Hydroxyquinolines

8-Hydroxyquinoline (aka oxine) is a chelating agent which has been used for the quantitative determination of metal ions. 8-Hydroxyquinoline (aka oxine) is a chelating agent which has been used for the quantitative determination of metal ions. In aqueous solution 8-Hydroxyquinoline has a pKa value of ca. 9.9 It reacts with metal ions, losing the proton and forming 8-Hydroxyquinolinato-chelate complexes. The aluminium complex is a common component of organic light-emitting diodes (OLEDs). Variations in the substituents on the quinoline rings affect its luminescence properties. In the photochemically induced excited-state zwitterionic isomers are formed in which the hydrogen atom is transferred from oxygen to nitrogen. The complexes as well as the heterocycle itself exhibit antiseptic, disinfectant, and pesticide properties, functioning as a transcription inhibitor. Its solution in alcohol is used in liquid bandages. It once was of interest as an anti-cancer drug. A thiol analogue,8-Mercaptoquinoline is also known. The roots of the invasive plant Centaurea diffusa release 8-hydroxyquinoline, which has a negative effect on plants that have not co-evolved with it.