Oxidized Pt clusters on a TiO2support as a robust electrocatalyst for the hydrogen evolution reaction.

Herein, we synthesized a Fe, Ni dual-metal embedded in porous nitrogen-doped carbon material to endow higher turnover frequency (TOF), lower H2O2 yield, and thus superior durability than for the single-atom catalyst for oxygen reduction in acid media. Quantitative X-ray absorption near edge structure (XANES) fitting and density functional theory (DFT) calculation were implemented to explore the active sites in the catalysts. The results suggest FeNi-N6 with type I (each metal atom coordinated with four nitrogen atoms) instead of type II configuration (each metal atom coordinated with three nitrogen atoms) dominates the catalytic activity of the noble-metal free catalyst (NMFC). Further, theoretical calculation reveals that the oxygen reduction reaction (ORR) activity trend of different moieties was FeNi-N6 (type I) > FeNi-N6 (type II) > Fe–N4 > Fe2–N6. Our research represents an important step for developing dual-metal doping NMFC for proton exchange membrane fuel cells (PEMFCs) by revealing its new structural configuration and correlation with catalytic activity.

A series of square-planar Pt(II) complexes [Pt(C^N)(O^O)] (1-5) (C^N ¼ 2-phenylpyridine, O^O denotes a series of b-diketonate ligands) is reported. Detailed studies of theoretical calculations, electrochemical and photophysical properties have shown that their excited states can be attributed to the mixing of 3 MLCT, 3 LLCT and 3 LC/ 3 ILCT transitions. For 1, the excited state is dominated by the C^N ligand. The excited states of complexes 2-5, however, are dominated by O^O ligands. Through variation of the b-diketonate ligands, the emission colors of 1-5 can be tuned from blue-green to yellow. Further investigations have revealed that the emission of 4 in the solid state can be attributed to the 3 MLCT and 3 LLL'CT transitions, which has been confirmed by X-ray diffraction studies as well as theoretical calculations. Moreover, exclusive staining of cytoplasm and low cytotoxicity have been observed for 1-4, which makes them promising candidates as phosphorescent probes for bioimaging.

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For the development of excellent optical probes for mercury(II), a series of simple conjugated polymers that contain phosphorescent iridium(III) complexes as receptors for mercury(II) were designed and synthesized. These conjugated polymers showed energy transfer from the polymer host to iridium(III) complex guest in both solution and the solid state. Unexpectedly, they can work as excellent polymer chemodosimeters for mercury(II) by utilizing the mercury(II)-induced decomposition of iridium(III) complex. They exhibit a pronounced optical signal change with switchable phosphorescence and fluorescence, even when the concentration of a solution of mercury(II) in THF was as low as 0.5 ppb. With the addition of mercury(II), the phosphorescent emission intensity of iridium(III) complexes was quenched completely. As the emission from polymer backbones increased, the emission wavelength was redshifted simultaneously, thereby realizing ratiometric detection. Excellent selectivity toward mercury(II) over other potentially interfering cations was also realized. In addition, an obvious emission color change of polymer solution from red to yellow-green was observed, thus realizing a "naked-eye" detection of mercury(II). More importantly, the solid films of these polymer chemodosimeters also exhibited high sensitivity and rapid response to mercury(II), thereby demonstrating the possibility of the fabrication of sensing devices with fast and convenient detection of mercury(II). The sensing mechanism was also investigated in detail. This is the first report on chemodosimeters based on conjugated polymers with phosphorescent iridium(III) complexes.

A complex reaction mechanism of oxidation of the anti-tubercular prodrug isoniazid (isonicotinic hydrazide, INH) by [IrCl] as a model for redox processes of such drugs in biological systems has been studied in aqueous solution as a function of pH between 0 and 8.5. Similar experiments have been performed with its isomer nicotinic hydrazide (NH). All reactions are overall second-order, first-order in [IrCl] and hydrazide, and the observed second-order rate constants k' have been determined as a function of pH. Spectrophotometric titrations indicate a stoichiometry of [Ir(iv)] : [hydrazide] = 4 : 1. HPLC analysis shows that the oxidation product of INH is isonicotinic acid. The derived reaction mechanism, based on rate law, time-resolved spectra and stoichiometry, involves parallel attacks by [IrCl] on all four protolytic species of INH and NH as rate-determining steps, depending on pH. These steps are proposed to generate two types of hydrazyl free radicals. These radicals react further in three rapid consecutive processes, leading to the final oxidation products. Rate constants for the rate-determining steps have been determined for all protolytic species I-IV of INH and NH. They are used to calculate reactivity-pH diagrams. These diagrams demonstrate that for both systems, species IV is ca. 10 times more reactive in the redox process than the predominant species III at the physiological pH of 7.4. Thus, species IV will be the main reactant, in spite of the fact that its concentration at this pH is extremely low, a fact that has not been considered in previous work. The results indicate that pH changes might be an important factor in the activation process of INH in biological systems also, and that in such systems this process most likely is more complicated than previously assumed.

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