Adamkiewicz-Hopkins-Cole reaction

The intense blue color which is obtained when tryptophan, in the presence of an aldehyde, is treated with concentrated sulfuric acid containing an oxidizing agent (Adamkiewicz-Hopkins-Cole reaction) was beheved to involve formation of a tetrahydro-j8-carboline intermediate, since most l,2,3,4-tetrahydro-j8-carbohne derivatives yield a similar color with concentrated sulfuric acid containing an oxidizing agent. The two colors have now been shown to have different absorption spectra. The nature of the carboline-blue color is still obscure. 

Brustier and coworkers utilized the Adamkiewicz-Hopkins-Cole reaction as an identity test for gramicidin121. The test detects the indole ring structure of the tryptophane residue. 

Shortly before Hopkins and Cole isolated tryptophane, they studied the Adamkiewicz reaction—the production of a violet colour when concentrated sulphuric acid is added to a protein dissolved in glacial acetic acid—and found that it was caused by the presence of glyoxylic acid in the glacial acetic acid, from which it arose by the action of sunlight. On applying the glyoxylic reaction to tryptophane a very intense colour was produced, and hence the presence of tryptophane in the protein molecule is the cause of this reaction. 

F. G. Hopkins and S. W. Cole. On the Proteid Reaction of Adamkiewicz, with Contribu-... 

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