Acide nitrilotriacétique

Nitrilotriacetic acid (NTA) is the aminopolycarboxylic acid with the formula N(CH2CO2H)3. It is a colourless solid that is used as a chelating agent, which forms coordination compounds with metal ions (chelates) such as Ca2+, Co2+, Cu2+, and Fe3+. Nitrilotriacetic acid is commercially available as the free acid and as the sodium salt. It is produced from ammonia, formaldehyde, and sodium cyanide or hydrogen cyanide. Worldwide capacity is estimated at 100 thousand tonnes per year. NTA is also cogenerated as an impurity in the synthesis of EDTA, arising from reactions of the ammonia coproduct. Older routes to NTA included alkylation of ammonia with chloroacetic acid and oxidation of triethanolamine. NTA is a tripodal tetradentate trianionic ligand. The uses of NTA are similar to those of EDTA, both being chelating agents. It is used for water softening and as a replacement to sodium and potassium triphosphate in detergents, and cleansers. In one application, NTA as a chelating agent removes Cr, Cu, and As from wood that had been treated with chromated copper arsenate. In the laboratory, this compound is used in complexometric titrations. A variant of NTA is used for protein isolation and purification in the His-tag method. The modified NTA is used to immobilize nickel on a solid support. This allows purification of proteins containing a tag consisting of six histidine residues at either terminus. The his-tag binds the metal of metal chelator complexes. Previously, iminodiacetic acid was used for that purpose. Now, nitrilotriacetic acid is more commonly used. For laboratory uses Ernst Hochuli et al. 1987 coupled the NTA ligand and Nickel-ions to agarose beads. This Ni-NTA Agarose is the most used tool to purify his tagged proteins via affinity chromatography. Ni(NTA)(aq)23views.png|Three views of the structure of [Ni(NTA)(H2O)2]−. File:Calcium complex of NTA trianion.svg|Structure of the nitrilotriacetate anion [Ca(NTA)(H2O)3]−.