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Information about Porphyrin

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Structure of porphine, the simplest porphyrin.
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Space-filling model of porphyrin
A porphyrin is a heterocyclic macrocycle derived from four pyrrole-like subunits interconnected via their α carbon atoms via methine bridges (=CH-). The macrocycle, therefore, is a highly conjugated system, and is consequently deeply coloured—the name porphyrin comes from a Greek word for purple. The macrocycle has 22 pi electrons. The parent porphyrin is 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 metals to form complexes. The metal 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 hemes; and heme-containing proteins, or hemoproteins, are found extensively in Nature. Hemoglobin and myoglobin are two O2-binding proteins that contain iron porphyrins.

Related to porphyrins are several other heterocycles, including corrins, chlorins, bacteriochlorophylls, and corphins. Chlorins (2,3-dihydroporphyrin) are more reduced, that contain more hydrogen, than porphyrins, featuring a pyrroline subunit. This structure occurs in chlorophyll. Replacement of two of the four pyrrolic subunits with pyrrolinic subunits results in either a bacteriochlorin (as found in some photosynthetic bacteria) or an isobacteriochlorin, depending on the relative positions of the reduced rings. Some porphyrin derivatives follow 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 pyrrole and substituted aldehydes. Acidic conditions are essential; formic acid, acetic acid, and propionic acid are typical reaction solvents, or 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 D-aminolevulinic acid (dALA) by the reaction of the amino acid glycine and succinyl-CoA, from the citric acid cycle. Two molecules of dALA combine to give porphobilinogen (PBG), which contains a pyrrole ring. Four PBGs are then combined through deamination into hydroxymethyl bilane (HMB), which is hydrolysed to form the circular tetrapyrrole uroporphyrinogen III. This molecule undergoes a number of further modifications. Intermediates are used in different species to form particular substances, but, in humans, the main end-product protoporphyrin IX is combined with iron to form 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:

Heme synthesis—note that some reactions occur in the cytoplasm and some in the mitochondrion (yellow)


EnzymesubstrateProductChromosomeECOMIMporphyria
ALA synthaseGlycine, succinyl CoAD-Aminolevulinic acid3p21.12.3.1.37125290none
ALA dehydrataseD-Aminolevulinic acidPorphobilinogen9q344.2.1.24125270ALA-Dehydratase deficiency
PBG deaminasePorphobilinogenHydroxymethyl bilane11q23.32.5.1.61176000acute intermittent porphyria
Uroporphyrinogen III synthaseHydroxymethyl bilaneUroporphyrinogen III10q25.2-q26.34.2.1.75606938congenital erythropoietic porphyria
Uroporphyrinogen III decarboxylaseUroporphyrinogen IIICoproporphyrinogen III1q344.1.1.37176100porphyria cutanea tarda
Coproporphyrinogen III oxidaseCoproporphyrinogen IIIProtoporphyrinogen IX3q121.3.3.3121300coproporphyria
Protoporphyrinogen oxidaseProtoporphyrinogen IXProtoporphyrin IX1q221.3.3.4600923variegate porphyria
FerrochelataseProtoporphyrin IXHeme18q21.34.99.1.1177000erythropoietic 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 organic chemistry, but none are of practical value. Porphyrin-based compounds are of interest in molecular electronics and supramolecular building blocks. 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

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An example of a porphyrins involved in host-guest chemistry reported by Sanders and coworkers in Angew. Chem., Int. Ed. Engl. 1995, 34, 1096-1099.
Porphyrins are often used to construct structures in supramolecular chemistry. These systems take advantage of the Lewis acidity of the metal, typically zinc. An example of a host-guest complex that was constructed from a 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.

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Major families of biochemicals
Peptides | Amino acids | Nucleic acids | Carbohydrates | Lipids | Terpenes | Carotenoids | Tetrapyrroles | Enzyme cofactors | Steroids | Flavonoids | Alkaloids | Polyketides | Glycosides
Analogues of nucleic acids:Types of TetrapyrrolesAnalogues of nucleic acids:
Bilanes: Bilirubin | Biliverdin | Urobilinogen | Urobilin
Chlorophylls: Protochlorophyllide | Chlorophyllide
Corrinoids: Cyanocobalamin
Phycobilins: Phycoerythrobilin | Phycocyanobilin | Phycourobilin | Phycoviolobilin
Porphyrins: Uroporphyrinogen (I, III) | Coproporphyrinogen (I, III) | Protoporphyrinogen IX | Protoporphyrin (IX)
A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." [1] In the chemical literature, organic chemists may consider any molecule containing a ring of seven, fifteen, or any arbitrarily large
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Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH.[1] Substituted derivatives are also called pyrroles.
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In chemistry, methine (also known as methylidyne) is a tri-valent functional group CH, derived formally from methane. The methine group consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen.
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conjugated system is a system of atoms covalently bonded with alternating single and multiple (e.g. double) bonds (e.g., C=C-C=C-C) in a molecule of an organic compound. This system results in a general delocalization of the electrons across all of the adjacent parallel aligned
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Purple in colloquial English usage is any shade of color occurring between blue and red; this color is sometimes confused with the more narrowly-defined spectral color violet.

In color theory a Purple is defined as any non-spectral color between violet and red.
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pi bonds (π bonds) are covalent chemical bonds where two lobes of one involved electron orbital overlap two lobes of the other involved electron orbital. Only one of the orbital's nodal planes passes through both of the involved nuclei.
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Porphin, sometimes spelled porphine, is the parent chemical compound for types of biochemically significant compounds called porphyrins. The chemical formula of porphin is C20H14N4.
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complex in chemistry usually is used to describe molecules or ensembles formed by the combination of ligands and metal ions. Originally, a complex implied a reversible association of molecules, atoms, or ions through weak chemical bonds.
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ion is an atom or molecule which has lost or gained one or more electrons, making it positively or negatively charged. A negatively charged ion, which has more electrons in its electron shells than it has protons in its nuclei, is known as an anion
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A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as
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Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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A hemoprotein (also haemoprotein), or heme protein, is a metalloprotein containing a heme prosthetic group, either covalently or noncovalently bound to the protein itself.
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Hemoglobin, also spelled haemoglobin and abbreviated Hb, is the iron-containing oxygen-transport metalloprotein in the red blood cells of the blood in vertebrates and other animals.
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Myoglobin is a single-chain globular protein of 153 amino acids, containing a heme (iron-containing porphyrin) prosthetic group in the center around which the remaining apoprotein folds.
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corrin is a macrocycle related to the porphyrin ring in hemoglobin, consisting of 4 pyrrole subunits, joined on opposite sides by a C-CH3 methylene link, on one side by a C-H methylene link, and with the two of the pyrroles joined directly.
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chlorin is a large heterocyclic aromatic ring consisting, at the core, of 3 pyrroles and one reduced pyrrole coupled through 4 methine linkages. Unlike a porphyrin, a chlorin is therefore largely aromatic but not aromatic through the entire circumference of the ring.
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Bacteriochlorophylls are photosynthetic pigments that occur in various phototrophic bacteria. They are related to chlorophylls, which are the primary pigments in plants, algae, and cyanobacteria.
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chlorin is a large heterocyclic aromatic ring consisting, at the core, of 3 pyrroles and one reduced pyrrole coupled through 4 methine linkages. Unlike a porphyrin, a chlorin is therefore largely aromatic but not aromatic through the entire circumference of the ring.
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Chlorophyll is a green pigment found in most plants, algae, and cyanobacteria. Its name is derived from ancient Greek: chloros = green and phyllon = leaf.
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Bacteriochlorophylls are photosynthetic pigments that occur in various phototrophic bacteria. They are related to chlorophylls, which are the primary pigments in plants, algae, and cyanobacteria.
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Hückel's rule estimates whether a planar ring molecule will have aromatic properties. The quantum mechanical basis for its formulation was first worked out by physical chemist Erich Hückel in 1931. It was first expressed succinctly as the 4n+2 (or 2+4n) rule by von Doering in 1951.
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Pyrrole, or pyrrol, is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH.[1] Substituted derivatives are also called pyrroles.
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