Substituent Effects in Carbon-Nanotube-Supported Copper Phenolato Complexes for Oxygen Reduction Reaction.

Unprotected mononuclear pyrene-modified (bispyridylaminomethyl)methylphenol copper complexes were designed to be immobilized at multiwalled carbon nanotube (MWCNT) electrodes and form dinuclear bis(μ-phenolato) complexes on the surface. These complexes exhibit a high oxygen reduction reaction activity of 12.7 mA cm and an onset potential of 0.

Effect of Monoelectronic Oxidation of an Unsymmetrical Phenoxido-Hydroxido Bridged Dicopper(II) Complex.

A (μ-hydroxido, μ-phenoxido)CuCu complex 1 has been synthesized using an unsymmetrical ligand bearing an N, N-bis(2-pyridyl)methylamine (BPA) moiety coordinating one copper and a dianionic bis-amide moiety coordinating the other copper(II) ion. Electrochemical mono-oxidation of the complex in DMF occurs reversibly at 213 K at E = 0.12 V vs Fc/Fc through a metal-centered process.

A Structurally Characterized Cu Complex Supported by a Bis(anilido) Ligand and Its Oxidative Catalytic Activity.

Three copper(II) complexes of the (R,R)-N,N'-bis(3,5-di-tert-butyl-2-aminobenzylidene)-1,2-diaminocyclohexane ligand, namely [Cu( L)], [Cu( LH)] and [Cu( LH )] , were prepared and structurally characterized. In [Cu( LH )] the copper ion lies in an octahedral geometry with the aniline groups coordinated in equatorial positions. In [Cu( L)] the anilines are deprotonated (anilido moieties) and coordinated to an almost square-planar metal ion.

Room-Temperature Characterization of a Mixed-Valent μ-Hydroxodicopper(II,III) Complex.

Bis(μ-hydroxo)dicopper(II,II) bearing a naphthyridine-based ligand has been synthesized and characterized in the solid state and solution. Cyclic voltammetry at room temperature displays a reversible redox system that corresponds to the monoelectronic oxidation of the complex. Spectroscopic and time-resolved spectroelectrochemical data coupled to theoretical results support the formation of a charge-localized mixed-valent Cu(II,III)2 species.

Efficient Inhibition of Telomerase by Nickel-Salophen Complexes.

Four nickel(II)-salophen complexes containing alkyl-imidazolium chains connected at the ortho or meta positions were prepared: N,N'-bis(2-hydroxy-4-methyl-3H-imidazol-1-iumbenzylideneamino)phenylenediamine (1), N,N'-bis(2-hydroxy-3-methyl-3H-imidazol-1-iumbenzylideneamino)phenylenediamine (2), N,N'-bis(2-hydroxy-3-methyl-3H-imidazol-1-iumbenzylideneamino)methyl-3H-imidazol-1-iumphenylenediamine (3), and N,N'-bis(2-hydroxy-4-methyl-3H-imidazol-1-iumbenzylideneamino)methyl-3H-imidazol-1-iumphenylenediamine (4). They protect G-quadruplex DNA (G4 -DNA) against thermal denaturation and show KA values in the range of 7.4×10(5) to 4×10(7)  m(-1) for G4 -DNA models.

Nickel(ii) radical complexes of thiosemicarbazone ligands appended by salicylidene, aminophenol and aminothiophenol moieties.

The nickel(ii) complexes of three unsymmetrical thiosemicarbazone-based ligands featuring a sterically hindered salicylidene (1), aminophenol (2) or thiophenol (3) moiety were synthesized and structurally characterized. The metal ion lies in an almost square planar geometry in all the complexes. The cyclic voltammetry (CV) curve of 1 shows an irreversible oxidation wave at E = 0.

Exploring the interaction of N/S compounds with a dicopper center: tyrosinase inhibition and model studies.

Tyrosinase (Ty) is a copper-containing enzyme widely present in plants, bacteria, and humans, where it is involved in biosynthesis of melanin-type pigments. Development of Ty inhibitors is an important approach to control the production and the accumulation of pigments in living systems. In this paper, we focused our interest in phenylthiourea (PTU) and phenylmethylene thiosemicarbazone (PTSC) recognized as inhibitors of tyrosinase by combining enzymatic studies and coordination chemistry methods.

A singlet ground state for a cobalt(II)-anilinosalen radical complex.

The cobalt(II) anilinosalen complex [Co(II)(L)] was prepared and subsequently oxidized by one electron. The resulting cation comprises a square planar low spin Co(II) ion anti-ferromagnetically exchange coupled to an anilinyl radical.

Stable anilinyl radicals coordinated to nickel: X-ray crystal structure and characterization.

Two anilinosalen and a mixed phenol-anilinosalen ligands involving sterically hindered anilines moieties were synthesized. Their nickel(II) complexes 1, 2, and 3 were prepared and characterized. They could be readily one-electron oxidized (E(1/2)=-0.

Structural and spectroscopic investigation of an anilinosalen cobalt complex with relevance to hydrogen production.

A Co(II) anilinosalen catalyst containing proton relays in the first coordination sphere has been synthesized that catalyzes the electrochemical production of hydrogen from acid in dichloromethane and acetonitrile solutions. The complex has been spectroscopically and theoretically characterized in different protonation and redox states. We show that both coordinated anilido groups of the neutral Co(II) complex can be protonated into aniline form.

Unsymmetrical binding modes of the HOPNO inhibitor of tyrosinase: from model complexes to the enzyme.

The deciphering of the binding mode of tyrosinase (Ty) inhibitors is essential to understand how to regulate the tyrosinase activity. In this paper, by combining experimental and theoretical methods, we studied an unsymmetrical tyrosinase functional model and its interaction with 2-hydroxypyridine-N-oxide (HOPNO), a new and efficient competitive inhibitor for bacterial Ty. The tyrosinase model was a dinuclear copper complex bridged by a chelated ring with two different complexing arms (namely (bis(2-ethylpyridyl)amino)methyl and (bis(2-methylpyridyl)amino)methyl).

Oxinobactin and sulfoxinobactin, abiotic siderophore analogues to enterobactin involving 8-hydroxyquinoline subunits: thermodynamic and structural studies.

The synthesis of two new iron chelators built on the tris-l-serine trilactone scaffold of enterobactin and bearing a 8-hydroxyquinoline (oxinobactin) or 8-hydroxyquinoline-5-sulfonate (sulfoxinobactin) unit has been described. The X-ray structure of the ferric oxinobactin has been determined, exhibiting a slightly distorted octahedral environment for Fe(III) and a Δ configuration. The Fe(III) chelating properties have been examined by potentiometric and spectrophotometric titrations in methanol-water 80/20% w/w solvent for oxinobactin and in water for sulfoxinobactin.

The versatile binding mode of transition-state analogue inhibitors of tyrosinase towards dicopper(II) model complexes: experimental and theoretical investigations.

We describe 2-mercaptopyridine-N-oxide (HSPNO) as a new and efficient competitive inhibitor of mushroom tyrosinase (K(IC) =3.7 μM). Binding studies of HSPNO and 2-hydroxypyridine-N-oxide (HOPNO) on dinuclear copper(II) complexes [Cu(2)(BPMP)(μ-OH)](ClO(4))(2) (1; HBPMP=2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol) and [Cu(2)(BPEP)(μ-OH)](ClO(4))(2)) (2; HBPEP=2,6-bis{bis[2-(2-pyridyl)ethyl]aminomethyl}-4-methylphenol), known to be functional models for the tyrosinase diphenolase activity, have been performed.

Hydrophilic and lipophilic iron chelators with the same complexing abilities.

A new series of iron chelators with the same coordination sphere as the water-soluble ligand O-trensox, but featuring a variable hydrophilic-lipophilic balance, have been obtained by grafting oxyethylene chains of variable length on a C-pivot tripodal scaffold. The X-ray structure of a ferric complex exhibiting tris(8-hydroxyquinolinate) coordination and solution thermodynamic properties (pK(a) of the ligands, stability constants of the ferric complexes) have been determined. The complexing ability (pFe(III) values) of the ligands are similar to that of O-trensox.