reproduced from Scientific American, September 1996, 275 (3)

This poster contribution is entitled "Probing stereospecific interaction with DNA". This represent our final objective and the topics discussed herein concern the synthetic strategies we applied in order to obtain new optically pure Ru(II) complexes designed to reach this goal.

The figure above was published a few years ago in a special issue of Scientific American about Cancer. One of the articles emphazised the importance of understanding the fundamental processes at the origin of the pathology. Particularly the study of the genetic material, DNA, requires the development of new molecular tools, as photoprobes and also of new active agents. In this field Ru(II) complexes are extensively studied.

This introduction is divided in several chapters presented on this page as thumbnails. Clicking on the different schemes and figures will lead you to full size pictures and to more comments and references. You can come back to this introduction page by using the links or browsing the back button.

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I. Photophysical Properties of Ru(II) Complexes

Ru(II) complexes are particularly well suited to study DNA as they present :

a strong absorption (Metal to Ligand Charge Transfer) in the visible range. The Ru(II) complexes can be irradiated by visible light, without affecting DNA which absorbs in the U.V.

an intense and environment-sensitive luminescence from their triplet 3MLCT state. A long luminescent lifetime increases the probability of reaction in the excited state and is an advantage in designing photoprobes also as it is easily detected.

due to the diversity of ligand accessible, the size, shape and hydrophobicity together with their spectroscopic characteristics, photophysics, and photochemistry (redox properties), may be easily tuned.

stable enantiomers which enables the potential use of these complexes as stereoselective probes.

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II.1. Interaction of Ru(II) Complexes and DNA

A large number of molecules are known to interact with DNA. The study of these interactions plays a significant role in the future development of new molecular tools and active agents. Some Ru(II) complexes are part of this category of compounds.

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Three modes of association between metal complexes and DNA are generally distingished :

External binding         Groove binding         Intercalation

and these different modes of binding can be favoured (again) by a judicious choice of the ligands which allows to modify the shape and hydrophobicity of the resulting complexes.

II.2. Photoreaction of Ru(II) Complexes and DNA

In our laboratory, Ru(II) complexes bearing p-deficient ligands such as TAP (=1,4,5,8-tetra-azaphenanthrene) were designed as photoreactive agents towards DNA. These complexes are able to form a "photo-adduct" with DNA, i.e. to form a covalent bond with a desoxyribonucleic base of DNA under visible illumination. This kind of photoreactions could be at the origin of biomedical applications.

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II.3. Usefull Photoprobes

The photophysical properties described in part I of this introduction are particularly convenient to design Ru(II) complexes as photoprobes of the genetic material. In this part, potential applications are described such as the light switch effect (first scheme) and the chiral recognition of secondary structure of DNA (second scheme).

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II.4. Chirality of Ru(II) Complexes

The octahedral geometry of Ru(II) complexes induces their chirality. The Ru(II) center complexed with 3 bidentate ligands present two different enantiomers as represented on this figure. The same chirality is present with complexes having two monodentate ligands in cis position such as [Ru(TAP)2(pyridine)2]2+, one of the complexes we tried to resolve in its enantiomers.

The left handed enantiomer or L   The right handed enantiomer or D

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