Spectrophotometric and electrochemical determination of the formation constants of the complexes Curcumin-Fe(Ill)-water and Curcumin-Fe(II)-water

The formation of complexes among the Curcumin, Fe(III) and Fe(II) was studied in aqueous media within the 5-11 pH range by means of UV-Vis spectrophotometry and cyclic voltammetry. When the reaction between the Curcumin and the ions present in basic media took place, the resulting spectra of the systems Curcumin-Fe(III) and Curcumin-Fe(II) presented a similar behaviour. The cyclic voltammograms in basic media indicated that a chemical reaction has taken place between the Curcumin and Fe(111) before that of the formation of complexes. Data processing with SQUAD permitted to calculate the formation constants of the complexes Curcumin-Fe(III), corresponding to the species FeCur (log beta(110) = 22.25 +/- 0.03) and FeCur(OH)(-) (log beta(11-1) = 12.14 +/- 0.03), while for the complexes Curcumin-Fe(II) the corresponding formation constants of the species FeCur(-) (log beta(110) = 9.20 +/- 0.04), FeHCur (logbeta(111) = 19.76 +/- 0.03), FeH(2)Cur(+) (log beta(112) = 28.11 +/- 0.02). (C) 2003 Elsevier B.V. All rights reserved.