# Synthesis, Structural Characterization, Luminescent Properties, and Antibacterial and Anticancer Activities of Rare Earth-Caffeic Acid Complexes

## TL;DR

Scientists created new luminescent complexes using rare earth metals and caffeic acid, which show promise for biomedical imaging and fighting bacteria and cancer.

## Contribution

The study introduces novel rare earth-caffeic acid complexes with combined luminescent and biological activities for potential biomedical applications.

## Key findings

- The complexes showed intense visible light emission and decay lifetimes of 0.054–0.064 ms.
- They exhibited strong antibacterial effects against E. coli, S. aureus, and P. aeruginosa.
- Sm(Caf)3·4H3O had the lowest IC50 of 15.5 µM against MCF7 breast cancer cells.

## Abstract

Rare earth elements (Ln: Sm, Eu, Tb, Dy) were complexed with caffeic acid (Caf), a natural phenolic compound, to synthesize novel luminescent complexes with enhanced biological activities. The complexes, formulated as Ln(Caf)3·4H2O, were characterized using infrared spectroscopy (IR), thermogravimetric analysis (TGA/DTA), mass spectrometry (MS), and fluorescence spectroscopy. Structural studies confirmed the coordination of caffeic acid via carboxylate and hydroxyl groups, forming stable hexacoordinate complexes. Luminescence analysis revealed intense emission bands in the visible spectrum (480–700 nm), attributed to f-f transitions of Ln3+ ions, with decay lifetimes ranging from 0.054 to 0.064 ms. Biological assays demonstrated significant antibacterial activity against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, with inhibition zones up to 44 mm at 200 µg/mL. The complexes also exhibited potent anticancer activity against MCF7 breast cancer cells, with Sm(Caf)3·4H3O showing the lowest IC50 value (15.5 µM). This study highlights the dual functionality of rare earth metal-caffeic acid complexes as promising candidates for biomedical imaging and therapeutic applications.