The CrOx/SiO2/Si(100) catalyst – a surface science approach to supported olefin polymerization catalysis

Depositing catalytically active particles onto flat, thin and oxidic support forms an attractive way to make supported catalyst suitable for surface science characterization. Here we show how this approach has been applied to the Phillips (CrO_x/SiO₂) ethylene polymerization catalyst. The model catalyst shows a respectable polymerization activity after thermal activation in dry air (calcination). Combining the molecular information from X‐ray Photoelectron Spectroscopy (XPS) and Secondary Ion Mass Spectrometry (SIMS) we can draw a molecular level of the activated catalyst that features exclusively monochromate species, which are anchored to the silica support via ester bonds with the surface silanol groups. These surface chromates form the active polymerization site upon contact with ethylene. Upon increasing calcination temperature we observe a decrease in chromium coverage as some of the surface chromate desorbs from the silica surface. Nevertheless, we also find an increasing polymerization activity of the model catalyst. We attribute this increase in catalytic activity to the isolation of the supported chromium, which prevents dimerization of the coordinatively unsaturated active site. Diluting the amount of chromium to 200 Cr‐atoms/nm² of silica surface enables the visualisation of polyethylene produced by a single active site.     

Observation of shish crystal growth into nondeformed melts

Thin films of isotactic polystyrene (iPS) were deformed on a carbon supported TEM grid at temperatures between 210 °C and 240 °C. The elongation of the supercooled polymer melt films is localized in a deformation zone due to the formation of cracks within the brittle carbon support film, whereas the adjoining areas stay in a relaxed state. Since the nucleation of fibrous (“shish”) crystals needs an orientation mechanism to align the molecular chains, their origin is located in the deformation zone. It is shown that the subsequent growth of the shish crystal can propagate into the relaxed melt although it has to surmount the adhesion to the carbon substrate. From these results the conclusion is drawn that the shish crystal growth can be an autocatalytic process, which induces a self‐orientation of the molecules in the growth front of the crystal tip and does not necessarily need an external flow field. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1183–1187, 2000     

Pd@SnO2 and SnO2@Pd Core@Shell Nanocomposite Sensors

Pd@SnO₂ and SnO₂@Pd core@shell nanocomposites are prepared via a microemulsion approach. Both nanocomposites exhibit high‐surface, porous matrices of SnO₂ shells (>150 m² g^?1) with very small SnO₂ crystallites (<10 nm) and palladium (Pd) nanoparticles (<10 nm) that are uniformly distributed in the porous SnO₂ matrix. Although similar by first sight, Pd@SnO₂ and SnO₂@Pd are significantly different in view of their structure with Pd inside or outside the SnO₂ shell and in view of their sensor performance. As SMOX‐based sensors (SMOX: semiconducting metal oxide), both nanocomposites show a very good sensor performance for the detection of CO and H₂. Especially, the Pd@SnO₂ core@shell nanocomposite is unique and shows a fast response time (τ₉₀ < 30 s) and a very good response at low temperature (<250 °C), especially under humid‐air conditions. Extraordinarily high sensor signals are observed when exposing the Pd@SnO₂ nanocomposite to CO in humid air. Under these conditions, even commercial sensors (Figaro TGS 2442, Applied Sensor MLC, E2V MICS 5521) are outperformed.     

New screening method for basic compounds in urine by on-line extraction-high-performance liquid chromatography with photodiode-array detection

A fully automated, qualitative screening HPLC method for the identification of basic compounds in urine has been developed. A 1-ml volume of urine was extracted by on-line extraction and separated on two coupled strong cation-exchange (SCX) columns (2 x LunaSCX, 150 mm x 4.6 mm, 5 microm) under isocratic conditions. The mobile phase consisted of a mixture of potassium dihydrogenphosphate buffer (pH 2.3) and acetonitrile. The use of photodiode-array detection (DAD, lambda = 190-800 nm) gave access to a library of approximately 2600 toxicologically relevant compounds. The validated method is reliable, simple and in addition successfully proven with the analysis of real biological specimen for the routine use.     

Application of proteomics to hordein screening in the malting process

This study was undertaken to investigate the effect of the malting process on hordein composition. For this purpose, combination of sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and the method of isotopic peptides labeling iTRAQ was used. Barley proteins are essential components determining the quality of both malt and beer. Since hordeins represent the most abundant proteins accounting for about 40-50% of total protein fraction of mature barley grain, our research was focused on them. In this respect, the proteins of interest were extracted from milled samples of barley grain, germinated barley grain (samples collected at different time intervals), green malt and malt, respectively. Particular hordein extracts were firstly fractionated via SDS- PAGE, which was used as a relatively rapid and reliable technique providing information about hordein profile of analyzed samples. Then, separated proteins were in-gel digested and resulting peptides were measured by mass spectrometry. In addition, the chosen proteins, after in-gel digestion, were subjected to the iTRAQ method and the screening of proteins during malting process was evaluated. Our results have revealed that most of the hordein components present in the barley grain can be found in all stages of the malting process as well as in the final malt. The amount of hordeins decreases during the malting process; in the case of C hordein, the protein decrease is approximately 65%. On the other hand, significant degradation of D hordein was detected. The suggested procedure can be used to follow the development of the hordein profile during germination, which is of great technological importance in beer production.