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 B₁₂ are natural chelators.

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