What porphyrins look like

Porphyrins are purple and they are pigments. Such characteristics, however, apply to several dye molecules. What is it that makes porphyrins special Through heme, an iron porphyrin, they are intimately associated with blood, and many of the redox enzymes involved in metabolic processes. Through chlorophyll, a reduced magnesium porphyrin, they orchestrate photosynthesis, without which life as we know it would be impossible. So what do porphyrins look like  

Interestingly, when the macrocyclic structure of porphyrin was first proposed by Kuster in 1912, nobody believed him, least of all Hans Fischer (the father of modern porphyrin chemistry), because such a large ring was thought to be intrinsically unstable. Fischer eventually came round to this structure when he and his Munich school of chemists finally succeeded in synthesising heme—the iron porphyrin in hemoproteins—from pyrrolic starting materials, in 1929. 

X-ray crystallography provides stunning confirmation of the porphyrin macrocyclic structure. In the main, this shows that porphyrins are essentially flat molecules. However, circumstances can prevail, when binding 

Distortion can occur for other reasons. For example, protonation of the two unprotonated central nitrogens, combined with bulky substituents on the methine bridging carbons, can twist the macrocycle, especially if the bulky substituents attempt to become planar with it. Oxidation of a porphyrin, so that it loses its aromaticity, but retains its integrity as a 

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