
were found to be 1.254 and
1.284 V vs. saturated calomel electrode respectively; the
reduction of ip and pip appears to be irreversible at ca.
-0.85 V. The photophysical properties of the complexes were
perturbed in the presence of calf thymus DNA. The distinct changes
including hypo- or hyper-chromicity at different UV/VIS absorption
bands, enhancements of integrated emission intensity and excited-state
lifetime, and efficiency of emission quenching by
[Fe(CN)
6
]
4-
all indicate the stronger
binding affinity to DNA of [Ru(bipy)
2
(pip)]
2+
over
that of [Ru(bipy)
2
(ip)]
2+
, consistent with the
greater planar area and extended π system of the pip ligand. The
luminescence of the complexes showed monoexponential decay at any
[DNA]∶[Ru] ratio. The circular dichroism signals of the dialysates
of the racemic complexes against calf thymus DNA suggest that the
complexes bind to the DNA with enantioselectivity favouring the Δ
isomers. These phenomena all suggest that the complexes bind through
intercalation of ip or pip into base pairs. The crystal structure of
[Ru(bipy)
2
(ip)][ClO
4
]
2
·H
2
O was determined; it contains the planar bidentate ligand ip and
two twisted bipy ligands with torsional angles between each bipyridine
ring pair of 5.7 and 8.6°.
][1,10]phenanthroline (pip) and
their (bipy)
2
Ru
2+
complexes
(bipy = 2,2′-bipyridine) have been synthesized and
characterized. The oxidation potentials of
[Ru(bipy)
2
(ip)]
2+
and
[Ru(bipy)
2
(pip)]
2+
were found to be 1.254 and
1.284 V vs. saturated calomel electrode respectively; the
reduction of ip and pip appears to be irreversible at ca.
-0.85 V. The photophysical properties of the complexes were
perturbed in the presence of calf thymus DNA. The distinct changes
including hypo- or hyper-chromicity at different UV/VIS absorption
bands, enhancements of integrated emission intensity and excited-state
lifetime, and efficiency of emission quenching by
[Fe(CN)
6
]
4-
all indicate the stronger
binding affinity to DNA of [Ru(bipy)
2
(pip)]
2+
over
that of [Ru(bipy)
2
(ip)]
2+
, consistent with the
greater planar area and extended π system of the pip ligand. The
luminescence of the complexes showed monoexponential decay at any
[DNA]∶[Ru] ratio. The circular dichroism signals of the dialysates
of the racemic complexes against calf thymus DNA suggest that the
complexes bind to the DNA with enantioselectivity favouring the Δ
isomers. These phenomena all suggest that the complexes bind through
intercalation of ip or pip into base pairs. The crystal structure of
[Ru(bipy)
2
(ip)][ClO
4
]
2
·H
2
O was determined; it contains the planar bidentate ligand ip and
two twisted bipy ligands with torsional angles between each bipyridine
ring pair of 5.7 and 8.6°.
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