Differential stability of DNA based on salt concentration

Intracellular positive ions neutralise negative charges on the phosphates of a DNA strand conferring greater strength on the hydrogen bonds that connect complementary strands into a double helix and so confer enhanced stability. Beyond a certain value of salt concentration, the DNA molecule displays a unstable nature {\it in vivo} as well as {\it in vitro}. We consider a wide range of salt concentrations and study the stability of the DNA double helix using a statistical model. Through numerical calculations we attempt to explain the different behaviour exhibited by DNA molecules in this range. We compare our results with experimental data and find a close agreement.