Mixed ligand cobalt(ii) picolinate complexes: synthesis, characterization, DNA binding and photocleavage

Abstract

Complexes of the type [Co(pic)(2)(NN)], where pic = picolinate, NN = dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (4) and 4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f][1,10]-phenanthroline-6,13-dione (bipyridyl-glycoluril) (bpg) (6) have been synthesized and characterized by elemental analysis, IR, UV-vis, NMR and ESI-MS spectroscopy and thermogravimetic analysis (TGA). Their physicochemical properties are compared with previously synthesized complexes, where NN = (H(2)O)(2) (1), 2,2'-bipyridine (bpy) (2), 1,10-phenanthroline (phen) (3) and dipyrido[3,2-a:2',3'-c]phenazine (dppz) (5). The crystal structures of the complexes 4-6 were solved by single-crystal X-ray diffraction. The complexes 4 and 5 crystallize from a mixture of chloroform and methanol in monoclinic and orthorhombic crystal systems, respectively, whereas complex 6 crystallizes from dimethyl sulfoxide (DMSO) in a tetragonal crystal system. The coordination sphere consists of two oxygen atoms and two nitrogen atoms from the two picolinates and two nitrogen atoms from the dpq, dppz or bpg ligand, respectively. Co(ii)/Co(iii) oxidation potentials have been determined by cyclic voltammetry. The DNA binding of complexes 1-5 has been investigated using thermal melting, fluorescence quenching and viscosity measurements, which indicate the partial intercalation of complex 5 with an apparent binding constant (k(app)) of 8.3 × 10(5) M(-1). DNA cleavage studies of complexes 1-5 have been investigated using gel electrophoresis in the presence of H(2)O(2) as an oxidizing agent and also by photoirradiation at 365 nm. The mechanistic investigations suggest that singlet oxygen ((1)O(2)) is the major species involved in the DNA cleavage by these complexes. The structures of complexes 2-6 were optimized with density functional theory (DFT) method (B3LYP/6-31G(d,p)). The low vertical ionization potential values indicate photoredox pathways for the DNA cleavage activity by complexes 4 and 5, which is corroborated by DNA cleavage experiments.

Probing of effective pyrazolone based metallonucleases: Molecular docking and in vitro biological critiques

“…The higher viscosity values are observed for each addition of complex to fixed concentrated solution of the DNA that indicates the relative viscosity of CT DNA is increased. These effects clearly suggest that the metal complexes are bound to DNA through intercalative binding mode …”

Spectroscopic and single‐crystal X‐ray diffraction studies of enantiomeric copper(II) Schiff base one‐dimensional coordination polymers with 4‐(2‐aminoethyl)benzenesulfonamide appendage: Comprehensive biological evaluation (DNA binding, cleavage, superoxide dismutase mimetic activity, topoisomerase I inhibition and cytotoxicity)

“…In order to investigate the DNA cleaving ability promoted by complex 1a , agarose gel electrophoretic mobility assay was performed by incubating supercoiled pBR322 DNA with the complex in 5 mM Tris–HCl/50 mM NaCl buffer solution at pH 7.2. A concentration‐dependent DNA cleavage was evaluated in the absence of any reducing agent by monitoring the relaxation of supercoiled, SC, form (Form I) of pBR322 DNA into nicked circular, NC, form (Form II) and/or linear, LC, form (Form III) . With an increase in concentration of complex 1a (5–30 μM), a more intensified Form II appeared (Figure ; lanes 2–7) with a gradual decrease in Form I, implying efficient single‐stranded DNA cleavage by the complex.…”

“…A concentration-dependent DNA cleavage was evaluated in the absence of any reducing agent by monitoring the relaxation of supercoiled, SC, form (Form I) of pBR322 DNA into nicked circular, NC, form (Form II) and/or linear, LC, form (Form III). [59] With an increase in concentration of complex 1a (5-30 μM), a more intensified Form II appeared ( Figure 6; lanes 2-7) with a gradual decrease in Form I, implying efficient single-stranded DNA cleavage by the complex. The cleavage activity of complex 1a was also assessed in the presence of exogenous activators, namely ascorbate (Asc), glutathione (GSH), H 2 O 2 and 3-mercaptopropionic acid (MPA), which demonstrated significant , which are hydroxyl radical scavengers, significant quenching was observed suggestive of the involvement of diffusible hydroxyl radicals in the oxidation of deoxyribose moiety of the sugar phosphate backbone, and therefore illustrates hydrolytic cleavage pathway mediated by complex 1a.…”

Bio-relevant complexes of novel N2O2 type heterocyclic ligand: Synthesis, structural elucidation, biological evaluation and docking studies

“…The increase in viscosity clearly suggests that the complexes bind to DNA via intercalation mode [37].…”