A<unk>  is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, organic chemists may consider any molecule containing a ring of seven, fifteen, or any arbitrarily large number of atoms to be<unk> c.
Macrocycle
Capsid
Electron shell
Nucleic acid
Ribozyme
Phospholipid
Vector 
Vector