Theoretical and spectroscopic evidence for coordination ability of 3,3′-benzylidenedi-4-hydroxycoumarin. New neodymium (III) complex and its cytotoxic effect

Theoretical and spectroscopic studies of 3,3′-benzylidenedi-4-hydroxycoumarin (bhc) have been performed. B3LYP/6-31G* calculations reproduced the experimental molecular structure of bhc and showed two O-H⋯O asymmetrical intramolecular hydrogen bonds with O⋯O distances 2.638 and 2.696 Å. The calculated Fukui functions and Molecular Electrostatic Potential for bhc and its deprotonated form, bhc2-, predicted that the most probable reactive sites for electrophilic attack and hydrogen bonds are the carbonyl oxygens, followed by the hydroxyl oxygens. The coordination ability of 3,3′-benzylidenedi-4-hydroxycoumarin has been proved in a complexation reaction with neodymium (III) ion. The new neodymium (III) complex of bhc was studied by elemental analyses, conductivity and other physical properties, mass spectra, 1H, 13C NMR, UV-Vis and IR spectroscopy. The data obtained are in agreement with the metal:ligand ratio of 1:1, and the formula Nd(bhc2−)(OH)(H2O), where bhc2-C25H14O62-. The vibrational analysis of the neodymium (III) complex, free bhc, and its monomeric building block, 4-hydroxycoumarin, showed that in the Nd(III) complex the ligand coordinates to the metal ion through both deprotonated hydroxyl groups. The participation of both carbonyl groups in coordination to the metal ion was confirmed by the significant shift of ν(CO) to lower wavenumber. The evaluation of the cytotoxic activity of the new Nd(III) complex on SKW-3 and HL-60/Dox cells revealed, that it is a potent cytotoxic agent and should be subset further to more detailed pharmacological and toxicological study.