Calorimetry of DNA-dye interactions in aqueous solution I. Proflavine and ethidium bromide.

The results of an investigation on the interaction of proflavine and of ethidium bromide with DNA (calf thymus) in dilute aqueous solution are reported. The binding of the two dyes by DNA has been studied by means of microcalorimetric and of equilibrium dialysis measurements. Data on the thermodynamics of dimerization of both proflavine and ethidium bromide in aqueous solution obtained on the basis of spectroscopic and/or calorimetric experiments are also reported. The enthalpy data show that dye-dimerization and dye "strong" interaction with DNA are energetically favourable and quite similar while only in the latter case the phenomenon is also entropy driven. This is taken as further evidence in support of the concept that "strong" interaction-of both proflavine and ethidium bromide with DNA means dye molecules intercalation into the native, double helical structure of the biopolymer.