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Fe^III, Cu^II and Zn^II Complexes of the Rigid 9-Oxido-phenalenone Ligand-Spectroscopy, Electrochemistry, and Cytotoxic Properties.

ABSTRACT: The three complexes [Fe(opo)₃], [Cu(opo)₂], and [Zn(opo)₂] containing the non-innocent anionic ligand opo^- (opo^- = 9-oxido-phenalenone, Hopo = 9-hydroxyphenalonone) were synthesised from the corresponding acetylacetonates. [Zn(opo)₂] was characterised using ¹H nuclear magnetic resonance (NMR) spectroscopy, the paramagnetic [Fe(opo)₃] and [Cu(opo)₂] by electron paramagnetic resonance (EPR) spectroscopy. While the EPR spectra of [Cu(opo)₂] and [Cu(acac)₂] in dimethylformamide (DMF) solution are very similar, a rather narrow spectrum was observed for [Fe(opo)₃] in tetrahydrofuran (THF) solution in contrast to the very broad spectrum of [Fe(acac)₃] in THF (Hacac = acetylacetone, 2,4-pentanedione; acac^- = acetylacetonate). The narrow, completely isotropic signal of [Fe(opo)₃] disagrees with a metal-centred S = 5/2 spin system that is observed in the solid state. We assume spin-delocalisation to the opo ligand in the sense of an opo^- to Fe^III electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of -1 to -3 V vs. the ferrocene/ferrocenium couple. However, for Cu^II and Fe^III the very first one-electron reductions are metal-centred. Electronic absorption in the UV to vis range are due to π-π* transitions in the opo core, giving Hopo and [Zn(opo)₂] a yellow to orange colour. The structured bands ranging from 400 to 500 for all compounds are assigned to the lowest energy π-π* transitions. They show markedly higher intensities and slight shifts for the Cu^II (brown) and Fe^III (red) complexes and we assume admixing metal contributions (MLCT for Cu^II, LMCT for Fe^III). For both complexes long-wavelength absorptions assignable to d-d transitions were detected. Detailed spectroelectrochemical experiments confirm both the electrochemical and the optical assignments. Hopo and the complexes [Cu(opo)₂], [Zn(opo)₂], and [Fe(opo)₃] show antiproliferative activities against HT-29 (colon cancer) and MCF-7 (breast cancer) cell lines in the range of a few µM, comparable to cisplatin under the same conditions.

SUBMITTER: Butsch K

PROVIDER: S-EPMC8070161 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The treatment of malignant cells that are deficient in oxygen due to the insufficient flow of blood is often seen as a major hindrance in radiotherapy. Such cells become radio-resistant because molecular oxygen, the natural and best radio-sensitizer, is depleted. Hence, to compensate this deficiency in oxygen, there is a need for agents that enhance radiation-induced damage of cells (radio-sensitizers) in a manner that normal cells are least affected. Simultaneously, agents capable of showing activity under hypoxic conditions are known as hypoxic cytotoxins that selectively and preferably destroy cells under hypoxic environments. 5-Nitroimidazoles fit both definitions. Their efficiency is based on their ability to generate the nitro radical anion that interacts with the strands of DNA within cells, either damaging or modifying them, leading to cell death. 5-Nitroimidazoles are important radio-pharmaceuticals (radio-sensitizers) in cancer-related treatments where the nitro radical anion has an important role. Since its generation leads to neurotoxic side effects that may be controlled through metal complex formation, this study looks at the possibility of two monomeric complexes of Ornidazole [1-chloro-3-(2-methyl-5-nitro-1H-imidazole-1-yl)propan-2-ol] with CuII and ZnII to be better radio-sensitizers and/or hypoxic cytotoxins than Ornidazole. The study reveals that although there is a decrease in nitro radical anion formation by complexes, such a decrease does not hamper their radio-sensitizing ability. Nucleic acid bases (thymine, cytosine, and adenine) or calf thymus DNA used as targets were irradiated with 60Co γ rays either in the absence or presence of Ornidazole and its monomeric complexes. Radiation-induced damage of nucleic acid bases was followed by high-performance liquid chromatography (HPLC), and modification of calf thymus DNA was followed by ethidium bromide fluorescence. Studies indicate that the complexes were better in performance than Ornidazole. CuII-ornidazole was significantly better than either Ornidazole or ZnII-ornidazole, which is attributed to certain special features of the CuII complex; aspects like having a stable lower oxidation state enable it to participate in Fenton reactions that actively influence radio-sensitization and the ability of the complex to bind effectively to DNA.

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Fe^III, Cu^II and Zn^II Complexes of the Rigid 9-Oxido-phenalenone Ligand-Spectroscopy, Electrochemistry, and Cytotoxic Properties.

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FeIII, CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand-Spectroscopy, Electrochemistry, and Cytotoxic Properties.

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OmicsDI is part of the ELIXIR infrastructure

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Fe^III, Cu^II and Zn^II Complexes of the Rigid 9-Oxido-phenalenone Ligand-Spectroscopy, Electrochemistry, and Cytotoxic Properties.