Methylene blue

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Chemical name	3,7-bis(Dimethylamino)- phenazathionium chloride Tetramethylthionine chloride
Chemical formula	}
Molecular mass	} g/mol
CAS number	^*
EC number	200-515-2
Density	} g/cm³
Melting point	} °C
Boiling point	Decomposes
SMILES	}
Chemical infobox

Methylene blue is an heterocyclic aromatic chemical compound with molecular formula: C₁₆H₁₈Cl N₃S. It has many uses in a range of different fields, such as biology or chemistry.

At room temperature it appears as a solid, odorless, dark green powder, that yields a blue solution when dissolved in water.

Methylene blue should not be confused with methyl blue, another histology stain, or with the methyl violets often used as pH indicators.

Uses

Chemistry

Methylene blue is widely used a redox indicator in analytical chemistry. Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent. The redox properties can be seen in a classical demonstration of chemical kinetics in general chemisty, the "blue bottle" experiment. Typically, a solution is made of dextrose, methylene blue, and sodium hydroxide. Upon shaking the bottle, oxygen oxidizes methylene blue, and the solution turns blue. The dextrose will gradually reduce the methylene blue to its colorless, reduced form. Hence, when the dissolved oxygen is entirely consumed, the solution will turn colorless.

Methylene blue is also used to make the reaction between Fehling's solution and reducing sugars more visible.

Biology

In biology methylene blue is used as a dye for a number of different staining procedures, such as Gram's stain, Wright's stain, and Jenner's stain. Since it is a temporary staining technique, methylene blue can also be used to examine RNA or DNA under the microscope or in a gel: as an example, a solution of methylene blue can be used to stain RNA on hybridization membranes in northern blotting to verify the amount of nucleic acid present. While methylene blue is not as sensitive as ethidium bromide, it is less toxic and it does not intercalate in nucleic acid chains, thus avoiding interference with nucleic acid retention on hybridization membranes or with the hybridization process itself.

Medicine

Owing to its reducing agent properties, methylene blue is employed as a medication for the treatment of methemoglobinemia, which can arise from ingestion of certain pharmaceuticals or broad beans. Basically, methylene blue acts reducing the heme from methemoglobin to hemoglobin, however since methylene blue is toxic, any methemoglobinemia treatment with this substance should be strictly evaluated by a doctor.
Methylene blue also blocks accumulation of cyclic guanosine monophosphate (cGMP) by inhibiting the enzyme guanylate cyclase: this action results in reduced responsiveness of vessels to cGMP-dependent vasodilators like nitric oxide and carbon monoxide.

WARNING Methylene Blue is known to increase CNS leves of serotonin over two-fold, extreme care must be given when administrating this drug to a patient using an SSRI, TCA, MAOI, or any other serotogenic agent, as Serotonin Syndrome could result.

Aquaculture

Methylene blue is used in aquaculture, particularly by tropical fish hobbyists, as a treatment for fish infected by the parasitic protozoa Ichthyophthirius multifilius (ich).

Pranks

Methylene blue is highly stable in the human body, and if ingested, it resists the acidic environment of the stomach as well as the many hydrolytic enzymes present. It is not significantly metabolized by the liver, and is instead quickly filtered out by the kidneys. A common prank amongst biochemists is to add small amounts of methylene blue (generally a few drops of a stain solution will suffice) to coffee, cola, or another dark beverage. The stain's color will be masked by the beverage, and its taste is fairly faint. Within a few hours, the methylene blue will have been removed by the prank victim's kidneys, causing his urine to change color. The urine may become green if little methylene blue was added; larger amounts create a deep blue color. The prank is fairly harmless if small amounts of methylene blue are used, although allergies are possible and it is advisable to use pharmaceutical-grade stain which has been carefully protected from contamination. The main risk of methylene blue pranks is generating a sense of panic in the victim.

External links

Thiazin dyes | Staining dyes | Histology | Redox indicators

Methylenblau | Blu di metilene | Methyleenblauw | Метиленовый синий