The EB-DNA Liquid Crystalline Complex with High Concentration of Mg2

The effects of ethidium bromide (EB) on the DNA cholesteric phase in the high ionic strength of Mg 2+ were investigated by polarized optical microscopy (POM), 31 P and 23 Na nuclear magnetic resonance (NMR). It was found that the cholesteric pitch in the EB-DNA cholesteric phase is obviously smaller than that in the EB-free DNA cholesteric solutions with the same ionic strength of Mg 2+ at room temperature. The fraction of liquid crystal phase in both the EB-free and the EB-DNA solutions is decreased with increasing the Mg 2+ concentration. But the fraction of liquid crystal phase in the EB-DNA solutions is higher than that in the EB-free DNA solutions at the same Mg 2+ concentration, which is attributed to the change of the surface charge distribution on the DNA chains and the stiffness of DNA due to intercalation of EB. The results of the 23 Na NMR experiments suggested that the intercalation of EB results in the changes of the ionic environment close to the DNA chains, by which the liquid crystal behavior of DNA is affected.