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Evidence for interstrand DNA covalent binding of two dinuclear Ru(II) complexes. Influence of the extra ring of the bridging ligand on the DNA interaction and cytotoxic activity

In this work, we report experimental and computational evidences for the intercalation into the DNA base pairs of the free quinones Quinizarin (Q), Naphthazain (N) and the interstrad covalent binding of their p -cymene di-Ruthenium(II) complexes (Cl 2 Ru 2 X, with X = N, Q bridging ligands). The intercalation extent for the N complex was larger than for Q, in good agreement with higher relative contour length and melting temperature for the same C X /C DNA ratio and with the computacional mean stacking distances between the ligand and the nearest base-pair (3.34Å and 3.19Å) for N and Q, respectively. However, the apparent binding constant of Q/DNA, two orders higher than that of N/DNA, denotes that the thermal stability of X/DNA complex is more related to the degree of intercalation than to the binding constants magnitude. Cl 2 Ru 2 X complexes undergo aquation, forming the aqua-derivatives [(H 2 O) 2 Ru 2 X] 2+ . These can further bind covalently to DNA via interstrand crosslinking, through both Ru centres and two N7 sites of consecutive Guanines, to give (DNA 1,2 )Ru 2 X complexes, by a mechanism similar to that of cisplatin. To the best of our knowledge, this type of interaction with dinuclear Ru(II) complexes has not been reported hitherto. The experimental and computational results reveal that the number of rings of the aromatic moiety and the covalent