Two new compounds have been identified in an original sample of mauveine dye made by Sir William Perkin over 150 years ago. 

Mauveine, with its characteristic purple-like colour, was the first synthetic dye molecule and its production is thought by many to mark the beginning of the modern organic chemical industry. 

The discovery of the two new compounds, both violet in colour, was made by Seixas de Melo and colleagues at the Universities of Coimbra and Lisbon, Portugal, during their analysis of a historic sample from the Science Museum in London.¹ 

The new compounds are structurally similar to mauveine A (with two methyl groups) and mauveine B (with three methyl groups), the two components already known to be present in the dye.² The components discovered by de Melo are mauveine B2, a structural isomer of mauveine B which differs in the location of a methyl group, and a structure with four methyl groups, called mauveine C. 

Tony Travis, an expert in the history of chemistry and technology at the Hebrew University of Jerusalem, Israel, welcomed the findings. 'Perkin thought that the commercial mauve dye consisted of more than one component,' said Travis. 'This work shows that even though Perkin was unable to establish the structures of these components, he was correct in his findings.' 

Using the same starting materials and procedure as Perkin, de Melo then made a fresh mauveine sample and compared its composition with that of the historical sample. The different molecular components were separated using high performance liquid chromatography (HPLC). The HPLC chromatograms of the two samples were similar and the new compounds, mauveine B2 and mauveine C, were present in both. 

De Melo believes the reason why these constituents have not been isolated before is because more efficient chromatographic techniques are now available. 

As little is known about the origin of the dye's colour or the effect of its interaction of light, de Melo investigated the spectroscopic and photophysical properties of the different mauveine compounds. According to de Melo, the violet colour and photostability of mauveine is probably a result of a small energy gap which favours nonradiative deactivation of the excited state of the components. 

'Perkin would be delighted...he spent years trying to establish the constitution and structure of the mauve dye both as a scientific puzzle and because he believed that the constitution would suggest how new derivatives might be made,' said Travis. 'These newly available structures suggest why Perkin failed to prepare a series of derivatives, as had been the case for aniline red.' 

In the future, de Melo hopes to extend the study to look at the stability of other ancient dyes including dracoflavilyum (a major constituent of Dragon's Blood), indigo and alizarin.  

Alison Stoddart