Chemical speciation of caffeic and p-coumaric acids with selected lanthanides

Structures, Antioxidant Properties, and Antimicrobial Properties of Eu(III), Gd(III), and Dy(III) Caffeinates and p-Coumarates

“…On the other hand, in the coordination of metal ions through the carboxylate anion, there is a change in the electronic charge distribution in the ligand molecule [ 39 , 40 ], which favors the transfer of hydrogen atom from the antioxidant to the radical. These conclusions are also consistent with the results of our previous work [ 38 ].…”

“…The tested concentrations of compounds are given in Section 2.5. The molar metal to ligand ratio was 1:1, which is consistent with the results obtained in our previous work, where we investigated the complexing ability of CFAH3 and p-CAH2 towards Eu(III), Gd(III), and Dy(III) cations over a wide range of pH values [19,38]. Both assays, DPPH and ABTS, are recognized as a mixed HAT (hydrogen atom transfer) and SET (single electron transfer) mechanism that is generally called SPLET (sequential proton loss-electron transfer) or SET-PT (single electron transfer-proton transfer) mechanism [37].…”

“…Absorbance measurements were carried out using the UV-VIS Carry 5000 spectrophotometer (Santa Clara, CA, USA) and Tecan Infinite 200 PRO microplate reader (Tecan, Männedorf, Switzerland). Solutions of Eu(III), Dy(III), and Gd(III) complexes with CFAH 3 and p-CAH 2 were prepared with a metal-ligand composition of 1:1, following the results of previous studies on the composition of lanthanide complexes with CFAH 3 and p-CAH 2 depending on pH [ 19 , 38 ]. First, an 10% methanolic CFAH 3 (0.001 and 0.0001 mol/L) and p-CAH 2 (0.05 and 0.005 mol/L) solutions were added to an aqueous solution of sodium hydroxide (0.1 mol/L) in a stoichiometric molar ligand/NaOH ratio of 1:1.…”