An osmium-peroxo complex for photoactive therapy of hypoxic tumors

Its limited therapeutic effect on hypoxic and refractory solid tumors has hindered the practical application of photodynamic therapy (PDT). Herein, we report our investigation of an osmium-peroxo complex (Os2), which is inactive in the dark, but upon light irradiation, can release a peroxo ligand O2•−, and is transformed into a cytotoxic osmium complex (Os1). The osmium-peroxo complex Os2 produces O2•− under light irradiation even in the absence of oxygen, and retains its phototoxicity in hypoxic tumors. Os1 is cytotoxic in the presence or absence of irradiation, behaves as a chemotherapeutic drug. The light-activated Os2 induces distinct ferroptosis, which is mediated by GSH degradation, lipid peroxide accumulation and down-regulation of glutathione peroxidase 4 (GPX4). In addition, Os2 causes photocatalytic oxidation of endogenous 1,4-dihydronicotinamide adenine dinucleotide (NADH) in living cancer cells, leading to ferroptosis. In vivo studies have confirmed that the Os2 can effectively inhibit the growth of solid hypoxic tumors in mice. A new strategy is proposed for the treatment of hypoxic tumors with metal-based drugs.

Electronic structure of Schiff-base peroxo{2,2′-[1,2-phenylenebis(nitrilomethanylylidene)]bis(6-methoxyphenolato)}titanium(IV) monohydrate: a possible model structure of the reaction center for the theoretical study of hemoglobin

An extensive characterization of [Ti(C22H18N2O6)]·H2O was performed by topological analysis according to Bader's quantum theory of atoms in molecules (QTAIM) from the experimentally (multipole model) and theoretically (DFT) determined electron density. To the best of our knowledge, this study is the first example of an experimental electronic structure of a coordination compound in which a peroxo anion is bonded to a 3d central atom. The titanium coordination polyhedron could be described as a deformed tetrahedral pyramid if the midpoint of the peroxide O—O bond (side-on mode) is considered to be in the quasi-apical position. According to the multipole model (MM) results, the titanium atom has a positive QTAIM charge of 2.05 e− which does not correspond to the formal Ti (IV) oxidation state. On the other hand, the peroxo oxygen atoms O(1) and O(2) have MM QTAIM charges of −0.27 and −0.12, respectively. This asymmetric charge density distribution on the peroxo oxygens is in agreement with the distorted orientation of the O2 moiety with respect to the titanium atom. Despite the fact that the overall MM charge of the O2 moiety is more remote from the formal −2 charge than from neutral O2, the O—O distance remains close to that in the peroxo O2 2− anion. In the case of DFT results, the titanium atom charge is also found to be close to +2, the O2 x− moiety charge is around −1, the optimized O—O distance is shorter by only ca 0.04 Å than the experimental value of 1.5005 (16) Å, and the DFT d-populations on titanium are found to be lower than the experimental MM value. This study is the first experimental electronic structure of a transition metal peroxo complex.

Comparative Studies on Synthesis, Characterization and Antibacterial Properties between Schiff Base Co(II) Complex and Peroxo Complex

A new Schiff base Co(II) complex and - peroxo complex were synthesized and characterized by thin layer chromatography (TLC), elemental analyses, magnetic moment, conductivity measurements, UV-Vis., IR and ESI-MS spectral studies. The cobalt ion was participated in direct complexation with the Schiff base (SB) ligand derived from o-aminobenzoic acid and cinnamaldehyde during the single pot reaction. IR spectral data showed that the Schiff base ligand coordinated to the metal ion through nitrogen of azomethine group and oxygen of carboxyl group (COO-). The molar conductance values indicated that both the complexes are non-electrolytic in nature. Antibacterial activity of the complexes was tested against four pathogenic bacteria namely Staphylococcus aureus, Bacillus cereus, Escherichia coli & Shigella dysenteriae with standard Kanamycin-30. The results showed that both type of complexes have moderate to strong antibacterial activity and the peroxo complex is relatively more potential towards all the tested organisms.

Generation and Reactivity of a NiIII2(μ-1,2-peroxo) Complex

Ni-based oxide materials are promising candidates for catalyzing the oxygen evolution reaction. The detailed mechanism of water splitting in these systems has been of interest with a goal of understanding the intermediate species vital for catalytic activity. A potential intermediate species prior to release of oxygen is a bridging Ni^III₂(<i>μ</i>-1,2-peroxo) complex. However, Ni₂(<i>μ</i>-1,2-peroxo) complexes are rare in general and are unknown with oxidation states higher than Ni^II. Herein, we report the isolation of such an unusual high-valent species in a Ni^III₂(<i>μ</i>-1,2-peroxo) complex, which has been characterized using single-crystal X-ray diffraction and X-ray absorption, NMR, and UV-vis spectroscopies. In addition, treatment with excess tetrabutylammonium chloride results in regeneration of the precursor Ni–Cl species, implicating the reversible release of oxygen or a reactive oxygen species. Taken together, this suggests that Ni^III₂(<i>μ</i>-1,2-peroxo) species are accessible and may be viable intermediates during the oxygen evolution reaction.

Generation and Reactivity of a NiIII2(μ-1,2-peroxo) Complex

Ni-based oxide materials are promising candidates for catalyzing the oxygen evolution reaction. The detailed mechanism of water splitting in these systems has been of interest with a goal of understanding the intermediate species vital for catalytic activity. A potential intermediate species prior to release of oxygen is a bridging Ni^III₂(<i>μ</i>-1,2-peroxo) complex. However, Ni₂(<i>μ</i>-1,2-peroxo) complexes are rare in general and are unknown with oxidation states higher than Ni^II. Herein, we report the isolation of such an unusual high-valent species in a Ni^III₂(<i>μ</i>-1,2-peroxo) complex, which has been characterized using single-crystal X-ray diffraction and X-ray absorption, NMR, and UV-vis spectroscopies. In addition, treatment with excess tetrabutylammonium chloride results in regeneration of the precursor Ni–Cl species, implicating the reversible release of oxygen or a reactive oxygen species. Taken together, this suggests that Ni^III₂(<i>μ</i>-1,2-peroxo) species are accessible and may be viable intermediates during the oxygen evolution reaction.