Determination of the surface coverage of Re/Al2O3 catalysts by ion scattering spectroscopy and low‐temperature CO adsorption

The surface coverage of a series of rhenia–alumina catalysts prepared by equilibrium adsorption was determined by low‐temperature CO adsorption. The results show a linear increase in the coverage of the Re oxide on the alumina support up to 24% with increasing Re loading from 0 to ca. 5.6 wt%. This is consistent with a uniform build‐up of the surface species. The coverage values measured by this method agreed very well with those obtained by ion scattering spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of the preparation method on the surface coverage of Mo/Al2O3 catalysts

Two series of Mo/Al₂O₃ catalysts were prepared by equilibrium adsorption and incipient wetness impregnation methods. The effect of preparation method on the surface coverages of the calcined catalysts was investigated by the combined use of CO₂ chemisorption, low temperature CO adsorption and ion scattering spectroscopy (ISS). For a given Mo loading, the CO₂ and CO adsorption results showed little difference between the two preparation methods. As previously noted, the CO₂ chemisorption method overestimated the Mo surface coverage. In contrast to the adsorption methods, the ISS technique gave different Mo surface coverage values for a given Mo content of the two series of catalysts. This apparent discrepancy was attributed to different repartition of the Mo phase between the internal and external surfaces which can only be detected by ISS. This interpretation is supported by the observed agreement between the coverage values measured from ISS and low temperature CO adsorption for presumably uniform catalysts obtained by the equilibrium adsorption method.     

Direct TLC-MALDI coupling using a hybrid plate

A new TLC-MALDI direct coupling method which recovers approximately 100% of the analyte is presented. The method makes use of a hybrid TLC-MALDI plate in which a silica layer and a MALDI layer are configured adjacently on a common backing. After TLC separation, the plate is rotated 90 degrees and the separated analyte spots are eluted from the silica layer to the MALDI layer via capillary action of the MALDI layer. Signal-to-noise ratios are significantly improved over previously reported coupling methods. Low-femtomole detection limits have been demonstrated for small cyclic peptides, which are comparable to detection limits for standard MALDI measurements.     

Quantification of immunoreactive viral influenza proteins by immunoaffinity capture and isotope-dilution liquid chromatography-tandem mass spectrometry

An immunocapture isotope dilution mass spectrometry (IC-IDMS) method was developed to quantify antibody-bound influenza hemagglutinins (HA) in trivalent influenza vaccines (TIV). Currently, regulatory potency requirements for TIV require HA quantification based on the single radial immunodiffusion (SRID) assay, which is time-consuming, laborious, and requires production of large quantities of reagents globally. In IC-IDMS, antiserum to the HA of interest captured viral proteins that were in the correct conformation to be recognized by the antibodies. The captured proteins were digested, and evolutionarily conserved tryptic peptides were quantified using isotope-dilution liquid chromatography-tandem mass spectrometry. IC-IDMS relies on antibody-antigen binding similar to SRID but incorporates the accuracy and precision of IDMS. Polyclonal antibodies (pAb-H3) prepared by injection of sheep with purified H3 HA captured 82.9% (55.26 fmol/μL) of the total H3 HA (66.69 fmol/μL) from the commercial TIV and 93.6% (57.23 fmol/μL) of the total H3 HA (61.14 fmol/μL) in purified virus. While other HA (H1, B), neuraminidase (N1, N2, NB), viral matrix proteins, and nucleoproteins were also captured by this antiserum, our results were not affected due to the specificity of the mass spectrometer. IC-IDMS is an accurate, precise, sensitive, and selective method to measure antibody-bound HA in purified virus and commercial vaccines.     

Aggregation in Natural Language Generation

The content of real‐world databases, knowledge bases, database models, and formal specifications is often highly redundant and needs to be aggregated before these representations can be successfully paraphrased into natural language. To generate natural language from these representations, a number of processes must be carried out, one of which is sentence planning where the task of aggregation is carried out. Aggregation, which has been called ellipsis or coordination in Linguistics, is the process that removes redundancies during generation of a natural language discourse, without losing any information.
The article describes a set of corpus studies that focus on aggregation, provides a set of aggregation rules, and finally, shows how these rules are implemented in a couple of prototype systems. We develop further the concept of aggregation and discuss it in connection with the growing literature on the subject. This work offers a new tool for the sentence planning phase of natural language generation systems.     

Surface structure and metathesis activity of photoreduced allyl‐based Mo/SiO2 catalysts

XPS and metathesis activity studies were performed on oxidic allylbased Mo/SiO₂ catalysts (0.5 wt% Mo) and the oxidic catalyst following photoreduction to various extents. XPS results and average oxidation state measurements from the amount of CO₂ formed during photoreduction, indicated that controlled photoreduction of the oxidic catalyst, in CO atmosphere, produces a mixture of Mo⁶⁺ and Mo⁴⁺ oxidation states with Mo⁴⁺ in abundances ranging from 0 to 100%. Propene metathesis activity studies were performed on the oxidic and photoreduced allylbased Mo/SiO₂ catalysts. The results indicated that metathesis activity appears on photoreduction and increases linearly with increasing abundance of Mo⁴⁺ present on the catalyst. The linear relationship between the % propene conversion and the % Mo⁴⁺ present on the catalyst is consistent with the proposed uniformity of the Mo species and with the hypothesis that the active site (or active site precursor) is associated with Mo⁴⁺.     

Quantitative characterization of a polystyrene/poly(alpha-methylstyrene) blend by MALDI mass spectrometry and size-exclusion chromatography

The use of coupled size-exclusion chromatography and MALDI mass spectrometry for quantitative measurement of the composition of technical polymer blends at the molecular level is described. The method is illustrated with a model binary blend consisting of polystyrene and poly(alpha-methylstyrene), both polymers having similar molecular weights and polydispersities. The proposed MALDI data treatment allows determination of the chemical composition of the blend, the molecular weights of the constituents, and the distributions of the homopolymers.