A macrocycle (MCY) is a type of molecule characterized by a ring structure containing at least 8 to 20 or more atoms in the ring. It is larger than typical organic rings, such as cycloalkanes or aromatic rings, but smaller than macromolecules.

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Macrocycles can be composed of a variety of atoms, including carbon, nitrogen, oxygen, and other elements. They often exhibit unique properties and can be synthesized or found naturally in various chemical and biological systems.