Porphyrins

Porphyrins are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). Porphyrins are aromatic. They are often deeply colored, and participate in electron delocalization reactions. Porphyrins are the conjugate acids of ligands that bind metals to form complexes. The metal ion usually has a charge of 2+ or 3+.

Structure and bonding

Porphyrins are tetrapyrrolic macrocycles. The name porphyrin comes from the Greek word πορφύρα (porphyra), meaning "purple". The most well-known porphyrins are heme, the pigment in red blood cells, and chlorophyll, the pigment in plants. Other porphyrins are found in the shells of certain sea creatures, such as the blue-ringed octopus.

Biosynthesis

The biosynthesis of porphyrins involves the formation of a pyrrole ring, followed by the linking of four of these rings to form a porphyrin. The process is highly regulated, as an excess of porphyrins can be toxic.

Role in biology

Porphyrins play a crucial role in biology, with many biological molecules being porphyrins or modified porphyrins. They are involved in the transport of oxygen and carbon dioxide in the blood (via hemoglobin), the photosynthesis process in plants (via chlorophyll), and in the liver where they help with the breakdown of red blood cells.

Medical significance

Porphyrins have significant medical importance. Abnormalities in porphyrin metabolism result in a group of diseases known as the porphyrias. These diseases can affect the nervous system and/or the skin, and can be acute or chronic. The treatment of porphyrias is symptomatic, and can include the avoidance of triggering factors, the use of medications to control symptoms, and in some cases, liver transplantation.

See also

• Heme
• Chlorophyll
• Porphyrin
• Pyrrole
• Heterocyclic compound
• Methine
• Electron delocalization
• Ligand
• Tetrapyrrolic
• Hemoglobin
• Porphyria

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