Thermostability of DNA Complexes with Mitoxantrone at Small Fillings

Thermostability of DNA complexes with anti-tumorous compound — mitoxantrone — at 0.011M and 0.11 M NaCl ionic strengths of solution by spectrophotometric and microcalorimetric methods has been studied. It was shown that at small fillings when one molecule of mitoxantrone corresponds to 250 or more base pairs of DNA, the thermostability of complexes strongly depends on the solution’s ionic strength; moreover, at an ionic strength of 0.011 M NaCl the melting temperature dependence on mitoxantrone concentration passes through a minimum. In the mentioned region of mitoxantrone concentration the melting enthalpy of the complexes increases linearly with mitoxantrone concentration enhancement. The observed phenomenon, which is not observed for ethidium bromide complexes with DNA, is qualitatively explained by the increasing of coil-shaped state of DNA–mitoxantrone complex due to additional freedom of rotation of mitoxantrone side groups.