EDTA - Ethylenediaminetetraacetic acid Definition
Definition and more information on EDTA.		Download PDF Version

EDTA is a widely-used acronym for the chemical compound ethylenediamine tetraacetic acid. EDTA refers to the chelating agent with the formula (HO2CCH2)2NCH2CH2N(CH2CO2H)2. This amino acid is widely used to sequester di- and trivalent metal ions. EDTA binds to metals via four carboxylate and two amine groups. EDTA forms specially strong complexes with Mn(II), Cu(II), Fe(III), and Co(III).[1]

Synthesis

EDTA is mostly synthesised from 1,2-diaminoethane (ethylenediamine), formaldehyde (methanal), water and sodium cyanide.[2] This yields the tetra sodium salt, which can be converted into the acidic forms by acidification.

Popular vs. chemical nomenclature

To describe EDTA and its various protonated forms, chemists use a more cumbersome but more precise acronym that distinguishes between EDTA4−, the conjugate base that is the ligand, and H4EDTA, the precursor to that ligand.

Coordination chemistry principles

In coordination chemistry, H4EDTA is a member of the aminocarboxylate family of ligands that includes imidodiacetic acid ("H2IDA") and nitrilotriacetic acid ("H3NTA"). More specialized relatives include N,N'-ethylenediaminediacetic acid ("H2EDDA") and 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid ("H4CyDTA"). These ligands are all formally derived from the amino acid glycine.

H4EDTA forms highly stable coordination compounds that are soluble in water. In these complexes, the ligand is usually either hexa- or pentadentate, EDTA4− or HEDTA3−, respectively. Such complexes are chiral, and [Co(EDTA)]− has been resolved into enantiomers.[3]  

Uses in Medicine:

• EDTA is used in chelation therapy for acute hypercalcemia, mercury poisoning and lead poisoning[4].
• Combined with chromium, EDTA is used to evaluate kidney function. It is administered intravenously and its filtration into the urine is monitored. This method is considered the gold standard for evaluating glomerular filtration rate, Cr-EDTA's sole way out of the body is via glomerular filtration as it is not secreted or metabolised in any other way.
• Used as anticoagulant for blood samples
• In veterinary ophthalmology EDTA may be used as an anticollagenase to prevent the worsening of corneal ulcers in animals.
• Some laboratory studies also suggest that EDTA chelation may prevent collection of platelets ([or plaque] which can otherwise lead to formation of blood clots and prevent blood flow) on the walls of blood vessels [such as arteries]. These ideas are theoretical, however. [3]

References

1. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
2. http://www.chm.bris.ac.uk/motm/edta/synthesis_of_edta.htm
3. Kirchner, S. Barium (Ethylenediaminetetracetato) Cobalt(III) 4-Hydrate" Inorganic Syntheses, McGraw-Hill: New York, 1957; Vol. 5, pages 186-188.
4. Ruth DeBusk et al. (2002). Ethylenediaminetetraacetic acid (EDTA). Retrieved on 2007-07-25.