AES investigations of plasma sprayed Al2O3 coatings on Ni

Summary The system of plasma sprayed Al₂O₃ on Ni substrates is investigated by means of AES/depth profiling. The influence of two process parameters — preoxidation procedure and spraying temperature — is examined. Rupture between substrate and ceramic layer occurs between a residual — or, in the case of excessive preoxidation, a superfluous — NiO layer on Ni, the thickness of the former depending on preoxidation conditions and the Al₂O₃ layer, the back side of which being partially covered with NiO. The thickness of this NiO layer increases up to about 1 m with the thickness of the initial NiO layer on the substrate, until this layer is about 1.3 m thick, and remains constant thereafter. The same dependence is observed for the width (0.1–1 m range) of the mixed oxide interface between the sprayed Al₂O₃ layer and the NiO layer below. These results represent the chemical contribution to adherence. Contrary to excessive preoxidation, an increase of the spraying temperature from 300°C to 500°C effects broader interfaces.This poster was awarded the First Prize in Poster Section C by the Deutscher Arbeitskreis für Spektroskopie (DASp)     

Influence of pH on formation and stability of phosphatidylcholine/phosphatidylserine coatings in fused-silica capillaries

The effect of pH on the formation and stability of phospholipid coatings in fused-silica capillaries in electrophoresis was investigated. A liposome solution consisting of 3 mM of 80:20 mol% phosphatidylcholine/phosphatidylserine (PC/PS) in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) buffer was used as coating material. The coating was prepared by a method described earlier and five steroids were used as neutral model analytes. First, the effect of pH of the coating solution on the formation and stability of phospholipid coatings was studied at pH 6.5-8.5. The pH of the background electrolyte (BGE) solution (HEPES) was either kept constant at pH 7.4 or made similar to the pH of the liposome coating solution. Results showed that attachment of the coating on the fused-silica wall mostly depends on the protonation of amines of the phospholipids and HEPES. The ability of the phospholipid coating to withstand changes in pH was then investigated by coating at pH 7.5 and separating steroids with acetic acid, 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), HEPES, or glycine BGE, adjusted to pH between 4.5 and 10.8. The results showed that with use of BGE solution at pH 10.8, the separation of steroids was not successful and the electroosmotic flow was high because of leakage of the phospholipid coating during preconditioning of the capillary with BGE solution. There was no phospholipid leakage with a BGE solution of pH 4.5, indicating that the protonated form of the functional groups of PS and HEPES participating in the attachment of the phospholipid coating to the capillary play an essential role in the success of the coating.     

Explorative data analysis of two-dimensional electrophoresis gels

Methods for classification of two-dimensional (2-DE) electrophoresis gels based on multivariate data analysis are demonstrated. Two-dimensional gels of ten wheat varieties are analyzed and it is demonstrated how to classify the wheat varieties in two qualities and a method for initial screening of gels is presented. First, an approach is demonstrated in which no prior knowledge of the separated proteins is used. Alignment of the gels followed by a simple transformation of data makes it possible to analyze the gels in an automated explorative manner by principal component analysis, to determine if the gels should be further analyzed. A more detailed approach is done by analyzing spot volume lists by principal components analysis and partial least square regression. The use of spot volume data offers a mean to investigate the spot pattern and link the classified protein patterns to distinct spots on the gels for further investigation. The explorative approach in analysis of 2-D gels makes it possible, in a fast and convenient way, to screen many gels in order to determine the protein patterns that form clusters and could be selected for further examination.     

Analysis of eleven iridoid glycosides by micellar electrokinetic capillary chromatography (MECC) and screening of plant samples by partial filling (MECC)-electrospray ionisation mass spectrometry

Of ammonium, lithium and sodium salts of dodecyl sulfate studied as surfactants in the separation of iridoid glycosides by micellar electrokinetic capillary chromatography (MECC), the last one gave the best results. Eleven neutral iridoid glycosides were separated by MECC with sodium dodecyl sulfate as surfactant, and the water–micelle partition coefficients of the compounds were calculated. The separation system was coupled via a coaxial sheath flow electrospray interface to a mass spectrometer, and the partial filling technique was used in the on-line analysis. Seven plant species belonging to five genera (Plantago, Veronica, Melampyrum, Succisa and Valeriana) were screened for the iridoid glycosides by the new method that was developed. The findings confirmed those of an earlier study on five of the iridoid glycosides. Some new iridoid glycosides were found in Plantago lanceolata, Veronica spicata and V. chamaedrys.     

Assay of human transthyretin-bound holo-retinol-binding protein with reversed-phase high-performance liquid chromatography

We describe a reversed-phase high-performance liquid chromatographic method for the determination of vitamin A-transporting (holo) transthyretin-bound (TTR) retinol-binding protein (RBP) concentrations in serum or plasma. Holo-TTR-RBP and free retinol derived primarily from free RBP are consistently observed with this chromatographic method. Holo-TTR-RBP concentrations determined by this method are highly correlated to holo-TTR-RBP concentrations measured by chromatography. This method has the advantage of using less expensive columns and having peak areas which are more proportional to their true concentrations in plasma, as determined by comparison to purified protein spectrophotometry and radial immunodiffusion. The percentage of RBP circulating as holo-TTR-RBP decreased significantly as the total concentration of RBP or retinol increased. Because purified holo-TTR-RBP did not dissociate under these chromatographic conditions, this suggests that more vitamin A circulates as holo-free RBP or free retinol in the blood of people with high serum RBP.     

Restricted diffusion in silica particles measured by pulsed field gradient NMR

The restricted diffusion coefficient of water through porous silica is measured by pulsed field gradient (PFG) NMR as a function of loading in order to develop a model for self-diffusion at full pore filling in sol-gel-made porous silica particles. This model describes the pore or intraparticle diffusion coefficient as a function of particle porosity, tortuosity, and the steric hindrance applied on the molecules by the pore space. The particle morphology is characterized by nitrogen adsorption and an appropriate tortuosity model is chosen in comparison with literature data. To characterize the material, NMR relaxation and diffusion studies at different degrees of pore filling were carried out in relation to the silica/water adsorption isotherm.     

A sugar's choice: coordination to a mononuclear or a dinuclear copper(II) complex?

We proposed a decisive role of the number of metal ions at the sugar binding site for carbohydrate-coordinating copper(II) complexes. To verify this hypothesis, we studied the binding of the representatively chosen carbohydrates D-ribose (7), D-mannose (8), D-glucose (9), and D-maltose (10) to structurally related mono- and dinuclear copper(II) complexes in alkaline solution. All carbohydrates coordinate to the metal complexes in a 1:1 molar ratio. Coordination of 7 or 8 to the dinuclear copper(II) complex 1 is about 0.5 order of magnitude stronger than the complex formation with related mononuclear complexes. On contrast, 9, which is an epimer of 8, coordinates stronger to either one of the mononuclear copper(II) complexes in alkaline aqueous solution.     

Mikroreflexionsmessungen zur Untersuchung dünner Oberflächenschichten

Zusammenfassung Es wird eine einfache optische Methode zur Dickenbestimmung dünner Oberflächenfilme beschrieben, die sich besonders zur Untersuchung von Korrosionsschichten eignet.

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Investigation of thin corrosion layers by microreflexion measurement

A simple optical method for the determination of thin surface films is described. It is especially suitable for the thin corrosion layer investigation.

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Mit 1 Abbildung

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Meinem verehrten Lehrer, Prof. Dr.H. Nowotny, gewidmet.     

Piperazine-based buffers for liposome coating of capillaries for electrophoresis

Anionic liposomes can be coated on fused-silica capillaries for electrophoresis in the presence of N-(hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) (HEPES) as background electrolyte (BGE) solution. In this work, the interaction of various compounds with zwitterionic and anionic phospholipid coatings was studied with HEPES at pH 7.4 as BGE solution. The chromatographic and electrophoretic behavior of three test sample solutions (anionic, cationic, and neutral) was investigated for evaluation of the phospholipid coatings. Our results show that hydrophobic interactions between analytes and the phospholipid coating are important for the migration of charged analytes. In addition, the performances of other piperazine-based buffers, i.e., N-(2-hydroxyethyl)piperazine-N'-(2-hydroxypropanesulfonic acid), piperazine-N,N'-bis(2-ethanesulfonic acid), and piperazine-N,N'-bis(hydroxypropane sulfonic acid), at pH 7.4, as liposome solvent and BGE solution were evaluated and compared with the performance of HEPES at pH 7.4. The anionic liposome solution comprised 80/20 mol% phosphatidylcholine/phosphatidylserine. A simple test solution was selected and the chromatographic and electrophoretic migration behavior of the analytes was evaluated. The results show that, in addition to HEPES, other piperazine-based buffers at pH 7.4 are suitable for coating of fused-silica capillaries with anionic liposomes.     

CHARACTERIZATION OF THE RED LIGHT INDUCED REDUCTION OF A PARTICLE ASSOCIATED b-TYPE CYTOCHROME FROM CORN IN THE PRESENCE OF METHYLENE BLUE*

Methylene blue transfers electrons to a membrane-associated b-type cytochrome in particulate fractions from corn coleoptiles. The K_m for methylene blue is less than 1 µM under optimal conditions. This reaction is destroyed by boiling, but not by 7 M urea. Kinetic analyses of the influence of light intensity on cytochrome reduction suggest that a first order photochemical reaction is limiting. Free EDTA may serve as an electron donor in this system at least at high methylene blue and protein concentrations. The photoactivity does not coincide either with mitochondrial or endoplasmic reticulum markers, and may be localized in plasma membrane. There is an estimated 5 times 10^-10 mol photoreducible cytochrome per g coleoptile tissue. Studies on the effect of pH on the reaction in the presence of methylene blue or thionine indicate that dye photoreduction itself is not rate-limiting. Wavelength dependence studies suggest that it is methylene blue monomer and not dimer which mediates the reaction. Although oxygen is apparently required for the reaction, neither superoxide nor excited singlet oxygen appear to be involved. The reaction mechanism is still unknown.