Interactions between drugs and nucleic acids. Part 1. Dichroic studies of doxorubicin, daunorubicin, and their basic chromophore, quinizarin

Abstract

The interpretation of the electronic spectra of complexes between DNA and antitumour drugs must rely on the knowledge of the directions of the transition moments of the drug chromophore. This paper reports the linear and circular dichroism studies (including magnetic c.d.) and semiempirical INDO/S calculations carried out in order to provide evidence for the directions of the transition dipole moments within the quinizarin chromophore present in the antitumour drugs daunorubicin and doxorubicin. The c.d. technique also demonstrated that these two drugs, in spite of the complex substitution pattern of the anthraquinone moiety, have the same sequence of u.v.–visible electronic transitions as the unsubstituted quinizarin. The partial orientation of the investigated molecules required to run their linear dichroism spectra was achieved by using liquid crystalline solvents (both thermotropic and aqueous lyotropic) according the modulated liquid-crystal–linear dichroism technique.