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 satur ...

tetrapyrrole. The corrin ring is also present in cobalamin ( 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 In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

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 se ...

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

Preparation

Corroles can be prepared by a two-step process, beginning with the condensation reaction 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''-meth ...

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

Comparison with porphyrins

Corrole and porphyrins 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 represented as ...

s for more about these side by side images of porphyrin, chlorin, and corrin structures:

Coordination complexes

Corroles have been attached to a wide range of

transition metals In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

main group In chemistry and atomic physics, the main group is the group of elements (sometimes called the representative elements) whose lightest members are represented by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, and fluorine as arra ...

elements, and lanthanides, actinides. and the diprotonated, neutral corrole

radical Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

. 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 Personalized medicine, also referred to as precision medicine, is a medical model that separates people into different groups—with medical decisions, practices, interventions and/or products being tailored to the individual patient based on thei ...

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