Recognition and characterization of binding modes of Δ- and Λ-[Ru(phen)_3]~2+ and Δ- and Λ-[Ru(phen)_2DPPZ]~(2+) by the ~(23)Na NMR relaxation and binding free energy parameters

摘要

~(23)Na 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, R_(2bB), and the relative polyelectrolyte contributions to the binding free energy, ΔG_(pe)/ΔG, was found. In particular for the intercalators Δ- and Λ-[Ru(phen)_2DPPZ]~(2+), a direct dependence on ΔG_(pe)/ΔG was observed, as already found for ethidium, propidium and dq2pyp; while [Ru(phen)_3]~(2+) complexes and the pure electrostatic Mg~(2+) showed an inverse dependence. These results have been discussed in terms of the polyelectrolyte interactions responsible for the R_(2bB) changes.