synopsisThe 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.

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