Recognition and characterization of binding modes of Δ- and Λ-[Ru(phen)3]2+ and Δ- and Λ-[Ru(phen)2DPPZ]2+ by the 23Na NMR relaxation and binding free energy parameters Original Research Article

23Na NMR relaxation rates were measured in Na–DNA aqueous solutions in the presence of Δ- or Λ-enantiomer of [Ru(phen)3]2+ and [Ru(phen)2DPPZ]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, R2bB, and the relative polyelectrolyte contributions to the binding free energy, ΔGpe/ΔG, was found. In particular for the intercalators Δ- and Λ-[Ru(phen)2DPPZ]2+, a direct dependence on ΔGpe/ΔG 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 R2bB changes.