[Study of the effect of halogen series anions on DNA molecular conformation in solution]

Effect of halogen-series anions (F-, Cl-, Br-, I-) in sodium, potassium and ammonium halogide solutions with ionic strengths of mu = 0.1, 0.01, and 0.005 M on the dimensions and thermodynamic rigidity of the DNA molecule in solution was studied by viscosimetry and flow birefrigence. Flow birefrigence measurements showed that close-range interactions along the macromolecular chain and accordingly the persistent length of DNA did not change with a change of anion. However, the specific volume of the molecule depends on the anion type. In our opinion, the observed effect is connected with the different ability of anions to "neutralize" the cation screening effect on DNA phosphates.