Synthesis, characterization and cytotoxicity of new Ho(III) and Er(III) complexes

New complexes of coumarin-3-carboxylic acid (HCCA) with holmium [Ho(III)] and erbium [Er(III)] were synthesized and their structures and spectral properties were investigated by elemental analysis, IR, Raman and NMR measurements. According to the experimental data of the complexes, their formulae and geometries have been suggested. Vibrational frequencies, IR intensities and Raman activities as well as H NMR chemical shifts of HCCA and its lanthanum [Ln(III)] complexes are presented. The comparative experimental spectral analyses of both the ligand and the Ln(III) complexes predicted the bidentate binding to Ho(III) and Er(III) through the deprotonated carboxylic oxygen and the carbonylic oxygen of the ligand. The cytotoxic/cytostatic properties of the ligand and the newly synthesized complexes of coumarin-3-carboxylic acid with Ho(III) and Er(III) were tested by MTT reduction assay against two mouse tumour cell lines, melanoma B16 and fibrosarcoma L929, as well as against normal mouse peritoneal macrophages. The proliferation inhibitory effect of the complexes compared to that of the ligand proved their cytotoxic/cytostatic properties against both the tumour cell lines. The complexes were less cytotoxic against normal mouse macrophages and modulated NO release by activated macrophages. The results are in accordance with our previously published data on the activity of lanthanide (III) complexes with coumarins.