Interaction of Mg2+ with DNA investigated by dielectric spectroscopy

Abstract Divalent ions, as Mg 2+ , strongly interact with polyelectrolytes, in particular with DNA and this binding involves two phosphate groups. In our laboratory we studied this interaction by dielectric spectroscopy. At radiofrequencies DNA shows a well-defined dielectric relaxation, due to monovalent counterion oscillations along the surface of the biopolymer. The dielectric response of the biopolymer is thus modified by the interaction with magnesium. In this communication we report on measurements at radiofrequencies, performed on Na-DNA aqueous solutions in the presence of increasing amounts of Mg 2+ ions. The dielectric relaxation is reduced as the magnesium content increases. This effect tends to saturate when the molar ratio Mg 2+ /nucleotide approaches the value of 0.25. A significant parameter i.e. length of the biopolymer subunit, estimated by dielectric relaxation time, appears to be modified, denoting also the existence of a structural effect. This new approach proved to be a valid tool in studying interaction processes among nucleic acids and divalent ions or, in general, charged macromolecules.