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Spectroscopy
Volume 22 (2008), Issue 2-3, Pages 187-198
http://dx.doi.org/10.3233/SPE-2008-0335

Role of H-bond formation in the photoreactivity of curcumin

Luca Nardo,1,2 Roberta Paderno,1 Alessandra Andreoni,1 Már Másson,2 Tone Haukvik,3 and Hanne Hjorth TØnnesen3

1CNISM–INFM–CNR and Department of Physics and Mathematics, University of Insubria at Como, Como, Italy
2Faculty of Pharmacy, University of Iceland, Hagi, Reykjavik, Iceland
3School of Pharmacy, University of Oslo, Oslo, Norway
4CNISM–INFM–CNR and Department of Physics and Mathematics, University of Insubria at Como, Via Valleggio, 11-22100 Como, Italy

Copyright © 2008 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

Curcumin is the main constituent of curry. In its ground state it shows chemo-preventive, chemo-therapeutic and anti-inflammatory effects. For its immunostimulating action it has been considered for the development of drugs suitable for treating AIDS and cystic fibrosis. Further biological action is induced in curcumin by photoactivation: in suitable environmental conditions electronically excited curcumin can act as a singlet oxygen generator. Moreover, cytotoxicity is enhanced by light exposure and antibacterial effects are photosensitized. This work is aimed to understand the photobiological action of curcumin by elucidating the deactivation mechanisms of its first excited singlet state. In particular we find evidence of the role of tautomerization in the excited state by measuring fluorescence lifetimes and quantum yields for such compound dissolved in solvents of different polarity and H-bonding capability. Degradation quantum yield and singlet oxygen generation efficiency were also measured in acetonitrile and methanol. The results emphasize the strong dependence of the deactivation processes from the environment. The deactivation phenomenology can be fully explained by postulating intramolecular proton transfer in the cis enol conformer to be the leading non-radiative deactivation pathway.