EDTA vs EGTA
EDTA and EGTA both are chelating agents. Both are polyamino carboxylic acids and have more or less the same properties.
EDTA
EDTA is the shortened name for Ethylene diamine tetraacetic acid. It is also known as (ethylene dinitrilo) tetraacetic acid. Following is the structure of EDTA.
The EDTA molecule has six sites where a metal ion can be bound. There are two amino groups and four carboxyl groups. The two nitrogen atoms of amino groups have an unshared electron pair in each. EDTA is a hexadentate ligand. Also, it is a chelating agent due to the ability to sequester metals ions. EDTA forms chelates with all cations except alkali metals and these chelates are sufficiently stable. The stability results from the several complexing sites within the molecule that gives rise to a cage like structure surrounding the metal ion. This isolates the metal ion from solvent molecules, thus prevent solvation. The carboxyl group of EDTA can dissociate donating protons; therefore, EDTA has acidic properties. The various EDTA species are abbreviated as H4Y, H3Y–, H2Y2-, HY3– and Y4-. At very low pH (acidic medium), the protonated form of EDTA (H4Y) is predominant. In contrast, at high pH (basic medium), fully deprotonated form (Y4-) predominates. And as the pH changes from low pH to high pH, other forms of EDTA predominate in certain pH values. EDTA is available as fully protonated form or either salt form. Disodium EDTA and calcium disodium EDTA are the most common salt forms available. The free acid H4Y and the dihydrate of the sodium salt Na2H2Y.2H2O are commercially available in reagent quality.
When dissolves in water, EDTA acts like an amino acid. It exists as a double zwitterion. In this occasion, the net charge is zero, and there are four dissociable protons (two protons are associated with the carboxyl groups and two associated with amine groups). EDTA is widely used as a complexometric titrant. Solutions of EDTA are important as a titrant because it combines with metal ions in a 1:1 ratio regardless of the charge on the cation. EDTA is also used as a preservative for biological samples. The small amounts of metal ions present in biological samples, and food can catalyze the air oxidation of compounds present in the samples. EDTA tightly complexes these metal ions, thus prevent them from catalyzing air oxidation. That is why is can be used as a preservative.
EGTA
EGTA is the abbreviated term for ethylene glycol tetraacetic acid. It is a chelating agent, and very much similar to EDTA. EGTA has a higher affinity for calcium ions than magnesium ions. EGTA has the following structure.
Similar to EDTA, EGTA also has four carboxyl groups, which can produce four protons upon dissociation. There are two amine groups and the two nitrogen atoms of amino groups have unshared electron pair in each. EGTA can be used as a buffer to resemble the pH of a living cell. This property of EGTA permits its usage in Tandem Affinity Purification, which is a protein purification technique.
|
What is the difference between EDTA and EGTA? • EDTA is Ethylene diamine tetraacetic acid and EGTA is ethylene glycol tetraacetic acid. • EGTA has a higher molecular weight than EDTA. • Other than the four carboxyl groups, two amino groups, EGTA also has another two oxygen atoms with unshared electrons. • EGTA has a higher affinity to calcium ions compared to EDTA. And EDTA has a higher affinity to magnesium ions compared to EGTA. • EGTA has a higher boiling point than EDTA.
|