Synthesis, crystal structure and photophysical properties of chlorido[(E)-3-hydroxy-2-methyl-6-(quinolin-8-yldiazenyl)phenolato]copper(II) monohydrate

A copper(II) complex with the (E)-2-methyl-4-(quinolin-8-yldiazen­yl)benzene-1,3-diol ligand was prepared and structurally characterized. The UV–Vis absorption spectra of the ligand and the complex are reported.

The reaction between copper(II) chloride dihydrate and the (E)-2-methyl-4-(quinolin-8-yldiazen­yl)benzene-1,3-diol ligand in aceto­nitrile leads to the formation of the title compound, [Cu(C₁₆H₁₂N₃O₂)Cl]·H₂O. The ligand is deprotonated and coordinates with three donor atoms (tridentate) to the Cu^II ion. Individual mol­ecules of the Cu^II complex are connected by chloride bridges, forming a one-dimensional coordination polymer. No photoisomerization to the cis isomer of the azo ligand was observed upon irradiation with UV light.

Cis-Divacant Octahedral Fe(II) in a Dimensionally Reduced Family of 2-(Pyridin-2-yl)pyrrolide Complexes

Four-coordinate transition-metal complexes can adopt a diverse array of coordination geometries, with square planar and tetrahedral coordination being the most prevalent. Previously, we reported the synthesis of a trinuclear Fe(II) complex, Fe₃TPM₂, supported by a 3-fold-symmetric 2-pyridylpyrrolide ligand [i.e., tris(5-(pyridin-2-yl)-1H-pyrrol-2-yl)methane] that featured a rare cis-divacant octahedral (CDO) geometry at each Fe(II) center. Here, a series of truncated 2-pyridylpyrrolide ligands are described that support mono- and binuclear Fe(II) complexes that also exhibit CDO geometries. Metalation of the tetradentate ligand bis[5-(pyridin-2-yl)-1H-pyrrol-2-yl]methane (H₂BPM) in tetrahydrofuran (THF) results in the binuclear complex Fe₂(BPM)₂(THF)₂ in which both Fe(II) ions are octahedrally coordinated. The coordinated THF solvent ligands are labile: THF dissociation leads to Fe₂(BPM)₂, which features five-coordinate Fe(II) ions. The Fe-Fe distance in these binuclear complexes can be elongated by ligand methylation. Metalation of bis[5-(6-methylpyridin-2-yl)-1H-pyrrol-2-yl]methane (H₂BPM^Me) in THF leads to the formation of four-coordinate, CDO Fe(II) centers in Fe(BPM^Me)₂. Further ligand truncation affords bidentate ligands 2-(1H-pyrrol-2-yl)pyridine (PyrPyrrH) and 2-methyl-6-(1H-pyrrol-2-yl)pyridine (Pyr^MePyrrH). Metalation of these ligands in THF affords six-coordinate complexes Fe(PyrPyrr)₂(THF)₂ and Fe(Pyr^MePyrr)₂(THF)₂. Dissociation of labile solvent ligands provides access to four-coordinate Fe(II) complexes. Ligand disproportionation at Fe(PyrPyrr)₂ results in the formation of Fe(PyrPyrr)₃ and Fe(0). Ligand methylation suppresses this disproportionation and enables isolation of Fe(Pyr^MePyrr)₂, which is rigorously CDO. Complete ligand truncation, by separating the 2-pyridylpyrrolide ligands into the constituent monodentate pyridyl and pyrrolide donors, affords Fe(Pyr)₂(Pyrr)₂ in which Fe(II) is tetrahedrally coordinated. Computational analysis indicates that the potential energy surface that dictates the coordination geometry in this family of four-coordinate complexes is fairly flat in the vicinity of CDO coordination. These synthetic studies provide the structural basis to explore the implications of CDO geometry on Fe-catalyzed reactions.

Recent Advances in One-Electron-Oxidized CuII -Diphenoxide Complexes as Models of Galactose Oxidase: Importance of the Structural Flexibility in the Active Site

The phenoxyl radical plays important roles in biological systems as cofactors in some metalloenzymes, such as galactose oxidase (GO) catalyzing oxidation of primary alcohols to give the corresponding aldehydes. Many metal(II)-phenoxyl radical complexes have hitherto been studied for understanding the detailed properties and reactivities of GO, and thus the nature of GO has gradually become clearer. However, the effects of the subtle geometric and electronic structural changes at the active site of GO, especially the structural change in the catalytic cycle and the effect of the second coordination sphere, have not been fully discussed yet. In this Review, we focus on further details of the model studies of GO and discuss the importance of the structural change at the active site of GO.

Formation of the CuII -Phenoxyl Radical by Reaction of O2 with a CuII -Phenolate Complex via the CuI -Phenoxyl Radical

Reaction of Cu(ClO₄ )₂ ⋅6 H₂ O with a tripodal 2N2O ligand, H₂ Me₂ NL, having a p-(dimethylamino)phenol moiety, in CH₂ Cl₂ /MeOH (1:1 v/v) under basic conditions under an inert gas atmosphere gave [Cu(Me₂ NL)(H₂ O)] (1). The same reaction carried out under aerobic conditions gave [Cu(Me₂ NL)(MeOH)]ClO₄ (2), which could be obtained also from the isolated complex 1 by reaction with O₂ in CH₂ Cl₂ /MeOH. The X-ray crystal structures of 1 and 2 revealed similar square-pyramidal structures, but 2 showed the (dimethylamino)phenoxyl radical features. Complex 1 exhibits characteristic Cu^II EPR signals of the d x 2 - y 2 ground state in CH₂ Cl₂ /MeOH at 77 K, whereas 2 is EPR-silent. The EPR and X-ray absorption fine structure (XAFS) results suggest that 2 is assigned to the Cu^II -(dimethylamino)phenoxyl radical. However, complex 1 showed different features in the absence of MeOH. The EPR spectrum of the CH₂ Cl₂ solution of 1 exhibits distortion from the d x 2 - y 2 ground state and a temperature-dependent equilibrium between the Cu^II -(dimethylamino)phenolate and the Cu^I -(dimethylamino)phenoxyl radical. From these results, Cu^II -phenoxyl radical complex 2 is concluded to be formed by the reaction of 1 with O₂ via the Cu^I -phenoxyl radical species.

Synthesis, Molecular Structure, Anticancer Activity, and QSAR Study of N-(aryl/heteroaryl)-4-(1H-pyrrol-1-yl)Benzenesulfonamide Derivatives

A series of N-(aryl/heteroaryl)-4-(1H-pyrrol-1-yl)benzenesulfonamides were synthesized from 4-amino-N-(aryl/heteroaryl)benzenesulfonamides and 2,5-dimethoxytetrahydrofuran. All the synthesized compounds were evaluated for their anticancer activity on HeLa, HCT-116, and MCF-7 human tumor cell lines. Compound 28, bearing 8-quinolinyl moiety, exhibited the most potent anticancer activity against the HCT-116, MCF-7, and HeLa cell lines, with IC50 values of 3, 5, and 7 µM, respectively. The apoptotic potential of the most active compound (28) was analyzed through various assays: phosphatidylserine translocation, cell cycle distribution, and caspase activation. Compound 28 promoted cell cycle arrest in G2/M phase in cancer cells, induced caspase activity, and increased the population of apoptotic cells. Relationships between structure and biological activity were determined by the QSAR (quantitative structure activity relationships) method. Analysis of quantitative structure activity relationships allowed us to generate OPLS (Orthogonal Projections to Latent Structure) models with verified predictive ability that point out key molecular descriptors influencing benzenosulfonamide's activity.

Oxygen Delivery as a Limiting Factor in Modelling Dicopper(II) Oxidase Reactivity

Deprotonation of ligand-appended alkoxyl groups in mononuclear copper(II) complexes of N,O ligands L₁ and L₂ , gave dinuclear complexes sharing symmetrical Cu₂ O₂ cores. Molecular structures of these mono- and binuclear complexes have been characterized by XRD, and their electronic structures by UV/Vis, ¹ H NMR, EPR and DFT; moreover, catalytic performance as models of catechol oxidase was studied. The binuclear complexes with anti-ferromagnetically coupled copper(II) centers are moderately active in quinone formation from 3,5-di-tert-butyl-catechol under the established conditions of oxygen saturation, but are strongly activated when additional dioxygen is administered during catalytic turnover. This unforeseen and unprecedented effect is attributed to increased maximum reaction rates v_max , whereas the substrate affinity K_M remains unaffected. Oxygen administration is capable of (partially) removing limitations to turnover caused by product inhibition. Because product inhibition is generally accepted to be a major limitation of catechol oxidase models, we think that our observations will be applicable more widely.

Heterodinuclear Ni(ii) and Cu(ii) Schiff base complexes and their activity in oxygen reduction

New hetero- and homo-dinuclear Cu/Ni complexes electropolymerise potentiodynamically on glassy carbon electrodes and the polymers reduce dioxygen in water.