Chelate-forming agents

Amino and thio analogues of these compounds, i.e., 0-ketoamines and thio-/3-diketones, have also been used as chelate-forming agents. 

CM Wai, KE Laintz. Extraction of metals using carbon dioxide as supercritical fluid with diketone as chelate-forming agent. US patent US5730874A, 1998. 

Chelating agents complex-forming agents having the ability to solubilize heavy metals. 

Another method to increase the number of metals associated with each macromolecule is to attach them, in a chelated form, to a carrier molecule with many sites of attachment. An example of this can be found in the work of Meade [29], His group has synthesized a fi-cyclodcxtrin from which seven Gd-DOTA complexes were attached using highly efficient click chemistry. The contrast agent was observed to accumulate in primary cancers but then localize in secondary metastases over the subsequent 48 hours. This is a particularly valuable property as one of the main problems with cancer treatment is the inability to detect these small secondary tumours in their early stages. 

Disodium edetate forms stable water-soluble complexes (chelates) with alkaline earth and heavy-metal ions. The chelated form has few of the properties of the free ion, and for this reason chelating agents are often described as removing ions from solution, a process known as sequestering. The stability of the metal-edetate complex is dependent on the metal ion involved and the pH. 

Edetic acid and edetate salts are used in pharmaceutical formulations, cosmetics, and foods as chelating agents. They form stable water-soluble complexes (chelates) with alkaline earth and heavy metal ions. The chelated form has few of the properties of the free ion, and for this reason chelating agents are often described as removing ions from solution this process is also called sequestering. The stability of the metal-edetate complex depends on the metal ion involved and also on the pH. The calcium chelate is relatively weak and will preferentially chelate heavy metals, such as iron, copper, and lead, with the release of calcium ions. For this reason, edetate calcium disodium is used therapeutically in cases of lead poisoning see also Section 18. 

To decrease hydrolysis and to increase selectivity we have employed complex-forming agents such as DTPA and tartaric acid ( 1 ) The results show that Am extraction in the NaOH-tartaric acid solution is approximately the same as that of Eu. At low concentrations of the alkali the distribution coefficients are small as the concentration increases, the extraction of Am and Eu sharply increases to reach a maximum at 2 M NaOH ( 99%) and to stay constant up to 10 M. The R = f/NaOH/ dependence by Am and Eu extraction in the form of tartrates by aliquat-336 was different, namely the extraction was high at low alkali concentrations and poor at NaOH concentration greater than 2 M. It may be assumed that DOP forms strong chelates with trivalent actinides and lantha-... 

Important examples are chelates formed with polycarboxylic acids or polyhydroxy-polycarboxylic acids like oxalic, tartaric, or citric acid, which can be used to stabilize acidic tungsten solutions (to prevent polycondensation), or chromogenic agents which react to colored chelates, like f.e. toluene-3,4-dithiol. Several chelates play an important role in the analytical chemistry of tungsten. 

Cerium(IV) was also used as an oxidizing agent in a study of the oxidation of the inert chelates formed with chromium(III) and oxalate ion. From kinetic measurements in aqueous sulfuric acid media, it was concluded that the oxidation of tris(oxalato)chromium(III) ion, cis-bis(oxalato)-chromate(III) ion, and the monooxalatochromium(III) ion follow initial second-order kinetics, and 1 mole of oxalate is oxidized to carbon dioxide for every 2 moles of cerium(IV) reduced to cerium(III). A detailed study of the oxidation of the bisoxalato chelate indicated that cerium(III) inhibits the reaction (197). 

USE As chelating agent [or trivalent iron from pH 7 to pH 10. Forms strong 1 l ferric chelates. The iron chelates formed will then chelate other heavy metal or alkaline earth ions. 

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