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| Names | |
|---|---|
| Preferred IUPAC name 4-{Bis[4-(dimethylamino)phenyl]methylidene}-N,N-dimethylcyclohexa-2,5-dien-1-iminium chloride | |
Other names
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| Identifiers | |
3D model (JSmol) | |
| 3580948 | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
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| DrugBank |
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| ECHA InfoCard | 100.008.140 |
| EC Number |
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| KEGG |
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| MeSH | Gentian+violet |
| RTECS number |
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| UNII |
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| UN number | 3077 |
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| Properties | |
| C25H30ClN3 | |
| Molar mass | 407.99 g·mol−1 |
| Melting point | 205 °C (decomposes) |
| 4 g/L at 25 °C[1] | |
| Pharmacology | |
| D01AE02 (WHO) G01AX09 (WHO) | |
| Hazards | |
| GHS labelling: | |
    | |
| Danger | |
| H302,H318,H351,H410 | |
| P273,P280,P305+P351+P338,P501 | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 1.2 g/kg (oral, mice) 1.0 g/kg (oral, rats)[2] |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Crystal violet orgentian violet, also known asmethyl violet 10B orhexamethyl pararosaniline chloride, is atriarylmethane dye used as ahistological stain and inGram's method of classifying bacteria. Crystal violet hasantibacterial,antifungal, andanthelmintic (vermicide) properties and was formerly important as atopicalantiseptic. The medical use of the dye has been largely superseded by more modern drugs, although it is still listed by theWorld Health Organization.
The namegentian violet was once used for a mixture of methylpararosaniline dyes (methyl violet), but it is considered a synonym forcrystal violet. The name refers to its colour, being like that of thepetals of certaingentian flowers; it is not made from gentians orviolets.
A number of possible routes can be used to prepare crystal violet.[3][4] The original procedure developed by the German chemists Kern andCaro involved the reaction ofdimethylaniline withphosgene to give 4,4′-bis(dimethylamino)benzophenone (Michler's ketone) as an intermediate.[5] This was then reacted with additional dimethylaniline in the presence ofphosphorus oxychloride andhydrochloric acid.[6]
The dye can also be prepared by thecondensation offormaldehyde anddimethylaniline to give aleuco dye:[3][4][7]
Second, this colourless compound isoxidized to the colouredcationic form (hereafter withoxygen, but a typicaloxidizing agent ismanganese dioxide, MnO2):
| Crystal violet(pH indicator) | ||
| below pH −1.0 | above pH 2.0 | |
| −1.0 | ⇌ | 2.0 |
When dissolved in water, the dye has a blue-violet colour with anabsorbance maximum at 590 nm and anextinction coefficient of 87,000 M−1 cm−1.[8] The colour of the dye depends on the acidity of the solution. At apH of +1.0, the dye is green with absorption maxima at 420 nm and 620 nm, while in a strongly acidic solution (pH −1.0), the dye is yellow with an absorption maximum at 420 nm.[citation needed]
The different colours are a result of the different charged states of the dye molecule. In the yellow form, all three nitrogen atoms carry a positive charge, of which two areprotonated, while the green colour corresponds to a form of the dye with two of the nitrogen atoms positively charged. At neutral pH, both extra protons are lost to the solution, leaving only one of the nitrogen atoms positive charged. ThepKa for the loss of the two protons are approximately 1.15 and 1.8.[8]
Inalkaline solutions,nucleophilichydroxyl ions attack theelectrophilic central carbon to produce the colourlesstriphenylmethanol orcarbinol form of the dye.[citation needed] Some triphenylmethanol is also formed under very acidic conditions when the positive charges on the nitrogen atoms lead to an enhancement of the electrophilic character of the central carbon, which allows thenucleophilic attack by water molecules. This effect produces a slight fading of the yellow colour.[citation needed]
Crystal violet is used as a humidity indicator, in silica gel for example, being orange when dry and going through green to violet when exposed to increasing amount of moisture.[9]
Crystal violet is used as a textile and paper dye, and is a component ofnavy blue andblack inks for printing, ball-point pens, and inkjet printers. Historically, it was the most common dye used in early duplication machines, such as themimeograph and theditto machine.[10] It is sometimes used to colourize diverse products such asfertilizer,antifreeze,detergent, andleather.[citation needed]Marking blue, used tomark out pieces inmetalworking, is composed ofmethylated spirits,shellac, and gentian violet.[11]
When conductingDNAgel electrophoresis, crystal violet can be used as a nontoxic DNA stain as an alternative tofluorescent, intercalating dyes such asethidium bromide. Used in this manner, it may be either incorporated into theagarose gel or applied after the electrophoresis process is finished. Used at a 10 ppm concentration and allowed to stain a gel after electrophoresis for 30 minutes, it can detect as little as 16 ng of DNA. Through use of amethyl orange counterstain and a more complex staining method, sensitivity can be improved further to 8 ng of DNA.[12] When crystal violet is used as an alternative tofluorescent stains, it is not necessary to useultraviolet illumination; this has made crystal violet popular as a means of avoiding UV-induced DNA destruction when performingDNA cloningin vitro.[citation needed]
Crystal violet can be used as an alternative toCoomassie brilliant blue (CBB) in staining ofproteins separated bySDS-PAGE, reportedly showing a 5x improved sensitivity vs CBB.[13]
The dye is used as ahistological stain, particularly inGram staining forclassifying bacteria.[14]
Inbiomedical research, crystal violet can be used to stain the nuclei of adherent cells.[15] In this application, crystal violet works as an intercalating dye and allows the quantification of DNA which is proportional to the number of cells.[citation needed]
Crystal violet is also used as atissue stain in the preparation oflight microscopy sections.[16] In laboratory, solutions containing crystal violet andformalin are often used to simultaneouslyfix and stain cells grown intissue culture to preserve them and make them easily visible, since most cells are colourless.
It is also sometimes used as a cheap way to put identification markings onlaboratory mice; since many strains of lab mice arealbino, the purple colour stays on theirfur for several weeks.[17]
Inforensics, crystal violet was used to developfingerprints. It is able to develop fingerprint marks from live human skin.[18]
Gentian violet hasantibacterial,antifungal,antihelminthic,antitrypanosomal,antiangiogenic, andantitumor properties.[19][20] It is used medically for these properties, in particular fordentistry, and is also known as "pyoctanin" (or "pyoctanine").[21] It is commonly used for:
In resource-limited settings, gentian violet is used to manage burn wounds,[22] inflammation of theumbilical cord stump (omphalitis) in theneonatal period,[23] oralcandidiasis inHIV-infected patients[24] andmouth ulcers in children withmeasles.[25]
Inbody piercing, gentian violet is commonly used to mark the location for placing piercings, includingsurface piercings.[citation needed]
Because of itsantimicrobial activity, it is used to treatich in fish. However, it usually is illegal to use in fish intended for human consumption.[26]
Crystal violet is one of the components ofmethyl violet, a dye first synthesized byCharles Lauth in 1861.[27] From 1866, methyl violet was manufactured by theSaint-Denis-based firm of Poirrier et Chappat and marketed under the name "Violet de Paris". It was a mixture of the tetra-, penta- and hexamethylatedpararosanilines.[28]
Crystal violet itself was first synthesized in 1883 byAlfred Kern [de] (1850–1893) working inBasel at the firm ofBindschedler & Busch.[6] To optimize the difficult synthesis which used the highly toxicphosgene, Kern entered into a collaboration with the German chemistHeinrich Caro atBASF.[5] Kern also found that by starting withdiethylaniline rather thandimethylaniline, he could synthesize the closely related violet dye now known as C.I. 42600 or C.I. Basic violet 4.[29]
The name "gentian violet" (orGentianaviolett in German) is thought to have been introduced by the German pharmacist Georg Grübler, who in 1880 started a company inLeipzig that specialized in the sale of staining reagents forhistology.[30][31] The gentian violet stain marketed by Grübler probably contained a mixture of methylatedpararosaniline dyes.[32] The stain proved popular and in 1884 was used byHans Christian Gram to stain bacteria. He creditedPaul Ehrlich for the aniline-gentian violet mixture.[33] Grübler's gentian violet was probably very similar, if not identical, to Lauth's methyl violet, which had been used as a stain byVictor André Cornil in 1875.[34]
Although the name gentian violet continued to be used for the histological stain, the name was not used in the dye and textile industries.[35] The composition of the stain was not defined and different suppliers used different mixtures. In 1922, theBiological Stain Commission appointed a committee chaired byHarold Conn to look into the suitability of the different commercial products.[30] In his bookBiological Stains, Conn describes gentian violet as a "poorly defined mixture of violetrosanilins".[35]
The GermanophthalmologistJakob Stilling is credited with discovering theantiseptic properties of gentian violet.[36] He published a monograph in 1890 on the bactericidal effects of a solution that he christened "pyoctanin", which was probably a mixture ofaniline dyes similar to gentian violet.[37] He set up a collaboration withE. Merck & Co. to market "Pyoktanin caeruleum" as an antiseptic.[38]
In 1902, Drigalski and Conradi found that although crystal violet inhibited the growth of many bacteria, it has little effect onBacillus coli (Escherichia coli) andBacillus typhi (Salmonella typhi), which are bothgram-negative bacteria.[39] A much more detailed study of the effects of Grübler's gentian violet on different strains of bacteria was published by John Churchman in 1912.[40] He found that mostgram-positive bacteria (tainted) were sensitive to the dye, while most gram-negative bacteria (not tainted) were not, and observed that the dye tended to act as abacteriostatic agent rather than abactericide.[citation needed]
One study in mice demonstrated dose-relatedcarcinogenic potential at several different organ sites.[41][42]
TheFood and Drug Administration in the US (FDA) has determined that gentian violet has not been shown by adequate scientific data to be safe for use in animal feed. Use of gentian violet in animal feed causes the feed to beadulterated and is a violation of theFederal Food, Drug, and Cosmetic Act in the US. On June 28, 2007, the FDA issued an "import alert" on farm-raised seafood from China because unapproved antimicrobials, including gentian violet, had been consistently found in the products. The FDA report states:
Like MG (malachite green), CV (crystal violet) is readily absorbed into fish tissue from water exposure and is reduced metabolically by fish to the leuco moiety, leucocrystal violet (LCV). Several studies by theNational Toxicology Program reported the carcinogenic andmutagenic effects of crystal violet in rodents. The leuco form induces renal, hepatic and lung tumor in mice."[43][44]
In 2019,Health Canada (HC) completed safety reviews on gentian violet and found it to be carcinogenic when in direct contact with the body. As a result, HC has worked with human and animal drug makers to discontinue and recall all drugs containing gentian violet, and recommended customers stop using and safely discard any remaining drug products that contain gentian violet. HC found the all medical devices containing gentian violet on the Canadian market to be safe over the short term, as these polyurethane foam dressings are very unlikely to cause contact with skin. HC recommends most people to limit the use of these dressings to 6 months, and pregnant and nursing people to avoid using it altogether, as there's not enough evidence to prove that prolonged use or use by pregnant/nursing people is safe.[45] This caused Canadian engineering schools to revisit the usage of this dye during orientation, in which students "purple" themselves by dunking into a tub containing a dilute solution of the dye.[46]
Residues in food and their evaluations – Conditions of use
