Complexing agents or Chelating agent

Definition: Complexometric agent are those agent which form complex with simple metal ion and transformed into complex ion by addition of reagent which is known as ligand. The complex formed is stable and water soluble. Similar to acid base titration (lewis principle) In complex formation metal ion accepts electron and ligand donate it. Thus in a ligand molecules there is presence of atleast one lone pair of electrone through which co-ordinate linkage with metal ion take place.

Ligand molecules may have no of site present in them like Co-ordinate linkage: Particular no. of ligand molecules associated with metal ion is called as co-ordinate linkage with metal ion take place. Ligand molecules may have no of site present in them like Unidentate: Cyanide ion Bidentate: Glycine and oxalic acid Multidentate: EDTA

Chelation therapy It is the administration of chelating agents to remove heavy metals from the body. For the most common forms of heavy metal intoxication—those involving lead, arsenic or mercury—the standard of care in the United States dictates the use of dimercaptosuccinic acid (DMSA). Other chelating agents, such as 2,3-dimercapto-1-propanesulfonic acid (DMPS) and alpha lipoic acid (ALA), are used in conventional and alternative medicine.

Chelation therapy is used as a treatment for acute mercury, iron (including in cases of thalassemia), arsenic, lead, uranium, plutonium and other forms of toxic metal poisoning. The chelating agent may be administered intravenously, intramuscularly, or orally, depending on the agent and the type of poisoning.

Complexing and chelating agents used in therapy Chelator Use Dimercaprol(BAL) •acute arsenic poisoning •acute mercury poisoning •lead poisoning (in addition to EDTA) Dimercaptosuccinic acid (DMSA) lead poisoning •arsenic poisoning •mercury poisoning Dimercapto-propane sulfonate (DMPS) severe acute arsenic poisoning •severe acute mercury poisoning Penicillamine Mainly in: copper toxicity Occasionally adjunctive therapy in: •gold toxicity •lead poisoning •rheumatoid arthritis Ethylenediaminetetraaceticacid (EDTA) •lead poisoning Deferoxamine and Deferasirox •acute iron poisoning •iron overload

Calcium disodium edetate Formula:C10H12CaN2Na2O8. xH2O Preparation: Prepared by boiling aqueous solution of disodium edetate with a slight excess quantity of calcium carbonate until CO2 ceases to evolve. The hot solution is filtered and the salt crystallized. Properties: – odorless, white, crystalline powder or granules and is a mixture of di-hydrate and tri-hydrate forms. – slight saline taste and is slightly hygroscopic. – freely soluble in water and very slightly soluble in alcohol. – The commercially available injection (human) has a pH of 6.5-8.

Uses: – CaEDTA is used as a chelating agent in the treatment of metal poisoning.

Ethylene diamine tetra acetic acid Ethylene diamine tetra acetic acid, widely abbreviated as EDTA, is a poly amino carboxylic acid and a colourless, water-soluble solid. Its conjugate base is named ethylene diamine tetra acetate. Its usefulness arises because of its role as a hexadentate ("six-toothed") ligand and chelating agent, i.e. its ability to "sequester" metal ions such as Ca2+ and Fe3+. After being bound by EDTA, metal ions remain in solution but exhibit diminished reactivity. EDTA is produced as several salts, notably disodium EDTA and calcium disodium EDTA.

Uses: – EDTA is used to bind metal ions in the practice of chelation therapy, e.g., for treating mercury and lead poisoning. It is used in a similar manner to remove excess iron from the body. This therapy is used to treat the complication of repeated blood transfusions, as would be applied to treat thalasaemia. Alternative medical practitioners believe EDTA acts as a powerful antioxidant to protect free radicals from injuring blood vessel walls, therefore reducing atherosclerosis. Assay: It is assayed by titration with 0.1 M lead nitrate using xylenol orange triturate as indicator.