Degree of polymerization of 5,6-dihydroxyindole-derived eumelanin from chemical degradation study

Hidekazu Okuda*, Kyoji Yoshino, Kazumasa Wakamatsu, Shosuke Ito, Takayuki Sota

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)


Summary: Eumelanin is a brown-black pigment comprising 5,6-dihydroxyindole (DHI) and its 2-carboxy derivative (DHICA), but the detailed structure of eumelanin is unclear. Chemical degradation is a powerful tool for analyzing melanin. H2O2 oxidation degradation of eumelanin affords pyrrole-2,3,5-tricarboxylic acid (PTCA) and pyrrole-2,3-dicarboxylic acid (PDCA). The ratio of PDCA to PTCA provides information about the eumelanin structure. In this article, we propose simple equations on the basis of previous experimental results on dimer yields for evaluating the yields of PTCA and PDCA from any DHI oligomers. Assuming the chemical disorder model of DHI-melanin, we solve an equation where a theoretical expression for the ratio of PDCA to PTCA is set to the corresponding experimental value to obtain a plausible Poisson distribution of DHI oligomers. The results demonstrate that the main contributors to DHI-melanin are tetramers and pentamers as shown by the mass spectrometry.

Original languageEnglish
Pages (from-to)664-667
Number of pages4
JournalPigment Cell and Melanoma Research
Issue number4
Publication statusPublished - 2014 Jul


  • 5,6-dihydroxyindole
  • Chemical disorder model
  • Degree of polymerization
  • Eumelanin
  • Hydrogen peroxide oxidation

ASJC Scopus subject areas

  • Oncology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Dermatology


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