UV-Dissipation Mechanisms in the Eumelanin Building Block DHICA

Annemarie Huijser, Alessandro Pezzella, Jonas K. Hannestad, Lucia Panzella, Alessandra Napolitano, Marco D'Ischia, Villy Sundstrom

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27 Citations (Scopus)

Abstract

The UV-dissipative mechanisms of the eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and the 4,7-dideutero derivative (DHICA-d2) in buffered H2O or D2O have been characterized by using ultrafast time-resolved fluorescence spectroscopy. Excitation of the carboxylate anion form, the dominating state at neutral pH, leads to dual fluorescence. The band peaking at λ=378 nm is caused by emission from the excited initial geometry. The second band around λ=450 nm is owed to a complex formed between the mono-anion and specific buffer components. In the absence of complex formation, the mono-anion solely decays non-radiatively or by emission with a lifetime of about 2.1 ns. Excitation of the neutral carboxylic acid state, which dominates at acidic pH, leads to a weak emission around λ=427 nm with a short lifetime of 240 ps. This emission originates from the zwitterionic state, formed upon excitation of the neutral state by sub-ps excited-state intramolecular proton transfer (ESIPT) between the carboxylic acid group and the indole nitrogen. Future studies will unravel whether this also occurs in larger building blocks and ESIPT is a built-in photoprotective mechanism in epidermal eumelanin.
Original languageEnglish
Pages (from-to)2424-2431
JournalChemPhysChem
Volume11
Issue number11
DOIs
Publication statusPublished - 2 Aug 2010
Externally publishedYes

Keywords

  • eumelanin
  • DHICA
  • isotope effects
  • proton transfer
  • time-resolved fluorescence

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