RESONANCE RAMAN SPECTRA AND TRANSFORM ANALYSIS OF ANTHRACYCLINES AND THEIR COMPLEXES WITH DNA

The absorption, second-derivative and resonance Raman spectra of some anthracyclines, namely idarubicin, epirubicin and 11-deoxycarminomycin in H2O and D2O solutions, and their complexes with DNA in H2O solutions, were measured. Transform analysis that links resonance Raman band intensities to resonant absorption was applied to idarubicin, epirubicin and their complexes with DNA to obtain the Franck-Condon factors. The results allowed us to provide details on the nature of the resonance Raman active modes, the mechanism of their resonant enhancement and the chromophore-DNA interaction. In particular, an interpretation involving excited-state charge transfer, associated in some cases with excited-state proton transfer, is proposed. This helps to rationalize the observed variations of the intensities of Raman-active modes of free anthracyclines in terms of variation of the transition moment direction. The intercalation of the chromophore among the DNA base pairs induces, via excitonic interactions, a change in both the magnitude and the direction of the transition moment of the chromophore.