Experimental studies of thermal denaturation of the Na-DNA system with respect to manning's model

The sodium and chloride activity coefficients in DNA solution were measured by selective electrodes. These experiments were performed for native and thermally denatured DNA. The ratio of activities in helix and coil states were compared with those given by Manning's model. These results are in good agreement with the theoretical values. We also compare the experimental values of the charge parameter XXX of DNA in the helix (XXX h) and coil (XXX c) configurations with the theoretical parameters appearing in Manning's model and which have been adjusted to correspond with the known conformation of the molecule. From this comparison, we deduce the change of enthalpy (Δ H) T m at the temperature of denaturation ( T m) of DNA. The value of (Δ H) T m thus calculated is smaller than the theorstical value and comparable with that observed experimentally by Privalov et al.