Model Building of Metal Oxide Surfaces and Vibronic Coupling Density as a Reactivity Index: Regioselectivity of CO2_2 Adsorption on Ag-loaded Ga2_2O3_3

The step-by-step hydrogen-terminated (SSHT) model is proposed as a model for the surfaces of metal oxides. Using this model, it is found that the vibronic coupling density (VCD) can be employed as a reactivity index for surface reactions. As an example, the regioselectivity of CO$_2$ adsorption on the Ag-loaded Ga$_2$O$_3$ photocatalyst surface is investigated based on VCD analysis. The cluster model constructed by the SSHT approach reasonably reflects the electronic structures of the Ga$_2$O$_3$ surface. The geometry of CO$_2$ adsorbed on the Ag-loaded Ga$_2$O$_3$ cluster has a bent structure, which is favorable for its photocatalytic reduction to CO.Comment: 18 pages, 11 figure

Mg-doped SrTiO₃ photocatalyst with Ag-Co cocatalyst for enhanced selective conversion of CO₂ to CO using H₂O as the electron donor

Photocatalytic conversion of CO₂ by H₂O is a promising method for solving energy and environmental problems. In this context, efficient photocatalysts that facilitate the selective conversion of CO₂ to the value-added chemical CO are essential. In this study, for the first time in the literature, we used an Mg-doped SrTiO₃ photocatalyst (Mg–SrTiO₃) for the photocatalytic conversion of CO₂ to CO using H₂O as the electron donor under monochromatic UV-light irradiation at 365 nm. Compared to pristine SrTiO₃, Mg–SrTiO₃, which was prepared via a flux method, exhibited dramatically enhanced conversion of CO₂ to CO in the presence of an Ag–Co cocatalyst. Moreover, the selectivity toward CO evolution was >99%, which indicates suppression of the unnecessary and competitive H₂ evolution. Scanning electron microscopy of Mg–SrTiO₃ revealed edge-shaved cubic particles, which were correlated to the anisotropic distribution of photogenerated electrons and holes and the consequent enhancement of photocatalytic activity. Furthermore, the Mg-doping temperature and amount used to prepare Mg–SrTiO₃ influenced the substitution of Ti⁴⁺ sites by Mg²⁺ in the bulk of SrTiO₃, thereby affecting the CO evolution. The apparent quantum efficiency of optimal Mg–SrTiO₃ in the photocatalytic conversion of CO₂ was determined to be 0.05%

Persistent Synapse Loss Induced by Repetitive LTD in Developing Rat Hippocampal Neurons

Synaptic pruning is a physiological event that eliminates excessive or inappropriate synapses to form proper synaptic connections during development of neurons. Appropriate synaptic pruning is required for normal neural development. However, the mechanism of synaptic pruning is not fully understood. Strength of synaptic activity under competitive circumstances is thought to act as a selective force for synaptic pruning. Long-term depression (LTD) is a synaptic plasticity showing persistent decreased synaptic efficacy, which is accompanied by morphological changes of dendritic spines including transient retraction. Repetitive induction of LTD has been shown to cause persistent loss of synapses in mature neurons. Here, we show that multiple, but not single, induction of LTD caused a persistent reduction in the number of dendritic synapses in cultured rat developing hippocampal neurons. When LTD was induced in 14 days in vitro cultures by application of (RS)-3,5-dihydroxyphenylglycine (DHPG), a group I metabotropic glutamate receptor (mGluR) agonist, and repeated three times with a one day interval, there was a significant decrease in the number of dendritic synapses. This effect continued up to at least two weeks after the triple LTD induction. The persistent reduction in synapse number occurred in the proximal dendrites, but not the distal dendrites, and was prevented by simultaneous application of the group I/II mGluR antagonist (S)-a-methyl-4-carboxyphenylglycine (MCPG). In conclusion, we found that repetitive LTD induction in developing neurons elicits synaptic pruning and contributes to activity-dependent regulation of synapse number in rat hippocampal neurons

Sugar-Recognizing Ubiquitin Ligases: Action Mechanisms and Physiology

F-box proteins, the substrate recognition subunits of SKP1–CUL1–F-box protein (SCF) E3 ubiquitin ligase complexes, play crucial roles in various cellular events mediated by ubiquitination. Several sugar-recognizing F-box proteins exist in both mammalian and plant cells. Although glycoproteins generally reside outside of cells, or in organelles of the secretory pathway, these lectin-type F-box proteins reside in the nucleocytoplasmic compartment. Mammalian sugar-recognizing F-box proteins commonly bind to the innermost position of N-glycans through a unique small hydrophobic pocket in their loops. Two cytosolic F-box proteins, Fbs1 and Fbs2, recognize high-mannose glycans synthesized in the ER, and SCFFbs1 and SCFFbs2 ubiquitinate excess unassembled or misfolded glycoproteins in the ERAD pathway by recognizing the innermost glycans, which serve as signals for aberrant proteins. On the other hand, endomembrane-bound Fbs3 recognizes complex glycans as well as high-mannose glycans, and SCFFbs3 ubiquitinates exposed glycoproteins in damaged lysosomes fated for elimination by selective autophagy. Plants express stress-inducible lectin-type F-box proteins recognizing a wider range of N- and O-glycans, suggesting that the roles of mammalian and plant lectin-type F-box proteins have diverged over the course of evolution to recognize species-specific targets with distinct functions. These sugar-recognizing F-box proteins interpret glycans in the cytosol as markers of unwanted proteins and organelles, and degrade them via the proteasome or autophagy

Visible-light-assisted selective catalytic reduction of NO with NH[3] on porphyrin derivative-modified TiO[2] photocatalysts

Accepted 16 Sep 2014.Porphyrin-derivative-modified TiO[2] photocatalysts showed high photocatalytic activity for the selective catalytic reduction of NO with NH[3] in the presence of O[2] under visible-light irradiation. Tetra(p-carboxyphenyl)porphyrin (TCPP) was the most effective photosensitizer among the five porphyrin derivatives investigated. NO conversion and N[2] selectivity of 79.0% and 100%, respectively, were achieved at a gas hourly space velocity of 50 000 h[−1]. UV–Vis and photoluminescence spectroscopies revealed the presence of two species of TCPP on the TiO2surface; one was a TCPP monomer and the other was an H-aggregate of the TCPP molecules. It was concluded that the TCPP monomer is an active species for the photo-assisted selective catalytic reduction (photo-SCR). Moreover, an increase in the fraction of H-aggregates with increasing TCPP loading amount resulted in a decrease in the photocatalytic activity of the photo-SCR

Role of Catalyst Support and Regioselectivity of Molecular Adsorption on a Metal Oxide Surface: NO Reduction on Cu/{\gamma}-alumina

The role of catalyst support and regioselectivity of molecular adsorption on a metal oxide surface is investigated for the NO reduction on a Cu/{\gamma}-alumina heterogeneous catalyst. For the solid surface, computational models of the {\gamma}-alumina surface are constructed based on the Step-by-Step Hydrogen Termination (SSHT) approach. Dangling bonds, which appear by cutting the crystal structure of a model, are terminated stepwise with H atoms until the model has an appropriate energy gap. The obtained SSHT models exhibit the realistic infrared (IR) and ultraviolet-visible (UV/Vis) spectra. Vibronic coupling density (VCD), as a reactivity index, is employed to elucidate the regioselectivity of the Cu adsorption on the {\gamma}-alumina and that of the NO adsorption on the Cu/{\gamma}-alumina in place of the frontier orbital theory that could not provide clear results. We discovered that the highly dispersed Cu atoms are loaded on Lewis-basic O atoms, which is known as anchoring effect, located in the tetrahedral sites of the {\gamma}-alumina surface. The role of the {\gamma}-alumina support is to raise the frontier orbital of the Cu catalyst, which in turn gives rise to the electron back-donation from the Cu/{\gamma}-alumina to NO. In addition, the penetration of the VCD distribution of the Cu/{\gamma}-alumina into the {\gamma}-alumina support indicates that the excessive reaction energies dissipate into the support after the NO adsorption and reduction. In other words, the support plays the role of a heat bath. The NO reduction on the Cu/{\gamma}-alumina proceeds even in an oxidative atmosphere because the Cu-NO bond is strongly bounded compared to the Cu-O2 bond

Enhanced CO evolution for photocatalytic conversion of CO2 by H2O over Ca modified Ga2O3

高効率で二酸化炭素を再資源化する光触媒の合成に成功 --CO2を「ひかり」と「みず」でリサイクル--. 京都大学プレスリリース. 2020-10-14.Artificial photosynthesis is a desirable critical technology for the conversion of CO2 and H2O, which are abundant raw materials, into fuels and chemical feedstocks. Similar to plant photosynthesis, artificial photosynthesis can produce CO, CH3OH, CH4, and preferably higher hydrocarbons from CO2 using H2O as an electron donor and solar light. At present, only insufficient amounts of CO2-reduction products such as CO, CH3OH, and CH4 have been obtained using such a photocatalytic and photoelectrochemical conversion process. Here, we demonstrate that photocatalytic CO2 conversion with a Ag@Cr-decorated mixture of CaGa4O7-loaded Ga2O3 and the CaO photocatalyst leads to a satisfactory CO formation rate (>835 µmol h−1) and excellent selectivity toward CO evolution (95%), with O2 as the stoichiometric oxidation product of H2O. Our photocatalytic system can convert CO2 gas into CO at >1% CO2 conversion (>11531 ppm CO) at ambient temperatures and pressures

Dual Ag/Co cocatalyst synergism for the highly effective photocatalytic conversion of CO2 by H2O over Al-SrTiO3

金属ナノ粒子で光触媒のモチベーションを上げることに成功 --人工光合成で二酸化炭素(CO2)の再資源化の新展開--. 京都大学プレスリリース. 2021-03-11.Loading Ag and Co dual cocatalysts on Al-doped SrTiO3 (AgCo/Al-SrTiO3) led to a significantly improved CO-formation rate and extremely high selectivity toward CO evolution (99.8%) using H2O as an electron donor when irradiated with light at wavelengths above 300 nm. Furthermore, the CO-formation rate over AgCo/Al-SrTiO3 (52.7 μmol h−1) was a dozen times higher than that over Ag/Al-SrTiO3 (4.7 μmol h−1). The apparent quantum efficiency for CO evolution over AgCo/Al-SrTiO3 was about 0.03% when photoirradiated at a wavelength at 365 nm, with a CO-evolution selectivity of 98.6% (7.4 μmol h−1). The Ag and Co cocatalysts were found to function as reduction and oxidation sites for promoting the generation of CO and O2, respectively, on the Al-SrTiO3 surface

The Structure of the Mammalian 20S Proteasome at 2.75 Å Resolution

AbstractThe 20S proteasome is the catalytic portion of the 26S proteasome. Constitutively expressed mammalian 20S proteasomes have three active subunits, β1, β2, and β5, which are replaced in the immunoproteasome by interferon-γ-inducible subunits β1i, β2i, and β5i, respectively. Here we determined the crystal structure of the bovine 20S proteasome at 2.75 Å resolution. The structures of α2, β1, β5, β6, and β7 subunits of the bovine enzyme were different from the yeast enzyme but enabled the bovine proteasome to accommodate either the constitutive or the inducible subunits. A novel N-terminal nucleophile hydrolase activity was proposed for the β7 subunit. We also determined the site of the nuclear localization signals in the molecule. A model of the immunoproteasome was predicted from this constitutive structure

Imparting CO₂ reduction selectivity to ZnGa₂O₄ photocatalysts by crystallization from hetero nano assembly of amorphous-like metal hydroxides

Imparting an enhanced CO₂ reduction selectivity to ZnGa₂O₄ photocatalysts has been demonstrated by controlled crystallization from interdispersed nanoparticles of zinc and gallium hydroxides. The hydroxide precursor in which Zn(II) and Ga(III) are homogeneously interdispersed was prepared through an epoxide-driven sol–gel reaction. ZnGa₂O₄ obtained by a heat-treatment exhibits a higher surface basicity and an enhanced affinity for CO₂ molecules than previously-reported standard ZnGa₂O₄. The enhanced affinity for CO₂ molecules of the resultant ZnGa₂O₄ leads to highly-selective CO evolution in CO₂ photo-reduction with H₂O reductants. The present scheme is promising to achieve desirable surface chemistry on metal oxide photocatalysts