  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.
