Circular dichroism of DNA: Temperature and salt dependence



The temperature dependence of the circular dichroism and ultraviolet absorbance of calf thymus DNA and poly dAT were measured in aqueous solutions of various 1–1 electrolytes. Although there was very little change in absorbance, the circular dichroism changed dramatically as a function of both temperature and solvent. There is a correlation of the heat of hydration of the cation and the magnitude of the temperature dependence of the circular dichroism. Our results are interpreted in terms of a large number (possibly a continuum) of intermediate secondary structures.