Abstract Single crystals of Eu 3 Ag 2 In 9 (I) and EuCu 2 Ge 2 (II) are grown from melts of the elements using In as a flux (Al 2 O 3 crucible in evacuated silica tubes, 1.
The identification of the rate-determining step (RDS) in the electrochemical CO/CO2 reduction to multi-carbon (C2+) products has been complicated by the deficiency of rigorous reaction kinetic data. This work describes an experimental analysis of the key reaction steps by exploring the effect of CO partial pressure on the activity of C2+ products. With the aid of a flow electrolyzer integrated with a gas diffusion electrode, the distinct reaction orders of CO and reaction mechanisms in forming different C2+ products were determined. Specifically, *CO dimerization is identified as the RDS for ethylene and ethanol production, as evidenced by the gradual transition of measured CO reaction order from second to zero as CO partial pressure increases from 0.05 to 1 atm. The formation of n-propanol is suggested to proceed via the *CO trimerization mechanism. The acetate generation mechanism might involve a critical step of *CO hydrogenation before C–C coupling. Kinetic studies reveal that product-specific active sites are responsible for activity and selectivity toward specific C2+ products over oxide-derived copper.
It is unknown why human corneal endothelium exhibits limited capacity to divide while the endothelia of other species, such as rabbit, divide in vivo at wounding and in culture. A potentially valuable source of information concerning why human endothelium has such a limited proliferative capacity lies in elucidating any differences in the molecular events governing the cell cycle of these two species. A recent study of the relative expression of cell cycle-associated proteins in donor corneas suggests that human corneal endothelial cells in vivo have not exited the cell cycle but are arrested in G1-phase. The purpose of the current study was to identify differences in cell cycle protein expression in human and rabbit endothelium that would explain the difference in their relative proliferative capacities. Specifically, the authors first ascertained the relative proliferative status of rabbit corneal endothelial cells in vivo. The expression and intracellular distribution of G1-phase regulatory proteins was then determined in both species, and the results were compared.Corneas from New Zealand white rabbits (weight range, 2 to 3 kg) and from human donors (age range, 6 months to 67 years) were fresh frozen, cryostat sectioned, and prepared for indirect immunofluorescence microscopy using an established protocol. The following monoclonal antibodies were localized in rabbit corneal endothelium only: cyclins D, E, A, and B1; protein kinase p34cdc2; and Ki67, a marker of actively cycling cells. Localization patterns for the following G1-phase regulatory proteins were compared in both human and rabbit corneal endothelia: the tumor suppressors, pRb, p53, and p16INK4, and the transcription factor, E2F. Reverse transcription-polymerase chain reaction studies were conducted to detect mRNA for Ki67 in human and rabbit corneal cells.Cyclins D, E, and A were localized in the cytoplasm of rabbit corneal endothelium, whereas cyclins B1 and p34cdc2 were detected in the nucleus. No Ki67 protein or mRNA expression was detected in the endothelium of either species. In human and rabbit endothelia, p53 and p16INK4 were localized to the cytoplasm, whereas pRb was detected in the nucleus. E2F exhibited a nuclear and a cytoplasmic localization in each species.The corneal endothelium of rabbits stained positively for cyclins D, E, and A and did not stain for Ki67, suggesting that, as in humans, rabbit corneal endothelium in vivo is arrested in G1-phase upstream from Ki67 synthesis. Cyclin E was located in the cytoplasm of rabbit cells, whereas it was found in the nucleus in human endothelium. The apparent difference in cellular distribution of cyclin E in these two species may be significant because this cyclin is active during the G1-/S-phase transition. It is possible that in situ human and rabbit corneal endothelial cells are arrested at different points within G1-phase and/or that the difference in relative proliferative capacity exhibited by the corneal endothelium in these two species may be caused by differences in their relative ability to overcome G1-phase arrest.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
In this work, we have discovered the anisotropic near-zero thermal expansion (NZTE) behavior in a family of compounds REAgxGa4–x (RE = La–Nd, Sm, Eu, and Yb). The compounds adopt the CeAl2Ga2 structure type and were obtained as single crystals in high yield by metal flux growth technique using gallium as active flux. Temperature-dependent single crystal X-ray diffraction suggests that all the compounds exhibit near zero thermal expansion along c direction in the temperature range of 100–450 K. Temperature-dependent X-ray absorption near-edge spectroscopic study confirmed ZTE behavior is due to the geometrical features associated within the crystal structure. The anisotropic NZTE behavior was further established by anisotropic magnetic measurements on selected single crystals. The atomic displacement parameters, apparent bond lengths, bond angles, and structural distortion with respect to the temperature reveal that geometric features associated with the structural distortion cause the anisotropic NZTE along c-direction. The preliminary magnetic studies suggest all the compounds are paramagnetic at room temperature except LaAgGa3. Electrical resistivity study reveals that compounds from this series are metallic in nature.
This study reveals the synthesis of gadolinium telluride (Gd2Te3), a non-noble metal alloy with a two-dimensional (2D) morphology, for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). 2D Gd2Te3 exhibits promising electrocatalytic activity for OER with an onset potential of 1.335 V vs RHE (η = 105 mV) and an overpotential of 1.459 V vs RHE (η = 229 mV) at 10 mA/cm2, rivalling benchmark catalysts such as IrO2 and RuO2. Gd2Te3 exhibited a large turnover frequency of 3.7 s–1 (at η = 420 mV) and a mass activity of 18.69 Ag1– (at η = 470 mV). The chronoamperometric durability studies revealed a consistent current density (>20 mA cm–2) for 8 h at 1.65 V, reflecting good electrocatalytic stability of the material. The competitive OER activity of 2D Gd2Te3 can be attributed to better valence and conduction band edge alignment with water oxidation–reduction levels that is also corroborated by density functional theory (DFT) studies. 2D Gd2Te3 also exhibited good ORR performance exhibiting an onset potential of 0.72 V vs RHE at 0.1 mA cm–2. The number of electron transfers, calculated from H2O2 percentages between 0.30 and 0.50 V vs RHE, revealed that Gd2Te3 follows the 4e– ORR pathway with OH– as the major intermediate product. Using DFT calculations, we further elucidate the role and importance of Gd in stabilizing and destabilizing the intermediates that reduce the overpotentials for both the OER and ORR.
We have demonstrated engineering of the electronic band gap of the hybrid materials based on POMs (polyoxometalates), by controlling its structural complexity through variation in the conditions of synthesis. The pH- and temperature-dependent studies give a clear insight into how these experimental factors affect the overall hybrid structure and its properties. Our structural manipulations have been successful in effectively tuning the optical band gap and electronic band structure of this kind of hybrids, which can find many applications in the field of photovoltaic and semiconducting devices. We have also addressed a common crystallographic disorder observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based hybrid materials. Through a combination of crystallographic, spectroscopic, and theoretical analysis of four new POM-based hybrids synthesized with tactically varied reaction conditions, we trace the origin and nature of the disorder associated with it and the subtle local structural coordination involved in its core picture. While the crystallography yields a centrosymmetric structure with planar coordination of Si, our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral coordination with broken inversion symmetry, corroborated by first-principles calculations.
Since preceding decades, the demand for hydrogen production through water splitting has increased exponentially. In addition to highly active catalyst, we require our catalyst to be stable for several hours and days. We report herein a ternary chalcogenide-based compound, (CuPd) 17 Se 15 , with electrochemical stability for 30000 cycles towards hydrogen evolution reaction. In addition, this work provide a unique strategy of improving activity through the introduction of tensile strain by the substitution of small and low cost copper atoms (inverse strain effect) at the active site (larger size than Cu) of the compound. Pd atom being in +2 oxidation state adsorbs hydrogen very weakly and Se, in its elemental state, binds weakly to H * adsorbate. However, the presence of Pd modulates the electronic structure of Se to have ∆G H* close to zero and favors the progress of the reaction. Cu substitution further lowers ∆G H* , thus favoring the reaction. This unique synergistic effect between the two processes is accountable for better activity, high stability of 30000 cycles and significantly high TOF of 126.3 s -1 for (CuPd) 17 Se 15 . We deconvoluted the strain, ligand and ensemble effect to understand the factors behind the enhancement of the activity. Figure 1. (a) Linear sweep voltammogram of the Cu-substituted catalyst showing prolonged stability of the catalyst even after 30000 cycles and (b) comparison of the Tafel slope of the catalyst before and after the degradation test. (c) Schematic representation of different possible sites of Cu substitution and (d) comparison of the change in Gibbs free energy of adsorption of H* before and after Cu substitution . Figure 1
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