Anchoring Triazole-Gold(I) Complex into Porous Organic Polymer To Boost the Stability and Reactivity of Gold(I) Catalyst

Stability and reactivity have been recognized as some critical issues for gold­(I) catalysts. Such issues can be well-circumvented by anchoring the gold­(I) complex onto the backbones of porous organic polymer (POP) followed by coordination with a triazole ligand as illustrated in the present work via a series of gold­(I)-catalyzed reactions. In this strategy, 1,2,3-triazole was used as the special “X-factor” to avoid the formation of solid AgCl involved in typical gold-activation processes. The catalyst could be readily recycled without loss of reactivity. Moreover, compared with the PPh₃-modified polystyrene beads, the POP support was advantageous by providing high surface area, hierarchical porosity, and better stabilization of cations. In some cases, significantly improved reactivity was observed, even more so than using the homogeneous system, which further highlighted the great potential of this heterogeneous gold catalyst

Small Particles of Chemically-Reduced Graphene with Improved Electrochemical Capacity

Chemically reduced graphenes (CRGs) of different sizes were prepared by the reduction of graphene oxide (GO) in different oxidation degrees, with hydrazine hydrate as the reducing agent. Compared with normally oxidized GO (46.9 wt %), the deeply oxidized GO particles have a higher oxygen content (50.4 wt %). The oxygen content of resulting CRG is correspondingly increased from 11.3 wt % of normal-sized CRG to 16.3 wt % of small-sized CRG, with a dramatic increase in specific surface area from 468.2 to 716.3 m²/g. More graphene edges, which were highly decorated by pseudocapacitive-active sites, were exposed in the small-sized CRG. As a result, small-sized CRG has a much higher specific capacitance (192.1 F/g) than that of normal-sized CRG (132.3 F/g), which is attribute to the contribution of both electrochemical double layer capacitance by an increased surface area and pseudocapacitance by extra surface functional groups

Electroenzymatic C–C Bond Formation from CO₂

Over the past decade, there has been significant research in electrochemical reduction of CO₂, but it has been difficult to develop catalysts capable of C–C bond formation. Here, we report bioelectrocatalysis of vanadium nitrogenase from Azotobacter vinelandii, where cobaltocenium derivatives transfer electrons to the catalytic VFe protein, independent of ATP-hydrolysis. In this bioelectrochemical system, CO₂ is reduced to ethylene (C₂H₄) and propene (C₃H₆), by a single metalloenzyme

The In Vivo Potential-Regulated Protective Protein of Nitrogenase in <i>Azotobacter vinelandii</i> Supports Aerobic Bioelectrochemical Dinitrogen Reduction In Vitro

Nitrogenase, the only enzyme known to be able to reduce dinitrogen (N₂) to ammonia (NH₃), is irreversibly damaged upon exposure to molecular oxygen (O₂). Several microbes, however, are able to grow aerobically and diazotrophically (fixing N₂ to grow) while containing functional nitrogenase. The obligate aerobic diazotroph, <i>Azotobacter vinelandii</i>, employs a multitude of protective mechanisms to preserve nitrogenase activity, including a “conformational switch” protein (FeSII, or “Shethna”) that reversibly locks nitrogenase into a multicomponent protective complex upon exposure to low concentrations of O₂. We demonstrate in vitro that nitrogenase can be oxidatively damaged under anoxic conditions and that the aforementioned conformational switch can protect nitrogenase from such damage, confirming that the conformational change in the protecting protein can be achieved solely by regulating the potential of its [2Fe-2S] cluster. We further demonstrate that this protective complex preserves nitrogenase activity upon exposure to air. Finally, this protective FeSII protein was incorporated into an O₂-tolerant bioelectrosynthetic cell whereby NH₃ was produced using air as a substrate, marking a significant step forward in overcoming the crippling limitation of nitrogenase’s sensitivity toward O₂

Sustainable Bioelectrosynthesis of the Bioplastic Polyhydroxybutyrate: Overcoming Substrate Requirement for NADH Regeneration

One of the main limitations to achieve sustainable synthesis of polyhydroxybutyrate (PHB) is the cost of NADH regeneration, as it requires a side enzymatic reaction usually including a NAD-dependent dehydrogenase enzyme with its substrate or other photo- and electrochemical approaches that create unwanted byproducts and the enzymatically inactive dimer NAD₂. Herein, a bioelectrocatalytic method combining both enzymatic and electrochemical approaches was used to regenerate enzymatically active NADH. The method employed a modified glassy carbon electrode that possesses both NADH regeneration and acetoacetyl-CoA (AcAcCoA) reduction features. The modified electrode exhibited an apparent Michaelis constant (<i>K</i>_M) value of 814 ± 11 μM and a maximum current density (<i>j</i>_max) of 27.9 ± 1.3 μA cm^–2 for NAD⁺ reduction and a <i>K</i>_M value of 47 ± 2 μM and <i>j</i>_max of 0.97 ± 0.03 μA cm^–2 for AcAcCoA reduction. The modified electrode was subsequently employed in the bioelectrosynthesis of the bioplastic PHB and yielded 1.6 mg in a 5 mL reaction mixture, indicating that the NADH was regenerated at least 8 times during the 16 h reaction

Confocal Raman Microscopy for the Determination of Protein and Quaternary Ammonium Ion Loadings in Biocatalytic Membranes for Electrochemical Energy Conversion and Storage

The need to immobilize active enzyme, while ensuring high rates of substrate turnover and electronic charge transfer with an electrode, is a centrally important challenge in the field of bioelectrocatalysis. In this work, we demonstrate the use of confocal Raman microscopy as a tool for quantitation and molecular-scale structural characterization of ionomers and proteins within biocatalytic membranes to aid in the development of energy efficient biofuel cells. A set of recently available short side chain Aquivion ionomers spanning a range of equivalent weight (EW) suitable for enzyme immobilization was investigated. Aquivion ionomers (790 EW, 830 EW and 980 EW) received in the proton-exchanged (SO₃H) form were treated with tetra-<i>n</i>-butylammonium bromide (TBAB) to neutralize the ionomer and expand the size of ionic domains for enzyme incorporation. Through the use of confocal Raman microscopy, membrane TBA⁺ ion content was predicted in calibration studies to within a few percent of the conventional titrimetric method across the full range of TBA⁺: SO₃^– ratios of practical interest (0.1 to 1.7). Protein incorporation into membranes was quantified at the levels expected in biofuel cell electrodes. Furthermore, features associated with the catalytically active, enzyme-coordinated copper center were evident between 400 and 500 cm^–1 in spectra of laccase catalytic membranes, demonstrating the potential to interrogate mechanistic chemistry at the enzyme active site of biocathodes under fuel cell reaction conditions. When benchmarked against the 1100 EW Nafion ionomer in glucose/air enzymatic fuel cells (EFCs), EFCs with laccase air-breathing cathodes prepared from TBA⁺ modified Aquivion ionomers were able to reach maximum power densities (<i>P</i>_max) up to 1.5 times higher than EFCs constructed with cathodes prepared from TBA⁺ modified Nafion. The improved performance of EFCs containing the short side chain Aquivion ionomers relative to Nafion is traced to effects of ionomer ion-exchange capacity (IEC, where IEC = EW^–1), where the greater density of SO₃^– moieties in the Aquivion materials produces an environment more favorable to mass transport and higher TBA⁺ concentrations

Highly Efficient and Selective Photocatalytic Oxidation of Sulfide by a Chromophore–Catalyst Dyad of Ruthenium-Based Complexes

Electronic coupling across a bridging ligand between a chromophore and a catalyst center has an important influence on biological and synthetic photocatalytic processes. Structural and associated electronic modifications of ligands may improve the efficiency of photocatalytic transformations of organic substrates. Two ruthenium-based supramolecular assemblies based on a chromophore–catalyst dyad containing a Ru–aqua complex and its chloro form as the catalytic components were synthesized and structurally characterized, and their spectroscopic and electrochemical properties were investigated. Under visible light irradiation and in the presence of [Co­(NH₃)₅Cl]­Cl₂ as a sacrificial electron acceptor, both complexes exhibited good photocatalytic activity toward oxidation of sulfide into the corresponding sulfoxide with high efficiency and >99% product selectivity in neutral aqueous solution. The Ru–aqua complex assembly was more efficient than the chloro complex. Isotopic labeling experiments using ¹⁸O-labeled water demonstrated the oxygen atom transfer from the water to the organic substrate, likely through the formation of an active intermediate, Ru­(IV)O

Highly Efficient and Selective Photocatalytic Oxidation of Sulfide by a Chromophore–Catalyst Dyad of Ruthenium-Based Complexes

Electronic coupling across a bridging ligand between a chromophore and a catalyst center has an important influence on biological and synthetic photocatalytic processes. Structural and associated electronic modifications of ligands may improve the efficiency of photocatalytic transformations of organic substrates. Two ruthenium-based supramolecular assemblies based on a chromophore–catalyst dyad containing a Ru–aqua complex and its chloro form as the catalytic components were synthesized and structurally characterized, and their spectroscopic and electrochemical properties were investigated. Under visible light irradiation and in the presence of [Co­(NH₃)₅Cl]­Cl₂ as a sacrificial electron acceptor, both complexes exhibited good photocatalytic activity toward oxidation of sulfide into the corresponding sulfoxide with high efficiency and >99% product selectivity in neutral aqueous solution. The Ru–aqua complex assembly was more efficient than the chloro complex. Isotopic labeling experiments using ¹⁸O-labeled water demonstrated the oxygen atom transfer from the water to the organic substrate, likely through the formation of an active intermediate, Ru­(IV)O

Role of SUMO-Specific Protease 2 in Reprogramming Cellular Glucose Metabolism

<div><p>Most cancer cells exhibit a shift in glucose metabolic strategy, displaying increased glycolysis even with adequate oxygen supply. SUMO-specific proteases (SENPs) de-SUMOylate substrates including HIF1α and p53,two key regulators in cancer glucose metabolism, to regulate their activity, stability and subcellular localization. However, the role of SENPs in tumor glucose metabolism remains unclear. Here we report that SUMO-specific protease 2 (SENP2) negatively regulates aerobic glycolysis in MCF7 and MEF cells. Over-expression of SENP2 reduces the glucose uptake and lactate production, increasing the cellular ATP levels in MCF7 cells, while SENP2 knockout MEF cells show increased glucose uptake and lactate production along with the decreased ATP levels. Consistently, the MCF7 cells over-expressing SENP2 exhibit decreased expression levels of key glycolytic enzymes and an increased rate of glucose oxidation compared with control MCF7 cells, indicating inhibited glycolysis but enhanced oxidative mitochondrial respiration. Moreover, SENP2 over-expressing MCF7 cells demonstrated a reduced amount of phosphorylated AKT, whereas SENP2 knockout MEFs exhibit increased levels of phosphorylated AKT. Furthermore, inhibiting AKT phosphorylation by LY294002 rescued the phenotype induced by SENP2 deficiency in MEFs. In conclusion, SENP2 represses glycolysis and shifts glucose metabolic strategy, in part through inhibition of AKT phosphorylation. Our study reveals a novel function of SENP2 in regulating glucose metabolism.</p></div

Porous Double-Walled Metal Triazolate Framework Based upon a Bifunctional Ligand and a Pentanuclear Zinc Cluster Exhibiting Selective CO₂ Uptake

The self-assembly of a custom-designed bifunctional ligand featuring both 1,2,3-triazolate and carboxylate donor groups with a pentanuclear zinc cluster generated in situ affords a double-walled metal triazolate framework (MTAF) material, MTAF-1 (Zn₅(μ₃-O)₂(C₉N₃H₅O₂)₅(H⁺)₄(H₂O)₁₇(C₃H₇NO)₁₀), which exhibits a surface area of 2300 m²/g and demonstrates interesting selective CO₂ uptake performances