VIVO and VIV Species Formed in Aqueous Solution by the Tridentate Glutaroimide–Dioxime Ligand – An Instrumental and Computational Characterization

Complexation of VIV in aqueous solution with glutaroimide–dioxime (H3L), a ligand proposed for the possible sequestration of uranium from seawater, was studied by the combined application of spectroscopic (EPR and UV/Vis), spectrometric (ESI‐MS), electrochemical (CV), and computational (DFT) techniques. The results indicate that a rare non‐oxido VIV species, with formula [VIVL2]2–, is formed in the pH range 3–5. It transforms into a usual VIVO complex, [VIVOL(OH)]2–, at pH > 6. The non‐oxido species is characterized by a "type 3" EPR spectrum with Az ≈ 126 × 10–4 cm–1 and a UV/Vis signal with ε > 2000 m–1 cm–1 in the visible region. The detection of VV species by ESI‐MS spectrometry was related to two possible oxidation processes, the first one in solution and the second one in‐source during the recording of the spectra. The cyclic voltammogram of [VIVL2]2– shows two quasi‐reversible processes, at E1/2 = –0.75 V and E1/2 = 0.03 V, assigned to the VIV/VIII reduction and VIV/VV oxidation, respectively. All the experimental results were verified by DFT calculations, which indicated that the geometry of the non‐oxido VIV complex is intermediate between an octahedron and a trigonal prism and allowed us to predict its 51V hyperfine coupling (HFC) tensor A, the electron absorption spectrum, the two redox processes in the cyclic voltammogram, and the electronic structure that, in turn, determines its EPR and UV/Vis behavior

Monomeric and dimeric oxidomolybdenum(V and VI) complexes, cytotoxicity, and DNA interaction studies: molybdenum assisted C═N bond cleavage of salophen ligands

Four novel dimeric bis-μ-imido bridged metal–metal bonded oxidomolybdenum(V) complexes [MoV2O2L′21–4] (1–4) (where L′1–4 are rearranged ligands formed in situ from H2L1–4) and a new mononuclear dioxidomolybdenum(VI) complex [MoVIO2L5] (5) synthesized from salen type N2O2 ligands are reported. This rare series of imido- bridged complexes (1–4) have been furnished from rearranged H3L′1–4 ligands, containing an aromatic diimine (o-phenylenediamine) “linker”, where Mo assisted hydrolysis followed by −C═N bond cleavage of one of the arms of the ligand H2L1–4 took place. A monomeric molybdenum(V) intermediate species [MoVO(HL′1–4)(OEt)] (Id1–4) was generated in situ. The concomitant deprotonation and dimerization of two molybdenum(V) intermediate species (Id1–4) ultimately resulted in the formation of a bis-μ-imido bridge between the two molybdenum centers of [MoV2O2L′21–4] (1–4). The mechanism of formation of 1–4 has been discussed, and one of the rare intermediate monomeric molybdenum(V) species Id4 has been isolated in the solid state and characterized. The monomeric dioxidomolybdenum(VI) complex [MoVIO2L5] (5) was prepared from the ligand H2L5 where the aromatic “linker” was replaced by an aliphatic diimine (1,2-diaminopropane). All the ligands and complexes have been characterized by elemental analysis, IR, UV–vis spectroscopy, NMR, ESI- MS, and cyclic voltammetry, and the structural features of 1, 2, 4, and 5 have been solved by X-ray crystallography. The DNA binding and cleavage activity of 1–5 have been explored. The complexes interact with CT-DNA by the groove binding mode, and the binding constants range between 103 and 104 M–1. Fairly good photoinduced cleavage of pUC19 supercoiled plasmid DNA was exhibited by all the complexes, with 4 showing the most promising photoinduced DNA cleavage activity of ∼93%. Moreover, in vitro cytotoxic activity of all the complexes was evaluated by MTT assay, which reveals that the complexes induce cell death in MCF-7 (human breast adenocarcinoma) and HCT-15 (colon cancer) cell lines

Temperature and solvent structure dependence of VO2+ complexes of pyridine-N-oxide derivatives and their interaction with human serum transferrin

The behaviour of the systems formed by VO2+, 2-hydroxypyridine-N-oxide (Hhpo) and 2-mercaptopyridine-N-oxide (Hmpo) was studied both in solution and in the solid state through the combined application of spectroscopic (EPR and UV-Vis spectroscopy) and DFT methods. The geometry of solid bis-chelated complexes [VOL2], with L = hpo and mpo, is square pyramidal, but it can change to cis-[VOL2S], where S is a solvent molecule, when these are dissolved in a coordinating solvent. The equilibrium between the square pyramidal and cis-octahedral forms is strongly affected by solvent and temperature. At room temperature, the predominant species is [VOL2], which gives a pink colour to the solutions; at lower temperatures, the equilibrium is shifted-partially or completely-toward the formation of cis-[VOL2S], which is green. In an acidic environment and in the presence of an excess of ligand, [VOL2] can transform into the tris-chelated complex [VL3](+), in which vanadium loses the oxido ligand and adopts a hexa-coordinated geometry intermediate between octahedral and trigonal prismatic. 1-Methylimidazole (1-MeIm), which represents a model for His-N coordination, forms mixed complexes with stoichiometry cis-[VOL2(1-MeIm)], occupying an equatorial position. In the ternary systems VO2+-Hhpo-hTf and VO2+-Hmpo-hTf at room temperature and pH 7.4, besides (VO)hTf and (VO)(2)hTf, the mixed species cis-VO(hpo)(2)(hTf) and VO(mpo)(hTf) are observed, with the equatorial binding of an accessible histidine residue. Finally, the contribution of the N-oxide group to (51)VA(z) and A(iso) hyperfine coupling constants, which can be important in the characterisation of similar species, is discussed

5,5′-Dibenzoimidazole as building block for a new 3D Co(II) coordination polymer: A combined EPR and DFT study using UB3LYP model

A new Co(II) three-dimensional coordination polymer, [Co(L)(L')](n) (1) [where L = 5,5'-dibenzoimidazole, and L' = doubly deprotonated terephthalic acid] has been synthesized hydro(solvo)thermally and its molecular and crystal structure have been elucidated through single crystal X-ray diffraction analysis. Each Coal) ion displays a slightly distorted trigonal bipyramidal geometry, the apical positions being occupied by the nitrogen atoms of two symmetry-related dibenzoimidazole ligands, while the oxygen atoms from three distinct terephthalic acids are in the equatorial plane. Considering the Co2C2O6 dimeric moieties as nodes, and the ancillary ligands as connectors, the structure can be simplified as a 8-c uninodal net of the type bcu, body centered cubic, with point symbol 4(24).6(4) and vertex symbol [4.4.4.4.4.4.4.4.4.4.4.4.4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).4(3).*.*.*.*]. The EPR spectra for 1 have been reported, showing g(parallel to) = 2.176 and g(perpendicular to) = 2.052 at RT (room temperature), and g(parallel to) = 2.172 and g(perpendicular to) = 2.060 at LNT (liquid nitrogen temperature). Finally, the electronic nature of the molecular geometry of 1 has been explored by DFT computation applying the UB3LYP/def2-TZVP level of theory, showing the energy difference between the high spin and low spin configurations. (C) 2019 Elsevier Ltd. All rights reserved