UV-Dissipation Mechanisms in the Eumelanin Building Block DHICA
Journal article, 2010

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.

Author

A. Huijser

Lund University

A. Pezzella

Universita degli Studi di Napoli Federico II

Jonas Hannestad

Chalmers, Chemical and Biological Engineering, Physical Chemistry

L. Panzella

Universita degli Studi di Napoli Federico II

A. Napolitano

Universita degli Studi di Napoli Federico II

M. d'Ischia

Universita degli Studi di Napoli Federico II

V. Sundstrom

Lund University

ChemPhysChem

1439-4235 (ISSN) 1439-7641 (eISSN)

Vol. 11 11 2424-2431

Subject Categories

Chemical Sciences

DOI

10.1002/cphc.201000257

More information

Latest update

4/11/2018