Characterization and Biological Evaluation of a (Cp*)Rh(III) Complex Featuring Phosphonate-Modified Bipyridine Ligands

Abstract We report the synthesis and biological activities of a (Cp*)Rh(III) complex containing 4,4’-bis(diethyl-methyl phosphonate)-2,2-bipyridine. The complex was characterized through various spectroscopic methods. Its DNA binding capacity was assessed using titration, viscosity measurements, and spectroscopic techniques including absorption, fluorescence, and circular dichroism (CD) spectroscopy. The findings revealed a positive absorption coefficient with a binding constant of 2.85 × 10⁴ M⁻ ¹. Additionally, the Rh complex showed a strong affinity for bovine serum albumin, with a binding constant that aligns with the observed DNA binding pattern. The cytotoxic effects of the complex were evaluated against selected cancer cell lines, such as MDA-MB-231 (human breast cancer) and A549 (human lung adenocarcinoma), as well as VERO (a normal human lung adenocarcinoma cell line) for comparison. The IC₅₀ values for MDA-MB-231 and A549 cells were determined to be 47.25 ± 0.05 µM and 48.75 ± 0.05 µM, respectively, indicating potent cytotoxicity at low micromolar concentrations. In contrast, the VERO normal cells exhibited significantly lower toxicity, with an IC₅₀ value of ≥ 1000 µM. Furthermore, the Rh complex was tested for its antimicrobial properties, demonstrating greater inhibitory activity compared to the free ligand.