Excited-State Intramolecular Hydrogen Atom Transfer and Solvation Dynamics of the Medicinal Pigment Curcumin

Date
2009-03-24
Authors
Adhikary, Ramkrishna
Mukherjee, Prasun
Petrich, Jacob
Kee, Tak
Petrich, Jacob
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Abstract

The potential use of the naturally occurring yellow-orange pigment curcumin as a photodynamic therapy agent is one of the most exciting applications of this medicinal compound. Although subnanosecond spectroscopy has been used to investigate the photophysical processes of curcumin, the time resolution is insufficient to detect important and faster photoinduced processes, including solvation and excited-state intramolecular hydrogen atom transfer (ESIHT). In this study, the excited-state photophysics of curcumin is studied by means of ultrafast fluorescence upconversion spectroscopy. The results show two decay components in the excited-state kinetics with time scales of 12−20 ps and ∼100 ps in methanol and ethylene glycol. The resulting prominent isotope effect in the long component upon deuteration indicates that curcumin undergoes ESIHT in these solvents. The short component (12−20 ps) is insensitive to deuteration, and multiwavelength fluorescence upconversion results show that this decay component is due to solvation of excited-state curcumin.

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<p>Reprinted (adapted) with permission from <em>Journal of Physical Chemistry B</em> 113 (2009): 5255, doi: <a href="http://dx.doi.org/10.1021/jp901234z" target="_blank">10.1021/jp901234z</a>. Copyright 2009 American Chemical Society.</p>
Keywords
Atomic spectroscopy, deuterium, ethylene, ethylene glycol, fluorescence, free radical reactions, hydrogen, methanol, photodynamic therapy, solvation, curcumin, decay components, deuteration, excited-state, fluorescence upconversion, intramolecular hydrogens, isotope effects, photophysics
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