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Ethylenediamine-''N'',''N'''-disuccinic acid (EDDS) is an aminopolycarboxylic acid. It is a colourless solid that is used as
chelating agent Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a polydentate (multiple bonded) ligand and a single central metal atom. These ligands are ...
that may offer a biodegradable alternative to EDTA, which is currently used on a large scale in numerous applications.


Structure and properties

EDDS has two
chiral centers In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups cr ...
, and as such three stereoisomers. These are the
enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...
ic (R,R) and (S,S) isomers and the achiral
meso Meso or mesos may refer to: * Apache Mesos, a computer clustering management platform * Meso, in-game currency for the massively multiplayer online role-playing game '' MapleStory'' * Meso compound, a stereochemical classification in chemistry * ...
(R,S) isomer. As a
biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...
replacement for EDTA, only the (S,S) stereoisomer is of interest. The (R,S) and (R,R) stereoisomers are less biodegradable, whereas the (S,S) stereoisomer has been shown to be very effectively biodegraded even in highly polluted soils.


Synthesis

EDDS was first synthesized from maleic acid and
ethylenediamine Ethylenediamine (abbreviated as en when a ligand) is the organic compound with the formula C2H4(NH2)2. This colorless liquid with an ammonia-like odor is a basic amine. It is a widely used building block in chemical synthesis, with approximately ...
. Some microorganisms have been manipulated for industrial-scale synthesis of (S,S)-EDDS from ethylenediamine and fumaric acid or maleic acid, which proceeds as follows:


From aspartic acid

(S,S)-EDDS is produced stereospecifically by the alkylation of an ethylenedibromide with L-
aspartic acid Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. Like all other amino acids, it contains an amino group and a carboxylic acid. Its α-amino group is in the pro ...
. Racemic EDDS is produced by the reaction of ethylenediamine with fumaric acid or maleic acid.


Coordination chemistry

In comparing the effectiveness of (S,S)-EDDS versus EDTA as chelating agents for
iron(III) In chemistry, iron(III) refers to the chemical element, element iron in its +3 oxidation number, oxidation state. In salt (chemistry), ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adjec ...
: Because of the lower stability for e(S,S)-EDDSsup>−, the useful range being roughly 3< pH(S,S)-EDDS<9 and 2EDTA<11. However, this range is sufficient for most applications. Another comparison that can be made between (S,S)-EDDS and EDTA is the structure of the chelated complex. EDTA’s six donor sites form five five-membered chelate rings around the metal ion, four NC2OFe rings and one C2N2Fe ring. The C2N2Fe ring and two of NC2OFe rings define a
plane Plane(s) most often refers to: * Aero- or airplane, a powered, fixed-wing aircraft * Plane (geometry), a flat, 2-dimensional surface Plane or planes may also refer to: Biology * Plane (tree) or ''Platanus'', wetland native plant * Planes (gen ...
, and two NC2OFe rings are perpendicular to the plane that contains the C2-symmetry axis. The five-membered rings are slightly strained. EDDS’s six donor sites form both five- and six-membered chelate rings around the metal ion: two NC2OFe rings, two NC3OFe rings, and one C2N2Fe ring. Studies of the crystal structure of the Fe S,S)-EDDSsup>− complex show that the two five-membered NC3OFe rings project out of the plane of the complex, reducing the equatorial ring strain that exists in the Fe DTAsup>− complex. The complex also has C2 symmetry.


Uses

(S,S)-EDDS is a biodegradable chelating agent that offers an alternative to EDTA, of which 80 million kilograms are produced annually. Under natural conditions, EDTA has been found to convert to ethylenediaminetriacetic acid and then cyclize to the
diketopiperazine A diketopiperazine (DKP), also known as a ''dioxopiperazine'' or ''piperazinedione'', is a class of organic compounds related to piperazine but containing two amide linkages. DKP's are the smallest known class of cyclic peptide. Despite their name, ...
, which accumulates in the environment as a persistent organic pollutant. (S,S)-EDDS was developed commercially as a biodegradable chelator and stabilizing agent in detergent and cosmetic formulations. When EDDS is applied in chemical-enhanced soil remediation in excessive case (e.g., when applied for ex-situ soil washing), higher extraction efficiency for heavy metals can be achieved and the amount of extraction is less independent with the EDDS dosage; On the other hand, during soil remediation which involves continuous flushing, metal extraction is often limited by the amount of EDDS. Under EDDS deficiency, initial unselective extraction of heavy metals was observed, followed by heavy metal exchange and re-adsorption of heavy metals that have lower stability constant with EDDS.


External links


Sigma Aldrich page on EDDS, containing a link to a MSDS


References

{{reflist, 2 Chelating agents Carboxylic acids Amines