Photoactive PtII and PdII complexes of N,N-diethyl-N′-3,4,5-trimethoxybenzoylthiourea: synthesis, crystal structures, DFT and cytotoxicity studies

Abstract

Photo-chemical isomerism of the cis-[Pd^II/Pt^II(L-κS,O)₂] complexes of N,N-di-ethyl-N′-3,4,5-trimethoxy-benzoylthiourea (HL) in acetonitrile reversibly produces geometric trans-[Pd^II/Pt^II(L-κS,O)₂] isomers in solution after irradiation with visible light, as determined by ¹H NMR, UV-vis and reverse phase chromatography (RP-HPLC). Single-crystal X-ray diffraction studies reveal that the new trans-[Pd^II/Pt^II(L-κS,OκS,O)₂] complexes crystallize in a triclinic P space group, with the sulfur and oxygen donor atoms arranged trans to each other in the six-membered chelate. Structural analysis of the cis- and trans-[Pd^II/Pt^II(L-κS,O)₂] complexes performed using time-dependent DFT at the B3LYP/CEP31-G level of theory reveals that the cis-[Pd^II/Pt^II(L-κS,O)₂] complexes are more stable than their trans-[Pd^II/Pt^II(L-κS,O)₂] counterparts. The cytotoxicity of the HL ligand and its corresponding cis-[Pd^II/Pt^II(L-κS,O)₂] and trans-[Pd^II(L-κS,O)₂] complexes was investigated against the human prostate cancer cell line (DUI45) and the normal embryonic kidney cell line (HEK-293). Cytotoxicity was evident after complexation with the HL ligand. In particular trans-[Pd^II(L-κS,O)₂] and cis-[Pt^II(L-κS,O)₂] complexes produced a significant dose-dependent decrease in cell viability of both cell lines. cis-[Pt^II(L-κS,O)₂] presented the most cytotoxic activity against DUI45 and comparable selectivity to doxorubicin, a commonly used anticancer drug, indicating its potential as a Pt-based anticancer compound.