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Spectroscopy
Volume 24 (2010), Issue 3-4, Pages 289-295
http://dx.doi.org/10.3233/SPE-2010-0430

Time-resolved EPR investigation of oxygen and temperature effects on synthetic eumelanin

Fosca Conti,1,3 Lucia Panzella,2 Alessandra Napolitano,2 Marco d᾽Ischia,2 and Antonio Toffoletti1

1Department of Chemical Sciences, University of Padova, Padova, Italy
2Department of Organic Chemistry and Biochemistry, University of Naples Federico II, Naples, Italy
3Department of Chemical Sciences, University of Padova, via Marzolo 1, I-35131 Padova, Italy

Copyright © 2010 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Synthetic eumelanin produced using 5,6-dihydroxyindole-2-carboxylic acid as precursor and H2O2/horseradish peroxidase as oxidative reagent, in form of dry powder, has been investigated under photoexcitation by TR-EPR spectroscopy. The formation of spin polarized radical pairs from triplet excited states of melanin has been observed both in absence and in presence of oxygen and has been followed as a function of the temperature in the range 140–290 K. The triplet mechanism explains the observed polarization pattern in net emission. In the presence of oxygen new radical pairs are formed by interaction of melanin with molecular oxygen.