Surface Chemistry and Interfacial Charge-Transfer Mechanisms in Photoinduced Oxygen Exchange at O2-TiO2 Interfaces

Regulation of CYLD activity and specificity by phosphorylation and ubiquitin-binding CAP-Gly domains

Non-degradative ubiquitin chains and phosphorylation events govern signaling responses by innate immune receptors. The deubiquitinase CYLD in complex with SPATA2 is recruited to receptor signaling complexes by the ubiquitin ligase LUBAC and regulates Met1- and Lys63-linked polyubiquitin and receptor signaling outcomes. Here, we investigate the molecular determinants of CYLD activity. We reveal that two CAP-Gly domains in CYLD are ubiquitin-binding domains and demonstrate a requirement of CAP-Gly3 for CYLD activity and regulation of immune receptor signaling. Moreover, we identify a phosphorylation switch outside of the catalytic USP domain, which activates CYLD toward Lys63-linked polyubiquitin. The phosphorylated residue Ser568 is a novel tumor necrosis factor (TNF)-regulated phosphorylation site in CYLD and works in concert with Ser418 to enable CYLD-mediated deubiquitination and immune receptor signaling. We propose that phosphorylated CYLD, together with SPATA2 and LUBAC, functions as a ubiquitin-editing complex that balances Lys63- and Met1-linked polyubiquitin at receptor signaling complexes to promote LUBAC signaling.

Structure and crystal phase transition effect of Sn doping on anatase TiO2 for dichloromethane decomposition

Efficient removal of chlorinated volatile organic compounds (CVOCs) has received great attention because of the considerable harm that they cause to the environment and to human health. Developing novel catalysts and exploring the catalytic activation and deconstruction mechanism of CVOCs molecule are always the focus in this field. Here, a set of Sn doped TiO₂ catalysts were investigated for the decomposition of dichloromethane (DCM). Rietveld refinement of the XRD patterns showed that Sn ions can uniformly disperse into TiO₂ and induce the crystal transition of anatase. Meanwhile, such decorating can induce an increase in specific surface area and affect the surface oxygen vacancy concentration of these samples, which have been demonstrated by N₂ adsorption and XPS, respectively. Catalytic performance tests indicated that the Sn_0.2Ti_0.8O₂ has the best activity for DCM decomposition, and a lower CH₃Cl selectivity than that of pure TiO₂. Computational results suggested the dominant surface (110) of rutile Sn_0.2Ti_0.8O₂ is more beneficial for the adsorption/dissociation of DCM molecule than that of anatase TiO₂ (101). That's because the anchoring of DCM to Sn sites and electron enrichment on the surface bridge oxygen atoms of rutile Sn_0.2Ti_0.8O₂ (110) can promote the nucleophilic substitution process for breaking of CCl bonds.

Optimization of the NO photooxidation and the role of relative humidity

Photocatalysis was recognised as a suitable process for the photoabatement of atmospheric pollutants. The photooxidation mechanism on TiO₂ has been widely studied. However, recent studies demonstrated that the very often-assumed photooxidation intermediated by the hydroxyl radical cannot explain all the experimental observations. Indeed, this study contributes for a new understanding of NO photooxidation. First, the adsorption equilibrium isotherms of NO, NO₂ and H₂O on the photocatalyst, Aeroxide^® P25 from Evonik Industries, were obtained. Also, the concentration of hydroxyl radicals was determined by photoluminescence. A comprehensive design of experiments was then followed; NO conversion and selectivity were obtained as a function of the relative humidity, irradiance, NO inlet concentration and residence time, following a response surface methodology (RSM). These results were then used to discuss the photooxidation mechanism of NO.

Catalytic role of bridging oxygens in TiO2 liquid phase photocatalytic reactions: analysis of H216O photooxidation on labeled Ti18O2

TiO₂ surface lattice oxygens are actively involved in the photocatalytic oxidation of water as demonstrated by isotopic tracing experiments with Ti¹⁸O₂.

Unraveling the photocatalytic mechanisms on TiO2 surfaces using the oxygen-18 isotopic label technique

During the last several decades TiO₂ photocatalytic oxidation using the molecular oxygen in air has emerged as a promising method for the degradation of recalcitrant organic pollutants and selective transformations of valuable organic chemicals. Despite extensive studies, the mechanisms of these photocatalytic reactions are still poorly understood due to their complexity. In this review, we will highlight how the oxygen-18 isotope labeling technique can be a powerful tool to elucidate complicated photocatalytic mechanisms taking place on the TiO₂ surface. To this end, the application of the oxygen-18 isotopic-labeling method to three representative photocatalytic reactions is discussed: (1) the photocatalytic hydroxylation of aromatics; (2) oxidative cleavage of aryl rings on the TiO₂ surface; and (3) photocatalytic decarboxylation of saturated carboxylic acids. The results show that the oxygen atoms of molecular oxygen can incorporate into the corresponding products in aqueous solution in all three of these reactions, but the detailed incorporation pathways are completely different in each case. For the hydroxylation process, the O atom in O₂ is shown to be incorporated through activation of O₂ by conduction band electrons. In the cleavage of aryl rings, O atoms are inserted into the aryl ring through the site-dependent coordination of reactants on the TiO₂ surface. A new pathway for the decarboxylation of saturated carboxylic acids with pyruvic acid as an intermediate is identified, and the O₂ is incorporated into the products through the further oxidation of pyruvic acid by active species from the activation of O₂ by conduction band electrons.

Catalytic role of TiO(2) terminal oxygen atoms in liquid-phase photocatalytic reactions: oxidation of aromatic compounds in anhydrous acetonitrile

On the basis of experiments carried out with controlled amounts of residual oxygen and water, or by using oxygen-isotope-labeled Ti(18) O2 as the photocatalyst, we demonstrate that (18) Os atoms behave as real catalytic species in the photo-oxidation of acetonitrile-dissolved aromatic compounds such as benzene, phenol, and benzaldehyde with TiO2 . The experimental evidence allows a terminal-oxygen indirect electron-transfer (TOIET) mechanism to be proposed, which is a new pathway that involves the trapping of free photogenerated valence-band holes at Os species and their incorporation into the reaction products, with simultaneous generation of oxygen vacancies at the TiO2 surface and their subsequent healing with oxygen atoms from either O2 or H2 O molecules that are dissolved in the liquid phase. According to the TOIET mechanism, the TiO2 surface is not considered to remain stable, but is continuously changing in the course of the photocatalytic reaction, challenging earlier interpretations of TiO2 photocatalytic phenomena.