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| Names | |
|---|---|
| Preferred IUPAC name 4-{[4-(Dimethylamino)phenyl](phenyl)methylidene}-N,N-dimethylcyclohexa-2,5-dien-1-iminium chloride | |
| Other names Aniline green; Basic green 4; Diamond green B; Victoria green B | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChEMBL | |
| ChemSpider |
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| ECHA InfoCard | 100.008.476 |
| KEGG | |
| UNII | |
| |
| |
| Properties | |
| C23H25ClN2 (chloride) | |
| Molar mass | 364.911 g/mol (chloride) |
| Pharmacology | |
| QP53AX16 (WHO) | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Moderately toxic, Extremeirritant |
| GHS labelling:[1] | |
    | |
| Danger | |
| H302,H318,H361d,H410 | |
| P264,P270,P280,P301+P312,P305+P351+P338,P310,P330,P501 | |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 80mg/kg (oral,mouse) |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Malachite green is anorganic compound that is used as adyestuff and controversially as an antimicrobial inaquaculture. Malachite green is traditionally used as a dye for materials such assilk,leather, andpaper. Despite its name the dye is not prepared from themineralmalachite; the name just comes from the similarity of color.
Malachite green is classified in the dyestuff industry as atriarylmethane dye and also using in pigment industry. Formally, malachite green refers to the chloride salt[C6H5C(C6H4N(CH3)2)2]Cl, although the term malachite green is used loosely and often just refers to the coloredcation. Theoxalate salt is also marketed. Theanions have no effect on the color. The intense green color of the cation results from a strong absorption band at 621 nm (extinction coefficient of105 M−1 cm−1).
| Malachite green (second transition)(pH indicator) | ||
| below pH 11.5 | above pH 13.2 | |
| 11.5 | ⇌ | 13.2 |
| Malachite green (first transition)(pH indicator) | ||
| below pH 0.2 | above pH 1.8 | |
| 0.2 | ⇌ | 1.8 |
Malachite green is prepared by the condensation ofbenzaldehyde anddimethylaniline to giveleuco malachite green (LMG):
Second, this colorless leuco compound, a relative oftriphenylmethane, is oxidized to the cation that is MG:
A typical oxidizing agent ismanganese dioxide.
Hydrolysis of MG gives analcohol:[2]
This alcohol is important because it, not MG, traverses cell membranes. Once inside the cell, it is metabolized into LMG. Only the cation MG is deeply colored, whereas the leuco and alcohol derivatives are not. This difference arises because only the cationic form has extended pi-delocalization, which allows the molecule to absorb visible light.
Theleuco form of malachite green was first prepared byHermann Fischer in 1877 by condensingbenzaldehyde anddimethylaniline in the molecular ratio 1:2 in the presence ofsulfuric acid.[3]
Malachite green is traditionally used as a dye. Kilotonnes of MG and related triarylmethane dyes are produced annually for this purpose.[4]
MG is active against theoomyceteSaprolegnia, which infects fish eggs in commercialaquaculture, MG has been used to treatSaprolegnia and is used as anantibacterial.[5] It is a very popular treatment againstIchthyophthirius multifiliis infreshwateraquaria. The principalmetabolite, leuco-malachite green (LMG), is found in fish treated with malachite green, and this finding is the basis of controversy and government regulation. See alsoAntimicrobials in aquaculture.
MG has frequently been used to catch thieves and pilferers. The bait, usually money, is sprinkled with the anhydrous powder. Anyone handling the contaminated money will find that on upon washing the hands, a green stain on the skin that lasts for several days will result.[citation needed]
Numerous niche applications exploit the intense color of MG. It is used as abiological stain formicroscopic analysis ofcell biology andtissue samples. In theGimenez staining method, basicfuchsin stains bacteria red or magenta, and malachite green is used as a blue-greencounterstain. Malachite green is also used inendospore staining, since it can directly stainendospores within bacterial cells; here asafranin counterstain is often used. Malachite green is a part of Alexander'spollen stain. Malachite green can also be used as asaturable absorber indye lasers, or as apH indicator between pH 0.2–1.8. However, this use is relatively rare. Leuco-malachite green (LMG) is used as a detection method for latent blood inforensic science.Hemoglobin catalyzes the reaction between LMG andhydrogen peroxide, converting the colorless LMG into malachite green. Therefore, the appearance of a green color indicates the presence ofblood.[6]
A set of malachite green derivatives is also a key component in a fluorescence microscopy tool called the fluorogen activating protein/fluorogen system. Malachite green is in a class of molecules called fluorophores. When malachite green's rotational freedom is restricted, it transforms from a non fluorescent molecule to a highly fluorescent molecule.[7] In the fluorogen activating protein tool, established by a group at Carnegie Mellon University, Malachite green binds a specific fluorogen activating protein to become highly fluorescent. Expression of the fluorogen activating protein as fusions of targeting domains can impart subcellular localization. Its use is similar to that ofGFP but has the added benefit of having a 'dark state' before the malachite green fluorophore is added. This is especially useful for FRET studies.
In 1992, Canadian authorities determined that eating fish contaminated with malachite green posed a significant health risk.[8] Malachite green was classified a Class II Health Hazard. Due to its low manufacturing cost, malachite green is still used in certain countries with less restrictive laws for nonaquaculture purposes. In 2005, analysts inHong Kong found traces of malachite green ineels and fish imported fromChina. In 2006, the United StatesFood and Drug Administration (FDA) detected malachite green in seafood from China,among others, where the substance is also banned for use in aquaculture.[9] In June 2007, the FDA blocked the importation of several varieties of seafood due to continued malachite green contamination.[10]
Malachite green has been banned in the United States since 1983 in food-related applications. The substance is also banned in the United Kingdom.[11] It is prohibited from the use in food in Macao.[12]
Animalsmetabolize malachite green to itsleuco form. Beinglipophillic (the leuco form has alog P of 5.70), themetabolite is retained incatfish muscle longer (HL = 10 days) than is the parent molecule (HL = 2.8 days).
TheLD50 (oral, mouse) is 80 mg/kg.[citation needed] Rats fed malachite green experience "a dose-related increase in liverDNA adducts" along with lungadenomas. Leucomalachite green causes an "increase in the number and severity of changes". As leucomalachite green is the primary metabolite of malachite green and is retained in fish muscle much longer, most human dietary intake of malachite green from eating fish would be in the leuco form. During the experiment, rats were fed up to 543 ppm of leucomalachite green, an extreme amount compared to the average 5 ppb discovered in fish. After a period of two years, an increase in lung adenomas in male rats was discovered but no incidences of liver tumors. Therefore, it could be concluded that malachite green caused carcinogenic symptoms, but a direct link between malachite green andliver tumor was not established.[13]
Although malachite green has almost no fluorescence in aqueous solution (quantum yield 7.9x10−5),[14] several research groups have developed technologies to detect malachite green. For example, Zhao et al., demonstrated the use of malachite green aptamer in microcantilever based sensors to detect low concentration of malachite green.[15]
