Manganese (Mn) complexes are widely studied because of their important catalytic properties in synthetic and biochemical reactions. A Mn (III) complex of an amidoamine ligand was synthesized using a tetradentate amidoamine ligand. In this study, the Mn (III) complex was evaluated for its biological activity by measuring its cytotoxicity in human breast adenocarcinoma cell line (MCF-7). Cytotoxic effects of the Mn (III) complex were determined using established biomarkers in an attempt to delineate the mechanism of action and the utility of the complex as a potential anticancer drug. The Mn (III) complex induces cell death in a dose- and time-dependent manner as shown by microculture tetrazolium assay, a measure of cytotoxic cell death. Our results demonstrated that cytotoxic effects were significantly increased at higher concentrations of Mn (III) complex and with longer time of treatment. The IC (Inhibitor concentration that results in 50% cell death) value of Mn (III) complex in MCF-7 cells was determined to be 2.5 mmol/L for 24 hours of treatment. In additional experiments, we determined the Mn (III) complex-mediated cell death was due to both apoptotic and nonspecific necrotic cell death mechanisms. This was assessed by ethidium bromide/acridine orange staining and flow cytometry techniques. The Mn (III) complex produced reactive oxygen species (ROS) triggering the expression of manganese superoxide dismutase 1 and ultimately damaging the mitochondrial function as is evident by a decline in mitochondrial membrane potential. Treatment of the cells with free radical scavenger, N, N-dimethylthiourea decreased Mn (III) complex-mediated generation of ROS and attenuated apoptosis. Together, these results suggest that the Mn (III) complex-mediated MCF-7 cell death utilizes combined mechanism involving apoptosis and necrosis perhaps due to the generation of ROS.

Nickel coordination chemistry with a biomimetic thiolate-imine-thioether SNSMe ligand is accompanied by diverse reactivity and multidentate ligand dynamics. Reaction of Ni­(acac)2 with 2 equiv of 2-(methylthio)-phenyl-benzothiazolidine (MPB) affords the bis­(arylimino-phenylene-thiolate) complex Ni­(κ2-SNSMe)2 (1; acac = acetylacetonate). Thermolysis of 1 in refluxing toluene is accompanied by imine C–C bond formation, yielding [Ni­(N2S2)] (2) with a redox-active ligand. Protonation of 1 with NHTf2 at a low temperature released 1 equiv of MPB, yielding crystals of the dimeric dication {[Ni­(μ-κ3-SNSMe)]2}­(NTf2)2 (3; Tf = SO2CF3) in high yield. In contrast, the same reaction at room temperature gave also paramagnetic complexes {Ni­[μ-Ni­(κ3-SNSMe)2]2}­(NTf2)2 (4) and {Ni­[μ-Ni­(κ3-SNSMe)2]3}­(NTf2)2 (5) that feature coordination of two or three pseudo-octahedral, paramagnetic Ni­(κ3-SNSMe)2 units to a central Ni­(II) dication via thiolate bridges. Remarkably, dissolution of 3 in a variety of solvents, including weakly coordinating CH2Cl2, rapidly generates a mixture of 4 and Ni­(NTf)2. Treatment of this mixture with Lewis bases L gave high yields of dimers {[Ni­(μ-κ3-SNSMe)­L]2}­(NTf2)2 for L = CNXylyl (6a) and {[Ni­(μ-κ3-SNSMe)]2(μ-dmpm)}­(NTf2)2 (6b; dmpm = bis­(dimethylphosphino)­methane) or monomers [Ni­(κ3-SNSMe)­L]­(NTf2) for L = PMe3 (7a) and P­(OMe)3 (7b). Addition of 2 equiv of the strong donor N-heterocyclic carbene ligand, IPr, to 3, however, led to thioether demethylation, affording neutral dithiolate complex Ni­(κ3-SNS)­(IPr) (8). Reaction products were characterized by NMR and mass spectrometry and complexes 1–5, 6a, 6b, 7a, and 8 by single-crystal X-ray diffraction.

NiO‐Mn2O3/C nanocomposite was synthesized from chitosan, a renewable biopolymer, NiO and MnO2 and pyrolyzed at 500 °C under nitrogen. The morphology of material was characterized with various microscopic analyses. The graphitic carbon showed metal nanoparticles dispersed on the nanocomposite that could be clearly differentiated. X‐ray photoelectron spectroscopy indicated the Mn species reduced from +4 to +3 oxidation state, while Ni species remained as NiO, which was further supported by X‐ray diffraction. The electrochemical behavior of NiO‐Mn2O3/C toward oxygen reduction reaction (ORR) in alkaline medium was investigated via cyclic voltammetry (CV). CVs revealed a ORR peak at 0.67 V vs. RHE with significantly high current density. Hydrodynamic studies indicated that NiO‐Mn2O3/C catalyzed ORR via a four‐electron reduction pathway. A high rate constant in the order of magnitude of 106 mol−1s−1 was obtained for ORR. This low‐cost, environmentally friendly and stable ORR catalyst derived from chitosan and doped with metal oxides proved to be a promising electrocatalyst for ORR and could alternatively find its application in alkaline fuel cells (AFCs).

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