| Summary: | Ruthenium(II) arene complexes of the general formula [RuCl(η<sup>6</sup>-<i>p</i>-cymene)(diamine)]PF<sub>6</sub> (diamine = 1,2-diaminobenzene (<b>1</b>), 2,3-diaminonaphthalene (<b>2</b>), 9,10-diaminophenanthrene (<b>3</b>), 2,3-diaminophenazine (<b>4</b>), and 1,2-diaminoanthraquinone (<b>5</b>) were synthesized. Chloro/aqua exchange was evaluated experimentally for complexes <b>1</b> and <b>2</b>. The exchange process was investigated theoretically for all complexes, revealing relatively fast exchange with no significant influence from the polycyclic aromatic diamines. The calf thymus DNA (CT-DNA) binding of the complexes increased dramatically upon extending the aromatic component of the diamines, as evaluated by changes in absorption spectra upon titration with different concentrations of CT-DNA. An intercalation binding mode was established for the complexes using the increase in the relative viscosity of the CT-DNA following addition of complexes <b>1</b> and <b>2</b>. Theoretical studies showed strong preference for replacement of water by guanine for all the complexes, and relatively strong Ru–N<sub>guanine</sub> bonds. The plane of the aromatic systems can assume angles that support non-classical interactions with the DNA and covalent binding, leading to higher binding affinities. The ruthenium arenes illustrated in this study have promising anticancer activities, with the half maximal inhibitory concentration (IC<sub>50</sub>) values comparable to or better than cisplatin against three cell lines.
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