Metal ions, influence

In the 1920s, the Russian chemist Il ya Il ich Chemyaev systematized reactions of complexes of several metals, particularly platinum(II and IV), by noting that a ligand bound to a metal ion influenced the ease of replacement of the group trans to it in the complex [139]. 

The fact that nitrite reacts with the iron of the heme compound was described earlier. Because such a large number of metal ions are present in meat, and because some occur in relatively high concentration, there has been considerable interest in them. For the most part, studies have dealt with how metal ions influence reactions of nitrite. The role of sodium chloride (which is used extensively in meat processing) must also be recognized both in terms of its functional role in making reactants in the meat more or less available, and in terms of reports that it directly influences nitrosation reactions (50). Ando (51) studied the effect of several metal ions on decomposition of nitrite, and in the absence of ascorbate, only Fe++ caused a loss of nitrite but in its presence, the effect of Fe " was more pronounced and Fe+++, Mg++, Ca++ and Zn++ showed similar effects. Lee e al. 

The equilibrium speciation of a metal ion influenced by cation exchange is dependent on the relative concentrations of the cations competing for the negatively charged sites on the particle s surface and their relative affinities for adsorption. Since one cation displaces another from the negatively charged sites, this process is termed cation exchange. 

How Does the Nature of the Metal Ion Influence Complexation If the metal-ligand complex is the result of electrostatic attraction between the metal ion and the ligand, then both charge and metal ion size are influential. For example, the stability constants (KM]) for phosphate complexes are as follows ... 

Myriad polydentate aza-macrocycles have been reported 41. The extent of the subject forces limitation of this discussion to only macrocycles containing a pyridine or dipyridine subunit. Most of these coronands have been synthesized by a SchifF base condensation of an aldehyde or ketone with a hfc-primary amine in the presence of a metal ion. The metal ion acts as a template, resulting in dramatic increases in yield of the desired cyclic product over linear polymerization products42 46. Lindoy and Busch45 have described this effect in two ways, kinetic and thermodynamic. If the metal ion controls the steric course of a series of stepwise reactions, the template effect is considered to be kinetic. If the metal ion influences an equilibrium in an organic reaction sequence by coordination with one of the reactants, the template effect is termed thermodynamic. It is the kinetic effect that is believed to be operative in most metal ion-assisted (in situ) syntheses of... 

It is a fact that metal ions influence the catalytic activity of enzymes. In case of amino acylase also it was reported that metal ions have high influence on its activity [4]. For the purpose to obtain further advantageous conditions of the resolution process, a study on the... 

In the hydrolysis of all these monophosphate esters, cleavage of the P—O bond occurs exclusively and in this respect resembles enzymatic reactions involving alkaline phosphatases. Although dipositive metal ions influence the hydrolysis of certain diesters of phosphoric acid, there is insufficient evidence for the postulation of chelated intermediates (186). 

Besides Fe", many other metal ions yield analogous results. The nature of the metal ion influences the critical energies of the insertion and abstraction steps in Schemes 20 and 21 and, thus, determines the overall reaction rate The detailed gas-phase chemistry between bare or ligated metal ions and a large variety of organic substrates, including alkynes, is thoroughly reviewed in Reference 19. 

For doped metal oxides, the aliovalent metal ions influence the overall defect concentrations via what is sometimes called the First Law of Doping. This law simply states that adding an aliovalent dopant increases the concentration of defects with opposite charges, and decreases the concentration of defects with charges of the same sign. 

Activation polarization is also characteristic of metal-ion deposition or dissolution. The value may be small for nontransition metals, such as silver, copper, and zinc, but it is larger for the transition metals, such as iron, cobalt, nickel, and chromium (see Table 5.1). The anion associated with the metal ion influences metal overpotential values more than in the case of hydrogen overpotential. The controlling step in the reaction is not known precisely, but, in some cases, it is probably a slow rate of hydration of the metal ion as it leaves the metal lattice, or dehydration of the hydrated ion as it enters the lattice. 

The antibacterial effect of metal ions and especially silver, copper and zinc ions is well known. Silver and silver ions are used in medicinal treatments ranging from severe burns to Legionnaires Diseases. Silver-based products are also applied in water purification processes. Metal ions achieve their antibacterial effect by two mechanisms First the metal ions influence the electrochemical potential between the internal and external parts of the cell, and second, after penetration of ions into the cell, they compete with other essential ions like magnesium, calcium and potassium and they aggregate with thiol groups of enzymes and proteins. 

Many reactions are known in which the presence of a metal ion influences the products of a reaction and the explanation for this may well lie in the different reactions of free and coordinated ligands. Peptide chemistry is one field in which this may prove to be of great importance. 

Correia, M.J.N. Marques, M.M. Ismael, M.R. Reis, M.T.A. (2005). Ionic Liquids as Extractants of Phenolic Compounds and Metal Ions Influence of the Type of Ionic Liquid. Proceedings of International Solvent Extraction Conference, ISBN 7-900692-02-9, Beijing, September 2005... 

The topology of MOFs depends on metal coordination. The bonding modes involving metal ions influence the MOF properties. The local metal environment in a MOF is often affected by activation (such as dehy-dration/desolvation) and adsorption of guest species. Therefore, the local structure of metal center needs to be characterized. 

Metal-mediated reactions involving water are essential to life and catalytic industrial processes [1-3]. In biological systems, metalloenzymes containing various divalent metal ions catalyze the hydrolysis of amide, carboxylic ester and phosphate ester bonds using both mono- and multinuclear active-site structural motifs [4—6], Mononuclear metal centers are also found within the active sites of enzymes that catalyze the hydration, or the addition of water, to CO2 [Zn(II)] and nitriles [Co(III)/Fe(III)j [7-10]. In many of these processes, formation of a metal hydroxide moiety via deprotonation of a metal-coordinated water molecule is a key proposed step in the reaction pathway. Thus, a substantial amount of research over the past several years has been directed at dehneating how the structural and electronic environments of biological metal ions influence the pKa of a metal-bound water molecule. In this regard, studies directed at the preparation, characterization and elucidation of the reactivity of discrete metal aqua and hydroxo complexes have been paramoimt [11-13]. 

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