Degradation trends identification

Pyrrolecarboxylic acids are the final products of oxidative degradation of eumelanins. The origin, reaction conditions, as well as the isolation and identification techniques used are the factors responsible for the different ratios of di-, tri-, and tetracarboxylic acids formed (7). Thus, untreated sepiomelanin and a number of synthetic melanins oxidized via KMNO4 showed the following trend in the relative ratios of pyrrolecarboxylic acids 2,3,5 2,3 = 2,3,4,5. The same samples after decarboxylation at 200°C followed the sequence 2,3,5 > 2,3 > 2,5 2,4 = 2,3,4,5. The decrease in 2,3,5 triacids and the increase in 2,3 diacids are attributed to the loss of carboxyl groups owing to the thermal treatment (7). Resistance to further oxidative degradation u der specific experimental conditions may substantially influence the ratio of the individual pyrrolecarboxylic acids formed (315). 

Garcia-Galan M, Diaz-Cruz M, Barceld D, Identification and determination of metabolites and degradation products of sulfonamide antibiotics. Trends Anal. Chem. 2008 27(11) 1008-1022. 

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