[Effect of solvent structure on amide reaction with native DNA molecules. II. Aqueous acetamide mixtures]

The influence of acetamide (AA) on the native DNA molecule conformation has been studied by methods of flow birefringence and viscometry. On one hand, it was shown that hydrodynamical and optical behaviour of the macromolecule at extremely low additions of AA is qualitatively the same as in the presence of nonelectrolytes which stabilize the water structure. On the other hand, the influence of intermediate and large AA concentrations on the native DNA molecule conformation is qualitatively the same as of corresponding urea concentrations, which is known to be a structure-breaker. The influence of AA on the thermostability of the native DNA molecule as well as on the stacking-association constant of adenosine has been studied by a spectrophotometric method. The obtained data confirm the hypothesis of the importance of ion-dipole interactions between nonelectrolytes and the phosphate groups of the DNA molecule.