Complex formation involving a metal ion and two or more polar groupings of a single molecule; in heme, the Fe2+ ion is chelated by the porphyrin ring. Chelation can be used to remove an ion from participation in biologic reactions, as in the chelation of Ca2+ of blood by EDTA, which thus acts as an anticoagulant.
[G. chēlē, claw]
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Examples: glitazone, GI cocktail, etc.