{{Short description|Chemical compound and histologic stain C12H10N3S}} {{Other uses}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 424770911 | ImageFile = Thionine.svg | ImageSize = | ImageAlt = | PIN = 3,7-Diamino-5λ<sup>4</sup>-phenothiazin-5-ylium | OtherNames = |Section1={{Chembox Identifiers | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 26754-93-8 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = 8CFV7T4334 | PubChem = 65043 | PubChem_Comment = (chloride salt) | ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} | ChemSpiderID = 10554883 | SMILES = C1=CC2=C(C=C1N)[S+]=C3C=C(C=CC3=N2)N | StdInChI_Ref = {{stdinchicite|changed|chemspider}} | StdInChI = 1S/C12H10N3S/c13-7-1-3-9-11(5-7)16-12-6-8(14)2-4-10(12)15-9/h1-6H,13-14H2/q+1 | StdInChIKey_Ref = {{stdinchicite|changed|chemspider}} | StdInChIKey = CBBMGBGDIPJEMI-UHFFFAOYSA-N }} |Section2={{Chembox Properties | C=12|H=10|N=3|S=1 | Formula_Charge = + | MolarMass = | Appearance = | Density = | MeltingPt = | BoilingPt = | Solubility = }} |Section3={{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} }}
'''Thionine''', also known as '''Lauth's violet''', is the salt of a heterocyclic compound. It was firstly synthesised by Charles Lauth. A variety of salts are known including the chloride and acetate, called respectively '''thionine chloride''' and '''thionine acetate'''. The dye is structurally related to methylene blue, which also features a phenothiazine core.<ref>Gérard Taurand, "Phenothiazine and Derivatives" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim, 2005.{{doi|10.1002/14356007.a19_387}}</ref> The dye's name is frequently misspelled with omission of the e, and is not to be confused with the plant protein thionin. The -ine ending indicates that the compound is an amine.<ref>{{cite journal |author=Kiernan JA |title=Classification and naming of dyes, stains and fluorochromes |journal=Biotech Histochem |volume=76 |issue=5–6 |pages=261–78 |year=2001 |pmid=11871748 |doi=10.1080/bih.76.5-6.261.278|s2cid=32479873 }}</ref><ref>Webster's Third New International Dictionary. G & C Merriam Co. 1976, p.2377.</ref>
==Dye properties and use== Thionine is a strongly staining metachromatic dye, which is widely used for biological staining.<ref>{{cite web |title=Stainsfile — Thionin |url=https://www.stainsfile.com/dyes/thionin/ |archive-url=https://web.archive.org/web/20240618153719/https://www.stainsfile.com/dyes/thionin/ |archive-date=18 June 2024 |access-date=30 October 2024}}</ref> Thionine can also be used in place of Schiff reagent in quantitative Feulgen staining of DNA. It can also be used to mediate electron transfer in microbial fuel cells.<ref>{{cite book|title=Handbook of Fuel Cells: Fundamentals, Technology, Applications, 4-Volume Set|year=2003|publisher=Wiley|isbn=978-0-471-49926-8|url=http://www.cbs.umn.edu/sites/default/files/public/downloads/0471499269.pdf|author=Eugenii Katz |author2=Andrew N. Shipway |author3=Itamar Willner |author3-link=Itamar Willner |editor=Wolf Vielstich|page=5|chapter=21}}</ref> Thionine is a pH-dependent redox indicator with E<sup>0</sup> = 0.06 at pH 7.0. Its reduced form, leuco-thionine, is colorless.
When both the amines are dimethylated, the product tetramethyl thionine is the famous methylene blue, and the intermediates are Azure C (Monomethyl thionine), Azure A (when one of the amines is dimethylated and the other remains a primary amine), and Azure B (Trimethyl thionine). When methylene blue is "polychromed" by ripening (oxidized in solution or metabolized by fungal contamination,<ref>[http://www.dako.com/08066_12may10_webchapter19.pdf Dako Education Guide - Special Stains and H & E ” second edition Chapter 19: '''On Chemical Reactions and Staining Mechanisms''' by John A. Kiernan, Subsection '''What is Giemsa’s stain and how does it color blood cells, bacteria and chromosomes?''' p172] {{Webarchive|url=https://web.archive.org/web/20120513002342/http://www.dako.com/08066_12may10_webchapter19.pdf |date=2012-05-13 }}</ref> as originally noted in the thesis of Dr D L Romanowski in 1890s), it forms thionine and all the Azure intermediates.<ref>{{cite journal | pmc = 2124692 | pmid=19867116 | volume=9 | journal=J Exp Med | pages=645–70 | author=Wilson TM | title=On the Chemistry and Staining Properties of Certain Derivatives of the Methylene Blue Group when Combined with Eosin | year=1907 | issue=6 | doi=10.1084/jem.9.6.645}}</ref><ref>Marshall, PN (1978) Romanowsky-type stains in haematology. Histochemical Journal 10: 1-29.</ref>
==Notes and references== {{Reflist}}
Category:Staining dyes Category:Phenothiazines