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American Heritage Dictionary:
por·phy·rin |
[Greek porphurā, shellfish yielding purple dye, purple + -IN.]
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Britannica Concise Encyclopedia:
porphyrin |
For more information on porphyrin, visit Britannica.com.
Word Overheard by Answers.com:
porphyria |
What made King Geoge III so very mad? The British ruler who presided over the loss of the American colonies in 1776 was diagnosed about two centuries too late with porphyria — a genetic disorder that causes psychiatric disturbances, among other things — and more recently researchers found arsenic in his hair (presumably from contaminated medication), which may have made him even madder:
"'It is extremely likely that his bouts of madness were due to severe porphyric attacks,' [biochemist Martin J.] Warren said. 'Arsenic may have precipitated his attacks, or made them much more severe.'"
Link: Arsenic Is Linked to British King's Episodes of Madness
Posted July 24, 2005.
See our Word Overheard blog to see interesting uses of strange words. 
McGraw-Hill Science & Technology Encyclopedia:
Porphyrin |
One of a class of cyclic compounds in which the parent macrocycle consists of four pyrrole-type units linked together by single carbon bridges. Several porphyrins with selected peripheral substitution and metal coordination carry out vital biochemical processes in living organisms. Chlorins, bacteriochlorins, and corrins (see structures) are related tetrapyrrolic macrocycles that are also observed in biologically important compounds.
The complexity of porphyrin nomenclature parallels the complex structures of the naturally occurring derivatives. Hans Fischer used a simple numbering system for the porphyrin nucleus (see structures) and a set of common names to identify the different porphyrins and their isomers. A systematic naming based on the 1–24 numbering system for the porphyrin nucleus was later developed by the International Union of Pure and Applied Chemistry (IUPAC) and the International Union of Biochemistry (IUB), and this system has gained general acceptance. The need for common names is clear after examination of the systematic names; for example, protoporphyrin IX has the systematic name 2,7,12,18-tetramethyl-3,8-divinyl-13,17-dipropanoic acid.
The aromatic character (hence stability) of porphyrins has been confirmed by measurements of their heats of combustion. In addition, x-ray crystallographic studies have established planarity of the porphyrin macrocycle which is a basic requirement for aromatic character. See also Delocalization.
Most metals and metalloids have been inserted into the central hole of the porphyrin macrocycle. The resulting metalloporphyrins are usually very stable and can bind a variety of small molecules (known as ligands) to the central metal atom. Heme, the iron complex of protoporphyrin IX, is the prosthetic group of a number of major proteins and enzymes that carry out diverse biological functions. These include binding, transport, and storage of oxygen (hemoglobin and myoglobin), electron-transfer processes (cytochromes), activation and transfer of oxygen to substrates (cytochromes P450), and managing and using hydrogen peroxide (peroxidases and catalases). See also Coordination complexes; Cytochrome.
Chlorophylls and bacteriochlorophylls are magnesium complexes of porphyrin derivatives known as chlorins and bacteriochlorins, respectively. They are the pigments responsible for photosynthesis. Several chlorophylls have been identified, the most common being chlorophyll a, which is found in all oxygen-evolving photosynthetic plants. Bacteriochlorophyll a is found in many photosynthetic bacteria.
Porphyrins and metalloporphyrins exhibit many potentially important medicinal and industrial properties. Metalloporphyrins are being examined as potential catalysts for a variety of processes, including catalytic oxidations. They are also being examined as possible blood substitutes and as electrocatalysts for fuel cells and for the electrochemical generation of hydrogen peroxide. The unique optical properties of porphyrins make them likely candidates for photovoltaic devices and in photocopying and other optical devices. A major area where porphyrins are showing significant potential is in the treatment of a wide range of diseases, including cancer, using photodynamic therapy. See also Catalysis.
Oxford Dictionary of Sports Science & Medicine:
porphyrin |
A class of pigments containing pyrolle rings and a metal. Porphyrins include the iron-containing haemoglobin, myoglobin, and cytochromes, and the magnesium-containing chlorophyll.
Oxford Dictionary of Biochemistry:
porphyrin |
| porphyria, porphyr+, porphobilinogen synthase | |
| porphyrinogen, porphyrinuria, porphyro+ |
Saunders Veterinary Dictionary:
porphyrin |
Any of a group of iron- or magnesium-free cyclic tetrapyrrole derivatives which forms the basis of the respiratory pigments of animals and plants. Porphyrins, in combination with iron, form hemes.
Mosby's Dental Dictionary:
porphyrin |
Any iron or magnesium-free pyrrole derivative occurring in many plant and animal tissues. Normal findings of porphyrins in urine are 60 mg to 200 mg/24-hour period.
Wikipedia on Answers.com:
Porphyrin |
Porphyrins are a group of organic compounds, many naturally occurring. One of the best-known porphyrins is heme, the pigment in red blood cells; heme is a cofactor of the protein hemoglobin. Porphyrins are heterocyclic macrocycles composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH-). Porphyrins are aromatic. That is, they obey Hückel's rule for aromaticity, possessing 4n+2 π electrons (n=4 for the shortest cyclic path) delocalized over the macrocycle. Thus porphyrin macrocycles are highly conjugated systems. As a consequence, they typically have very intense absorption bands in the visible region and may be deeply colored; the name porphyrin comes from a Greek word for purple. The macrocycle has 26 pi electrons in total. The parent porphyrin is porphine, and substituted porphines are called porphyrins.
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Contents
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Porphyrins are the conjugate acids of ligands that bind metals to form complexes. The metal ion usually has a charge of 2+ or 3+. A schematic equation for these syntheses is shown:
A porphyrin without metal in its cavity is a free base. Some iron-containing porphyrins are called hemes. Heme-containing proteins, or hemoproteins, are found extensively in nature. Hemoglobin and myoglobin are two O2-binding proteins that contain iron porphyrins. Various cytochromes are also hemoproteins.
Several other heterocycles are related to porphyrins. These include corrins, chlorins, bacteriochlorophylls, and corphins. Chlorins (2,3-dihydroporphyrin) are more reduced, contain more hydrogen than porphyrins, and feature a pyrroline subunit. This structure occurs in a chlorophyll molecule. 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.
The "committed step" for porphyrin biosynthesis is the formation of δ-aminolevulinic acid (δ-ALA, 5-ALA or dALA) by the reaction of the amino acid glycine with 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:
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 Adler and Longo.[3] The synthesis of simple porphyrins such as meso-tetraphenylporphyrin (H2TPP) is also commonly done in university teaching labs.[4]
The Rothemund synthesis is an condensation and oxidation starting with pyrrole and an aldehyde. In solution-phase synthesis, acidic conditions are essential;[citation needed] formic acid, acetic acid, and propionic acid are typical reaction solvents, or p-toluenesulfonic acid or various Lewis acids can be used with a non-acidic solvent. A large amount of side-product is formed and is removed, usually by recrystallization or chromatography.
Modern green chemistry variants have been developed in which the reaction is performed adsorbed on acidic silica gel with microwave irradiation[5] or at high temperature in the gas phase.[6] In these cases, no additional acid is required.
Although natural porphyrin 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), catalyze a variety of reactions in organic synthesis, but none of them 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.)
In 2008, the corporation Destiny Pharma Ltd reported successful clinical trials of an intra-nasally applied porphyrin XF-73 against methicillin-resistant Staphylococcus aureus.[7]
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.[8] A guest-free base porphyrin is bound to the center by coordination with its four-pyridine substituents.
The field of organic geochemistry, the study of the impacts and processes that organisms have had on the Earth, had its origins in the isolation of porphyrins from petroleum. This finding helped establish the biological origins of petroleum. Petroleum is sometimes "fingerprinted" by analysis of trace amounts of nickel and vanadyl porphyrins.
Chlorophyll is a magnesium porphyrin, and heme is an iron porphyrin, but neither porphyrin is present in petroleum.[citation needed] On the other hand, nickel and vanadyl porphyrins could be related to catalytic molecules from bacteria that feed primordial hydrocarbons.
Lewis structure for meso-tetraphenylporphyrin
UV-vis readout for meso-tetraphenylporphyrin
Light-activated porphyrin. Monatomic oxygen. Cellular aging
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
 | metalloporphyrin |
| etioporphyrin |
| mesoporphyrin III |
 | What contribute to porphyrin colour? |
| Are the porphyrin in bacteria metalfree? |
| How can convert porphyrinogen to porphyrin? |
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 | American Heritage Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| Word Overheard by Answers.com. © 1999-present by Answers Corporation. All rights reserved. Read more |
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| McGraw-Hill Science & Technology Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Oxford Dictionary of Sports Science & Medicine. The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved. Read more |
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Oxford Dictionary of Biochemistry. Oxford University Press. Oxford Dictionary of Biochemistry and Molecular Biology © 1997, 2000, 2006 All rights reserved. Read more | |
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| Saunders Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Mosby's Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
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| Wikipedia on Answers.com. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article Porphyrin. Read more |
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