Photorelease of Pyridyl Esters in Organometallic Ru(II) Arene Complexes

Cytotoxicity of Ruthenium(II) Arene Complexes Containing Functionalized Ferrocenyl β-Diketonate Ligands

The synthesis and characterization of 24 ruthenium(II) arene complexes of the type [(p-cym)RuCl(Fc-acac)] (where p-cym = p-cymene and Fc-acac = functionalized ferrocenyl β-diketonate ligands) are reported, including single-crystal X-ray diffraction for 21 new complexes. Chemosensitivity studies have been conducted against human pancreatic carcinoma (MIA PaCa-2), human colorectal adenocarcinoma p53-wildtype (HCT116 p53+/+) and normal human retinal epithelial cell lines (APRE-19). The most active complex, which contains a 2-furan-substituted ligand (4), is 5x more cytotoxic than the analogs 3-furan complex (5) against MIA PaCa-2. Several complexes were screened under hypoxic conditions and at shorter-time incubations, and their ability to damage DNA was determined by the comet assay. Compounds were also screened for their potential to inhibit the growth of both bacterial and fungal strains.

Ruthenium-arene complexes bearing naphthyl-substituted 1,3-dioxoindan-2-carboxamides ligands for G-quadruplex DNA recognition

Quadruplex nucleic acids - DNA/RNA secondary structures formed in guanine rich sequences - proved to have key roles in the biology of cancers and, as such, in recent years they emerged as promising targets for small molecules. Many reports demonstrated that metal complexes can effectively stabilize quadruplex structures, promoting telomerase inhibition, downregulation of the expression of cancer-related genes and ultimately cancer cell death. Although extensively explored as anticancer agents, studies on the ability of ruthenium arene complexes to interact with quadruplex nucleic acids are surprisingly almost unknown. Herein, we report on the synthesis and characterization of four novel Ru(ii) arene complexes with 1,3-dioxoindan-2-carboxamides ligands bearing pendant naphthyl-groups designed to bind quadruplexes by both stacking and coordinating interactions. We show how improvements on the hydrolytic stability of such complexes, by substituting the chlorido leaving ligand with pyridine, have a dramatic impact on their interaction with quadruplexes and on their cytotoxicity against ovarian cancer cells.

Bioorthogonal Catalytic Activation of Platinum and Ruthenium Anticancer Complexes by FAD and Flavoproteins

Recent advances in bioorthogonal catalysis promise to deliver new chemical tools for performing chemoselective transformations in complex biological environments. Herein, we report how FAD (flavin adenine dinucleotide), FMN (flavin mononucleotide), and four flavoproteins act as unconventional photocatalysts capable of converting PtIV and RuII complexes into potentially toxic PtII or RuII -OH2 species. In the presence of electron donors and low doses of visible light, the flavoproteins mini singlet oxygen generator (miniSOG) and NADH oxidase (NOX) catalytically activate PtIV prodrugs with bioorthogonal selectivity. In the presence of NADH, NOX catalyzes PtIV activation in the dark as well, indicating for the first time that flavoenzymes may contribute to initiating the activity of PtIV chemotherapeutic agents.

A Red-Light-Activated Ruthenium-Caged NAMPT Inhibitor Remains Phototoxic in Hypoxic Cancer Cells

We describe two water-soluble ruthenium complexes, [1]Cl₂ and [2]Cl₂ , that photodissociate to release a cytotoxic nicotinamide phosphoribosyltransferase (NAMPT) inhibitor with a low dose (21 J cm^-2 ) of red light in an oxygen-independent manner. Using a specific NAMPT activity assay, up to an 18-fold increase in inhibition potency was measured upon red-light activation of [2]Cl₂ , while [1]Cl₂ was thermally unstable. For the first time, the dark and red-light-induced cytotoxicity of these photocaged compounds could be tested under hypoxia (1 % O₂ ). In skin (A431) and lung (A549) cancer cells, a 3- to 4-fold increase in cytotoxicity was found upon red-light irradiation for [2]Cl₂ , whether the cells were cultured and irradiated with 1 % or 21 % O₂ . These results demonstrate the potential of photoactivated chemotherapy for hypoxic cancer cells, in which classical photodynamic therapy, which relies on oxygen activation, is poorly efficient.

Synthesis and Structural Evaluation of Organo-Ruthenium Complexes with β-Diketonates

Four novel ruthenium organometallic complexes: [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-bromophenyl)-1,3-butanedione)Cl] (1), [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-bromophenyl)-1,3-butanedione)pta]PF₆ (2), [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-iodophenyl)-1,3-butanedione)Cl] (3) and [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-iodophenyl)-1,3-butanedione)pta]PF₆ (4) were synthesized and characterized by elemental analysis, infrared (IR), UV-Vis, NMR and mass spectroscopy and single-crystal X-ray diffraction. The crystal structures and spectroscopic data were compared to the previously published complexes [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-chloro-phenyl)-1,3-butanedione)Cl] (5) and [(η⁶-p-cymene)Ru(4,4,4-trifluoro-1-(4-chlorophenyl)-1,3-butanedione)pta]PF₆ (6). The pairs of complexes 1 and 3 as well as 2 and 4 are isostructural, with the former crystallizing in triclinic P-1 and the latter in monoclinic P2₁/c. The ruthenium(II) ion is found in a pseudo-octahedral "piano-stool" geometry in all compounds. Bond lengths and angles are consistent with other complexes of this type. Complexes 2 and 4 exhibit some moderate dynamic disorder. The lack of hydrogen bonding and major π-π interactions means that most of intramolecular interactions are fairly weak and involve halogen atoms present. This was further confirmed by ¹H-NMR spectra, where a significant difference is observed only on the ligand near the halogen atom, following an expected trend. The combined data show that the difference in any activity depends substantially on the type of the ligand's substituted halogen atom.

Azobenzene-based ruthenium(ii) catalysts for light-controlled hydrogen generation

Photo-controlled hydrogen generation catalysts were developed based on ruthenium(ii) azobenzene-containing half-sandwich complexes.

Special issue: practical applications of metal complexes

In 1913 Alfred Werner received the Nobel Prize in Chemistry for his work that was of great importance for the development of coordination chemistry. In the years that followed numerous complexes consisting of metal ions and organic ligands were isolated, thus building a strong connection between inorganic and organic chemistry. Coordination compounds have many interesting properties which find diverse applications in numerous aspects of human life. Fourteeen contributions were received for this Special Issue covering very different aspects of metal complexes and their practical applications. The highest number of manuscripts deals with the biological activity of complexes which might potentially be used in the clinical practice. Authors have tested their cytotoxicity, antibacterial activity and enzyme inhibition. Their optical properties were studied in view of their potential use in photodynamic therapy. Moreover, optical properties could also be used for bioanalysis. It is also known that metal complexes are useful catalysts and a few such examples are also described herein. Many other interesting properties and facts about the isolated and described complexes are also reported (radioactivity, design of metal-organic frameworks, etc.).