DNA Binding Properties of Sc(III) Complexes Derived from Rare-earth(iii) Ions and Semicarbazone of 8-hydroxyquinoline-2-carbaldehyde

The complex [ScL₂(NO₃)]₂ was prepared by Sc(NO₃)₃ · 6H₂O with 2-[(8-hydroxyquinolinyl)methylene]hydrazinecarboxamide (LH), and characterized by X-ray structure analysis (СIF file CCDC no. 1502531), where ligand L acts as a tetradentate ligand, binding to Sc(III) through the phenolate oxygen atom, nitrogen atom of quinolinato unit, the C=N group and O=C(NH₂)–N– group, and forming a Sc(III) complex with 1 : 2 metal to ligand stoichiometry, also forming two almost orthogonal ligand planes by eight-coordination at Sc(III) center with geometry of double-capped triangular prism. In addition, one free nitrate ion as charge-balance anion is found in the crystal cell. Then a series of rare-earth(III) complexes were prepared by M(NO₃)₃ · 6H₂O with ligand LH, where M(III) = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and their DNA binding properties were investigated. It’s found that these rare-earth(III) complexes could bind strongly to calf thymus DNA (CT-DNA) by the mode of intercalation with the binding constants at 10⁴–10⁵ M^–1, compared to ethidium bromide (EB), especially Sc(III) and Gd(III) complexes present stronger DNA binding properties than the others, while ligand LH presented a higher DNA binding property than its complexes. Moreover, cell cytotoxicity assay showed that uterine cervix carcinoma cell line (HeLa) presented low viabilities in the present of LH and representative complexes, and a concentration dependence, especially LH presents a higher inhibitory ability on HeLa cell viability than its complexes at lower concentration, which is consistent with the results of their DNA binding abilities.