The effect of ionic strength of helix-coil transitions in nucleic acid

The thermal denaturation of the nucleic acid is considered as a first-order phase change, the transition temperature of which is determined only by the ionic strength of the solvent and the free energy. An equation is derived which relates the transition temperature to ΔG_E, the differene in electrostatic free energy between the native and denatured nucleic acids. The adoption of cylindrical models for both native and denatured nucleic acid enables ΔG_E to be estimated at various ionic strengths. Application of the theory then yields estimates for the enthalpy and entropy of denaturation and the free energy of the stabilising forces in the helix.