Sequential Proton-Coupled Electron Transfer Mediates Excited-State Deactivation of a Eumelanin Building Block

Research output: Contribution to journalArticle

Abstract

Skin photoprotection is commonly believed to rely on the photochemistry of 5,6-dihydroxyindole (DHI)- and 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-based eumelanin building blocks. Attempts to elucidate the underlying excited-state relaxation mechanisms have been partly unsuccessful due to the marked instability to oxidation. We report a study of the excited-state deactivation of DHI using steady-state and time-resolved fluorescence accompanied by high-level quantum-chemistry calculations including solvent effects. Spectroscopic data show that deactivation of the lowest excited state of DHI in aqueous buffer proceeds on the 100 ps time scale and is 20 times faster than in methanol. Quantum-chemical calculations reveal that the excited-state decay mechanism is a sequential proton-coupled electron transfer, which involves the initial formation of a solvated electron from DHI, followed by the transfer of a proton to the solvent. This unexpected finding would prompt a revision of current notions about eumelanin photophysics and photobiology.

Details

Authors
  • Juan J. Nogueira
  • Alice Corani
  • Amal El Nahhas
  • Alessandro Pezzella
  • Marco D’Ischia
  • Leticia González
  • Villy Sundström
Organisations
External organisations
  • University of Vienna
  • University of Naples Federico II
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry
Original languageEnglish
Pages (from-to)1004-1008
Number of pages5
JournalThe Journal of Physical Chemistry Letters
Volume8
Issue number5
Publication statusPublished - 2017 Mar 2
Publication categoryResearch
Peer-reviewedYes