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. 2013 May 2;4(9):1383-8.
doi: 10.1021/jz400437q. Epub 2013 Apr 10.

Excited-State Proton-Transfer Processes of DHICA Resolved: From Sub-Picoseconds to Nanoseconds

Alice Corani  1 , Alessandro Pezzella  2 , Torbjörn Pascher  1 , Thomas Gustavsson  3 , Dimitra Markovitsi  3 , Annemarie Huijser  1 , Marco d'Ischia  2 , Villy Sundström  1
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Excited-State Proton-Transfer Processes of DHICA Resolved: From Sub-Picoseconds to Nanoseconds

Alice Corani et al. J Phys Chem Lett. .

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 × 10(8) s(-1).

Keywords: DHICA; ESPT; eumelanin; solvent; time-resolved fluorescence.

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