Effect of ionic ordering in conductivity experiments of DNA aqueous solutions

TL;DR

This study investigates how ionic ordering affects the electrical conductivity of DNA aqueous solutions with varying KCl salt concentrations and temperatures, revealing the role of counterion behavior and complex formation.

Contribution

The paper introduces a phenomenological model based on electrolyte theory that explains ionic ordering effects and counterion mechanisms in DNA solutions with salt.

Findings

Conductivity is higher in DNA solutions without salt below 0.4 M salt concentration.

Above the critical concentration, salt solutions exhibit higher conductivity than DNA solutions with salt.

Counterion condensation and complex formation influence the conductivity behavior.

Abstract

The effects of ionic ordering in DNA water solutions are studied by conductivity experiments. The conductivity measurements are performed for the solutions of DNA with KCl salt in the temperature range from 28 to 70 C. Salt concentration vary from 0 to 2 M. The conductivity of solutions without DNA but with the same concentration of KCl salt are also performed. The results show that in case of salt free solution of DNA the melting process of the double helix is observed, while in case of DNA solution with added salt the macromolecule denaturation is not featured. For salt concentrations lower than some critical one (0.4 M) the conductivity of DNA solution is higher than the conductivity of KCl water solution without DNA. Starting from the critical concentration the conductivity of KCl solution is higher than the conductivity of DNA solution with added salt. For description of the experimental data phenomenological model is elaborated basing on electrolyte theory. In framework of the developed model a mechanism of counterion ordering is introduced. According to this mechanism under the low salt concentrations electrical conductivity of the system is caused by counterions of DNA ion-hydrate shell. Increasing the amount of salt to the critical concentration counterions condense on DNA polyanion. Further increase of salt concentration leads to the formation of DNA-salt complexes that decreases the conductivity of the system.