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UV-Dissipation Mechanisms in the Eumelanin Building Block DHICA

A. Huijser ; A. Pezzella ; Jonas K. Hannestad (Institutionen för kemi- och bioteknik, Fysikalisk kemi) ; L. Panzella ; A. Napolitano ; M. d'Ischia ; V. Sundstrom
Chemphyschem (1439-4235). Vol. 11 (2010), 11, p. 2424-2431.
[Artikel, refereegranskad vetenskaplig]

The UV-dissipative mechanisms of the eumelanin building block 5,6-dihydroxyindole-2-carboxylic acid (DHICA) and the 4,7-dideutero derivative (DHICA-d(2)) 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 lambda = 378 nm is caused by emission from the excited initial geometry. The second band around lambda = 450 nm is owed to a complex formed between the monoanion 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 lambda = 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.

Denna post skapades 2011-01-21. Senast ändrad 2012-02-17.
CPL Pubid: 135745


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Institutioner (Chalmers)

Institutionen för kemi- och bioteknik, Fysikalisk kemi (2005-2014)



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