THE INTERCALATION OF ETHIDIUM-BROMIDE IN THE CHROMONIC LYOTROPIC PHASES OF DRUGS AND NUCLEIC-ACIDS

Chromonic liquid crystalline phases are formed by a variety of drug an d dye/water systems. In contrast to conventional lyotropic phases (whe re micelle formation underlies the mesogenic properties), in chromonic systems the molecules stack in columns. The different chromonic phase s are different arrangements of these columns. We have examined the so lution of ethidium bromide (EB) in the well-documented chromonic Intal /water system. EB is a widely used nucleic acid stain which changes co lour when intercalated into DNA and which becomes fluorescent. We have charted the changes in the temperature/composition phase diagram of t he Intal/water system caused by adding EB. Although there are changes in the position of the phase boundaries, the overall pattern remains q ualitatively the same-implying that the host phase is accepting EB as a similar chromonic molecule. The intercalation of EB molecules in the chromonic host phase results in optical effects-a metachromic colour change and fluorescence, similar to those occurring when the dye stain s DNA. These observations strengthen our belief that the central stack of bases in DNA can be regarded as being chromonic in nature.