When the model polynucleotide poly(dG-dC)∙poly(dG-dC) [polyGC] is titrated with a strong acid (HCl) in unbuffered aqueous solutions containing the chlorides of the alkali metals in the concentration range 0.010 M-0.600 M, two transitions in the absorbance vs. pH plots are evidenced, characterized by the constants pK_a(1) and pK_a(2).

The limiting values at infinite saline concentrations of these two constants, namely pK^∞_a(1) and pK^∞_a(2) obtained making use of the “one site saturation constant” equation or, in turn, of the double logarithmic plot: pK_a vs. log([salt]^-1), exhibit a clear dependence on the nature of the cations.

The effects of the different alkali cations on the pK^∞_a values follow the Hofmeister series. In fact, the pK^∞_a(1) and the pK^∞_a(2) values are smaller for Li⁺ and Na⁺ than for Rb⁺ and Cs⁺, with K⁺ at the border between the two, showing that the transitions require higher concentrations of protons to occur in the presence of high concentrations of the cosmotropic ions.

Key words: Hofmeister effect; Alkaline cations; Model polynucleotides; UV-spectroscopy.

This article can be cited as:
Marta Airoldi, Giuseppe Gennaro, Marcello Giomini, Anna Maria Giuliani, Mauro Giustini. Effect of the Alkaline Cations on the Stability of the Model Polynucleotide Poly(dG-dC)∙Poly(dG-dC) J. Biomol Struct Dyn 29(3)585-594(2011).