David Dolphin and Wijesekera, T.
Encyclopedia of Science and Technology McGraw-Hill Publishing Company, New York
Vol. 14, 209-212
Porphyrins are a class of cyclic compounds in which the par- ent macrocycle consists of four pyrrole-type units linked together by single carbon bridges. Several por- phyrins with selected peripheral substitution and metal coordination carry out vital biochemical pro- cesses in living organisms. Chlorins, bacteriochlorins, and corrins are related tetrapyrrolic macrocycles that are also observed in biologically important com- pounds