chemistry

Porphyrin

Porphyrin is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Porphyrin rather than just read about it. In short: Porphyrins ( POR-fər-ins) are heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−), so they are cyclic tetrapyrroles. In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream.

Key takeaways

Porphyrin belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Porphyrin to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Porphyrin from memory before moving on to harder problems.

Reference excerpt

Porphyrins ( POR-fər-ins) are heterocyclic, macrocyclic, organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−), so they are cyclic tetrapyrroles. In vertebrates, an essential member of the porphyrin group is heme, which is a component of hemoproteins, whose functions include carrying oxygen in the bloodstream. In 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. With a total of 26 π-electrons the porphyrin ring structure is a coordinated aromatic system. One result of the large conjugated system is that porphyrins absorb strongly in the visible region of the electromagnetic spectrum, i.e. they are deeply colored. The name "porphyrin" derives from Greek πορφύρα (porphyra) 'purple'.

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. Additionally, the metal is often not centered in the N4 plane. For free porphyrins, the two pyrrole protons are mutually trans and project out of the N4 plane. These nonplanar distortions are associated with altered chemical and physical properties. Chlorophyll-rings are more distinctly nonplanar, but they are more saturated than porphyrins.

Complexes of porphyrins

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, where M = metal ion and L = a ligand:

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

Ancient porphyrins A geoporphyrin, also known as a petroporphyrin, is a porphyrin of geologic origin. They can occur in crude oil, oil shale, coal, or sedimentary rocks. Abelsonite is possibly the only geoporphyrin mineral, as it is rare for porphyrins to occur in isolation and form crystals. The field of organic geochemistry had its origins in the isolation of porphyrins from petroleum. These findings helped establish the biological origins of petroleum. Petroleum is sometimes "fingerprinted" by analysis of trace amounts of nickel and vanadyl porphyrins. Metalloporphyrins in general are highly stable organic compounds, and the detailed structures of the extracted derivatives made clear that they originated from chlorophyll.

Biosynthesis In non-photosynthetic eukaryotes such as animals, insects, fungi, and protozoa, as well as the α-proteobacteria group of bacteria, 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. In 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 porphobilinogen synthase 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:

Laboratory synthesis

A common synthesis for porphyrins is the Rothemund reaction, first reported in 1936, which is also the basis for more recent methods described by Adler and Longo. The general scheme is a condensation and 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. This technique has been applied in macular degeneration using verteporfin. 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. 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.

Molecular electronics and sensors Porphyrin-based compounds are of interest as possible components of molecular electronics and photonics. Synthetic porphyrin dyes have been incorporated in prototype dye-sensitized solar cells.

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

Toxicology Heme biosynthesis is used as biomarker in environmental toxicology studies. While excess production of porphyrins indicate organochlorine exposure, lead inhibits ALA dehydratase enzyme.

Photochemistry Free-base porphyrins, including naturally occurring protoporphyrin IX (PPIX), function as viable photoredox catalysts under red-light irradiation. Red light provides deeper tissue and media penetration, making this approach suitable for aqueous biomolecule functionalization.

Gallery

Related species

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

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Porphyrin

Start with the simplest possible case. Write down what Porphyrin claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Porphyrin before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Porphyrin ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Porphyrin

In research: Porphyrin appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Porphyrin in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Porphyrin is common in secondary-school and first-year university syllabi. It links to neighbouring topics Biomolecules, Chelating agents, Metabolism, so understanding it makes those chapters shorter.
In everyday life: Look for Porphyrin outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Porphyrin in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Porphyrin means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Porphyrin out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Porphyrin in simple terms?

Why does Porphyrin matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Porphyrin?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Porphyrin.