Lithium ion induced stabilization of the liquid crystalline DNA

A comparative study of the effects of alkali metal ions Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺ on the liquid crystalline organization of high-molecular-weight calf thymus DNA using polarized light microscopy was performed. Major differences in the behavior of Li⁺ as compared to the other ions were found. Critical DNA concentration expected to exhibit anisotropic behavior was found to be the same for all the monovalent ions, except for Li⁺. DNA initially showed cholesteric textures, which later changed to higher ordered columnar phase for all ions, with the cholesteric-columnar transition facilitated upon increasing the size of the counter-ion. For Li⁺ ion, a nematic schlieren-like texture was formed initially, which after a few days changed to a highly stable (for more than 2 months) biphasic cholesteric-columnar arrangement. The observed differences between Li⁺ and other alkali metal ions could be rationalized on the basis of the higher number of hydration water molecules of Li⁺ and its complexation behavior. Highly stable DNA mesophases may find applications in the field of nanoelectronics, in designing biosensing units, and in DNA chips.