Combination Of Metal Salts Research Articles

Vitamin-E Supplementation Ameliorates Chromium-and/or Nickel Induced Oxidative Stress in Vivo

The present study was designed to investigate the in vivo effects of nickel chloride [NiCl2; 8, and 16 mg/kg body weight (b wt)] and/or Potassium dichromate (K2Cr2O7; 5 and 10 mg/kg b wt) in the liver of adult mice. The beneficial effects of vitamin E (2 mg/kg) along with their combination were also studied. The antioxidative indices including oxidative lipid peroxidation (LPO) and antioxidative enzymes such as glutathione (GSH), total sulfhydryl (-SH) groups, total ascorbic acid (TAA), superoxide dismutase (SOD) and catalase (CAT) were evaluated in the hepatic tissue using well established techniques. Nickel and/or chromium treatments to mice revealed a significant decline in the levels of these antioxidant parameters as compared to control. Concomitantly a significant increase in lipid peroxidation was obtained. These data indicated that the treatment induced oxidative stress in the hepatic tissue of treated mice, which was more pronounced by combination of metal salts. But supplementation of vitamin E with NiCl2 + K2Cr2O7 to mice exerted no significant alterations in the liver antioxidant system as compared to control, thus indicating its ameliorative role. These findings suggest that vitamin E prevents LPO and protects the antioxidant system in the mouse liver.

Diastereo- and Enantioselective Synthesis of Bicyclic α-Methylene-δ-valero­lactones by Asymmetric Michael Reaction

A synthesis of optically active a-methylene-δ-valerolactones 7 and 13 with 97% ee was achieved by employing a highly stereoselective Michael reaction between chiral imines 2, 9 and the acrylate 3. Reduction of the carbonyl group of the resulting adducts 4 and 10 with KBH 4 followed by lactonization and HWE reaction with formaldehyde yielded the lactones 7 and 13 as mixtures of diastereoisomers. Diastereoselectivity in the reduction of chiral 5-oxoalkanoic acids 4 and 10 was improved by combination of metal salt and hydride reducing agent.

Catalytic Asymmetric Mannich Reactions of Glycine Derivatives with Imines. A New Approach to Optically Active α,β-Diamino Acid Derivatives

Imines of glycine alkyl esters react with imines in a diastereo- and highly enantioselective Mannich reaction in the presence of chiral copper(I) complexes as the catalyst to give optically active alpha,beta-diamino acid derivatives. A series of imines of glycine esters derived from glycine and aromatic carbonyl compounds has been screened as substrates for the Mannich reaction with different imines in the presence of various combinations of metal salts and chiral ligands. The benzophenone imine of glycine esters was found to react with N-protected imines in a diastereoselective fashion giving functionalized alpha,beta-diamino acid esters with excellent enantioselectivities. The most effective chiral catalysts are chiral copper(I) complexes having phosphino-oxazoline (P,N)-ligands, and among these ligands, those derived from (1R,2S)-dihydroxy-1,2,3,4-tetrahydronaphthalene gave the best results. The scope of this new catalytic asymmetric reaction of the benzophenone imine glycine esters is demonstrated for the reaction with different N-protected-C-aryl and C-alkyl imines giving the Mannich adducts with excellent optical purity. Furthermore, the synthetic aspects of the reaction are presented by converting the Mannich adducts into alpha,beta-diamino acid derivatives. The relative and absolute configuration of the Mannich adduct have been determined and based on the stereochemical outcome of the reaction a tetrahedral chiral-copper(I)-imino glycine alkyl ester intermediate is proposed. In this intermediate the Re-face of the benzophenone imine glycine ester is shielded by the chiral ligand leaving the Si-face available for approach of the Si-face of the imine. A series of semiempirical calculations has been performed to support the structure of the tetrahedral chiral-copper(I) complex and to account for the influence of the substituents in the chiral phosphino-oxazoline ligands.

Mechanism of collector adsorption in fluorite flotation

Fluorite is a strategically important mineral. Commercial deposits of fluorite are widespread throughout the world and its availability is essential to industry.1 The method of concentrating fluorite depends on the final application. Whereas a metallurgical-grade fluorite is obtained by gravity and magnetic separation methods, flotation is the major concentration process for the production of acid-grade fluorite. Selective flotation of fluorite from calcite presents many problems because the two minerals have the same cation, Ca++, in their crystal lattices. As a consequence of their similar physical and chemical surface properties anionic collectors float calcite alongside fluorite, and the depressants used for calcite also inhibit the flotation of fluorite. In the separation of fluorite from calcite by flotation various fatty acids (especially, oleic acid and sodium oleate), oleic acid emulsions with petroleum sulphonates, different mixtures of fatty acids, tall oils, alkyl amino-bis-methylene phosphoric acids, alkyl sulphonates, mixtures of oleic and naphtenic acids and amines are used as collectors. Various regulating agents, such as sodium silicate, sodium silicate–metal salt combinations, phosphates, tannic acid, quebracho, starches and sodium ligno-sulphonates, are used to depress calcite and to increase selectivity.2–5 The adsorption of collectors and depressants is largely controlled by the charge at the particle surface. The results produced by different investigations differ considerably and vary widely with minerals of different origin. The investigations reported here were undertaken with the aim of providing an electrophoretic and infrared spectroscopic characterization of fluorite and calcite as a basis for further flotation studies and for controlling the adsorption of electrolytes by exploiting differences in the surface charge.

Probing polystyrene cationization in matrix-assisted laser/desorption ionization

It has been observed that the use of the salts of transition metals other than silver, copper or palladium as the cationizing agent, often fails to cationize polystyrenes in matrix-assisted laser/desorption ionization (MALDI). This work shows that the ability of MALDI to reduce metals to the oxidation state +1 is critically important to polystyrene cationization. Without this reduction, MALDI tends to fail to form polystyrene–metal cations. In addition, this work demonstrates the importance of the use of a good combination of metal salts and matrix in polystyrene cationization. Finally, the implications of this work in the MALDI time-of-flight analysis of polystyrenes are discussed.

X-Y-ZH Systems as potential 1,3-dipoles : Part 15 . Amine generated azaallyl anios versus metallo-1,3-dipoles in cycloadditions of α-amino acid esters. Facile regio- and stereo-specific formation of pyrrolidines

Kinetic studies of the deprotonation of arylidene imines of alanine and phenylglycine esters by tertiary amines and pyridine and cycloaddition of the resultant 4π-azaallyl anions to N-phenylmaleimide show the expected dependance on the p-substituent in the aryl ring. e.g. p-NO 2 > H > OMe >fs NMe 2. A combination of metal salt (silver, lithium. or zinc) and triethylamine in THF, dipolar aprotic solvents (MeCN, DMSO, DMF) or N-methylacetamide effects regio- and stereo-specific or highly stereo-selective inter- and intra-molecular cycloaddition of imines of phenylglycine. alanine and glycine esters to a range of dipolarophiles probably via metallo-1,3-dipole formation at room temperature. Silver acetate is a more efficient and selective catalyst than lithium bromide and reactions in acetonitrile, DMSO or N-methylacetamide, are especially rapid (O.1–3.5h).