Porphyrin

Source: Wikipedia, the free encyclopedia.
Not to be confused with
Perforin or Porphyran
.
Porphine, the parent porphyrin.

Porphyrins (

plants, an essential porphyrin derivative is chlorophyll, which is involved in light harvesting and electron transfer in photosynthesis
.

The parent of porphyrins is porphine, a rare chemical compound of exclusively theoretical interest. Substituted porphines are called porphyrins.[1] With a total of 26 π-electrons, of which 18 π-electrons form a planar, continuous cycle, the porphyrin ring structure is often described as aromatic.[2][3] One result of the large conjugated system is that porphyrins typically absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored. The name "porphyrin" derives from the Greek word πορφύρα (porphyra), meaning purple.[4]

Structure

Porphyrin complexes consist of a square planar MN4 core. The periphery of the porphyrins, consisting of sp2-hybridized carbons, generally display small deviations from planarity. "Ruffled" or saddle-shaped porphyrins is attributed to interactions of the system with its environment.[5] Additionally, the metal is often not centered in the N4 plane.[6] For free porphyrins, the two pyrrole protons are mutually trans and project out of the N4 plane.[7] These nonplanar distortions are associated with altered chemical and physical properties. Chlorophyll-rings are more distinctly nonplanar, but they are more saturated than porphyrins.[8]

Complexes of porphyrins

Main article: Transition metal porphyrin complexes

Concomitant with the displacement of two N-H protons, porphyrins bind metal ions in the N4 "pocket". The metal ion usually has a charge of 2+ or 3+. A schematic equation for these syntheses is shown:

H2porphyrin + [MLn]2+ → M(porphyrinate)Ln−4 + 4 L + 2 H+, where M = metal ion and L = a ligand
  • Representative porphyrins and derivatives
  • Derivatives of protoporphyrin IX are common in nature, the precursor to hemes.
    Derivatives of protoporphyrin IX are common in nature, the precursor to hemes.
  • Octaethylporphyrin (H2OEP) is a synthetic analogue of protoporphyrin IX. Unlike the natural porphyrin ligands, OEP2− is highly symmetrical.
    Octaethylporphyrin (H2OEP) is a synthetic analogue of protoporphyrin IX. Unlike the natural porphyrin ligands, OEP2− is highly symmetrical.
  • Tetraphenylporphyrin (H2TPP)is another synthetic analogue of protoporphyrin IX. Unlike the natural porphyrin ligands, TPP2− is highly symmetrical. Another difference is that its methyne centers are occupied by phenyl groups.
    Tetraphenylporphyrin (H2TPP)is another synthetic analogue of protoporphyrin IX. Unlike the natural porphyrin ligands, TPP2− is highly symmetrical. Another difference is that its methyne centers are occupied by phenyl groups.
  • Simplified view of heme, a complex of a protoporphyrin IX.
    Simplified view of heme, a complex of a protoporphyrin IX.
  • A macrocycle of 40 porphyrin molecules, model
    A macrocycle of 40 porphyrin molecules, model
  • A macrocycle of 40 porphyrin molecules, STM image
    A macrocycle of 40 porphyrin molecules, STM image

Ancient porphyrins

A geoporphyrin, also known as a petroporphyrin, is a porphyrin of geologic origin.

crude oil, oil shale, coal, or sedimentary rocks.[9][10] Abelsonite is possibly the only geoporphyrin mineral, as it is rare for porphyrins to occur in isolation and form crystals.[11]

The field of

vanadyl porphyrins.[citation needed
]

Biosynthesis

In non-photosynthetic

plants, algae, bacteria (except for the α-proteobacteria group) and archaea, it is produced from glutamic acid via glutamyl-tRNA and glutamate-1-semialdehyde. The enzymes involved in this pathway are glutamyl-tRNA synthetase, glutamyl-tRNA reductase, and glutamate-1-semialdehyde 2,1-aminomutase
. This pathway is known as the C5 or Beale pathway.

Two molecules of dALA are then combined by

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 B biosynthesis pathway and its modulators. Major enzyme deficiences are also shown.
Enzyme Location
Substrate
 Product Chromosome EC
OMIM
Disorder
ALA synthase
 Mitochondrion
succinyl CoA
 δ-Aminolevulinic acid 3p21.1 2.3.1.37 125290 X-linked dominant protoporphyria, X-linked sideroblastic anemia
ALA dehydratase
 Cytosol δ-Aminolevulinic acid Porphobilinogen 9q34 4.2.1.24 125270 aminolevulinic acid dehydratase deficiency porphyria
PBG deaminase Cytosol Porphobilinogen Hydroxymethyl bilane 11q23.3 2.5.1.61 176000 acute intermittent porphyria
Uroporphyrinogen III synthase Cytosol
Hydroxymethyl bilane
 Uroporphyrinogen III 10q25.2-q26.3 4.2.1.75 606938
congenital erythropoietic porphyria
Uroporphyrinogen III decarboxylase Cytosol Uroporphyrinogen III Coproporphyrinogen III 1p34 4.1.1.37 176100 porphyria cutanea tarda, hepatoerythropoietic porphyria
Coproporphyrinogen III oxidase Mitochondrion Coproporphyrinogen III Protoporphyrinogen IX 3q12 1.3.3.3 121300 hereditary coproporphyria
Protoporphyrinogen oxidase Mitochondrion Protoporphyrinogen IX Protoporphyrin IX 1q22 1.3.3.4 600923 variegate porphyria
Ferrochelatase Mitochondrion Protoporphyrin IX Heme 18q21.3 4.99.1.1 177000 erythropoietic protoporphyria

Laboratory synthesis

Main article: Rothemund reaction
4-methylbenzaldehyde and pyrrole in refluxing propionic acid

A common synthesis for porphyrins is the

oxidation process starting with pyrrole and an aldehyde
.

Potential applications

Photodynamic therapy

Porphyrins have been evaluated in the context of photodynamic therapy (PDT) since they strongly absorb light, which is then converted to heat in the illuminated areas.[15] This technique has been applied in macular degeneration using verteporfin.[16]

PDT is considered a noninvasive cancer treatment, involving the interaction between light of a determined frequency, a photo-sensitizer, and oxygen. This interaction produces the formation of a highly reactive oxygen species (ROS), usually singlet oxygen, as well as superoxide anion, free hydroxyl radical, or hydrogen peroxide.[17] These high reactive oxygen species react with susceptible cellular organic biomolecules such as; lipids, aromatic amino acids, and nucleic acid heterocyclic bases, to produce oxidative radicals that damage the cell, possibly inducing apoptosis or even necrosis.[18]

Molecular electronics and sensors

Porphyrin-based compounds are of interest as possible components of

dye-sensitized solar cells.[20][21]

Biological applications

Porphyrins have been investigated as possible anti-inflammatory agents[22] and evaluated on their anti-cancer and anti-oxidant activity.[23] Several porphyrin-peptide conjugates were found to have antiviral activity against HIV in vitro.[24]

Toxicology

Heme biosynthesis is used as

ALA dehydratase enzyme.[25]

Gallery

  • Lewis structure for meso-tetraphenylporphyrin
    Lewis structure for meso-tetraphenylporphyrin
  • UV–vis readout for meso-tetraphenylporphyrin
    UV–vis readout for meso-tetraphenylporphyrin
  • Light-activated porphyrin. Monatomic oxygen. Cellular aging
    Light-activated porphyrin. Monatomic oxygen. Cellular aging

Related species

In nature

Several heterocycles related to porphyrins are found in nature, almost always bound to metal ions. These include

Caption text
N4-macrocycle Cofactor name metal comment
chlorin chlorophyll magnesium several versions of chlorophyll exist (sidechain; exception being chlorophyll c)
bacteriochlorin bacteriochlorophyll (in part) magnesium several versions of bacteriochlorophyll exist (sidechain; some use a usual chlorin ring)
sirohydrochlorin (an isobacteriochlorin) siroheme iron Important cofactor in sulfur assimilation
biosynthetic intermediate en route to cofactor F430 and B12
corrin vitamin B12 cobalt several variants of B12 exist (sidechain)
corphin Cofactor F430 nickel highly reduced macrocycle

Synthetic

A benzoporphyrin is a porphyrin with a benzene ring fused to one of the pyrrole units. e.g. verteporfin is a benzoporphyrin derivative.[26]

Non-natural porphyrin isomers

Porphycene, first porphyrin isomer, synthesised from bipyrrole dialdehyde through McMurry coupling reaction

The first synthetic porphyrin isomer was reported by Emanual Vogel and coworkers in 1986.[27] This isomer [18]porphyrin-(2.0.2.0) is named as porphycene, and the central N4 Cavity forms a rectangle shape as shown in figure.[28] Porphycenes showed interesting photophysical behavior and found versatile compound towards the photodynamic therapy.[29] This inspired Vogel and Sessler to took up the challenge of preparing [18]porphyrin-(2.1.0.1) and named it as corrphycene or porphycerin.[30] The third porphyrin that is [18]porphyrin-(2.1.1.0), was reported by Callot and Vogel-Sessler. Vogel and coworkers reported successful isolation of [18]porphyrin-(3.0.1.0) or isoporphycene.[31] The Japanese scientist Furuta[32] and Polish scientist Latos-Grażyński[33] almost simultaneously reported the N-confused porphyrins. The inversion of one of the pyrrolic subunits in the macrocyclic ring resulted in one of the nitrogen atoms facing outwards from the core of the macrocycle.

Various reported Isomers of porphyrin

See also

  • A porphyrin-related disease: porphyria
  • Porphyrin coordinated to iron: heme
  • A heme-containing group of enzymes: Cytochrome P450
  • 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
    methyl coenzyme M reductase
    (MCR)
  • Nitrogen-substituted porphyrins: phthalocyanine

References

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  4. ^ Harper D, Buglione DC. "porphyria (n.)". The Online Etymology Dictionary. Retrieved 14 September 2014.
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  10. doi:10.1016/j.tetlet.2003.08.007
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  11. doi:10.1016/0146-6380(89)90038-7
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  12. doi:10.1021/ja01295a027
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  13. doi:10.1021/ja01313a510
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  14. doi:10.1021/jo01288a053
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  15. ^ Giuntini F, Boyle R, Sibrian-Vazquez M, Vicente MG (2014). "Porphyrin conjugates for cancer therapy". In Kadish KM, Smith KM, Guilard R (eds.). Handbook of Porphyrin Science. Vol. 27. pp. 303–416.
  16. PMID 17636693
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  17. PMID 19659920
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  18. PMID 26317756
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  20. doi:10.1142/S1088424610002689
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  24. PMID 34033716
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  25. ISBN 978-1-4665-0260-4
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  26. S2CID 260491296
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  27. doi:10.1002/anie.198602571
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  28. S2CID 246165814
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  29. doi:10.1002/jpp.328
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  30. doi:10.1002/anie.199316001
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  32. doi:10.1021/ja00081a047
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  33. doi:10.1002/anie.199407791
    .

External links

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