Any of a class of coordination or complex compounds consisting of a central atom of a metal (usually a transition element ) attached to a large molecule ( ligand ).
Any ligand that can bind to the metal at two or more points to form a ring structure, more stable than a nonchelated compound of the same general chemical formula , is a chelating agent. The process of binding to the metal is called chelation. Chelating agents such as EDTA salts are used in medicine to remove toxic metals (e.g., lead , cadmium ) from the body. Others are used in analysis as indicators and in industry to extract metals. The iron-binding porphyrin group in hemoglobin , the magnesium-binding porphyrin in chlorophyll , and the cobalt-binding porphyrin in vitamin B 12 are natural chelators.