Catalytic Mechanism of Liquid-Metal Indium for Direct Dehydrogenative Conversion of Methane to Higher Hydrocarbons.

There is a great interest in direct conversion of methane to valuable chemicals. Recently, we reported that silica-supported liquid-metal indium catalysts (In/SiO2) were effective for direct dehydrogenative conversion of methane to higher hydrocarbons. However, the catalytic mechanism of liquid-metal indium has not been clear. Here, we show the catalytic mechanism of the In/SiO2 catalyst in terms of both experiments and calculations in detail. Kinetic studies clearly show that liquid-metal indium activates a C-H bond of methane and converts methane to ethane. The apparent activation energy of the In/SiO2 catalyst is 170 kJ mol-1, which is much lower than that of SiO2, 365 kJ mol-1. Temperature-programmed reactions in CH4, C2H6, and C2H4 and reactivity of C2H6 for the In/SiO2 catalyst indicate that indium selectively activates methane among hydrocarbons. In addition, density functional theory calculations and first-principles molecular dynamics calculations were performed to evaluate activation free energy for methane activation, its reverse reaction, CH3-CH3 coupling via Langmuir-Hinshelwood (LH) and Eley-Rideal mechanisms, and other side reactions. A qualitative level of interpretation is as follows. CH3-In and H-In species form after the activation of methane. The CH3-In species wander on liquid-metal indium surfaces and couple each other with ethane via the LH mechanism. The solubility of H species into the bulk phase of In is important to enhance the coupling of CH3-In species to C2H6 by decreasing the formation of CH4 though the coupling of CH3-In species and H-In species. Results of isotope experiments by combinations of CD4, CH4, D2, and H2 corresponded to the LH mechanism.

The Active Center of Co-N-C Electrocatalysts for the Selective Reduction of CO2 to CO Using a Nafion-H Electrolyte in the Gas Phase.

To contribute a solution for the global warming problem, the selective electrochemical reduction of CO2 to CO was studied in the gas phase using a [CO2(g), Co-N-C cathode | Nafion-H | Pt/C anode, H2/water] system without using carbonate solutions. The Co-N-C electrocatalysts were synthesized by partial pyrolysis of precursors in inert gas, which were prepared from various N-bidentate ligands, Co(NO3)2, and Ketjenblack (KB). The most active electrocatalyst was Co-(4,4'-dimethyl-2,2'-bipyridine)/KB pyrolyzed at 673 K, denoted Co-4,4'-dmbpy/KB(673K). A high performance of CO formation (331 µmol h-1 cm-2, 217 TOF h-1) at 0.020 A cm-2 with 78% current efficiency was obtained at -0.75 V (SHE) and 273 K under strong acidic conditions of Nafion-H. Characterization studies using extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy-energy-dispersive X-ray (TEM-EDX), X-ray diffraction (XRD), and temperature-programmed desorption with mass spectrometry (TPD-MS) indicated the active site as Co coordinated with four N atoms bonding the surface of KB, abbreviated Co-N4-C x structure. A model of the reduction mechanism of CO2 on the active site was proposed.

Disposition of Iridium on Ruthenium Nanoparticle Supported on Ketjenblack: Enhancement in Electrocatalytic Activity toward the Electrohydrogenation of Toluene to Methylcyclohexane.

Electrohydrogenation of toluene (TL) to methylcyclohexane (MCH) has been recognized as a promising technology for the hydrogenation process in the organic hydride hydrogen storage system. Recently, we found that the Ketjenblack (KB)-supported Ru-Ir alloy electrocatalyst showed a high electrocatalytic activity for the electrohydrogenation of TL to MCH, and there was the synergy of Ir electrocatalysis for the formation of adsorbed hydrogen species (Had) (H+ + e- → Had) and Ru catalysis for hydrogenation of TL (6Had + TL → MCH). In this paper, the Ir-modified Ru nanoparticle supported on KB (Ir/Ru/KB) electrocatalyst was synthesized by using a modified spontaneous deposition method. The method enables to control the surface structure of Ru-Ir nanoparticles. The Ir/Ru/KB cathode showed higher electrohydrogenation activity than the Ru-Ir alloy/KB cathodes even at lower loadings of precious Ir. Characterization studies using a scanning-transmission electron microscope with an energy-dispersive X-ray spectrometer and X-ray absorption fine structure proved selective and uniform modification of Ru nanoparticle with Ir. Cyclic voltammetry measurements in H2SO4 aqueous solution indicated higher electrochemical active surface areas of Ir at the Ir/Ru/KB electrocatalysts than that at the Ru-Ir alloy/KB electrocatalysts, which is the reason for the strong synergy of Ru and Ir for the electrohydrogenation of TL to MCH.

Theoretical Study on the C-H Activation of Methane by Liquid Metal Indium: Catalytic Activity of Small Indium Clusters.

The mechanism of C-H activation of methane by liquid indium, which is the first step of the dehydrogenative conversion of methane to higher hydrocarbons, was investigated using density functional theory calculations. In the first-principle molecular dynamics trajectory at the experimental temperature (1200 K), low-coordinated indium atoms continuously appear on the disordered liquid surface. The C-H cleavage is endothermic on clean surfaces, while the low-coordinated indium atoms reduce the endothermicity significantly. In small indium clusters, which are models of low-coordinated atoms on a surface, the calculated activation energy is much smaller than that on the clean surface. The energy level of the methane C-H σ* orbital is reduced by the interaction with the indium 5pσ orbitals. In2 shows the lowest activation energy and exothermicity in the C-H bond cleavage.

Garcinia vilersiana bark extract activates the Nrf2/HO-1 signaling pathway in RAW264.7 cells.

Garcinia vilersiana is a traditional medicinal plant in Vietnam. The petroleum ether extract of stem bark of Garcinia vilersiana (GVE) was prepared to evaluate its potential to activate Nrf2, a transcription factor of antioxidant and detoxifying enzymes. Exposure of mouse macrophage RAW264.7 cells to GVE (0.625-2.5 µg/ml) resulted in a significant activation of Nrf2, as evaluated by nuclear accumulation of this transcription factor, and increased antioxidant response element (ARE) binding activity in a time- and concentration-dependent manner. As a result, GVE caused ARE-dependent up-regulation of heme oxygenase-1 (HO-1) in the cells. These results suggest that GVE contains components that have the ability to activate the Nrf2/ARE/HO-1 signaling pathway, leading to cellular protection.

A fuel-cell reactor for the direct synthesis of hydrogen peroxide alkaline solutions from H(2) and O(2).

The effects of the type of fuel-cell reactors (undivided or divided by cation- and anion-exchange membranes), alkaline electrolytes (LiOH, NaOH, KOH), vapor-grown carbon fiber (VGCF) cathode components (additives: none, activated carbon, Valcan XC72, Black Pearls 2000, Seast-6, and Ketjen Black), and the flow rates of anolyte (0, 1.5, 12 mL h(-1)) and catholyte (0, 12 mL h(-1)) on the formation of hydrogen peroxide were studied. A divided fuel-cell system, O(2) (g)|VGCF-XC72 cathode|2 M NaOH catholyte|cation-exchange membrane (Nafion-117)|Pt/XC72-VGCF anode|2 M NaOH anolyte at 12 mL h(-1) flow|H(2) (g), was effective for the selective formation of hydrogen peroxide, with 130 mA cm(-2) , a 2 M aqueous solution of H(2)O(2)/NaOH, and a current efficiency of 95 % at atmospheric pressure and 298 K. The current and formation rate gradually decreased over a long period of time. The cause of the slow decrease in electrocatalytic performance was revealed and the decrease was stopped by a flow of catholyte. Cyclic voltammetry studies at the VGCF-XC72 electrode indicated that fast diffusion of O(2) from the gas phase to the electrode, and quick desorption of hydrogen peroxide from the electrode to the electrolyte were essential for the efficient formation of solutions of H(2)O(2)/NaOH.

Triamcinolone acetonide-assisted pars plana vitrectomy improves residual posterior vitreous hyaloid removal: ultrastructural analysis of the inner limiting membrane.

OBJECTIVE: To determine whether triamcinolone acetonide (TA) can facilitate residual posterior vitreous hyaloid removal in pars plana vitrectomy (PPV), we examined the ultrastructure of inner limiting membrane (ILM) removed in TA-assisted PPV for diabetic macular edema (DME). PATIENTS AND METHODS: In this retrospective series of 38 eyes of 37 patients who underwent PPV and ILM removal for diffuse DME with posterior hyaloid attachment, 24 eyes underwent standard PPV without TA (control group), and 14 eyes underwent TA-assisted PPV (TA group). Excised ILMs during PPV were examined by transmission electron microscopy (control group, n = 20; TA group, n = 10) or scanning electron microscopy (control group, n = 4; TA group, n = 4). RESULTS: Transmission electron microscopy clearly demonstrated that the ratio of the posterior vitreous hyaloid remaining on ILM was significantly lower (P = 0.0187) in the TA group than in the control group and also that TA-assisted PPV successfully removed posterior hyaloid in five of seven eyes with TA granules remaining on the retinal surface even after surgical separation of the posterior vitreous. Scanning electron microscopy enabled spatial analysis of the residual posterior hyaloid on ILM, which appeared in a patchy fashion in the control group. CONCLUSIONS: TA-assisted PPV clearly demonstrated the residual posterior hyaloid on ILM and allowed more efficient removal of the posterior hyaloid than standard PPV.

Creation of a mixed poly(ethylene glycol) tethered-chain surface for preventing the nonspecific adsorption of proteins and peptides.

Using a heterotelechelic poly(ethylene glycol) (PEG) possessing a mercapto group at one end and an acetal group at the other end (acetal-PEG-SH), the authors constructed a reactive PEG tethered-chain surface on a surface plasmon sensor (SPR) gold chip for biosensing with high sensitivity. Nonspecific bovine serum albumin adsorption on the PEG tethered-chain surface was significantly influenced by the density of the PEG chain, and was almost completely suppressed by increasing the PEG density through the repetitive treatment of the chip surface with acetal-PEG-SH. The PEG density was increased even more by adding an underbrushed layer made of shorter-PEG-SH-chain molecules (2 kDa, hereafter 2k) to the surface made of longer-PEG-SH-chain molecules (5 kDa, hereafter 5k). SPR measurement then gave an estimate of the adsorption of a series of proteins with varying sizes and isoelectric points on the PEG chain surface having an underbrushed layer (PEG5k/2k surface). As compared to other SPR surfaces, viz., a commercial carboxymethyl dextran and conventional PEG5k tethered-chain surface without an underbrushed layer, the mixed PEG5k/2k surface showed almost complete inhibition of the nonspecific adsorption not only of high-molecular-weight proteins but also of low-molecular-weight peptides.

Cellular migration associated with macular hole: a new method for comprehensive bird's-eye analysis of the internal limiting membrane.

OBJECTIVE: To elucidate the pathogenesis of macular hole formation, focusing in particular on the possible role of cellular migration on the cortical vitreous and internal limiting membrane (ILM) around the macular hole. METHODS: To gain a comprehensive overview of the ILM excised in macular hole surgery (n = 36), the ILMs were carefully unfolded and spread out onto glass slides as continuous flat sheets that each contained a macular hole. The specimens were observed by light microscopy and transmission electron microscopy (n = 9), and the cellular distribution was analyzed by scanning electron microscopy in a quantitative manner (n = 27). Immunohistochemistry for glial fibrillary acidic protein and cytokeratin 18 was carried out for cellular characterization. Cellular proliferation was assessed by immunohistochemistry for proliferating cell nuclear antigen and Ki-67. RESULTS: Cellular migration was not apparent around the macular hole in the early stage of development of the macular hole (stage 2, 0 microm). As the macular hole passed through the later stages of development, cellular migration developed around the macular hole (stage 3, 84 microm) and the area of cellular migration gradually enlarged (stage 4, 420 microm). The immunophenotypic analysis showed that these cells were mainly glial fibrillary acidic protein-positive glial cells and cytokeratin 18-positive retinal pigment epithelial cells. The proliferating cell nuclear antigen and Ki-67 immunohistochemistry showed that some of these cells were proliferating on the ILM. CONCLUSIONS: Cellular migration on the ILM is not necessary for the initial formation of a macular break. Cellular migration developed after the macular break occurred, and the migration and proliferation increased gradually from the macular hole. CLINICAL RELEVANCE: This study provides a new method for understanding the ultrastructural analysis of the pathogenesis of the macular hole.

Ultrastructure of internal limiting membrane in myopic foveoschisis.

PURPOSE: To reveal the pathogenesis of myopic foveoschisis (MF). DESIGN: Clinicopathological report. METHODS: Internal limiting membranes (ILMs) were collected from ten patients with MF and five patients with idiopathic macular hole (IMH) as a control. Samples were subjected to transmission electron microscopic study. Characteristics of the ILM were compared between the two groups. RESULTS: Collagen fiber and cell debris were identified on the inner surface of ILM in seven eyes (70%) with MF, significantly more (P < .05) than found in IMH subjects (0%). More fibrous glial cells were likely to be found on the inner surface of ILM. No significant difference in fibroblast-like cell adhesion was observed. CONCLUSIONS: Collagen fiber and cellular component are suggested to play an important role in developing MF. ILM peeling may be essential for vitrectomy for MF.

Active control of methanol carbonylation selectivity over Au/carbon anode by electrochemical potential.

Electrochemical oxidative carbonylation of methanol was studied over Au supported carbon anode in CO. The major carbonylation products were dimethyl oxalate (DMO) and dimethyl carbonate (DMC). The minor oxidation products were dimethoxy methane (DMM) and methyl formate (MF) from methanol and CO(2). Influences of various reaction conditions were studied on carbonylation activities and selectivities. The selectivities to DMO and DMC can be controlled by the electrochemical potential. Electrocatalysis of Au/carbon anode was studied by cyclic voltammetry (CV), stoichiometric reactions among Au(3+), methanol, and CO, and UV-vis spectra. The Au/carbon anode was characterized by XRD, SEM, and BE images before and after the carbonylation. These experimental facts strongly suggest that transition of oxidation states of Au affects changing of the carbonylation selectivities to DMO and DMC. Au(0) is the active species for the selective DMO formation by direct electrochemical carbonylation at low potentials (<+1.2 V (Ag/AgCl)). On the other hand, Au(3+) is the active spices for the selective DMC formation by indirect electrochemical carbonylation through Au(3+)/Au(+) redox at high potentials (>+1.3 V).

The involvement of the rho-kinase pathway and its regulation in cytokine-induced collagen gel contraction by hyalocytes.

PURPOSE: To investigate the involvement of the Rho-kinase pathway in collagen gel contraction by hyalocytes. METHODS: An in vitro type I collagen gel contraction assay using cultured bovine hyalocytes was performed to evaluate the effect of PDGF-BB and TGF-beta2. The effect of both cytokines on the phosphorylation of myosin light chain (MLC) was analyzed by Western blot analysis. To confirm the involvement of the Rho-kinase pathway in the collagen gel contraction, the effects of Y27632, a specific Rho-kinase inhibitor were examined. The effect of hydroxyfasudil, another potent Rho-kinase inhibitor, was also evaluated. The expression of alpha-smooth muscle actin (alphaSMA) was analyzed by Western blot analysis to examine the myofibroblast-like transdifferentiation of the hyalocytes. RESULTS: Maximum collagen gel contraction was observed within 24 hours after treatment with PDGF-BB and much stronger contraction with TGF-beta2, whose effect was time dependent, at least up to 5 days. Although transient and maximum MLC phosphorylation by PDGF-BB was observed at approximately 4 hours after stimulation (180.8%, P <0.01), TGF-beta2-elicited MLC phosphorylation occurred in a time-dependent manner at least up to 24 hours (220.0%, P <0.01) and was maintained up to 5 days. Y27632 demonstrated significant inhibition of collagen gel contraction induced by both cytokines. Hydroxyfasudil dose-dependently (0.03-20.00 microM) prohibited the phosphorylation of MLC, and inhibited collagen gel contraction at a concentration corresponding to that which inhibited MLC phosphorylation. TGF-beta2, but not PDGF-BB, also caused myofibroblast-like transdifferentiation with alphaSMA overexpression, which was downregulated by hydroxyfasudil in part (P <0.01). CONCLUSIONS: The hyalocytes have a contractile property in the presence of PDGF-BB and TGF-beta2. Whereas PDGF-BB initiates collagen gel contraction by transient activation of the Rho-kinase pathway, sustained activation of the Rho-kinase pathway and myofibroblast-like transdifferentiation appears to be involved in the TGF-beta2-dependent contractile properties of hyalocytes.

Selectivity control of carbonylation of methanol to dimethyl oxalate and dimethyl carbonate over gold anode by electrochemical potential.

New and unique electrocatalysis of gold for the carbonylation of methanol to dimethyl oxalate (DMO) and dimethyl carbonate (DMC) was found. The selectivity to DMO and DMC could be controlled over gold anode by electrochemical potential, as you like. Drastic changes of gold electrocatalysis was due to changes of the oxidation state of gold, Au0 or Au3+.

Clearance of apoptotic photoreceptors: elimination of apoptotic debris into the subretinal space and macrophage-mediated phagocytosis via phosphatidylserine receptor and integrin alphavbeta3.

The effective phagocytotic clearance of apoptotic debris is fundamental to the maintenance of neural tissues during apoptosis. Retinal photoreceptors undergo apoptosis after retinal detachment. Although their induction phase of apoptosis has been well discussed, their phagocytotic process remains quite unclear. We herein demonstrate that apoptotic photoreceptors are selectively eliminated from their physiological localization, the outer nuclear layer, to the subretinal space, and then phagocytosed by monocyte-derived macrophages. This could be shown by an ultrastructural and immunophenotypic analysis. Moreover, in chimera mice expressing transgenic green fluorescent protein in bone marrow-derived cells, the local infiltration of macrophages could be detected after retinal detachment-induced photoreceptor apoptosis. The local injection of an antibody blocking the phosphatidylserine receptor (PSR) or a peptide (GRGDSP)-blocking integrin alphavbeta3 revealed that phagocytotic clearance involves the PSR as well as integrin alphavbeta3 in vivo. Importantly, the level of blockade obtained with these reagents was different. Although anti-PSR increased the frequency of apoptotic cells that fail to bind to macrophages, GRGDSP prevented the engulfment (but not the recognition) of apoptotic photoreceptor cells by macrophages. To our knowledge, this is the first report describing the mechanisms through which apoptotic photoreceptors are selectively eliminated via a directional process in the subretinal space.

Indocyanine green-assisted peeling of the epiretinal membrane in proliferative vitreoretinopathy.

BACKGROUND: We stained the internal limiting membrane of patients suffering from proliferative vitreoretinopathy with indocyanine green solution during proliferative vitreoretinopathy surgery to improve the visibility of the membranes, and thereby histopathologically confirmed the excised epiretinal membranes. METHODS: Three patients underwent a standard three-port pars plana vitrectomy with indocyanine green staining. After performing a subtotal vitrectomy we spread 0.5% indocyanine green solution, approximately 1 ml, on the retinal surface and peeled off the epiretinal membranes. RESULTS: The epiretinal membranes did not stain clearly, while the internal limiting membranes did stain clearly. We could therefore distinguish the epiretinal membranes from the retina. We cut the internal limiting membrane, grasped it, and peeled off the internal limiting membrane underlying the epiretinal membranes using vitreoretinal forceps. A histopathologic examination confirmed the presence of proliferative cells and an extracellular matrix underlying the internal limiting membranes. CONCLUSION: The technique for staining the epiretinal membranes in proliferative vitreoretinopathy using indocyanine green gives better visualization and allows surgeons to remove the epiretinal membranes more safely and effectively, as well as with less risk of retinal damage.