Porphine


Porphine or porphin is an organic chemical compound with formula. The molecule consists of four pyrrole-like rings joined by four methine groups to form a larger macrocycle ring, which makes it the simplest of the tetrapyrroles. It is an aromatic and heterocyclic compound, solid at room temperature.
Porphine does not occur in nature, and is almost only of theoretical interest; however, substituted derivatives include many biochemically significant compounds called porphyrins, with the dominant example being protoporphyrin IX. Many synthetic analogues are also known, including octaethylporphyrin and tetraphenylporphyrin.

Structural characteristics of porphine and its derivatives

Porphine is planar. The two NH centers are trans.

Complex with metal in the center

Concomitant with the displacement of two N-H protons, porphine binds metal ions at its center. The insertion of the metal center is slow in the absence of catalysts. In nature, these catalysts are called chelatases. When there is no metal ion bound to the nitrogens in the center, then the compounds are called free porphine or free porphyrin. If they are bonded to a metal in the center, then they are bound. A porphyrin with an iron atom of the type found in myoglobin, hemoglobin, or certain cytochromes is called heme. See the Porphyrin article for further details.
Compounds similar to porphine are the parent compounds for similar ring systems with other central metal atoms in biochemistry. These include chlorin, which has a magnesium ion in several types of chlorophyll; bacteriochlorin, found in bacteriochlorophyll; and corrin, which has a cobalt center in cobalamin.