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

The bifunctional Ru(II) complex [Ru(BPY)2POQ-Nmet]2+ (1), in which the metallic unit is tethered by an aliphatic chain to an organic DNA binder, was designed in order to increase the affinity toward nucleic acids. The interaction of 1 with DNA was characterised from luminescence and absorption data and compared with the binding of its monofunctional metallic and organic analogues, [Ru(BPY)2(ac)phen]2+ (2) and Nmet-quinoline (3). The bifunctional complex has a binding affinity one order of magnitude higher than that of each of its separated moieties. Absorption changes induced upon addition of DNA at different pH indicate protonation of the organic sub-unit upon interaction with DNA under neutral conditions. The combination of the luminescence data under steady-state and time-resolved conditions shows that the attachment of the organic unit in 1 induces modifications of the association modes of the metallic unit, owing to the presence of the aliphatic chain which probably hinders the metallic moiety binding. The salt dependence of the binding constants was analysed in order to compare the thermodynamic parameters describing the association with DNA for each complex. This study demonstrates the interest of the derivatisation of a Ru(II) complex with an organic moiety (ia the bifunctional ligand POQ-Nmet) for the development of high affinity DNA probes or photoreactive agents.

Experimental and density functional theory study of the vibrational properties of 2-mercaptobenzimidazole in interaction with gold

The vibrational properties of the 2-mercaptobenzimidazole (MBI) molecule in interaction with gold were examined by a combined approach of FTIR measurements and density functional theory (DFT). A complete assignment of the 42 normal modes of MBI has been performed on the basis of DFT calculations at the B3PW91 level in complement to the Raman and FTIR spectra. Calculations demonstrated that, on the deprotonated MBI molecule, the negative charge is localized on the sulfur atom, favoring the formation of a gold-sulfur bond upon reaction of MBI with gold. This was confirmed by the very good agreement between the calculated spectrum and the experimental spectra of different gold-MBI compounds, indicating that the vibrational properties of adsorbed MBI are chiefly determined by the coordination through the sulfur atom. © 2006 American Chemical Society.