Porforiinid

Porforiinid (porphyrins) are a family of heterocyclic macrocycles composed of four pyrrole rings linked by methine bridges, forming a planar 18 π-electron system. The macrocycle has a central cavity that can coordinate a metal ion, producing metalloporphyrins such as iron protoporphyrin IX in heme and magnesium protoporphyrin IX in chlorophyll. Porphyrins are typically brightly colored and often exhibit fluorescence due to their extended conjugation.

In biology, porphyrins are essential cofactors in many enzymes and processes. The heme group in hemoglobin and myoglobin facilitates oxygen transport, while heme-containing cytochromes participate in cellular electron transfer. Chlorophylls in plants are magnesium-porphyrin complexes responsible for light absorption during photosynthesis. Porphyrins also occur as prosthetic groups in various other proteins, extending to different microbial and enzymatic systems.

Chemically, porphyrins can be synthesized and modified by altering substituents on the meso- positions of the macrocycle, enabling a wide range of derivatives. They are relatively planar and can coordinate a variety of metals, with properties such as strong visible-light absorption and fluorescence that are useful in research and applications. Their chemistry supports diverse functionalizations, enabling tuning of solubility, redox behavior, and photophysical characteristics.

Applications span research and technology, including photodynamic therapy for cancer and infections, fluorescence imaging, catalysis, and materials science such as dye-sensitized solar cells. In humans, disorders of heme biosynthesis—porphyrias—can lead to the buildup of porphyrin intermediates, causing symptoms such as photosensitivity and, in some forms, neurological disturbances.