DNA Persistent Length in Solutions of Different pH

In this study, the changes in the DNA native conformation induced by pH changes in the alkaline and acidic regions were examined. It was shown by the methods of low gradient viscometry and flow birefringence that protonation and deprotonation of nitrogen bases inside the double helix cause a change in the persistent length of DNA. The pK values shift with the change in the ionic strength of the solution (NaCl concentration). The additional charges appearing on the DNA bases are not shielded by counterions from the solution. The increase and decrease in the volume of the DNA coil in solution resulting from protonation and deprotonation of base pairs, respectively, are mainly determined by changes in the persistent length of the macromolecule. The stability of the double-helical conformation of DNA ensures the steadiness of the equilibrium rigidity of this macromolecule. The emergence of charges on the bases, resulting from DNA protonation or deprotonation, weakens and even disrupts the hydrogen bonds between complementary bases. However, at the first stage, this occurs without altering the stacking interactions of base pairs, as reflected in the absorption spectra of DNA and in the stability of the DNA persistent length at different pH levels.