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Type: Journal article
Title: Excited-state dynamics of the medicinal pigment curcumin in a hydrogel
Author: Harada, T.
Lincoln, S.
Kee, T.
Citation: Physical Chemistry Chemical Physics, 2016; 18(40):28125-28133
Publisher: Royal Society of Chemistry
Issue Date: 2016
ISSN: 1463-9076
Statement of
Takaaki Harada, Stephen F. Lincoln and Tak W. Kee
Abstract: Curcumin is a yellow polyphenol with multiple medicinal effects. These effects, however, are limited due to its poor aqueous stability and solubility. A hydrogel of 3% octadecyl randomly substituted polyacrylate (PAAC18) has been shown to provide high aqueous stability for curcumin under physiological conditions, offering a route for photodynamic therapy. In this study, the excited-state photophysics of curcumin in the PAAC18 hydrogel is investigated using a combination of femtosecond transient absorption and fluorescence upconversion spectroscopy. The transient absorption results reveal a multiexponential decay in the excited-state kinetics with fast (1 ps & 15 ps) and slow (110 ps & ≈5 ns) components. The fast decay component exhibits a deuterium isotope effect with D2O in the hydrogel, indicating that the 15 ps decay component is attributable to excited-state intramolecular hydrogen atom transfer of curcumin in the PAAC18 hydrogel. In addition, solvent reorganisation of excited-state curcumin is investigated using multiwavelength femtosecond fluorescence upconversion spectroscopy. The results show that the dominant solvation response (τ = 0.08 ps) is a fast inertial motion owing to the presence of bulk-like water in the vicinity of the hydrophobic octadecyl substituents of the PAAC18 hydrogel. The results also show an additional response with longer time constants of 1 and 6 ps, which is attributable to translational diffusion of confined water molecules in the three-dimensional, cross-linking network of the octadecyl substituents of PAAC18. Overall, we show that excited-state intramolecular hydrogen atom transfer and solvent reorganisation are major photophysical events for curcumin in the PAAC18 hydrogel.
Keywords: Curcumin; Hydrogels; Solvents; Spectrometry, Fluorescence; Solubility; Hydrophobic and Hydrophilic Interactions
Rights: This journal is © the Owner Societies 2016
RMID: 0030056726
DOI: 10.1039/c6cp05648b
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Appears in Collections:Biochemistry publications

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