Structure and Dynamics of the Deprotonated Demethoxycurcumin and Bisdemethoxycurcumin Anions

The curcuminoids are polyphenols found in the spice turmeric, where its principal polyphenol, curcumin, has been attributed with many of turmeric's beneficial therapeutic properties. However, as curcumin has a low bioavailability, other curcuminoids, which have fewer terminal methoxy substituents and have been reported to have a higher bioavailability, have been investigated as possible therapeutics. In this article, we report the results of the first gas-phase ion spectroscopy study of the deprotonated anionic forms of two prevalent curcuminoids: demethoxycurcumin and bisdemethoxycurcumin. The results indicate that the deprotonated curcuminoid anions have an electronic structure very similar to that of the deprotonated curcumin anion, with one bound electronically excited state and two low-lying anion resonances. Furthermore, all of the deprotonated curcuminoid anions have similar adiabatic detachment energies and show clear evidence of internal conversion following photoexcitation. Therefore, the curcuminoids studied here may be expected to perform a similar biological and/or therapeutic role to curcumin, given their similar electronic structure and energy transfer dynamics.