Structure of porphine, the simplest porphyrin.

Space-filling model of porphyrin

A porphyrin is a heterocyclic macrocycle derived from four pyrroline subunits interconnected via their α carbon atoms via methine bridges (=CH-). A macrocycle is as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic organic Chemical compounds which differ in the position In chemistry methine (also known as methylidyne or methyne) is a tri-valent Functional group CH derived formally from Methane. Porphyrins are aromatic and they obey Hückel's rule for aromaticity in that they possess 4n+2 pi electrons which are delocalized over the macrocycle. In Organic chemistry, Hückel's rule estimates whether a Planar ring Molecule will have Aromatic properties The macrocycle, therefore, is a highly-conjugated system, and, as a consequence, is deeply coloured - the name porphyrin comes from a Greek word for purple. A chemically conjugated system is a system of atoms Covalently bonded with alternating single and multiple (e Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Purple is a general term for the range of shades of Color occurring between Red and Blue. The macrocycle has 22 pi electrons. In Chemistry, pi bonds ( π bonds) are covalent Chemical bonds where two lobes of one involved electron orbital overlap two lobes The parent porphyrin is porphine, and substituted porphines are called porphyrins. Porphin, sometimes spelled porphine, is the parent Chemical compound for types of biochemically significant compounds called Porphyrins The Chemical Many porphyrins occur in nature, such as in green leaves and red blood cells, and in bio-inspired synthetic catalysts and devices. A blood cell (also called blood corpuscle) is any cell of any type normally found in Blood.

Complexes of porphyrins and related molecules

Porphyrins bind metals to form complexes. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across The term complex in Chemistry is usually used to describe molecules or ensembles formed by the combination of Ligands and metal Ions. The metal ion, usually with a charge of 2+ or 3+, resides in the central N₄ cavity formed by the loss of two protons. An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Most metals can be inserted. A schematic equation for these syntheses is shown:

H₂porphyrin + [ML_n]²⁺ → M(porphyrinate)L_n-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. A heme ( American English) or haem ( British English) is a Prosthetic group that consists of an Iron atom contained in the center of Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl A hemoprotein (also haemoprotein) or Heme Protein, is a Metalloprotein containing a heme Prosthetic group, either covalently Hemoglobin and myoglobin are two O₂-binding proteins that contain iron porphyrins. Hemoglobin ( also spelled haemoglobin and abbreviated Hb or Hgb) is the Iron -containing Oxygen -transport Metalloprotein Myoglobin is a single-chain globular Protein of 153 Amino acids containing a Heme ( Iron -containing Porphyrin) Prosthetic

Related to porphyrins are several other heterocycles, including corrins, chlorins, bacteriochlorophylls, and corphins. A corrin is a Macrocycle related to the Porphyrin ring in Hemoglobin, consisting of 4 Pyrrole subunits joined on opposite sides by a C-CH3 In Organic chemistry, a chlorin is a large Heterocyclic Aromatic ring consisting at the core of three Pyrroles and one Pyrroline Bacteriochlorophylls are Photosynthetic pigments that occur in various Phototrophic bacteria. F430 is the Prosthetic group of the Enzyme Methyl Chlorins (2,3-dihydroporphyrin) are more reduced, that contain more hydrogen, than porphyrins, featuring a pyrroline subunit. In Organic chemistry, a chlorin is a large Heterocyclic Aromatic ring consisting at the core of three Pyrroles and one Pyrroline This structure occurs in chlorophyll. Chlorophyll is a green Pigment found in most Plants Algae and Cyanobacteria. 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. Bacteriochlorophylls are Photosynthetic pigments that occur in various Phototrophic bacteria. Photosynthesis is a Metabolic pathway that converts Light Energy into Chemical energy. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Some porphyrin derivatives follow Hückel's rule, but most do not. In Organic chemistry, Hückel's rule estimates whether a Planar ring Molecule will have Aromatic properties

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. Pyrrole, or pyrrol, is a Heterocyclic Aromatic Organic compound, a five-membered ring with the formula C 4 An aldehyde is an organic compound containing a terminal Carbonyl group. 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. p -Toluenesulfonic acid (PTSA is an Organic compound with the formula CH3[[benzene C6H4]] SO3H Lewis acids such as boron trifluoride etherate and ytterbium triflate have also been known to catalyse porphyrin formation. Boron trifluoride is the Chemical compound with the formula BF3 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. Biosynthesis is a phenomenon wherein Chemical compounds are produced from simpler Reagents Biosynthesis unlike Chemosynthesis, takes place within living D-Aminolevulinic acid (dALA or δ-ALA or 5-aminolevulinic acid is the first compound in the Porphyrin synthesis pathway the pathway that leads to Hemoglobin in mammals In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Glycine (abbreviated as Gly or G) is the Organic compound with the formula NH2CH2COOH Succinyl-Coenzyme A, generally abbreviated as Succinyl-CoA or SucCoA is a combination of Succinic acid and Coenzyme A. The citric acid cycle, also known as the tricarboxylic acid cycle ( TCA cycle) or the Krebs cycle, (or rarely the Szent-Györgyi–Krebs cycle Two molecules of dALA combine to give porphobilinogen (PBG), which contains a pyrrole ring. Porphobilinogen (PBG is a Pyrrole involved in Porphyrin metabolism Pyrrole, or pyrrol, is a Heterocyclic Aromatic Organic compound, a five-membered ring with the formula C 4 Four PBGs are then combined through deamination into hydroxymethyl bilane (HMB), which is hydrolysed to form the circular tetrapyrrole uroporphyrinogen III. Deamination is the removal of an Amine group from a Molecule. Hydroxymethylbilane, also known as preuroporphyrinogen, is a molecule involved in the metabolism of Porphyrin. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions In the synthesis of Porphyrin, Uroporphyrinogen III is created by the enzyme Uroporphyrinogen III synthase, and the enzyme Uroporphyrinogen III decarboxylase 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. In the metabolism of Porphyrin, protoporphyrin IX is created by the enzyme Protoporphyrinogen oxidase, and the enzyme Ferrochelatase converts it into Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 A heme ( American English) or haem ( British English) is a Prosthetic group that consists of an Iron atom contained in the center of 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 Mendelian Inheritance in Man project is a Database that catalogues all the known Diseases with a genetic component, and—when possible—links them 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)

Applications

Although natural porphyin complexes are essential for life, synthetic porphyrins and their complexes have limited utility. Erythropoietic protoporphyria (EPP is a relatively mild form of Porphyria, although very painful which arises from a deficiency in the enzyme Ferrochelatase, leading Complexes of meso-tetraphenylporphyrin, e. g. , the iron-(III) chloride complex (TPPFeCl) catalyse a variety of reactions in organic chemistry, but none is of practical value. Organic chemistry is a discipline within Chemistry which involves the scientific study of the structure properties composition reactions, and preparation Porphyrin-based compounds are of interest in molecular electronics and supramolecular building blocks. For quantum mechanical study of the Electron distribution in a molecule see Stereoelectronics. Phthalocyanines, which are structurally related to porphyrins, are used in commerce as dyes and catalysts. A phthalocyanine is a macrocyclic compound having an alternating nitrogen atom-carbon atom ring structure. Synthetic porphyrin dyes that are incorporated in the design of solar cells are the subject of ongoing research. See Dye-sensitized solar cells.

In 2008 the UK corporation Destiny Pharma reported successful clinical trials of an intranasally applied porphorin XF-73 against methicillin-resistant Staphylococcus aureus. ^[5][6]

Supramolecular chemistry

An example of a porphyrins involved in host-guest chemistry reported by Sanders and coworkers in Angew. In Supramolecular chemistry, host-guest chemistry describes complexes that are composed of two or more Molecules or Ions held together in unique Chem. , Int. Ed. Engl. 1995, 34, 1096-1099.

Porphyrins are often used to construct structures in supramolecular chemistry. Supramolecular chemistry refers to the area of Chemistry that focuses on the Noncovalent bonding interactions of molecules 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. In Supramolecular chemistry, host-guest chemistry describes complexes that are composed of two or more Molecules or Ions held together in unique A macrocycle is as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule ^[7] A guest-free base porphyrin is bound to the center by coordination with its four pyridine sustituents.

See also

• A porphyrin-related disease: porphyria
• Porphyrin coordinated to iron: heme
• Porphyrin coordinated to magnesium: chlorophyll
• The one-carbon-shorter analogues: corroles, including Vitamin B12 which is coordinated to a cobalt
• Corphins, the highly-reduced porphyrin coordinated to nickel that binds the F430 active site in methyl coenzyme M reductase (MCR)
• Nitrogen-substituted porphyrins: phthalocyanine

References

External links

• Porphynet - an informative site about porphyrins and related structures