A study of DNA/BSA interaction and catalytic potential of oxidovanadium(v) complexes with ONO donor ligands

The study of DNA/BSA interaction and the catalytic potential of four mononuclear oxidoalkoxido vanadium(v) [V^VO(L^1-4)OEt] (1-4) and one dinuclear oxidoalkoxido mixed-ligand vanadium(v) [{VO(L²)OEt}₂(Q)]{Q = 4,4'-bipyridine}(5) complexes, with tridentate binegative aroylazine ligands are reported [where H₂L¹ = anthranylhydrazone of 2-hydroxy-1-napthaldehyde, H₂L² = salicylhydrazone of 2-hydroxy-1-napthaldehyde, H₂L³ = benzoylhydrazone of 2-hydroxy-1-acetonaphthone, H₂L⁴ = anthranylhydrazone of 2-hydroxy-1-acetonaphthone]. All the complexes are characterized by elemental analysis as well as various spectroscopic techniques. Single crystal X-ray diffraction crystallography of 2 reveals that the metal centre is in distorted square pyramidal geometry with O₄N coordination spheres, whereas 5 exhibits a distorted octahedral geometry around the metal center. In addition, all the complexes (1-5) show moderate DNA binding propensity which is investigated using UV-vis absorption titration, circular dichroism, thermal denaturation and fluorescence spectral studies. The experimental results show that the complexes effectively interact with CT-DNA through both minor and major groove binding modes, with binding constants ranging from 10⁴-10⁵ M^-1. Among 1-5, complexes 3 and 4 show higher binding affinity towards CT-DNA than others and at the same time also exhibit negative ΔT_m values of about ∼1.5 and 1.0 °C which resembles the properties shown by cisplatin. All complexes show moderate photo-induced cleavage of pUC19 supercoiled plasmid DNA with complex 3 showing the highest photo induced DNA cleavage activity of ∼48%. In coherence with the DNA interaction studies, 3 and 4 also exhibit good binding affinity towards BSA in the range of 10¹⁰-10¹¹ M^-1, which is also supported by their ability to quench the tryptophan fluorescence emission spectra of BSA. All the complexes show remarkable photo-induced BSA cleavage activity (>90%) at a complex concentration of 50 μM. The catalytic potential of 1-5 is also tested for the oxidative bromination of styrene, salicylaldehyde and oxidation of methyl phenyl sulphide. All the reactions show a high percentage of conversion (>90%) with a high turnover frequency (TOF). Particularly, in the oxidative bromination of styrene the percentage of conversion and TOF vary from 96-98% and 8000-19 600 (h^-1) respectively, which signifies the potential of these oxidovanadium(v) complexes to stimulate research for the synthesis of a better catalyst.