This article needs attention from an expert in Chemistry. The specific problem is: narrow and therefore unscholarly content for this fundamental article, which at least needs, i, clearer and more thoughtfully sourced modern definitions/explanations, ii, sourcing and iii broadening of remaining content to include functional applications of this title concept (cf. Macrocyclic stereocontrol), to begin to move article toward an encyclopedic.WikiProject Chemistry (or its Portal) may be able to help recruit an expert.(April 2015)
A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, macrocycles varyingly include molecules containing rings of 8 or more atoms, or 12 or more atoms.[page needed] In general, coordination chemists define a macrocycle more narrowly as a cyclic molecule with three or more potential donor atoms that can coordinate to a metal center. A well-known example is the group of drugs known as macrolides. The IUPAC definition notes that a "cyclic macromolecule has no end-groups but may nevertheless be regarded as a chain," and that "macrocycle is sometimes used [in the literature] for molecules of low relative molecular mass that are not considered 'macromolecules.
Crystal structure of a Zn(II) ion coordinated to cyclen and ethanol reported in Inorg. Chem., 1997, 4579-4584.
The macrocyclic effect was discovered in 1969.[non-primary source needed] Coordination chemists study macrocycles with three or more potential donor atoms in rings of greater than nine atoms, as these compounds often have strong and specific binding with metals.[page needed] This property of coordinating macrocyclic molecules is termed the macrocycle effect, and is a special example of the chelate effect. This so-called macrocyclic effect is thought to be a combination of the entropic effect seen in the chelate effect, together with an additional energetic contribution that comes from the preorganized nature of the ligating groups (that is, no additional strains are introduced to the ligand on coordination).
Macrocycles have been in use for several decades as synthetic dyes. Phthalocyanine is a porphyrin analogue, which is arguably the most useful, in uses as dyes and pigments since their discovery in 1928, due to their dark-blue colour. However, there are many other uses for them. Their name comes from their synthetic precursor, phthalodinitrile.[page needed]