Pyrolysis-gas chromatography of pheomelanins

Abstract

Pheomelanins are the red-brown polymeric pigments found in the skin and hair of red-headed humans and are also responsible for the colour of red feathers and the fur of many animals. Natural pigments were isolated from red hen feathers and red human hair. Model synthetic pheomelanins were prepared from 5-S-cysteinyldopa, 2-S-cysteinyldopa and l-dopa by enzymatic oxidation with mushroom tyrosinase. A GCV gas chromatograph equipped with a Curie-point pyrolyser, a flame photometric detector selective for sulphur compounds and a flame ionization detector were used for analyses. Samples of pheomalenins were pyrolysed at 770°C under a flow of helium and all analyses were performed on glass columns packed with Carbowax 20M chemically bonded to Chromosorb W. The peaks were identified by means of a pyrolyser-gas chromatograph-mass spectrometer system. The mechanisms of formation of the major pyrolysis products, identified as benzothiazole and 1,4-benzothiazine derivatives, are discussed in relation to the structure of pheomelanins. Computational data analysis and evaluation of the pyrograms obtained based on pattern recognition were used for differentiation of the polymers studied with regard to their chemical structure.