Recognition and characterization of binding modes of Δ- and Λ-[Ru(phen)3]2+ and Δ- and Λ-[Ru(phen)2DPPZ]2+ by the NMR relaxation and binding free energy parameters

Na-23 NMR relaxation rates were measured in Na-DNA aqueous solutions in the presence of Delta- or Lambda-enantiomer of [Ru(phen)(3)](2+) and [Ru(phen)(2)DPPZ](2+). From the analysis of the spin-lattice and spin-spin relaxation rates evidence is given that a decrease of the quadrupolar coupling constant for the slow motions occurs, due to the structural and dynamical modifications of DNA induced by the binding of the ruthenium complexes. Furthermore a linear dependence between the changes of the broad component, R-2bB, and the relative polyelectrolyte contributions to the binding free energy, Delta G(pe)/Delta G, was found. In particular for the intercalators Delta- and Lambda-[Ru(phen)(2)DPPZ](2+), a direct dependence on Delta G(pe)/Delta G was observed, as already found for ethidium, propidium and dq2pyp; while [Ru(phen)(3)](2+) complexes and the pure electrostatic Mg2+ showed an inverse dependence. These results have been discussed in terms of the polyelectrolyte interactions responsible for the R-2bB changes.