Porphyrin



    A porphyrin is a heterocyclic porphine, and substituted porphines are called porphyrins. Many porphyrins occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices.

Complexes of porphyrins and related molecules

Porphyrins bind ion, usually with a charge of 2+ or 3+, resides in the central N4 cavity formed by the loss of two protons. Most metals can be inserted. A schematic equation for these syntheses is shown:

H2porphyrin + [MLn]2+ → M(porphyrinate)Ln-4 + 4 L + 2 H+

A porphyrin in which no metal is inserted in its cavity is sometimes called a free base. Some iron-containing porphyrins are called myoglobin are two O2-binding proteins that contain iron porphyrins.

Related to porphyrins are several other heterocycles, including Hückel's rule, but most do not.

Laboratory synthesis

One of the more common syntheses for porphyrins is based on work by Paul Rothemund.[1][2] His techniques underpin more modern syntheses such as those described by Alder and Longo.[3] The synthesis of simple porphyrins such as meso-tetraphenylporphyrin is also commonly done in university teaching labs.[4]

In this method, porphyrins are assembled from p-toluenesulfonic acid can be used with a non-acidic solvent. Lewis acids such as boron trifluoride etherate and ytterbium triflate have also been known to catalyse porphyrin formation. A large amount of side-product is formed and is removed, usually by chromatography.

Biosynthesis

The "committed step" for porphyrin biosynthesis is the formation of heme. Bile pigments are the breakdown products of heme.

The following scheme summarizes the biosynthesis of porphyrins, with references by EC number and the OMIM database. The porphyria associated with the deficiency of each enzyme is also shown:

 
Enzyme substrate Product Chromosome EC OMIM porphyria
ALA synthase Glycine, succinyl CoA D-Aminolevulinic acid 3p21.1 2.3.1.37 125290 none
ALA dehydratase D-Aminolevulinic acid Porphobilinogen 9q34 4.2.1.24 125270 ALA-Dehydratase deficiency
PBG deaminase Porphobilinogen Hydroxymethyl bilane 11q23.3 2.5.1.61 176000 acute intermittent porphyria
Uroporphyrinogen III synthase Hydroxymethyl bilane Uroporphyrinogen III 10q25.2-q26.3 4.2.1.75 606938 congenital erythropoietic porphyria
Uroporphyrinogen III decarboxylase Uroporphyrinogen III Coproporphyrinogen III 1q34 4.1.1.37 176100 porphyria cutanea tarda
Coproporphyrinogen III oxidase Coproporphyrinogen III Protoporphyrinogen IX 3q12 1.3.3.3 121300 coproporphyria
Protoporphyrinogen oxidase Protoporphyrinogen IX Protoporphyrin IX 1q22 1.3.3.4 600923 variegate porphyria
Ferrochelatase Protoporphyrin IX Heme 18q21.3 4.99.1.1 177000 erythropoietic protoporphyria

Applications

Although natural porphyin complexes are essential for life, synthetic porphyrins and their complexes have limited utility. Complexes of meso-tetraphenylporphyrin, e.g., the iron-(III) chloride complex (TPPFeCl) catalyse a variety of reactions in Phthalocyanines, which are structurally related to porphyrins, are used in commerce as dyes and catalysts. Synthetic porphyrin dyes that are incorporated in the design of solar cells are the subject of ongoing research. See Dye-sensitized solar cells.

Supramolecular chemistry

  Porphyrins are often used to construct structures in macrocycle composed of four porphyrins.[5] A guest-free base porphyrin is bound to the center by coordination with its four pyridine sustituents.

See also

References

  1. ^ P. Rothemund (1936). "A New Porphyrin Synthesis. The Synthesis of Porphin". J. Am. Chem. Soc. 58 (4): 625-627. doi:10.1021/ja01295a027.
  2. ^ P. Rothemund (1935). "Formation of Porphyrins from Pyrrole and Aldehydes". J. Am. Chem. Soc. 57 (10): 2010-2011. doi:10.1021/ja01313a510.
  3. ^ A. D. Adler, F. R. Longo, J. D. Finarelli, J. Goldmacher, J. Assour and L. Korsakoff (1967). "A simplified synthesis for meso-tetraphenylporphine". J. Org. Chem. 32 (2): 476-476. doi:10.1021/jo01288a053.
  4. ^ Falvo, RaeAnne E.; Mink, Larry M.; Marsh, Diane F.. "Microscale Synthesis and 1H NMR Analysis of Tetraphenylporphyrins". J. Chem. Educ. 1999 (76): 237.
  5. ^ Sanders and coworkers in Angew. Chem., Int. Ed. Engl. 1995, 34, 1096-1099.
Bilanes: Bilirubin | Biliverdin | Urobilinogen | Urobilin
Chlorophylls: Protochlorophyllide | Chlorophyllide
Corrinoids: Cyanocobalamin
Phycobilins: Phycourobilin | Phycoviolobilin
Porphyrins: Uroporphyrinogen (I, III) | Coproporphyrinogen (I, III) | Protoporphyrinogen IX | Protoporphyrin (IX)
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