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1.
  • Corani, Alice, et al. (författare)
  • Excited-State Proton-Transfer Processes of DHICA Resolved: From Sub-Picoseconds to Nanoseconds
  • 2013
  • Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:9, s. 1383-1388
  • Tidskriftsartikel (refereegranskat)abstract
    • Excited-state proton transfer has been hypothesized as a mechanism for UV energy dissipation in eumelanin skin pigments. By using time resolved fluorescence spectroscopy, we show that the previously proposed, but unresolved, excited-state intramolecular proton transfer (ESIPT) of the eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA) occurs with a time constant of 300 fs in aqueous solution but completely stops in methanol. The previously disputed excited-state proton transfer involving the 5- or 6-OH groups of the DHICA anion is now found to occur from the 6-OH group to aqueous solvent with a rate constant of 4.0 x 10(8) s(-1).
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2.
  • Corani, Alice, et al. (författare)
  • Superior photoprotective motifs and mechanisms in eumelanins uncovered.
  • 2014
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:33, s. 11626-11635
  • Tidskriftsartikel (refereegranskat)abstract
    • Human pigmentation is a complex phenomenon commonly believed to serve a photoprotective function through the generation and strategic localization of black insoluble eumelanin biopolymers in sun exposed areas of the body. Despite compelling biomedical relevance to skin cancer and melanoma, eumelanin photoprotection is still an enigma: What makes this pigment so efficient in dissipating the excess energy brought by harmful UV-light as heat? Why has Nature selected 5,6-dihydroxyindole-2-carboxylic acid (DHICA) as the major building block of the pigment instead of the decarboxylated derivative (DHI)? By using pico- and femtosecond fluorescence spectroscopy we demonstrate herein that the excited state deactivation in DHICA oligomers is 3 orders of magnitude faster compared to DHI oligomers. This drastic effect is attributed to their specific structural patterns enabling multiple pathways of intra- and interunit proton transfer. The discovery that DHICA-based scaffolds specifically confer uniquely robust photoprotective properties to natural eumelanins settles a fundamental gap in the biology of human pigmentation and opens the doorway to attractive advances and applications.
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