porphyrin

/ˈpɔːfɪɹɪn/

IPA: /P AO0 R F ER0 IH1 N/

noun
  1. 1

    Any of a class of heterocyclic compounds containing pyrrole rings arranged in a square or other similar shape; they are important in biochemistry in a form with a metal atom in the central cavity (hemoglobin with iron, chlorophyll with magnesium, etc.).

Source: https://en.wiktionary.org/wiki/porphyrin