Metals and chelates

Most laboratory measurements of trace metal uptake are performed by manipulation of the metal and chelator concentration, and therefore it is often impossible to distinguish between a thermodynamic and a kinetic dependence on the free-ion activity. In fact, only limited work has tested, in detail,... 

Titration with chelators of a metalloenzyme preparation from which extraneous metals and chelators have been removed produces a characteristic enhancement of the intrinsic protein fluorescence (excitation at 280 nm, emission at 350 nm) (13). This fluorescence enhancement by nonfluorescent chelators is instantaneous, reversible by excess added divalent metal ions, and can occur without loss of activity. Different chelators give different characteristic amounts of fluorescence enhancement at saturation, demonstrating the specific effect of the chelator on the fluorescence of the apparent metalloenzyme-chelator complex. In contrast, if the effect of chelators were simply to complex with Mg2 after its dissociation from the metalloenzyme, the resulting apoenzyme should have identical fluorescence properties regardless of which chelator was utilized. 

Soares FA, Farina M, Santos FW, Souza D, Rocha JB, Nogueira CW (2003) Interaction between metals and chelating agents affects glutamate binding on brain synaptic membranes. Neurochem Res 28 1859-1865... 

Bader H, Wilkes AB, Jean DH. 1970. The effect of hudroxylamine, mercaptans, divalent metals and chelators on (Na+ + K+)-ATPase. Biochim Biophys Acta 198 583-593. 

Trialkyl- and triaryl-phosphines, -arsines and -stibines are all good donors toward rf-group transition metals and chelating di- and tri-phosphines and -arsines have been especially widely used as 7r-acid ligands (Section 22-13). The oxides, R3MO, also form many complexes, but they function simply as donors. Trialkyl- and triaryl-phosphines, -arsines and -stibines generally react with alkyl and aryl halides to form quaternary salts ... 

Johnston, R., 1964. Sea water, the natural medium of phytoplankton. II. Trace metals and chelation, and general discussion. J. Mar. Biol. Assoc. U.K., 44 87—109. 

The mechanisms by which the chelates enter plants are not well understood. The chelating substances keep the metals soluble in the soil and are usually taken up by plants with the metals (Holmes and Brown, 1955). In some cases both the metal and chelate are absorbed in corresponding amounts but often the two components are separated in the roots, and the metal enters without the equivalent amount of the carrier. There is also evidence that some of the benefits derived from chelating agents are the result of increased translocation of the metal from the roots to the shoots. Many factors, such as pH, plant species, and metal involved affect the process. In fact, some plants do not respond to additions of chelate metals and the reasons are still in doubt. 

In other words, it was motivated by the semiconductor behavior of the materials. However, due to the combined effect of the conduction mechanism and the number of metal and chelating groups, the decreased in activation energy was observed. 

Alkoxycarbonylcarbenes, which are frequently used for cyclopropanation, have been reviewed by Marchand and Brockway.In conjunction with a copper complex of an asymmetric ligand, ethyl diazoacetate will condense with 2,5-dimethyl-hexa-2,4-diene to give optically active chrysanthemic ester.With a cobalt complex of (+ )-camphorquinone dioxime, enantioselectivities as high as 70 % could be obtained in the addition of diazoacetate to 1,1-disubstituted olefins. As would be expected, choice of both metal and chelate is critical in such asymmetric syntheses. ... 

The concentration of Cu is usually low in food samples, therefore developing sensitive and selective methods for Cu quantification are required. Among the electrochemical techniques, stripping analysis following adsorption accumulation of Cu chelates has demonstrated high sensitivity however after some time of accumulation, metal and chelates may strongly adsorb on the electrode surface. Most of the authors used the standard addition method not only to minimize the food matrix effects, but also to improve the resolution of the voltammetric technique. An ASV procedure at a platinum rotatory disk electrode without the need of Cu-complex formation has been proposed to determine the Cu content of tequila samples [26]. 

The use of the waste iron-EDTA solution is an important idea that has also been considered in the past. EDTA-containing boiler wastes have been spread on dormant alfalfa. The farm plots treated with diluted boiler wastes produced more crop than the untreated plots. This probably is due to the ammonia and iron contained in the boiler cleaning wastes. More attempts to reuse the valuable metals and "chelated micronutrients" should be investigated. 

Transition metals will promote oxidative reactions by hydrogen abstraction and by hydroperoxide decomposition reactions that lead to the formation of free radicals. Prooxidative metal reactivity is inhibited by chelators. Chelators that exhibit antioxidative properties inhibit metal-catalyzed reactions by one or more of the following mechanims prevention of metal redox cycling occupation of all metal coordination sites thus inhibiting transfer of electrons formation of insoluble metal complexes stearic hinderance of interactions between metals and oxidizable substrates (e.g., peroxides). The prooxidative/antioxidative properties of a chelator can often be dependent on both metal and chelator concentrations. For instance, ethylene diamine tetraacetic acid (EDTA) can be prooxidative when EDTAiiron ratios are <1 and antioxidative when EDTAiiron is >1. The prooxidant activity of some metal-chelator complexes is due to the ability of the chelator to increase metal solubility and/or increase the ease by which the metal can redox cycle. 

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