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).
Excited-State Proton-Transfer Processes of DHICA Resolved: From Sub-Picoseconds to Nanoseconds / Corani, A; Pezzella, Alessandro; Pascher, T; Gustavsson, T; Markovitsi, D; Huijser, A; D'Ischia, Marco; Sundstrom, V.. - In: THE JOURNAL OF PHYSICAL CHEMISTRY LETTERS. - ISSN 1948-7185. - 4:9(2013), pp. 1383-1388. [10.1021/jz400437q]
Excited-State Proton-Transfer Processes of DHICA Resolved: From Sub-Picoseconds to Nanoseconds
PEZZELLA, ALESSANDRO;D'ISCHIA, MARCO;
2013
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).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
