The development of low-cost, efficient, and robust electrocatalysts of the hydrogen evolution reaction (HER) is a crucial step toward the conversion and storage of sustainable and carbon-neutral energy resources, such as solar energy. Not only the HER catalysts need to be composed of inexpensive elements, they are also desirable to be prepared at low energy cost. In this work, we report that nickelsulfide (Ni-S) films prepared by facile potentiodynamic deposition are active HER catalysts in aqueous media. Notably, the Ni-S films showed catalytic activity in water with a wide range of pH values (0 to 14), as well as in natural water. In pH 7 phosphate buffer, a current density of 60 mA cm À2 could be achieved with a Tafel slope of 77 mV dec À1 and a Faradaic efficiency of 100%. A long-term bulk electrolysis of the Ni-S film exhibited steady current over 100 h with no deactivation, demonstrating its superior stability in neutral water. Further, an initial activation process was observed, which is likely due to the increase in the effective surface area of the Ni-S film under electrocatalytic conditions. A suite of characterization techniques, including X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, were conducted to probe the composition and structure of the Ni-S film, revealing that its major component is Ni 3 S 2 which was preserved under electrocatalytic conditions.

The delivery of controlled amounts of carbon monoxide (CO) to biological targets is of significant current interest. Very few CO-releasing compounds are currently known that can be rigorously controlled in terms of the location and amount of CO released. To address this deficiency, we report herein a new metal-free, visible-light-induced CO-releasing molecule (photoCORM) and its prodrug oxidized form, which offer new approaches to controlled, localized CO delivery. The new photoCORM, based on a 3-hydroxybenzo[ g]quinolone framework, releases 1 equiv of CO upon visible-light illumination under a variety of biologically relevant conditions. This nontoxic compound can be tracked prior to CO release using fluorescence microscopy and produces a nontoxic byproduct following CO release. An oxidized prodrug form of the photoCORM is reduced by cellular thiols, providing an approach toward activation in the reducing environment of cancer cells. Strong noncovalent affinity of the nonmetal photoCORM to albumin enables use of an albumin:photoCORM complex for targeted CO delivery to cancer cells. This approach produced cytotoxicity IC values among the lowest reported to date for CO delivery to cancer cells by a photoCORM. This albumin:photoCORM complex is also the first CO delivery system to produce significant anti-inflammatory effects when introduced at nanomolar photoCORM concentration.

The properties of the extended flavonol 3-hydroxy-2-phenyl-benzo[g]chromen-4-one (2a) in DMSO : aqueous buffer solutions at pH ¼ 7.4, including in the presence of metal ions, surfactants and serum albumin proteins, have been examined. Absorption and emission spectral studies of 2a in 1 : 1 DMSO : PBS buffer (pH ¼ 7.4) indicate that a mixture of neutral and anionic forms of the flavonol are present. Notably, in 1 : 1 DMSO : TRIS buffer (pH ¼ 7.4) only the neutral form of the flavonol is present. These results indicate that the nature of the buffer influences the acid/base equilibrium properties of 2a. Introduction of a Zn(II) complex of 2a À to a 1 : 1 DMSO : aqueous buffer (TRIS or PBS, pH ¼ 7.4) solution produces absorption and emission spectral features consistent with the presence of a mixture of neutral 2a along with Zn(II)-coordinated or free 2a À . The nature of the anionic species present depends on the buffer composition. PBS buffered solutions (pH ¼ 7.4) containing the surfactants CTAB or SDS enable 2a to be solubilized at a much lower percentage of DMSO (3.3-4.0%). Solutions containing the cationic surfactant CTAB include a mixture of 2a and 2a À whereas only the neutral flavonol is present in SDScontaining buffered solution. Compound 2a is also solubilized in TRIS buffer solutions at low cocentrations of DMSO (3.3%, pH ¼ 7.4) in the presence of serum albumin proteins. Stern-Volmer analysis of the quenching of the inherent protein fluorescence indicates static binding of 2a to the proteins. The binding constant for this interaction is lower than that found for naturally-occurring flavonols (quercetin or morin) or 3-hydroxyflavone. Compound 2a binds to Site I of bovine and human serum albumin proteins as indicated by competition studies with warfarin and ibuprofen, as well as by docking investigations. The quantum yield for CO release from 2a (l irr ¼ 419 nm) under aqueous conditions ranges from 0.0006(3) when the compound is bound to bovine serum albumin to 0.017(1) when present as a zinc complex in a 1 : 1 DMSO : H 2 O solution. Overall, the results of these studies demonstrate that 2a is a predictable visible light-induced CO release compound under a variety of aqueous conditions, including in the presence of proteins. Scheme 2 Acid/base equilibrium of 2a.This journal is

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Carbon monoxide (CO) is a signaling molecule in humans. Prior research suggests that therapeutic levels of CO can have beneficial effects in treating a variety of physiological and pathological conditions. To facilitate understanding of the role of CO in biology, molecules that enable fluorescence detection of CO in living systems have emerged as an important class of chemical tools. A key unmet challenge in this field is the development of fluorescent analyte replacement probes that replenish the CO that is consumed during detection. Herein, we report the first examples of CO sense and release molecules that involve combining a common CO-sensing motif with a light-triggered CO-releasing flavonol scaffold. A notable advantage of the flavonol-based CO sense and release motif is that it is trackable via fluorescence in both its pre- and postsensing (pre-CO release) forms. In vitro studies revealed that the PdCl2 and Ru­(II)-containing CORM-2 used in the CO sensing step can result in metal coordination to the flavonol, which minimizes the subsequent CO release reactivity. However, CO detection followed by CO release is demonstrated in living cells, indicating that a cellular environment mitigates the flavonol/metal interactions.

Aliphatic oxidative carbon-carbon bond cleavage reactions involving Cu(II) catalysts and O2 as the terminal oxidant are of significant current interest. However, little is currently known regarding how the nature of the Cu(II) catalyst, including the anions present, influence the reaction with O2. In previous work, we found that exposure of the Cu(II) chlorodiketonate complex [(6-Ph2TPA)Cu(PhC(O)CClC(O)Ph)]ClO4 (1) to O2 results in oxidative aliphatic carbon-carbon bond cleavage within the diketonate unit, leading to the formation of benzoic acid, benzoic anhydride, benzil, and 1,3-diphenylpropanedione as organic products. Kinetic studies of this reaction revealed a slow induction phase followed by a rapid decay of the absorption features of 1. Notably, the induction phase is not present when the reaction is performed in the presence of a catalytic amount of chloride anion. In the studies presented herein, a combination of spectroscopic (UV-vis, EPR) and density functional theory (DFT) methods have been used to examine the chloride and benzoate ion binding properties of 1 under anaerobic conditions. These studies provide evidence that each anion coordinates in an axial position of the Cu(II) center. DFT studies reveal that the presence of the anion in the Cu(II) coordination sphere decreases the barrier for O2 activation and the formation of a Cu(II)-peroxo species. Notably, the chloride anion more effectively lowers the barrier associated with O-O bond cleavage. Thus, the nature of the anion plays an important role in determining the rate of reaction of the diketonate complex with O2. The same type of anion effects were observed in the O2 reactivity of the simple Cu(II)-bipyridine complex [(bpy)Cu(PhC(O)C(Cl)C(O)Ph)ClO4] (3).

Metal-flavonolate compounds are of significant current interest as synthetic models for quercetinase enzymes and as bioactive compounds of importance to human health. Zinc-3-hydroxyflavonolate compounds, including those of quercetin, kampferol, and morin, generally exhibit bidentate coordination to a single Zn center. The bipyridine-ligated zinc-flavonolate compound reported herein, namely bis(μ-4-oxo-2-phenyl-4H-chromen-3-olato)-κO:O,O;κO,O:O-bis[(2,2'-bipyridine-κN,N')zinc(II)] bis(perchlorate), {[Zn(CHO)(CHN)](ClO)}, (1), provides an unusual example of bridging 3-hydroxyflavonolate ligation in a dinuclear metal complex. The symmetry-related Zn centers of (1) exhibit a distorted octahedral geometry, with weak coordination of a perchlorate anion trans to the bridging deprotonated O atom of the flavonolate ligand. Variable-concentration conductivity measurements provide evidence that, when (1) is dissolved in CHCN, the complex dissociates into monomers. H NMR resonances for (1) dissolved in d-DMSO were assigned via HMQC to the H atoms of the flavonolate and bipyridine ligands. In CHCN, (1) undergoes quantitative visible-light-induced CO release with a quantum yield [0.004 (1)] similar to that exhibited by other mononuclear zinc-3-hydroxyflavonolate complexes. Mass spectroscopic identification of the [(bpy)Zn(O-benzoylsalicylate)] ion provides evidence of CO release from the flavonol and of ligand exchange at the Zn center.

The study results of the copper alloying effect on the microstructure and thermal coefficient of linear expansion (TCLE) of high aluminum alloys for special purposes based on the Al – (20÷30)% Si system are presented. It was found that alloy building of Al – 20% Si with copper in large quantities eliminates the linear expansion anomaly characteristic to the binary alloy and leads to a significant decrease in the thermal expansion coefficient over the entire temperature range of the tests. It was shown that Al–30%Si–20÷40% Cu alloys have stable TCLE in the low-temperature test interval. Metallographic analysis of high alloys showed that copper introduced in amounts of more than 20% contributes to a change in the morphology of the silicon phase and triple eutectic.