Nickel-EDTA chelate

EDTA (ethylenediaminetetraacetic acid) forms stable metal chelates with a number of metal ions. Using this reagent as a complexing- agent, arsenic, bismuth, and selenium can be determined without any interference in the presence of nickel and cobalt. The cobalt-EDTA chelate is stable in 5 M HCl solution, whereas the corresponding bismuth complex is not. The influence of copper on the determination of arsenic can also be eliminated with EDTA, but not in the determination of selenium. Thiourea has been used to eliminate the influence of copper in the determination of antimony and sodium oxalate to eliminate the influence of copper and nickel in the determination of tin. An addition of thiosemicarbazide and 1,10-phenanthro-line reduces the interference of copper, nickel, platinum, and palladium in the determination of arsenic. 

The first enzyme that was demonstrated to contain nickel was urease (urea amidohydrolase) from jack bean. It catalyzes the hydrolysis of urea to ammonia and carbon dioxide. The protein has a multimeric structure with a relative molecular mass of 590,000 Da. Analysis indicated 12 nickel atoms/mol. Binding studies with the inhibitors indicated an equivalent weight per active site of 105,000, corresponding to 2 nickel atoms/active site. During removal of the metal by treatment with EDTA at pH 3.7, the optical absorption and enzymatic activity correlated with nickel content. This, combined with the sensitivity of the enzyme to the chelating agents acetohydroxamic acid and phos-phoramidate, indicates that nickel is essential to the activity of the enzyme (1). 

EDTA was determined in human plasma and urine by capillary electrophoresis/MS [85]. Using a BC stable labile isotope, the detection and quantitation limits were found to be 7.3 and 14.6 ng/mL, respectively. The running buffer was pH 3.5 ammonium formate/formic acid buffer, at an inlet pressure 50 mb and a separation potential of -30 KV. The same authors [86] utilized this technique for the determination of EDTA as the nickel chelate in environmental water. 

The immobilization of trimeric LHCII is demonstrated in Fig. 13(B). After the nickel ion activation (5), a 1 pM solution of trimeric recombinant LHCII prepared in NaP + DM buffer (20 mM sodium phosphate, pH 7.4, 0.1 % (w/v) n-dodecyl-/ -D-maltoside) was introduced into the flow cell (1). For each cycle, the protein solution was incubated in the loop for 30 min, followed by buffer rinse (2), EDTA (3), and SDS (4) regeneration. EDTA was used to competitively chelate the nickel ions and break the linkage between NTA and Histidine. SDS, as mentioned in Section 4.2, was used to detach any remaining physically adsorbed proteins. As shown in Fig. 13(B), the immobilization/regeneration cycles from (1) to (5) can be well reproduced and the baseline after every cycle stabilized at a response close to the starting level. This indicates that the... 

Chromel is an alloy composed of nickel, iron, and chromium. A 0.6472-g sample was dissolved and diluted to 250.0 mL. When a 50.00-mL aliquot of 0.05182 M EDTA was mixed with an equal volume of the diluted sample, all three ions were chelated, and a 5.11-mL back-titration with 0.06241 M copper(II) was required. The chromium in a second 50.0-mL aliquot was masked through the addition of hexamethylenetetramine titration of the Fe and Ni required 36.28 mL of 0.05182 M EDTA. Iron and chromium were masked with pyrophosphate in a third 50.0-mL aliquot, and the nickel was titrated with 25.91 mL of the EDTA solution. Calculate the percentages of nickel, chromium, and iron in the alloy. 

Derivatives of [14]N4(10) (cyclam) even in low doses have a good efficiency in reducing the lethal response to nickel. These macrocycles significantly enhance the urinary and biliary excretion of Nr and restore the altered levels of other trace metal ions such as Cu-+, Zn-, and Fe They are more efficient in this application than linear chelating agents such as EDTA or triethylenetetraamine (Athar et al., 1987 Misra et al., 1988). 

Metal chelation may enhance or inhibit the Fenton reaction, depending on the metal and the chelator in question. Chelation of iron (II) by EDTA enhances the formation of hydroxyl radical, while deferoxamine, another chelator, reduces its formation. This is significant because peptides or proteins can chelate metals in the body, thus influencing the resulting degree of damage. The formation of hydroxyl radicals by nickel (II) and cobalt (II) is enhanced by this type of chelation. In addition to the Fenton and Haber-Weiss reactions, metals can also catalyze the formation of the hydroxyl radical via reaction with hypochlorite (HOCl), which is prodnced by neutrophils. ... 

The biocidal properties of nickel are modified by many variables. For example, nickel is most lethal at pH 8.3 and least lethal to freshwater crustaceans and fishes at pH 6.3 less toxic to algae when copper is reduced or absent and chelating agents, such as EDTA, are present most lethal to echinoderm embryos prior to gastmlation and more toxic to estuarine amphipods and clams under conditions of decreased salinity in the 0.5-3.5% range and increased temperature in the 5-15°C range. 

The reaction of superoxotitanium(IV) with a number of substrates has been monitored by stopped-flow techniques/ In 1 M perchloric acid, the oxidation of iodide and bromide proceeded with second-order ratde constants of 1.1 x 10 M s and 2M s respectively. It is proposed that the reduction of superoxotitanium(IV) proceeds by a one-electron mechanism. Based on proton dependences, the species TiO " is more reactive than the protonated form Ti02(0H)2. The chromium chelate, bis(2-ethyl-2-hydroxybutyrato)oxochro-mate(V), is reduced by iodide, generating a Cr(IV) intermediate. The reaction is considered to proceed through formation of an iodine atom (T) for which both Cr(V) and Cr(IV) compete. In aqueous solution, [Co(EDTA)] forms a tight ion pair with I . Upon irradiation of this ion pair at 313 nm, reduction of [Co(EDTA)] to [Co(EDTA)] occurs with oxidation of 1 to IJ. The results may be interpreted on the basis of a mechanism in which [Co(EDTA)] and V are the primary photoproducts where the latter subsequently disproportionate to I3 and 1 . The kinetics and mechanism of the oxidation of 1 by a number of tetraaza macrocyclic complexes of Ni(III) have been reported. Variations in rate constants and reaction pathways are attributable to structural differences in the macrocyclic ligands. Of interest is the fact that with some of the Ni(III) complexes, spectrophotometric evidence has been obtained for an inner-sphere process with characterization of the transient [Ni(III) L(I)] intermediates. Iodide has also been used as a reductant for a nickel(III) complex of R-2-methyl-1,4,7-triazacylononane. In contrast to the square-planar macrocycles, the octahedral... 

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