EDDS

エチレンジアミン-N , N'-ジコハク酸（EDDS）はアミノポリカルボン酸の一種です。無色の固体で、キレート剤として使用され、現在多くの用途で大規模に使用されているEDTAに代わる生分解性の代替品となる可能性があります。

EDDSは2つのキラル中心を持ち、そのため3つの立体異性体が存在する。^{[ 1 ]} これらはエナンチオマーである(R,R)および(S,S)異性体と、アキラルなメソ(R,S)異性体である。EDTAの生分解性代替品として、(S,S)立体異性体のみが注目される。(R,S)および(R,R)立体異性体は生分解性が低いが、(S,S)立体異性体は高度に汚染された土壌でも非常に効果的に生分解されることが示されている。^{[ 2 ]}

EDDSは最初にマレイン酸とエチレンジアミンから合成されました。^{[ 3 ] [ 4 ]}いくつかの微生物は、エチレンジアミンとフマル酸またはマレイン酸からの(S,S)-EDDSの工業規模合成のために操作されています。^{[ 5 ]}

鉄(III)のキレート剤として(S,S)-EDDSとEDTAの有効性を比較すると：

^{[Fe(S,S)-EDDS] −}の安定性が低いため、有用な範囲はおおよそ 3< pH _(S,S)-EDDS <9 および 2<pH _EDTA <11 です。ただし、この範囲はほとんどの用途には十分です。^{[ 6 ]}

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, 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)-EDDS]⁻ 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[EDTA]⁻ complex.^[7] The complex also has C₂ symmetry.

(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, which accumulates in the environment as a persistent organic pollutant.^[8][9] (S,S)-EDDS was developed commercially as a biodegradable chelator and stabilizing agent in detergent and cosmetic formulations.^[10] 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;^[11] 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.^[12]

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