New platinum (II) and palladium (II) complexes of coumarin-thiazole Schiff base with a fluorescent chemosensor properties: Synthesis, spectroscopic characterization, X-ray structure determination, in vitro anticancer activity on various human carcinoma cell lines and computational studies

A new coumarin-thiazole based Schiff base (Ligand, L) and its Pd(II), Pt(II) complexes; ([Pd(L)₂] and [Pt(L)₂]), were synthesized and characterized using spectrophotometric techniques (NMR, IR, UV–vis, LC-MS), magnetic moment, and conductivity measurements. A single crystal X-ray analysis for only L was done. The crystals of L have monoclinic crystal system and P21/c space group. To gain insight into the structure of L and its complexes, we used density functional theory (DFT) method to optimize the molecules. The photophysical properties changes were observed after deprotonation of L with CN⁻ via intermolecular charge transfer (ICT). Additionally, as the sensor is a colorimetric and fluorimetric cyanide probe containing active sites such as coumarin-thiazole and imine (CH = N), it showed fast color change from yellow to deep red in the visible region, and yellow fluorescence after CN⁻ addition to the imine bond, in DMSO. The reaction mechanisms of L with CN⁻, F⁻ and AcO⁻ ions were evaluated using ¹H NMR shifts. The results showed that, the reaction of L with CN⁻ ion was due to the deprotonation and addition mechanisms at the same time. The anti-cancer activity of L and its Pd(II) and Pt(II) complexes were evaluated in vitro using MTT assay on the human cancer lines MCF-7 (human breast adenocarcinoma), LS174T (human colon carcinoma), and LNCAP (human prostate adenocarcinoma). The anti-cancer effects of L and its complexes, on human cells, were determined by comparing the half maximal inhibitory concentration (IC₅₀) values. The activity results showed that, the Pd(II) complex of L has higher anti-tumor effect than L and its Pt(II) complex against the tested human breast adenocarcinoma (MCF-7), human prostate adenocarcinoma (LNCAP), and human colon carcinoma (LS174T) cell lines.