Malachite green is an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

that is used as a

dyestuff A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

and controversially as an antimicrobial in

aquaculture Aquaculture (less commonly spelled aquiculture), also known as aquafarming, is the controlled cultivation ("farming") of aquatic organisms such as fish, crustaceans, mollusks, algae and other organisms of value such as aquatic plants (e.g. lot ...

. Malachite green is traditionally used as a dye for materials such as

silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from th ...

leather Leather is a strong, flexible and durable material obtained from the tanning, or chemical treatment, of animal skins and hides to prevent decay. The most common leathers come from cattle, sheep, goats, equine animals, buffalo, pigs and hog ...

, and

paper Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses or other vegetable sources in water, draining the water through fine mesh leaving the fibre evenly distribu ...

. Despite its name the dye is not prepared from the

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

malachite Malachite is a copper carbonate hydroxide mineral, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses, in fracture ...

; the name just comes from the similarity of color.

Structures and properties

Malachite green is classified in the dyestuff industry as a triarylmethane dye and also using in pigment industry. Formally, malachite green refers to the chloride salt ₆H₅C(C₆H₄N(CH₃)₂)₂l, although the term malachite green is used loosely and often just refers to the colored

cation An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

. The

oxalate Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...

salt is also marketed. The

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s have no effect on the color. The intense green color of the cation results from a strong absorption band at 621 nm ( extinction coefficient of ). Malachite green is prepared by the condensation of

benzaldehyde Benzaldehyde (C6H5CHO) is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful. It is a colorless liquid with a characteristic almond-like odor. ...

and dimethylaniline to give leuco malachite green (LMG): :C6H5CHO + C6H5N(CH3)2 -> (C6H5N(CH3)2)2C6H5 + H2O Second, this colorless leuco compound, a relative of

triphenylmethane Triphenylmethane, or triphenyl methane, is the hydrocarbon with the formula (C6H5)3CH. This colorless solid is soluble in nonpolar organic solvents and not in water. Triphenylmethane is the basic skeleton of many synthetic dyes called triarylmeth ...

, is oxidized to the cation that is MG: :C₆H₅CH(C₆H₄N(CH₃)₂)₂ + HCl + O₂ → ₆H₅C(C₆H₄N(CH₃)₂)₂l + H₂O A typical oxidizing agent is

manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for is for dry-ce ...

. Hydrolysis of MG gives an

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

: : ₆H₅C(C₆H₄N(CH₃)₂)₂l + H₂O → C₆H₅C(OH)(C₆H₄N(CH₃)₂)₂ + HCl 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.

Preparation

The leuco form of malachite green was first prepared by Hermann Fischer in 1877 by condensing

and dimethylaniline in the molecular ratio 1:2 in the presence of

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...

Uses

Malachite green is traditionally used as a dye. Kilotonnes of MG and related triarylmethane dyes are produced annually for this purpose. MG is active against the oomycete '' Saprolegnia'', which infects fish eggs in commercial

, MG has been used to treat '' Saprolegnia'' and is used as an

antibacterial An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...

. It is a very popular treatment against ''

Ichthyophthirius multifiliis ''Ichthyophthirius multifiliis'', often termed "Ich", is a parasitic ciliate described by the French parasitologist Fouquet in 1876. Only one species is found in the genus which also gave name to the family. The name literally translates as "the ...

'' in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does incl ...

aquaria. The principal

metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, ...

, leuco-malachite green (LMG), is found in fish treated with malachite green, and this finding is the basis of controversy and government regulation. See also Antimicrobials 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.

Niche uses

Numerous niche applications exploit the intense color of MG. It is used as a biological stain for

microscopic The microscopic scale () is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded as the scale be ...

analysis of

cell biology Cell biology (also cellular biology or cytology) is a branch of biology that studies the structure, function, and behavior of cells. All living organisms are made of cells. A cell is the basic unit of life that is responsible for the living an ...

and tissue samples. In the Gimenez staining method, basic fuchsin stains bacteria red or magenta, and malachite green is used as a blue-green

counterstain A counterstain is a stain with colour contrasting to the principal stain, making the stained structure easily visible using a microscope. Examples include the malachite green counterstain to the fuchsine stain in the Gimenez staining technique ...

. Malachite green is also used in endospore staining, since it can directly stain

endospore An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., n ...

s within bacterial cells; here a safranin counterstain is often used. Malachite green is a part of Alexander's pollen stain. Malachite green can also be used as a saturable absorber in

dye laser A dye laser is a laser that uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths, often spanning 50 to 100 ...

s, or as a

pH indicator A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, ...

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 in

forensic science Forensic science, also known as criminalistics, is the application of science to criminal and civil laws, mainly—on the criminal side—during criminal investigation, as governed by the legal standards of admissible evidence and criminal ...

Hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythroc ...

catalyzes the reaction between LMG and

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3 ...

, converting the colorless LMG into malachite green. Therefore, the appearance of a green color indicates the presence of

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

. 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. 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 of GFP but has the added benefit of having a 'dark state' before the malachite green fluorophore is added. This is especially useful for FRET studies.

Regulation

In 1992, Canadian authorities determined that eating fish contaminated with malachite green posed a significant health risk. 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 non

purposes. In 2005, analysts in

Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a List of cities in China, city and Special administrative regions of China, special ...

found traces of malachite green in eels and fish imported from

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

. In 2006, the United States

Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food ...

(FDA) detected malachite green in seafood from China, among others, where the substance is also banned for use in aquaculture. In June 2007, the FDA blocked the importation of several varieties of seafood due to continued malachite green contamination. Malachite green has been banned in the United States since 1983 in food-related applications. The substance is also banned in the United Kingdom. It is prohibited from the use in food in Macao. Animals metabolize malachite green to its leuco form. Being lipophillic (the leuco form has a log ''P'' of 5.70), the

is retained in

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive, ...

muscle longer ( HL = 10 days) than is the parent molecule (HL = 2.8 days).

Toxicity

The (oral, mouse) is 80 mg/kg. Rats fed malachite green experience "a dose-related increase in liver DNA adducts" along with lung

adenoma An adenoma is a benign tumor of epithelial tissue with glandular origin, glandular characteristics, or both. Adenomas can grow from many glandular organs, including the adrenal glands, pituitary gland, thyroid, prostate, and others. Some adenom ...

s. 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 and liver tumor was not established.

Detection

Although malachite green has almost no fluorescence in aqueous solution (

quantum yield The quantum yield (Φ) of a radiation-induced process is the number of times a specific event occurs per photon absorbed by the system. Applications Fluorescence spectroscopy The fluorescence quantum yield is defined as the ratio of the numb ...

7.9x10⁻⁵), 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.Effect of Receptor Attachment on Sensitivity of Label Free Microcantilever Based Biosensor Using Malachite Green Aptamer https://doi.org/10.1016/j.snb.2019.126963

References

External links

{{Commons category, Malachite green
U.S. National Institutes of Health

Triarylmethane dyes Staining dyes PH indicators Antimicrobials Aromatic amines Fish medicine Dimethylamino compounds