Corrin is a heterocyclic compound. Although not known to exist on its own, the molecule is of interest as the parent macrocycle related to the cofactor and

chromophore A chromophore is the part of a molecule responsible for its color. The word is derived . The color that is seen by our eyes is that of the light not Absorption (electromagnetic radiation), absorbed by the reflecting object within a certain wavele ...

in vitamin B₁₂. Its name reflects that it is the "core" of vitamin B₁₂ (

cobalamin Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. One of eight B vitamins, it serves as a vital cofactor (biochemistry), cofactor in DNA synthesis and both fatty acid metabolism, fatty acid and amino a ...

s). Compounds with a corrin core are known as "corrins". There are two chiral centres, which in natural compounds like cobalamin have the same

stereochemistry Stereochemistry, a subdiscipline of chemistry, studies the spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which are defined ...

Coordination chemistry

Upon deprotonation, the corrinoid ring is capable of binding

cobalt Cobalt is a chemical element; it has Symbol (chemistry), symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. ...

. In vitamin B₁₂, the resulting complex also features a benzimidazole-derived ligand, and the sixth site on the octahedron serves as the catalytic center. The corrin ring resembles the porphyrin ring. Both feature four pyrrole-like subunits organized into rings. Corrins have a central 15-membered ring whereas porphryins have an interior 16-membered ring. All four nitrogen centers are linked by

conjugation Conjugation or conjugate may refer to: Linguistics *Grammatical conjugation, the modification of a verb from its basic form *Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics *Complex conjugation, the change o ...

structure, with alternating double and single bonds. In contrast to porphyrins, corrins lack one of the carbon groups that link the pyrrole-like units into a fully conjugated structure. With a conjugated system that extends only 3/4 of the way around the ring, and does not include any of the outer edge carbons, corrins have a number of non-conjugated sp³ carbons, making them more flexible than porphyrins and not as flat. A third closely related biological structure, the chlorin ring system found in

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

, is intermediate between porphyrin and corrin, having 20 carbons like the porphyrins and a conjugated structure extending all the way around the central atom, but with only 6 of the 8 edge carbons participating. Corroles (octadehydrocorrins) are fully aromatic derivatives of corrins.

Coordination chemistry

References

Further reading