Comparing Chelating Agents

IDS is structurally similar to EDDS, but is a simpler structure with just an amine bridge between the two aspartic acid components. It is also achiral, but still readily biodegradable owing the structural similarity to L-aspartic acid [30]. Although IDS easier to synthesize than EDDS, the loss of one amine group makes it a weaker chelant, particularly for transition metal ions. IDS was recognized by the US EPA with the Presidential Green Chemistry Award in 2001. 

ID S is synthesized by the reaction of ammonia with maleic anhydride in water. The synthesis of EDDS and IDS is also in accordance with the 3rd Principle of Green Chemistry Design Less Hazardous Chemical Synthesis, although they are still not perfectly green as there still some hazardous components. This can be a difficult principle to achieve completely as many reactive chemicals in the chemist s toolbox are often hazardous. 

let us consider the properties of all the available chelants in a general sense, and then look at their strengths and weaknesses. 

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Best in class approach. The best in class approach is based on a continuum in order to compare chemicals or materials within a particular functional class such as surfactants or chelating agents used for cleaning products. 

Elution of the bound antibody-enzyme conjugate occurs by only a slight shift in pH to acidic conditions or through the inclusion of a metal-chelating agent like EDTA or imidazole in the binding buffer. Either method of elution is mild compared to most immunoaffinity separation techniques (discussed in the previous section). Thus, purification of the antibody-enzyme complex can be done without damage to the activity of either component. 

Aluminum-deficient Y zeolites prepared by partial removal of aluminum with a chelating agent (e.g. EDTA) also show improved thermal and hydrothermal stability compared to the parent zeolite. The optimum stability was found in the range of 25 to 50 percent of framework A1 extraction (8). However, the maximum degree of dealumination is also affected by the SiO /Al O ratio in the parent zeolite a higher ratio appears to allow more advanced dealumination without loss of crystallinity (8,25,45). Above 50 or 60 percent dealumination, significant loss of crystallinity was observed. Calcination of the aluminum-deficient zeolite resulted in a material with a smaller unit cell size and lower ion-exchange capacity compared to the parent zeolite. 

Other compounds that have been tested for their inhibiting action include carboxylic acids, hydrazine hydrate, chelating compounds, aniline and related compounds and petroleum-based compounds. The influence of various chelating agents such as TEA, EDTA, DPTA, HEDTA and Chel-138 on their ability to control corrosion has been investigated [70]. All the chemicals are reported to reduce the compressive strength of concrete. The strengths were particularly low in the presence of TEA and EDTA, compared to the reference. In the presence of 0.1 N NaCl solution at pH 10... 

It is also observed that chelating agents (polydentate ligands) form more stable complexes than a comparable number of donor atoms in monodentate ligands. Consider the following example of Ni+ complexes with four ammonia molecules (each monodentate) and two ethylenediamine... 

For patients who are unable to tolerate penicillamine, trientine, another chelating agent, may be used in a daily dose of 1-1.5 g. Trientine appears to have few adverse effects other than mild anemia due to iron deficiency in a few patients. Zinc acetate administered orally increases the fecal excretion of copper and is sometimes used for maintenance therapy. The dose is 50 mg three times a day. Zinc sulfate (200 mg/d orally) has also been used to decrease copper absorption. Zinc blocks copper absorption from the gastrointestinal tract by induction of intestinal cell metallothionein. Its main advantage is its low toxicity compared with that of other anticopper agents, although it may cause gastric irritation when introduced. 

A recent paper by Harkness 101a) has done much to clarify the field. It was found that Zn2 chelating agents such as cysteine, EDTA, and o-phenanthroline (each 1 mil/) are all potent inactivators of crystalline placental phosphatase for instance, 15 min preincubation with 10 /Jl/ EDTA at pH 10.5 gave 95% inhibition. Full activity was immediately restored by addition of 100 fiM Zn2+ compared to only 25% recovery with Mg2. Preincubation of apophosphatase with 500 fiM Zn2+ gave a 30-fold increase in activity while the corresponding values for Mg2 and Co2 were 0.5 and 5-fold, respectively. 

Lee, C.H., R. Bagdon, and Y.W. Chien. 1996. Comparative in vitro spermicidal activity and synergistic effect of chelating agents with nonoxynol-9 on human sperm functionality. J Pharm Sci 85 91. 

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