Synthesis, spectroscopic, theoretical study, and biological activities of vanadium(IV) and vanadium(V) complexes with isonipecotic acid

Vanadium(IV) and vanadium(V) complexes 1–7 have been synthesized by the reaction of isonipecotic acid with VOSO4 · 3 H2O, VCl3(THF)3, and NH4VO3 at different metal/ligand ratios under stirring/ reflux conditions. The synthesized complexes have been characterized by elemental analyses and UV/Vis and FT-IR spectra. The FT-IR spectroscopic data suggest bidentate nature of the ligand, which is also confirmed by semiempirical study. Electrostatic surface potential (ESP) map shows that the coordinating oxygen atoms in complex 1 have more negative charges than the V=O oxygen atom. The dipole moment vectors of the optimized structures of complexes 1 and 5 are not aligned along the V=O bond due to the lack of symmetry. DNA binding study of complexes 1–7 showed that increase of the DNA concentration is accompanied by considerable decrease of the absorbance and by a 1–4-nm blue shift of the absorption maximum, indicating intercalative binding mode of the complexes to the DNA base pairs. In vitro DNA damage protection assay showed that complexes 1 and 3 exhibited plasmid DNA protection by scavenging oxidation products.