Liquid-crystalline phases formed by DNA duplexes containing pyrophosphate groups

We have studied the interaction between synthetic DNA molecules containing pyrophosphate (PP) groups in various positions, which makes it possible to control the charge distribution along the DNA chain. The PP groups were either symmetrically arranged at the ends or at the center of DNA molecules or uniformly distributed along these molecules. It is shown that, similar to nonmodified DNA, the synthetic PP-modified DNA molecules can form cholesteric liquid crystals. Minima of the pair interaction potential are found, conditions of the symmetry of this potential are formulated, and the dependence of conformation angles on the effective charge is determined. The results of calculations show that the system exhibits polymorphism (i.e., several phases of cholesteric liquid crystals can exist in DNA solutions).