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Names of Porphyrins

The names of the porphyrins of interest consist of a word and a number, e.g., uroporphyrin III

    The word denotes the kinds of substituents found on the ring, and the number denotes how they are arranged.

There are three important words:

  • uroporphyrin contains A and P only:
  • coproporphyrin contains M and P only (A has been changed to M):
  • protoporphyrin contains M and P and V (some P has been changed to V):

There are two important numbered series, I and III.

Series II and IV do not occur in natural systems.

  • In series I the substituents repeat in a regular manner, e.g., AP AP AP AP (starting with ring I).

This is somewhat reminiscent of a Shakespearean sonnet, in which the rhyme scheme is ABAB CDCD EFEF GG.

  • In series III the order of substituents in ring IV is reversed: AP AP AP PA.

This is (at the end) somewhat reminiscent of the rhyme scheme of a Petrarchan sonnet: ABBA ABBA CDE CDE.

Animation with sound emphasizes the difference between the AP AP AP AP sequence of substituents in the I-series of porphyrins and the AP AP AP PA sequence in the III-series.

If three kinds of groups are present, as in the protoporphyrins, naming can become more complicated, and the naming conventions are not altogether uniform. Heme, for example, is derived from the III series, but its immediate precursor is variously referred to as protoporphyrin III or protoporphyrin IX.

Here is a diagram of some examples of porphyrins with their correct names:

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