Interaction of Ru(II) Complexes
reproduced from N.
Turro, J. Barton and D. Tomalia, Acc. Chem. Res., 1991,
Three modes of association between metal complexes and DNA
are generally distingished :
External binding Groove binding Intercalation
Clicking on one of the complex will bring
you to more information about the association mode represented.
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External association of the complexe in the atmosphere of
ions of the DNA polyelectrolyte.
This association is electrostatic in nature (Ru(II) complexes
are 2+ positively charged and the DNA phosphate sugar backbone
is negatively charged). This association mode was proposed for
[Ru(BPY)3]2+ as the luminescence
enhancement of this complex upon binding to DNA is strongly dependent
on the ionic strenght. Cations as Mg2+ usually interacts also
in this way.
J. Kelly, A. Tossi, D. McConnell, Oh
Uigin, Nucl. Acids Res., 1985, 13, 6017
Adsorption of the complexe in the DNA grooves.
The molecules approaches within van der Waals contact and resides
in the DNA groove. Hydrophobic and/or hydrogen-bonding are usually
important components of this binding process, and provide stabilisation.
The antibiotic netropsin is a model groove-binder (to see the
X-ray structure of this
groove-binder click on the molecule). Geometric and steric
factors also play a role as shown with [Ru(TMP)3]2+
(TMP = 3,4,7,8-tetramethyl phenanthroline) where the methyl groups
H. Mei, J. Barton, J. Am. Chem. Soc.,
1986, 108, 7414
Intercalation of a planar ligand of the complex in the DNA
base pairs stack.
This association involves the insertion of a planar fused aromatic
ring system between the DNA base pairs, leading to significant
p-electron overlap. This mode of binding
is stabilised by stacking interactions and is thus less sensitive
to ionic strenght relative to the two other binding modes. This
mode of binding is usually favoured by the presence of an extended
fused aromatic ligand as PHEHAT  or DPPZ .
Indeed with less extended aromatic systems, the intercalation
is usually prevented through clashing of the ancillary ligands
with the phosphodiester backbone, so that only partial intercalation
can occur as it is the case for [Ru(phen)3]2+ .
find more information concerning the potential application, i.e.
the light switch effect, of PHEHAT complexes in another part of
the introduction concerning the photoprobes.
A battery of complementary methods is necessary to determine
the binding modes of a complex to DNA. These methods can be used
to evidence the effect of association of the complex on
the properties of DNA or/and on the
properties of the complex itself.
Particularly, intercalation can be evidenced by
 C. Moucheron, A. Kirsch-De Mesmaeker,
J. Physical Organic Chemistry, 1998, 11,
 I. Haq, P. Lincoln, D. Suh, B. Norden,
B. Chowdhry, J. Chaires, J. Am. Chem. Soc., 1995,
 P. Lincoln, B. Norden, J. Phys. Chem.
B, 1998, 102, 9583-9594
 J. Coury, J. Anderson, L. McFail-Isom,
L. Williams, L. Bottomley, J. Am. Chem. Soc., 1997,
 P. Lincoln, A. Broo and B. Norden, J.
Am. Chem. Soc., 1996, 118, 2644-2653
A. Tossi, J. Kelly, Photochemistry and Photobiology, 1989,
 G. Orellana, A. Kirsch-De Mesmaeker,
J. Barton and N. Turro, Photochemistry and Photobiology,
1991, 54, 499-509
 M. Eriksson, M. Leijon, C. Hiort, B.
Norden, A. Gräslund, JBiochemistry, 1994, 33,
Note that for metal complexes, binding
modes may be more complicated than
for organic molecules, and that neither intercalation, nor groove
binding are unambiguous concepts but rather names used to denominate
a group of DNA binding modes having important common features.
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