Difference Between Porphyrin and Protoporphyrin

The key difference between porphyrin and protoporphyrin is that porphyrin is a group of aromatic chemicals which has four modified pyrrole subunits interconnected to each other, whereas protoporphyrin is a derivative of porphyrin which has propionic acid groups.

Both porphyrin and protoporphyrin are deeply coloured chemical species. These are macrocyclic organic compounds which contain several cycles of carbon interconnected with each other forming a single large molecule.

1. Overview and Key Difference
2. What is Porphyrin
3. What is Protoporphyrin
4. Side by Side Comparison – Porphyrin vs Protoporphyrin in Tabular Form
5. Summary

What is Porphyrin?

Porphyrin is a large organic compound containing four modified pyrrole subunits interconnected to each other. These ring structures are attached to each other via methine bridges at alpha carbon atoms. The methine bridge has the chemical formula –CH=. The parent molecule of porphyrin is porphine. It is a rare chemical species. Porphyrins form via substitution of porphine.

Difference Between Porphyrin and Protoporphyrin

Figure 01: Appearance and Structure of Porphyrin

Porphyrins have a planar structure which is a continuous cycle, and we can define it as aromatic. It is a conjugated system containing alternating pi bonds and single bonds. These chemicals are deeply coloured compounds since they can absorb wavelengths of the electromagnetic radiation in the visible range; for example, heme, which has a deep red colour, is a well-known porphyrin that occurs naturally.

Moreover, porphyrins can act as conjugate acids ligands that bind with metal ions to form complexes. Here, the metal ion is either +2 or +3 charged. However, if the porphyrin exists without a metal ion, we say the core of the porphyrin is empty, and it is a free base. Iron-containing porphyrins are named as heme.

Apart from that, if we consider the origin of porphyrin, geologically it forms from protoporphyrin. These source compounds can occur in crude oil, oil shale, coal, sedimentary rocks, etc. Further, we can synthesize these molecules. The synthesis may occur in biological routines as well. Here, particular eukaryotic species such as insects, animals, fungi, etc. can biosynthesize porphyrins.

What is Protoporphyrin?

Protoporphyrin is a derivative of porphyrin. It is an organic compound having a complicated structure. It has a deep colour due to the absorption of electromagnetic radiation in the visible range. Moreover, these compounds are not soluble in alkali water. It is an important compound for living organisms as a precursor for compounds such as haemoglobin, chlorophyll, etc.

Protoporphyrin has a porphyrin core, and therefore, it is aromatic. It has a planar geometry except for the bent N-H bonds. Also, this compound is derived from porphyrin via the substitution of the outer hydrogen atom in pyrrole rings with four methyl groups, two vinyl groups and two propionic acid groups. Besides, this compound exists in nature; we can also synthesize it.

What is the Difference Between Porphyrin and Protoporphyrin?

Protoporphyrin is a derivative of porphyrin. The key difference between porphyrin and protoporphyrin is that porphyrin is a group of aromatic chemicals which has four modified pyrrole subunits interconnected to each other, whereas protoporphyrin is a derivative of porphyrin which has propionic acid groups.

Below infographic tabulates the difference between porphyrin and protoporphyrin.

Summary – Porphyrin vs Protoporphyrin

Reference:

1. “Synthesis Of The Tetracyclic Skeleton Of The Galanthamine-Type Amaryllidaceae Alkaloids”. Vol 2009, no. 11, 2009, p. 235. ARKAT USA, Inc., doi:10.3998/ark.5550190.0010.b21.
2. “Porphyrin”. Wikipedia.Org, 2019, Available here.
3. “Protoporphyrin IX.” Wikipedia, Wikimedia Foundation, 25 Aug. 2019, Available here.

Image Courtesy:

1. “Porphin-18e” By Alsosaid1987 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “PPIXtransH” By Smokefoot – Own work (CC BY-SA 4.0) via Commons Wikimedia