Caffeic Acid/Eu(III) Complexes: Solution Equilibrium Studies, Structure Characterization and Biological Activity.

Area of Science:

• Coordination Chemistry
• Bioinorganic Chemistry
• Analytical Chemistry

Background:

• Caffeic acid (CFA) is a natural antioxidant with known biological roles.
• Research on CFA complexes with lanthanide metals, like Europium(III) (Eu(III)), is limited.
• Understanding the structure-property relationships of metal complexes is crucial for their applications.

Purpose of the Study:

• To synthesize and characterize the Eu(III)/CFA complex.
• To investigate the chemical speciation of Eu(III)/CFA in aqueous solutions.
• To evaluate the biological activities, including antioxidant and antimicrobial properties, of the Eu(III)/CFA complex.

Main Methods:

• Multi-analytical techniques: FT-IR, FT-Raman, elemental analysis, TGA.
• Solution behavior studies: Potentiometric and UV-Vis titrations, 1H-NMR, ESI-MS.
• Biological assays: Electrophoretic mobility, antioxidant capacity tests, minimum inhibitory concentration (MIC).

Main Results:

• The solid-state complex has a 1:3 metal-to-ligand ratio: [Eu(CFA)3(H2O)3]·2H2O.
• In aqueous solution (pH 6-10), 1:1 species ([Eu(CFA)] and [Eu(CFA)(OH)]-) were predominant.
• Eu(III)/CFA exhibited reduced antioxidant activity but increased antibacterial efficacy compared to free CFA.

Conclusions:

• The study elucidates the structural and solution behavior of the Eu(III)/CFA complex.
• The enhanced lipophilicity of the Eu(III) complex likely contributes to its improved antibacterial activity.
• This research provides foundational chemical and biological data for lanthanide-caffeic acid systems.