Chelator concentrations

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,... 

The rate of inactivation by chelators is strongly dependent on temperature, pH, and protein concentration (13). Between 16° and 30° the activation energy for the chelator-dependent loss of activity is 41 kcal at pH 8.2. At 30° the rate of inactivation is over 200-fold faster at pH 8.7 than at pH 7.2. The inactivation is much faster in dilute than in concentrated enzyme solutions as the protein concentration is increased, correspondingly more rigorous conditions must be employed to observe inactivation. The rate of inactivation appears to exhibit saturation kinetics with respect to chelator concentration. At high EDTA levels the inactivation rate approaches a maximum which is independent of chelator concentration (13). 

Values of KD have been estimated by fluorescence titration and by measurement of the rate of inactivation as a function of chelator concentration (13). In general, those chelators that form the most stable complexes with Mg2 also bind most strongly to the metalloenzyme, though far less strongly than to free Mg2. Chelators with bulky non-... 

Apparently the toxicity of copper to plankton depends upon the free metal concentration, as is shown in experiments with varying chelator concentrations (7, ). Calculations using the REDEQL computer model for metal speelation (, 9 ) related data from toxicity experiments to free metal concentrations. Partial growth inhibition is found in the activity -11 -9... 

Several other organic acids which modify iron absorption are also listed in Table V. EDTA has received much attention for it forms a highly stable iron chelate, and one would expect it to inhibit iron absorption. When sodium ferric EDTA (NaFeEDTA) was fed directly as a liquid, inhibition of iron absorption was observed both in rats (A) and in man (40, 48). Inhibition increased with Increasing chelate concentration. This effect was also observed when NaFeEDTA was added to a diet, but only when the molar ratio of disodium EDTA to iron was 2 1 or greater (33). The inhibition was observed when NaFeEDTA was added to a standard meal described as "a typical American dinner," or when it was added to a semisynthetic meal (a diet designed to yield low iron bioavailability) (33). 

J. Riviello, Determination of Transition Metals by Ion Chromatography Using Chelation Concentration . Preliminary Report, Dionex Corporation, Sunnyvale 1988. 

L.R. Adams, PPB Level Transition Metals (Fe, Cu, Ni, Mn) in 50% Caustic by Ion Chromatography Using Chelation Concentration , Presentation Symposium Advances in Ion Exchange Chromatography and Electrochemical Detection. Newport Beach, CA, USA 1989. 

Chelators such as EDTA, nitrilotriacetic acid (NTA), 1,2-aminocyclohexane 7V,7V,7V ,N7-tetraacetic (DCyTA), and ethylene glycol-bis(2-aminoethyl)-(V,(V, 7V ,7V -tetraacetic acid (EGTA) have been studied extensively and are well summarized (Peters, 1999). Chelator concentration and reaction pH influence metal complexation and the success of removal from soils. Sun et al. (2001) observed that batch extraction methods result in 1 1 molar extraction ratios of EDTA/metal (Pb, Cd, Zn, Cu) and reveal which metal is more or less soluble in EDTA solutions. Column leaching studies, however, relate the elution patterns and recalcitrance of the metals to desorption and dissolution by EDTA. There is concern over the detrimental effects on soil quality from using chelators because of their biotoxicity, persistence in soil environment, and their removal of beneficial micro-and macronutrients, which leave the washed soil infertile for revegetation when it is backfilled. 

A pertinent question concerning the uses of intracellular Ca chelators is whether or not the chelator significantly perturbs the cell. The chelator will obviously act as a Ca buffer in addition to all other Ca +-binding biomolecules in the cell. The buffer effect is probably not of any major consequence, since the cell may adjust to the new situation by an increase in total Ca"", especially if the chelator concentration is in the /aM range. The chelators could, however, interact with and inhibit intracellular enzymes or other molecules, an... 

The usual practice is to add the chelating agent, HR, to the organic phase. It distributes between the two phases, and in the aqueous phase it dissociates as a weak acid. The metal ion, M"+, reacts with nR to form the chelate MR , which then distributes into the organic phase. The distribution ratio is given by the ratio of the metal chelate concentration in the organic phase to the metal ion concentration in the aqueous phase. The following equation can be derived ... 

If the complex (or chelate) concentration within the Hquid amine or epoxyamine prepolymer was higher than its solubihty Hmit, complexes (or chelates) crystallized. Sharp needle-like crystals were observed with modified IPDA what-... 

As stated above, cyclopentanones, cyclobutenones, and indenes have been observed as by-products in the DBR. Wulff has studied the effect of solvent, chelation, concentration, and alkyne substitution on the product distribution. He reported that simple a,(3-unsaturated chromium carbene complexes typically show excellent selectivity for the benzannulated product. This selectivity is not sensitive to changes in solvent or substituents on the acetylene. However, the reactions of aryl complexes with acetylenes are very sensitive to the nature of both the solvent and the acetylene. For aryl chromium complexes, the highest selectivities and yields for the benzannulated product arise with solvents of low coordinating ability hexane and benzene. Solvents with intermediate coordinating ability and small size... 

If we have to separate two metals M and N having the same valence n, at a given pH and a chelate concentration Chk,o, then... 

The two principal operating costs are for power and chemicals. The power cost is primarily determined by the sum of the solution pump and the air blower power requirements. When a large pressure differential exists between the absorber and the oxidizer, pumping costs increase rapidly. To counter this effect, the solution circulation rate can be reduced by increasing its iron chelate concentration. 

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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