23Na NMR study of DNA thermal transconformation in presence of cysteamine radioprotector.

DNA thermal transconformation is studied in absence and in presence of the cysteamine radioprotector, by observing the delta nu 1/2 variation of 23Na NMR peaks. The sodium state (Free or Bound) is discussed with the help of a two states model with RF and RB relaxation rates. The delta nu 1/2 behaviour during the DNA transconformation shows clearly the electrostatic interaction with cysteamine which is accompanied by an Na+ ejection out of phosphate sites. The temperature dependence of delta nu 1/2 in all cases leads to the conclusion that RBc (the average relaxation rate of sodium nuclei that remain bound in the coil state of DNA) tends to zero.