hydroxyquinoline

Hydroxyquinoline is a family of heterocyclic aromatic compounds derived from quinoline by substitution with one or more hydroxyl groups on the ring. The hydroxy group can occupy several positions, giving rise to isomers such as 2-, 4-, 5-, 6-, 7-, and 8-hydroxyquinoline. Among them, 8-hydroxyquinoline (also called oxine) is the most widely studied.

8-Hydroxyquinoline contains a hydroxyl group adjacent to the ring nitrogen. When deprotonated, it forms the quinolinolate anion, a strong bidentate ligand that coordinates many metal ions. This chelating ability underpins its use in coordination chemistry and analytical chemistry, including colorimetric and fluorimetric assays for metals such as aluminum, zinc, copper, and iron. 8-Hydroxyquinoline derivatives are also used in materials science; for example, aluminum tris(8-hydroxyquinoline) (Alq3) is a well-known emissive material in organic light-emitting diodes (OLEDs).

Beyond 8-hydroxyquinoline, other hydroxyquinoline derivatives (notably 5-chloro-7-iodo-8-hydroxyquinoline, clioquinol) have been explored as antimicrobial, antiparasitic, and pharmaceutical leads, though safety considerations have limited their clinical use in some cases. As a class, hydroxyquinolines are repeatedly studied for metal-binding properties, fluorescence, and potential therapeutic or diagnostic applications.