The effects of Mg 2+, Ca 2+, Mn 2+, Co 2+ and Ni 2+ on the thermal stability of Salmon Sperm DNA were investigated by employing differential scanning calorimetry method. For the divalent cations, the shielding effect plays the dominant role in the interaction of nucleic acid chains when they are in low concentrations, as reflected in the moderate increasing of DNA melting temperature. Along with increasing concentration, both alkaline earth metal ions and transitional metal ions were found to lower the DNA melting temperature, indicating possible direct interaction between the divalent cations with the bases in the DNA molecules. The effectiveness increases with the order Mg 2+, Ca 2+, Mn 2+, Co 2+ and Ni 2+. It was found for the first time that the presence of Mn 2+ triggered the biphasic-melting behavior of the Salmon Sperm DNA when the concentration of the cation was increased to a value about 2 times of phosphorous in DNA.
