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Biological inorganic chemistry : Structure and reactivity / by I. Bertini, H. B. Gray, E. I. Stiefel, J. S. Valentine
No full textInhibition of Ascorbate Oxidase by 2-methyl-2,4-pentanediol and other polyols
No full textThe organic alcohol 2-methyl-2,4-pentanediol, which is used as cosolvent in the aqueous buffer to induce crystallization of ascorbate oxidase, acts as a competitive inhibitor of ascorbic acid in the oxidase reaction. Glycerol and ethylene glycol show similar, but smaller inhibitory effects. The lower activity exhibited by crystalline ascorbate oxidase with respect to the native enzyme has been shown to depend on the ageing of the proteine solution during crystallization and not by specific effects due to the presence of 2-methyl-2,4-pentanediol
Schiff base complexes of oxo cations. I. Uranyl complexes with tetradentate optically active Schiff bases of salicylaldehyde
No full textThe synthesis and properties of uranyl complexes with tetradentate ligands of formula UO2 (saldiamine). L (where saldiamine is the Schiff base N,N′diamine bis(salicylideneimine), L is a solvent molecule and the diamines are ethylenediamine, (+) propylenediamine, (+) and meso butanediamine, (+) and meso cyclohexanediamine, (-) and meso stilbenediamine) are reported. I.R., electronic and circular dichroism spectra are also discussed
Optically active complexes of Schiff bases. Part 5. An investigation of some solvent and conformational effects on the equilibriums between cobalt(II) Schiff-base complexes and dioxygen
No full textThe reaction between dioxygen and some cobalt(II) Schiff-base complexes, [CoL], has been studied in dimethyl-formamide and pyridine [L = ethylene-, 1,2-diphenylethylene-, butane-2,3-diyl-, and 1,2-cyclohexylene-bis-(salicylideneiminato)]. Equilibrium constants for the oxygenation reaction in both solvents have been obtained through manometric and spectrophotometric measurements. Steric effects of conformational origin are indicated and are discussed on the basis of the possible stereochemistry and conformation of the complexes in solution
Asymmetric synthesis of beta-phenylserines by condensation of benzaldehyde with zinc(II) and copper(II) complexes of (1R)-3-hydroxymethylenebornan-2-one glycine imines
No full textThe condensation between benzaldehyde and the zinc(II) and copper(II) complexes of the glycine imines of (1R)-3-hydroxymethylenebornan-2-one in the presence of strong bases has been studied. The diastereo- and enantio-selectivity of the reaction together with the spectroscopic characterization of the metal complexes and the corresponding enolate intermediates are reported
Asymmetric oxidation of sulphides, catalysed by chloroperoxidase
No full textChloroperoxidase oxidation of sulphides affords the corresponding sulphoxides having the (R) absolute configuration in up to 92% enantiomeric excess (e.e.)
DOUBLE STEREOSELECTION IN THE SULFOXIDATION REACTION CATALYZED BY TITANIUM COMPLEXES OF N-SALICYLIDENE-L-AMINO ACIDS
No full textEffect of strain in the proximal ligand on the binding of nitric oxide and carbon monoxide to chelated protoheme complexes
Full text linkThe binding of NO and CO to chelated protoheme-L-histidine methyl ester (HM-H), protoheme-glycyl-L-histidine methyl ester (HM-GH), and free protoheme (HM) has been studied in methanol-DMSO solution. In all cases, the NO adducts are five-coordinated indicating that binding of NO occurs with displacement of the axial base and confirms the strong negative trans effect exerted by NO in heme complexes, though it is found that the presence of strain in the iron-histidine bond of HM-H has a positive influence on NO binding, making it thermodynamically more favorable than for HM-GH. The equilibrium constants thus decrease in the series HM>HM-H>HM-GH. In contrast to NO, CO has a positive trans effect, and therefore, an opposite trend is observed in the binding of this ligand to the heme complexe
Enantio-differentiating catalytic oxidation by a biomimetic trinuclear copper complex containing L-histidine residues
No full textThe trinuclear complex [Cu3PHI]6+, derived from a ligand containing two chiral L-histidine residues, performs the catalytic oxidation of L- and D-Dopa with remarkable enantio-differentiation; this depends on the anchoring effect provided by the copper center which is not participating in the catalytic reaction and recognizes the chirality of the substrate
Synthesis and characterization of new chiral octadentate nitrogen ligands and related copper(II) complexes as catalysts for stereoselective oxidation of catechols
No full textThree new octadentate ligands, namely (R)-N,N',-dimethyl-N,N'-bis{3-[bis(1-methyl-2-imidazolylmethyl)]aminopro pyl}-1,1'-binaphthyl-2,2'-diamine, (R)-DABN-3Im(4), (R)-N,N'-dimethyl-N,N'-bis{4-[bis(1-methyl-2-benzimidazolylmethyl)lamino butyl}-1,1'-binaphthyl-2,2'-dia-mine, (R)-DABN-4BZ(4), and (S)-N2,N6-dimethyl-N2,N6-bis{2'-[bis(1-methyl-2-benzimidazolylmethyl)]am inomethyl}benzyl-2,6-diamino-1-exanol acetate, L-Lys-4BZ(4), were employed for the synthesis of dinuclear and trinuclear copper(II) complexes. The ligands contain two side arms of different nature and length which carry tridentate aminobis(benzimidazole) or aminobis(imidazole) residues as metal binding sites (A sites) connected to a central (R)-1,1'-binaphthyl-2,2'-diamine or L-lysine residue which can bind a third metal ion (B site). The chiroptical properties of the ligands and the complexes have been described. The complexes were tested as catalysts in the oxidation of 3,5-di-tert-butylcatechol, L-, D-Dopa and L-, D-Dopa methyl esters by dioxygen to give the corresponding quinones. The catalytic efficiency is moderate, but the complexes exhibit significant enantio-differentiating ability towards L-, D-Dopa methyl esters, albeit their enantio-differentiating ability towards L-, D-Dopa is lower. The (R)-1,1'-binaphthyl-2,2'-diamine spacer in the (R)-DABN complexes has much stronger recognition power than the aliphatic L-lysine spacer in the L-Lys complexes. In addition, the highest stereoselectivity in the catalytic oxidation is obtained with the (R)-DABN-3Im(4) complexes, containing carbon chains of three atoms between the (R)-1,1'-binaphthyl-2,2'-diamine groups and the tridentate donor units at the A metal binding sites. In all cases, the preferred enantiomeric substrate has the L configuration, which is dictated by the chirality of the spacer residue. (c) 2005 Elsevier B.V. All rights reserved
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