Thionine
{{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-5λ4-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.Gérard Taurand, "Phenothiazine and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.{{doi|10.1002/14356007.a19_387}} 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.{{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 }}Webster's Third New International Dictionary. G & C Merriam Co. 1976, p.2377.
Dye properties and use
Thionine is a strongly staining metachromatic dye, which is widely used for biological staining.{{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}} 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.{{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}} Thionine is a pH-dependent redox indicator with E0 = 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,[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 }} as originally noted in the thesis of Dr D L Romanowski in 1890s), it forms thionine and all the Azure intermediates.{{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}}Marshall, PN (1978) Romanowsky-type stains in haematology. Histochemical Journal 10: 1-29.