| Abstract: | The thermal effect of magnesium ions on the helix–coil transition of DNA was studied calorimetrically by a modified differential scanning calorimeter (DSC). It was found that the transition temperature of DNA depends on both the DNA and magnesium ion concentrations. The dependence of the helix–coil transition of DNA on the mole ratio of magnesium ions to DNA(P) can be classified into two groups. When this mole ratio is less than 1, magnesium ions tend to stabilize the double-helix DNA, so that the transition temperature increases linearly and the heat of transition increases significantly with increasing mole ratio. When the mole ratio is more than 1, magnesium ions tend to destabilize the double-helix DNA, so that DNA precipitates when the temperature is raised above the transition temperature. In this case, both the transition temperature and the heat of transition decrease with increasing mole ratio. |
