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José A C Broekaert

Publications and source records attributed to José A C Broekaert.

7 recordsLinked to original sources
PubMed2006

Structural characterization of beta-sheeted oligomers formed on the pathway of oxidative prion protein aggregation in vitro.

The pathology of transmissible spongiform encephalopathies (TSEs) is strongly associated with the structural conversion of the cellular prion protein (PrPC) into a misfolded isoform (PrPSc) that assembles into amyloid fibrils. Since increased levels of oxidative stress have been linked to prion diseases, we investigated the metal-induced oxidation of human PrP (90-231). A novel in vitro conversion assay based on aerobic incubation of PrP in the presence of elemental copper pellets at pH 5 was established, resulting in aggregation of highly beta-sheeted prion proteins. We show for the first time that two discrete oligomeric species of elongated shape, approx. 25 mers and 100 mers, are formed on the pathway of oxidative PrP aggregation in vitro, which are well characterized regarding shape and size using small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and electron microscopy (EM). Considering that small oligomers of highly similar size have recently been reported to show the highest specific infectivity within TSE-infected brain tissues of hamsters, the novel oligomers observed in this study are interesting candidates as agent causing neurodegenerative and/or self-propagating effects. Moreover, our results significantly strengthen the theory that oxidative stress might be an influence that leads to substantial structural conversions of PrP in vivo.

Amino Acid Sequence↗
PubMed2005

Direct analysis of Al2O3 powders by total reflection X-ray fluorescence spectrometry.

A direct analysis procedure for the determination of trace impurities of Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga in Al2O3 ceramic powders by total reflection X-ray fluorescence spectrometry (TXRF) is described. The powders were analysed in the form of slurries containing 1-10 mg mL(-1) of powder. The use of the procedure in the case of powders with differing grain size and for different slurry concentrations was investigated. Three different quantification possibilities were compared, namely the use of Al as a matrix component, the use of Fe as a trace element contained in the sample or of Co added in concentrations of 200 microg g(-1) as internal standard. The homogeneity of elemental distributions in sample layers deposited on the TXRF quartz carriers by evaporating 5 microL of the 10 mg mL(-1) slurries was studied by scanning the 4- to 5-mm-diameter spots of two samples by synchrotron radiation TXRF at Hasylab. For powders with differing graininess but mainly finer than about a few 10 microm, no systematic influence of the grain size on the accuracy of the determinations of Ca, V, Fe, Ni, Cu and Zn could be observed. The measurement precision, however, seemed to be limited by inhomogeneous distributions of the trace elements in the samples as testified by the synchrotron radiation TXRF scans. Detection limits of the developed TXRF procedure for Ca, V, Cr, Mn, Fe, Ni, Cu, Zn and Ga were found to be in the 0.3-7 microg g(-1) range and were shown to increase slightly with the grain size of the samples. Quantification using Al (matrix) as internal standard led to systematically higher values out of the accuracy required, whereas the other two approaches in all cases led to reliable results.

Aluminum Oxide↗
PubMed2004

Some trends in the development of microplasmas for spectrochemical analysis.

The development of microplasmas for spectrochemical analysis by optical methods is discussed. Recent achievements in miniaturization are highlighted, especially for three types of plasmas, namely high-frequency plasmas, dc-discharges and microwave plasmas. The potentials of each of these groups of plasmas as sources for atomic emission spectrometry are discussed. Literature citations and experiments indicate that the plasmas are also very useful as atom reservoirs for atomic absorption spectrometry. Methods of sampling, including feeding with gas chromatography effluents, the use of electrothermal vaporization, and the evolution of gaseous species (as shown for the case of Hg vapor), are discussed as prominent interfaces to make use of these sources for elemental analysis.

Electrodes↗
PubMed2002

Nonaqueous capillary electrophoresis with indirect electrochemical detection.

Nonaqueous capillary electrophoresis (NACE) which makes use of organic solvents in place of conventional aqueous electrophoresis buffers is gaining increasing importance among modern separation techniques. Recently, it has been shown that amperometric detection in conjunction with acetonitrile-based NACE offers an extended accessible potential range and an enhanced long-term stability of the amperometric responses generated at solid electrodes. The present contribution takes advantage of the latter aspect to develop reliable systems for NACE with indirect electrochemical detection (IED). In this context, several compounds such as (ferrocenylmethyl)trimethylammonium perchlorate, tris(1,10-phenanthroline)cobalt(III) perchlorate and bis(1,4,7-triazacyclononane)nickel(II) perchlorate were studied regarding their suitability to act as electroactive buffer additives for IED in NACE. The performance characteristics for the respective buffer systems were evaluated. Tetraalkylammonium perchlorates served as model compounds for the optimization of the NACE-IED system. Target analytes choline and acetylcholine could easily be separated and determined by means of NACE-IED. In the case of a buffer system containing 10(-4) M tris(1,10-phenanthroline)cobalt(III) perchlorate the limits of detection were 2.5 x 10(-7) M and 4.6 x 10(-7) M for choline and acetylcholine, respectively. With the elaborated analytical procedure choline could be determined in pharmaceutical preparations.

Acetonitriles↗