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.[1] 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.[2][3]
| |
| Names | |
|---|---|
| Preferred IUPAC name
3,7-Diamino-5λ4-phenothiazin-5-ylium | |
| Identifiers | |
3D model (JSmol) |
|
| ChemSpider |
|
| ECHA InfoCard | 100.008.611 
|
PubChem CID |
|
| UNII | |
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| C12H10N3S+ | |
| Molar mass | 228.29 g·mol−1 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
Thionine is a strongly staining metachromatic dye, which is widely used for biological staining.[4] 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.[5] 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,[6] as originally noted in the thesis of Dr D L Romanowski in 1890s), it forms thionine and all the Azure intermediates.[7][8]
