Zeta potentials of fluoride anion result in the instability of DNA hairpin

High dose intake of fluoride results in fluorosis and our previous experiments at single-molecule level using magnetic tweezers have proved that fluoride anions destabilize DNA hairpin and its equilibrium critical force decreases with increasing concentration of fluoride anions. One possible mechanism is that a fluoride anion competes with a DNA base and forms a hydrogen bond with its complementary base. The Isothermal Titration Calorimetry experiments suggest that the fluoride anion does not form a hydrogen bond with a DNA base. With increasing concentration of fluoride anions, decreasing Zeta potentials for different oligonucleotides enhance the electrostatic repulsion between complementary oligonucleotides, which accounts for the decreasing association constant and destabilization of DNA hairpin. Molecule dynamics simulation was further performed to determine the ion distribution around the oligonucleotide, radial distribution functions (RDFs) indicate that the fluoride anion distributes far from the oligonucleotide in comparison with the chloride anion, which is the possible mechanism that decreases Zeta potentials with the increasing concentration of fluoride anions.