Ligand environment and light: two triggers for controlling cytotoxicity of ruthenium nitrosyl complexes

Photoinduced nitric oxide (NO) release for complexes [RuNO(L)2(NO2)2OH], where L = methyl isonicotinate (1), ethyl isonicotinate (2), methyl nicotinate (3) and ethyl nicotinate (4) was studied in DMSO, MeCN and water solutions (PBS, CTAB) using spectroscopic methods (UV-vis, IR, EPR) and spectrometric techniques (ESI-МS). Additionally, we present methodological evidence for improving the calculation of the quantum yield (QY) of NO release through the utilization of a combined IR-UV-vis-spectroscopy flow-through setup. According to DFT calculations, the production of nitric oxide occurs through the photoinduced cleavage of the Ru-NO bond, triggered by irradiation at 445 or 532 nm. This cleavage is a consequence of charge transfer from the orbitals of the Ru-OH group and the equatorial ligands (HOMO, HOMO-1) to the Ru-NO antibonding orbital (LUMO). The cytotoxicity and photoinduced cytotoxicity of the investigated compounds were assessed against the breast adenocarcinoma cell line MCF-7. Moreover, the investigation of the lipophilic properties of compounds 1-4 unveiled a significant influence of their lipophilicity on cytotoxic behavior, allowing for the modification of cytotoxicity through changes in the ligand L or by light irradiation.