Mechanism of UVA Degradation of Synthetic Eumelanin

Weiyao Li, Zhao Wang, Ming Xiao, Toshikazu Miyoshi, Xiaozhou Yang, Ziying Hu, Cheng Liu, Steven S.C. Chuang, Matthew D. Shawkey*, Nathan C. Gianneschi, Ali Dhinojwala

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Eumelanin is a ubiquitous natural pigment that has a broad absorption across ultraviolet (UV, 100-400 nm) and visible wavelengths (400-700 nm) and can protect against radiation. Synthetic eumelanin with properties similar to natural eumelanin has been made using dopamine or dihydroxyindole. Here, we use solid-state nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy to elucidate the chemical structure of synthetic eumelanins (made from dopamine and l-3,4-dihydroxyphenylalanine precursors) and investigate how their structures change after intensive UVA (315-400 nm) exposure. We first confirm that polydopamine has indole units. Upon UV exposure, the pyrrole ring in this indole unit remains intact, and a fraction of the six-membered benzyl ring is broken and the indole potentially converted to furo[3,4-b]pyrrole. This change in the chemical structure is accompanied by a release of carbon dioxide. In addition, the sepia (natural) eumelanin used for comparison is more stable than the synthetic eumelanin. Understanding the UVA degradation mechanism of eumelanin will help reveal the role of eumelanin in skin cancer and in the design of more efficient UV stabilizers.

Original languageEnglish (US)
Pages (from-to)4593-4601
Number of pages9
Issue number12
StatePublished - Dec 9 2019

ASJC Scopus subject areas

  • Bioengineering
  • Materials Chemistry
  • Polymers and Plastics
  • Biomaterials


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