Chelating agents mechanism

DispEcement. In many of the appHcations of chelating agents, the overall effect appears to be a displacement reaction, although the mechanism probably comprises dissociations and recombinations. The basis for many analytical titrations is the displacement of hydrogen ions by a metal, and the displacement of metal by hydrogen ions or other metal ions is a step in metal recovery processes. Some analytical pM indicators function by changing color as one chelant is displaced from its metal by another. 

The rate of peroxide decomposition and the resultant rate of oxidation are markedly increased by the presence of ions of metals such as iron, copper, manganese, and cobalt [13]. This catalytic decomposition is based on a redox mechanism, as in Figure 15.2. Consequently, it is important to control and limit the amounts of metal impurities in raw rubber. The influence of antioxidants against these rubber poisons depends at least partially on a complex formation (chelation) of the damaging ion. In favor of this theory is the fact that simple chelating agents that have no aging-protective activity, like ethylene diamine tetracetic acid (EDTA), act as copper protectors. 

These two mechanisms (DNA damage by OH or by activation of nucleases) are not mutually exclusive, i.e. they could both take place (Fig. 13.1). Indeed, there is evidence consistent with the existence of both mechanisms. Their relative importance may depend on the cell type used and on how the oxidative stress is imposed (Halliwell and Aruoma, 1991). For example, chelating agents that bind iron ions into chelates unable to generate OH (such as desferrioxamine. 

Palmer 1989 Robinson et al.1983). However, the ratio was almost certainly affected by initial chelation with Ca-DPTA, followed by daily intravenous therapy with the chelating agent, Zn-DPTA, treatments that would have increased the urinary excretion of americium (Breitenstein and Palmer 1989). The above not withstanding, the observations made on this subject demonstrate that fecal excretion was an important pathway of excretion in this subject long after mechanical clearance of americium from the respiratory tract would have been complete. This is consistent with observations made in nonhuman primates that show that americium is excreted into bile (see Section 3.4.4.4). However, the extent to which the biliary excretion pathway in humans might resemble that of nonhuman primates is not known. 

Yadav RS, Mishra P, Mishra R, Kumar M, Pandey AC (2010) Growth mechanism and optical property of CdS nanoparticles synthesised using amino-acid histidine as chelating agent under sonochemical process. Ultrason Sonochem 17 116-122... 

The book focuses on three main themes catalyst preparation and activation, reaction mechanism, and process-related topics. A panel of expert contributors discusses synthesis of catalysts, carbon nanomaterials, nitric oxide calcinations, the influence of carbon, catalytic performance issues, chelating agents, and Cu and alkali promoters. They also explore Co/silica catalysts, thermodynamic control, the Two Alpha model, co-feeding experiments, internal diffusion limitations. Fe-LTFT selectivity, and the effect of co-fed water. Lastly, the book examines cross-flow filtration, kinetic studies, reduction of CO emissions, syncrude, and low-temperature water-gas shift. 

Reaction with chelating agents. Such reactions have been used primarily for partial dealumination of Y zeolites. In 1968, Kerr (8,21) reported the preparation of aluminum-deficient Y zeolites by extraction of aluminum from the framework with EDTA. Using this method, up to about 50 percent of the aluminum atoms was removed from the zeolite in the form of a water soluble chelate, without any appreciable loss in zeolite crystallinity. Later work (22) has shown that about 80 percent of framework aluminum can be removed with EDTA, while the zeolite maintains about 60 to 70 percent of its initial crystallinity. Beaumont and Barthomeuf (23-25) used acetylacetone and several amino-acid-derived chelating agents for the extraction of aluminum from Y zeolites. Dealumination of Y zeolites with tartaric acid has also been reported (26). A mechanism for the removal of framework aluminum by EDTA has been proposed by Kerr (8). It involves the hydrolysis of Si-O-Al bonds, similar to the scheme in Figure 1A, followed by formation of a soluble chelate between cationic, non-framework aluminum and EDTA. 

There is no reason to believe that replacement of water by the donor groups of a chelating agent is fundamentally different from replacement when only unidentate ligands are involved. However, the multiplicity of steps may increase the difficulty in understanding the detailed mechanism, and mainly for this reason the simpler bidentate ligands have been most studied. 

Pharmacology Wilson disease (hepatolenticular degeneration) is an inherited metabolic defect resulting in excess copper accumulation, possibly because the liver lacks the mechanism to excrete free copper into the bile. Hepatocytes store excess copper, but when their capacity is exceeded, copper is released into the blood and is taken up into extrahepatic sites. Treat this condition with a low copper diet and chelating agents that bind copper to facilitate its excretion from the body. Trientine is a chelating compound for removal of excess copper from the body. 

Mechanism of Action A chelating agent that contains two sulfhydryl groups that form a stable, nontoxic chelate 5-membered heterocyclic ring with heavy metals. Therapeutic Effect Prevents the metal from combining with sulfhydryl groups on physiologic proteins and keeps them inactive until they can be excreted. 

Mechanism of Action A chelating agent that reduces blood concentration of heavy melals, especially lead, forming stable complexes. Therapeutic Effect Allows heavy metal excretion in urine. 

Mechanism of Action A chelating agent that forms a soluble chelate with calcium, resulting in rapid decrease in plasma calcium concentrations. Therapeutic Effect Allows calcium to be excreted in urine. 

Mechanism of Action An oral chelating agent that forms complexes by binding metal ions, particularly copper. Therapeutic Effect Binds to copper and induces cupruresis. Pharmacokinetics None reported. 

Fig. 8. Mechanism proposed for the transfer of iron from low molecular weight chelates to apotransferrin involving the intermediate ternary complex of protein-iron-chelate. The polynuclear iron must be depolymerized prior to its binding by the protein. The presence of excess chelating agents, particularly citrate, leads to the formation of the bis complex which reacts rapidly...

Order with respect to the polyisoprenyllithium concentration [PILi3. In the propagation reaction we have determined the order with respect to polyisoprenyllithium in absence of any chelating agent at 18°C (figure 6). We found 0.3, value which may be assimilated to 0.25 as given by BYWATER AND WORSFOLD 0). The following mechanism is proposed Q) ... 

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