A combined experimental and theoretical investigation on the Cu(II) sensing behavior of a piperazinyl moiety based ligand, and catecholase and biological activities of its Cu(II) complex in combination with pyridine 2,5-dicarboxylate

New copper(II) μ-Alkoxo-μ-carboxylato double-bridged complexes as models for the active site of catechol oxidase: Synthesis, spectral characterization and DFT calculations

A series of four copper(II) μ-Alkoxo-μ-carboxylato double bridged complexes, [{Cu₂(L)}₂][(μ–O₂C–CO₂] 1, [{Cu₂(L)}₂(μ–O₂C–(CH₂)CO₂] 2, [{Cu₂(L)}₂(μ–O₂C–CH₂–CO₂] 3 and [{Cu₂(L)}₂(μ–O₂C–C₆H₄–CO₂] 4 (H₃L = 4-bromo-2-((E)-((3-(((E)-5-chloro-2-hydroxybenzylidene) amino)-2-hydroxypropyl) imino) methyl)-6-methoxyphenol and μ-dicarboxylate ions = oxalate, malonate, succinate and terephthalate) have been synthesized and characterized using several physicochemical techniques. The tridentate nature of H₃L is interpreted from IR spectra. The Epr spectra of these complexes are characteristic of the quintet state (S = 2) in central features and the triplet state (S = 1) of these tetranuclear complexes. The electrochemical potential of these complexes was investigated using CV (cyclic voltammetry) and DPV (differential pulse voltammetry). All complexes showed quasi reversible reduction peaks in the cathodic region. To explore the stability of these complexes, quantum chemical parameters like electronegativity, ionization potential, electron affinity, global hardness and softness, and electrophilicity were estimated and discussed. The synthesized complexes have been designed as structural and functional models of the catechol oxidase enzymes to investigate the catecholase activity. Additionally, superoxide dismutase activity data of all complexes have also been evaluated and compared with known SOD mimics.

Synthesis, molecular structure and antioxidant activity of bis [L(μ2-chloro)copper(II)] supported by phenoxy/naphthoxy-imine ligands

A new series of Cu(II) complexes [bis[{(μ₂-chloro)-2-MeO-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-OC₆H₂)}Cu(II)] (Cu1); bis[{(μ₂-chloro)-2-MeS-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-(OC₆H₂)}Cu(II)] (Cu2); bis[{(μ₂-chloro)-2-MeO-Ph-CH₂-(N=CH)-2-(OC₁₀H₆)} Cu(II)] (Cu3); bis[{(μ₂-chloro)-2-MeS-Ph-CH₂-(N=CH)-2-(OC₁₀H₆)}Cu(II)] complex (Cu4); bis[{2-MeS-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-(OC₆H₂)}Cu(II)] (Cu5)] have been synthesized and characterized by elemental analysis, IR, UV-Visible and by X-ray crystallography for Cu1, Cu4 and Cu5. In the solid state, Cu1 features of a chloro-bridged dimer complex with κ² coordination of the monoanionic phenoxy-imine ligand onto the copper center. On the other hand, the molecular structure of Cu4 reveals the naphthoxy-imine ligand with pendant S-group coordinated to the copper atom in tridentate meridional fashion. Treatment of [Cu(OAc)₂·H₂O] with two equiv. of [2-MeS-Ph-CH₂-(N=CH)-2,4-tert-butyl-2-(HOC₆H₂)] led to a monomeric complex Cu5, with the ONS-donor Schiff base acting as a bidentate ligand. The redox behavior was explored by cyclic voltammetry. The reduction/oxidation potential of Cu(II) complexes depends on the structure and conformation of the central atom in the coordination compounds. Antioxidant activities of the complexes, Cu1 - Cu5, were determined by in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radicals (DPPH) and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radicals (ABTS⁺). The dinuclear compounds Cu1-Cu4, from the concentration of 5 μM, presented a good activity in scavenging DPPH radical. In addition, most of the Cu(II) complexes showed ABTS^.+ radical-scavenging activity. The monomeric complex Cu5 at all concentrations tested showed antioxidant inability. The cytotoxicity of the Cu1 and Cu3 was determined in V79 cell line by reduction of 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay.

Tetradentate iminophenolate copper complexes in rac-lactide polymerization

Copper(II) nitrate complexes of 2-(((2-((2-aminoethyl)amino)ethyl)imino)methyl)phenol, 2-(((2-((2-aminoethyl)amino)ethyl)imino)methyl)-4,6-dichlorophenol, 2-(((2-(piperazin-1-yl)ethyl)imino)methyl)phenol and (2,4-di-tert-butyl-6-(((2-(piperazin-1-yl)ethyl)imino)methyl)phenol, as well as a copper(II) acetate complex of 2-(((2-(piperidin-1-yl)ethyl)imino)methyl)phenol, have been prepared and characterized by X-ray diffraction studies. In combination with benzyl alcohol, all complexes are active in rac-lactide polymerization at 140 °C in molten monomer to provide moderately heterotactic polylactic acid. Most complexes showed complicated reaction kinetics, indicative of two interconverting active species. Molecular weight control was poor and a strong tendency toward intramolecular transesterification led to oligomeric products. There was no indication that the basic site of the ligand is participating in the polymerization reaction by deprotonation of the alcohol nucleophile.

New Pyrazole-Hydrazone Derivatives: X-ray Analysis, Molecular Structure Investigation via Density Functional Theory (DFT) and Their High In-Situ Catecholase Activity

The development of low-cost catalytic systems that mimic the activity of tyrosinase enzymes (Catechol oxidase) is of great promise for future biochemistry technologic demands. Herein, we report the synthesis of new biomolecules systems based on hydrazone derivatives containing a pyrazole moiety (L1-L6) with superior catecholase activity. Crystal structures of L1 and L2 biomolecules were determined by X-ray single crystal diffraction (XRD). Optimized geometrical parameters were calculated by density functional theory (DFT) at B3LYP/6-31G (d, p) level and were found to be in good agreement with single crystal XRD data. Copper (II) complexes of the compounds (L1-L6), generated in-situ, were investigated for their catalytic activities towards the oxidation reaction of catechol to ortho-quinone with the atmospheric dioxygen, in an attempt to model the activity of the copper containing enzyme tyrosinase. The studies showed that the activities depend on four parameters: the nature of the ligand, the nature of counter anion, the nature of solvent and the concentration of ligand. The Cu(II)-ligands, given here, present the highest catalytic activity (72.920 μmol·L^-1·min^-1) among the catalysts recently reported in the existing literature.

Synthesis, crystal structure, DFT/TDDFT calculation, photophysical properties and DNA binding studies of morpholino moiety ligand based two Cu(ii) complexes in combination with carboxylates

Two Cu(II) compounds have been characterized by structure analyses and DFT/TD-DFT calculations. Both the complexes potentially bind with CT-DNA and corresponding binding constants are in the order of 10⁵ M⁻¹.