Surface and interface studies with ASPIC

Magnetic properties at surfaces and interfaces have been investigated performing Perturbed Angular Correlation (PAC) measurements in the UHV chamber ASPIC (Apparatus for Surface Physics and Interfaces at CERN) using different PAC probes. The results are: (i) determination of magnetic hyperfine fields of Se on Fe, Co, Ni which are explained by a theoretical study on the magnetic hyperfine fields of 4sp-elements in adatom position on Ni and Fe;(ii) static magnetic hyperfine fields in ultrathin Pd on Ni(0 0 1) which indicate an induced magnetic order in Pd;(iii) the observation of induced fluctuating magnetic interactions in Pd when thick Pd is in contact with Ni. Monolayer-resolved measurements of the magnetic hyperfine fields in magnetized Pd are in accordance with theoretical predictions of the layer dependence of the induced magnetic moments in Pd. This revised version was published online in July 2006 with corrections to the Cover Date.     

Modelling of the Phase Separation Behaviour of Semiflexible Diblock Copolymers

Silver salts are dissolved in poly(butyl methacrylate) to derive polymer electrolytes via coordinative interaction between the silver ion and the carbonyl oxygen atom. The dissolved silver ions react subsequently with propylene to form reversible silver/olefin complexes that can be utilized as olefin carriers for facilitated olefin transport. The complexation behavior and its effects on propylene transport were investigated by means of Raman and FT‐IR spectroscopy, as well as dielectric thermal analysis.     

Arsenic compounds in terrestrial organisms. IV. Green plants and lichens from an old arsenic smelter site in Austria

Two lichens and 12 green plants growing at a former arsenic roasting facility in Austria were analyzed for total arsenic by ICP–MS, and for 12 arsenic compounds (arsenous acid, arsenic acid, dimethylarsinic acid, methylarsonic acid, arsenobetaine, arsenocholine, trimethylarsine oxide, the tetramethylarsonium cation and four arsenoriboses) by HPLC–ICP–MS. Total arsenic concentrations were in the range of 0.27 mg As (kg dry mass)⁻¹ (Vaccinium vitis idaea) to 8.45 mg As (kg dry mass)⁻¹ (Equisetum pratense). Arsenic compounds were extracted with two different extractants [water or methanol/water (9:1)]. Extraction yields achieved with water [7% (Alectoria ochroleuca) to 71% (Equisetum pratense)] were higher than those with methanol/water (9:1) [4% (Alectoria ochroleuca) to 22% (Deschampsia cespitosa)]. The differences were caused mainly by better extraction of inorganic arsenic (green plants) and an arsenoribose (lichens) by water. Inorganic arsenic was detected in all extracts. Dimethylarsinic acid was identified in nine green plants. One of the lichens (Alectoria ochroleuca) contained traces of methylarsonic acid, and this compound was also detected in nine of the green plants. Arsenobetaine was a major arsenic compound in extracts of the lichens, but except for traces in the grass Deschampsia cespitosa, it was not detected in the green plants. In contrast to arsenobetaine, trimethylarsine oxide was found in all samples. The tetramethylarsonium cation was identified in the lichen Alectoria ochroleuca and in four green plants. With the exception of the needles of the tree Larix decidua the arsenoribose (2′R)‐dimethyl[1‐O‐(2′,3′‐dihydroxypropyl)‐5‐deoxy‐β‐D ‐ribofuranos‐5‐yl]arsine oxide was identified at the low μg kg⁻¹ level or as a trace in all plants investigated. In the lichens an unknown arsenic compound, which did not match any of the standard compounds available, was also detected. Arsenocholine and three of the arsenoriboses were not detected in the samples. Copyright © 2000 John Wiley & Sons, Ltd.     

Arsenic Compounds in Terrestrial Organisms I: Collybia maculata,Collybia butyracea and Amanita muscaria from Arsenic Smelter Sites in Austria

Three mushroom species from two old arsenic smelter sites in Austria were analyzed for arsenic compounds. The total arsenic concentrations were determined by ICP–MS. Collybia maculata contained 30.0 mg, Collybia butyracea 10.9 mg and Amanita muscaria 21.9 mg As kg⁻¹ dry mass. The arsenic compounds extracted with methanol/water (9:1) from the dried mushroom powders were separated by HPLC on anion-exchange and reversed-phase columns and detected by ICP-MS using a hydraulic high-pressure nebulizer. In Collybia maculata almost all arsenic is present as arsenobetaine. Collybia butyracea contained mainly arsenobetaine (8.8 mg As kg⁻¹ dry mass) and dimethylarsinic acid (1.9 mg As kg⁻¹). Amanita muscaria contained arsenobetaine (15.1 mg As kg⁻¹), traces of arsenite, dimethylarsinic acid and arsenate, and surprisingly arsenocholine (2.6 mg As kg⁻¹) and a tetramethylarsonium salt (0.8 mg As kg⁻¹). © 1997 by John Wiley & Sons, Ltd.     

Polyelectrolyte adsorption and stabilization of silica-suspensions

The adsorption of cationic polyelectrolytes on colloidal silica-particles is investigated. The polyelectrolytes poly(diallyl-dimethyl-ammoniumchloride) PDADMAC of different molar mass have been used. The adsorbed amount is influenced by the ionic strength and pH of the suspension and the molar mass of the macromolecule. The adsorption determines the zetapotential of the covered particles. The electrostatic interaction between the particles as well as the structure of the adsorbed polyelectrolytes play an important role in the stabilization and flocculation behaviour of the polyelectrolyte covered suspensions.     

Chemical vapour deposition polymerization of substituted [2.2]paracyclophanes

Chemical vapour deposition polymerisation of substituted [2.2]paracyclophanes is applied to the functionalised coating of stainless steel surfaces. Poly[o-trifluoroacetyl-p-xylylene-co-p-xylylene] ( 2a ), poly[o-hydroxymethyl-p-xylylene-co-p-xylylene] ( 2b ), poly[o-amino-p-xylylene-co-p-xylylene] ( 2c ) and poly(p-xylylene-2,3-dicarboxylic anhydride) ( 2d ) were deposited as thin layers.     

Characterization of a poly(ethersulphone) by on-line coupling of size exclusion chromatography with NMR and FTIR spectroscopy

An on-line detection „on the flow”︁ during the size exclusion chromatography run using FTIR and NMR spectrometers was applied to investigate the liquid chromatographic separation process of oligomers and to identify the separated chromatographic compounds. The FTIR and NMR detectors give real-time information about the chemical structure and functional groups of the eluated species. The preferences and limits of the on-line coupling were discussed using an oligomeric hydroxyl terminated poly(ethersulphone) as an example. Molecular weights could be calculated from the ¹H-NMR spectra of the separated species using the intensities of end-group and main-chain signals. Residues of N-methylpyrrolidone which was used as solvent in the oligomer synthesis were identified by the FTIR detector.     

Synthesis and characterization of semifluorinated polymers and block copolymers

The goal of the investigation presented here was to evaluate the influence of semifluorinated side chains on the bulk structure and the surface properties of polysulfones with different chain structure. Thus, segmented block copolymers consisting of polysulfone and semifluorinated aromatic polyester segments as well as polysulfones having semifluorinated side chains randomly distributed over the polymer backbone were synthesized and characterized. Oxydecylperfluorodecyl side chains were used because of their strong tendency for self-organization. The influence of the chain architecture on the self-organization as well as on the surface properties, particularly the wetting behavior, was examined. It could be shown that despite of the higher self-organizing tendency of block copolymers the surface properties of both polymer types are comparable and depend only on the concentration of side chains.     

Durable Mesenchymal Stem Cell Labelling by Using Polyhedral Superparamagnetic Iron Oxide Nanoparticles

Small polyhedral superparamagnetic iron oxide (SPIO) nanoparticles (<10 nm) coated with a thin layer of silica were prepared (SPIO@SiO₂ and SPIO@SiO₂‐NH₂). Surface modification of the small polyhedral silica‐coated SPIO nanoparticles with amines led to substantially higher mesenchymal stem cell (MSC) labelling efficiency without the use of additional transfecting agents. Therefore, amine surface‐modified nanoparticles (SPIO@ SiO₂‐NH₂) appeared to be the preferred candidate for MSC labelling. In vitro studies demonstrated that controlled labelling of SPIO@SiO₂ and SPIO@SiO₂‐NH₂ did not cause MSC death or proliferation inhibition. MSCs labelled with SPIO@SiO₂‐NH₂ nanoparticles retained differentiation potential and showed osteogenic, adipogenic and chondrogenic differentiations. The noncytotoxic polyhedral SPIO@SiO₂‐NH₂ nanoparticle‐labelled MSCs were successfully implanted in rabbit brain and erector spinae muscle, and demonstrated long‐lasting, durable MRI labelling efficacy after 8–12 weeks.