Synthesis, DNA binding and cytotoxicity studies of luminescent Ln(III) thiophencarboxylate complexes

Lanthanide complexes, due to their photophysical and biological properties, are interesting as luminescent probes in bioimaging. A series of new thiophencarboxylate (tph) trivalent lanthanide complexes of the composition [Ln2(tph)4(OAc)2(phen)2] (LnIII= Gd (1), Eu (2), Sm (3), Tb (4)) was synthesized by the reaction of incomplete ion exchange of the corresponding lanthanide acetates with thiophencarboxylic acid and subsequent addition of 1,10-phenanthroline (phen). The resulting compounds were characterized using single crystal X-ray diffraction, FTIR spectroscopy, and elemental analysis. According to the X-ray data, compounds 1–4 are isostructural binuclear heterocarboxylate bridged complexes. The photo physical analysis of complexes 1–4 showed intense lanthanide-centered luminescence due to ligand excitation. The PLQY of complex 2 is 30%. The cytotoxicity of the complexes was tested in vitro against SKOV3, HCT116, A549, SKBR3 cancer cells and non-tumor culture of human dermal fibroblasts (HDF). The europium complex 2 demonstrated activity against ovarian adenocarcinoma (SKOV3) with an IC50 of 2.7 and a selectivity index of 3. Stability of the aqueous solutions of the complexes was confirmed by UV–vis spectroscopy. DNA binding of complexes was investigated by electronic absorption spectroscopy and low-gradient viscometry measurements. Detailed analysis revealed that these complexes interacted with DNA through intercalation binding. © 2025