Quantitative analysis of the effect of derivatisation of with a quinoline moiety on the [Ru(BPY)(2)phen](2+) with a quinoline moiety on the interaction with DNA

The bifunctional Ru(II) complex [Ru(BPY)(2)POQ-Nmet](2+) (1), in which the metallic unit is tethered by an aliphatic chain to an organic DNA binder, w as designed in order to increase the affinity toward nucleic acids. The int eraction of 1 with DNA was characterised from luminescence and absorption d ata and compared with the binding of its monofunctional metallic and organi c analogues, [Ru(BPY)(2)(ac)phen](2+) (2) and Nmet-quinoline (3). The bifun ctional complex has a binding affinity one order of magnitude higher than t hat of each of its separated moieties. Absorption changes induced upon addi tion of DNA at different pH indicate protonation of the organic sub-unit up on interaction with DNA under neutral conditions. The combination of the lu minescence data under steady-state and time-resolved conditions shows that the attachment of the organic unit in 1 induces modifications of the associ ation modes of the metallic unit, owing to the presence of the aliphatic ch ain which probably hinders the metallic moiety binding. The salt dependence of the binding constants was analysed in order to compare the thermodynami c parameters describing the association with DNA for each complex. This stu dy demonstrates the interest of the derivatisation of a Ru(II) complex with an organic moiety (via the bifunctional ligand POQ-Nmet) for the developme nt of high affinity DNA probes or photoreactive agents.