A corrole is an

aromatic In chemistry, aromaticity is a chemical property of cyclic (ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to sat ...

tetrapyrrole Tetrapyrroles are a class of chemical compounds that contain four pyrrole or pyrrole-like rings. The pyrrole/pyrrole derivatives are linked by ( =- or -- units), in either a linear or a cyclic fashion. Pyrroles are a five-atom ring with four ca ...

. The

corrin Corrin is a heterocyclic compound. It is the parent macrocycle related to the substituted derivative that is found in vitamin B12. Its name reflects that it is the "core" of vitamin B12 ( cobalamins).Nelson, D. L.; Cox, M. M. "Lehninger, Princ ...

ring is also present in

cobalamin Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. It is one of eight B vitamins. It is required by animals, which use it as a cofactor in DNA synthesis, in both fatty acid and amino acid metabolism. It ...

( vitamin B₁₂). The ring consists of nineteen

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes ...

atoms, with four

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seve ...

atoms in the core of the molecule. In this sense, corrole is very similar to

porphyrin Porphyrins ( ) are a group of heterocyclic macrocycle organic compounds, composed of four modified pyrrole subunits interconnected at their α carbon atoms via methine bridges (=CH−). The parent of porphyrin is porphine, a rare chemical ...

Preparation

Corroles can be prepared by a two-step process, beginning with the

condensation reaction In organic chemistry, a condensation reaction is a type of chemical reaction in which two molecules are combined to form a single molecule, usually with the loss of a small molecule such as water. If water is lost, the reaction is also known as a ...

of a

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. ...

with

pyrrole Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4 H4 NH. It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-met ...

. The open-ring product, a bilane (or tetrapyrrane), is cyclized by oxidation, typically with ''p''-chloranil:

Comparison with porphyrins

Corrole and

s differ in several ways. Corroles are triprotic, whereas porphyrins are diprotic. Because of the 3- charge of the triply deprotonated ligand, metallocorroles are formally high-valent. Several are redox-noninnocent, with a corrole radical-dianion ligand. A second difference between corroles and porphyrins is the size of the metal-binding cavity, i.e., 17- vs 18-membered rings. See "Porphyrins and similar compounds" in

Conjugated system In theoretical chemistry, a conjugated system is a system of connected p-orbitals with delocalized electrons in a molecule, which in general lowers the overall energy of the molecule and increases stability. It is conventionally represent ...

s for more about these side by side images of

chlorin In organic chemistry, chlorins are tetrapyrrole pigments that are partially hydrogenated porphyrins. The parent chlorin is an unstable compound which undergoes air oxidation to porphine. The name chlorin derives from chlorophyll. Chlorophylls ...

, and

structures:

Coordination complexes

Corroles have been attached to a wide range of transition metals, main group elements, and lanthanides,

actinides The actinide () or actinoid () series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium. The actinide series derives its name from the first element in the series, actinium. The info ...

. and the diprotonated, neutral corrole radical. Additionally, corroles and their metal complexes have been demonstrated to be useful as imaging agents in tumor detection, oxygen sensing, for prevention of heart disease, in synthetic chemistry as oxo, imido, and nitrido transfer agents, and as catalysts for the catalytic reduction of oxygen to water, and hydrogen production form water under aerobic conditions. Protein-corrole particles have been investigated as carriers of theranostic cargo for tumor targeting.{{cite book, first1=James , last1=Teh , first2=Lali Medina, last2=Kauwe, title=Metal Ions in Bio-Imaging Techniques, publisher=Springer, year=2021, pages=299–314, chapter=Chapter 10. Magnetic Resonance Contrast Enhancement and Therapeutic Properties of Corrole Nanoparticles, doi=10.1515/9783110685701-016, s2cid=233677374

References

Chelating agents Tetrapyrroles Macrocycles