Defect-induced anisotropic surface reactivity and ion transfer processes of anatase nanoparticles

Surface reactivity and ion transfer processes of anatase TiO₂ nanocrystals were studied using lithium bis(trifluoromethylsulfone)imide (LiTFSI) as a probing molecule. Analysis of synthesized anatase TiO₂ by electron microscopy reveals aggregated nanoparticles (average size ~8 nm) with significant defects (holes and cracks). With the introduction of LiTFSI salt, the Li⁺-adsorption propensity towards the surface along the anatase (100) step edge plane is evident in both x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analysis. Ab initio molecular dynamics (AIMD) analysis corroborates the site-preferential interaction of Li⁺ cations with oxygen vacancies and the thermodynamically favorable transport through the (100) step edge plane. Using ⁷Li nuclear magnetic resonance (NMR) chemical shift and relaxometry measurements, the presence of Li⁺ cations near the interface between TiO₂ and the bulk LiTFSI phase was identified, and subsequent diffusion properties were analyzed. The lower activation energy derived from NMR analysis reveals enhanced mobility of Li⁺ cations along the surface, in good agreement with AIMD calculations. On the other hand, the TFSI^– anion interaction with defect sites leads to CF₃ bond dissociation and subsequent generation of carbonyl fluoride-type species. The multimodal spectroscopic analysis including NMR, electron paramagnetic resonance (EPR), and x-ray photoelectron spectroscopy (XPS) confirms the decomposition of TFSI^– anions near the anatase surface. The reaction mechanism and electronic structure of interfacial constituents were simulated using AIMD calculations. Overall, this work demonstrates the role of defects at the anatase nanoparticle surface on charge transfer and interfacial reaction processes.     

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.     

Conversion of Methane into Methanol and Ethanol over Nickel Oxide on Ceria–Zirconia Catalysts in a Single Reactor

The conversion of methane into alcohols under moderate reaction conditions is a promising technology for converting stranded methane reserves into liquids that can be transported in pipelines and upgraded to value‐added chemicals. We demonstrate that a catalyst consisting of small nickel oxide clusters supported on ceria–zirconia (NiO/CZ) can convert methane to methanol and ethanol in a single, steady‐state process at 723 K using O₂ as an abundantly available oxidant. The presence of steam is required to obtain alcohols rather than CO₂ as the product of catalytic combustion. The unusual activity of this catalyst is attributed to the synergy between the small Lewis acidic NiO clusters and the redox‐active CZ support, which also stabilizes the small NiO clusters.     

Complexation of metals with piperazine-containing azamacrocyclic fluorophores

Azamacrocyclic fluorophores containing piperazine units were synthesized using sequential rhodium-catalyzed regioselective hydroformylation-reductive amination. A piperazine unit is introduced into the macrocycles to act simultaneously as electron donor and binding site. The macrocycles chelate divalent cations, either Zn2+ or Co2+, which considerably enhanced fluorescence. Complexation with Zn2+ was additionally confirmed by NMR.     

Creation of variable concentrations of defects on TiO2(110) using low-density electron beams

Low density (˜μA/cm²) 0.48 and 1.0 keV electron beams have been used to create surface defects on a TiO₂(110) surface. These electron-beam induced defects were examined primarily by X-ray photoelectron spectroscopy (XPS) with supporting ultraviolet photoemission spectroscopy (UPS). Glancing and normal emission XPS spectra of nearly defect-free surfaces revealed that Ti atoms on the surface were similar to the bulk Ti, while some surface oxygen atoms were different from the bulk oxygen. XPS of Ti 2p_3/2 was used to quantify the defect concentration and to examine the defect electronic structure. Based on our calculation of defect concentrations and the comparison of our results with results and models from the literature, we conclude that oxygen vacancies induced by electron beams in the current study are mostly from the bridging oxygen sites, in agreement with the previous work. A range of defect concentrations with similar electronic structure, mainly composed of Ti³⁺, have been induced by low-density electron beams. Beam energy and exposure were the experimental variables. The rates of defect formation at low beam exposure were beam-energy dependent, with a faster growth rate at 0.48 keV than at 1.0 keV. These defects were similar to those by thermal annealing in vacuum, but a higher concentration of defects could be obtained with longer beam exposure. However, the e-beam induced defects were different from those produced by Ar⁺ ion bombardment since both this and previous studies have found defects produced by Ar⁺ ion bombardment to be complex, with a variety of different local environments where oxygen and titanium surface atoms coexist.     

PCA-Based Analysis of X-Ray-Excited Auger Spectra from Non-ordered Ag(110)

Principal-components analysis (PCA) followed by factor analysis enables one to decompose the structure of Auger lines originating from large effects such as energy shifts induced by chemical effects. The aim of the present contribution is to show that PCA can also be effectively used for detection of composed structure in a set of Auger spectra even if the observed changes in line shape are very subtle. The analysed set of X-ray-excited MNN Auger spectra from Ag(110) shows a clear correlation between peak shifts and peak widths. This correlation can be explained as a result of the composed structure of the recorded Auger lines. It is suggested that the resultant Auger lines may consist of a number of constituents, each referred to Ag atoms differing in the value of their co-ordination number.     

Structural Insights into the Incorporation of the Mo Cofactor into Sulfite Oxidase from Site‐Directed Spin Labeling

Mononuclear molybdoenzymes catalyze a broad range of redox reactions and are highly conserved in all kingdoms of life. This study addresses the question of how the Mo cofactor (Moco) is incorporated into the apo form of human sulfite oxidase (hSO) by using site‐directed spin labeling to determine intramolecular distances in the nanometer range. Comparative measurements of the holo and apo forms of hSO enabled the localization of the corresponding structural changes, which are localized to a short loop (residues 263–273) of the Moco‐containing domain. A flap‐like movement of the loop provides access to the Moco binding‐pocket in the apo form of the protein and explains the earlier studies on the in vitro reconstitution of apo‐hSO with Moco. Remarkably, the loop motif can be found in a variety of structurally similar molybdoenzymes among various organisms, thus suggesting a common mechanism of Moco incorporation.