A mesophase (liquid crystal) state of DNA complexes with anthracycline antibiotics

In the presence of polyethyleneglycol water-salt solutions, DNA is condensed to a kind of mesophase (liquid crystals). The peculiar properties of this phase caused by anisotropic orientations have been analyzed by circular dichroism (CD) of condensed particles of DNA complexed with dyes, i.e. anthracycline antibiotics (daunomycin, aclacinomycin A), actinomycin, and ethidium bromide. The anthracycline complexes show intense CD bands in the visible and the UV region. Daunomycin induces a typical reversal of the sign of these CD bands with increasing occupation of the double helix contrary to the other ligands. This characteristic effect and its partial reversal after removal of daunomycin from the condensed particles can be the result of the change of the direction of the mesophase helical twist owing to an energy change of interaction between DNA molecules, and partially to a modification of base-plane inclination (tilt), too. This new type of DNA complex state is characterized in detail.