Processes metal ions

Figure 3. Schematic illustration of core/shell nanoparticle formation via redox transmetalation process. Metal ions (Mu) of reactant metal complexes (Mn-L ) are reduced on the surface of Mi nanoparticles while neutral Mi atoms are oxidized to Mi " by forming a Mi-ligand complex (Mi-Lj) as a resultant reaction byproduct. Repeating this process results in the complete coverage of shell layers on core metals. (Reprinted from Ref [145], 2005, with permission from American Chemical Society.)...

In natural processes, metal ions are often in high oxidation states (2 or 3), whereas in chemical systems the metals are in low oxidation states (0 or 1). This fact inverts the role of the metal center, such that it acts as a one-electron sink in a natural system, but as a nucleophile in an artificial ones (see other chapters of this book and the review by Aresta et al. [109]). Nevertheless, important biochemical processes such as the reversible enzymatic hydration of C02, or the formation of metal carbamates, may serve as natural models for many synthetic purposes. Starting from the properties of carbonic anhydrase (a zinc metalloenzyme that performs the activation of C02), Schenk et al. proposed a review [110] of perspectives to build biomimetic chemical catalysts by means of high-level DFT or ah initio calculations for both the gas phase and in the condensed state. The fixation of C02 by Zn(II) complexes to undergo the hydration of C02 (Figure 4.17) the use of Cr, Co, or Zn complexes as catalysts for the coordination-insertion reaction of C02 with epoxides and the theoretical aspects of carbamate synthesis, especially for the formation of Mg2+ and Li+ carbamates, are discussed in the review of Schenk... 

A9.7.3.1 Environmental transformation of one species of a metal to another species of the same does not constitute degradation as applied to organic compounds and may increase or decrease the availability and bioavailability of the toxic species. However as a result of naturally occurring geochemical processes metal ions can partition from the water column. Data on water column residence time, the processes involved at the water - sediment interface (i.e. deposition and re-mobilization) are fairly extensive, but have not been integrated into a meaningful database. Nevertheless, using the principles and assumptions discussed above in A9.7.1, it may be possible to incorporate this approach into classification. 

Nonenzymatic hydrolysis of RNA assisted by metals (312-316) as well as by some ribozymes (317, 318) presumably follows the mechanism described above. Metals may be involved in the deprotonation of the 2 -OH group (319). Ribozymes, now recognized as metalloenz5mies (318,320,321), correspond to selected sequences of RNA able to cleave the same strand (intramolecular process) or an RNA sequence on a different strand (intermolecular process). Metal ions are necessary to ribozymal activity (318). They promote the folding of the secondary structure of RNA into an active tertiary structure, and it is difficult to discriminate between their structural and/or catalytic role (322, 323). 

As a complexation process, metal-ion binding to a SAM presents a ligand-exchange equilibrium for the metal ions between the solution and the surface. In contrast with solution-based systems, direct in situ quantitative measurement of the composition of a SAM is experimentally challenging. Therefore, a variety of in situ... 

The indirect electrolysis that uses metallic couples such as Ag(II), Ce (IV), Co(III), and Fe (III) as redox reagents is called Mediated Electrochemical Oxidation (MEO) [4]. In this process, metal ions in acidic solutions are oxidized... 

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. 

The oxidation of hydrocarbons follows a radical chain reaction. Hydroperoxide radicals are formed and these radicals react to give various oxygenated products [for the detailed mechanism see Cheung, Tanke, and Torrence (2000)]. The oxidation of hydrocarbons can be non-catalytic. For catalytic processes metal ions, for example, Mn, Co, Ni, and Cr, are used as catalysts. 

In electrodepostion processes metal ions are reduced to metal atoms at the cathode of an electrolysis cell. The shape of the cathode can be adjusted to obtain the precipitated metal in a desired form. 

As an adjective applied to metals base represents the opposite of noble, i.e. a base metal would be attacked by mineral acids, base exchange An old term used to describe the capacity of soils, zeolites, clays, etc. to exchange their cations (Na, K, Ca ) for an equivalent of other cations without undergoing structural change. An example of the general process of ion exchange. ... 

So far the four metal ions have been compared with respect to their effect on (1) the equilibrium constant for complexation to 2.4c, (2) the rate constant of the Diels-Alder reaction of the complexes with 2.5 and (3) the substituent effect on processes (1) and (2). We have tried to correlate these data with some physical parameters of the respective metal-ions. The second ionisation potential of the metal should, in principle, reflect its Lewis acidity. Furthermore the values for Iq i might be strongly influenced by the Lewis-acidity of the metal. A quantitative correlation between these two parameters... 

In resolving complex metal-ion mixtures, more than one masking or demasking process may be utilized with various aliquots of the sample solution, or applied simultaneously or stepwise with a single aliquot. In favorable cases, even four or five metals can be determined in a mixture by the application of direct and indirect masking processes. Of course, not all components of the mixture need be determined by chelometric titrations. For example, redox titrimetry may be applied to the determination of one or more of the metals present. 

Extraction of metal ions Extraction processes Extraction resistance Extractive distillation... 

Butane-Naphtha Catalytic Liquid-Phase Oxidation. Direct Hquid-phase oxidation ofbutane and/or naphtha [8030-30-6] was once the most favored worldwide route to acetic acid because of the low cost of these hydrocarbons. Butane [106-97-8] in the presence of metallic ions, eg, cobalt, chromium, or manganese, undergoes simple air oxidation in acetic acid solvent (48). The peroxidic intermediates are decomposed by high temperature, by mechanical agitation, and by action of the metallic catalysts, to form acetic acid and a comparatively small suite of other compounds (49). Ethyl acetate and butanone are produced, and the process can be altered to provide larger quantities of these valuable materials. Ethanol is thought to be an important intermediate (50) acetone forms through a minor pathway from isobutane present in the hydrocarbon feed. Formic acid, propionic acid, and minor quantities of butyric acid are also formed. 

Ion Flotation and Foam Separation. Ions and dissolved surfactant molecules can be removed from solutions by the agency of foam. In this case ions are sandwiched in foam films. The scientific basis of these processes is weU understood and successes of metal ion recovery from solutions including U, Pt, Au, as weU as different surfactants (detergents) have been reported in the Hterature. 

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