Premelting effects in DNA under saltfree conditions

We have studied the electrical conductivity of NaDNA solutions under “saltfree” conditions at temperatures well below the melting point of DNA, using radio‐frequency dielectric and noise measurements. A conductivity discontinuity is observed at a temperature well below that at which the usual denaturation processes and trans conformation may commence. The radio‐frequency permittivity also exhibits a discontinuity at the same temperature. For the premelting phase, the conductivity versus temperature curves consist of two linear regions with a change in slope occurring at 23°C. This effect is related to the behavior of the ionic sheath covering the DNA macromolecule. The activation energy of the alternative current conductivity as well as that the equivalent noise conductivity results as 3.11 kcal/mole below and 4.08 kcal/mole.