Synthesis of Novel Aromatic Nitroxides as Potential DNA Intercalators. An EPR Spectroscopical and DFT Computational Study

The synthesis and electron paramagnetic resonance (EPR) spectroscopic properties of three novel aromatic nitroxides and potential DNA intercalators, the carbazole-based 3,6-dimethylcarbazole-9-oxyl, as well as the acridane-based 9-acridanylidenemalonitrile-10-oxyl and 9-ethylacridanylidenecyanoacetate-10-oxyl, are described. The two acridane-based nitroxides can be isolated and are stable in solution as well as in the solid state for several days. Continuous wave X-band EPR measurements and density functional theory (DFT) calculations demonstrated that the spin density is delocalized over the whole molecule in all three cases. Furthermore, the DFT calculations provided insight into the molecular and electronic structures of these nitroxides and yielded hyperfine coupling constants which are in very good agreement with the experimental data allowing therefore an unambiguous assignment of the hyperfine couplings.