Catalytic Effect Of Metal Ions Research Articles

Studies on clavulanic acid. Part 2. The catalytic effect of metal ions on the hydrolysis of clavulanic acid

The metal (II)-ion-catalysed hydrolysis of clavulanic acid in water shows saturation kinetics. A 1:1 complex is formed between the metal ion and clavulanic acid, which is attacked by hydroxide ion ca. 2 × 106 times as fast as the unco-ordinated clavulanic acid. The catalytic effect produced by the copper(II) ion on the decomposition of the methyl ester of clavulanic acid shows a much smaller rate enhancement, indicating that the site of co-ordination for the clavulanic acid involves the ionized carboxylate group. The co-ordination sites of the clavulanic acid are the β-lactam nitrogen and the carboxylate group. The association constants between clavulanate ion and several transition metal ions have been determined. The order of rate enhancement brought about by the metal ion is CuII > ZnII > CdII > CoII > NiII > MnII. The reaction is inhibited by the presence of anions co-ordinating with the copper(II) ion.

Chemical and physical modification of proteins by the hydroxide ion.

Proteins are exposed to alkaline conditions during solubilization and/or purification, during food storage and processing, in removal of toxic constituents, and for characterization. During alkali treatment, there are changes in solubility and aggregation, hydrolysis, elimination reactions involving the side chains of certain amino acids, racemization of amino acid residues, addition of compounds to proteins, fragmentation of the peptide chain, as well as modification or elimination of nonprotein constituents. The rates of these reactions are affected by pH, temperature, cations (in some cases), ionic strength (in some cases), protein concentration, and to some extent by the specific nature of the protein. The general mechanisms and stoichiometry of these reactions are described. Other constituents of high protein foods also undergo reactions in alkaline solutions and the products of these reactions may in turn react with proteins. We have described the effect of alkali on enediol formation and fragmentation of carbohydrates, the hydrolysis of lipids in alkaline solution and effect on rate of peroxidation of the polyunsaturated fatty acids, the oxidation of amino acid residues, especially methionine, the oxidation of phenols to benzoquinones, and the catalytic effect of metal ions in alkaline solutions. Alkali treatment is also used in the specific modification of proteins to distinguish between O-glycosyl and amide-linked glycosyl groups, to effect specific cleavage of peptide bonds via beta elimination, in the formation of anhydrotrypsin, anhydrochymotrypsin, anhydrosubtilisin and thiol-subtilisin, and in formation of intrachain crosslinking in proteins.

Quantum-chemical study of electronic structure and enthalpy of decomposition of azodicarbonamide

Azodicarbonamide (ADA) is widely used in industry as a blowing agent in the production of foamed plastics, artificial leathers, and foamed polyvinyl chloride [i]. One of the possible means for regulating the process of ADA decomposition is catalysis by compounds of various metals [2]. In investigating the mechanism of ADA decomposition, it is important to understand the features of the electronic structure of the azodicarbonamide and the reasons for the catalytic effects of metal ions in this process. In this connection, we have investigated the spatial structure of different conformers of ADA and its chelates with zinc ion and zinc oxide, using the SCF--LCAO-MO method in the CNDO/2 approximation [3]. The calculations of the conformers were performed with complete optimization of the geometry in accordance with a program using the gradient method to find the minimum in the total energy [4]. In calculating the enthalpy of ADA decomposition, we used the MINDO/3 method [5].

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a plantimum electrode

The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO4 were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi3+. This indicates the accelerating effect of Bi3+ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb2+, Hg2+, Tl+, Ag+ and Sb3+, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as Mad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co2+, Zn2+, Fe3+ and Ni2+, exhibit no catalytic effect. These facts suggest that the presence of a Mad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the Mad, for example, Cuad, Cdad, Inad, Snad and Moad display no catalytic action. The catalytic activity depends on the degree of surface coverage by the Mad. The maximal effect of the Mad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the Mad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the 13C NMR spectra for the oxidation products, the adsorbed water on the Mad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.

Catalytic effects of metal submonolayers formed by faradaic adsorption on the anodic oxidation of ascorbic acid at a platinum electrode

The catalytic effects of metal ions on the anodic oxidation of ascorbic acid on a Pt electrode in 1 M HClO 4 were studied by linear sweep voltammetry. The anodic peak due to a two-electron oxidation of ascorbic acid shifts to the negative potential side on the addition of Bi 3+. This indicates the accelerating effect of Bi 3+ on the oxidation of ascorbic acid. The presence of other metal ions, such as Pb 2+, Hg 2+, Tl +, Ag + and Sb 3+, also exerts similar effects. These metal ions were adsorbed on a Pt electrode at underpotentials and the adsorbed metals (denoted as M ad) still remain on the electrode surface until the electrode potential goes up to and beyond the peak potential of the oxidation of ascorbic acid. On the other hand, metal ions forming no adsorbed layer on Pt, such as Co 2+, Zn 2+, Fe 3+ and Ni 2+, exhibit no catalytic effect. These facts suggest that the presence of a M ad on Pt is essential for the promotion of the anodic oxidation of ascorbic acid. However, there is a difference in the catalytic action among the M ad, for example, Cu ad, Cd ad, In ad, Sn ad and Mo ad display no catalytic action. The catalytic activity depends on the degree of surface coverage by the M ad. The maximal effect of the M ad is attained in the submonolayer region. The effects of metal ions were discussed on the basis that the M ad plays its major role in the removal of the adsorbed ascorbic acid occupying active sites on the electrode surface, and provides effective sites for the activation of adjacent water molecules. Furthermore, from the 13C NMR spectra for the oxidation products, the adsorbed water on the M ad appears to function by promoting the subsequent hydration steps, following the electron-transfer step of ascorbic acid.

Coordination polymers. IX

Poly-(butanediol-1,4-adipate) and poly-(diethyleneglycol-succinate) polyesters and their “ionized” derivatives, containing Mg2+ and Zn2+ ions with different stoichiometric ratios to the chain-end COOH groups of the polyesters have been investigated by derivatograph.The thermal decompositions of the metal-containing polyesters differ significantly from those of the unionized polyesters. These differences are connected with the chemical repeating unit of the polyesters and the chemical nature of the metal ions, and proportional to the amount of the latter.An explanation is given of the catalytic effect of metal ions on the process of decomposition of the polyesters.

Complexes of dioxouranium(VI) with pyridoxal and glycine

The catalytic effect of metal ions upon transamination reactions of aminoacids by pyridoxal and its derivatives has been demonstrated through formation of intermediate metal complexes of Schiff bases [1–5]. In our laboratory the role of dioxouranium(VI) ions in biochemical processes is under investigation and several complexes between UO 2+ 2 and biomolecules have been hitherto prepared and studied. Recently, the interaction of dioxouranium(VI) acetate with the ligand pyridoxal has been studied and the bonding of dioxouranium(VI) to phenolic and aldehydic oxygen atoms of pyridoxal has been proved [6,7]. The influence of uranyl ions on aminoacid-pyridoxal complexes has been investigated as well. The pyridoxal-glycine-uranyl acetate system has been studied both in solution and in solid state by electronic spectra and i.r. measurements respectively. The electronic spectra of an equimolar mixture of methanolic pyridoxal and glycine show peaks near 360 nm and 320 nm. The peaks markedly increase, when uranyl is added in equimolar amount, as a function of time with a red shift to 390 nm and 343 nm respectively. The band at 278 nm, due to the phenolic group of pyridoxal, appears also slightly shifted to 275 nm and two isosbestic points are present at 290 nm and 275 nm. The resulting spectrum of methanolic pyridoxal-glycine-uranyl complex is identical to that of a pyridoxylidene-glycine-dioxouraniuim(VI) mixture. The results obtained in the solid state indicate that ternary complexes 1:1:1 are formed and the elemental analysis is in agreement with the formulation: UO 2(C 8H 8NO 2)(C 2H 3NO 3)(CH 3COO)2H 2O. The i.r. spectrum of the uranyl solid complex was compared with the spectra of the free components. Changes in the i.r. absorptions are observed in particular in the regions where the azomethine CN stretching, the phenolic carbon–oxygen stretching and the asymmetric carboxyl stretching respectively occur. In fact, the azomethine stretch , v CN, is assignable to the strong band near 1610 cm −1 and the v COO and v CO to the absorption peaks near 1570 cm −1 and 1510 cm −1 respectively.

Catalytic effects of metal ions on the anodic oxidation of ascorbic acid at a platinum electrode.

The catalytic effects of several metal ions on the anodic oxidation of ascorbic acid (I) at a platinum electrode were studied by a linear sweep voltammetry in 1M perchloric acid. Contrary to the air-oxidation of I, Bi3+ and Pb2+ exhibit a marked effect whereas Cu2+ shows a minor one.

ChemInform Abstract: SYNTHESIS OF VINCA ALKALOIDS AND RELATED COMPOUNDS. II. STEREOSELECTIVE AND ENANTIOSELECTIVE SYNTHESIS OF (+)‐VINCAMINE

AbstractKondensation der Komponenten (I) und (II) und Hydrierung des Produkts (III) liefern das Acetat (IVa), das zum racemischen Alkohol (IVb) verseift wird.

Synthesis of vinca alkaloids and related compounds—II : Stereoselective and enantioselective synthesis of (+)-vincamine

Addition of α-acetoxy acrilic acid (-)-menthyl ester to enamine 1 produces about 40% asymmetric induction. The compound obtained, 9b, can be converted into (+)-vincamine with ease and in good yield. The catalytic effect of metal ions on the epimerisation of the vincamine-epivincamine system was investigated.

Catalytic effect of metal ions on photochemical reactions of molecular oxygen, III. Photochemical autoxidation of sulfite catalyzed by manganese(II) ions

The rate of photoinitiated autoxidation of sulfite is influenced by manganese(II) ions even in trace concentrations. An increase in the concentration of manganese(II) ions in the reaction system increases the quantum yield of the photoinitiated reaction.

Reactive intermediate products in the reaction of p-toluenediazonium sulfate, thiocyanate ion and some kinds of metal ions (author's transl)

Catalytic effect of metal ions on the reaction of p-toluenediazonium sulfate and thiocyanate ion was examined with p-tolyl thiocyanate produced using gas-liquid chromatography. The catalytic actiono f bivalent and trivalent iron ions was apparently more effective than that of univalent copper. From these reactions, double complexes of p-toluenediazonium ion with metal thiocyanate of general formula [chemical formula] were isolated. These substances rapidly decomposed when heated above their mp, yielding p-tolyl thiocyanate, which is the same compound obtained by the reaction of the solution of diazonium salts with metal thiocyanates. This is a strong evidence that these double complexes were actually formed in the Sandmeyer reaction.

Metal ion catalysis of phosphoryl hydrolysis from thiolphosphate monoesters

The catalytic effect of metal ions on the hydrolysis of ethyl-S-phosphate (1a), cysteamine-S-phosphate (1b), and 2-carboxyethyl-S-phosphate (1c) has been investigated. Fe(III) and Al(III) markedly inhibit the rate of hydrolysis of all three thiolphosphates, decreasing k abs by ca. 10 2 at pH 3; Zn(II) and Mn(II) are almost without effect on the hydrolysis rates of 1b and 1c; and Cu(II) in less than substrate concentration increases k abs by 10 2 for 1b and 1c but has no effect on 1a. The requirement of a suitably located ligand for catalysis is obvious. The mechanism of the Cu(II)-catalyzed hydrolysis of 1b has been examined in detail and includes the following pertinent characteristics: (1) rate-determining formation of two hydrolytically labile complexes from monoanion (NH 2RSPO 3H -) and/or dianion (NH 2RSPO 3 2-) and Cu(H 2O) 1 2+; (2) product inhibition by cysteamine because of the formation of a catalytically inactive cysteamine-Cu(II) complex; and (3) incursion of an oxidative Cu(II)-catalyzed conversion of cysteamine to cystamine at pH 7, which relieves product inhibition. The synthetic phosphorylating potential of this reaction in acetonitrile-alcohol solvent mixtures indicates its utility in the synthesis of simple phosphate monoesters. A rationale for the effectiveness of Cu(II) catalysis in these systems is offered.

The Catalytic Effect of Metal Ions on the Hydrolysis of Disodium Pyrophosphite

The Catalytic Effect of Metal Ions on the Hydrolysis of Disodium Pyrophosphite

Rate Studies on the Anaerobic Degradation of Ascorbic Acid IV: Catalytic Effect of Metal Ions

The effect of different metal ions on the rate of the anaerobic degradation of ascorbic acid in aqueous solution has been studied. Among the bivalent metal ions tested, Pb 2+ was the most powerful catalyst, followed by Zn 2+ , Co 2+ , Fe 2+ , Mn 2+ , Ni 2+ , Ca 2+ , and Mg 2+ . Also the trivalent metal ions Al 3+ and Cr 3+ catalyzed the process, Al 3+ being more active than Cr 3+ . The experimental results seem to indicate that the metal ions form complexes with ascorbic acid.

The Spectrophotometric Determination of a Small Amount of l-Ascorbic Acid with the Iron(III)-1, 10-Phenanthroline Reagent

Abstract A simple and accurate spectrophotometric method with the iron(III) -1, 10-phenanthroline reagent has been established for the determination of a small amount of l-ascorbic acid ; it has been applied to the measurement of the catalytic effects of metal ions on the autoxidation of l-ascorbic acid.