The stoichiometric complexes of the DNA samples of rather different molecular masses:  300−500 b.p. (DNA1) and 5000−10000 b.p. (DNA2) with dodecyldimethylammonium (DODA) chloride as a cationic amphiphile were prepared. DNA1−DODA and DNA2−DODA complexes are soluble in low polar organic solvents, in particular, in chloroform, as well as the complexes of ordinary linear polyelectrolytes with micelle-forming ionic surfactants. The solution behavior of the DNA−DODA complexes was studied by ultracentrifugation, viscometry, isothermal diffusion, and electrical birefringence techniques. It has been found that the DNA−DODA complex species in their dilute solutions in chloroform and a chloroform−acetone mixture (2:1) are represented by individual complex macromolecules retaining a double spirality, but strongly compacted. The latter is contrasting with other polyelectrolyte−surfactant complexes, which behave in chloroform as in a good solvent, taking expanded random coil conformations. The possible reason of such a basic difference is discussed and considered to be the result of an inherent tendency of the DNA double helix to be compacted if not ionized. This tendency has been detected due to a unique compromise between the thermodynamic solubility and complete electric neutrality of DNA−surfactant complex macromolecules in low polar organic solvent.

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