Chelates

Chelates are chemical compounds in which a ligand binds to a central metal ion at two or more attachment sites, forming a coordination ring that includes the metal. The ligand, called a chelating or chelating agent, is typically multidentate (polydentate). The resulting species is a metal chelate or chelated complex. Chelation increases the stability of the metal–ligand complex compared with analogous complexes formed by monodentate ligands, a phenomenon known as the chelate effect.

Common chelating agents include ethylenediaminetetraacetic acid (EDTA), diaminotriacetic acid, DTPA, and natural chelators such as citric acid and oxalate. In biology, examples include siderophores that capture iron, and metalloproteins that coordinate metal ions.

Applications span agriculture, medicine, and environmental science. In agriculture, iron chelates such as Fe-EDTA or Fe-EDDHA are used to supply micronutrients to plants in calcareous or alkaline soils. In medicine, chelation therapy uses agents such as deferoxamine, dimercaprol, or EDTA to bind and remove excess metals from the body in cases of poisoning or overload. In industry and environmental remediation, chelators solubilize and mobilize metals for recovery or facilitate sequestration and removal of hazardous metals from water and soil.

Formation constants quantify chelate stability. While chelation is beneficial in many contexts, improper use can redistribute metals to sensitive tissues or cause side effects, so chelating agents are used under controlled conditions.