ABSTRACT
The second way for ordering rigid, linear, low-molecular-mass nucleic acid molecules is the phase exclusion of these molecules from water-salt solutions because of the “correlation interaction” (attraction) [1,2] between nucleic acid segments whose phosphate group negative charges are neutralized with positively charged counterions. Since the moving force of this process is the change in the enthalpy of the system, this way of phase exclusion is called an “enthalpy condensation.” For realization of this process, the polycations that neutralize a large number (80-90%) of negative charges of nucleic acid phosphate groups are needed. Then the attraction between the nucleic acid (NA) molecules becomes strong enough to induce a spontaneous condensation. The attraction forces at condensation are mostly electrostatic (electrodynamic) by nature, including the London dispersion forces and the dipole-induced dipole interaction. These forces, which are relatively small at long distances between NA molecules, increase sharply as the NA molecules approach one another, while the attraction energy increases as 1/r5. The value of the dispersion force is proportional to the Hamaker empiric constant A, which is ~4 × 10-14 erg for organic molecules interacting in water, that is, about 1 kT at room temperature. For the attraction at a distance of approximately 30Å, the value of A varies from 2 to 5 kT.
