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SynopsisWe have studied the electrical conductivity of NaDNA solutions under "saltfree" conditions a t 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 a t which the usual denaturation processes and trans conformation may commence. The radio-frequency permittivity also exhibits a discontinuity a t the same temperature. For the premelting phase, the conductivity versus temperature curves consist of two linear regions with a change in slope occurring a t 23OC. 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.

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synopsisMeasuring the equivalent noise resistance of Na-DNA solutions in NaCl provides in formation about the free ion atmosphere. In an Arrhenius type diagram, the helix -+ coil transition is clearly brought out. A calculation of the number of free ions in the solution, as a function of temperature, reveals once more the process of ejection of compensating Na + ions from the macromolecules during the thermal transconformation.