[Volume effect and change in compressibility in intercalation of ethidium bromide and daunomycin in DNA]

A combination of high-precision and density techniques was used to investigate the binding of ethidium bromide and daunomycin to DNA. It was shown that intercalation is accompanied by a decrease in apparent volume and adiabatic compressibility of DNA, which were -28 cm3mol-1 and -20.10(-4) cm3mol-1bar-1 for binding of ethidium to DNA, and -28 cm3mol-1 and -18.10(-4) cm3mol-1bar-1 for daunomycin, respectively. The values obtained have been compared with those of the hydration contributions of atomic groups to the apparent molar volume and apparent molar compressibility of the ligands as well as the contribution of intrinsic compressibility of DNA. The volume effects in the intercalation of ligands correspond to the values expected for the dehydration of aromatic heterocyclic rings. On other hand, negative compressibility changes may be explained by a decrease of the intrinsic compressibility of DNA and possible increase of its hydration as result of conformational changes upon ligand binding.