Insight on the chelation of aluminum(III) and iron(III) by curcumin in aqueous solution

In this work we have studied the complexation of curcumin (HCur, 1,7-bis-(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) with AI(III) and Fe(III) at 37 degrees C and in 0.1,6 M NaCl. The protonation constant of curcumin was also determined to evaluate the competition of the ligand for the metal cations and H+. Speciation profiles obtained by potentiometric titrations show that in aqueous solution a complexation occurs at 1:1 ligand-to-cations ratio. With the aim to define the coordination sites of curcumin with these metal ions a mass spectrometry and IJV-Vis spectroscopy characterization was carried out. It was found that aluminum binds to the keto-enol moiety of curcumin, while iron binds to the guaiacol (2-methoxyphenol) one. This unexpected experimental evidence was supported by a thorough computational study. (C) 2019 Elsevier B.V. All rights reserved.