The challenge of cyclic and acyclic schiff bases and related derivatives

The Tautomerism of Heterocycles: Five-membered Rings with Two or More Heteroatoms

Tridentate/tetradentate Schiff base ligands L1 and L2, derived from the condensation of o-vanillin or pyridine-2-aldehyde with N,N-dimethylethylenediammine, react with nickel acetate or perchlorate salt and azide, cyanate, or thiocyanate to give rise to a series of dinuclear complexes of formulas [Ni(L1)(μ1,1-N3)Ni(L1)(N3)(OH2)]·H2O (1), {[Ni(L1)(μ1,1-NCS)Ni(L1)(NCS)(OH2)][Ni(L1)(μ-CH3COO)Ni(L1)( NCS) (OH2)]} (2) {[2A][2B]}, [Ni(L1)(μ1,1-NCO)Ni(L1)(NCO)(OH2)]·H2O (3), and [Ni(L2-OMe)(μ1,1-N3)(N3)]2 (4), where L1 = Me2N(CH2)2NCHC6H3(O-)(OCH3) and L2 = Me2N(CH2)2NCHC6H3N. We have characterized these complexes by analytical, spectroscopic, and variable-temperature magnetic susceptibility measurements. The coordination geometry around all of the Ni(II) centers is a distorted octahedron with bridging azide, thiocyanate/acetate, or cyanate in a μ1,1 mode and μ2-phenolate oxygen ion for 1−3, respectively, or with a double-bridging azide for 4. The magnetic properties of the complexes were studied by magnetic sus...

Crystal structure and magnetic interactions in nickel(II) dibridged complexes formed by two azide groups or by both phenolate oxygen-azide, -thiocyanate, -carboxylate, or -cyanate groups.

Pseudomonas aeruginosa is an opportunistic pathogen, synthesizing two major siderophores, pyoverdine (Pvd) and pyochelin (Pch), to cover its needs in iron(III). If the high affinity and specificity of Pvd toward iron(III) (pFe = 27.0) was well described in the literature, the physicochemical and coordination properties of Pch toward biologically relevant metals (Fe(III), Cu(II) or Zn(II)) have been only scarcely investigated. We report a thorough physico-chemical investigation of Pch (potentiometry, spectrophotometries, ESI/MS) that highlighted its moderate but significantly higher affinity for Fe3+ (pFe = 16.0 at p[H] 7.4) than reported previously. We also demonstrated that Pch strongly chelates divalent metals such as Zn(II) (pZn = 11.8 at p[H] 7.4) and Cu(II) (pCu = 14.9 at p[H] 7.4) and forms predominantly 1 : 2 (M2+/Pch) complexes. Kinetic studies revealed that the formation of the ferric Pch complexes proceeds through a Eigen-Wilkins dissociative ligand interchange mechanism involving two protonated species of Pch and the Fe(OH)2+ species of Fe(III). Our physico-chemical parameters supports the previous biochemical studies which proposed that siderophores are not only devoted to iron(III) shuttling but most likely display other specific biological role in the subtle metals homeostasis in microorganisms. This work also represents a step toward deciphering the role of siderophores throughout evolution.

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Pyochelin, a siderophore of Pseudomonas aeruginosa: Physicochemical characterization of the iron(III), copper(II) and zinc(II) complexes

A complex moiety containing copper (II) has been anchored covalently into the organic-modified Si−MCM-41 to prepare a new catalyst. The amine group containing organic moiety 3-aminopropyl-triethoxysilane has been first anchored on the surface of Si−MCM-41 via silicon alkoxide route. The amine group upon condensation with salicyldehyde affords a bidentate ligand in the mesoporous matrix for anchoring copper(II) ions. The prepared catalyst has been characterized by UV−vis, electron paramagnetic resonance (EPR), and infrared (IR) spectroscopic analysis, small-angle X-ray diffraction, and N2 sorption study. A remarkable difference in the pore structure has been observed after the immobilization of copper(II) complex in Si−MCM-41. The catalyst showed excellent catalytic efficiency in epoxidation reactions with various olefinic compounds including styrene and allyl alcohol, using tert-BuOOH as oxidant. Notably, styrene shows unprecedented high conversion (97%) as well as epoxide selectivity (89%) with tert-BuOO...

Anchoring of copper complex in MCM-41 matrix: a highly efficient catalyst for epoxidation of olefins by tert-BuOOH.

Synthesis and studies of Cu(II)-thiolato complexes: bioinorganic perspectives

The Schiff base (L), synthesized from 2-(dimethylamino)ethylamine and salicylaldehyde acts as a tridentate ligand. This ligand, when stirred with 1 equiv of KOH in methanol, undergoes partial hydrolysis of the imine bond. This solution readily takes up Mn(II)/Mn(III) acetate or Fe(III) chloride/perchlorate to form mixed-ligand Mn(III) or Fe(III) complexes, respectively. The neutral dark brown complex, [Mn(L-H)(NCS){o-(CHO)C6H4O-}] (1), crystallizes in the presence of thiocyanate in the orthorhombic space group Pbca with a = 15.271(8), b = 19.522(7), c = 13.213(7) A; Z = 8; R = 0.060; and Rw = 0.062. The coordination geometry around Mn(III) ion is distorted octahedral with donation from one L-H, one salicylaldehyde and, one thiocyanate ligand. With Fe(III), the dark red complex isolated in the solid state is found to be a neutral μ-oxo Fe(III) dimer with the formula [{o-(CHO)C6H4O-}(L-H)Fe]2O (3). The structure of 3 has been solved and successfully refined in the monoclinic space group C2/c with a = 18.558...

Syntheses and X-ray Structures of Mixed-Ligand Salicylaldehyde Complexes of Mn(III), Fe(III), and Cu(II) Ions: Reactivity of the Mn(III) Complex toward Primary Monoamines and Catalytic Epoxidation of Olefins by the Cu(II) Complex

Mononuclear manganese(III) complexes with imine/amine and phenolate ligation: X-ray structural, spectroscopic and electrochemical studies

Synthesis and characterization of copper(II) and nickel(II) complexes with ligands having N2S*2S2 (S* = thioether) donors: pseudo-reversible CuIII/CuII couple

Rameshwer Shukla

Papers

Synthesis and studies of Cu(II)-thiolato complexes: bioinorganic perspectives

Syntheses and X-ray Structures of Mixed-Ligand Salicylaldehyde Complexes of Mn(III), Fe(III), and Cu(II) Ions: Reactivity of the Mn(III) Complex toward Primary Monoamines and Catalytic Epoxidation of Olefins by the Cu(II) Complex

Mononuclear manganese(III) complexes with imine/amine and phenolate ligation: X-ray structural, spectroscopic and electrochemical studies

Synthesis and characterization of copper(II) and nickel(II) complexes with ligands having N2S2S2 (S = thioether) donors: pseudo-reversible CuIII/CuII couple

Synthesis of cryptands having tritopic receptor sites by [2+3] Schiff base condensation using Cs(I) ion as the template