A compound to dye for

I am indebted to my colleague Bystander, who reminds me that we are approaching the 150th anniversary of the discovery of 4-((4-aminophenyl)(4-imino-2,5-cyclohexadien-1-ylidene)methyl)-2-methylbenzenamine monohydrochloride. This useful purple-red dye was found as a result of research into coal tar (aniline) dyes.

While one can follow the system of chemical nomenclature, one often wonders about the origin of some medicinal names. Footler’s theory is that for some of them the letter tiles remaining at the end of an inter-departmental Scrabble competition are used. How else would you explain Xyzal or even Qvar?

We do know, however, that the above compound is possibly unique in that its common name, magenta, commemorated a battle.

The Battle of Magenta was fought on 4 June 1859 near the town of Magenta in northern Italy. It took place during the Second Italian War of Independence and resulted in a decisive victory for Napoleon III’s French-Sardinian forces against the Austrian army.

Magenta is used for colouring textiles and leather and in the commercial preparation of other dyes. It highlights mitochondria when cells are viewed under the microscope because cell membranes and nuclei do not take up the stain. Magenta also stains collagen and smooth muscle and, in aqueous solution with alcohol, is a useful stain for bacteria.

To many pharmacists, magenta will be best known as a constituent of Castellani’s paint, which also contains phenol, resorcinol, boric acid and acetone. The paint was developed in 1905 by Aldo Castellani (1874–1971), an Italian pathologist and bacteriologist who specialised in tropical diseases.

Although rarely used nowadays, magenta paint is effective against Gram positive bacteria and some pathogenic yeasts and fungi particularly when used where two areas of skin touch or rub together.