Thionine, also known as Lauth's violet, is the salt of a

heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...

. 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 Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. Methylene blue is a thiazine dye. As a medication, it is mainly used to treat methemoglobinemia by converting the ferric iron in hemoglobin ...

, which also features a

phenothiazine Phenothiazine, abbreviated PTZ, is an organic compound that has the formula S(C6H4)2NH and is related to the thiazine-class of heterocyclic compounds. Derivatives of phenothiazine are highly bioactive and have widespread use and rich history. T ...

core. The dye's name is frequently misspelled with omission of the e, and is not to be confused with the plant protein

thionin Thionins are a family of small proteins found solely in higher plants. Typically, a thionin consists of 45–48 amino acid residues. 6–8 of these are cysteine forming 3–4 disulfide bonds. They include phoratoxins and viscotoxins. Alpha- and ...

. The -ine ending indicates that the compound is an

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

Dye properties and use

Thionine is a strongly staining metachromatic dye, which is widely used for biological staining. Thionine can also be used in place of

Schiff reagent : The Schiff test is an early organic chemistry named reaction developed by Hugo Schiff, and is a relatively general chemical test for detection of many organic aldehydes that has also found use in the staining of biological tissues. The Schiff ...

in quantitative

Feulgen stain Feulgen stain is a staining technique discovered by Robert Feulgen and used in histology to identify chromosomal material or DNA in cell specimens. It is darkly stained. It depends on acid hydrolysis of DNA, therefore fixating agents using stron ...

ing of DNA. It can also be used to mediate electron transfer in

microbial fuel cell Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system that generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds (also known as fuel or electron donor) on the anode to oxid ...

s. Thionine is a pH-dependent

redox indicator A redox indicator (also called an oxidation-reduction indicator) is an indicator which undergoes a definite color change at a specific electrode potential. The requirement for fast and reversible color change means that the oxidation-reduction e ...

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

, and the intermediates are

Azure C Azure may refer to: Colour * Azure (color), a hue of blue ** Azure (heraldry) ** Shades of azure, shades and variations Arts and media * ''Azure'' (Art Farmer and Fritz Pauer album), 1987 * Azure (Gary Peacock and Marilyn Crispell album), 2013 ...

(Monomethyl thionine),

Azure A Azure A is an organic compound with the chemical formula C14H14ClN3S. It is a light blue to dark blue dye. It is used as a screening test for mucopolysaccharides. It can also be used to stain lysosome in blood smears, and is often used in Giemsa ...

(when one of the amines is dimethylated and the other remains a primary amine), and

Azure B Azure may refer to: Colour * Azure (color), a hue of blue ** Azure (heraldry) ** Shades of azure, shades and variations Arts and media * ''Azure'' (Art Farmer and Fritz Pauer album), 1987 * Azure (Gary Peacock and Marilyn Crispell album), 2013 ...

(Trimethyl thionine). When

is "polychromed" by ripening (oxidized in solution or metabolized by fungal contamination, as originally noted in the thesis of Dr D L Romanowski in 1890s), it forms thionine and all the Azure intermediates.Marshall, PN (1978) Romanowsky-type stains in haematology. Histochemical Journal 10: 1-29.

Notes and references

{{Reflist Staining Phenothiazines