Capturing the Genesis of an Active Fischer–Tropsch Synthesis Catalyst with Operando X‐ray Nanospectroscopy

A state‐of‐the‐art operando spectroscopic technique is applied to Co/TiO₂ catalysts, which account for nearly half of the world's transportation fuels produced by Fischer–Tropsch catalysis. This allows determination of, at a spatial resolution of approximately 50 nm, the interdependence of formed hydrocarbon species in the inorganic catalyst. Observed trends show intra‐ and interparticular heterogeneities previously believed not to occur in particles under 200 μm. These heterogeneities are strongly dependent on changes in H₂/CO ratio, but also on changes thereby induced on the Co and Ti valence states. We have captured the genesis of an active FTS particle over its propagation to steady‐state operation, in which microgradients lead to the gradual saturation of the Co/TiO₂ catalyst surface with long chain hydrocarbons (i.e., organic film formation).     

Site-selective EXAFS in mixed-valence compounds using high-resolution fluorescence detection: a study of iron in Prussian Blue

A quantitative analysis is presented for the site-selective Fe K-edge absorption spectra of Prussian Blue: Fe(4)[Fe(CN)(6)](3) x xH(2)O (x = 14-16). The site-selective spectra were recorded using high-resolution fluorescence detection of the K beta emission from a polycrystalline sample. The K beta fluorescence lines arising from the high-spin and low-spin sites are shifted in energy. Since the emission features partially overlap, fluorescence-detected absorption spectra using different emission energies represent different linear combinations of the pure high-spin and low-spin EXAFS. A numerical method was used to extract the individual site EXAFS spectra from the experimental data. The analysis yields a range of solutions. A unique solution can be obtained if homovalent model compounds are used to simulate the K beta fluorescence emission from the two Fe sites in Prussian Blue. EXAFS analysis of the range of spectra obtained in the numerical method yields almost identical interatomic distances for the different spectra while the Debye-Waller factors vary considerably. The distances obtained in the EXAFS fit correspond to the crystallographic distances.     

Inhibition of peroxynitrite-induced nitration of tyrosine by glutathione in the presence of carbon dioxide through both radical repair and peroxynitrate formation

Peroxynitrite (ONOO-/ONOOH) is assumed to react preferentially with carbon dioxide in vivo to produce nitrogen dioxide (NO2*) and trioxocarbonate(1-) (CO3*-) radicals. We have studied the mechanism by which glutathione (GSH) inhibits the NO2*/CO3*--mediated formation of 3-nitrotyrosine. We found that even low concentrations of GSH strongly inhibit peroxynitrite-dependent tyrosine consumption (IC50 = 660 microM) as well as 3-nitrotyrosine formation (IC50) = 265 microM). From the determination of the level of oxygen produced or consumed under various initial conditions, it is inferred that GSH inhibits peroxynitrite-induced tyrosine consumption by re-reducing (repairing) the intermediate tyrosyl radicals. An additional protective pathway is mediated by the glutathiyl radical (GS*) through reduction of dioxygen to superoxide (O2*-) and reaction with NO2* to form peroxynitrate (O2NOOH/O2NOO-), which is largely unreactive towards tyrosine. Thus, GSH is highly effective in protecting tyrosine against an attack by peroxynitrite in the presence of CO2. Consequently, formation of 3-nitrotyrosine by freely diffusing NO2* radicals is highly unlikely at physiological levels of GSH.     

Synthesis of a chiral steroid ring D precursor starting from carvone

A chiral five-membered, silyl enol ether containing, steroid ring D precursor has been synthesized from carvone. This silyl enol ether has been applied in the synthesis of a chiral C17 functionalized steroid skeleton using the addition of a carbocation, generated with ZnBr₂ from a Torgov reagent, followed by cyclization of the adduct by treatment with acid.     

Selective interface detection: mapping binding site contacts in membrane proteins by NMR spectroscopy

Intermolecular contact surfaces are important regions where specific interactions mediate biological function. We introduce a new magic angle spinning solid state NMR technique, dubbed "selective interface detection spectroscopy" (SIDY). In this technique, 13C-attached protons (1Hlig) are dephased by 1H-13C REDOR. A spin diffusion period is then used to enhance long distance 1H-1H correlations, and the results are detected by a short period of cross polarization to the 13C isotope labels. This SIDY approach allows selective observation of the interface between 13C-labeled and unlabeled moieties. We have used SIDY to probe the ligand-protein binding surface between a uniformly isotopically labeled ligand cofactor, U-13C20-11-cis-retinal, and its binding site in rhodopsin (Rho), an unlabeled, membrane-embedded G-protein coupled receptor (GPCR). The observed 1HGPCR-13Clig correlations indicate multiple close contacts between the protein and the ionone ring of the ligand, in agreement with binding studies. The polyene tail of the ligand displays fewer strong correlations in the SIDY spectrum. Some correlations can be assigned to the protein side chains lining the ligand binding site, in agreement with the crystal structure.     

Bioactive Ca10(PO4)6(OH)2−TiO2 composite coating prepared by sol-gel process

The sol-gel prepared titania (TiO₂) has recently been demonstrated with a promising bioactivity [1]. It forms a chemical bond with the living bone in the body, although the bonding is not very strong. The present study is intended to improve the bone-bonding ability of the titania gel. The goal is achieved by impregnating the titania with hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂). The processing route includes the following steps: (1) the titania sol solution was prepared; (2) the solution was mixed with fine hydroxyapatite (HA) powders; (3) the mixture was used to produce a coating on a commercial pure titanium (c.p. Ti) or Ti6A14V plate by a dip coating technique; (4) the coating was fired at 400–600°C. The resulting coating is a composite consisting of hydroxyapatite embedded in the matrix of the titania gel. Such HA-TiO₂ composite coating is capable of inducing the hydroxyapatite precipitation from a simulated body fluid. When implanted in femurs of goat, the composite coating shows a bonding with bone. Its bone-bonding strength is twice as high as that of the pure titania gel coating. The results indicate that impregnating with hydroxyapatite is a promising way to increase the bioactivity of the titania gel.     

Determination of total mercury in workroom air by atomic absorption or x-ray fluorescence spectrometry after collection on carbon-loaded paper

The routine determination of total mercury in workroom air of an alkali chloride electrolysis plant equipped with mercury cells, is described. The procedure is based on atomic absorption spectrometry (a.a.s.) (cold vapour technique) or x-ray fluorescence spectrometry (x.r.f.s.) after collection on carbon-loaded paper fixed in a disposable Millipore filter holder. The lowest quantity of mercury that can be determined is 0.2 μg by a.a.s. and 2 μg by x.r.f.s. Samples taken in the plant gave a relative standard deviation of about 2 % for a.a.s. and 3 % for x.r.f.s.     

Coprecipitation as a means of separation in substoichiometric isotope dilution analysis

Chromium has been determined by isotope dilution in artificial standards and in standard alloys using the substoichiometric principle. As a substoichiometric reaction the reduction of Cr(VI) to Cr(III) was used, followed by separation of these species by coprecipitation of the trivalent chromium on a Ti(OH)₄ precipitate. For amounts smaller than 1 μg the standard method had to be modified owing to spontaneous reduction of hexavalent chromium in the solution. Interferences from other metals, if they occur, can be easily overcome. The method is simple and inexpensive.