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The aim of the present study was to develop zinc sulfide nanoparticles (ZnS NPs) and to study their cytotoxicity against the KG-1A (human acute myeloid leukemia) cell line. ZnS NPs were synthesized using the pyrolytic method and characterized by X-ray diffraction, dynamic light scattering, surface zeta potential, scanning electron microscopy and atomic force microscopy. Cell viability study and flow cytometric analysis confirmed the potent cytotoxic effects of ZnS NPs on cancer cells in a dose-dependent fashion. Successful uptakes of ZnS NPs by leukemic cells were confirmed by phase contrast fluorescence microscopy. pH-dependent dissolution of ZnS NPs was done using atomic absorption microscopy to understand the cell-specific internalization of Zn(+) . This internalization of NPs facilitated the generation of excess reactive oxygen species (ROS), followed by tumor necrosis factor alpha (TNF-α) secretion which caused severe DNA damage as observed in the comet assay and altered the mitochondrial membrane potential (MMP) in leukemic cells. Surprisingly ZnS NPs had no toxic effects on normal lymphocytes at doses up to 50 µg ml(-1) . Pre-treatment with ROS and TNF-α inhibitor confirmed that these nanoparticles were able to kill leukemic cells by generating an excess amount of ROS and thereby initiated TNF-α mediated apoptosis pathway. These findings clarify the mechanism with which ZnS NPs induced anticancer activities in vitro. To elicit its utilities and its application to cancer treatment in vivo is under investigation.

A mononucleating (HL(1)) and a dinucleating (HL(2)) "end-off" compartmental ligand have been designed and synthesized by controlled Mannich reaction using p-cresol and bis(2-methoxyethyl)amine, and their formation has been rationalized. Six complexes have been prepared on treating HL(1) and HL(2) with Zn(II)X2 (X = Cl(-), Br(-), I(-)) with the aim to investigate their hydrolytic activity on phosphoester bond cleavage. Interestingly, the mononucleating ligand was observed to yield dinuclear complexes, [Zn2(L(1))2X2] (1-3), while the potential dinucleating ligand generated mononuclear complexes, [Zn(HL(2))X2] (4-6). Four (1-4), out of six complexes studied, were characterized by single-crystal X-ray diffraction (XRD): the Zn ion exhibits trigonal bipyramidal and tetrahedral coordination spheres in the di- and mononuclear complex, respectively. The hydrolytic kinetics, followed spectrophotometrically with 4-nitrophenylphosphate (4-NPP) in buffered dimethylformamide (DMF) (97.5% DMF, v/v) because of solubility reasons, under excess substrate conditions (substrate:complex = 20:1), indicated that the complexes enormously accelerate the rate of phosphomonoester hydrolysis with first order rate constants (kcat) in the range 2-10 s(-1) at 25 °C. In each case kinetic data analyses have been run by Michaelis-Menten treatment. The efficacy in the order of conversion of substrate to product (p-nitrophenolate ion) follows the trend 1 > 2 > 3 > 4 > 5 > 6, and the ratio of kcat of an analogous dinuclear to mononuclear complex is ≃2. An electrospray ionization-mass spectrometry (ESI-MS) study has revealed the dissociation of the centrosymmetric dinuclear complex to two mononuclear species instead of a syn-cooperative catalysis. Density functional theory (DFT) calculations have been performed to rationalize our proposed mechanistic pathway for phosphatase activity. The comparative analysis concludes the following facts under experimental conditions: (1) the halide bound to the active site affects the overall rate in the order: Cl(-) > Br(-) > I(-) regardless of nuclearity; (2) dinuclear complexes prevail over the mononuclear ones.

Water electrolysis is among the simplest methods to generate hydrogen, which can be used as a clean and renewable energy source. Within this process, the oxidation of water into molecular oxygen is considered as the bottleneck reaction because it involves the transfer of four electrons toward the oxidation of a highly stable small molecule. Challenges in this area include the development of stable and effective electro-and photocatalysts that utilize readily available metal ions. Herein we report a copper− peptidomimetic complex as an electrocatalyst for water oxidation, which is both highly stable and efficient. Inspired by enzymatic catalysis, which is largely based on intramolecular cooperativity between a metal center and functional organic molecules located on one scaffold, we have designed and synthesized a peptoid trimer bearing a 2,2′-bipyridine (bipy) ligand, an −OH group, and a benzyl group. Both experimental and computational data reveal that binding of Cu II to this peptoid in aqueous medium occurs via the bipy group and two hydroxyl moieties from the solution. Based on a systematic electrochemical study, we show that this complex is an active electrocatalyst for water oxidation in aqueous phosphate buffer solution enabling oxygen evolution at pH 11.5 with a turnover frequency of 5.8 s −1 and a Faradaic efficiency of up to 91%. Importantly, this catalyst is highly stable over at least 15 h of electrolysis. Thus, we could reuse it for at least 9 times in 40 min electrolysis experiments, demonstrate that it retains its activity in every experiment, and obtain oxygen evolution with an overall turnover number record (based on moles oxygen to moles catalyst) of >56 in 6 h. Moreover, based on electrochemical experiments, spectroscopic data, and density functional theory-D3 calculations, we identified a key peroxo intermediate and propose an intramolecular cooperative catalytic path for this reaction, which suggests that the −OH group has a major role in the high stability of the complex.

Water electrolysis is among the simplest method for generating hydrogen as an alternative renewable fuel. A major challenge associated with this process is the development of cheap, simple, and environmentally benign catalysts that lead to a minimum overpotential for water oxidation. Inspired by the Mn4CaOx cluster that catalyzes water oxidation in photosystem II, described here is the synthesis and characterization of the manganese cluster [Mn12O12(O2CC6H2(OH)3)16(H2O)4] (Mn12TH) along with its electrocatalytic activity at pH 6. Electrochemical, spectroscopic, and electron microscopy studies show that Mn12TH is a homogeneous electrocatalyst for water oxidation and enables oxygen evolution with a reaction rate of 22 s−1, high Faradic efficiency (93 %), and an overpotential of only 74 mV, the lowest reported to date. Based on the electrochemical data, the organic ligands, which can be described as the second coordination sphere of the catalytic manganese core, play a key role in facilitating the oxidation process and accelerating the reaction.