Scientific publications

Photoluminescence and X-ray photoelectron spectroscopy studies of Mn2+ doped ZnS nanocrystals in inorganic-organic hybrid coatings prepared by a sol-gel process are presented. A 25-fold enhancement of photoluminescence was observed after UV irradiation for 6 h in an ambient atmosphere. X-ray photoelectron spectroscopy results indicate a chemical shift of binding energy from ZnS to ZnSO4 after UV irradiation. X-ray diffraction results show a decrease of ZnS nanocrystal size during UV irradiation. The cause of these phenomena was discussed based on a photochemical reaction on ZnS nanocrystal surface.

The synthesis of BaSnO3 powders has been investigated at lyothermal conditions (temperature of 250 °C; t = 6 h), starting from SnO2·xH2O and Ba(OH)2 and methanol, ethanol, isopropanol and acetone as solvents. Among them isopropanol was found to be the most suitable medium for preparing BaSnO3. By addition of the modifier Genapol X-080 during the processing, the BET specific surface area of the end-powder was increased by a factor of 10. The as-prepared powder consisted of BaSn(OH)6. The thermal behavior, the crystallization behavior and the structure evolution of the powder during heating treatment have been studied with the TG-DTA-MS, XRD and FTIR. The weight loss of the as-prepared powder of about 12 wt% heated up to 1200 °C is mainly attributed to the dehydration around 260 °C which leads to the structure rearrangement and the building of the [SnO6] octahedra. At this temperature BaSn(OH)6 converts to an amorphous phase, from which BaSnO3 nucleates and grows with increasing temperature. The obtained BaSnO3 powders had a BET specific surface area of 16.56 m2/g and a primary crystallite size of 49 nm.

Perovskite-type BaSnO3 powders with a particle size of 30-60 nm have been prepared from tin oxide hydrate (SnO2 ∙ xH2O) gel via the hydrothermal synthesis route. The reactivity of the synthesized SnO2 ∙ xH2O was found to be dependent on the pH value of the mixture of tin chloride and the ammonia solution. The most reactive SnO2 ∙ xH2O gel was obtained at a pH value near 2. The hydrothermal products derived from this reactive gel were characterized with thermograrimetric/differential thermal analysis, Fourier transform infrared spectrometry, X-ray diffraction and high-resolution scanning electron microscopy. The BaSn(OH)6 phase in the as-prepared powder was found to convert into an amorphous phase other than into the BaSnO3 phase. The BaSnO3 powder crystallizing from the amorphous phase at 260°C for 4 h has better sintering properties than the commercial one.

Reaction of ligand LH2 (4,5-bis[carboxymethylthio]-1,3-dithiol-2-thione) with neodymium silyl-amide (Nd[N(TMS)2]3; TMS= -SiMe3), in a ratio 2:1, yields a neodymium-dithiolene-carboxylato complex (1) (Nd(LH)L). Similarly, reaction of 2 equivalents of L'H2 (4,5-bis[2-hydroxyethyl)thio]-1,3-dithiol-2-thione) and one equivalent of neodymium silyl-amide (Nd[N(TMS)2]3) allowed the isolation of complex 2, with a ligand:metal ratio of 3:2. ATR-IR spectrum of 1 displays a broad band characteristic of an OH group showing that one carboxylate group remains protonated. Emission spectrum of complex 1 under excitation in the visible region (at 360 nm i.e. on the ligand) displayed typical emission bands of the Nd3+, showing that energy transfer from the ligand to the lanthanide was achieved (i.e. "antenna effect"). No significant quenching from the remaining -OH group was detected. In the case of complex 2, the main emission bands characteristic of the Nd3+ ion have been observed, by excitation at 495 nm.

The reaction between [(Ph2Si)2O3]4[Al(OH)]4 (1) or [(Ph2Si)2O3]4[Al(OLi)]4 (2) with sodium ethoxide, or lithium hydroxide in presence of CuI·H2O leads to the formation of new alumopolysiloxane compounds. Indeed, transformations of 1 under the partial incorporation of the reactants are found giving rise to new heteroleptic inorganic macrocycles. The molecular structure of [(Ph2Si)2O3]4[Al(ONa)]2[Al(OH)(NaOEt)]2·2Et2O (3) and [(Ph2Si)2O3]4[Al(OLi)]2[Al(OH)(LiOH)]2·2Et2O·2THF (4) have been determined by single-X-ray diffraction analysis. Both alumosiloxanes 3 and 4 are constituted by a twelve-membered ring.

Heterogeneous thin films may be beneficial for sensoring devices. The electrical conductivity of nanoscale metallic particles being embedded in a matrix of non conducting material should exhibit higher sensitivity to mechanical stress and strain compared to homogeneous films. The production of heterogeneous films may follow different routes. This paper describes the attempt to embed Ag nanoclusters emitted from a gas aggregation cluster source into a growing matrix of alumina originating from sputter sources. The characteristics of the cluster source are first resumed, with their mean masses ranging from approx. 1000 to 100,000 atoms per cluster. The expelled and soft landed clusters are extensively examined by transmission electron microscopy verifying their crystalline form. Yet the use of a radio frequency driven sputter source for the embed material destroys and annihilates the Ag clusters even at very low sputter power. If a reactive direct current sputter process is performed within an oxidising sputter gas instead, the Ag clusters are oxidised to different oxides, but they survive as crystalline entities as verified by X-ray diffraction investigations. A simple subsequent heat treatment reduces the Ag oxides to metallic Ag clusters.

Background: Chitin self-assembly provides a dynamic extracellular biomineralization interface. The insoluble matrix of larval shells of the marine bivalve mollusc Mytilus galloprovincialis consists of chitinous material that is distributed and structured in relation to characteristic shell features. Mollusc shell chitin is synthesized via a complex transmembrane chitin synthase with an intracellular myosin motor domain. Results: Enzymatic mollusc chitin synthesis was investigated in vivo by using the small-molecule drug NikkomycinZ, a structural analogue to the sugar donor substrate UDP-N-acetyl-Dglucosamine (UDP-GlcNAc). The impact on mollusc shell formation was analyzed by binocular microscopy, polarized light video microscopy in vivo, and scanning electron microscopy data obtained from shell material formed in the presence of NikkomycinZ. The partial inhibition of chitin synthesis in vivo during larval development by NikkomycinZ (5 μM-10 μM) dramatically alters the structure and thus the functionality of the larval shell at various growth fronts, such as the bivalve hinge and the shell's edges. Conclusion: Provided that NikkomycinZ mainly affects chitin synthesis in molluscs, the presented data suggest that the mollusc chitin synthase fulfils an important enzymatic role in the coordinated formation of larval bivalve shells. It can be speculated that chitin synthesis bears the potential to contribute via signal transduction pathways to the implementation of hierarchical patterns into chitin mineral-composites such as prismatic, nacre, and crossed-lamellar shell types.

It is widely accepted that the functional and morphological differentiation of cells is initiated and determined by the interaction of molecules of the extracellular matrix and adhesion molecules of the cell membrane. To assess the influence of the underlying matrix on the characteristics of cells, enterocyte-like Caco-2 cells were cultivated on substrates commonly used for cell culture as well as on glass coated with hydrophobic layers. Providing the same starting conditions for growth, the parameters investigated on pre-confluent Caco-2 cells were the number of adhering cells, the proliferative activity and the degree of differentiation indicated by the expression of three brush border enzymes. Whereas tissue culture treated polystyrene elicited highest rates of adhesion, proliferation, and differentiation, even glass altered the pattern of brush border enzyme expression. The hydrophobic surfaces strongly decreased the adhesion and the proliferation but the surviving cells exhibited a pronounced higher degree of differentiation. Interestingly, each subtype of hydrophobic matrix triggered a different pattern of brush border enzyme expression. Thus, the development of a certain phenotype of a cell can not only be triggered by certain components of the extracellular matrix but also by artificially prepared surface coatings of the underlying matrix. In the future it seems to be feasible that cells can be programmed by tailoring the surface of the underlying substrate.

For optimal compatibility with biopharmaceutical manufacturing and gene therapy, heterologous transgene control systems must be responsive to side-effect-free physiologic inducer molecules. The arginine-inducible interaction of the ArgR repressor and the ArgR-specific ARG box, which synchronize arginine import and synthesis in the intracellular human pathogen Chlamydia pneumoniae, was engineered for arginine-regulated transgene (ART) expression in mammalian cells. A synthetic arginine-responsive transactivator (ARG), consisting of ArgR fused to the Herpes simplex VP16 transactivation domain, reversibly adjusted transgene transcription of chimeric ARG box-containing mammalian minimal promoters (PART) in an arginine-inducible manner. Arginine-controlled transgene expression showed rapid induction kinetics in a variety of mammalian cell lines and was adjustable and reversible at concentrations which were compatible with host cell physiology. ART variants containing different transactivation domains, variable spacing between ARG box and minimal promoter and several tandem ARG boxes showed modified regulation performance tailored for specific expression scenarios and cell types. Mice implanted with microencapsulated cells engineered for ART-inducible expression of the human placental secreted alkaline phosphatase (SEAP) exhibited adjustable serum phosphatase levels after treatment with different arginine doses. Using a physiologic inducer, such as the amino acid L-arginine, to control heterologous transgenes in a seamless manner which is devoid of noticeable metabolic interference will foster novel opportunities for precise expression dosing in future gene therapy scenarios as well as the manufacturing of difficult-to-produce protein pharmaceuticals. © 2007 The Author(s).