Chemistry Reference
In-Depth Information
equivalent intercalates.
74
Furthermore, the groove complementarity necessary for
intercalation means that the mononuclear complex exhibits enantioselectivity,
whereas the (relatively) loosely associating dinuclear species does not. Jiang and
coworkers have surveyed a number of dinuclear complexes featuring bridges derived
from bpy.
75 - 78
They all bind via a nonintercalative mode with modest binding affi ni-
ties, however in a number of cases they exhibit intriguing enantiopreferences in
which the L enantiomer appears to be the stronger binding.
75,78
11.3.1 Stereoisomers and Their Separation
A critical issue in the investigation of the interaction of the dinuclear species with
DNA has been the ability to control the stereochemistry of the component metal
centres. This has been achieved by a combination of techniques - stereoselective
synthesis and chromatography.
79,80
The stereoselective synthesis has utilized the
chiral mononuclear precursors D / L - [Ru(pp)
2
(py)
2
]
2+
81
and D / L - [Ru(pp)
2
(CO)
2
]
2+
/
[Ru(pp)(pp
)(CO)
2
]
2+
82
(pp and pp
),
which can undergo substitution under conditions which allow the retention of the
chiral integrity of the metal centre. The chromatographic technique has involved
cation exchange, in which the counteranion has been chosen so that it differentially
associates with the stereoisomers to be separated.
83 - 85
The technique has allowed
the routine separation of diastereoisomers,
86 - 91
the resolution of enantiomers,
86,89,90
the separation of geometric isomers
89,92
and the separation of chiral helical forms.
93
The combination of the stereoselective and chromatographic techniques has been
used for the separation of stereoisomers of dinuclear and trinuclear species.
92,94,95
′
′
are bidentate polypyridyl ligands; pp
≠
pp
′
11.3.2 Interaction of Dinuclear Complexes with Duplex DNA
1
H NMR experiments with the D
L , D
D and
L
L stereoisomers of [{Ru(Me
2
bpy)
2
}
2
( m -
bpm)]
4+
(see Figure 11.4) demonstrated that the ruthenium(II) complexes bound
duplex DNA in the minor groove, but with relatively weak affi nity (
K
10
3
M
− 1
).
90
Given the relative dimensions of the metal complex and the DNA grooves, it was
somewhat surprising that the ruthenium complex bound in the minor groove: the
≈
MM
M
M
MM
meso
{
Λ∆
}
{
ΛΛ
}
rac
{
∆∆
}
Figure 11.4
A schematic representation of the three stereoisomers of a symmetric dinuclear
ruthenium complex
